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Gas phase ion-moleculae chemistry of an analogous series of aryl transition-metal carbonyl compounds… Taylor, Sandra M. 1992

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GAS PHASE ION- MOLECULE CHEMISTRYOF AN ANALOGOUS SERIESOF ARYL TRANSITION-METAL CARBONYL COMPOUNDSBY FOURIER TRANSFORM ION CYCLOTRON RESONANCEMASS SPECTROMETRYbySANDRA M. TAYLORB. A., University of British Columbia, 1956M. Sc., University of BrItish Columbia, 1958A THESIS SUBMITTED IN PARTIAL FULFILMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIESDepartment of ChemistryWe accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAAugust, 1992(c) Sandra M. Taylor, 1992In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Ubrary shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. it is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.Department of ChemistryThe University of British ColumbiaVancouver, CanadaDate August 31, 1992DE.6 (2188)AbstractThe gas phase ion-molecule chemistry of an analogous series of five aryl transition-metal carbonyl compounds has been examined using FT-ICR-MS techniques. Under 25 eV(positive ion) and 2.5 eV (negative ion) electron ionisation, ionic fragments of thefollowing compounds were generated: CpV(CO)4; BzCr(CO)3CpMn(CO)3;BuFe(CO)3;and CpCo(CO)2; {where Cp =fl5-C5H5; Bz =16-CH;Bu =r14-CH6).Ion-moleculereaction products were temporally monitored. Kinetic analyses showed that reactionpathways for each reactive cation fragment involved interaction with the neutral parentmolecule, either by electron or ligand transfer, or by condensation with simultaneouscarbonyl ejection. Condensations resulted in generation of higher molecular weightpolynuclear ionic cluster fragments such as: (CpV)3(CO)3;(BzCr)2CO3;and(BuFe)2(CO).In general, the reactivity of any cationic species varied directly with electrondeficiency and coordination site availability of the central metal core. Some reactive cationsexhibited unexpected reactivity patterns, despite their large formal electron deficiency,suggesting possession of unusual bonding configuration within cluster cores. Severalreactive cations exhibited excited state behaviour, reacting more rapidly than their groundstate counterparts. Reaction rate constants approximated those predicted by Langevin forunpolarised gas phase bimolecular processes.Smaller, highly electron-deficient daughter cations, e.g. CpV and BzCrCO, werereactive with respect to some small molecular addition reagents such as ammonia ordioxygen. Several important hydride adducts were also observed. On the other hand,anion-molecule chemistry was less complicated: anion daughter fragments reacted solely byformation of one or two stable clusters; and were relatively unreactive with respect toaddition reagent molecules.IITABLE of CONTENTSAbstract iiTable of Contents liiList of Figures viList of Tables xiiiAcknowledgment xvChapter 1 General Introduction : Experimental Procedures 1I Introduction 21. Transition Metals 22. Organo-Transition Metal Compounds 43. Transition Metal Carbonyl Compounds 54. Aryl Transition Metal Compounds 75. 11-Alkenyl Transition Metal Carbonyl Complexes 86. An Analogous Series of “Aryl” Transition Metal Carbonyls127. Structures of Compounds Examined 148. Gas Phase Techniques 15II Experimental Procedure 151. Experimental Parameters 152. Chemical Compounds 163. Principles of Ion Cyclotron Resonance 17III References 19Chapter 2 Ion Molecule Chemistry of CpV(CO)4 26I Introduction 27II Results and Discusion 281. Positive Ion Chemistry 28Ill2. Reactions with Small Molecules 573. Negative Ion Chemistry 614. Reactions with Small Molecules 63III Conclusions 66IV References 77Chapter 3 Ion Molecule Chemistry of BzCr(CO)3 79I Introduction 80II Results and Discusion 821. Positive Ion Chemistry 822. Negative Ion Chemistry 105III Conclusions 108IV References 115Chapter 4 Ion Molecule Chemistry of CpMn(CO)3 117I Introduction 118II Results and Discusion 1191. Positive Ion Chemistry 1192. Negative Ion Chemistry 138III Conclusions 141IV References 149Chapter 5 Ion Molecule Chemistry of BuFe(CO)3 151I Introduction 152II Results and Discusion 1551. Positive Ion Chemistry 1552. Negative Ion Chemistry 171III Conclusions 173IV References 180Chapter 6 Ion Molecule Chemistry of CpCo(CO)2 184ivI Introduction 185II Results and Discusion 1871. Positive Ion Chemistry 1872. Reactions with Gases N2, CO and CO2 2053. Negative Ion Chemistry 2114. Reactions with Gases N2, CO and CO2 214III Conclusions 214IV References 220Chapter 7 General Discussion and Conclusions 223I General Periodic Trends 224II Kinetic Results 2271. General Trends 2272. Decay Rates 2323. Electron Transfer Reactions 2334. Condensation (Clustering) Reactions 2345. Ligand Exchange Reactions 2366. Excited State Reactions 237III General Conclusions 240IV Further Research Projects 243V References 246Appendices 250Appendix I Kinetic Development 2511. Evaluation of Pseudo-First Order Rate Constants (k’) 2512. Evaluation of Second Order Rate Constants (k) 2523. Evaluation of Neutral Reactant Gas Pressures [M] 253Appendix II. Schematic Diagram of FT - ICR Reaction Cell 257FT-ICR Mass Spectrometer Instrumentation 258VList of FiguresFigure 2.1(a). FT-ICR Positive Ion Mass Spectrum of CpV(CO)4;0 msec.; 25 eV; p = 6.OxlO8 torr 29Figure 2.1(b). FT-ICR Positive Ion Mass Spectrum of CpV(CO)4;300 msec.; 25 eV; p = 6.OxlO-8 torr 30Figure 2.1(c). FT-ICR Positive Ion Mass Spectrum of CpV(CO)4;600 msec.; 25 eV; p = 6.0x108 torr 31Figure 2.1(d). FT-ICR Positive Ion Mass Spectrum of CpV(CO)4;25 sec.; 25 eV; p = 6.OxlO8 torr 32Figure 2.2. Temporal Behaviour of Primary Fragment Cations ofCpV(CO)4 35Figure 2.3. Temporal Behaviour of Binuclear Cluster Cations ofCpV(CO)4 36Figure 2.4. Temporal Behaviour of Trinuclear Cluster Cations ofCpV(CO)4 37Figure 2.5(a). Multiple Resonance Mass Spectrum of CpV;0 msec.; p = 6.OxlO’8 torr 38Figure 2.5(b). Multiple Resonance Mass Spectrum of CpV’and Cation Products; 200 msec; ; p = 6.OxlO8 torr 39Figure 2.6. Temporal Behaviour of CpV and Cation Products 40Figure 2.7(a). Multiple Resonance Mass Spectrum of CpV(CO)3;0 msec ; p = 6.OxlO8 torr 41Figure 2.7(b). Multiple Resonance Mass Spectrum of CpV(CO)3’and Cation Products; 200 msec 42Figure 2.8. Temporal Behaviour of CpV(CO)3 and Cation Products 43vFigure 2.9(a). Multiple Resonance Mass Spectrum of (CpV)2O;0 msec.; p = 6.OxlO8 torr 44Figure 2.9(b). Multiple Resonance Mass Spectrum of (CpV)204and Cation Products; 600 msec 45Figure 2.10. Temporal Behaviour of (CpV)2CO and Cation Products 46Figure 2.11. Positive Ion Mass Spectrum of CpV(CO)4:Ammonia Chemical Ionization; 70 cv; p = .01 torr 59Figure 2.12. Positive Ion Mass Spectrum of CpV(CO)4:Methane Chemical Ionization; 70 eV; p = .01 torr 60Figure 2.13. FT-ICR Negative Ion Mass Spectrum of CpV(CO)4;0 msec.; 2.5 eV; p = 6.OxlO8 torr 62Figure 2.14. Negative Ion Mass Spectrum of CpV(CO)4:Ammonia Chemical Ionization; 70 eV; p = .01 torr 64Figure 2.15. Negative Ion Mass Spectrum of CpV(CO)4:Methane Chemical Ionization; 70 eV; p = .01 torr 65Figure 2.16. Relative Abundances of Cation Clusters of CpV(CO)4;500 insec 68Figure 2.17. Relative Abundances of Cation Clusters of CpV(CO)4;1000 msec 69Figure 2.18. Relationship Between Reactivity and Electron Deficiencyfor the CpV(CO)4 System 71Figure 2.19. Deviations from Simple Pseudo-First Order Decay Behaviourin the CpV(CO)4 System 73Figure 2.20. Clastogram for Cations of CpV(CO)4 75Figure 3.1. FT-ICR Positive Ion Mass Spectrum of BzCr(CO)3;0 msec.; 25 eV; p = 6.OxlO8 torr 84vuFigure 3.2. Temporal Behaviour of Primary Fragment Cations ofBzCr(CO)3 87Figure 3.3. Temporal Behaviour of Binuclear and Trinuclear ClusterCations of BzCr(CO)3 88Figure 3.4(a). Multiple Resonance Mass Spectrum of Cr’;o msec.; p = 6.OxlO8 torr 89Figure 3.4(b). Multiple Resonance Mass Spectrum of Cr’- and CationProducts; 5000 msec; p = 6.OxlO8 torr 90Figure 3.5. Temporal Behaviour of Cr and Cation Products 91Figure 3.6(a). Multiple Resonance Mass Spectrum of BzCr(CO)2’-0 msec.; p = 6.OxlO8 torr 92Figure 3.6(b). Multiple Resonance Mass Spectrum of BzCr(CO)2and Cation Products; 5000 msec 93Figure 3.7. Temporal Behaviour of BzCr(CO)2and Cation Products 94Figure 3.8(a). Multiple Resonance Mass Spectrum of C6H;0 msec.; p = 6.OxlO8 torr 102Figure 3.8(b). Multiple Resonance Mass Spectrum of C6Hand Cation Products; 500 msec 103Figure 3.9. Temporal Behaviour of C6H and Cation Products 104Figure 3.10. FT-ICR Negative Ion Mass Spectrum of BzCr(CO)3;0 msec.; 2.5 eV; p = 6.OxlO8 torr 107Figure 3.11. Relationship Between Reactivity and Electron Deficiencyfor the BzCr(CO)3 System 110Figure 3.12. Simple Pseudo-First Order Decay Behaviour and Deviationsin the BzCr(CO)3 System 112Figure 3.13. Clastogram for Cations of BzCr(CO)3 114VII’Figure 4.1. FT-ICR Positive Ion Mass Spectrum of CpMn(CO)3;0 msec.; 25 eV; p = 6.OxlO8 torr 120Figure 4.2. Temporal Behaviour of Primary Fragment Cations ofCpMn(CO)3 123Figure 4.3. Temporal Behaviour of Binuclear Cluster Cations ofCpMn(CO)3 124Figure 4.4. Temporal Behaviour of Trinuclear Cluster Cations ofCpMn(CO)3 125Figure 4.5(a). Multiple Resonance Mass Spectrum of CpMn;0 msec.; p = 6.OxlO8 torr 126Figure 4.5(b). Multiple Resonance Mass Spectrum of CpMnand Cation Products; 5000 msec.; p = 6.OxlO8 torr 127Figure 4.6. Temporal Behaviour of CpMn and Cation Products 128Figure 4.7(a). Multiple Resonance Mass Spectrum of (CpMn)2O)3;0 msec.; p = 6.OxlO8 torr 129Figure 4.7(b). Multiple Resonance Mass Spectrum of (CpMn)2O)3and Cation Products; 5000 msec 130Figure 4.8. Temporal Behaviour of (CpMn)2O)3 and CationProducts 131Figure 4.9. FT-ICR Negative Ion Mass Spectrum of CpMn(CO)3;0 msec.; 2.5 eV; p = 6.OxlO8 torr 139Figure 4.10. Temporal Behaviour of Primary Fragment Anions ofCpMn(CO)3 140Figure 4.11. Relationship Between Reactivity and Electron Deficiencyfor the CpMn(CO)3 System 143Figure 4.12. Deviations from Simple Pseudo-First Order Decay Behaviourin the CpMn(CO)3 System 145ixFigure 4.13. FT-ICR Positive Ion Mass Spectrum of CpMn(CO)3;o msec.; 25 eV; p = 6.OxlO8 torr; p(H2) = 6.OxlO7 torr 146Figure 4.14. Clastogram for Cations of CpMn(CO)3 148Figure 5.1. FT-ICR Positive Ion Mass Spectrum of BuFe(CO)3;o msec.; 25 eV; p = 6.OxlO8 torr 156Figure 5.2. Temporal Behaviour of Primary Fragment Cations ofBuFe(CO)3 159Figure 5.3. Temporal Behaviour of Binuclear Cluster Cations ofBuFe(CO)3 160Figure 5.4. Temporal Behaviour of Trinuclear Cluster Cations ofBuFe(CO)3 161Figure 5.5(a). Multiple Resonance Mass Spectrum of BuFe;0 msec.; p = 6.OxlO8 torr 162Figure 5.5(b). Multiple Resonance Mass Spectrum of BuFeand Cation Products; 1000 msec.; p = 6.OxlO8 torr 163Figure 5.6. Temporal Behaviour of BuFe and Cation Products 164Figure 5.7. Temporal Behaviour of Fe and Cation Products 165Figure 5.8. Temporal Behaviour of (BuFe)2CO and Cation Products 166Figure 5.9. FT-ICR Negative Ion Mass Spectrum of BuFe(CO)3;0 msec.; 2.5 eV; p = 6.OxlO8 torr 172Figure 5.10. Relationship Between Reactivity and Electron Deficiencyfor the BuFe(CO)3 System 175Figure 5.11. Deviations from Simple Pseudo-First Order Decay Behaviourin the BuFe(CO)3 System 177Figure 5.12. Clastogram for Cations of BuFe(CO)3 178Figure 6.1. FT-ICR Positive Ion Mass Spectrum of CpCo(CO)2;0 msec.; 25 eV; p = 6.OxlO8 torr 188xFigure 6.2. Temporal Behaviour of Primary Fragment Cations ofCpCo(CO)2 190Figure 6.3. Temporal Behaviour of Secondary Cluster Cations ofCpCo(CO)2 191Figure 6.4(a). Multiple Resonance Mass Spectrum of Co0 msec.; p = 6.OxlO8 torr 193Figure 6.4(b). Multiple Resonance Mass Spectrum of Coand Cation Products; 500 msec.; p = 6.OxlO’8 torr 194Figure 6.5. Temporal Behaviour of Co and Cation Products 195Figure 6.6. Temporal Behaviour of CpCo and Cation Products 196Figure 6.7. Temporal Behaviour of CpCoCO and Cation Products 197Figure 6.8. Temporal Behaviour of CpCo(CO)2and Cation Products 198Figure 6.9. Relationship Between Reactivity and Electron Deficiencyfor the CpCo(CO)2 System 204Figure 6.10. Temporal Behaviour of N2 and Cation Products;p(N2) = 6.OxlO7torr 206Figure 6.11. Temporal Behaviour of CO and Cation Products;p(CO) = 6.OxlO7torr 207Figure 6.12. Temporal Behaviour of CO2 and Cation Products;p(C02) = 6.OxlO7torr 208Figure 6.13. FT-ICR Negative Ion Mass Spectrum of CpCo(CO)2;500 msec.; 2.5 eV; p = 6.OxlO8 torr 212Figure 6.14. Temporal Behaviour of Primary Fragment Anions ofCpCo(CO)2 213Figure 6.15. Deviations from Simple Pseudo-First Order Decay Behaviourin the CpCo(CO)2 System 217Figure 6.16. Clastogram for Cations of CpCo(CO)2 219xTIXUO!p1UWflJJSUIJiuopdSSUJAJ13I-JAZV“LILSZIIDUOpU)J)3JJO‘‘!U!PW1PS.1VList of TablesTable 2.1. Sample Mass Table for CpV(CO)4 Ions 33Table 2.2. Disappearance Rates for CpV(CO)4Cations 47Table 2.3. Relative Electron Transfer Rates for CpV(CO)4 Cations 50Table 2.4. Relative Clustering Rates for CpV(CO)4 Cations 52Table 2.5. Relative CO Ligand Loss Rates for CpV(CO)4 Cations 54Table 2.6. Relative Rates of CO Ligand Addition for CpV(CO)4Cations 56Table 3.1. Sample Mass Table for BzCr(CO)3 Ions 85Table 3.2. Disappearance Rates for BzCr(CO)3 Cations 95Table 3.3. Relative Electron Transfer Rates for BzCr(CO)3 Cations 97Table 3.4. Relative Clustering Rates for BzCr(CO)3 Cations 100Table 4.1. Sample Mass Table for CpMn(CO)3Ions 121Table 4.2. Disappearance Rates for CpMn(CO)3Cations 132Table 4.3. Relative Electron Transfer Rates for CpMn(CO)3Cations 134Table 4.4. Relative Clustering Rates for CpMn(CO)3 Cations 137Table 5.1. Sample Mass Table for BuFe(CO)3 Cations 157Table 5.2. Disappearance Rates for BuFe(CO)3 Cations 168Table 6.1. Sample Mass Table for CpCo(CO)2 Ions 189Table 6.2. Disappearance Rates for CpCo(CO) Cations 199Table 6.3. Relative Electron Transfer Rates for CpCo(CO)2Cations 201Table 6.4. Relative Rates of Reaction of CpCo(CO)2with Some SmallMolecules 210Table 7.1. Energy Parameters for the First Transition Metal Series 226Table 7.2 Comparative Rates for Transition Metal Ions(Monometallic) 229xliiTable 7.3 Comparative Rates for Transition Metal Ions(Bimetallic) 230Table 7.4 Comparative Rates for Transition Metal Ions(Trimetallic) 231Table 7.5 Initial Abundances - Excited State Ions 239Table A.1 Molecular Polarisibility and Pressures 255xivAcknowledgmentMay I express my gratitude to my supervisor, Professor M. B.Comisarow, to committee members Professors E. Ogryzlo and A. Bree; tomy colleagues Shu-Ping Chen, Ziyi Kan and Zamas Lam for helpfuldiscussions and suggestions; to Eva Szende, Dave Steiner, Glenn Rouse,Ben Clifford and Irene Rodway for encouragement and support; to mypatient and empathetic children, Norman, Ren&, Angela, Cohn, andHillary; to my parents Kay and Ted Cardinall; to the knowledgeable andunstinting assistance of the staffs of the chemistry office, the mechanicaland electronic shops; but mostly to my best friend, Jim Fitzsimmons.Thank-you everyone.xvCHAPTER 1A General Introduction toGas PhaseAryl-Transition Metal-Carbonyl ChemistryandExperimental Procedures1I Introduction1. Transition MetalsSince prehistoric time, transition metals have been esteemed for their great beautyand economic value. The very word ‘metal’ implies brilliant lustre and endurance,properties inherent in those elements arrayed along the central transition block of themodem periodic table. From earliest times, native gold, silver and mercury were accessiblein pure form. With the discovery of fire and then ore extraction, other pure metals, such ascopper, tin (Bronze Age) and later, iron (Iron Age), have enormously enhanced humansurvival and comfort. Tools made from such materials are sharp, hard and durable, lendingthemselves readily to the ingenuity of the user. Possession of such metals has acted as acultural lever, enabling a people to achieve agricultural success, prevail over enemies,procure materials for clothing and shelter, etc. As small cultural enclaves developed intolarger organised groups, highly-valued silver and gold also became the currency ofcommercial transaction. Early civilisations in China, India and pre-Columbian Americadeveloped sophisticated techniques for the procurement of these and other precious metalssuch as platinum, zinc, mercury and lead[1181.In classical Greece, intellectuals with time for speculative activity began laying thefoundation for European theoretical science. During the early Medieval period, scholars insuch intellectual outposts as Toledo, Cordova, Cairo and Baghdad examined closely someof the empirical properties of all known, economically valuable metals. Muslim scientistsJabir, Razi and Avicenna (721 - 1036 A.D.), the first true empiricists, carefully developedand documented procedures for metal separation and assaying[57’118l.These techniques,summarised much later by Agricola in De Re Metallica (1550 A.D.), are still used, largelyunchanged, today. At the same time, in accordance with the spirit of the European2Renaissance, new ideas and practices began to be implemented in the study of all mannerof natural phenomena, including the nature and behaviour of known transition metals andtheir compounds[17’5”18]•With the technological upheaval caused by the Industrial Revolution after 1700A.D., new metallurgical procedures were devised in order to take advantage of globalentrepreneurial opportunities. Heavy industrial processes such as the Bessemer process forsteel production required high-melting, refractory metal construction materials[17’571.Thevaluable properties which some transition metals bestowed upon their alloys becamerecognized. Many new transition metal elements were discovered; for example: cobalt (byBrandt, in 1735); nickel (Cronstedt, 1751); manganese (Gahn, 1774); titanium (Gregor,1791); chromium (Vauquelin, 1797); vanadium (del Rio, 1801); and scandium (Nilson,1876)[121]. These and other valuable metals grew in importance, in highly-refined form aswell as in bulk.In the late 1800’s and early 1900’s, commercial synthesis of strategic materialssuch as methane, sulfuric acid and ammonia became increasingly essential, and successfuldevelopment of new and effective catalysts became mandatory. Most industrial processesrequired transition metal catalysts, their reactions proceeding heterogeneously on solid-support surfaces inside production chambers. For example, in the Deacon process, cupricchloride catalysed the oxidation of hydrogen chloride to produce chlorine (1883); finely-divided platinum was essential in the Contact oxidation of sulfur dioxide (1898)[17,571. TheHaber process (1913) utilized platinum or iron oxide catalysts for nitrogenhydrogenation[’7l.Fischer and Tropsch (1925) engineered the use of catalytic nickel oriron for the production of methane from carbon monoxide[371.Commercial hydrogenationof vegetable oils and ethylene became economically feasible through the action of ‘Raney’nickel (1927) and cobalt (1933)[171. Methanol became available by means of zinc oxidecatalysed reduction of carbon monoxide in 1934[17,571.3As well as their catalytic function, large amounts of durable and refractorytransition metal alloys in the form of materials and machinery were developed for use inconstruction and operation of factories producing new materials. Unique alloys werefabricated for specific tasks, such as for drilling, die-making, heat resistance, inertness tocorrosion, electrical conductivity, etc. (e.g.; Monel metal, Nichrome, Prestal, Wood’salloy, ‘stainless’ steel, etc.)[121lAt the beginning of the twentieth century, almost all the stable transition metalelements had been isolated and characterised. During this century, transition metals andtheir compounds have become more important than ever for the industrial success of amodern economy. Understanding the mechanism of catalytic activity is crucial fordeveloping new industrial materials with unique properties; and for creating innovativealloy compositions and semi-conductive materials for new electronic and structuraltechnologies. In the last part of the twentieth century, the increase in production andexpanded use of petroleum, fissile materials, plastics and pharmaceuticals as well assophisticated research in such fields as computer and space technology, environmentalmonitoring, new industrial production and bio-engineering has made obligatory anunderstanding of transition metal chemistry.2. Organo-Transition Metal CompoundsHistorically, modern organo-transition metal chemistry began in 1827 with Zeise’sdiscovery of an ethylene complex of platinum, K[(C2H4)PtCl3j ’11.In 1919 Hemsynthesised the first‘6-arene chromium complexes[53].Expansion of the petroleumindustry after 1898 and the need for high octane aircraft fuels during World War I led to thedevelopment of organometallic anti-knock agents such as tetraethyllead; organoleadcomplexes were first synthesised by Pfeiffer in 19O4[1. Reihien prepared butadienyl iron4tricarbonyl in 1930[100], and later its use as an anti-knock agent was patented by Veitmanin 1947[1191.Some important recent developments in organo-transition metal chemistry wereinitiated with the discovery of ferrocene in 1951 by Kealy and Pauson[67]and byMiller[78l. The sandwich structure proposed for this complex by Wilkinson in 1952[1241led to radical new ideas concerning structure and the nature of chemical bonding, as well asto the synthesis of vast numbers of new and unique organo-transition metal compounds,such as the dicyclopentadienyl cobalt cation characterised by E. 0. Fischer in 1952[381.Investigation into the mechanism of transition-metal catalysed hydrogenation insolution was begun by Halpern in 1955[521. In the same year, the existence of fluxionalityin some organo-transition metal complexes was recognised by Cotton and Willcinson[1261.The first covalent metal-metal bonds were proposed for the compound [CpMo(CO)3]2 ifl195 8[1271 and the first dinitrogen organo-ruthenium complex identified by Allen and Senoffin 1965[11. Commercially, other sophisticated organo-transition metal catalysts have beendesigned for non-destructive, low pressure and low temperature industrial processes,especially in fields such as new drug development and enzyme research.3. Transition Metal Carbonyl CompoundsThe first characterised transition-metal carbonyl complex, PtC12(C0) wasprepared in 1868 by Schutzenberger[107].In 1890 Mond identified nickel tetracarbonyl,Ni(C0)4,in corrosion residues from nickel pipes[82 and in the next year (1891) preparedand characterised iron carbonyl, Fe(CO)5[83.Reihien (1930) synthesised one of the firstorgano-transition metal carbonyl compounds possessing an unsaturated hydrocarbonligand, butadienyl iron tricarbonyl,i4-CH6Fe(CO)3[’°°].During the decades after 1950,other transition metal carbonyl complexes derived from unsaturated precursors wereprepared; for example, CpMn(CO)3 in 1955[961; [CpMo(CO)3]2in 1958[127]; and50s3(CO)11C(CH2)in 1982[621. Hypotheses regarding such phenomena as d-7u backbonding[63’8498I;metal-metal interactions in clusters[911’1664];multiple-decker sandwichstructures[70721101; fluxionality[8’120];and agostic bonding[7980Iare continually beingmodified through ongoing study of the large assortment of these and other new andunusual complexes recently becoming available. Advances in spectroscopic techniquessuch as NMR, XRD and UV-vis-IR spectroscopy have enabled the characterisation ofstructural parameters of these materials, mainly in solid and liquid phases and in solution.Over the past decade there has been increasing interest in the gas phase chemistry oftransition metal carbonyl complexes[20’4699310816J In order to take advantage of thesubtle and versatile capabilities of mass spectrometry, gas phase techniques have beendeveloped for manipulating and examining transition metal complexes, utilizing guided ionbeam[4-6’511;flowing afterglow[”3”4I;or Fourier transform ion cyclotron resonancemass spectrometry [13,21,47,74,1221; coupled with EI[44’77.925l;CID[ 122,1291 or laserionisation[45’5891.Free of matrix and solvent interferences, transition metal carbonylmolecules and their ions in the gas phase can undergo a wealth of ion-molecularinteractions within the ion source of the mass spectrometer and such studies can yield bothstructural and thermodynamic information regarding these materials and the mechanism ofinteraction with their ion fragments[3l843,65,75]Using ICR in 1973, Dunbar[29]observed anion-molecule condensations in themetal carbonyl systems of Cr(CO)6, Ni(CO)4and Fe(CO), which resulted in formation ofbimetallic cluster anions. Later, Beauchamp[40’1]examined fragment cations and clusterion products in the Fe(CO)5 system, observing cluster fragments containing up to four ironatoms. Ion-molecule clustering has been monitored in these and many other metal carbonylsystems, such as those of Fe(CO)5[43l,Re2(CO)107577],Ni(CO)4[41,Cr(CO)6[12’43l,CoNO(CO)3[], Mn2(CO)lo[761 and0s(CO)10H85].In the latter study, fragment ioniccluster cores containing up to 15 metal atoms were identified. The relationship betweenreactivity of fragment ions and ion clusters and the electron unsaturation of their central6metal atoms has been examined by Ridge[761 and Russell[43]and others. Multiple bondingbetween metal atoms has been invoked to explain some of the kinetic behaviour of theseions[ 1O2] As well, efficiencies of reactions of certain metal-carbonyl ions with neutralmolecules have been explained as depending upon electronic mobility within the complexitself[1041.Other ICR studies have concentrated on ion-molecule interactions between noncarbonyl ligated transition metal ions and their parent neutral molecules. For example,Schildcrout[1041 has observed polynuclear clusters containing up to three metal atoms andfive ligand moieties (M3L5)in the mass spectra of CrL3,FeL3,CoL3 and CoL2 whereL=bidentate ligands bonded to the metal through oxygen atoms. Ligand binding energieshave been determined by a number of techniques such as by CID[5586611 11,photodissociation[47M89J,and thermochemical methods[23’1121.4. Aryl Transition Metal CompoundsThe recognition of the unusual properties of tetraethyl lead encouraged preparationof other alkyl- and aryl- complexes of transition-metals. Methyl platinum compounds(1907)[971 and alkyl gold complexes (1934)[141 were discovered early in this century, aswas Hem’s peculiar benzene chromium compound[53l.Transition metal complexes withunsaturated, aryl-type hydrocarbon ligands have been a subject of intense interest since1951, with the synthesis of ferrocene[67’781.Characterisation of metallocenes containingvanadium, chromium, manganese, iron and cobalt by Wilkinson, Cotton and Birminghamin 1956[125] led to greater understanding of the unique Cp ligand and its mode of it-bonding to these metals.Transition metal complexes and ions containing unsaturated, aryl-type hydrocarbonligands have been studied more recently in the gas phase using ion cyclotron resonancemass spetrometry. Examining the ion-molecule chemistry of ferrocene (Cp2Fe) and7nickelocene (Cp2Ni), Beauchamp[25’411found that the parent cation (i.e., Cp2metal) waskinetically stable, whereas the daughter cations, therefore the ions (metal) and (Cpmetal)+ were reactive, and subsequently underwent charge exchange with the parentmolecule to produce Cp2metal+, or else condensed with the parent neutral molecule to formlarger cluster ions, Cp2metal2 and Cp3metal2 (the well-known “triple-decker sandwich”ion) which has been examined both experimentally[55’106”30and theoretically[9’56721.Innegative ion experiments, only the stable parent anion (i.e., Cp2metalj, generated by initialelectron capture, was observed in the Cp2Ni and Cp2Fe systems[25’41l.5. 11-Alkenyl Transition Metal Carbonyl ComplexesPerhaps the earliest example of the “piano-stool”, or “half-sandwich type” ofcompound (in which the transition metal center is linked both to carbonyl units, and inmulti-hapto fashion, to unsaturated alkene ligands) wasT4-butadienyl iron tricarbonyl, firstprepared by Reihlen in 1930[b001. Syntheses of new members of this class have continuedto the present. Some examples are: Cp2Ti(CO)2 (by Murray in 1959)[861;[C4HC0(CO)2](by E. Fischer, 1961)[391; Cp allyl iron carbonyl (by Green and Nagy, 1963)[5°1; benzenevanadium tetracarbonyl cation (by Calderazzo, 1964)[15]; Cp4Fe4(CO) (by King,1966)[681. In these complexes the ailcene-metal linkage consists of strong multiple it-bonding between the conjugated double bond system of the hydrocarbon ligand and thecentral metal atom. The bound alkyl group consequently modifies the electronic structureand electropositivity of the metal, and simultaneously acts as a partial steric barrier towardincoming reactive groups.In one of the first gas phase studies of such complexes, MUller[871 noted thatfollowing ionisation, the ions and neutral molecules ofr5-cyclopentadieny1 transitionmetal carbonyl complexes of chromium, manganese, cobalt and vanadium interacted to8produce secondary, bimetallic ion clusters consisting of various amounts of Cp and COunits, for example, Cp2V2(CO)3.In 1973, MUller and Goll[88l examined ion-molecule interactions of neutralCpNiNO and its fragment cations. Again, cluster cation products containing two nickelatoms were produced. Reactions of product cation CpNiCO+ with small moleculesapparently proceeded via simple addition combined with NO loss. In 1977, Corderman andBeauchamp[26lpostulated that the marked non-reactivity of the cluster anion Cp2Co2(CO)2in the negative ion-molecule regime of CpCo(CO)2probably reflected partial doublebonding between cobalt atoms within the cluster.In a seminal positive ion study, Parisod (1980) showed that complex reactionpathways could be resolved by multiple resonance techniques, in which individual ions orgroups of ions could be removed from the reaction cell, thus simplifying kineticmeasurements on the remaining reactants. As a result of this technique, many fragmentcations and their multi-metallic cluster products in each of the CpMn(CO)3, CpCr(CO)2NOand CpCr(CO)2NS systems were shown to be relatively unreactive[921.Other important features of these latter three systems were: firstly, that clusterswere generated containing up to 3 Cp-metal moieties, and secondly, that most of theobserved ionic cluster products in these systems retained the 1:1 ratio of Cp-metalstoichiometry, indicating that Cp-metal bonds were very stable, retaining their integritythroughout entire ion-molecule reaction regimes.However, the high mobility of CO residues under the same experimental conditionsdemonstrated the relative lability of metal-carbonyl bonds in these ion clusters. Finally, inthe latter two systems { CpCr(CO)2N0 and CpCr(CO)2NS }, unusual rupture of NO andNS ligands, with retention of metal-nitrogen linkages within the ion cluster, was seen insome cluster products, whereas comparable CO links appeared to remain undisturbed[92l.Comparing the CpCr and CpMn systems previously discussed, Chen[181 noted thatin the cation-molecule cluster chemistry of CpCr(NO)2CH3,Cp-metal bonds also tended to9remain intact during the electron ionisation procedure, as well as throughout subsequention-molecule interactions, and retained 1 : 1 Cp-to-metal ratios in most product ions.Exceptions to this, where 1: 1 Cp-to-metal stoichiometry was not maintained, were foundonly where bare metal cations underwent condensation with the parent neutral molecule, orin highly oxygenated ionic cluster products of chromium (e.g. Cp2Cr3O ,Cp4Cr5(NO)03j. These oxygenated clusters, containing more metal atoms than Cpligands, were postulated to possess either chromium-oxygen multiple bonding, or loweredcyclopentadienyl hapticity[18].Gas phase reactivities of a series of ion products of several substituted T16-areneCr(CO)3 complexes were studied by Freiser in 1991[89]. In most cases, 1:1 arene-to-Crstoichiometry was preserved throughout ion molecule interactions; principal reactionchannels involved ion-molecule condensation, accompanied by CO loss.Recently, Kan (1991) has found that reactivities of daughter cation products in thehexadienone iron (r4 -C6HOFe(CO)3system varied directly with electron deficiency ofthe central iron atom[651.Kinetic trends in these and in other metal-carbonyl systems havebeen related earlier to coordination unsaturation and formal electron deficiency of thecentral metal atom. Anomalies in kinetic activity have been attributed to enhanced metal-metal bonding or to carbonyl ligand restructuring within the metal cluster cores[101’02.Theoretical models of some of these metal-ligand clusters have been considered byLauher[70721 and Teo[117] Closely-packed polyhedral metal cores with attendant clustervalence molecular orbitals (CVMO), have been invoked by Ridge and others[M,7981,lOhlto explain observed kinetic stability patterns. Some fundamental aspects of ion reactivity inthese systems, such as metal-ligand bond energies[44’755l, ligandexchange[’69’7491108l,interaction with small molecules[12’4914], and ability to activatecarbon bonds[2198596°continue to be of great interest in the development ofstructural understanding of these important materials. With regard to cluster formation,fundamental comparisons have been drawn with respect to bonding reactivity and catalytic10behaviour of larger metal cluster ions, with bulk metal surfaces where the metal centres areextremely unsaturated with respect to their ligands[48’7128110161.Multiple or partialmultiple bonding between metal atoms within clusters have long been invoked in order toexplain spectroscopic and reactivity differences[27’1278].As well as coordination saturation, reactivity of bare metal ions depends upon theirelectronic state; bare metal cations in excited states may react in pathways or at rates whichgreatly differ from those of the corresponding ground-state cation[7’30359091 314]•116. An Analogous Series of “Aryl” Transition-MetalCarbonylsAn examination of “homologous series”, wherein one chosen variable within agroup of related substances differs in a consecutive, orderly manner, can be invaluable indetermining trends, testing models of chemical behaviour, thus yielding insight into thefundamental mechanisms of interaction on the molecular scale[111. Subtle chemicalgradations between two members permit discrimination between the effects of that variableand of others, and enable exact parameters to be measured, and relationships to bedetermined. In the present study, organic compounds of five consecutive first rowtransition metals (vanadium to cobalt) are examined. These five metals are of vitaleconomic importance, being catalytically active, and forming essential components ofstructural, electrical and tool alloys. Their chemical properties, both similarities anddifferences, arise from their electronic structure consisting of partly-filled 3d and 4sorbitals in the valence shell.The present work comprises a study of quasi-homologous (‘analogous’)compounds consisting of complexes of this sequence of five early third-period, transitionmetals (vanadium (Z=23), chromium (Z=24), manganese (Z=25), iron (Z=26) and cobalt(Z=27) }. Each complex in the series contains both a conjugated hydrocarbon (‘aryl type’)ligand bonded in multi-it fashion, and several carbonyl ligands, all linked to the centraltransition metal. Each member of the series is ligand-saturated, containing an 18 - electrontransition metal core, as follows:5-CHV( O)4(Chapter 2);T16-CHCr(CO)3(Chapter 3);rj5-CHMn(CO) (Chapter 4);fl-C4H6Fe(CO)3 (Chapter 5); and 5-C5Ho(CO)2(Chapter 6). An attempt to correlate the results for all five systems ispresented in Chapter 7. Since this series is not perfectly homologous (i.e., the complexescontain differing numbers of carbonyl ligands, and all arene ligands are not identical) it hasbeen labelled an “analogous series”. Obviously, chemical differences in this series arise12from differences in electronic constitution of the central metal atom, as well as arene type,and number of CO ligands present. Yet, their closely-related structures and similar overallcomposition make a comparative study of the ion-molecule chemistry of this analogous”series of compounds potentially informative and interesting.137. Structures of Compounds Examinedi) Tetracarbonyl (i - cyclopentadienyl) vanadiumoc 0ii) Tricarbonyl Cq6 - benzene) chromiumCrOC I CoC0iii) Tricarbonyl (q5 - cyclopentadienyl) manganeseoc’’Mn“COiv) Tricarbonyl (1-4-4 - butadienyl) ironv) Bicarbonyl (T)5- cyclopentadienyl) cobalt148. Gas Phase TechniquesChemical interactions with the solvent often obscure and complicate thechemistry of metal complexes. Accordingly, gas phase techniques such as massspectrometry can be extremely useful in the elucidation of solvent-free behaviour.However, most mass spectrometric methods require volatile sample materials or else somespecial volatilisation procedure in order to attain sufficient sample pressure for ion-molecule interactions to be observed and quantified. Moreover, some organometallics areinvolatile or thermally unstable. Fortunately, such compounds can be examined under thelow pressure conditions of ICR-MS. at normal, non-destructive temperatures. Subjectmolecules can be introduced under high vacuum into the reaction cell of the ICRinstrument, ionised with. a burst of electrons, and the presence, appearance, anddisappearance of daughter ions monitored at exact time intervals.It was hoped that gas phase analysis of the kinetic behaviour and ion chemistry ofthe members of this analogous series of transition metal complexes would yield someinsight into electronic trends among these important transition metals. Accordingly,attempts were made to conduct all parallel experiments, under experimental conditionswhich were as identical as possible.II Experimental Procedure1. Experimental ParametersAll experiments were performed using prototypic FT-ICR mass spectrometricinstrumentation which had been assembled at the University of British Columbia in 1973,equipped with a 1.9 Tesla electromagnet, and later updated by the installation of a NicoletFTMS 1000 computer-directed electronic console. A cubic cell (16.4 cm3 volume) served15as the ion trap and reaction chamber, into which reagents were introduced through leakvalves at ambient temperature. Typical operating parameters were as follows: electron beamenergy ranges: 10-70 eV (positive El); 1-5 eV (negative El); trapping voltage ranges:±l.OV; reagent pressure ranges: 10-6- io-9 torr; ion trapping time spans: 0 - 25 sec.Reagent pressures were monitored with a Varian model 971-0018 ionization gauge:constant system pumping speed and sample introduction rates were maintained duringcomplete experimental sequences in order to maximise pressure equilibration betweenpressure gauges and reaction cell.Corroborating structural and adduct composition data were obtained for CpV(CO)4with a Nermag R10-1OC quadrupole mass spectrometer equipped with DCI capability. Inthese latter experiments parameters were as follows: collision gas pressure: 0.01 torr;electronbeam energy: 70 eV (positive and negative El); monitoring time: 0-10 seconds.2. Chemical CompoundsPure specimen compounds were obtained from Alfa Products. No impurities otherthan carbon monoxide, and benzene in the tricarbonyl benzene chromium study, fromproduct decomposition, were observed in the mass spectra of any member of the series.Gaseous impurities were removed by freeze-pump-thaw cycles. Liquid samples were firstpurified by distillation under vacuum and stored cold under argon.Sample materials of low volatility were introduced by means of a shortened, heatedinlet system. Before admission into the reaction chamber, all sample materials werethoroughly degassed, and during admission were further degassed until no impuritiesappeared in their mass spectra. Highly volatile samples were held frozen in liquid nitrogen,carbon dioxide or ice during sample admission. Collision gases were introduced using asecondary inlet while maintaining constant pressure within the reaction chamber.163. Principles of Ion Cyclotron ResonanceIn a fixed magnetic field, charged particles (ions) are subject to a centripetal(Lorenz) force causing them to be constrained in a helical paths along the axis of themagnetic field. The frequency ti of this helical motion is given by ti5 = qB/m where q isthe charge on the ion, m is the ion mass and B is the magnetic field strength. To preventions from escaping the magnetic field region, similarly-charged plates are situated at thefront and back of the helical pathways. The frequency of revolution of such a trapped ion iscalled its ion cyclotron frequency.Identical ions thus electrically trapped can absorb energy from an externally appliedalternating electric field, causing them to become excited as their velocity and orbital radiusincrease in a coherent spiral. If the applied frequency exactly matches that of the ioncyclotron frequency, the ions will move as packets in a larger coherent orbit and are said tobe in resonance. When the ac electric field is terminated, the new expanded orbital radius ofthe ion collection remains constant. If the collection of ions passes close to a pair ofsensing plates, an image current is established within the plates, whose frequency dependsupon the mass-to-charge ratio (m/e) of the cycling ions, and whose intensity depends uponthe numbers of ions within the ion packet in transit[21’21.When an assortment of ions of differing masses is trapped, a range of radiofrequencies, corresponding to the range of ion masses, can be used to energize all ions intoresonance, and the sensed signal becomes a composite mixture of all their ion cyclotronfrequencies. By computer-directed Fourier analysis, this signal can be sorted into thecomponent ion frequencies and amplitudes, and this array then converted into masses andabundances of each type of ion, thus generating a mass spectrum of all the ions present(“single pulse resonance”). Many identical repetitions of this process will enhance thesensitivity of this mass spectrum[21221•17If the collection of resonant ions is energised either by a strong single radiofrequency (“double resonance”), or by a band of radio frequencies (“triple resonance”), theions whose cyclotron resonances are in these ranges can be excited until they are ejectedfrom the trapping zone[92l. Then the remaining ions can be detected as before (i.e., by“single resonance”). This procedure enables any specific ion mass to be expelled from thereaction cell in order to identify its ion products by difference; or, packages of ions to beeliminated from an ion mixture in order to quantify the disappearance of a single reactiveion and monitor its ion products[3’2126473109”31.A schematic diagram of the FTICR reaction cell is illustrated in Figure A.1. in Appendix II, page 257.In practice, pressures of reactant molecules (Pm) in the ICR trapping zone weremaintained at low, constant pressures, typically in the range i0- - 109 torr. Parameterssuch as ionising electron energies, electron flux, beam time, trapping voltage and ambienttemperature were held as constant as possible. Each mass spectrum was generated andcomputer scanned 100-1000 times; and duplicate or triplicate series were performed foreach set of timed experiments.Calibration masses were chosen from available calibration compounds deuteriumoxide, nitrogen and methyl bromide, and from three or four ions present in the massspectra with as wide a mass range as possible. To simplify kinetic analyses, small moleculeexperiments were conducted at conveniently large pressure ratios; i.e.: pressure of smallreactant gases was 10-100 times greater than pressure of each specimen compound. Kineticbehaviour was monitored for 0 - 25 seconds. Intensities of each reactant ion werenormalised as proportions of total ions present, i.e.;Relative intensity of ion i=[IjJ / E ([Iai + [Ib] +. . . + [Inj)before kinetic analysis. Slopes of linear semilog plots were used to calculate pseudo-firstorder rate constants, typically with ±5% precision. Because of uncertainty in pressurecalibration, second order rate constants were estimated to be accurate within ± 30% only.18III References(1) Allen, A. D.; Senoff, C. V. J. Chem. Soc. Chem. Commun. 1965, 621.(2) Allison, J.; Freas, R. B.; Ridge, D. P. J. Am. Chem. Soc. 1979, 101, 1332.(3) Allison, J. Prog. Inorg. Chem. 1986,34, 627.(4) Aristov, N.; Armentrout, P. B. J. Am. Chem. Soc. 1984, 106, 4065.(5) Armentrout, P. B.; Hafle, L. F.; Beauchamp, J. L. J. Am. Chem. Soc. 1981,103, 6501.(6) Annentrout, P. B.; Beauchamp, J. L. .1. Am. Chem. Soc. 1981, 103, 784.(7) Armentrout, P. B. in Gas Phase Inorganic Chemistry; Russell, D. H.; PlenumPress, New York, 1989; pp 1 - 42.(8) Benfield, R. E.; Johnson, B. F. G. J. Chem. Soc., Dalton Trans. 1980, 1743.(9) Bottomley, F.; Grein, F. Inorg. Chem. 1982,21, 4170.(10) Bottomley, F.; Paez, D. E.; White, P. S. J. Am. Chem. Soc. 1982, 104, 5651.(11) Bottomley, F.; Sutin, L. Adv. Organomet. Chem. 1988,28, 339.(12) Bricker, D. L.; Russell, D. H. J. Am. Chem. Soc. 1987, 109, 3910.(13) Buchanan, M. V. Fourier Transform Mass Spectrometry; Comstock, M. J.;American Chemical Society: Washington, D. C., 1987.(14) Burawoy, A.; Gibson, C. S. J. Chem. Soc. 1934, 860.(15) Calderazzo, F. Inorg. Chem. 1964,3, 1207.(16) Castleman Jr., A. W.; Keesee, R. G. Chem. Rev. 1986, 86, 589.(17) Cavell, A. C. An Introduction to Chemistry; Macmillan and Co., Ltd.: London,1957.(18) Chen, S.-P.; Comisarow, M. B. Ann. Conf. ASMS All. Top. 1989, 37, 323.(19) Chen, H.; Lin, H.-Y.; Sohlberg, K.; Ridge, D. P. Ann. Conf. ASMS All. Top.1991,39, 1596.(20) Chini, P. J. Organomet. Chem. 1980,200, 37.19(21) Comisarow, M. B. J. Chem. Phys. 1978, 69, 409.(22) Comisarow, M. B.; Buchanan, M. V. ACS Symposium Series 359, 1987, 1 -20.(23) Connor, J. A. Top. Curr. Chem. 1977, 71, 71.(24) Constable, E. C. Metals andLigandReactivity; Ellis Horwood Ltd.: Chichester,England, 1990.(25) Corderman, R. R.; Beauchamp, J. L. Inorg. Chem. 1976, 15, 665.(26) Corderman, R. R.; Beauchamp, J. L. Inorg. Chem. 1977, 16, 313.(27) Cotton, F. A.; Walton, R. A. Struct. Bond. 1985, 62, 1.(28) Crabtree, R. H. Chem. Rev. 1985, 85, 245.(29) Dunbar, R. C.; Ennever, J. F.; Fackler, J. P., Jr. Inorg. Chem. 1973, 12, 2734.(30) Elldnd, J. L.; Armenirout, P. B. J. Phys. Chem. 1984, 88, 5454.(31) Elkind, J. L.; Armentrout, P. B. J. Phys. Chem. 1985, 89, 5626.(32) Elkind, 3. L.; Armentrout, P. B. J. Chem. Phys. 1986, 84, 4862.(33) Elkind, J. L.; Armentrout, P. B. J. Phys. Chem. 1986, 90, 5736.(34) Elkind, 3. L.; Armentrout, P. B. J. Phys. Chem. 1986, 90, 6576.(35) Ellcind, J. L.; Armentrout, P. B. J. Chem. Phys. 1987, 86, 1868.(36) Eller, K.; Schwarz, H. Chem. Rev. 1991,91, 1121.(37) Fischer, F.; Tropsch, H. D.R.P. 1922, 1925., # 411416; 484337.(38) Fischer, E. 0.; Pfab, W. Z. Naturforsch. 1952, 7B, 377.(39) Fischer, E. 0.; Kuzel, P.; Fritz, H. P. Z. Natuiforsch. 1961, 16B, 138.(40) Foster, M. S.; Beauchamp, J. L. J. Am. Chem. Soc. 1971, 93, 4924.(41) Foster, M. S.; Beauchamp, J. L. .1. Am. Chem. Soc. 1975, 97, 4808.(42) Freas, R. B.; Dunlap, B. I.; Waite, B. A.; Campana, J. E. J. Chem. Phys. 1987,86, 1276.(43) Fredeen, D. J. A.; Russell, D. H. .1. Am. Chem. Soc. 1985, 107, 3762.(44) Fredeen, D. J. A.; Russell, D. H. J. Am. Chem. Soc. 1986, 108, 1860.20(45) Freiser, B. S. Anal. Chim. Acta 1985, 178, 137.(46) Freiser, B. S. Chemtracts-Anal. Phys. Chem. 1989, 1, 65.(47) Freiser, B. S. in Bonding Energetics in Organometallic Compounds; Marks, T.;American Chemical Society, Washington, D. C., 1990; pp 55-69.(48) Geusic, M. E.; Morse, M. D.; Smalley, R. E. .1. Chem. Phys. 1985, 82, 590.(49) Gord, J. R.; Freiser, B. S. J. Am. Chem. Soc. 1989, 111, 3.(50) Green, M. L. H.; Nagy, P. L. I. J. Chem. Soc. 1963, 189.(51) Halle, L. F.; Armentrout, P. B.; Beauchamp, J. L. Organometallics 1982, 1,963.(52) Halpern, J. Inorg. Chim. Acta 1985, 100, 41.(53) Hem, F. Ber. D. Chem. Ges. 1919,52, 195(54) Hettich, R. L.; Jackson, T. C.; Stanko, E. M.; Freiser, B. S. J. Am. Chem. Soc.1986, 108, 508.(55) Hettich, R. L.; Freiser, B. S. J. Am. Chem. Soc. 1987, 109, 3537.(56) Hoffman, R. Science 1981, 211, 995.(57) Holmyard, E. J. Makers of Chemistry; Clarendon Press: Oxford, 1931.(58) Houriet, R.; Halle, L. F.; Beauchamp, J. L. Organometalllcs 1983, 2, 181.(59) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1983, 105, 5197.(60) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1983, 105, 7485.(61) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1985, 107, 5870.(62) Johnson, B. F. G.; Lewis, J.; Raithby, P. R.; Swankey, S. W. J. Organomet.Chem. 1982,231, C65.(63) Johnston, R. D. Adv. Inorg. Chem. Radiochem. 1970, 13, 471.(64) Kaldor, A.; Cox, D. M.; Trevor, D. J.; Zakin, M. R. Metal Clusters;Trager, F. zu Putlitz, G.; Springer: Berlin, 1986.(65) Kan, Z.; Comisarow Ann. Conf. ASMS All. Top. 1991, 39, 461.(66) Kappes, M. M.; Staley, R. H. J. Phys. Chem. 1981,85, 942.21(67) Kealy, T. J.; Pauson, P. J. Nature 1951, 168, 1039.(68) King, R. B. Inorg. Chem. 1966,5, 2227.(69) Lane, K. R.; Sallans, L.; Squires, R. R. .1. Amer. Chem. Soc. 1986, 108, 4368.(70) Lauher, J. W.; Elian, M.; Summerville, R. H.; Hoffman, R. J. Am. Chem. Soc.1976, 98, 3219.(71) Lauher, J. W. .1. Am. Chem. Soc. 1979, 101, 2604.(72) Lauher, 3. W. .1. Organomet. Chem. 1981,213, 25.(73) Marshall, A. G.; Grosshans, P. B. Anal. Chem. 1991, 63, 215A.(74) McDonald, R. N.; Schell, P. L. Organomet. 1988, 7, 1806.(75) Meckstroth, W. K.; Ridge, D. P. mt. J. Mass Spectrom. Ion Proc. 1984, 61,149.(76) Meckstroth, W. K.; Ridge, D. P.; Reents, W. D., Jr. J. Phys. Chem. 1985, 89,612.(77) Meckstroth, W. K.; Ridge, D. P. J. Am. Chem. Soc. 1985, 107, 2281.(78) Miller, S. A.; Tebboth, J. A.; Tremaine, J. F. J. Chem. Soc. 1952, 632.(79) Mingos, D. M. P. Acc. Chem. Res. 1984, 17, 311.(80) Mingos, D. M. P.; May, A. S. in The Chemistry ofMetal Cluster Complexes;Shriver, D. F.; Kaesz, H. D. Adams, R. D.; VCH Publishers, New York, 1990;pp 11 - 119.(81) Mingos, D. M. P.; Slee, T.; Zhenyang, L. Chem. Revs. 1990, 90, 383.(82) Mond, L.; Langler, C.; Quinche, F. Trans. Chem. Soc. 1890, 749.(83) Mond, L.; Langler, C. Trans. Chem. Soc. 1891,59, 1090.(84) Muetterties, E. L.; Rhodin, T. N.; Band, E.; Brucker, C. F.; Pretzer, W. R.Chem. Rev. 1979, 79, 91.(85) Mullen, S. L.; Marshall, A. G. J. Am. Chem. Soc. 1988, 110, 1766.(86) Murray, J. G. J. Am. Chem. Soc. 1959, 81, 752.(87) Muller, J.; Fenderl, K. Chem. Ber. 1970, 103, 3128.22(88) Muller, J.; Goll, W. Chem. Ber. 1973, 106, 1129.(89) Operti, L.; Vaglio, G. A.; Gord, 3. R.; Freiser, B. S. Organometallics 1991, 10,104.(90) Oriedo, I. V.; Russell, D. H. Ann. Conf. ASMS All. Topics 1991, 39, 1610.(91) Pan, Y. H.; Ridge, D. P. J. Am. Chem. Soc. 1989, 111, 1150.(92) Parisod, G.; Comisarow, M. B. Adv. Mass Spectrom. 1980, 8A, 212.(93) Pearson, R. G. Inorg. Chem. 1984,23, 4675.(94) Pfeiffer, P.; Truskier, P. Ber. D. Chem. Ges. 1904, 37, 1125.(95) Pignataro, S.; Foffani, A.; Grasso, F.; Cantone, B. Z. Physik. Chem. (Frankfurt)1965,47, 106.(96) Piper, T. S.; Cotton, F. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1955, 1, 165.(97) Pope, W. J.; Peachey, S. J. J. Chem. Soc. Transactions 1909, 571.(98) Pruchnik, F. P. Organometallic Chemistry of the Transition Elements; Fackler Jr.,J. P.; Plenum Press: New York, 1990.(99) Reents, J., W. D. ; Strobel, F.; Freas, R. B.; Wronka, J.; Ridge, D. P. J. Phys.Chem. 1985, 89, 5666.(100) Reihlen, H.; Gruhi, A.; Hessling, G. v.; Pfrengle, 0. Liebig’s Annalen DerChemie 1930,482, 161.(101) Ridge, D. P.; Meckstroth, W. K. in Gas Phase Inorganic Chemistry; Russell, D.H.; Plenum Press, New York, 1989; pp 93-113.(102) Russell, D. H.; Fredeen, D. A.; Tecklenburg, R. E. in Gas Phase InorganicChemistry; Russell, D. H.; Plenum Press, New York, 1989; pp 115-135.(103) Russell, D. H. Ann. Con!. ASMS All. Top. 1990, 38, 1261.(104) Schildcrout, S. M. Inorg. Chem. 1980, 19, 224.(105) Schultz, R. H.; Elkind, 3. L.; Armentrout, P. B. J. Am. Chem. Soc. 1988, 110,411.(106) Schumacher, E.; Taubenest, R. Helv. Chim. Acta 1964,47, 1525.23(107) Schutzenberger, P. Annalen 1868, 15, 100.(108) Sellers-Hahn, L.; Russell, D. H. J. Am. Chem. Soc. 1990, 112, 5953.(109) Sharpe, P.; Richardson, D. E. Coord. Chem. Revs. 1989, 93, 59.(110) Shriver, D. F.; Kaesz, H. D.; Adams, R. D. The Chemistry ofMetal ClusterComplexes; VCH Publishers, Inc.: New York, 1990.(111) Simoes, J. A. M.; Beauchamp, J. L. Chem. Revs. 1990, 90, 629.(112) Skinner, H. A.; Connor, J. A. Pure Appi. Chem. 1985,57, 79.(113) Squires, R. R. Chem. Rev. 1987, 87, 623.(114) Squires, R. R.; Lane, K. R. in Gas Phase Inorganic Chemistry; Russell, D. H.;Plenum Press, New York, 1989; pp 43-91.(115) Strobel, F.; Ridge, D. P. .1. Am. Soc. Mass. Spectrom. 1990, 1, 192.(116) Sung, S.-S.; Hoffman, R. J. Am. Chem. Soc. 1985, 107, 578.(117) Teo, B. K.; Longoni, G.; Chung, F. R. K. Inorg. Chem. 1984,23, 1257.(118) Thompson, C. J. S. The Lure and Romance of Chemistry; George C. Harrop andCo. Ltd.: London, 1932.(119) Veitman, P. L. U.S.P. 1946, # 2409167.(120) Wade, K. Transition Metal Clusters; Johnson, B. F. G.; J. Wiley and Sons: NewYork, 1980.(121) Weast, R. C. Handbook of Chemistry and Physics 1974,54, B4- 38.(122) Weddle, G. H.; Allison, 3.; Ridge, D. P. J. Am. Chem. Soc. 1977, 99, 105.(123) Wilkins, C. L.; Chowdhury, A. K.; Nuwaysir, L. M.; Coates, M. L. MassSpectrometry Reviews 1989, 8, 67.(124) Wilkinson, G.; Rosenbium, M.; Whiting, M. L.; Woodward, R. B. J. Am. Chem.Soc. 1952,74, 2125.(125) Wilkinson, G.; Cotton, F. A.; Birmingham, 3. M. J. Inorg. Nucl. Chem. 1956,2, 95.(126) Wilkinson, G.; Cotton, F. A. Prog. Inorg. Chem. 1959, 1, 1.24(127) Wilson, F. C.; Shoemaker, D. P. J. Chem. Phys. 1958, 27, 809.(128) Wronka, J.; Ridge, D. P. J. Am. Chem. Soc. 1984, 106, 67.(129) Wronka, J.; Forbes, R.; Laukien, F.; Ridge, D. P. J. Phys. Chem. 1987, 91,6450.(130) Zagorevskii, D. V.; Nekrasov, Y. S.; Nurgalieva, G. A. J. Organomet. Chem.1980,194, 77.(131) Zeise, W. C. Ann. Phys. 1827, 9, 932.25CHAPTER 2Ion Molecule Chemistry ofTetracarbonyl (ri5 - Cyclopentadienyl) Vanadium{ CpV(CO)4 }26I IntroductionTetracarbonyl(r5-cyclopentadienyl) vanadium, CpV(CO)4, is an orange-colouredcrystalline, air-sensitive solid, melting at l39 C and subliming at 90 C (0.5 mm Hg).First prepared by Fischer and Hafner in 1954[b01, its molecular geometry resembles a“four-legged piano stool”, a square pyramidal V(CO)4 unit capped by a pinacoidpentagonali5-Cp unit. The crystal structure was first elucidated in 1967133].oc?’çgoVanadium carbonyls and organo-vanadium carbonyls have been of marked interestsince the synthesis in 1956 of the vanadium homologue of ferrocene; i.e., Cp2V, orvanadocene by Willdnson[34l.Some related organo-vanadium species, first synthesised insolution, were Cp2V2(CO)5 in 1970[241; the Cp2V(CO) cation[71, and vanadiumcarbonyls, V(CO)4and V(CO)5[211.Gas phase reactions of bare, as well as complexed vanadium ions have beenexamined since the positive ion mass spectral analyses on CpV(CO)4 by Winters[35landMuller[23] from 1965 to 1970. In these studies, series of daughter cations showingsuccessive losses of CO and Cp ligands were observed. Energetics of bonds involvingvanadium atoms in the gas phase have been analysed and collated[1’5630l.Bond order,bond strength and kinetics of gaseous V when combined with hydrogen[9l;alkane, alkeneand alkyne units[2’417];and oxygen[’8’26lhave been examined.Other mass spectral analyses have yielded evidence of gas phase cation-moleculecondensations resulting in generation of bimetal clusters such as Cp2V2(CO)3, first notedby Fischer and Schneider[11land MUller[23lin 1970. In the latter study, Cp2V2(CO)O..527ions were seen in the mass spectra of Cp2V2(CO)5. However, gas phase kinetic studies onthese and related ions, and on other Cp-vanadium carbonyls have not yet been performed.The present study, involving CpV(CO)4 positive and negative ion-molecule chemistry byFT-ICR-MS provides some useful information regarding the behaviour of bare and ligatedorgano-vanadium ions in the gas phase.II Results and Discussion1. Positive Ion Chemistrylonisation by a 25 eV electron beam on tetracarbonyl(5-cyclopentadienyl)vanadium, CpV(CO)4, generates fragment ions in the following proportions: CpV (42%),CpVCO (10%), CpV(CO)2 (14%), CpV(CO)3 (4%), CpV(CO)4(12%), V (7%) andminor amounts ofC3HV (5%). This ion distribution compares with that of Winters[351,who found the following cation distributions using 70 eV electron ionisation: CpV (41%),CpVCO (2.5%), CpV(CO)2+(4.3%), CpV(CO)3+(1.5%), CpV(CO)4 (3.3%), V(24%), C3HV(13%). Typical examples of FT - ICR mass spectra measured at 6.0x108torr pressure, exhibiting these ions immediately after electron ionisation, and subsequently,are as follows: Figure 2.1(a), initial cation fragments; Figure 2.1(b), after 300 msec hadelapsed; Figure 2.1(c), after 600 msec; and Figure 2.1(d), after 25 seconds. A table oftypical experimental data showing masses of ions and their intensities is shown in Table2.1.28zuJI-JLUMASS in AMUFigure 2.1(a). FT-ICR Positive Ion Mass Spectrum of600CpV(CO)4; 0 msec.; 2.5 eV; p = 6.OxIO8torr0 100 200 300 400 50029100’ii-80-z6O-I:::i. 11_______________________1,_______________________________________I I I. I0 100 200 300 400 500 600MASS in AMU.Figure 2.1(b). FT-ICR Positive Ion Mass Spectrum ofCpV(CO)4; 300 msec.; 25 eV; p = 6.OxlO8torr3010080(I)z60.40200Figure 2.1(c). FT-ICR Positive Ion Mass Spectrum ofCpV(CO)4;600 msec.; 2.5 eV; p = 6.Ox 10-8 torr200 300 400MASS in AMU31100-80-Iz60-40-2O-— I0 100 200 300 400 500 600MASS in AMUFigure 2.1(d). FT-ICR Positive Ion Mass Speàr.rum ofCpV(CO)4; 25 sec.; 25 eV; p =6. Oil 08 torr32TABLE 2.1Sample Mass Table for CpV(CO)4 Cations (5000 msec)Formula Measured Massa Expected Massa z (pum) Ret. mt. (%)51V (99.76%) 50.9335 50.9435 10 2.6C3HV 89.8995 89.9670 68 2.0C5HV 115.9865 115.9826 41) 13.3CpVCO 144.0002 143.9775 23 2.7CpV(C0) 171.9898 171.9724 17 3.7C p V (C 0)3 199.9358 199.9673 32 28.9CpV(CO)4 227.9626 227.9622 100(CpV)2 231.8427 231.9657 123 2.0(CpV)0 259.8998 259.9606 61 5.1(CpV)(C0) 287.9427 287.9555 13 7.0(CpV)(C0)3 315.9517 315.9504 2.6(CpV)(C0)4 3439555 343.9453 11 8.1(CpV)3 347.9488(CpV)30 375.9437(CpV)3(C0) 403.9750 403.9387 36 7.3(CpV)30 431.7990 431.9335 135 19.4(CpV)0)4 459.9129 459.9284 13.5a in daltonsb calibrant mass33General temporal behaviour patterns for each fragment ion were determined by thesingle resonance technique, in which the ions were generated by El, allowed to react overmeasured time periods, then analyzed by FT-ICR. During reaction periods of up to 25seconds, the following polynuclear ion cluster fragments were generated:Cp2V2(CO)o, 1 ,2,3,4Cp3V3(CO)2,3,4Cp4V4(CO)3,4Typical formation and disappearance behaviour of primary, (CpV)i(CO)o..4fragment cations are illustrated in Figure 2.2. Figures 2.3 and 2.4 show analogoustemporal behaviour patterns of some of the most prominent binuclear cluster cations, i.e.,(CpV)2O4,and trinuclear cluster cations, i.e., (CpV)3O4Application of FT-ICR multiple resonance techniques developed earlier[251permitted identification of reaction products of each daughter ion. Using multipleresonance, individual ion species were selected and products generated by that ion weretemporally monitored. For example, Figure 2.5(a,b) shows two multiple resonance spectraof CpV ion, initially and at 200 msec, after its ion products had been allowed to form. Aplot of temporal behaviour of CpV and its products is illustrated in Figure 2.6. Analogousspectra for the CpV(CO)3 ion, taken at at the same time intervals, are shown in Figure2.7(a,b), and temporal plots of this ion and its products are shown in Figure 2.8. Anexample of analogous spectra, measured initially and at 600 msec, and temporal behavioralplots for an important secondary cation cluster, (CpV)2(CO), and its reaction products,are shown in Figure 2.9(a,b) and Figure 2.10, respectively.Kinetic data obtained from temporal ion monitoring were used to obtain initialrelative rates of formation and decay of each ion product. Table 2.2 lists rate constants forthe disappearance of the principal reactive ions over time. Monitoring the temporal historyof each ion product revealed an interrelated series of reactive pathways which aresummarized in the following paragraphs.34800->1600- CpV CpV(CO)4.-400- / CpV(CO)3CpV(CO)2CpVCO +200-:0-I I I0 200 400 600 800 1000TIME (msec)Figure 2.2. Temporal Behaviour of PrimaryFragment Cations ofCpV(CO)435250-(CpV)2O200-G)150- (CpV)2O (CpV)2O3/(CpV)2+i00_ (CpV)2O450-__________________________12I I I I I0 200 400 600 800 100CTIME (msec)Figure 2.3. Temporal Behaviour of BinuclearCluster Cations of CpV(CO)436600-500- (CpV)3O400-a, (CpV)3O4C— 300- +a, (CpV)3O2(CpV)3I;______200-100-H0 200 400 600 800 bOaTIME (msec)Figure 2.4. Temporal Behaviour of TrinuclearCluster Cations of CpV(CO)437100-80-z60-I I I I I0 100 200 300 400 500 600MASS In AMUFigure 2.5(a). Multiple Resonance Mass Spectrum ofCpV; 0 msec.; p =6.OxlO8Lorr38100-80-z6O-0——I0 100 200 300 400 500 600MASS in AMUFigure 2.5(b). Multiple Resonance Mass Spectrum of CpV+and Cation Products; 200 msec; p = 6.Ox 108 torr39800-600 CpVCpVCO400- + CpV(CO)4(CpV)2020:-,___ (CPV):(CO)+\0 200 400 600 800 1000TIME (msec)Figure 2.6. Temporal Behaviour of CpV andCation Products4010080>.IC,,z6O40I I iI I0 100 200 300 400 500 600MASS in AMUFigure 2. 7(a). Multiple Resonance Mass Spectrum ofCpV(CO)3+; 0 msec.; p 6.OzlO8tort41100-80-Iz6O-0- I El Jr ,,0 100 200 300 400 500 600MASS in AMUFigure 2.7(b). Multiple Resonance Mass Spectrum ofCpV(CO)3 and Cation Products; 200 msec;p = 6.OxlO8 torr42CpV(CO)415-(CPV)2(CO)2\0 50 100 150 200TIME (msec)Figure 2.8. Temporal Behaviour of CpV(CO)3+and Cation Products43zwI-J‘UFigure 2.9(a). Multiple Resonance Mass Spectrum of(CpV)2CO: 0 msec; p = 6.Ol08 Lorr100MASS In AMU44100-80-Iz6O-z—H40-2O-l 1i i ___1j —0 100 200 300 400 500 600MASS in AMUFigure 2.9(b). Multiple Resonance Mass Spectrum of(CpV)2CO and Cation Products; 600 msec;p = 6.OxlO-84514- (CpV)312- (CpV)2O>-10-z /(CpV)3( O28-z— 6- CpV(CO)4—_I_zo 4..2-I I I I I0 200 400 600 800 100CTIME (msec)Figure 2.10. Temporal Behaviour of (CpV)2C0+ andCation Products46TABLE 2.2Disappearance Rates for Vanadium CationsRate Constant (k’) Rate Constant (k)(sec-1) * (x109 molec.cm3se)#V 0.604 2.61CpV 0.382 1.65CpVCO 0.227 0.98CpV(CO)2 0.120 0.52CpV(CO)3 0.0255 0.12CpV(CO)4 0.010 0.043(CpV)2 0.259 1.12(CpV)O 0.211 0.91(CpV)2O 0.101 0.44(CpV)O3 0.0394 0.17(CpV)2O)4 <.005 <0.02(CpV)3O2 <.005 <0.02(CpV)O 0.0413 0.18(CpV)3O)4 0.0749 0.32(CpV)4O)3 <.005 <0.02* Calculated from linear first-order rate plots; all data ± 10%# Calculated from experimental parameters:pressure = 6.OxlO8 torr; temperature = 350°K; a = 22.36;all data ± 30%47PRINCIPAL REACTIVE PATHWAYS IN THE CpV(CO)4 SYSTEMPrimary (Eli fragmentation of the neutral parent CpV(CO)4 molecule occurs asfollows:CpV(CO)4 + e —+ CpV(CO)o,1,234, V (minor C3HV)Ion-Molecule Reactions (low’ + CpV(CO)4 — products)Class 1. Charge transfer from neutral parent molecule to ion-molecule productcation:(CpV)(CO)o,1,2,3 + CpV(CO)4 — CpV(CO)4 +...(CpV)2CO)o,1,2,3,4 + ‘p ‘I +(CpV)O)2,3,4 + “ —4 “ +(CpV)4O)3,4 + “ —* +V+ + I’ “ +.Relative rates of electron transfer for some of these processes are given in Table2.3. The prevalence of electron transfer processes from the neutral CpV(CO)4 molecule toeach reactive cation in this system reflects the fact that electron affinities in all these CpVionic cluster fragments exceed the ionization potential of the neutral CpV(CO)4 molecule;an expected trend, since formal electron count per vanadium atom in each ion is lower thanthat in the neutral molecule. Ions with very large formal electron-deficient vanadium cores,such as in CpV or CpVCO, should be expected to react rapidly in this mode, and this isobserved; e.g., CpV (with 9 electrons per vanadium atom) reacts approximately 2.3 timesfaster than CpV(CO)2 (13 electrons per V atom), and CpVCO (11 electrons per V atom)reacts 1.6 times faster in producing CpV(CO)4. Again, (CpV)2 reacts approximately 2.8times faster, and (CpV)2CO reacts 2.0 times faster, than does (CpV)O.[In somecases the assumption has been made that simple electron transfer from neutral molecule tothe ion cluster fragment is occurring according to the equation(CpV)2O3+ + CpV*(CO)4 —, CpV*(CO)4+ +48rather than carbonyl transfer from the neutral combined with fracturing and loss of a CpVunit from (CpV)2(CO)3]49TABLE 2.3Relative Electron Transfer Rates for Vanadium CationsReacting with Neutral CpV(CO)4 Molecules12_u Rate Constant (k) Relative Rate #(x109 molec:cm3sec-)*V 2.61 100CpV 0.541 21CpVCO 0.372 14CpV(CO)2 0.238 9CpV(CO)3 0.06a 2(CpV)2 0.368 14(CpV)O 0.273 10(CpV)2O 0.134 5(CpV)O3 0.02 1(CpV)3O 0.043 2(CpV)O4+ <0.02 <1* Calculated from total decay rate constant of reacting cation;all data ± 10%# Relative to V rate taken as 100; all data ± 30%a May be due to carbonyl addition contribution as well.50Apparently all ionic species present, including all polynuclear ionic clusterfragments such as (CpV)3(CO)3, (CpV)O4and (CpV)4 clusters eventually absorban electron transferred from the parent molecule (which is ever-present in large excess).Consequently, CpV(CO)4 becomes the predominant ionic species present after 25 sec.Class 2. Ion-molecule condensation reactions with simultaneous ejection of upto 7 CO ligands. Principal reaction paths for each fragment ion are summarised in thefollowing equations:Primary fragment ion condensations:CpV + CpV(CO)4 -4 (CpV)2O)o,1, + nCOCpVCO + —÷ (CpV)O)o,3+ +CpV(CO)2 + — CpV)2(CO)o,1,(4* + nCOCpV(CO)3 + — (CpV)CO(O*),l,3 + HCpV(CO)4 + —* (CpV)2O1,4 +Binuclear ionic cluster condensations:(CpV)2 + CpV(CO)4 —* (CpV)3O)(1*),2,+ + nCO(CpV)O1,2,3 + —, (CpV)3O24 + H(CpV)2O4 + —* (CpV)O, +Trinuclear ionic cluster condensations:(CpV)3O)2,,4+ + CpV(CO)4 -4 (CpV)O)(2*),3,+ + n CO[* ion intensities less than 5% 1Overall relative clustering rates for the more abundant cations are listed in Table2.4. Rates decrease with cluster size, and numbers of carbonyl ligands present in thereacting cation.Condensation with the parent neutral molecule, with simultaneous loss of one ormore CO ligands, is a prominent reaction path in many other aryl transition-metal carbonyl51TABLE 2.4Relative Clustering Rates for Vanadium CationsReacting with Neutral CpV(CO)4 MoleculesJrni Rate Constant (k) Relative Rate #(x109 molec.cm3se)*CpV4 1.02 100CpVCO .355 35CpV(CO)2 .199 20CpV(CO)3 .028 3CpV(CO)4 .017 2(CpV)2 .290 30(CpV)2CO .411 40(CpV)2(CO)2 .208 20(CpV)2(CO)3 .100 10(CpV)2(CO)4 <.02 <2(CpV)3(CO)2 <.02 <2(CpV)3(CO)3 .065 6(CpV)3(CO)4 .260 26* Calculated from total decay rate constant including allclustering pathways; all data ± 10%# Relative to CpV rate taken as 100; all data ± 30%52systems recently investigated by many authors, including Fredeen[13’4l;Foster[12];Meckstroth[19’20];Parisod[25];and Mullen[221.In the present system, further condensationresulting in generation of larger cluster ions containing Cp5V5, Cp6V6 or larger cores mayoccur, but as yet has not been detected. If the process of condensation with the parentmolecule must compete with electron transfer from the parent, then for the highly electron-deficient ions such as those in this system, a cluster can be generated during one collisionwith the parent neutral, but may gain an electron from the neutral molecule in a subsequentcollision, losing its positive charge and becoming “invisible” to the detector. In eachpolynuclear series clustering rates apparently are largest for reactive ions with 2 or 3 COligands; rates dwindle when the number of CO units present in the ion is large (i.e. > 3).Class 3. Carbonyl Transfer(1) Loss of CO ligands by some reacting cations: (y = number of CO ligands lostsubsequently by the following reacting ions):(CpV)(CO)2 (y = 1,2) (CpV)(CO)3(y = 1,2,3);(CpV)(CO)4 (y = 1,2,3,4); (CpV)2O (y = 1);(CpV)2(CO)2 (y = 1,2); (CpV)2O3(y = 1,2,3);(CpV)2O4(y = 1);(CpV)3O,4(y = 1)Table 2.5 lists relative rates of CO loss for some of these ions. Cations which arerelatively rich in CO (e.g., CpV(CO)4tCp2V(CO),or Cp3V3(CO)4)and which maybe excited and possess excess kinetic energy after electron ionization or rebound fromcollisions with neutrals, react by ejecting one or more CO ligands. Measured CO loss ratesreflect this to some degree: for instance relative rates of CO ejection by ions CpV(CO)3;CpV(CO)2;and CpVCO are in the ratios 10 : 7 : <2, as shown in Table 2.5. on thefollowing page.53TABLE 2.5Relative CO Ligand Loss Rates for Vanadium CationsReacting with Neutral CpV(CO)4 Moleculeshrn Rate Constant (k) Relative Rate(x109 molec..lcm3sec.l)*CpVCO <.010 <.2CpV(CO)2 .043 .7CpV(CO)34 .061 1.0CpV(CO) .018 .3(CpV)2O .048 .8(CpV)O4 .052 .9(CpV)2O3 .026 .45(CpV)O4 <.010 <.2(CpV)3O2 <.010 <.2(CpV)O .048 .8(CpV)3O4 <.010 <.2* Calculated from total decay rate constant including all COligand loss pathways; all data ± 10%Relative to CpV(CO)3 rate taken as 1.0; all data ± 30%54(2) Addition of CO ligands by some reactive cations: (z = number of CO ligandsabstracted from the neutral parent molecule by the following reacting ions):CpV (z = 1,2,3);CpVCO (z = 1,2);CpV(CO)2 (z = 1);(CpV)2 (z = 1,2);(CpV)2CO (z = 1,2);(CpV)2O)2 (z = 1);(CpV)O)3 (z = 1);(CpV)3O)2 (z = 1,2);(CpV)3(CO)3 (z = 1).Table 2.6 on the following page lists comparative CO absorption rates for some ofthese ions. The preceding ions, which are ligand unsaturated and “carbonyl - poor” (e.g.CpV, Cp2V2CO or Cp3V3(CO)2) abstract one or more CO ligands from the parentneutral CpV(CO)4.During any specific ion-molecule interaction, the strong a-basicity ofCO ligands in the neutral CpV(CO)4 molecule should favor their addition to cations ofgreater ligand unsaturation, (i. e. CO transfer to CpV, Cp2V2tCp3(CO))ratherthan their remaining attached to a neutral, electron-saturated, “CO - rich” CpV(CO)4 parentmolecule. Experimental rates of carbonyl abstraction generally exhibit this: for example, therelative rate of single CO absorption by CpVCO and CpV(CO)2 are in the approximateratios 5: 1; and by (CpV)2O and (CpV)2O)2 in the ratios 3: 1 , as shown in Table2.6.55TABLE 2.6Relative Rates of CO Ligand Additionfor Vanadium CationsReacting with Neutral CpV(CO)4 MoleculesRate Constant (k) Relative Rate #(x109 mo1ec.lcm3secl)*CpV .100 1.0CpVCO .216 2.2CpV(CO)2 .043 .4CpV(CO)3 .013 ** .1(CpV)2 .494 5.0(CpV)O .173 1.7(CpV)2O .048 .5(CpV)O3 .026 .3(CpV)2O4 <.020 <.2(CpV)3O2 <.020 <.2(CpV)O .048 .5(CpV)3O4 <.020 <.2* Calculated from total decay rate constant including all COligand additions; all data ± 10%# Relative to CpV rate taken as 1.0; all data ± 30%** May be via electron transfer process only56Class 5. Hydrogen Exchange ReactionsThe appearance of protonated ions, CpV(CO)34H,implies that one of twoprocesses occur: either the molecular cation donates a proton to a neutral molecule, i. e.:C5HV(CO)4+ CpV’(CO)4— CpV’(CO)3,4(HY +C5H4V(CO) +or else the neutral molecule donates a hydrogen atom to the molecular ion; i.e.:CpV(CO)4 + C5HV’(CO)4— CpV(CO)3,4(H) +C5H4V(CO) +(Note: without discriminatory isotopic experiments, these processes are indistinguishable.)Initial rates of these reactions are similar to those of clustering and CO loss processes, butafter 25 seconds the abundance of CpV(CO)4W (which possesses an 18-electron metalcentre) slowly increases with respect to that of the molecular ion, CpV(CO)4 (17 electronmetal centre).2. Reactions with Small MoleculesSome experiments were conducted using molecules H2, 02 and N2 as collisiongases with neutral CpV(CO)4. Because of the experimental difficulties encountered (i.e.; inmaintaining constant gas pressures, applying multiple resonance techniques to multiple,closely-spaced masses, and temporally monitoring a complex mixture of many adductproducts), results were equivocal although many adduct product cations were observed,for example, CpVO2t CpV(CO)O, CpVH2-i-, CpV(CO)4.In order to substantiate this adduct formation, high pressure, quadrupole massanalyses were performed. Reactivities of small molecules with neutral CpV(C0)4 werestudied in desorption chemical ionisation (DCI) experiments using available chemicalionization gases ammonia, methane and isobutane. Positive DCI spectra of CpV(CO)4using ammonia as a CI gas show many ammoniated adducts, for example, CpVNH3+.Analogous adduct ions containing CH5 (i.e., CH3+2)adducts were observed in positiveDCI spectra using CH4 and isobutane as chemical ionisation gases (e.g., CpVCH5).57Addition products observed for each reagent gas molecule are summarised here andrepresentative mass spectra (Figures 2.11-12) are shown on the following pages.Cation Addition Products of CpV(CO)41 .Ammonia CI adduct formationi. protonation: CpV(CO)4H (amu 229)ii. ammonia adduct formation: CpV(NH3)l,2, (amu 133, 150,167); bi- and trinuclear adduct formation: (CpV)2(CO)l,2(NH3) + (amu 294, 322);(CpV)2(CO)2,3NH(amu 306, 334); and (CpV)O)2,NH.(amu421, 449). Figure2.11 is a typical positive ion ammonia DCI spectrum of CpV(CO)4, showing the presenceof some of these protonated and ammoniated adducts.2. Methane adductsi. protonation: CpV(CO)4H (amu 229)ii. methylated adduct formation:CpV(H)i,2(CH3)i,2 (amu 132, 133, 147, 148); (CpV)2H)H3+(amu248, 249, 263, 264); (CpV)CO(H (amu 276, 277); and(CpV)2(CO)3H)1H)(amu 304-348). Figure 2.12 is a representative methanepositive ion DCI spectrum showing some of the adduct ions including severalhydrogenated and methylated species.3. Isobutane adductsi. protonation: CpV(CO)4H (amu 229)ii. methylated adduct formation: CpV(H)1,(C3)i,(amu 132,133, 147, 148). These adducts are similar to those produced by methane DCI in 2. above.Protonation and adduct formation are the general processes occurring in each of thethree cases. Most of the adduct cations contain from one to three addition ligands (NH3,CH5,CO or H) per CpV unit, depending upon ligand unsaturation of the fragment ion;58tIERtIAG’SIDI4R*.2.C4.8]O7—FlJ—B9FILLii:STIQ0,rou891OO8254...4i:iuu:31.OSCi47—B9SPELifrLIrI-2.’I•.:.i.424T1C434?445_—____________________________________________________2241032449-2150100150200250300350400450500Figure2.11.PositiveIonMassSpectrumofCpV(CO)4:AmmoniaChemicalIonization;70eV;p.01LorrHHAC’IDAU2.314.FILEAlSi?os—Iic—aeI00—6246400RT—00:27.7sCal1—5e—51-—BASESPECTRLJI1—22<6246400)T1C—18693120_______________________________________________________29X20305V150VIII2492.73I.’..i.”•’1.1..l....,...‘‘I•.,.“.,.....•I...I....18010012014016018020022024026029030032034036030400Figure2.12.PositiveIonMassSpectrumofCpV(CO)4:MethaneChemicalIonization;70eV;p.01torr0’ 0e.g., addition of ligands such as N113, CH4 and H atoms is strongly favored by ions suchas CpV+ because of the large coordination unsaturation and available space about theirmetal centres.3. Negative Ion ChemistryElectron impact (2.5 eV) on CpV(CO)4 produces the following anions:CpV(CO)4 + e — CpV(CO)2 (60 %), CpV(CO)3 (30%)This anion abundance distribution compares with that of MUller[23]using 70 eV El:CpV(CO)2 (33 %), CpV(CO)3 (67%). Further reaction and clustering of these productswas not observed for up to 1000 milliseconds. This unreactive behavior may reflect the factthat these anions are not highly electron deficient compared to their parent molecule, andconsequently are relatively slow to interact with it. Figure 2.13 on the following page is atypical negative ion mass spectrum of CpV(CO)4 showing the two unreactive negative ionproducts, CpV(CO)2 and CpV(CO)3.61100•80’Iz60-40-20-I I I.0 100 200 300 400 500 600MASS in AMUFigure 2.13. FT-ICR Negative Ion Mass Spectrum ofCpV(CO)4; 0 msec.; 2.5 eV; p 6.OxlO8torr624. Reactions with Small MoleculesUsing the same technique as for the generation of positive daughter ion adducts,CpV(CO)4 molecules were reacted with ammonia, methane and isobutane DCI gases innegative ion mode. Mass spectra for these experiments (Figure 2.14-15) are shown on thefollowing pages.Anion Addition Products of CpV(CO)41. Ammonia adductsi. deprotonation of the Cp ligand:C5H4V(CO)3,4 (amu 199,227)ii.aminated adduct formation: CpVCO(NH2)1,2 (amu 160, 176)A typical spectrum showing some of these adduct peaks is shown in Figure 2.14.2. Methane adductsi. deprotonation:C5H4V(CO)3, (amu 199,227)ii. methylated adduct formation: CpVCO(CH4)1,2 (amu 160, 176)Atypical spectrum showing these adduct peaks is shown in Figure 2.15.3. Isobutane adductsi. deprotonation: C5H4V(CO)3, (amu 199, 227)ii. methylated adduct formation: CpV(H)1,2(CH31,2(amu 132-3, 147-8)63C64.B]09—lIAR-GB09—IIAR-88Figure2.14.NegativeIonMassSpectrumofCpV(CO)4:AmmoniaChemicalIonization;70eV;p=.01torrERtIAG-SEOARU2.31LEA:ST111003993600EASERT—00s42.3SC194—39IcRHAC-IDU2.3C64.•i09-HAR-OQFILEatSTI2o-ealOOP—2543616RT—01142.5•Cl—77—50B(SESPECTRIkl2OO(2543616)rIC=50g€44eID20Xt0X_(2OeQJ7 JO0I.”.I.I,.w•••.i.••801001201401601902002202402602903003230360380ooFigure2.15.NegativeIonMassSpectrumofCpV(CO)4:MethaneChemicalIonization;70eV; p=.01torr0\ “IUnlike positive ion DCI adduct spectra (Figure 2.11-2.12) but in accord with thepresent FT-ICR data (e.g. Figure 2.13), the negative ion DCI spectra showed no bi- ortrinuclear fragment ion adducts, and very few mononuclear adduct ions, e.g.,CpVCONH2 (in ammonia); and CpVCOCH4 and CpVCO(CH4)2(in methane orisobutane). This unreactive behaviour may be a result of nonreactivity consistent with theanions CpV(CO)2 and CpV(CO)3,or may simply be due to kinetic effects, i.e., low anionreactant concentrations. Some ligated adducts were present, however, and like cationadducts, anion adducts contained from one to three ligands (i.e., NH2 CH4 or CO) perCpV moiety, depending on the degree of ligand unsaturation of the negative fragment ioncores. Deprotonation reactions occurred in all three cases because of the lower protonaffinity of CpV(CO)4compared to NH3,CH4 and iso-butane.III ConclusionsGENERAL FEATURES OF THE CpV(CO)4 SYSTEM1) All of the principal cations initially formed by electron impact on CpV(CO)4,i.e., V, CpV(CO)4, are chemically reactive with parent neutral, whereas both daughteranions, CpV(CO)2,3, are unreactive.2) Electron transfer, which is essentially a competition with the parent molecule forelectrons, appears to be one of the most important reaction pathways for all the cationicspecies in this system. Rates of electron transfer were listed in Table 2.2. Indeed, for thebare metal cation V, electron transfer, rather than condensation, is the principal mode ofinteraction with the parent molecule. This behaviour of V+ contrasts with that of the otherbare metal cations of the BzCr(CO)3 (Chapter 3), CpMn(CO) (Chapter 4), BuFe(CO)3(Chapter 5), and CpCo(CO)2 (Chapter 6) systems studied here, as well as of bare metalions in earlier studies.663) Cluster formation is a dominant reaction pathway for all the cations in thisCpV(CO)4 system except for that of the bare metal cation, V. Several new cationscontaining three and four vanadium atoms were seen here for the first time, i.e.,(CpV)3O)i..4 and (CpV)4(CO)2..4ions. Some evidence of even larger cationscontaining five vanadium atoms, for example, (CpV)5O)4 was also observed. Theintegrity of the Cp-V bond within these cluster cores tended to be maintained throughoutsuccessive condensation hierarchies; i.e., in (CpV)2, (CpV)3, (CpV)4, etc., cationic clusterfragments. This behaviour was noted throughout all five metal systems of the analogousseries in this study (i.e., in the CpV(CO)4, BzCr(CO)3CpMn(CO)3,BuFe(CO)3andCpCo(CO)2 systems). Metal-aryl bond integrity seen here is a reflection of the powerfulmultiple d-n, metal-aryl electronic interactions that exist throughout this analogous series ofcomplexes.4) Clustering dwindles with formation of (CpV)3+, or larger cores at pressurespresently used (10-6 - l0- torr); (CpV)4cation cluster fragments were observed in verylow yields only in the higher pressure ranges or after long reaction times. Relativeclustering rates as listed in Table 2.4, depend inversely upon cation size and carbonylcoordination number. Apparent cluster termination may be a consequence of ligandcrowding around the central vanadium core of each ion-molecule cluster. Also, excessvibrational energies in the transition state complex formed by collisions between anyspecific cation and the neutral molecule may not favour formation of larger (i.e., (CpV)5,etc.) cation clusters This may also explain the mobility of CO units seen in some of theprimary cations.5) The cations CpV, CpV(CO)4, (CpV)2(CO)2, and (CpV)3(CO)3 appearkinetically stable compared to other ions in the same (CpV) series. To illustrate this,Figures 2.16 and 2.17 show ion abundances at 500 msec and 1000 msec versus ionicmass. Relatively large intensities of ions (CpV)2(CO)2 and (CpV)3(CO)3 appear here as67100-CpV I(cPV)i Seriesl+ /CpV(CO)4 I(CpV)3 Seriesl(C p400(Cp V)4 Seriesl:(Cp V)5 SerieslION MASS (amu) ; 500 msecFigure 2.16. Relative Abundances of Cation Clustersof CpV(CO)4 at 500 msec/(CpV)2O I(cpV)2>‘..cnC)C.2Series80-604020-0-I200— I300 560 6006810080>1C.,)40.2200Figure 2.17. Relative Abundances of Cation Clustersof CpV(CO)4 at 1000 msecCpV(CO)4200ION300MASS (amu) ; 1000 msec69peaks on the intensity plots, whereas other ions in each series, such as (CpV)2C0+ and(CpV)3(CO)2, are of relatively low intensity. As suggested in earlier papers, theanomalously large numbers of certain ions such as these may be the consequence ofincreased metal-metal bond order, or of enhanced CO ligand hapticity[8”9’2836l.The large intensity of CpV(CO)4, illustrated in Figures 2.16 and 2.17, is notsurprising, since it is the molecular ion and expectedly abundant immediately after 25 eVelectron ionization. This ion dominates the entire reaction regime, because of its relativeelectronic stability and also because it is the principal product of all the electron transferreactions.However, large and persistent intensities of the ions CpV+, CpV(CO)3+,(CpV)2(CO)2 and (CpV)3O are unexpected, especially since all possess largeformal electron deficiencies. Some degree of multiple metal-metal bonding within the lattertwo ions; (CpV)2(CO)2and (CpV)3(CO)3, may contribute to their unusual lack ofreactivity. This behaviour resembles that seen in some cationic Cr2 complexes, as notedelsewhere[19’208361.CpV+, possessing 9 electrons and a very strong Cp-vanadium linkage[30,maypossess enhanced electronic (i.e, half-full metal orbital) stability. But apparent anomalies,as shown by CpVt CpVCO, and CpV(CO)4, are possibly unrelated to bondingphenomena, but may be related to the presence of highly-reactive, excited states of some ofthese ion reactants.6) Figure 2.18 on the following page illustrates the relationship between pseudofirst order decay rate constants for each reacting cation (summarised in Table 2.2) andformal electron deficiencies for several of the more abundant cations of this system. Suchplots have proved useful for predicting unusual bonding patterns within ion clusters[20’81.The relationship between rate and electron deficiency is fairly well-behaved here. The steep70-.cjCc-)-.‘0.01Figure 2.18. Relationship Between Reactivity andElectron Deficiency for Cationsin the CpV(CO)4 System(CpV)2C0 +pV(CO)4 + CpVCpVCO +86428Electron Deficiency per V Atom1471slope between electron deficiencies of one to four implies that ions falling in this region onthe graph will predictably be highly reactive toward many nucleophilic reagents. Thereactive centres in these ions are unprotected from nucleophiic attack, their central metal-metal cores having few shielding carbonyl ligands. As discussed later, the DCIexperiments corroborate this conclusion. Other, more electron-rich ions such as(CpV)2(CO)3 may possess stabilising multiple- or partial multiple-bonded vanadium-vanadium cores, surrounded by a protective sheath of ligands.7) In accounting for temporal behaviour of the vanadium cations, the participationof excited states among some or all of the primaiy cations in the CpV(CO)4 system must beconsidered. The energy difference between ground and first excited state bare vanadiumcations is only 0.33 eV[6], therefore it is not surprising that many smaller daughter ionspossess excited electronic configurations after ionisation by 25 eV electrons. There areseveral lines of evidence for the existence of excited states in the CpV(CO)4 system. Theseare: i) non-linear pseudo-first order (semi-log) decay behaviour shown by some of thesmaller cation cluster fragments, e.g., V+ and CpV+, illustrated in Figure 2.19 on thefollowing page; ii) marked mobility of CO ligands, especially in smaller cation clusterfragments; iii) lack of parallel anomalous behaviour in the anion regime (where reactingions are generated at much lower energies); and iv) reappearance of the molecular ionCpV(CO)4 after its initial disappearance (note Figure 2.19), suggesting that the initialspecies of CpV(CO)4+ may be excited and reactive, whereas the final species is in theground state and kinetically more stable. From intercepts of the semilog rate plots, someestimation of the proportions of excited and ground state ions can be made. For the barevanadium cation, V+, the proportion of excited state ions was thus calculated to beapproximately 45%; for CpV; 81%; and for the molecular cation, CpV(CO)4; 30%.Since greater opportunity for relaxation should exist for larger cations (more vibrationalmodes) than for smaller ones such as monatomic V+, residual energy would be expected tobe retained longer in the smaller ion species; and in fact this was observed in most cases.72U)CC)C.2CpV4-1-2.3.4.5TIME (sec)Figure 2.19. Deviations from Pseudo-First Order DecayBehaviour in the CpV(CO)4 System0 5 10 15 2073As Russell has noted[29],bare metal cations such as Fe in the Fe(CO)5system, areapparently able to retain excess excitation energy even after many collisions; and thereactivity of such excited state ions may differ widely from that of the correspondingground state ions. Excited state reactivity differences between ground and excited statemetal ions have been measured for small cations in the Cr(CO)6[27l;Fe(C0)5[29l;Co2NO[15];and Mn2(CO)lO[31’2]systems as well.For the larger vanadium cations in this system, kinetic semi-log rate plots measuredhere are linear, suggesting ground state reactive behaviour.8) As discussed in paragraph 6), most small, ligand-unsaturated vanadium ionfragments are very susceptible to addition by adduct molecules. FTMS experiments ondaughter cations of CpV(CO)4 using 02, H2 and N2 produced many oxycations andhydrogenated cation adducts, although the spectra were very complex and difficult tointerpret. However, in the higher pressure (0.01 torr) DCI experiments, multiple adductswere generated from the daughter cations of CpV(C0)4,using ammonia, methane andisobutane as CI reagent gases. Depending upon the CI gas used, these adducts included avariety of ammoniated, methylated and protonated species, containing ligand groups suchas NH3 and CH (n=l-5). This rich assortment of addition products reflects thevulnerability of CpVCO fragment cations toward incoming nucleophilic groups.9) Threshold energies for the appearance of positive ions and their abundance withvarying electron energy of ionisation in the CpV(C0)4 system are shown in the clastogramin Figure 2.20. The data shown in Figure 2.20 for appearance of cations with ionisingvoltage are generally in accord with earlier results obtained by other mass spectrometricmethods. [23,35]7460IU)Z 50LUI40zQ 30LU>10-JLU070Figure 2.20. Clastogram for Cations of CpV(CO)4CpV(CO)40 10 20 30 40 50 60El BEAM VOLTAGE7510) The structural geometries of the new binuclear and trinuclear cluster cationsgenerated in this system are not well understood yet. Several possibilities for arrangementof multiple vanadium-Cp groups exist: either as intimately bound metal-metal cores; as Cpmetal-Cp-metal alternating chains; or as some combination of both models. Most probably,these multinuclear cluster ions resemble the V-V central single-bonded core structure in(TI5-CpV)z-(ril—CO)3(2.CO[4].Only a few other multi-vanadium carbonyl clusters,prepared with difficulty in solution, such as Cp3V3(CO)9 and Cp4V4(CO)4[16have beenstudied at the present time (1992).Further detailed FT-ICR studies into long-term clustering processes of these andother vanadium complexes may provide information regarding these interesting complexions. Multiple resonance MS-MS experiments with small molecular addition agents such asH2, 02, N2; and laser photodissociation to induce rupture of secondary and tertiarypolynuclear ion clusters, will help elucidate structural geometry and yield a clearerconformational picture. Moreover, dual-cell or drift cell collisional relaxation techniqueswith higher pressure inert gases may enable resolution of excited and ground statereactivities[291.76IV References(1) Allison, 3. Prog. Inorg. Chem. 1986,34, 627.(2) Aristov, N.; Armentrout, P. B. J. Am. Chem. Soc. 1984, 106, 4065.(3) Aristov, N.; Armentrout, P. B. J. Am. Chem. Soc 1986, 108, 1806.(4) Aristov, N.; Armentrout, P. B. J. Phys. Chem. 1987, 91, 6178.(5) Armentrout, P. B.; Halle, L. F.; Beauchamp, 3. L. J. Amer. Chem. Soc. 1981,103, 6501.(6) Armentrout, P. B. in Gas Phase Inorganic Chemistry; Russell, D. H.; PlenumPress, New York, 1989; pp 1 - 42.(7) Calderazzo, F.; Bacciarelli, S. Inorg. Chem. 1963,2, 721.(8) Cotton, F. A.; Walton, R. A. Struct. Bond. 1985, 62, 1.(9) Elkind, 3. L.; Armentrout, P. B. J. Phys. Chem. 1985, 89, 5626.(10) Fischer, E. 0.; Hafner, W. Z. Naturforsch. 1954, 9B, 503.(11) Fischer, E. 0.; Schneider, R. J. J. Chem. Ber. 1970, 103, 3584.(12) Foster, M. S.; Beauchamp, J. L. J. Am. Chem. Soc. 1975, 97, 4808.(13) Fredeen, D. J. A.; Russell, D. H. J. Am. Chem. Soc. 1985, 107, 3762.(14) Fredeen, D. A.; Russell, D. H. J. Am. Chem. Soc. 1987, 109, 3903.(15) Gord, 3. R.; Freiser, B. S. J. Am. Chem. Soc. 1989, 111, 3754.(16) Herrman, W. A.; Plank, J.; Reiter, B. .1. Organomet. Chem. 1978, 164, C25.(17) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1985, 107, 5870.(18) Kappes, M. M.; Staley, R. H. J. Phys. Chem. 1981, 85, 942.(19) Meckstroth, W. K.; Ridge, D. P. mt. J. Mass Spectrom. Ion Proc. 1984, 61,149.(20) Meckstroth, W. K.; Freas, R. B.; Reents, W. D., Jr.; Ridge, D. P. Inorg. Chem.1985,24, 3139.77(21) Morton, J. R.; Preston, K. F. Organometallics 1984,3, 1386.(22) Mullen, S. L.; Marshall, A. G. J. Amer. Chem. Soc. 1988, 110, 1766.(23) MUller, J.; Fenderl, K. Chem. Ber. 1970, 103, 3141.(24) Otto, E.; Fischer, E. 0.; Schneider, R. 3. J. Chem. Ber. 1970, 103, 3884.(25) Parisod, G.; Comisarow, M. B. Adv. Mass Spectrom. 1980, 8A, 212.(26) Pope, R. M.; VanOrden, S. L.; Buckner, S. W. Organometallics 1991, 10,1089.(27) Reents, J., W. D. ; Strobel, F.; Freas, R. B.; Wronka, J.; Ridge, D. P. J. Phys.Chem. 1985, 89, 5666.(28) Ridge, D. P.; Mecksiroth, W. K. in Gas Phase Inorganic Chemistry; Russell, D.H.; Plenum Press, New York, 1989; pp 93-113.(29) Russell, D. H. Ann. Conf. ASMS All. Top. 1990, 38, 1261.(30) Skinner, H. A.; Connor, 3. A. Pure Appi. Chem. 1985,57, 79.(31) Strobel, F.; Ridge, D. P. J. Phys. Chem. 1989, 93, 3635.(32) Strobel, F.; Ridge, D. P. J. Am. Soc. Mass. Spectrom. 1990, 1, 192.(33) Wilford, 3. B.; Whitla, A.; Powell, H. M. J. Organomet. Chem. 1967, 8, 495.(34) Wilkinson, G.; Cotton, F. A.; Birmingham, 3. M. J. Inorg. Nuci. Chem. 1956,2, 95.(35) Winters, R. E.; Kiser, R. W. J. Organometal. Chem. 1965,4, 190.(36) Wronka, J.; Ridge, D. P. J. Am. Chem. Soc. 1984, 106, 67.78CHAPTER 3Ion Molecule Chemistry ofTricarbonyl ( 6 - Benzene) Chromium{ 6 - C6H6 Cr(CO)3 }79I IntroductionFirst prepared and characterised in 1957 by E. Fischer and Ofele[111,tricarbonyl(rj6-benzene) chromium is an involatile yellow, crystalline, air-sensitive solid, melting at162° C and subliming at 130° C (2 mm Hg). Interatomic distances and conformation,measured by Bailey and Dahi in 1965[1 showed that in the solid state, the Cr(CO)3moietyhas trigonal pyramidal shape with the CO ligands lying directly below alternate C-C bondsof the benzene ligand, with C3v symmetry.Croc”The energetics and reactivity of bare chromium ions in the gas phase have beenanalysed by several authors, e.g. Armentrout[31 and Connor[91.Reactions of ground andexcited state Cr’- ions with hydrogen have been studied[10’426l.Trends in Cr-O, Cr-Hand Cr-C bond strengths and electronic structure, compared with those of other transitionmetals have also been analysed[2’359l.Reactivity of transition metal carbene cations, suchas Cr=CH2, was studied[16l.Beauchamp[171 measured the reactivity of the CrO cationwith alkenes.Chromium carbonyl complexes have been of mass spectrometric interest since 1965when Winters studied Cr(CO)6 and its ions by conventional methods[35’6.The same year(1965), Pignataro also measured the anion fragments of Cr(CO)6 produced by electronionisation[24].Chromium hexacarbonyl and its ions exhibit rich ion-molecule chemistry:80ion-molecule chemistry of Cr(CO)6 was observed by Fredeen in 1985[12], who latercompared the ion-molecule chemistry of carbonyl compounds of Cr, Mn, Fe, Co andNi [12,27] Bricker and Russell studied the interaction of the Cr(CO)5 anion withdioxygen[61.In 1990, Sellers-Hahn successfully reacted chromium carbonyl cations withvarious ligand exchange reagents[28l.Pan (1989) proposed that the reactive, 17-electronCr(CO)5 anions readily underwent ligand substitution via an electron transfermechanism[22].Aryl chromium compound chemistry was initiated by Wilkinson in1956[1 with the synthesis of bis-(r16-benzene) chromium, (16-CH)2Cr. Its massspectral behaviour was studied by Pignataro in 1967[251 and MUller in 1970[20].Aryl chromium carbonyl compounds were also examined in Pignataro’s work:primary daughter ions of benzene chromium tricarbonyl and some arene derivatives wereexamined as well[25]. In 1973, the appearance potentials and dissociation energies of T6-C6Hr(CO)3 and its various cation fragments were measured by Muller[19l andGilbert[13].Other aryl chromium carbonyl systems have been examined with mass spectraltechniques. Using differential ion ejection techniques in 1980, Parisod and Comisarow[23lexamined the positive ion-molecule reactions of dicarbonyl nitrosyl(r5-cyclopentadienyl)chromium, CpCr(CO)2N0 and clicarbonyl thionitrosyl(q5-cyclopentadienyl) chromium,CpCr(CO)2NS. Clustering with simultaneous expulsion of ligands was observed in bothsystems, and unusual nitrogen-oxygen and nitrogen-sulfur rupturing, along withsimultaneous ejection of stable small molecules such as molecular N2 and pyridine,occurred in both systems[23l.Arene ligand mobility in aryl chromium tricarbonyls in solution has been kineticallyexamined by Traylor[31,32]• Lability of the arene group apparently involves mobilisation ofthe Cr(CO)3 unit along its substituent it systems, but benzene-chromium linkages remainedunaffected in their studies.In 1989, Chen observed extensive, complex clustering in the gas phase cation-molecule chemistry of CpCr(NO)2CH3using FT-ICR-MS[81. An assortment of81polynuclear cation clusters, some containing up to five Cr atoms, were generated.Resembling the NO and NS ligand systems examined by Parisod[231,some reactionchannels showed NO ligand rupture (with molecular N2 loss) and retention of oxygenatoms by the chromium cluster core. Like Cp-V linkages in the CpV(CO)4 systemexamined here, Cp-Cr linkages were relatively stable compared to those of Cr-NO and CrCH3•In 1985, Cetini et. al. looked at CIMS interactions of several arene chromiumtricarbonyl complexes with propene, benzene and toluene, noting that the predominant ionproducts were the molecular parent and hydrogenated adduct ions[7l. Recently (1991),ion-molecule studies of a selection of aryl-ligand chromium carbonyl complexes wereconducted by Operti and Freiser using FTMS[211.Aryl ligand groups included toluene,mesitylene and several oxygenated phenyl ligands. Each of the daughter cations in thesesystems was kinetically active except for the parent cation, Cr(L)(CO)3; and in each caseself-condensation processes followed a variety of reaction pathways depending somewhatupon the aryl ligand (L). Polynuclear cluster cations containing up to five chromium atomsand four aryls were detected.The present study includes an examination of the kinetics of positive and negativeion-molecule reactions of q5-C6Hr(CO)3 [“BzCr(CO)3”].II Results and Discussion1. Positive Ion ChemistryUnder 25 eV El positive ionizing conditions, cation fragments of BzCr(CO)3 weredetermined in the following proportions: Cr=29%; B z=43 %; BzCr=10%;BzCrCO=3%; BzCr(CO)2=4%; BzCr(CO)3=10%. These data compare with Pignataroand Lossing’s 1967 data[251 using 70 eV El: Cr=30%; Bz=20%; CrCO=10%;B zCr=35 %; B zCrCO=5%; BzCr(CO)2=<5 %; BzCr(CO)=20%. Under similar82£8uU!UATSiSUO11wnmoiqoionpoidiojjqisstwJojdwtspui‘jainjuuoqsssiuwujuoTiiiodpu!.IduThxoqs£(o3)IDZHjowiuiodsssrnuuoAj1!SOdJDJ-JodXiv[61]01+E(OD)1DZH%>+(OD).OzH%Z=+OD1DZH%O÷1DZH%÷ODD%E9÷1DPOJ(6961)isrjpuiinissuopuo100- -8060zID0— L[LI. I T1 -0 100 200 300 400 500 600MASS In AMUFigure 3.1. FT-ICR Positive Ion Mass Spectrum ofBzCr(CO)3; 0 msec.: 25 eV; p = 6.Ox 10884TABLE 3.1Sample Mass Table for BzCr(CO)3 Cations (1000 msec)Formula Measured Massa Exoected Massa (pumi Rel. mt. (%)50Cr (4.31%) 49.9333 49•945 4.252Cr.(83.76%) 52.0234 51.9400 83 81.253Cr (9.55%) 53.0258 52.9401 86 8.654Cr.(2.38%) 53.9384-- <252CrCO 79.9075 79.9349 27 6.8C6H652Cr 129.9850 129.9870 2b 43.8BzCrCO 157.9827 157.9819 8 14.7BzCr(CO)2 185.9971 185.9768 20 68.2BzCr(CO)3 213.9707 213.9717 100(BzCr)2 259.9633 259.9744 11 8.4(BzCr)2C0 287.9693-- <2(BzCr)2 (CO) 2 315.9861 315.9643 23 4.4(BzCr)2(CO)3 344.0511 343.9592 92 11.9Bz2C r 208.1381 208.0339 104 17.6BzCr2CO 209.9848 209.9224 59 5.7BzCr2(CO) 237.9742 237.9173 57 5.3BzCr(CO)3 266.0608 265.9122 149 9.2a in daltonsb calibrant mass85In this system, each primary cation fragment is reactive except for the parentBzCr(CO)3 ion. At reaction times of up to 25 seconds, all the following polynuclearcluster cation fragments are generated:Symmetric clusters (Bz=Cr)(BzCr)2CO)O,1,2,3 +(BzCr)3CO)2,3Asymmetric clusters (Bz< or >Cr)Bz2CrBzCr2(CO)1,2,3BzCr3(CO),46Typical temporal behaviour of primary fragment ions at pressures of 6.0x108toriis illustrated in Figure 3.2. Figure 3.3 shows analogous temporal behaviour of some of theprincipal binuclear and trinuclear ionic clusters. An example of a set of triple resonancespectra for the Cr ion, taken initially and later at 5000 msec is given in Figure 3.4(a,b),illustrating the cation products of this single ion. An example of the temporal behaviour ofthis ion and its reaction products is shown in Figure 3.5. Analogous triple resonancespectra at 0 and 5000 msec are shown in Figure 3.6(a,b) for the BzCr(CO)2 ion; temporalbehaviour of this ion and its daughter ion products is illustrated in Figure 3.7. Ionscontaining chromium were identified by their chromium isotopic distribution: i.e.,50Cr—4.31%;52Cr=83.76%;53Cr=9.55%; Cr=2.38%. For each reactive ion, decay rateconstants for reaction of each cation with the parent neutral molecule BzCr(CO)3 weremeasured from the slopes of linear pseudo-first order plots; these values are listed in Table3.2.860.30- Bz’0.25-0.20- Cr + BzCr(CO)3 +0.15-BzCrCO +0110- BzCr(CO)20.05-1’0 1’5 2’OTime (sec)Figure 32. Temporal Behaviour of PrimaryFragment Cations of BzCr(CO)387010 . Bz2Cr0.08- (BzCr)2(CO)3 +(I)C0.06-—BzCr2(CO)2 + (BzCr)3(CO)3+::::;.TIME (msec)Figure 3.3. Temporal Behaviour of Binuclear andTrinuclear Cluster Cations of BzCr(CO)388100-80-Iz60-40-20-0— i’-’ I I I I0 100 200 300 400 500 600MASS in AMUFigure 3.4(a). Multiple Resonance Mass Spectrum of Cr;o nisec.; p = 6.OxlO889MASS in AMUFigure 3.4(b). Multiple Resonance Mass Spectrum of Crand Cation Products; 5000 msec.; p = 6.0108100’80-z60-40-20-411‘p.[b --i--I I -I---0 100 200 300 400 500 600900.20:;:0.050.00Figure 3.5 Temporal Behaviour of Cr+ andCation ProductsBzCr(CO)3 +BzCr2(CO)3 +Bz2Cr3(CO)6 +0 5 10 15 20TIME (sec)91100-—80-z1 I I I0 100 200 300 400 500 600MASS in AMUFigure 3.6(a). Multiple Resonance Mass Spectrum ofBzCr(CO)2; 0 msec.; p = 6.OxlO8 gj92100-80-z60-40-20 —0— 1 ‘ : — I0 100 200 300 400 500 600MASS In AMUFigure 3.6(b). Multiple Resonance Mass Spectrum ofBzCr(CO)2 and Caiion Products; 5000 mseC;p = 6.OxlO893BzCr(CO)2 +06-0.5- BzCr(CO)3 + (BzCr)3(CO)3 +C(BzC—1 r)2(CO)3 +03-Se(+(Bzr.A0.2.0.1-I ‘I I I0 10 15 20TIME (sec)Figure 3.7. Temporal Behaviour of BzCr(CO)2and Cation Products94TABLE 3.2Disappearance Rates for Chromium CationsReacting with Neutral BzCr(CO)3 Moleculeskn Rate Constant (k’) Rate Constant (k)(sec1) * (x109 molec.4cm3se)#Cr 0.566 2.33BzCr 0.374 1.54BzCrCO 0.298 1.23BzCr(CO)2 0.227 0.93BzCr2CO <0.005 <0.02BzCr2(CO) 0.480 1.98BzCr2(CO)3 0.250 1.03(BzCr)2 <0.005 <0.02(BzCr)2CO <0.005 <0.02(BzCr)CO 0.057 0.24(BzCr)2CO3 0.032 0.13(BzCr)CO+ 0.025 0.10(BzCr)3CO 0.027 0.11* Calculated from linear first-order rate plots; all data ± 10%# Calculated from experimental parameters:pressure = 6.OxlO8 torr; temperature = 350°K; cx = 21.25;all data ± 30%95As revealed by the multiple resonance technique, interacting pathways of principaldaughter cations in the BzCr(CO)3 system are summarized in the following section. Thepredominant reaction type is that of condensation with the parent neutral molecule;however, electron transfer from the parent neutral molecule, which was prominent in thevanadium system also, is exhibited by several of the smaller daughter cations in thissystem.PRINCIPAL REACTIVE PATHWAYS IN THE BzCr(CO)3SYSTEMPrimary (ED fragmentation of the neutral parent BzCr(CO)3 molecule occurs asfollows:BzCr(CO)3 + e- — BzCr(CO)O,l,2,3,Cr’, C6H (+ minor C3H3Cr)Ion-Molecule Reactions (Cation + BzCr(CO)3 —* products)Class 1. Charge transfer from neutral parent molecule to fragment daughter cation:Cr + BzCr(CO)3 —* BzCr(CO)3 +..BzCr2(CO)l,2,3 + ‘I H (*) +BzCr(CO)01 + “ “ +(BzCr)2CO,3+ —.* “ (*) ++ ‘I BzCr(CO)i,2,3+ +(* low intensity)Some relative rates of electron transfer are given in Table 3.3 on the followingpage. Like the vanadium system, rates of electron transfer from the neutral BzCr(CO)3molecule to reactant cations in this system are apparently governed by electron affinities ofthese BzCr cationic cluster fragments (in turn related to formal electron count per chromiumatom in each ion cluster), compared to the ionization potential of the neutral BzCr(CO)3molecule.96TABLE 3.3Relative Electron Transfer Rates for Chromium CationsReacting with Neutral BzCr(CO)3 Moleculesurn Rate Constant (k) Relative Rate #(x109 molec:cm3se)*Cr 1.44 100BzCr 0.848 59BzCrCO 0.761 53BzCr(CO)2 0.597 41BzCr2COBzCr2(CO) 0.535 37BzCr2(CO)3 0.239 17(BzCr)2(BzCr)2CO - - - --(BzCr)CO 0.119 <1(BzCr)2(CO)3 0.041 <1* Calculated from total decay rate constant of reacting cation;all data ± 30%# Relative to Cr rate taken as 100; all data ± 10%97Ions with very large formal electron-deficient chromium cores, such as Cr+,BzCr, BzCrCO, etc., should predictably react rapidly in this mode, and indeed this isobserved: for example, BzCr (11 electrons per chromium) reacts approximately 1.1 timesas fast as BzCrCO (13 electrons per chromium), and 1.4 times as fast as BzCr(CO)2 (15electrons per Cr) in generating BzCr(CO)3 by electron transfer (see Table 3.3). As wasdone for the vanadium system, the assumption has been made that the process involvessimple electron transfer from neutral molecule to ion cluster fragment, e.g.;(BzCr)2(CO)3 + BzCr*(CO)3 —f BzCr*(CO)3+ +rather than complex fracturing with BzCr loss by (BzCr)2CO)3.Reactant cations which undergo electron transfer with the parent molecule includeCr+ and the mononuclear and polynuclear ionic cluster fragments BzCr(CO)o,i,2+and(BzCr)2(CO)2,3. Asymmetric cluster cores such as BzCr2(CO)2,3are also reactive withrespect to electron transfer.Class 2. Ion-molecule condensation reactions with simultaneous ejection of upto 4 CO ligands. Principal reaction paths for each fragment ion are as follows:Primary fragment ion condensations:Asymmetric cluster formationCr + BzCr(CO)3 —* BzCr2(CO)1,3+ + n COC6H+ + BzCr(CO)3 — (Bz)2Cr + + n COSymmetric cluster formationBzCr + BzCr(CO)3 —> (BzCr)CO)(o*,l* ,,3+ nCOBzCr(CO)192 + (BzCr)2CO)2,3 +The parent molecular ion, BzCr(CO)3+, and the dibenzenechromium ion, Bz2Cr’were unreactive for the 25-second duration test period.98Binuclear ionic cluster condensations:Asymmetric cluster formationBzCr2(CO)l ,2,3 + BzCr(CO)3 —* Bz2Cr3(CO),(46) + fl COSymmetric cluster fonnation(BzCr)2CO,3+ BzCr(CO)3 - (BzCr)3CO)2, + n COThe preceding reaction schemes illustrate the wide variety of binuclear andtrinuclear clusters generated. Relative overall clustering rates for chromium ions are listedin Table 3.4 on the following page. As was the case for the cations of CpV(CO)4,clustering of these cations depends inversely upon carbonyl number and cluster size.Except for the lack of CO ligand exchange pathways, in most cases reactionchannels in this chromium system mirror those observed in the CpV(CO)4 system.However, many of these ions also condense by extraction of one benzene from a neutralmolecule to produce the extremely stable, 17-electron dibenzenechromium ion, Bz2Cr.99TABLE 3.4Relative Clustering Rates for Chromium CationsReacting with Neutral BzCr(CO)3 MoleculesRate Constant (k) Relative Rai#(x109 molec:cm3secl) *Cr 0.885 100BzCr 0.691 78BzCrCO 0.465 53BzCr(CO)2 0.337 38BzCr2CO <0.020 <2BzCr2(CO) 1.44 160BzCr2(CO)3 0.794 90(BzCr)2 <0.020 <2(BzCr)2CO <0.020 <2(BzCr)CO 0.115 13(BzCr)2CO3 0.091 10(BzCr)CO <0.020 <2(BzCr)3CO+ <0.020 <2* Calculated from total decay rate constant including allclustering pathways; all data ± 30%# Relative to Cr rate taken as 100; all data ± 10%100Symmetric clusters are produced (in which Bz Cr, as for example, in(BzCr)2CO)2 which resemble those seen in the vanadium system (Chapter 1), whereasasymmethc clusters (where Bz < or> Cr as in BzCr2(CO)3+or Bz2Cr+) are similar tothose generated in the manganese system (Chapter 3). In most cases clustering rates appearto dwindle with cluster size, as occurs in the CpV(CO)4system. Small clusters maypossess sandwich structures with alternating benzene-chromium-benzene arrangements(analogous to ferrocene) or, more plausibly, with some central multi-chromium cluster coreinto which further metal addition is still spatially possible. The marked parallel betweenthese reactions and those of the vanadium system (Chapter 2) probably reflects thesimilarity in reactivity and structure of the two transition metals, Vanadium and Chromium,and their complexes. The marked CO ligand mobility in the vanadium system, not seen forthis chromium analogue, may be a result of excess energy injected by the ionisationprocedure, rather than from any fundamental structural or energetic differences between thetwo systems.Class 3. Reactions with Benzene and CO cationsAs noted in the preceding section, at reagent gas pressures of 6x107 torr (neutralBzCr(CO)3 pressure = 6x109)the following reactions occur:Bz + M - BzCr(CO)l,2,3 + nCO Charge transferBz + M —* Bz2Cr + 3C0 ClusteringCO + M— HCO + ... H atom transferHCO + M —* MW + ... Proton transferTwo triple resonance spectra showing benzene cation initially and its cation productions at 500 msec are shown in Figure 3.8(a,b); temporal behaviour of benzene cation andits product cations is shown in Figure 3.9 on the following pages. Benzene cation (Bz+)reacts principally by electron transfer from neutral BzCr(CO)3molecule to Bz, thusmaking the latter species charge neutral and invisible to the detector.101100’80-z60-zIi0— 10 100 200 300 400 500 600MASS In AMUFigire 3.8(a). Multiple Resonance Mass Spectrum ofC6H6; 0 msec.; p = 6.OxlO8102100’80-z‘‘ II0— 10 100 200 300 400 500 600MASS in AMUFigure 3.8(b). Multiple Resonance Mass Spectrum ofC6H6 and Cation Products; 500 msec;p = 6.Ox 108 tort1030.4-Bz40.3 BzCr(CO)3 +(0 T T.1 TC— 02- T TBzCr(CO)2 + Bz2Cr +4-.0.1- /1/iBzCrCO +-0 10 15 20TIME (sec)Figure 3.9. Temporal Behaviour of C6H6 andCation Products104Electron transfer from a neutral molecule to a benzene cation is thermodynamicallyfavored whenever the ionization potential of benzene (9.25 eV) exceeds that of the neutralreactant, in this case, 7.3 eV for BzCr(CO)3. As Munson notes recently[11,this makesbenzene attractive as a selective reagent gas in CIMS for characterising aromatic mixturescontaining components of differing ionisation potential. Loss of CO by the neutralBzCr(CO)3 molecule during this transfer process is seen in some of the products; i.e. inBzCr(CO)l,2, suggesting that some collisional energy, effecting CO ligand loss, istransferred as well during reaction.As well, benzene cation undergoes condensation with neutral BzCr(CO)3 toproduce dibenzene chromium cation, Bz2Cr+. After formation, this stable cation, having17 valence electrons, is apparently inert to further ion-molecule interaction.The other small cation reactant, CO+, reacts first by hydrogen atom extraction fromthe neutral BzCr(CO)3 molecule, followed by proton donation to a second neutral toproduce the hydrido-form of the molecular cation, BzCr(CO)3W.Reactions of CO+ and HCO+ ions have been reviewed elsewhere[151.Identicalbehaviour is seen in the present CpCo(CO)2 system (Chapter 6) where hydrogen is firstextracted from the neutral molecule by gaseous molecular ions N2+, CO+ and C02+,producing reactive HN2,HCO, and HCO2,respectively. Subsequently these reactivecations then donate a proton to a second neutral molecule to produce the hydride ion,CpCo(CO)2W. In this chromium system, HCO reacts by proton donation to generate thehydride ion BzCr(CO)3H. Other hydrogenated chromium carbonyl ions have beencharacterised, such as HCr(CO)5, formed by hydride ion addition to Cr(CO)6[18l.2. Negative Ion ChemistryIn 1987 Bricker and Russell studied the ion-molecule reaction of the Cr(CO)çanion with molecular oxygen[6].They noticed that anion products generated using thermal105ionisation methods were different from those products formed after electron ionisation(i.e., thermal ionisation of Cr(CO)6molecules gave oxygenated ion products while El didnot), suggesting that electronically-excited Cr(CO)5 anion, formed by thermaldecomposition of Cr(C0)6, plays an important part in reactions with 02. In this system, noproducts containing multi-chromium cluster cores were observed.In the present study, under 1-5 volt El negative ion monitoring, neutral BzCr(CO)3undergoes electron capture to produce daughter anions Cr(CO)3, Cr(CO)4, and Cr(C0)5,completely rupturing the benzene-chromium linkage even using El voltages as low as 1 eV(i.e., benzene-chromium linkages are not retained in anionic products). Figure 3.10 on thefollowing page is a typical negative ion mass spectrum of BzCr(C0)3 showing peakscorresponding to Cr(CO)3, Cr(C0)4and &(CO)5.Temporal monitoring of Cr(C0)3,4,ç daughter ion fragments for 25 seconds atpressures of 6.OxlO8 torr showed slow accumulation of CO ligands by both Cr(CO)3(13-electron) and Cr(CO)4 (15-electron) reactant ions, eventually resulting in the final,unreactive (17-electron) product ion, Cr(CO)ç. Unequivocal evidence of excited statereactants such as non-linear semilog kinetics was not seen. Probable reaction paths are asfollows:Cr(CO)3- + M —* Cr(CO)4- +Cr(CO)4- + M —> Cr(CO)5- +10610080>.Iz60zw>40I—Iw200600MASS in AMUFigure 3.10. FT-ICR Negative Ion Mass Spectrum ofBzCr(CO)3; 0 msec.; 2.5 eV; p = 6.OxlO8torr1070 100 200 300 400 500III ConclusionsGENERAL FEATURES OF THE BzCr(CO)3 SYSTEM1) Except for the unreactive parent molecular ion, BzCr(CO)3+,all of the cationsinitially formed by electron impact on BzCr(CO)3are chemically reactive with the parentneutral; whereas the principal daughter anion, Cr(CO)5 is unreactive. Only carbonylatedchromium anions were detected; the aryl-chromium linkage did not survive the ionisationprocess.2) As seen in the vanadium case, most cations in the BzCr(CO)3 system underwentelectron transfer with their parent neutral molecule, generating BzCr(CO)3’-. Rates ofelectron transfer are listed in Table 3.1. Like V, Cr’- also reacts by charge exchange withthe neutral, but unlike V, Cr’- reacts as well by unsymmetrical clustering with the parentneutral molecule.3) As in the vanadium system, the integrity of the aryl-Cr bond within cluster corestends to be retained in the cationic system throughout successive reaction hierarchies; i.e.,in (BzCr)2 and (BzCr)3cluster cores. Condensation rates as listed in Table 3.4 reveal thatthis reactive pathway is strongly correlated with carbonyl coordination number and clustersize, as was the case for vanadium ions. However, in contrast with the vanadium anionsystem, where Cp-V linkages remained intact, Bz-Cr linkages are labile in the negative ionregime; only oxy-chromium anions, Cr(CO)345were observed.4) Clustering dwindles after formation of trinuclear cluster ions, i.e., (BzCr)3cores, at pressures used (106109 torr); (BzCr)4 cation cluster fragments were observed inlow yields, only at higher pressure ranges or after long reaction times. As in the vanadiumsystem, these clustering processes are in competition with electron transfer pathways.1085) Stability of cationic clusters is directly related to formal electron deficiency of thecentral chromium core. Figure 3.11 on the following page shows electron deficienciesplotted against pseudo-first order rate constants for principal cation clusters in theBzCr(CO)3 system. In Figure 3.11, single metal fragment ions are plotted as open squares;while cluster products are plotted as circles.Since metal-metal bond order in each cluster is not known, each cluster point wasplotted more than once, corresponding to bond orders of one, two or three, respectively.(The exact placement of cluster points on this diagram depends upon the electron countarbitrarily considered to contribute to chromium-chromium bonds (i.e., 2, 4 or 6 electronsper Cr-Cr bond.) Points for most clusters fall closest to the curve with triple metal-metalbonding; this is strong evidence for multiple bond order in these ions. As is apparent, theunreactive, stable cations Bz2Cr’ and BzCr(CO)3+,each possessing 17 valence electrons,predictably disappear slowly.Formal electron counts in the asymmetric clusters, (e. g. BzCr2(CO)o,i+) dependupon whether Cr-Cr linkages are considered to be present or absent. The rapid rate ofdecay of these ions suggests that metal-metal linkages in these unsymmetric product ionspossess low coordination, and are unprotected by ligand spheres, hence vulnerable toattack during further collisions. On the other hand, the slower decay rates of the symmetricclusters, (e. g., (BzCr)2(CO)2,3) again give support to the multiple-bonded central Crcore models. The steep slope on the left side in Figure 3.11 indicates that ions with electrondeficiencies above 2 are highly reactive, with probable strong reactivity toward one- ortwo- electron donor reagents such as ammonia and carbon monoxide.10974.4 [BzCr2 i3’:B c20 0.1- BzCrCO+BzCr(CO)3 +5’ II//Bz2Cr 2(C14 1f ‘f iJzcrco + I24 r fI I I I I2 4 6 8 10 12Electron Deficiency per Cr AtomFigure 3.11. Relationship Between Reactivityand Electron Deficiency forCations in the BzCr(CO)3 System1106) Like the smaller, highly electron-deficient cations of vanadium, those ofchromium are also extremely susceptible to adduct formation, rapidly accepting newligands such as 02, 0, H2 , H. Precise measurements of these adduct products was notpossible because of low product ion concentrations. Interestingly, in reactions with carbonmonoxide at elevated CO pressures (pressure of CO=6.0x107torr), protonation of theneutral molecule was the overall result. The final product of this pathway was the hydridocation, BzCr(CO)3H. Other hydrogenated chromium ions formed in the gas phase such asHCr(CO) are known to exist in the gas phase[18].7) As in the vanadium system, excited state ion participation by the bare metalcation, in this case Cr, probably occurs in this BzCr(C0)3regime as well. To illustratethis, curved kinetic pseudo-first order semi-log plots for Cr, BzCr and BzCrC0, areshown together in Figure 3.12 on the following page.111(I)CC)CC20.10.01Figure 3.12.2000TIME (msec)5000Pseudo-First Order Decay Behaviourand Deviations for Cationsin the BzCr(CO)3 System112Since the energy difference between the electronic ground state and the first excitedstate is much larger for Cr than for V (i.e., 1.52 eV compared to 0.33 eV)[31, a small butstill significant portion of chromium cations (comparable to that of V) would be expectedto exist in excited states during ionisation, and hence would make a contribution to alternatekinetic pathways. Assuming that reaction rates or pathways differ for excited and groundstate ions, the approximate proportion of excited state Cr, BzCr and BzCrCO obtainedfrom extrapolation of the semi-log plots are 63%, 42% and 45% respectively. These dataare summarised in Figure 7.5; Chapter 7. This phenomenon of altered reactivity in excitedstate chromium ions has been considered earlier by several authors including Kiser[301,Armentrout[10]and Reents[261.Reactions of several excited state transition metal cationswith benzene have resulted in formation of metal-benzene- or benzyne- cations such asC6H-metal and C6H4-metal ions[33l, not seen for ground state ions. Similarly, thecations BzCr+ and Bz2Cr+ are produced in the present system, and may possibly be aproduct of excited state Cr.Pseudo-first order semi-log plots for the larger daughter cation fragments in thissystem (i.e., BzCrCO, etc.) are linear, indicating that ground state ions predominate forthe larger cation fragments.8) A representative clastogram illustrating the appearance and abundances ofpositive ions of the BzCr(CO)3 system with respect to ionisation energy is shown in Figure3.13 on the following page. Results are in general accord with those measured by earlierworkers using sector instruments[19’25].9) Structures of the multi-chromium cluster ions observed here are still unknown.Probably these clusters consist of chromium atoms in multiple-bonded central chromiumcores, surrounded externally by protective ligands, such as exist in the trichromiumdianion, Cr3(CO)12S129].Few multi-chromium clusters are known, however, apparentlyrequiring stabilisation through multiple chromium-oxygen or chromium-sulfur linkageswithin the central core[8’291.11350- BzCr(CO)340. BzCr(CO)2LU Cr+Iz— 30.z BzCrCO BzCr20-LU‘Ilv____uJ0-0 10 20 30 40 50 60 70El BEAM VOLTAGEFigure 3.13. Clastogram for Cations of BzCr(CO)3114IV References(1) Ailgood, C.; Yee, C. M.; Munson, B. Anal. Chem. 1991, 63, 721.(2) Armentrout, P. B.; Halle, L. F.; Beauchamp, J. L. J. Amer. Chem. Soc. 1981,103, 6501.(3) Armentrout, P. B. in Gas Phase Inorganic Chemistry; Russell, D. H.; PlenumPress, New York, 1989; pp 1 - 42.(4) Bailey, M. F.; Dahi, L. F. Inorg. Chem. 1965,4, 1314.(5) Bottomley, F.; Sutin, L. Adv. Organomet. Chem. 1988,28, 339.(6) Bricker, D. L.; Russell, D. H. .1. Am. Chem. Soc. 1987, 109, 3910.(7) Cetini, G.; Gambino, 0.; Lausarot, P. M.; Operti, L.; Vaglio, G. A.; Valle, M.;Volpe, P. Inorg. Chim. Acta 1985, 104, 69.(8) Chen, S.-P.; Comisarow, M. B. Ann. Conf. ASMS All. Top. 1989, 37, 323.(9) Connor, J. A. Top. Curr. Chem. 1977, 71, 71.(10) Elkind, J. L.; Armenirout, P. B. J. Chem. Phys. 1987, 86, 1868.(11) Fischer, E. 0.; Ofele, K. Chem. Ber. 1957, 90, 2532.(12) Fredeen, D. J. A.; Russell, D. H. J. Am. Chem. Soc. 1985, 107, 3762.(13) Gilbert, J. R.; Leach, W. P.; Miller, 3. R. J. Organomet. Chem. 1973,49, 219.(14) Halle, L. F.; Armentrout, P. B.; Beauchamp, J. L. J. Am. Chem. Soc. 1981,103, 962.(15) Harrison, A. G. Chemical Ionization; Wiley - Interscience: New York, 1984.(16) Jacobson, D. B.; Freiser, B. S. .1. Am. Chem. Soc. 1985, 107, 5870.(17) Kang, H.; Beauchamp, J. L. J. Am. Chem. Soc. 1986, 108, 5663.(18) Lane, K. R.; Squires, R. R. J. Am. Chem. Soc. 1985, 107, 6403.(19) Muller, 3.; Göser, P. Chem. Ber. 1969, 102, 3314.(20) Muller, 3.; Fenderl, K. Chem. Ber. 1970, 103, 3128.115(21) Operti, L.; Vaglio, G. A.; Gord, J. R.; Freiser, B. S. Organometallics 1991, 10,104.(22) Pan, Y. H.; Ridge, D. P. J. Am. Chem. Soc. 1989, 111, 1150.(23) Parisod, G.; Comisarow, M. B. Adv. Mass Spectrom. 1980, 8A, 212.(24) Pignataro, S.; Foffani, A.; Grasso, F.; Cantone, B. Z. Physik. Chem. (Frankfurt)1965,47, 106.(25) Pignataro, S.; Lossing, F. P. J. Organometal. Chem. 1967, 10, 531.(26) Reents, 3., W. D. ; Strobe!, F.; Freas, R. B.; Wronka, 3.; Ridge, D. P. J. Phys.Chem. 1985, 89, 5666.(27) Russell, D. H.; Fredeen, D. A.; Tecklenburg, R. E. in Gas Phase InorganicChemistry; Russell, D. H.; Plenum Press, New York, 1989; pp 115-135.(28) Sellers-Hahn, L.; Russell, D. H. J. Am. Chem. Soc. 1990, 112, 5953.(29) Shriver, D. F.; Kaesz, H. D.; Adams, R. D. The Chemistry ofMetal ClusterComplexes; VCH Publishers, Inc.: New York, 1990.(30) Sullivan, R. E.; Kiser, R. W. J. Chem. Phys. 1968,49, 1978.(31) Traylor, T. G.; Stewart, K. J.; Goldberg, M. J. J. Am. Chem. Soc. 1984, 106,4444.(32) Traylor, T. G.; Stewart, K. J. J. Am. Chem. Soc. 1986, 108, 6977(33) VanOrden, S. L.; Cooper, B. T.; Pope, R. M.; Buckner, S. W. Ann. Conf. ASMSAll.Topics 1991,39, 1614.(34) Willdnson, G.; Cotton, F. A.; Birmingham, 3. M. J. Inorg. Nucl. Chem. 1956,2, 95.(35) Winters, R. E.; Kiser, R. W. Inorg. Chem. 1965,4, 157.(36) Winters, R. E.; Kiser, R. W. J. Chem. Phys. 1966, 44, 1964.116CHAPTER 4Ion Molecule Chemistry ofTricarbonyl r5- Cyclopentadienyl) Manganese{ CpMn(CO)3}117I IntroductionTricarbonyl(fl5-cyclopentadienyl) manganese, CpMn(CO)3is a pale yellow,crystalline solid subliming at 60° C (1 atm) and melting at 77° C. First prepared andcharacterised by Piper, Cotton and Wilkinson in 1955[211, this complex is reactive withoxygen, water and polar solvents, readily undergoing electrophilic substitution, its spatialgeometry resembling that of a “three-legged piano stool”.ocMn co0Ion-molecule chemistry of ligated manganese ions has been the subject of severalstudies over the past few years[1’2330].Anion reactions of mono- and dimanganesedecacarbonyl complexes have been monitored and interpreted by Junk[12’27]andMeckstroth[15,6].The reactivity of the dimanganese cation Mn2 with dioxygen[31,andbases[131 has been analysed, and its photodissociative properties by Jarrold[11l. Bondenergies of manganese-hydrogen[2’2l,Mn-CO[2’80],M-CH210,Mn-Cp[8’23l,and MnO[2] linkages have been determined.The first dicyclopentadienyl complex of manganese, manganocene (Cp2Mn), wasfirst prepared by Wilkinson in 1956[281, and this complex was later mass analysed byWinters in 1965[291. A comparison of aryl-manganese and other aryl transition metals hasbeen theoretically treated by Burdett[7land others[8,30l118Muller (1968-70) was first to examine CpMn(CO)3and some of its derivativesmass spectrometrically[17’8].Some of the cation fragments were observed to condense,producing bimanganese clusters such as Cp2Mn2(CO)3.In 1976 Lichtenberger measuredphotoelectronic spectra of CpMn(CO)3and some derivatives, including those of thedioxygen and ammoniated complexes[141.Positive ion-molecule kinetics of theCpMn(CO)3system was first studied by Fr-ICR-MS in 1980[191. In this work, cationdaughter products were observed to undergo a wide variety of condensation reactions withthe parent neutral molecule CpMn(CO)3, generating cluster ions containing up to at leastthree Mn atoms. The following work involves a detailed study of ion-molecule interactionsand products of CpMn(CO)3 under a variety of experimental conditions.II Results and Discussion1. Positive Ion ChemistryIn most experiments, cation-molecule chemistry was monitored for a 25 secondtime span. Under 25 ev El and pressures of 6.0x108 torr, the following assembly ofdaughter ions was obtained: Mn (5%), CpMn (4 1%), CpMnCO (11%), CpMn(CO)2(5%), CpMn(CO)3(22%), these products identical and in similar proportions to thosemeasured by Parisod[19](Mn (8%), CpMn (28%), CpMnCO (15%), CpMn(CO)2(8%), CpMn(CO)3(30%)). A typical mass spectrum showing principal daughter cationsis shown in Figure 4.1, and a sample mass table given in Table 4.1.119100’80-z60-:::0- r1 I I0 100 200 300 400 500 600MASS in AMUFigure 4.1. FT-ICR Positive Ion Mass Spectrum ofCpMJ1(CO)3; 0 nisec.; 25 eV; p = 6.0x108Lorr120TABLE 4.1Sample Mass Table for CpMn(CO)3 Cations (500 msec)Formula Exoected Massa Measured Massa z (ppm’) Ret. mt. (%)55Mn (100%) 54.9375 54.9721 35b 25.5C5HMn 119.9767 120.0616 90 100CpMnCO 147.9716 147.9853 14 18.7CpMn(CO)2 175.9665 175.9847 18 8.2CpMn(CO)3 203.9614 203.9614 0b 43.0(CpMn) 239.9538 240.1052 151 9.4(CpMn)20 267.9488 267.9875 39 8.3(CpMn)O) 295.9437 295.9995 56 2.3(CpMn)(CO)3 323.9386 323.9772 39b 2.5(CpMn)O) 415.9208 415.8127 108 2.2a daltonsb calibrant mass121All the primary fragment cations except for the molecular ion, CpMn(CO)3+, reactfurther with the CpMn(CO)3neutral molecule. Subsequent ion-molecule interactionsproduce symmetrical (Cp = Mn) polynuclear cluster ions, including binuclear clusters suchas (CpMn)2(CO)2, trinuclear clusters such as (CpMn)3O)2,and several asymmetrical(Cp <Mn) clusters, e.g.: CpMn2(CO)2, Cp2Mn3(CO)5.Cation clusters generated are asfollows:Symmetric clusters (Cp=Mn)(CpMn)2(CO)o,1,2,3 +(CpMn)3O)(l*),2,+Asymmetric clusters (Cp< or >Mn)CpMn2(CO)o,1*),2,(3) +CpMn3(CO)(4*),5+CP2Mn+(* low intensity)Typical formation and disappearance of primary fragment ions is illustrated inFigure 4.2. Temporal behaviour of binuclear and of trinuclear ionic clusters is shown inFigures 4.3 and Figure 4.4.Figure 4.5(a,b) displays two triple resonance spectra of CpMn ion, initially and at5000 msec, after its ion products had been allowed to form. Temporal behaviour of this ionand its daughter ion products is illustrated in Figure 4.6; analogous spectra for the(CpMn)2(CO)3cation cluster, measured at identical time intervals, are shown in Figure4.7(a,b) and temporal plots of these product ions are shown in Figure 4.8. For eachreactive ion, decay rate constants for reaction of each cation with the parent neutralmolecule CpMn(CO)3 were measured from the slopes of linear pseudo-first order semi-logplots; these values are listed in Table 4.2.1220.35- CpMn +0.30- CpMn(CO)3 +IU)Ca,0.20-___0.15- + CpMnCO’Mn CpMn(CO)20.10-____0.05-______‘* .I 1 I I0 5 10 15 20TIME (sec)Figure 4.2. Temporal Behaviour of PrimaryFragment Cations of CpMn(CO)31230.18.0.16.)+>1 0.14. b!PMfl)2(CO +0.12.0.10- :cpMn)2(co)2 +0.08. /Ifr.a— ,,0.06. r / /C) I0.04.____________0.02-I I0 10 15 20TIME (sec)Figure 4.3. Temporal Behaviour of BinuclearCluster Cations of CpMn(CO)31248 102X (CpMn)3(CO)2 +6./ Cp2Mn3(CO)54. (CpMn)3(CO)3 +2 (CpMn)3C0 +TIME (sec)Figure 4.4. Temporal Behaviour of TrinuclearCluster Cations of CpMn(CO)3125100-80-z60-i—1— I 10 100 200 300 400 500 600MASS in AMUFigure 4.5(a). Muliiple Resonance Mass Spectrum of CpMn;o msec.; p = 6.OxlO8torr12610080-z60-0— I’ 10 100 200 300 400 500 600MASS in AMUFigure 4.5(b). Multiple Resonance Mass Spectrum of CpMnand Cation Products; 5000 msec.;p = 6.OzlO8 torr127TIME (sec)Ylgure 46. Temporal Behaviour of CpMn+ andCation ProductsCl)CC0.4-0.3-0.2-0.1CpMn +CpMn(CO)3 +Cp2Mn +(CpMn)2C0 +(CPMn)2/ -I—v- -c•_—,--q -4.-I I6 I5 I10 I15 I20128100’80-z60-0— I 1 I I I0 100 200 300 400 500 600MASS in AMUFigure 4.7(a). Multiple Resonance Mass Spectrum of(CpM.n)2(CO)3+; 0 msec.; p = 6.0x108 torr129100-80->.I-.60-4o-20-0— i. Ii I—0 100 200 300 400 500 600MASS in AMUFigure 4.7(b). Multiple Resonance Mass Spectrum of(CpMn)2(CO)3 and Cation Products; 5000 msec;p = 6.OxlO81300.4-0.3’ (CpMn)2(CO)3 +C CpMn(CO)3C0.2- /(CpMn)3(CO)2 +_/I.,- I // (CpMn)3(CO)3 +0.1-__________I I0 10 15 20TIME (sec)Figure 4.8. Temporal Behaviour of (CpMn)2(CO)3and Cation Products131TABLE 4.2Disappearance Rates for Manganese CationsReacting with Neutral CpMn(CO)3 MoleculesRate Constant (k’) Rate Constant (k)(sec1) * (x109 molec.cm3se)4tMn 0.532 2.02CpMn4 0.393 1.49CpMnCO 0.211 0.80CpMn(CO)2 0.183 0.70(CpMn)2 0.094 0.36(CpMn)2O 0.080 0.30(CpMn)O) 0.060 0.23(CpMn)2(CO)3-’- 0.044 0.17(CpMn)O <0.01 <0.04(CpMn)3(CO)2’ 0.017 0.07(CpMn)3O) 0.01 0.04* Calculated from linear first-order rate plots; all data ± 10%# Calculated from experimental parameters as follows:pressure = 6.OxlO-8 torr; temperature = 350°K; x = 19.53;all data ± 30%132Interacting pathways are summarized in the following section. The predominantreaction pathway is condensation with the parent neutral molecule; however, electrontransfer from the parent neutral molecule, which was prominent in the vanadium systemalso, is exhibited by several of the smaller daughter cations in this system.Reactive pathways determined by temporal monitoring of individual ions aresummarized in the following section.PRINCIPAL REACTIVE PATHWAYS IN THE CpMn(CO)3SYSTEM:Primary (Eli fragmentation of the neutral parent CpMn(CO)3 molecule occurs asfollows:CpMn(CO)3 + e —> CpMn(CO)0,123, Mn (+ minor C3HMn)Ion-Molecule Reactions (Ion + CpMn(CO)3 —+ products)Class 1. Charge transfer from neutral parent molecule to reacting cation:(CpMn)(CO)o,l,2 + + CpMn(CO)3 —* CpMn(CO)3 +(CpMn)2O)o,1,3+ + — “ +(CpMn)O)(l*), ++—* ‘I +Mn+ + +Some relative rates of electron transfer are given in Table 4.3. Electron affinities inall these Cp-Mn ionic cluster fragments are expected to exceed the ionization potential ofthe neutral CpMn(CO)3 molecule, since formal electron count per manganese atom in eachion is lower than that in the neutral molecule. Ions with very large formal electron-deficientmanganese cores, such as Mn+, CpMir, CpMnCO+, etc., should react rapidly in thismode and in fact CpMn+ (11 electrons per Manganese atom) does react approximatelytwice as fast as the cation CpMnCO (13 electrons per Mn atom), and three times as fast133TABLE 4.3Relative Electron Transfer Rates for Manganese CationsReacting with Neutral CpMn(CO)3 Molecules1Q11 Rate Constant (k) Relative Rate #(x109 molec.cm3se)*Mn-’- 1.35 100CpMn’- 0.753 56CpMnCO 0.36 1 27CpMn(CO)2 0.224 17(CpMn) 0.076 5.6(CpMn)CO’- 0.061 4.5(CpMn)2O) 0.034 2.5(CpMn)O)3 0.072 5.3(CpMn)30’- <0.04 <1(CpMn)O)2 0.065 4.8(CpMn)3O) <0.04 <1* Calculated from total decay rate constant of reacting cation;all data ± 30%# Relative to Mw’- rate taken as 100; all data ± 10%134as CpMn(CO)2 (15 electrons per Mn atom), in producing CpMn(CO)3,as is shown inTable 4.3. (Again, it is assumed that these processes simply involve electron transfer fromneutral molecule to ion cluster fragment, e.g.;(CpMn)2O)3 + CpMn*(CO)3 —f CpMn*(CO)3+ +rather than complex fracturing of (CpMn)2(CO)3 followed by loss of one CpMn unit.)As in the vanadium system, all fragment ionic species, including all polynuclearionic cluster fragments such as (CpMn)2(CO)3and (CpMn)3(CO)2 undergo electrontransfer from the parent molecule CpMn(CO)3 (Table 4.3). As a consequence, themolecular ion CpMn(CO)3 becomes the predominant ionic species after 10-25 seconds.Class 2. Ion-molecule condensation reactions with simultaneous ejection of upto five CO ligands. Principal reaction paths for each fragment ion are as follows:Primary fragment ions:Symmetric cluster formation (Cp=Mn)CpMn + CpMn(CO)3 —> (CpMn)2(CO)o,1,2+ + n COCpMn(CO)1,+ + “ —* (CpMn)(CO)o,,3+ +Asymmetric cluster formation (Cp< or >Mn)Mn +— CpMn2(CO) +CpMn + CpMn +The molecular parent ion, CpMn(CO)3+and the manganocene ion, Cp2Mn+, werekinetically unreactive for 25 seconds.Binuclear ionic cluster fragment condensations:Symmetric cluster formation (Cp=Mn)(CpMn)2 + CpMn(CO)3— (CpMn)3O)(1*,2,+ + n CO(CpMn)O)1,2,3+ + “ — (CpMn)O),4*)+ +135Asymmetric cluster formation (Cp<Mn)CpMn2(CO) + CpMn(CO)3 — Cp2Mn3(CO)(4*,5+ +Because of low intensities of products, further polymerization forming clusterscontaining more than three manganese atoms was not measured.Overall relative clustering rates for the more abundant cations are listed in Table4.4. In general, rates decrease with cluster size, and numbers of carbonyl ligands presentin the reacting cation, like the clustering rates in the vanadium and chromium systems.136TABLE 4.4Relative Clustering Rates for Manganese CationsReacting with Neutral CpMn(CO)3 MoleculesIn Rate Constant (k) Relative Rate #(x109 molec..lcm3secl)*Mn 0.669 100CpMn+ 0.741 110CpMnCO 0.441 66CpMn(CO)2 0.471 70(CpMn)2 0.281 42(CpMn)2O 0.243 36(CpMn)O)+ 0.190 28(CpMn)2O)3 0.152 25(CpMn)3O <0.04 <10(CpMn)O)z <0.04 <10(CpMn)3O) <0.04 <10* Calculated from total decay rate constant including allclustering pathways; all data ± 30%# Relative to Mn rate taken as 100; all data ± 10%1372. Negative Ion ChemistryUsing 2.5 eV negative ionisation and pressure of 6.0x108 torr, CpMn(CO)3produces the product anions CpMtr, CpMnCO and CpMn(CO)2. Daughter anions CpMrrand CpMnC(Y subsequently reacted with the parent neutral to generate the dimeric production Cp2Mn2(CO)2 according to the following scheme:CpMn(CO)0,1- + M — Cp2Mn(CO) - +CpMn(CO)2- was kinetically unreactive.A typical negative ion mass spectrum of CpMn(CO)3 is shown in Figure 4.9,showing CpMn(CO)2 (17 electrons) and Cp2Mn2(CO)2 (29 electrons). SomeCp2Mn2(CO)2 forms already during beam time. A temporal plot showing anion behaviouris given in Figure 4.10. Both anion products CpMn(CO)2 and (CpMn)2O)2 are long-lived and unreactive in the gas phase. The CpMn(CO)2 fragment is known to be weaklycoordinated to solvent THF in solution, and is a strong coupling agent[24l , so that thedimeric ion Cp2Mn2(CO)2 may be isolable in solution.Not surprisingly, the negative ion-molecule chemistry of CpMn(CO)3 stronglyresembles that of CpV(CO)4, in that Cp-metal linkages are retained, chemistry is simple,and only a few anion products were detected.138100-80-60-4020-I’,0- ——______—I I I0 100 200 300 400 500600MASS in AMUFigure 4.9. FT-ICR Negative Ion MassSpectrum ofCpMn(CO)3; 0 msec.; 2.5 eV; p = 6.Ox 108 torr139CpMn(CO)20.40.3-(CpMn)2(CO)2C MnCO0.2-0.1- CpMnI I ‘1 I I I0 200 400 600 800 1000TIME (msec)Figure 4.10. Temporal Behaviour of PrimaryFragment Anions of CpMn(CO)3140III ConclusionsGENERAL FEATURES OF THE CpMn(CO)3 SYSTEM1) Except for the molecular ion, CpMn(CO)3all of the cations initially formed byelectron impact on CpMn(CO)3 are chemically reactive with parent neutral, whereas onlytwo daughter anions, CpMn(CO)01are reactive. CpMn(CO)2-(17 electrons) andCp2Mn2(CO) (29 electrons per ion) are unreactive. Including the Mn-Mn bondingelectrons, possibly of partially or completely multiple character, electron density on eachMn atom will range from 15.5 (Mn-Mn single bond) to 17.5 (Mn-Mn triple bond).2) Electron transfer, as seen in the vanadium (Chapter 2) and chromium (Ch. 3)systems, is a prominent pathway for most cations in this manganese system. Relative ratesof electron transfer for manganese ions were listed in Table 4.1. Like Cr+, the bare metalcation Mn+ reacts either by accepting an electron from the neutral, or condensing with theneutral to produce asymmetric, manganese-rich clusters.3) As was observed in the vanadium (Chapter 2) and chromium (Chapter 3)systems, here the integrity of aryl-metal bonds within cluster cores is usually retainedthroughout successive reaction hierarchies; i.e., cluster products containing increasinglylarge (CpMn)2, (CpMn)3 and (CpMn)4 cores retain 1:1 stoichiometry. However, in onereaction product of CpMn+, the Cp-Mn bond was fractured, producing Cp2Mn+(manganocene cation) in low intensity, a very stable 16-electron ion product. This pathwayparallels that of the reaction between Bz and BzCr(CO)3,which generates Bz2Cr (17electrons) in the BzCr(CO)3 system; and between Co and CpCo(CO)2in the cobaltsystem, which yields Cp2Co (18 electrons).4) Clustering dwindles after the formation of (CpMn)3+ cores at current pressures(ranging from 10-6 - l0 torr); (CpMn)4 cation cluster fragments were observed in verylow yields only in the higher pressure ranges, or after long reaction times. Overallclustering rates were listed in Table 4.4. This cluster termination was also observed in both141the vanadium and chromium systems; and is apparently a consequence of ligand crowdingaround the metal core as well as coordination saturation of the metal.5) The cations CpMn, CpMn(CO)3, (CpMn)2(CO) and (CpMn)3(CO)2appear relatively unreactive compared to other ions in the same (CpMn) series. Theprominent daughter cation CpMn, with 11 electrons and a strong Cp-manganeselinkage[23],may possess enhanced electronic stability, as CpV may do. Similarly, theabundant molecular cation CpMn(CO)3+, like CpV(CO)4 in the vanadium system (Ch. 2),dominates the entire reaction regime because of its relative electronic stability (17 electrons)and because it is the sole product of all electron transfer reactions. Some of the otherunreactive cations may possess altered hapticities or increased metal-metal bonding order.6) Disappearance rates for reactive cations in this manganese system are directlyrelated to formal electron deficiency. Figure 4.11 illustrates rate decay data for primary(CpMn)i cations (upper curve) and secondary-tertiary, (CpMn)2,3 cations (lower curve)compared with formal electron deficiencies for several of the more abundant cations of thissystem. The upper curve is drawn for ions containing one manganese atom; the lowercurve assumes multiple (double or triple) metal-metal bonding in bi- and trinuclear cationclusters. In both upper and lower curves, rate constants vary in a fairly direct manner withelectron deficiency of the central metal. These electron-deficient ions are expected to berelatively more reactive with respect to one- or two-electron donor agents. The data pointfor initial decay of CpMn(CO)3 (which species later becomes unreactive) is included forcomparison.14264 CO)3472__________eriesl0.1.0 86 (CpMn)2 +4-.‘_______2(CpMn)2,3 SerIej(CpMn)3(CO)3 +0.018I I I I2 6 8 10 12Electron Deficiency per Mn AtomFigure 4.11. Relationship Between Reactivity andElectron Deficiency for Cationsin the CpMn(CO)3 System1437) The participation of excited states of some of the smaller cation fragments of theCpMn(CO)3 system, as seen in both vanadium and chromium systems, must beconsidered, as they have been in earlier studies [4,9,25,26J• Non-linear pseudo-first orderdecay rate behaviour of ions Mn, CpMn and CpMn(CO)3is illustrated in semi-logkinetic plots in Figure 4.12, these cations perhaps exhibiting such behaviour. The energydifference between ground state and first excited state Mn is 1.17 eV[4]; therefore duringthe ionisation procedure, large numbers of excited ions may be formed. As shown inFigure 4.12, the initial downward curvature in the semilog decay rate plot forCpMn(CO)3 suggests initial, excited-state reactivity which is collisionally quenched aftera few milliseconds, leaving unreactive, stable CpMn(CO)3 only. Using extrapolatedvalues of initial concentrations of ground and excited state ions from the semi-log plots,and assuming that excited state ions are more reactive than the corresponding ground state,the proportions of excited state ions were estimated to be as follows: Mnt 77%; CpMn,83%; CpMn(CO)3, 48%. The other fragment cations in this system showed linear semi-log behaviour, and so were assumed to be thermalised.8) The CpMn(C0)3 molecule appears to be less reactive than the vanadium orchromium analogues with respect to small molecular adduct reagents H2, N2 and 02although quantitative data have not yet been obtained. Some evidence of addition of atomic0 or H (appearance of CpMn(CO)3O(amu 220) and CpMn(C0)3H (amu 205)) wereobserved in the product spectra. A sample mass spectrum showing several mono- and di-hydrogenated ions, for example the hydrido-molecular ion, CpMn(C0)3H(amu 205) isillustrated in Figure 4.13. As shown by Lichtenberger[14l,the ionisation potentials ofCpMn(CO)2N2 and CpMn(CO)2NH are similar to that of CpMn(C0)3,so thatsubstitution of N2 or NH3 for one CO ligand in CpMn(C0)3should occur at high reactantpressures.1440.1CC)‘I0.01Figure 4.12. Deviations from Pseudo-First OrderDecay Behaviourin the CpMn(CO)3 SystemCpMn(CO)3 +284+TIME (sec)14510080>1ICl)z6O.40200600Figure 4.13. FT-ICR Positive Ion Mass Spectrum ofCpMn(CO)3; 0 msec.; 25 eV; p =6. Ox 10-8 torr;p(H2) = 6.0x107torr0 100 200 300 400 500MASS in AMU1469) A clastogram for appearance of positive fragment ions in this CpMn(CO)3system with ionising energies is shown in Figure 4.14. In general, ion distributions are inagreement with appearance energies of the ion fragments as determined by MU1ler17’81.10) Like the vanadium and chromium cluster ions observed (Chapters 2,3), thegeometries of the binuclear and trinuclear ionic cluster manganese fragments are not yetwell understood, although the results here strongly suggest that in at least some of thecluster products, multiple-bonded, metal-metal cores exist, surrounded on their perimetersby carbonyls, each metal bonded to one Cp ligand. Increased central metal stabilisation byoxygen, hydrogen or other atomic ligands may be experimentally feasible; and should beexamined in future work.147>-ICl)zLUIz0LU>I-JLiiFigure 4.14. Clastogram for Cations of CpMn(CO)3CpMn(CO)2504030201000 10 20 30 40 50 60El BEAM VOLTAGE70148IV References(1) Allison, J. Prog. Inorg. Chem. 1986, 34, 627.(2) Armentrout, P. B.; Halle, L. F.; Beauchamp, J. L. J. Am. Chem. Soc. 1981,103, 6501.(3) Armentrout, P. B.; Loh, S. K.; Ervin, K. M. J. Am. Chem. Soc. 1984, 106,1161.(4) Armentrout, P. B. in Gas Phase Inorganic Chemistry; Russell, D. H.; PlenumPress, New York, 1989; pp 1 - 42.(5) Bjarnason, A. Organomet. 1991, 10, 1244.(6) Bjarnason, A. Anal. Chem. 1991, 61, 1889.(7) Burdett, J. K.; Canadell, E. Organomerallics 1985,4, 805.(8) Connor, J. A. Top. Curr. Chem. 1977, 71, 71.(9) Elkind, J. L.; Armentrout, P. B. J. Chem. Phys. 1986, 84, 4862.(10) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1985, 107, 5870.(11) Jarrold, M. F.; Illies, A. J.; Bowers, M. T. J. Am. Chem. Soc. 1985, 107,7339.(12) Junk, G. A.; Svec, H. J. .1. Chenz. Soc. A 1970, 2102.(13) Larsen, B. S.; Freas, R. B. I.; Ridge, D. P. .1. Phys. Chem. 1984, 88, 6014.(14) Lichtenberger, D. L.; Sellmann, D.; Fenske, R. F. J. Organomet. Chem. 1976,117, 253.(15) Meckstroth, W. K.; Freas, R. B.; Reents, W. D., Jr.; Ridge, D. P. Inorg. Chem.1985,24, 3139.(16) Meckstroth, W. K.; Ridge, D. P. J. Am. Chem. Soc. 1985, 107, 2281.(17) Muller, J.; Heberhold, M. J. Organomet. Chem. 1968, 13, 399.(18) Muller, J.; Fenderl, K. Chem. Ber. 1970, 103, 3141.149(19) Parisod, G.; Comisarow, M. B. Adv. Mass Spectrom. 1980, 8A, 212.(20) Pearson, R. G. Inorg. Chem. 1984,23, 4675.(21) Piper, T. S.; Cotton, F. A.; Wilkinson, G. J. Inorg. Nuci. Chem. 1955, 1, 165.(22) Schilling, J. B.; Goddard ifi, W. A.; Beauchamp, J. L. J. Am. Chem. Soc.1986, 108, 582.(23) Skinner, H. A.; Connor, J. A. Pure Appi. Chem. 1985,57, 79.(24) Stone, F. G. A. Phil. Trans. R. Soc. Lond. 1982, A308, 87.(25) Strobel, F.; Ridge, D. P. J. Phys. Chem. 1989, 93, 3635.(26) Strobe!, F.; Ridge, D. P. J. Am. Soc. Mass. Spectrom. 1990, 1, 192.(27) Svec, H. J.; Junk, G. A. J. Am. Chem. Soc. 1967, 89, 2836.(28) Wilkinson, G.; Cotton, F. A.; Birmingham, J. M. J. Inorg. Nuci. Chem. 1956,2, 95.(29) Winters, R. E.; Kiser, R. W. J. Organometal. Chem. 1965,4, 190.(30) Ziegler, T.; Tschinke, V. in Periodic Trends in the Bond Energies ofTransitionMetal Complexes; Marks, T.; American Chemical Society, Washington, D. C.,1990; pp 279-292.150CHAPTER 5Ion Molecule Chemistry ofTricarbonyl (1-4 i - Butadienyl) Iron{ C4H6Fe(CO)3 }151I IntroductionTricarbonyl (1-4r-butadieny1) iron compound,C4H6Fe(CO)3(hereafter calledBuFe(CO)3for convenience), is a pale orange, soft solid at room temperature, melting at19° C and boiling at 64° C (13 mm Hg). First synthesised by Rheilen, GrUhl, Hessling andPfrengle in 193O[1, it became the subject of a patent in 1947 taken by Veltman[61].Later,Hallam and Pauson ascertained its n-bonded structure (1956 - 1958)[24,251.Crystallographic measurements on tricarbonyl (1-4rj-butadienyl) iron, an 18valence-electron, single-iron compound, were first made by Mills and Robinson in1963[]; and its ionization potential measured photoelectronically by Dewar and Worley in19697O[14,661, and by Connor in 1974[111. Davis used electron diffraction methods todetermine its gas phase structure in 1970[13]. The solid state structures of tricarbonyl (1-4-14-butadienyl) iron complexes were studied by NMR in 1969[44,681 and by ESR in1981[40,411..Fe -IC0152Kinetics of reactions involving bare iron ions in the gas phase have beendetermined with hydrogen[151;chlorobenzene[31;alkanes[7’22311; alkenes[32]; andthiols[571.Bond energies of iron-carbon, iron-iron and other iron linkages have been subjectsof study for several years. For example, Freiser looked at the Fe-O bond in 1984. Energiesof Fe-Cobalr links in mono- and clustered iron carbonyls and reactions of thisheteronuclear core cation were measured by Jacobson[35’6]in 1984-5.Iron carbonyl compounds have been examined since the inception of organometallicchemistry, with such work as that of Mond on the characterisation of Fe(CO) in 1891[481.In the gas phase, iron carbonyl ions have been examined by Foster and Beauchamp in19715[19,201; and by Russell[231 and Ridge[521 in 1985.Reactive mechanisms of iron alkyl ions such as FeCH3+ have been considered byJacobson and Freiser[33’41,and the Fe-benzyne cation by Huang and Freiser[2630].Aryl iron compounds have been in the forefront in transition metal organometallicchemistry since Miller, Pauson and Wilkinson discovered and characterised ferrocene in19512[38,46,641. “Sandwich” and later “triple-decker sandwich” structures have beenimportant in the development of new structural and bonding concepts ever since thattime[6’42]. In 1964, Schumaker and Taubenest observed the “triple-decker sandwich”cations Cp3Fe and Cp3Ni2in mass spectra of gas phase ferrocene and nickelocene[58l.ICR was used by Beauchamp[12’211,Dunbar and Faullc[181,and Lin[431 in order to examinethe reactive behavior of ferrocene ions. The reaction of CpFe+ with ethane was studied byChen and Ridge[’0].Aryl iron carbonyl complexes have been studied both structurally andmechanistically[451.Negative ion gas phase studies of some aryl iron carbonyls revealedthat after electron capture by the parent neutral molecule, further reaction pathways153involved aryl restructuring within the iron complex ion, followed by consecutivedecarbonylations[4’5601.A tetra-iron complex in solution,Cp4Fe(CO) was synthesizedand characterised by King in 1966[J. Von Gustorf (1971)[621 and Williams-Smith(1972)[651 synthesized and characterised a closely-related bi-iron complex, dibutadienyliron carbonyl, Bu2Fe(CO).Negative ion fragmentation of C4H6 isomeric homologs of BuFe(CO)3 wasexamined by Blake in 1979[4’5land Krusic in l982[’]; its reactions with molecularhydrogen, in l985[1; cyclic voltammetry of BuFe(CO)3in solution was studied by Muffin l985[1. In 1987 Wang and Squires[63lexamined gas phase positive and negative ionfragmentation patterns of 1,3 butadiene iron tricarbonyl,fl4-BuFe(CO)3, and the reactivityof its negative ions with small molecules such as 02, NO and CO2.concluding that the ri4-C4H6 ligand would exchange with many incoming substituent groups such as n-C3H5,hydride, and CO ligands. Recently, iron has been shown to participate in some unusualbridging activity between oxygen, carbon and hydrogen atoms within aromaticmolecules [4’5]•For these, and for other reasons,fl4-BuFe(CO)3 was chosen for this study.Although cyclobutadiene ought to have been chosen as the aryl ligand corresponding to theother members of this series, it was decided to use the 1 ,3-butadiene analogue instead.Having less bond strain than does cyclobutadiene, ligated 1 ,3-butadiene was expected toproduce simpler mass spectral fragmentation patterns, and to yield mechanistic data moreconsistent with those of the other metal systems examined. Ion-molecule kinetic behaviourof both positive and negative fragment ions ofr4-BuFe(CO)3has been examined in thepresent study.154II Results and Discussion1 Positive Ion ChemistryUsing 25 eV electron ionisation onfl4-BuFe(CO)3 at 6.0x108 torr nominalpressure, the following positive daughter ions were produced: Fe=2l%; FeCO=3%;BuFe=27%; BuFeCO=9%; BuFe(CO)2=l2%; BuFe(CO)3=8%, these proportionsbeing generally in accord with those observed by Wang and Squires in 1987[631. (WangSquires: Fe = 19%; BuF&=17%; BuFeCO=10%; BuFe(CO)2+=26%; BuFe(CO)3=7%at 70 eV El.) Figure 5.1 is a typical positive mass spectrum, showing the principaldaughter cation fragments of BuFe(CO)3, Table 5.1 lists mass data for a sample FT-ICRexperiment.15510080-Iz60-0—0 100 200 300 400 500 600MASS in AMUFigure 5.1. FT-ICR Positive Ion Mass Spectrum ofBuFe(CO)3; 0 msec.; 25 eV; p = 6.0x108torr156TABLE 5.1Sample Mass Table for BuFe(CO)3 Cations ( 500 msec)Formula Nominal Massa Measured Massa Expected Massa t (ppm Rd. mt. (%)54Fe 54 53.9344 53.9391 47 7.456Fe 56 55.9332 559344 12b 73.657Fe 57 56.9348 56.9349 1 3.0Bu54Fe 108 107.9828 5.4Bu56Fe 110 109.9678 109.9814 14 100Bu57Fe 111 110.9746 7.8Bu54FeCO 136 135.9120 2.2Bu56FeCO 138 137.9200 137.9763 56 35.5Bu57FeCO 139 138.9310 3.1Bu54Fe(CO)2 164 163.9683 4.1u56Fe(CO) 166 165.9674 165.9712 437Bu57Fe(CO)2 167 166.9874 4.3Bu54Fe(CO)3 192 192.0401 3.0u56Fe(CO) 194 194.0524 194.0551 3b 29.3Bu57Fe(CO)3 195 195.0428 3.2a based throughout on l2C onlyb calibrant mass157In this system, each primary cation is reactive except for the parent molecular ion,BuFe(CO)3. At reaction times of up to 25 seconds, all the following polynuclear clustercation fragments, identified by their iron isotope distribution, are generated:Symmetric clusters (where BuFe)(BuFe)2(CO)O,l,2,3+(BuFe)3(CO)1,234 +Asymmetric (iron-rich) clusters (where Bu<Fe)BuFe2(CO)23+Bu2Fe3(CO),3+Typical temporal decay of reactive primary fragment ions (i.e., Fe, FeCO+,BuFet BuFeCO, and BuFe(CO)2)and temporal persistence of BuFe(CO)3isillustrated in Figure 5.2. Figure 5.3 shows temporal growth and decay behaviour of someof the principal binuclear cationic clusters (i.e., BuFe2(CO)2,3, (BuFe)CO01);and Figure 5.4 shows temporal growth and decay behaviour of the most abundanttrinuclear cationic clusters (i.e., Bu2Fe3(CO)2,3(BuFe)3(CO)2,3j.An example of a setof triple resonance spectra for the BuFe+ ion, taken initially and later at 1000 msec is givenin Figure 5.5(a,b), illustrating the products of this single ion.Early temporal behaviour of BuFe and its cation products is shown in Figure 5.6.Comparable temporal behaviour plots for another primary ion, Fe+, and for a secondaryion, (BuFe)2CO are shown in Figures 5.7 and 5.8 respectively. These results show that awide variety of binuclear and trinuclear clusters are generated. Reaction pathways revealedby multiple resonance for principal daughter cations of the BuFe(CO)3 system aresummarized in the following section.1580.25. BuFe’+Fe0.20- BuFe(CO)2’C /‘C)0.15- BuFeCOC) BuFe(CO)3 +0.10- FeCO +C)_______0.05-0.00. I 1 I0 2000 4000 6000 8000TIME (msec)Figure 5.2. Temporal Behaviour of PrimaryFragment Cations of BuFe(CO)31597x102- (BuFe)2C0 + BuFe2(CO)3 +6- (BuFe)2(CO)3 +Cl) 5.CC 4.G)‘I,2-BuFe2(CO)2BuFe)(C )+fl1-(BuFe)20-0 2000 4000 6000 8000TIME (msec)Figure 5.3. Temporal Behaviour of BinuclearCluster Cations of BuFe(CO)31607x1 020CCC)IFigure 5.4. Temporal Behaviour of TrinuclearCluster Cations of BuFe(CO)3Bu2Fe3(CO)3 +5432Bu2Fe3(CO)2 +04000 6000TIME (msec)8000161100- —‘I.80-z60-0— I I I I .10 100 200 300 400 500 600MASS in AMUFigure 5.5(a). Multiple Resonance Mass Sperunt of BuFe;o nisec.; p = 6.0x108torr162100-80-z60-0 100 200 300 400 500 600MASS In AMUFigure 5.5(b). Multiple Resonance Mass Spectrum of BuFeand Cation Products; 1000 msec.; p = 6.Ox 108 go1630.6.BuFe +0.5’ (BuFe)3(CO)3(1)0.4- (BuFe)2(CO)3 +C0.3- (BuFe)2”(BuFe)2C0 +.! 0.2-___a0.1-______Ill-—ky0.0-I I 1 1 I0 200 400 600 800 1000TIME (msec)Figure 5.6. Temporal Behaviour of BuFe+and Cation Products164FeBu2Fe3(CO)2 +0.3- BuFe2(CO)2Bu2Fe3(CO)3 +0.2- BuFe2(CO)3—1;---t-+l----0.1-•200 400 600 800 1000TIME (msec)Figure 5.7. Temporal Behaviour of Fe+and Cation Products165Iia)Ca)I130.300.250.200.150.100.050.00Figure 5.8. Temporal Behaviour of (BuFe)2C0+and Cation Products+IOOC400TIME (msec)166Decay rate constants obtained from first order rate plots for each iron cation whichreacts with the parent neutral molecule BuFe(CO)3are listed in Table 5.2. The predominantreactive process undergone by most daughter cations is that of clustering with the parentneutral. Charge exchange with the parent neutral molecule, prominent in the vanadium,chromium and manganese systems, is evidently not exhibited by the daughter cations inthis system. Because the iron cation reactive pathways involve clustering only, rateconstants listed in Table 5.2 are identical to overall clustering rates. As was the case for thecations of CpV(CO)4,BzCr(CO)3and CpMn(CO)3,clustering rates of iron cations dependinversely upon carbonyl number and cluster size (Table 5.2).167TABLE 5.2Disappearance Rates for Iron CationsReacting with Neutral BuFe(CO)3 MoleculesRate Constant (k’) Rate Constant (k)(sec1) * (x109 molec.cm3sec-)#Fe 0.417 1.49BuFe 0.347 1.24BuFeCO 0.326 1.16BuFe(CO)24 0.185 0.66BuFe(CO)3 0.010 0.04FeCO 0.271 0.97(BuFe)2 0.140 0.50(BuFe)2CO <0.01 <0.04* Calculated from linear first-order rate plots; all data ± 10%# Calculated from experimental parameters:pressure = 6.OxlO8 torr; temperature = 3500K; x = 18.3;all data ± 30%168PRINCIPAL REACTIVE PATHWAYS IN THE BuFe(CO)3 SYSTEMPrimary (EU fragmentation of the neutral parent BuFe(CO)3 molecule occurs asfollows:BuFe(CO)3 + e —* BuFe(CO)0,123, Fe , FeCOIon-Molecule Reactions (Cation + BuFe(CO)3 —* products)Condensation reactions with simultaneous ejection of up to 4 CO ligands. Principalreaction paths for each fragment ion are as follows:Primary fragment ions:Asymmetric (Bu<Fe) cluster formation*Fe + BuFe(CO)3 —* BuFe2(CO),3+ + n COFeCO + BuFe(CO)3 —* BuFe2(CO),3+ + n COSymmetric (Bu=Fe) cluster formation*BuFe + BuFe(CO)3 — (BuFe)2CO)(o*),l,,3+ +BuFeCO + -4 (BuFe)CO)(Ø* ,1+ +BuFe(CO)2 + — (BuFe)2(CO)2,3+ +The parent molecular ion, BzCr(CO)3+was unreactive for 25 seconds.Binuclear ionic cluster fragment condensations:Asymmetric cluster formation*BuFe2(CO),3+ + BuFe(CO)3 —* BuFe(CO)2,3+ + n COSymmetric cluster formation*(BuFe)2CO1,3+ + BuFe(CO)3 - (BuFe)3CO)(l*),2,4+ + n CO169[*Note: Iron is tetraisotopic, having the following isotopic distribution:54Fe=5.90%; 56Fe=91.52%; 57Fe=2.25%; 58Fe=O.33%. Mass ambiguity can arise fromconfusion of 56Fe with 2 CO ligands (i.e., 2x28 amu=56 amu). Therefore, ion productswere characterised only if they appeared in sufficiently large intensities to permitrecognition of iron isotopic patterns.]Except for the absence of electron transfer pathways, in most cases reactivity ofions in this iron system closely mirror those observed in the CpV(CO)4, BzCr(CO)3andCpMn(CO)3 systems, this BuFe(CO)3system most closely resembling that of chromium;with principal pathways involving condensation with the parent neutral BuFe(CO)3molecule, resulting in the generation of larger, multi-iron-containing clusters. Symmetricclusters (Bu=Fe, e.g. (BuFe)2(CO)2) resemble those observed in the chromium system,as well as asymmetric, “iron-rich” clusters (Bu<Fe, e.g., BuFe2(CO)3) formed bycondensations of Fe+ and FeCO+, resemble those generated in both the chromium andmanganese systems. Clustering rates appearing to dwindle with cluster size and ligandsaturation, as observed in the three other systems examined. Both types of clusters retainedtheir aryl : iron ratios during subsequent interactions, as was also observed in the CpV,BzCr and CpMn systems. As seen here as well as in the other complexes in this study,reactivity in general varies directly with formal electron deficiency.The “iron-rich” clusters BuFe2(CO)2,3 andBu2Fe3(CO)2, may possess doubleand triple-decker sandwich structures similar to those demonstrated to exist in ferrocene(Cp2Fe) and Cp3Fe2ion[38,465M1. “Sandwich” structures containing alternating ironbutadiene-iron linkages are found in a few substituted ferrocene and ferrocene-like systems(e.g.[6]), but most multi-iron cluster complexes consist of multi-iron cores surrounded by170ligand shells, as exemplified by the multi-iron carbonyl complex, Fe3(CO)12. The markedsimilarity between reactions of BuFe(CO)3 and those of the other transition metal systemsstudied here probably reflects closely-related composition of the clusters, as well as similarelectronic structure within the first transition series (i.e., V. Cr, Mn, Fe and Co)complexes[1,2,59] Structural uniformity (i.e. central multi-metal cluster core arrangements)within the present ion complexes may be inferred; on the other hand, the larger electrondensity of the iron atom core compared to those of vanadium, chromium or manganesemay permit multi-sandwich chain formation.Presumably, highly stable electron distribution within the iron-ligand core in any ofthese ions does not favour electron transfer pathways: in contrast with the other metalsystems studied here, in the BuFe(CO)3 system there is no apparent charge-exchangeequilibration with the parent neutral molecule, which in the other systems results ineventual molecular ion domination of the cation population. Instead, clustering ofmonomeric BuFe(CO)3 with its daughter ions produces successively larger, multi-ironclusters.2. Negative Ion ChemistryIn accordance with observations of Wang and Squires, using 2.5 eV electronimpact and 6.Ox1O8 torr nominal pressure, just one anion, BuFe(CO)2, dominates thenegative ion mass spectrum of14-BuFe(CO)3.(Wang[63i, BuFe(CO)2 =87%; in thisstudy: BuFe(CO)2 =74%.) This anion product was unreactive for 25 seconds. Figure 5.9is a typical FT-ICR negative ion mass spectrum of BuFe(CO)3. Not surprisingly,interaction such as adduct formation with N2, CO or C02, by the 17-electron anion171>-IzLU>-jLU1008060402000 100 200 300 400 500 600MASS in AMUFigure 5.9. FT-ICR NegaLive Ion Mass Spectrum ofBuFe(CO)3; 0 msec.; 2.5 eV; p = 6.Ox 108172BuFe(CO)2 was not observed at reagent gas pressures of up to 10-6 torr. However, in anearlier study, BuFe(CO)2 was observed to react with strong proton-donors such asCF3O2Hby accepting one proton per anion[45l. For this reason, self-protonationproducts were sought, but not observed here.The negative ion-molecule chemistry of BuFe(CO)3 strongly resembles that ofCpV(CO)4, BzCr(CO)3, and CpMn(CO)3, in that aryl-metal linkages in the anion productsare retained, anion chemistry is simple, and only a few, unreactive anion species observed.III ConclusionsGENERAL FEATURES OF THE BuFe(CO)3 SYSTEM1) Except for the molecular ion BuFe(CO)3,all of the cations initially formed byelectron impact on BuFe(CO)3are chemically reactive with parent neutral, whereas thesingle daughter anion BuFe(CO)2 (17 electrons) is unreactive. Cation distributionfollowed a pattern similar to those of the other complexes studied here, i.e., electron loss,then successive decarbonylations, followed by olefin loss. All intermediate cations werepresent in the initial mass spectrum.2) Electron transfer reactions, important in the vanadium, chromium andmanganese systems, were not observed here. The bare metal cation Fe+ reacted bycondensation with a neutral molecule to produce asymmetric, iron-rich clusters. Parallelbehaviour, in which metal-rich cores are generated by condensation of the bare metal cationwith a neutral molecule, was seen in the analogous Cr+ and Mn+ systems studied here, andhas been observed in many other similar studies[50’11.1733) The integrity of the Bu-Fe bond within cluster cores is usually sustainedthroughout successive reaction hierarchies, so that cation cluster cores of increasing size,such as BuFe2, (BuFe)2, and (BuFe)3appear in the mass spectra. Such clusters have beenthe subject of much speculation with regard to internal bonding and reactivity[37’5469].4) Clustering dwindles after the formation of tn-iron, (BuFe)3 cores, at pressurespresently used (10-6 - io- torr); hence (BuFe)4 or larger cation cluster fragments were notobserved. Some or all of these cluster cations probably possess double or triple metal-metalbonds, as suggested earlier[67].With increasing cluster size and concomitant coordinationsaturation of the iron core, the properties may approximate that of the bulk metal, resultingin stable metal centres which are unreactive with respect to further ligation[69.5) Reaction decay rate constants for cations in this BuFe system, as seen in all theother analogous systems studied here, appear to be directly related to formal electrondeficiency, as discussed in earlier reviews[54’5l.In Figure 5.10, pseudo-first order rateconstants (for clustering pathways) are compared with formal electron deficiencies for eachdaughter cation in this system. As is the case for the fragment cations of vanadium,chromium and manganese, clustering rates vary with electron deficiency of the centralmetal iron atom in a fairly well-behaved manner. For this iron system, the steep slopebetween electron deficiencies of zero and two (Figure 5.10) suggests that nucleophilicreagent species with one or two-electron donor properties would react readily with suchiron fragment ions, as postulated by Ridge in 1984[67].174Fe’1’lwe0420.01Figure 5.10. Relationship Between Reactivityand Electron Deficiencyfor Cations in the BuFe(CO)3 System6BuFe(BuFe)2 FeCOBuFe(CO)2 +8Electron Deficiency per Fe Atom1756) Participation by excited state cations, as seen in the present vanadium, chromiumand manganese systems, and in earlier studies[16’7561 probably occurs in this iron systemas well. Non-linear pseudo-first order (semi-log) decay rate behaviour of ions Fe+ andBuFe, is shown in Figure 5.11. Initial rapid rates of decay of the two cations are followedby slower decay, as would be expected if both the initial excited state iron cations (whichlater become relaxed), as well as ground state iron cations, are disappearing. The smallerions Fe+ and BuFe+ may absorb and retain excess energy from the ionisation process, andhence react more rapidly (or in more than one mode), than do their ground statecounterparts. By extrapolation of the plots in Figure 5.11, excited state content for both thesmall ions can be estimated as follows: Fe, 52%; BuFe, 65%. Values for these and otherexcited state cations are collected in Table 7.5, Chapter 7.The energy difference between ground and first excited state Fe is only 0.25eV[2’561,much less than that injected during the 25 eV ionisation procedure, hence much ofthe product Fe+ and some of the other small fragment cations react via excited statepathways before collisional relaxation has time to occur.7) A clastogram for appearance of BuFe(CO)3cations with ionising voltage isillustrated in Figure 5.12, following Figure 5.11. Successive losses of CO are followed byC4H6 loss from the BuFe(CO)3parent ion as energy is increased; behaviour was asexpected from similar studies [9,51]•8) A study of addition chemistry of BuFe(CO)3 was attempted using reactant gasesdioxygen, nitrogen and hydrogen. Many addition products were observed, some with veryclosely-spaced masses. The complex iron isotopic pattern of bi-iron and tn-iron speciesmade resolution of the products difficult; consequently identification of all ion products1767BuFe +>‘ 4%43Cl)0-i-FeI I0 200 400 600 800 1000TIME (msec)Figure 5.11. Deviations from Pseudo-First OrderDecay Behaviour in the BuFe(CO)3 System17750-I BuFe(CO)3BuFe(CO)240-i ÷z I \ BuFe— I / Fez 30-I.‘/2 BuFeCOLii 20. FeCO>10--JLU0-0 10 20 30 40 50 60 70El BEAM VOLTAGEFigure 5.12. Clastogram for Cations of BuFe(CO)3178was not successful. Nevertheless, the pattern of generation of multiple adducts containingone or two oxygen or hydrogen atoms seems to mirror that seen in the other metal systems.Further studies utilising higher pressures of reagent gases and iron isotope labelling willyield information regarding the addition chemistry of these iron clusters.179IV References(1) Allison, 3. Prog. Inorg. Chem. 1986,34, 627.(2) Armentrout, P. B. in Gas Phase Inorganic Chemistry; Russell, D. H.; PlenumPress, New York, 1989; pp 1 - 42.(3) Bjarnason, A.; Taylor, J. W. Organomet. 1990, 9, 1493.(4) Blake, M. R.; Garnett, J. L.; Gregor, I. K. .1. Organomet. Chem. 1979, 178,C37.(5) Blake, M. R.; Garnett, 3. L.; Gregor, I. K.; Wild, S. B. J. Chem. Soc., Chem.Commun. 1979, 496.(6) Burdett, J. K.; Canadell, E. Organometallics 1985,4, 805.(7) Byrd, G. D.; Bumier, R. C.; Freiser, B. S. J. Am. Chem. Soc. 1982, 104,3565.(8) Cassady, C. 3.; Freiser, B. S. J. A,n. Chem. Soc. 1984, 106, 6176.(9) Chen, 5.-P.; Comisarow, M. B. Ann. Conf. ASMS All. Topics 1989, 37, 323.(10) Chen, H.; Lin, H.-Y.; Sohlberg, K.; Ridge, D. P. Ann. Conf. ASMS All. Topics1991,39, 1596.(11) Connor, 3. A.; Derrick, L. M. R.; Hall, M. B.; Hillier, I. H. Mol. Phys. 1974,28, 1193.(12) Corderman, R. R.; Beauchamp, 3. L. Inorg. Chem. 1976, 15, 665.(13) Davis, M. L.; Speed, C. S. J. Organomet. Chem. 1970,21, 401.(14) Dewar, M. J. S.; Worley, S. D. J. Chem. Phys. 1969,50, 654.(15) Elkind, J. L.; Armentrout, P. B. J. Am. Chem. Soc. 1986, 108, 2765.(16) Ellcind, 3. L.; Armentrout, P. B. J. Chem. Phys. 1987, 86, 1868.180(17) Elkind, J. L.; Armentrout, P. B. J. Phys. Chem. 1987, 91, 2037.(18) Faulk, 3.; Dunbar, R. C. Ann. Conf. ASMS All. Topics 1987, 35, 920.(19) Foster, M. S.; Beauchamp, 3. L. J. Am. Chem. Soc. 1971, 93, 4924.(20) Foster, M. S.; Beauchamp, 3. L. J. Am. Chem. Soc. 1975, 97, 4808.(21) Foster, M. S.; Beauchamp, J. L. J. Am. Chem. Soc. 1975, 97, 4814.(22) Freas, R. B.; Ridge, D. P. J. Am. Chem. Soc. 1980, 102, 7129.(23) Fredeen, D. J. A.; Russell, D. H. J. Am. Chem. Soc. 1985, 107, 3762.(24) Hallam, B. F.; Pauson, P. L. J. Chem. Soc. 1956, 3030.(25) Hallam, B. F.; Pauson, P. L. J. Chem. Soc. 1958, 642.(26) Huang, Y.; Freiser, B. S. J. Am. Chem. Soc. 1989, 111, 2387.(27) Huang, Y.; Freiser, B. S. Inorg. Chem. 1990,29, 1102.(28) Huang, Y.; Freiser, B. S. J. Am. Chem. Soc. 1990, 112, 5085.(29) Huang, Y.; Freiser, B. S. J. Am. Chem. Soc. 1990, 112, 1682.(30) Huang, Y.; Freiser, B. S. Inorg. Chem. 1990,29, 2052.(31) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1983, 105, 5197.(32) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1983, 105, 7485.(33) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1984, 106, 3900.(34) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1984, 106, 3891.(35) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1984, 106, 4623.(36) Jacobson, D. B.; Freiser, B. S. .1. Am. Chem. Soc. 1985, 107, 1581.(37) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1986, 108, 27.(38) Kealy, T. I.; Pauson, P. J. Nature 1951, 168, 1039.(39) King, R. B. Inorg. Chem. 1966,5, 2227.181(40) Krusic, P. 3.; San Filippo Jr., 3.; Hutchinson, B.; Hance, R. L.; Daniels, L. M. J.Am. Chem. Soc. 1981, 103, 2129.(41) Krusic, P. J.; San Filippo Jr., 3. .1. Am. Chem. Soc. 1982, 104, 2645.(42) Lauher, J. W.; Elian, M.; Summerville, R. H.; Hoffman, R. J. Am. Chem. Soc.1976, 98, 3219.(43) Lin, L.; Kutal, C. R.; Amster, I. J. Ann. Conf. ASMS All. Topics 1991,39,1616.(44) Maddox, M. L.; Stafford, S. L.; Kaesz Adv. Organomet. Chem. 1965,3, 1.(45) McDonald, R. N.; Schell, P. L.; Chowdury, A. K. J. Am. Chem. Soc. 1985,107, 5578.(46) Miller, S. A.; Tebboth, J. A.; Tremaine, J. F. J. Chem. Soc. 1952, 632.(47) Mills, 0. S.; Robinson, G. Acta Crystallogr. 1963, 16, 758.(48) Mond, L.; Langer, C. Trans. Chem. Soc. 1891,59, 1090.(49) Murr, N. L.; Payne, J. D. J. Chem. Soc. Chem. Commun. 1985, 162.(50) Operti, L.; Vaglio, G. A.; Gord, J. R.; Freiser, B. S. Organometallics 1991, 10,104.(51) Parisod, G.; Comisarow, M. B. Adv. Mass Spectrom. 1980, 8A, 212.(52) Reed, D. T.; Meckstroth, W. K.; Ridge, D. P. J. Phys. Chem. 1985, 89, 4578.(53) Reihien, H.; Gruhi, A.; Hessling, G. v.; Pfrengle, 0. Liebig’s Annalen DerChemie 1930,482, 161.(54) Ridge, D. P.; Meckstroth, W. K. in Gas Phase Inorganic Chemistry; Russell, D.H.; Plenum Press, New York, 1989; pp 93-113.(55) Russell, D. H.; Fredeen, D. A.; Tecklenburg, R. E. in Gas Phase InorganicChemistry; Russell, D. H.; Plenum Press, New York, 1989; pp 115-135.182(56) Russell, D. H. Ann. Conf. ASMS All. Top. 1989, 38, 1261.(57) Sallans, L.; Lane, K. R.; Freiser, B. S. J. Am. Chem. Soc. 1989, 111, 865.(58) Schumacher, E.; Taubenest, R. Helv. Chim. Acta 1964,47, 1525.(59) Skinner, H. A.; Connor, 3. A. Pure Appi. Chem. 1985,57, 79.(60) Squires, R. R. Chem. Rev. 1987, 87, 623.(61) Veltman, P. L. U. S. P. 2., 409,167 Chem. Abs. 1946,41, 595.(62) von Gustorf, E. K.; Buchkremer, 3.; Pfaifer, Z.; Grevels, F.-W. Angew. Chem.mt. Ed. 1971, 10, 260.(63) Wang, D.; Squires, R. R. Organometallics 1987, 6, 905.(64) Wilkinson, G.; Rosenbium, M.; Whiting, M. L.; Woodward, R. B. J. Am. Chem.Soc. 1952, 74, 2125.(65) Williams-Smith, D. L.; Wolf, L. R.; Skell, P. 5. J. Am. Chem. Soc. 1972, 94,4042.(66) Worley, S. D. J. Chem. Soc. Chem. Commun. 1970, 980.(67) Wronka, 3.; Ridge, D. P. J. Am. Chem. Soc. 1984, 106, 67.(68) Young, D. A. T.; Holmes, 3. R.; Kaesz, H. D. J. Am. Chem. Soc. 1969, 91,6968.(69) Zakin, M. R.; Cox, D. M.; Whetten, R. L.; Trevor, D. J.; Kaldor, A. Chem.Phys. Leu. 1987, 135, 223.183CHAPTER 6Ion Molecule Chemistry ofBicarbonyl (fl5 - Cyclopentadienyl) Cobalt{ CpCo(CO)2 }184I IntroductionBicarbonyl (qS-cyclopentadienyl) cobalt, CpCo(CO)2is a dark red reactive liquidat room temperature, melting at -22° C and boiling at 750 C (20 mm Hg); first synthesisedby Fischer (1954) and Piper, Cotton and Wilkinson (1955), the complex is unstable atroom temperature, especially in the presence of oxygen[8’37].Its structure resembles that ofa two-legged piano stool:The properties of aryl cluster compounds containing cobalt have been of interest forsome time: for example, King first prepared and characterised the trimetallic clusterCp3Co3(CO)3 in solution in 1966[24]; hydrides such as (CpC0H)4 were prepared insolution by reduction of (CpC0NO)2 in 1973[]; solid state geometry of (CpC0H)4 wasdetermined in 1975 by Huttner[171.Ligand substitution reactions of anions Co(CO)2(NO),C3HSCo(CO)2-,C3o(CO)3 and CpCo(CO)2 in the gas phase were studied byMcDonald and Schell in 1988[29]. More recently Mevs (1991) studied electron transferchemistry of the Cp3Co3(CO)3 cluster in solution[30l.Mass spectral studies on CpCo(CO)2 were begun by Winters and Kiser in1965 [471, and later MUller (1970) examined positive ion mass spectral fragmentation185patterns of CpCo(CO)2 and determined appearance potentials for several of its daughterproduct cations. Evidence for formation of bimetal clusters such as Cp2Co2(CO)3 in themass spectra of this system was noted[32]. In 1977, Corderman and Beauchamp studiedthe kinetic behaviour of the negative ion products of CpCo(CO)2 using ICR methods[71.They observed only two anions in the negative ion spectrum, CpC0CO and CpCo(CO)2,noting that the latter anion was kinetically unreactive, while the former ion, CpCoCO,rapidly clustered with the parent neutral to form unreactive Cp2Co2(CO)2. Reactions withPF3, NO, and small anions by carbonyl-ligand displacement, were also noted[61.Bondlengths and angles in this cluster anion, Cp2Co2(CO) were determined in 1977 byShore[41]and reexamined in 1979 by Pinhas and Hoffman[361.In 1981, Jones and Staleystudied positive ion-molecule reactions of CpCo(CO)2, noting that product ion Cp2Co (an18 electron ion) was an important cluster product[23l.These results were complicated bythe presence of excess cyclopentadiene in the reaction chamber.Many recent studies on the reactivity of gaseous atomic cobalt and ligated cobaltions have examined reactivity with respect to alkanes[58; cycloalkanes[1’2”9035l;alkenes[11]; dioxygen[’2;aldehydes and ketones[141;ethers[28l; thiols[39l; butanes[451.Reactivities of bare cobalt ions with respect to activation of C-H, C-C and other bonds, andbond strengths of Co-H, Co-C, Co-O and other linkages, have beenquantified[3”1,42,43,44] and related to electronic structure and stability of the central metalcore[’2734423].The present work extends the earlier gas phase positive and negative ion - moleculestudies of CpCo(CO)2 and its daughter ion fragments by examining long-time (25 second)kinetic behaviour of pure CpCo(CO)2 and its daughter ions as well as some of its reactionswith small molecules CO, C02 and N2.186II Results and Discussion1. Positive Ion ChemistryUnder 25 eV electron ionization and gauge pressure of 6.0x108torr, the followingfragment daughter cation distribution was observed for positive ions of CpCo(CO)2:Co=4%, CpCo=3 1%, CpCoCO=7 %, CpCo(CO)2= 13%, CoCO=4%, CO=24%.(These data compare with those of Winters and Kiser: Co=24%, CpCo=39%,CpCoCO=10%, CpCo(CO)2=10% with 70 eV EI[47]; Jones and Staley: CpCo=15%,CpCoCO=14%, CpCo(CO)2=39% with 12 eV EI[231) An example of a FT-ICR massspectrum exhibiting these positive ions immediately after generation is shown in Figure6.1. Table 6.1 lists the mass data for a typical experiment.Like the CpV(CO)4 system ( Chapter 2) but unlike the BzCr(CO)3,CpMn(CO)3and BuFe(CO)3 systems (Chapters 3, 4 and 5 respectively), all of the daughter fragmentsincluding the molecular ion, CpCo(CO)2, in this CpCo(CO)2 system are kineticallyreactive. Typical temporal behaviour patterns of primary fragment ions Co+, CpCo+,CpCoCO and CpCo(CO)2,determined by single resonance techniques, are illustrated inFigure 6.2. At reaction times of up to 25 seconds, the following product cations aregenerated:CpCoCOH ; CpCo(CO)2H +; CpCo(CO)3,4+;Cp2Co; (CpCo)2O,3(CpCo)2(CO) ÷Figure 6.3 shows formation and disappearance patterns of four of the mostabundant of these secondary cationic clusters.187100-80-zII— -I 1 I 1 I0 100 200 300 400 500 600MASS in AMUFigure 6.1. FT-ICR Positive Ion Mass Spectrum ofCpCo(CO)2; 0 nisec.; 25 eV; p = 6.OxlO8torr188TABLE 6.1Sample Mass Table for CpCo(CO)2 Cations (500 msec)Formula Measured Massa Expected M055 t\ (npm) Rel. Tnt. (%)59Co (100%) 58.9759 58.9327 35CpCo 123.9344 123.9718 37 13.0CpCoCO 151.9765 151.9667 98 4.0CpCo(CO)2 179.9635 179.9617 2b 65.6CpCo(CO)3 207.9513 207.9566 5 2.5CpCoCOH 152.9975 152.9746 23 2.9CpCo(CO)2H 180.9381 180.9695 31 39.7Cp2Co 189.0010 189.0109 10b 100.0(CpCo)O 303.9340(CpCo)2O)3 331.7840 331.9289 145 3.1a in daltonsb calibrant mass1890.30- CpCo’0.25- CpCo(CO)2 +0.20-C) 0.15-0.10- Co CpCoCO0.05-0 1000 2000 3000 4000 5000TIME (msec)Figure 6.2. Temporal Behaviour of PrimaryFragment Cations of CpCo(CO)21900.4. Cp2Co-0.3. (CpCo)2(CO)3 +_CpCo(CO)2H +C0.2.0.10 10 15 20TIME (sec)Figure 6.3. Temporal Behaviour of SecondaryCluster Cations of CpCo(CO)2191Application of FT-ICR multiple resonance permitted identification of reactionproducts from each daughter ion by successive isolation of each ion followed by productmonitoring. Figure 6.4(a,b) displays two multiple resonance spectra of the Co+ ion,initially and at 500 msec, after its ion products had formed. Figure 6.5 illustrates theresultant temporal behaviour of Co+ and its cation products. Comparable temporalbehaviour of the CpCo ion and its cation products is illustrated in Figure 6.6; for the ionCpCoCO, in Figure 6.7; and for the molecular ion CpCo(CO)2, in Figure 6.8. Pseudofirst order rate constants for the disappearance of reactive cobalt cations reacting with theparent neutral molecule CpCo(CO)2 are listed in Table 6.2. Principal reactive pathways ofthese ions are summarized in the following sections.19210080-Iz4O-200•• I I I I I0 100 200 300 400 500 600MASS in AMUFigure 6.4(a). Multiple Resonance Mass Spectrum ofCo; 0 msec.; p = 6.0x108toi’19310080>.Iz60-40-20O— I i 1”I I I0 100 200 300 400 500 600MASS in AMUFigure 6.4(b). Multiple Resonance Mass Spectrum of Coand Cation Products; 500 msec.: p = 6.Ox 108 r.orr194CoU)C).E 0C)0.10.0Figure 6.5. Temporal Behaviour of Co+and Cation Products0.3 CpCo(CO)2 +CpCo(CO)2H +(CpCo)(CO)3 +TIME (msec)1950.6. +CCoCp2Co +0.5. CpCo(CO)2 +I—U)0.4.CpCo(CO)2H + (CpCo)2(CO)3 +0.3.>0.2.____C) —12 120.1__i:—!—040 500 1000 1500 2000TIME (rnsec)Figure 6.6. Tempora’ Behaviour of CpCo+and Cation Products1960.7-CpC0CO+ (CpCo)2(CO)3 +0.6-0.5- CpCo(CO)2H +C)A CpCoCOH +v.4-0.3- CpCo( O)2 CP2CO0.2-—0.1-____________0.0-=—— —i———I I I I0 500 1000 1500 2000TIME (msec)Figure 6.7. Temporal Behaviour of CpCoCO+and Cation Products1970.7-CpCo(CO)2 +0.6- (CpCo)2(CO)3 +0.5- Cp2CoC0.4- \ CpCo(CO)2H+0.3- 1____0.2-___- CpCo(CO)3 +0.0- pI I I I0 500 1000 1500 2000TIME (msec)Figure 6.8. Temporal Behaviour of CpCo(CO)2and Cation Products198TABLE 6.2Disappearance Rates for Cobalt CationsReacting with Neutral CpCo(CO)2 MoleculesRate Constant (k’) Rate Constant (k)(sec1) * (x109 molec:cm3sec-)#Co 0.589 1.93CpCo 0.384 1.26CpCoCO 0.211 0.69CpCoCOH 0.251 0.82CpCo(CO)2+ 0.207 0.68CpCo(CO)H 0.127 0.42CpCo4 0.01 0.03(CpCo)2O3 <0.01 <0.03* Calculated from linear first-order rate plots; all data ± 10%# Calculated from experimental parameters:pressure = 6.OxlO8 torr; temperature = 350°K; a = 16.72;all data ± 30%199PRINCIPAL REACTIVE PATHWAYS IN THE CpCo(CO) CATIONSYSTEM1.Primary (Efl fragmentation of the neutral parent CpCo(CO)2 molecule occurs asfollows:CpCo(CO)2 + e— CpCo(CO)Oj,2 , Co (and minor CoCO andC3H3Co)2.Ion-Molecule Reactions (Cation + CpCo(CO)2 —4 products)Class 1. Electron transfer from neutral parent molecule to ion-moleculeproduct cation:Co + CpCo(CO)2 —> CpCo(CO)2 +CpCo(CO)oj+ + --4 +Relative rates of electron transfer for these three processes are given in Table 6.3.Electron transfer from neutral CpCo(CO)2 molecules to daughter cations in this systemparallels exactly those processes seen in the vanadium (i.e., Chapter 2), chromium(Chapter 3), manganese (Chapter 4) and iron (Chapter 5) systems: again reflecting the factthat electron affmities of the cobalt daughter fragment cations exceed the ionization potentialof the neutral molecule. As in the five other transition metal systems, ions with large formalelectron-deficient cobalt atom cores should react relatively rapidly, for example, Co+ (with8 electrons) predictably reacts approximately three times as fast as CpC0CO+ (15electrons). Relative rates of electron transfer are listed in Table 6.3.200TABLE 6.3Relative Electron Transfer Rates for Cobalt CationsReacting with Neutral CpCo(CO)2 MoleculesIan Rate Constant (k) Relative Rate #(x109 molec.cm3se)*Co 1.93 100CpCo 0.656 34CpCoCO 0.262 14* Calculated from total decay rate constant of reacting cation;all data ± 30%# Relative to Co rate taken as 100; all data ± 10%201Class 2. Ion-molecule reactions with transfer of various ligands fromneutral molecule to ion, or condensation. Principal reactions of each fragment ion are asfollows:Primary fragment ion reactions:CpCo(CO)o,, + CpCo(CO)2 — CpCo + neutral fragmentsCpCoCO + — CpCoCOH + +CpCo(CO)2 + —* CpCo(CO)2H +CpCo(CO)2 + —* CpCo(CO)3,4+ +The preceding reactions involve transfer of Cp, H or CO ligands from neutralmolecule to reactive cation.Secondary ion condensations:CpCo(CO)1,2H+ CpCo(CO)2 -4 (CpCo)2O,3+These preceding reactions involve simultaneous condensation of the cation with aneutral molecule, and ejection of hydrogen and carbonyl ligands.Condensation with the parent neutral molecule and generation of multi-metal coreclusters has been a prominent feature in each of the vanadium, chromium, manganese andiron aryl transition-metal carbonyl systems as well (Chapters 2-5). However, in this cobaltsystem, condensation proceeds via the hydrogenated intermediates CpCo(CO)1,2W andterminates with bicobalt clusters; further condensations and generation of cluster ionscontaining Co3 or Co4 cores are not observed. In this CpCo(CO)2 system, condensationmust compete with formation of electronically stable (18 electron), kinetically unreactiveCp2Co by Cp ligand transfer from neutral molecule to reactive cations.The cluster cations, Cp2Co and Cp2Co2(CO)2,3are unreactive for 25 seconds.In contrast with the work of Jones and Staley[231,(where cyclopentadiene was present inthe reaction chamber, producing complicating cyclopentadienyl dimer ions and Cp adductions in the mass spectra), cyclopentadiene dimers and their cluster products were notobserved in the present mass spectra. In this study the predominant clustering channels202proceed solely via the hydrogenated intermediates, i.e., CpCo(CO)l,2H. Since all of thefinal cation products possess veiy low coordination unsaturation (i.e., Cp2Co+ possesses18 electrons per central cobalt atom; CpCo(CO)2H, 18 electrons; Cp2Co2(CO)2,3, 16.5and 17.5 electrons per central metal respectively, assuming singly-bonded cobalt in thebimetal clusters) further condensations are apparently kinetically unfavorable and indeedare not seen here.As observed earlier in other systems, as well as in the V, Cr, Mn, and Fe systemsstudied here, ion-molecule reactivity rates in the Co system depend strongly upon electrondeficiency of the central metal atom. This generalisation is especially true in the cobaltsystem. Figure 6.9 illustrates this: pseudo-first order rate constants for disappearance ofeach reactant cation are plotted against electron deficiency per cobalt atom and show a wellbehaved relationship, with a steep slope at electron deficiencies between zero and one. Incontrast with the four other metal systems studied here, clustering reactions in the Cosystem appear to be of minor importance compared to ligand (H, Cp or CO) or electrontransfer from the parent neutral molecule. The dominant reaction channels in this cobaltsystem are those in which 18-electron configuration is approached or achieved, as forexample, via the single ligand transfer reactions shown above.2036 CpCoCOH4 / .L.CpCo2’CpCoCO Co0.1.. / CpCo(CO)2 +6’4 CpCo(CO)2H +2 Cp2Co +o.oi CpCo)2(CO)3 +8I I I I0 ‘4 6 8 10Electron Deficiency per Co AtomFigure 6.9. Relationship Between Reactivityand Electron Deficiencyfor Cations in the CpCo(CO)2 System2042. Reactions with Gases N2, CO, and C02At pressures of 6x107 torr, all three reagent gases underwent electron ionisation,followed by hydrogen species exchange with neutral CpCo(CO)2 molecules, as follows:1. Nitrogen Reactions*N2 + CpCo(CO)2 — NH + .. (H atom transfer)N2H + —* CpCo(CO)l,2H + . .(Proton transfer)Temporal behaviour of N2 and its principal products is shown in Figure 6.10.(* pseudo-first kinetic order in N2 andN2H)2. Carbon Monoxide Reactions*CO + CpCo(CO)2 —> COH ÷ . . (H atom transfer)COH + —* CpCo(CO)1,2H + . .(Proton transfer)Temporal behaviour of CO and its principal products is shown in Figure 6.11.(* pseudo-first kinetic order in CO2 and COH+)3. Carbon Dioxide Reactions*CO2 + CpCo(CO)2 — CO2H +..(H atom transfer)CO2H + “— CpCo(CO)1,2H+ . (Proton transfer)Temporal behaviour of CO2 and its principal products is shown in Figure 6.12.(* pseudo-first kinetic order in CO2 and CO2H)205N2SI0.20. 1HN2’1 .,_CpCo(CO)2H +C -_015-__aCCpCoCOH0.10-0.05-I I I0 1000 2000 3000TIME (msec)Figure 6.10. Temporal Behaviour of N2and Cation Products: p (N2) = 6.OxlO-7 torr;p(CpCo(CO)2) = 6.OxlO8 torr2060.35.0.30. +0.25.CpCo(CO)2H +C CoCOHOalO”0.05-AAA1 I • 1 •0 2000 4000 6000TIME (msec)Figure 6.11. Temporal Behaviour of CO+and Cation Products: p(CO) = 6.OxlO7 torr;p(CpCo(CO)2) = 6.OxlO8 torr2076x1 02-TTiL_._Po)2 +5. CO2U)4” HCO24) 3.2- CpCoCOHI I ‘‘ I • I0 400 800 1200TIME (msec)Figure 6.12. Temporal Behaviour of CO2and Cation Products: p(C02) = 6.OxlO7 torr;p(CpCo(CO)2) = 6.OxlO-8 torr208In each of the preceding three reactant ion sequences, transfer of a hydrogen atomfrom a neutral molecule to a reagent gas cation is followed by proton transfer to a secondneutral molecule. Values for pseudo-first order rate constants (k’) obtained from linearsemilog plots from data such as in Figures 6.10 - 12 are listed in Table 6.4, along withsecond order rate constants (k”). These latter quantities were estimated from ambientpressure of neutral CpCo(CO)2, assuming that concentration of the latter reactant(CpCo(CO)2) remains always in large excess of the ion reactant (i.e., N2, COP, etc.)formed from electron ionisation of N2, CO or C02.Calculated values of second order rate constants listed in Table 6.4 are close to theupper (theoretical collision) limit for bimolecular ion-molecule reactions in the gas phase(10- molecule-cm3se -)[161,and are comparable with rates measured earlier for othersmall cation-molecule interactions( 10-11 - 10 molecule- ‘cm3see-1)[4,43,461 In eachsequence of reactions, the predominant final cation product is CpCo(CO)2H (18electrons); again, the abundance of this product ion reflects its inherent electronic stabilityin the gas phase. The first reaction in each sequence involves abstraction of a hydrogenatom from the Cp ligand of CpCo(CO>. The second reaction involves proton transfer fromthe newly-hydrogenated reagent gas cation (N2H, COH or CO2H) to the cobalt centerin another neutral molecule, generating the final product cation, CpCo(CO)1,2H. Theexistence of proton transfer from N2H+, COH+ and CO2H+ permits an approximation ofthe proton affinity of CpCoCO and CpCo(CO)2 moieties: since proton affinities of N2,CO2 and CO are 117.4, 128.6, and 141.4 kcallmole respectively[15,proton affinities ofthe two cobalt species must therefore be at least 140 kcal/mole. On the other hand,hydrogen atom affmities of N2t CO and CO2 must be larger than that of CpCo(CO)2 inorder for intermediates N2Ht COH and CO2Hto be detected and quantified.209TABLE 6.4Relative Rates of Reaction of CpCo(CO)2with Some Small MoleculesReactant Ion k”(sec-1) (molec.-icm3se -1)*N2 10.4 3.4 x 10-8HN2 3.74 1.2 x 10-8CO+ 6.98 2.3 x 10-8HCO 7.65 2.5 x 10-8CO2 2.11 6.9 x iO-HCO2 2.17 7.1 x iO-* Estimated from ambient CpCo(CO)2pressure = 6.0 x 10-8 torrTemperature 3000K; pressure of reactant gas = 6.0 x iO torrall data ± 30%2102. Negative Ion ChemistryUnder 2.5 eV electron impact and at 6.Ox10”8 torr gauge pressure, only thenegative ions CpCoCO (17 electrons) and parent anion CpCo(CO)2 (19 electrons) weregenerated as follows: CpC0CO = 49%; CpCo(CO)2 = 41%. This distribution isconsistent with measurements made by Beauchamp using 70 eV EI[7]: CpCoCO = 16%;CpCo(CO)2 = 84%. Further reaction of CpCoCO with the parent neutral produced onlyone anion cluster, Cp2Co2(CO)2 (17.5 electrons per metal). Both parent anion,CpCO(CO)2 and cluster anion, Cp2Co2(CO)2 were unreactive for 25 seconds. Anexample of a FT-ICR negative ion mass spectrum of CpCo(CO)2, measured at 500 msec,is shown in Figure 6.13; and the temporal behaviour of these anions is illustrated in Figure6.14 on the following page.211z-JuJFigure 6.13. FT-ICR Negative Ion Mass Spectrum ofCpCo(CO)2; 500 msec.; 2.5 eV; p = 6.0x108tort1008060402000 100 200 300 400 500MASS In AMU60021206->10.5-kCpCo(CO)2rjii0.4- (CpCo)2(CO)2—0.3-C)0.2.C)0CO -0.1-I I 1 I I -?0 2000 4000 6000 8000TIME (msec)Figure 6.14. Temporal Behaviour of PrimaryFragment Anions of CpCo(CO)2213The only observable reaction of the anion daughter fragments in this system is thatof condensation of CpCoCO with its parent neutral molecule:CpC0CO - + CpCo(CO)2 —* Cp2o(CO) - + COLike positive ions in this CpCo(CO)2 system, as well as all of the negative ionsstudied in the vanadium, chromium, manganese and iron systems, a tendency towardpossession of an 18-electron metal core configuration appears to govern the negative ionchemistry of CpCo(CO)2. The Co-Co bond within the binuclear clusterCp2o(CO) isknown to be unusually short for a single bond, thus increasing the electron density of eachcobalt atom to nearly 18 electrons, resulting in notable stability[36’41l.4. Reactions with Gases N2, CO, and C02At reagent pressures of iO torr, charge exchange, adduct formation or furtheranion condensation reactions were not observed in the presence of N2, CO, or C02 reagentgases. Although the Cp2o(CO) cluster is notably unreactive, the lack of observedreactivity may also be kinetic, a result of low anion concentration and low reagent gaspressures.III ConclusionsGENERAL FEATURES OF THE CpCo(CO)2 SYSTEM1) All of the daughter cations initially formed by electron impact on CpCo(CO)2arechemically reactive with the parent neutral molecule, whereas only one daughter anion,CpCoCO, is reactive. In general the abundance distribution of these ions after formation214by electron impact is in agreement with appearance potentials in the literature[38].Sequential elimination of one or two carbonyl ligands requires approximately 2.5 eV each;while rupture of the much stronger CpCo linkage requires at least 7 eV; therefore the mostprominent ions in the mass spectrum using low energy electron ionisation (25 eV) areexpected to be the parent ion CpCo(CO)2, completely and partially decarbonylated ions;i. e., CpCo+ and CpC0CO+, as well as the bare Co+ cation.2) All of the daughter cations, Co, CpCo, and CpCoCO undergo electrontransfer with the parent neutral molecule, producing CpCo(CO)2. Relative rates of theseprocesses were listed in Table 6.3. The bare metal cation Co+ reacts principally by electrontransfer, like V in the CpV(CO)4 system.3) Three cations, CpCo, CpCoCO and CpCo(CO)2 apparently can abstract oneCp ligand from a neutral molecule, rupturing the Cp-Co linkage and generating Cp2Co.This latter cation, an extremely stable 18 electron species, becomes one of the predominantproducts in later mass spectra, whereas in the other four metal systems, formation ofaryl2metal (i.e., Cp2Mn, Bz2Cr, etc.) was of minor importance. Electronic saturationof the central metal cobalt atom, and consequent high kinetic stability of Cp2Co probablyaccounts for this.In all other ion-molecule pathways the Cp-Co linkage is maintained throughoutligand exchange and condensation regimes; i.e., in formation of CpCo(CO)2H and(CpCo)2O)2,3.4) Clustering terminates with the formation of bicobalt, (CpCo)2 cores atexperimental pressures (106- iO9 torr); cation cluster fragments containing more than twocobalt atoms were not observed. Cluster termination in this system may be a consequenceof ligand crowding around the central cobalt core, electronic saturation of the ion-moleculeclusters afready formed, or else low neutral molecule pressures dictated by the experimentalprocedure. Clustering channels compete with the formation of CpCo and clusteringroutes are constrained by prerequisite formation of the precursor, CpCo(CO)2H+.2155) The hydrogenated cations CpCoCOW (16 electron) and CpCo(CO)2H (18-electron) are important precursors to cluster formation in this cobalt system. Suchhydrogenated cations are only of minor importance in the other four systems. This may besimply a reflection of the importance of coordination saturation (i.e. 18-electronconfiguration) in all species of the later transition elements such as cobalt, nickel andcopper. Several other hydrogenated transition metal clusters in solution or as solids areknown; for example: Cr(CO)3H[25’]; (CpC0H)4[33];CrCpH(CO)3,TcCpH[9lO]; andMoCpH[l3],but gas phase ion-molecule studies of their cluster chemistry have not yetbeen undertaken.6) Evidence for participation by excited state daughter ion fragments in this cobaltsystem, such as was found in the other four systems, was observed only for the bare metalcation, Co+. For the other reactive cations, pseudo-first order semi-log plots are reasonablylinear, unlike the results obtained for the vanadium, chromium and manganese systems.Figure 6.15 on the following page shows a non-linear kinetic semi-log plot for ion Co.Similar plots for the larger ions, CpCo, CpCoCO, and CpCo(CO)2+are reasonablylinear, indicating ground state configurations only.An approximation of 67% population of excited state Co+ ions was obtained fromthe extrapolated slope in Figure 6.15. The first excited state (5F, 41 configuration) of Cois only 0.43 eV above the ground state (3F, 4s° configuration) energy[] so that afterionisation with 25 eV electrons, large numbers of excited Co+ ions should be presentbefore relaxation can occur. (This is similar to the V+ case, where the energy differencebetween the lowest two states is 0.33 eV; and to the Mn case; 1.17 eV[3l). Theseconclusions are in contrast with those of other authors, wherein reactivity differencesbetween cobalt carbonyl ions such as Co4(CO)4 (which is non-reactive with respect tocyclohexane) and co4(CO)5+(which is reactive) were attributed to the existence of lowlevel empty coordination sites on cobalt in the latter ion, rather than to excited state cobalt216CpCo(CO)2+2>1• 0.1-C 86C— 4I—9 CpC(U -a0.01 -86I I I0 500 1000 1500Relative Time (msec)Figure 6.15. Pseudo-First Order Decay Behaviourof Some Cations in the CpCo(CO)2 System217ion reactants[35].7) Reactions with several addition reagents (e.g., N2, CO. and C02) eventuallygenerated adducts containing one atom of hydrogen, i.e., CpCo(CO)2H+, typifying thetendency of later transition metals to form complexes with low coordination number. Noproduct cations containing more than one extra, new ligand were observed in this cobaltsystem.8) A clastogram showing the appearance of fragment cations of CpCo(CO)2 withelectron ionising energies is illustrated in Figure 6.16. Predictably, larger cationspredominate at lower energies whereas smaller cation fragments appear at higher energies.9) Each of the bicobalt cluster ions, (CpCo)2(CO)2,3 and (CpCo)2Oprobably consist of central cobalt-cobalt cores surrounded by single Cp and CO ligands, orby bridging CO ligands, like multi-cobalt central core compounds synthesized earlier, suchas Cp3Co3(CO)3 (King[24l);Cp2Co2(PPh)(Coleman and Dahl[6]); and Cp4Co4FL (MUller and Dörner[33l).The notable stability of all these condensed phase species, as in the ions Cp2Co2(CO)2and (CpCo)2(CO)2,3probably arises from short cobalt-cobalt bond lengths, as well asligand arrangements[30’641]•218>-50- CpCoCOU)Z CpCo(CO)21±! 40-z CpCo—z 30-Q Cow 20. CoCO10-_Iw0- —A0 10 20 30 40 50 60 70El BEAM VOLTAGEFigure 6.16 Clastogram for Cations of CpCo(CO)2219IV References(1) Armentrout, P. B.; Halle, L. F.; Beauchamp, J. L. J. Am. Chem. Soc. 1981,103, 6624.(2) Armentrout, P. B.; Beauchamp, J. L. J. Am. Chem. Soc. 1981, 103, 6628.(3) Armentrout, P. B. in Gas Phase Inorganic Chemistry; Russell, D. H.; PlenumPress, New York, 1989; pp 1 - 42.(4) Bricker, D. L.; Russell, D. H. J. Am. Chem. Soc. 1987, 109, 3910.(5) Chen, H.; Lin, H.-Y.; Sohlberg, K.; Ridge, D. P. Ann. Conf. ASMS All. Topics1991,39, 1596.(6) Coleman, 3. M.; Dahi, L. F. J. Am. Chem. Soc. 1967, 89, 542.(7) Corderman, R. R.; Beauchamp, J. L. Inorg. Chem. 1977, 16, 3135.(8) Fischer, E. 0.; Jira, R. Z. Naturforsch. 1954, 9B, 618.(9) Fischer, E. 0.; Hafner, W.; Stahl, H. 0. Inorg. Synth. 1963, 7, 136.(10) Fischer, E. 0.; Schmidt, M. W. Chem. Ber. 1969, 102, 1954.(11) Freas, R. B.; Ridge, D. P. .1. Am. Chem. Soc. 1984, 106, 825.(12) Gord, J. R.; Freiser, B. S. .1. Am. Chem. Soc. 1989, 111, 3754.(13) Green, M. L. H.; McCleverty, J. A.; Pratt, L.; Wilkinson, G. J. Chem. Soc.1961, 4854.(14) Halle, L. F.; Crowe, W. E.; Armentrout, P. B.; Beauchamp, 3. L. Organometallics1984,3, 1694.(15) Harrison, A. G. Chemical Ionization Mass Spectrometry; CRC Press: BocaRaton, Florida, 1983.(16) Henchman, M. in Ion-Molecule Reactions; Franklin, 3. L.; Plenum Press, NewYork, 1972; pp 101 - 259.(17) Huttner, G.; Lorenz, H. Chem. Ber. 1975, 108, 973.220(18) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1983, 105, 5197.(19) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1984, 106, 3900.(20) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1984, 106, 3891.(21) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1985, 107, 1581.(22) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1986, 108, 27.(23) Jones, R. W.; Staley, R. H. mt. J. Mass Spectrom. Ion Phys. 1981, 39, 35.(24) King, R. B. Inorg. Chem. 1966,5, 2227.(25) Lane, K. R.; Squires, R. R. J. Am. Chem. Soc. 1985, 107, 6403.(26) Lane, K. R.; Sallans, L.; Squires, R. R. Organometallics 1985,4, 408.(27) Lichtenberger, D. L.; Calabro, D. C.; Kellogg, G. E. Organometallics 1984,3,1623.(28) Lin, L.; Kutal, C. R.; Amster, I. J. Ann. Conf. ASMS. All. Topics 1991, 39,1616.(29) McDonald, R. N.; Schell, P. L. Organometallics 1988, 7, 1806.(30) Mevs, J. M.; Gennett, T.; Geiger, W. E. Organometallics 1991, 10, 1229.(31) Mingos, D. M. P.; May, A. S. in The Chemistry ofMetal Cluster Complexes;Shriver, D. F.; Kaesz, H. D. Adams, R. D.; VCH Publishers, Inc., New York,1990; pp 11 - 119.(32) Muller, J.; Fenderl, K. Chem. Ber. 1970, 103, 3141.(33) Muller, J.; Domer, H. Angew. Chem., mt. Ed. Engl. 1973, 12, 843.(34) Orieclo, J. V.; H., R. D. Ann. Conf. ASMS. All. Topics 1991, 39, 1610.(35) Pan, Y. H.; Sohlberg, K.; Ridge, D. P. J. Am. Chem. Soc. 1991, 113, 2406.(36) Pinhas, A. R.; Hoffman, R. Inorg. Chem. 1979, 18, 654.(37) Piper, T. S.; Cotton, F. A.; Wilkinson, G. J. Inorg. Nuci. Chem. 1955, 1, 165.(38) Rosenstock, H. M.; Draxi, K.; Steiner, B. W.; Herron, J. T. Energetics ofGaseous Ions; American Chemical Society and American Institute of Physics:Washington, D. C., 1977.221(39) Sallans, L.; Lane, K. R.; Freiser, B. S. J. Am. Chem. Soc. 1989, 111, 865.(40) Schilling, 3. B.; Goddard III, W. A.; Beauchamp, 3. L. J. Am. Chem. Soc.1986, 108, 582.(41) Shore, N. E.; Ilenda, C. S.; Bergmann, R. G. J. Am. Chem. Soc. 1977, 98,256.(42) Simoes, I. A. M.; Beauchamp, J. L. Chem. Revs. 1990, 90, 629.(43) Skinner, H. A.; Connor, 3. A. Pure and Applied Chemistry 1985,57, 79.(44) Squires, R. R. J. Am. Chem. Soc. 1985, 107, 4385.(45) Tsarbopoulos, A.; Allison, J. Organometallics 1984,3, 86.(46) VanOrden, S. L.; Pope, R. M.; Buckner, S. W. Organometallics 1991, 10,1089.(47) Winters, R. E.; Kiser, R. W. J. Organomet. Chem. 1965,4, 190.222CHAPTER 7GENERAL DISCUSSIONANDCONCLUSIONS223I. General Periodic TrendsFirst row transition metals consist of those elements with progressively-filled 3dand 4s outer electronic orbitals, from element 21, Scandium on the left side of the series toelement 30, Zinc on the right. In general, ionisation energy increases and atomic radiusdecreases across the period because of the increasing effective nuclear charge exerted onelectrons by the atomic nucleus. Coordination number tends to lessen from left to right, assize and therefore space about the metal centre diminishes, and also as outer orbitalsbecome increasingly filled. Consequently, although fewer, metal-ligand bonds generallytend to be stronger in late transition metal complexes (of Ni, Cu and Zn) than in earlierones (of Sc, Ti andV)[45l.Although transition metal cations are smaller than the corresponding atom becausethe electronic orbitals are more constrained by the nuclear charges than they are in atoms,anions tend to be larger than their corresponding atom. Moreover, metals on the left handside of the transition series tend to exhibit a greater variety of cationic oxidation states thando those on the right, owing to their less populated electronic levels as well as weakereffective nuclear charge.Certain electronic arrangements in transition metal atoms or ions are stabilised bypossession of half-full or full electronic orbital configurations. For example, ground stateCr (3d5 4s0) is regarded as being less reactive than neighbouring ground state analogues,Fe (3d64s1) or V(3d4)[’6’8404548]Gas phase metal ion thermochemical data from mass spectrometry were scarce untilthe development of ion beam[3’1321]and laser techniques[26’321 over the past ten years.These techniques have demonstrated that general trends for gas phase ions across the firsttransition period are not easily predictable. For example, measured electron affinity (EA) ofgaseous metal atoms increases from vanadium (12 kcallmol) to chromium (15 kca]Jmol);then drops markedly for manganese (<0 kcallmol), thereupon increasing steadily to copper224(28 kcallmol). lonisation potentials increase unevenly from scandium (152 kcallmol) toiron (182 kcal/mol), then decrease to nickel (175 kcal/mol)[24’39].According to Armentrout and others, strengths of gas phase transition metal cationligand bonds (such as Mt-H; M-CH3M-O) increase slightly from vanadium tomanganese or iron, then decrease with atomic number to copper (e.g., for Cr+H, D=33kcal/mol; for Fe-H, D=50 kcalJmol; for Ni-H, D=40 kcal/mol[3’]).Squires and Sallans have shown that metal-hydrogen bond strengths (M-H)decrease unevenly from scandium (48 kcal/mol) to iron (30 kcal/mol), then increase tocopper (60 kcal/mol), whereas acidities of metal hydrides remain relatively constant acrossthe period (341±5 kcal/mol), because of the compensation of electron affinity values withmetal-hydrogen bond strengths[54’60].Metal-oxygen linkages tend to be especially strong:Cr-O, 77 kcal/mol; Fe-O, 68 kcal/mol.Metal-aryl bonds (M-Cp; M-benzene) have been shown thermochemically to beuniformly rather strong (e.g., D=88 kcal/mol for Cp-vanadium; 71 kcal/mol for Cp-iron);whereas metal-CO bonds are uniformly moderately weak (e.g., D=37 kcal/mol forvanadium; 25 kcal/mol for chromium; 33 kcal/mol for cobalt)[17’5968l.First row transitionmetal bond strength data from studies of Armentrout, Connor, Freiser and Squires aresummarised in Table 7.1 [3,4,17,26,54,59,60,61,68] on the following page.225TABLE 7.1Energy Parameters for the First Transition Metal Series*Metal Sc Ti V Cr Mn Fe Co Ni Cu ZnEAa 4.4 1.8 12.1 15.4 <0 3.8 15.3 26.7 28.3 <0Jb 151 157 155 156 171 181 181 176 178 216Ec 0.31 0.10 0.33 1.52 1.17 0.25 0.43 1.08 2.81M-Cp - - -- 87.6 67.6 50.7 70.7 63.8 58.8M-CO -- -- 37 25 24 28.1 32.5 35.1 --M-Bz -- -- 68.1 39.0M-M 38 30 57 36 10 24 40 61 47M-H 47.5 38 37.9 41.2 <32 29.6 42.2 60 60 20.5M-H+ -- -- 47.3 27.7 47.5 47.3 44M+-H 56.2 54.2 48.2 32.5 48.4 49.8 46.6 39.5 22.1 60M-CH3 59 58 50 30 51 58 51 47 30 71M-O - - - - - - 77 57 68 65 45a electron affinity; b ionisation potential of the gaseous ion;C energy difference between ground and first excited state ofunivalent metal cation.* Values from references 3, 4, 17, 26, 54, 59, 60, 61All values expressed as kcal/mole at 298 OK226II. Kinetic Results1. General TrendsThe present mass spectral measurements on aryl-transition metal-carbonylcomplexes generally reflect the trends seen in earlier studies; especially withrespect to initial fragmentation patterns. Ion-molecule interactions also exhibit patternswhich are not inconsistent with the preceding thermodynamic data: for instance; arylligands were persistently unreactive throughout ion-molecule reactive pathways;CO ligands are moderately mobile; and new bonds were readily generatedthrough additive or substitutive pathways, either by abstraction of ligands from the neutralmolecule, or else by hydrogen, oxygen or other substituent insertion by reactive smallmolecular gases. Final ion products typically tended to retain aryl-metal stoichiometry,maintain low carbonyl content, and general reactivity varied with electrondeficiency of the central metal; i.e., in all five aryl transition-metal systems, thechemical behaviour of ions varied approximately with electronic density about the centralmetal.In all five systems, since cations are more electron deficient than correspondinganions; cation-molecule chemistry was rich, with reactant ions undergoing multiple,simultaneous interactive pathways. Except for the five molecular ions, all cations reacted inone of two modes: either by accepting an electron from the neutral molecule (chargetransfer); or by condensing with a neutral molecule to produce successively larger clusterions (clustering).In contrast with cation-molecule chemistry, in all five systems anion-moleculechemistry was limited to relatively simple clustering or ligand exchange, whence onlyone or two unreactive anion products were generated. This aryl-metal-carbonyl anion227chemistry contrasts with that of metal-carbonyl anion systems, in which multiple,interacting pathways have been observed[l,25,36A6l.Reaction rate constants were evaluated by conventional procedures[27outlined in the Appendix, by assuming that concentrations of the parent neutral moleculeare always much larger than that of any reacting ion generated either during the electronionisation or by subsequent ion-molecule interactions in the FTICRMS reaction cell.Pseudo-first order rate constants were obtained from linear slopes of the semilog rate plotsfor each reactive cation. Values of these rate constants (In k’) were plotted against electrondeficiency in Figures 2.18, 3.11, 4.11, 5.10 and 6.9, each one illustrating a monotonictrend of reactivity as a function of electron deficiency or coordination unsaturation for thesuite of cations generated in each system.Second order rate constants for the bimolecular ion-molecule reactions wereestimated by assuming that initial concentrations are zero for all other cations except the ionof interest: a condition occurring directly after multiple resonance ejection of all ions exceptthe reactant cation in question. The proportion of any ion product present in a productmixture at several subsequent time periods was used to obtain its rate of formation. Secondorder rate constants were computed using neutral reactant gas concentrations estimated bymethods of Bartmess[6’7]and Chen[151 using molecular polarisibility values as determinedby Aroney and Le Févre.Tables of calculated second order rate constants (kA, kB, etc.) and relativerate constants (lOOk’B / k’A; lOOk’c / k’; etc.) are listed for reactions of vanadiumcations in Table 2.2 - 5 in Chapter 2; for chromium cations, Table 3.2 in Chapter 3; formanganese cations, Table 4.2 in Chapter 4; for iron cations, Table 5.2 in Chapter 5; andfor cobalt cations, Table 6.2 in Chapter 6. A summary of second order reactionrate constants for cations in the five metal systems is presented in the tables on thefollowing pages. Table 7.2 lists absolute decay rates for monometallic cations, their rates228TABLE 7.2Comparative Rates for Transition Metal Ions (Monometallic)1.Cation decay rates (x109 molec:lcm3sec.l)*Metal M ArM ArMCO ArM(CO)2 ArM(CO)3ArM(CO)4V 2.61 1.65 0.98 0.52 0.12 0.043eCr 2.33 1.54 1.23 0.93 <0.05Mn 2.02 1.49 0.80 0.70 O.18Fe 1.49 1.24 1.16 0.66 <0.05Co 1.93 1.26 0.69 0.682. Electron transfer rates (x109 molec.lcm3secl)*Metal M ArM ArMCO ArM(CO)2 ArM(CO)3 ArM(CO)4V 2.61 0.541 0.372 0.238 0.06Cr 1.44 0.848 0.761 0.597Mn 1.35 0.753 0.36 1 0.224Fe <0.05 <0.05 <0.05 <0.05Co 1.93 0.656 0.2623. Cation clustering rates (x109 molec..lcm3s4)*Metal M ArM ArMCO ArM(CO)2 ArM(CO)3ArM(CO)4V <0.02 1.02 0.355 0.199 0.028 0.017eCr 0.885 0.691 0.465 0.337 <0.05Mn 0.669 0.741 0.441 0.471 <0.05Fe 1.49 1.24 1.16 0.66 <0.05Co <0.05 0.60 0.36 0.41*All data ± 30% ; M = metal ; Ar = aryl group; e = excited state only229TABLE 7.3Comparative Rates for Transition Metal Ions (Bimetallic)1.Cation decay rates (x109 molec..lcm3secl)*Metal (ArM)2 (“)2CO (“)2CO) (“)2CO)3 (“)2CO)4V 1.12 0.91 0.44 0.17 <0.02Cr <0.02 <0.02 0.24 0.13Mn 0.36 0.30 0.23 0.17Fe 0.50 <0.04 <0.04 <0.04Co <0.032. Electron transfer rates (x109 molec.lcm3secl)*Metal (ArM)2 (“)2CO (“)2CO) (“)2CO)3 (“)2CO)4V 0.368 0.273 0.134 0.02 <0.02Cr ---- 0.119 0.041Mn 0.076 0.061 0.034 0.072Fe <0.05 <0.05 <0.05 <0.05Co3. Cation clustering rates (x109 molec.lcm3secl)*Metal (ArM)2 (“)2CO (“)2CO) (“)2CO)3 (“)2CO)4V 0.290 0.411 0.208 0.100 <0.02Cr <0.02 <0.02 0.115 0.091Mn 0.281 0.243 0.190 0.152 <0.05Fe 0.50 <0.04 <0.04 <0.04Co <0.03*All data ± 30% ; M = metal ; Ar = aryl group230TABLE 7.4Comparative Rates for Transition Metal Ions (Trimetallic)1.Cation decay rates (x109 molec.lcm3secl)*Metal (ArM)3 (“)3CO (“)3CO)2 (“)3CO) (“)3CO)4V <0.02 0.18 0.32Cr ---- ---- 0.10 0.11Mn ---- <0.04 0.07 0.04Fe -- --Co ---- ---- ---- <0.032. Electron transfer rates (x109 molec.4cm3se)*Metal (ArM)3 (“)3CO (“)3CO)2 (“)3CO) (“)3CO)4V ---- -------- 0.043 <0.02Cr---- ----Mn <0.04 0.065 <0.04Fe----Co----3. Cation clustering rates (x109 molec.4cm3se)*Metal (ArM)3 (“)3CO (“)3CO)2 (“)3CO) (“)3CO)4V <0.02 0.065 0.26Cr <0.02 <0.02Mn <0.04 <0.04 <0.04Fe 0.50 <0.04 <0.04 <0.04Co ---- ---- ---- ----*All data ± 30% ; M = metal ; Ar = aryl group231of electron transfer, and condensation (clustering) rates; Table 7.3 lists these parameters forbimetallic cluster cations; and Table 7.4, for trimetallic cations.In the preceding Tables 7.2-7.4, values for pseudo-first order rate constants areaccurate to ± 10%; however uncertainty in molecular polarisibilities may produce ±30%uncertainty in absolute second order rate constant values.2. Decay RatesA comparison of absolute second order decay rate constants of monometalliccations in all five systems is given in the upper section in Table 7.2. In general, decayrates for reacting cations declines with coordination saturation. Table 7.2 alsoshows that for metals with similar coordination, decay rate constants have the same orderof magnitude. For example, for the five bare metal cations, decay rate constants vary from1.5 x109 and 2.6 x109 (molec.1cm3 sec-1).Rate constants for the decay of bimetallic reactant cations are listed in Table 7.3.These rate constants are about one order of magnitude smaller than those of theirmonometallic counterparts, although just as for the monometallic ions, the general patternof rate constant attenuation with increasing coordination follows the same trends as formonometallic ions. Table 7.4, presenting all data obtained for trimetallic cations, isincluded here for completeness, and although incomplete, demonstrates the same trends asshown by mono- and bimetallic cations. These rate constants (10 - 10-10 molec:cm3s1) are of similar magnitude to those determined for other organometallic gas phase systems[14,22,25,34,35,50-2,64] Most of the second order rate constants reported here are close topredicted Langevin collision rates for unpolarised reactants (10w molec:cm3se)indicating that the present processes are probably highly efficient with respect to collisionalfrequency, and also are strongly accelerated by the polarisability of each neutral moleculeas it reacts with cation or anion species[23’30412556M].2323. Electron Transfer ReactionsElectron transfer reactions dominated the chemistry of all cations inthe vanadium system, were important in the chromium and manganese systems, were ofminor importance or absent in the iron and cobalt systems, as summarised in Tables 7.2-7.4. Table 7.2 lists electron transfer rates for monometallic cations; Table 7.3, forbimetallic cations; and Table 7.4, for trimetallic cations.Absolute rates of electron transfer for reactive metal ions of equal coordination wereof very similar magnitude. For example: for monometallic ion CpVt k = 0.54xlO9molec.1cm3sec, and for CpCo, k = 0.66xlO9molec.-1c3se;for bimetallic ions(CpV)2(CO)2t k = 0.13x109molec:cmsec- and for (BzCr)2(CO)2,k = 0.12x10-9molec.-1cm3sec-;for trimetallic ions (CpV)3(CO)3, k = .043x 1O molec:1cm3sec-1 andfor (CpMn)3(CO)2t k = .065x10-9molec:1cm3se For any one metal, rates diminish ascoordination increases in each table from right to left (corresponding to periodic tableposition of the central metal), and as cluster size increases from monometallic ion fragmentto bi- and trimetallic cluster.These trends of diminishing reactivity apparently reflect the relativeelectron deficiency of the central transition metal core of each cationcompared with that of its neutral molecule. On the other hand, the tendency of reactivecations across the vanadium-cobalt transition series to undergo charge transfer dependsupon the electron-donating property of the aryl ligand as well. For example, 17-electronmolecular cations (e.g., CpV(CO)4, BzCr(CO)3CpMn(CO)3are important endproducts in the rarified gas phase environment within the ICR mass spectrometer, becauseeven though solvating molecules are not present to stabilise them, these cations may becoordination-saturated by partial electron donation from their aryl ligand (and carbonylligands) to the metal centre.233Only in the iron system were iron cation fragments inactive withrespect to electron transfer from the neutral molecule. In this system, reactingcations preferentially condensed with the neutral molecule instead. Possibly, electrondonation from the less-aromatic,4-butadienyl ligand to the central iron atom of themolecular cation is not pronounced enough to favour preferential formation and subsequentelectronic stabilisation of a 17-electron BuFe(CO)3. The principal reactive mode in thisiron system is condensation with the parent neutral molecule, with formation of largerclusters, rather than ligand addition or electron exchange with the neutral molecule.All bare metal cations except Fe+ reacted by electron transfer; and also, all exceptV+ and Co+ formed asymmetric, metal-rich clusters by condensing with a neutralmolecule. Similar reactive patterns in which bare metal cations either condense or absorbelectrons have been seen in related systems[14’’512l.4. Condensation (Clustering) ReactionsAs is apparent in Tables 7.2-7.4, cluster formation rates did not varygreatly with central metal present, but diminished with cluster size. Forinstance, for monometallic cations ArMCO+, rates vary from O.36-1.2(xl09molec:1cm3sec);for bimetallic cations (ArM)2CO)2, rates vary from <0.04-0.21(xl09molec.1cm3sec); and for trimetallic cations (ArM)3(CO)3, rates vary from <0.02-0.07(x109molec:cmse).No cluster containing more than four aryl-metal units was observed inlarge quantity. This rate diminution may be due to spatial constraint and ligand saturation inthe multi-metal core clusters[33A4,6.Some cluster ions such as (CpV)3(CO)3t Bz2Cr and (CpMn)3O)2wererelatively long-lived in the gas phase, owing either to electronic stability (e.g., Cp2CotBz2Crj, or possibly to multiple metal-metal bonding within the central core, or ligandrestructuring and repositioning. Carbonyl ligand saturation around the core may act as a234shield against further reactivity. Such modes of cluster stabilisation, and ligandrestructuring in order to increase stability have been examined closely by many authors[2,11,12,19,25,31,37,38,43,65,68]In all final cluster ion products carbonyl coordination number remainedrelatively low (i.e., 0-6 carbonyls; and typically only 2-4 CO ligands per cluster),indicating that the metal atoms are concentrated in the central cores of the clusters withlimited space for carbonyl ligation. Metal-carbonyl linkages, always in the forefront inorganometallic studies[11,12,25,36,46,47,621 play an important role in the present studiesbecause of their action as coordination shields about the central metal cores. Tables 7.2-7.4show rates of clustering for all cations in the five systems.In all five metal systems, strong, multi-haptic aryl-to-metal linkages weremaintained throughout most of the reaction sequences. Appearance potentialsfor El rupture of these linkages are large: they vary from approximately 12 eV (benzenechromium) to 20 eV (Cp-vanadium)[24’39l.On the other hand, as seen in all systems thecarbonyl linkage was easily broken (appearance energies predictably range from 0.5to 2 eV per metal-CO link[24’39])both during ionisation as well as during subsequentinteractions. Freed from spatial constraint caused by the presence of many carbonylligands, reactive centres of aryl-metal cation fragments are able to approach the neutralmolecule easily: close approach of a reactant cation to the reactive core of a neutral moleculecan favour subsequent electron transfer or formation of a new metal-metal bond, generatinga larger cluster product.The relation between transition metal-carbonyl linking, metal-hydrogen linking andreduction of oxycarbon molecules such as CO is of fundamental importance inunderstanding the catalytic action of these transition metal centers, which cansimultaneously bind and later release both CO and hydrogen. Essential components ofreduction catalysts, these metal centres operate both homogeneously as gaseous molecularclusters, as well as heterogeneously, embedded upon solid surfaces.235Many of the reactive ionic species in all five transition metal systems examined hereretained, as well as released CO ligands during ion-molecule interactions. Furthermoremost, and probably all underwent hydrogen ligation, in which new metal-hydrogen linkswere generated. Under higher pressures and temperatures, this same activity mimics theheterogeneous catalytic behaviour of cobalt or nickel in Fischer-Tropsch or Raney typecatalysis on supported solid surfaces, or in buIk[28384762671.5. Ligand Exchange ReactionsDetailed examination of cation chemistry revealed that for all five metal systems,many cations underwent ligand exchanges with neutral molecules. In thevanadium cation system alone, most cations underwent carbonyl transferreactions. In the vanadium, manganese and cobalt systems, transfer ofhydrogen from neutral to cation occurred. Addition reaction pathways were seenin most systems: reactions with small molecular gases such as CH4,N2, H2 and CO2resulted in new, addition product formation. Parallel adduct formation by reactive ions hasbeen studied previously in many systems[1’9”02034661l.Together with electron transferand cluster formation, generation of hydride addition products such as cationsCpCo(CO)1,2Ht CpV(CO)4Ht etc., is one of the most prominent features of cation-molecule interaction in these metal systems.Metal-hydride ions are produced here by one of two apparentmechanisms; firstly, by donation of a proton from a more acidic cation to one oflesser acidity. An example of this is in the cobalt system, where a protonated nitrogenmolecule-cation (N2H) donates a proton to a neutral CpCo(CO)2 molecule, i.e.;N2H + CpCo(CO)2— CpCo(CO)2H+ N2The second mechanism for generation of kinetically stable (i.e., long-lived) hydrideions is hydrogen atom transfer (which is equivalent to combined proton and electron236transfer), in which the final product cation becomes stabiised by the addition of the extraelectron donated by the hydrogen ligand.An example of this type of reaction, in the cobalt system, is the formation ofCpCo(CO)2W end product from the reactant molecular cation, CpCo(CO)2, i.e.;CpCo(CO)2 + CpCo(CO)2 —* CpCo(CO)2H + neutral fragments6. Excited State ReactionsEvidence for reactive pathways involving excited state ions wasobserved in all five of the metal systems studied. For example, most of the baremetal cations, as well as the CpV(CO)4 molecular ion itself, apparently reacted with theneutral molecule before collisional relaxation had occurred. Several other studies, in whichionisation is effected by high energy electrons, have shown the existence of kineticparticipation by excited state reactantAll five bare metal cations exhibited non-linear disappearance rates, showing thatfor each reacting ion at least two species may be participating, most likely a ground statespecies and at least one excited state species. These relationships were shown in Figures2.19, 3.12, 4.12, 5.11 and 6.15. As well, in most of the five systems the simple arylmetal+ cation (CpV+, BzCr, etc.) as well as certain other larger cations showed nonlinearkinetic behavior.Participation by excited state cations occurred in all five metalsystems, producing non-linear semi-log kinetic plots which were extrapolated to zero timein order to obtain initial proportions of excited and non-excited state ion concentrations. Alist of initial ion abundances in their excited and ground states is shown in Table 7.5 on thefollowing page. Smaller ions in each metal system evidently were more readily excited,while apparently, larger fragment ions remained essentially in ground states duringmonitored time periods.237Table 7.5Initial Abundances- Excited State IonsION % excited state* % ground state*45 55CpV 81 19CpV(CO)4 30 70Cr 63 38BzCr 42 58BzCrCO’ 45 55Mw’- 77 23CpMn-’- 83 17CpMn(CO)3+ 48 52Fe 52 48BuFe 65 3567 33*Data calculated from intercepts of semilog rate plots*Most values ± 25%238Excitation of cation fragments was not unexpected, considering the high energies(at least 25 eV) injected during the electron ionisation process. In the low pressure regimesrequired experimentally (lO6lO-9 torr), collisional relaxation of reactant species does notalways have time to occur before ion-molecule interactions have begun. Residual energymay be retained by these and by even larger ions for many milliseconds. Even themolecular ion in both the vanadium and manganese systems also apparently underwentinitial excited state reactions, which later subsided.Excitation may be translational, vibrational-rotational or electronic, although in thecase of bare metal ions, only translational or electronic excitation can occur. Because ofhigher kinetic energies (from translational excitation) or differing electronic configurations(from electronic excitation), excited state bare metal ions would be expected to react morerapidly, or in different modes than their ground state counterparts. Earlier studies haveshown both of these behaviour patterns[4’21159531.In the present study, only in thosecases where both ground state and excited state ions are reactive can evidence of differentrates be measured (and consequently, different species distinguished).In Table 7.5, initial proportions of excited state ions are large, varying from 30% to83% of total ion populations. In most systems, the smaller ions showed larger proportionsof excited states, as in the chromium system where Cr+* = 63%, BzCr+* = 42% andBzCrCO+*= 45%. Since relaxation can occur by vibrations, collisions or ejection ofenergetic fragments, the larger ions with greater number of vibrational modes and large sizeshould predictably be more rapidly relaxed. Lifetimes of these excited state ions are of theorder of milliseconds, this evidence supporting the view that possibly these ions are excitedvibrationally or translationally rather than electronically.239III General ConclusionsIn summary, rates of reaction of cations are directly related to electrondeficiency of the central metal atoms, rather than which specific metal is present inthe metallic core of the ion. In general, cluster ions having electron counts much less than18 per metal were highly reactive; and those ions whose electron deficiencies were lessthan 2 electrons per metal atom were relatively unreactive, reflecting their lack of reactivesite accessibility, both electronic and spatial. This behaviour, noted earlier by Ridge[51landRussell[52], is a prominent feature of the present five systems. The apparently well-behaved relationship between rate constants and electron deficiency of reactant ions isobvious from Figures 2.18, 3.11, 4.11, 5.10 and 6.9. Each of the five plots shows lowreactivity of ions with formal 17- or 18-electron per metal counts, as for example, inCpV(CO)4, (17 electrons); Bz2Cr’ (17 e); (CpMn)3(CO)3, (18 e); BuFe(CO)3,(17 e);and CpCo(CO)2W(18 e). Conversely, ions with large electron deficiencies such as CpV(9 e); CpMnCO (13 e); BzCr(CO)2 (15 e) disappeared rapidly.All the above five plots show steep slopes for electron deficiencies above two,indicating that reactivity sharply increases when one or two-electron sites are vulnerable toattack by an incoming reactant species: since there is a vacant coordination site for reactionon the surface of the active ion. For vanadium and manganese ions the steep part of thedeficiency curve is spread over 0-5 electron deficiency, pointing to a less rigid electronicrequirement for incoming reactants.For chromium and iron ions, ions with electron deficiencies of 1 to 3 showpronounced increase in reactivity, reflecting that 1-, or 2-electron reagents may interactstrongly with these ions. For cobalt ions, the increase appears at the one electron deficiencypoint; exhibiting the strong tendency for cobalt to engage in one-electron interactions. Thepresence of low-lying vacant or partially-vacant coordination sites for formation of adducttransition states appears to be the governing criterion for all interaction within this240analogous series of complexes. Because the cobalt ions have valence shells which arealmost full, (as well as a larger nuclear charge) they are more selective with respect tomulti-metal clustering.Addition of small molecules to ions of the five complexes followed the same“electron deficient” behaviour trend discussed in the preceding paragraph. In all systems,all five molecular ions are observed to accept readily one hydrogen atom (ineffect, accepting an electron plus a proton), thus becoming 18-electron species, thehydrogenated molecular cation, M1I+. Formation of similar hydride species has beenobserved previously in many systems[3’22056671;and is especially prominent in thepresent cobalt system, where CpCo(CO)H+ dominates the mass spectra.Hydrogenated species (e.g., CpMn(CO)3Hl,2) were also seen in the CpMn(CO)3system, in which mono- and dihydrogen adducts were generated by reaction withmolecular H2, as was shown in Figure 4.13. Hydrogenation provides greater electronicsaturation, and consequently greater gas phase stability for these ions. Again, catalytichydrogenation or dehydrogenation by a transition metal depends upon its ability to bindand later release hydrogen under specific conditions[4’289’67].The pervasiveness ofmetal-hydrogen cluster fragments in these five systems accentuates the reactivity ofhydrogen species with these metals.Certain highly-stable species, formed by abstraction of a ligand from theneutral molecule, are dominant products in the mass spectra of all five systems:examples are: cations CpCo+, Bz2Cr, and CpMn2(CO)+;and anions Cr(CO)4,andCr(CO)ç. The abundances of these ions emphasise the high stability of the Cp-to-metal,Bz-to-chromium or Cr-to-oxygen linkages. Most of these ions are well known in theliterature, having been synthesised in solution and solid phases; a few which have beenobserved here; i.e., (CpV)2(CO)3+, CpCo(CO)2H+, may be sufficiently stable to beprepared in solution.241Interactions between ligated metal cations and molecular or ionicspecies of the reagent gases were observed in all systems. Addition reactionswere limited kinetically by the low concentrations mandated in FT-ICR, so that in order toexamine further addition chemistry, higher reagent gas pressures will be required. Inproof, many adduct cations of vanadium were observed in the high pressure DCIexperiments using NH3 and CH4 chemical ionisation reagent gases, which were notdetected at low pressures.Some FT-ICR-MS evidence of adducts containing N2, N atoms, 02, 0 atoms andH2 were observed in the vanadium, chromium, manganese and iron systems, but becauseof very low abundances, or difficulty in interpretation of extremely complex isotopicpatterns, could not be quantified. Further study of these and other adducts involvingsecondary ionisation or secondary resonance ejection techniques will enable a moredefinitive analysis of their chemistry.In the cobalt system, ion-molecule interactions involving small reactive cationsN2, C0, C02N2Ht C0H, and C02H with neutral CpCo(C0)2molecules werequantifiable. The overall result of these interactions amounts to abstraction of a hydrogenatom by the small cation from the Cp ligand of one neutral, followed by proton donation tothe central cobalt atom of another neutral, creating the extremely unreactive, 18-electronion, CpCo(C0)H. Similar hydrogen-metal stabilising linkages in some gas phasechromium and iron cation clusters have been proposed by Kan[35] to explain theanomalously large abundance of certain ions.Proportions of excited state cations are large (Table 7.5), for the smallerfragments generated by El in all five systems. Excited state cations reacted faster than theirnonexcited state counterparts in all cases. The excited molecular ions CpV(C0)4 andCpMn(C0)3+ were reactive, whereas after relaxation (by means of reaction or simplythrough collisional de-excitation), their nonexcited forms were not, presumably because ofstable, 17-electron configurations.242No addition reactions were apparent in the anion systems of any metalselected for this study. This may be solely a result of kinetic factors: i.e., low anionconcentrations characteristically produced by El, and low pressure regimes dictated in FTICR procedures. The only exception was seen in the chromium system, where Cr03 andCr04- both accepted an additional CO from neutral BzCr(C0)3 molecules. As well,because anions possess greater inherent electron saturation than do their cationcounterparts, they are less active kinetically.IV Further Research ProjectsMore detailed investigations into ion-molecule interactions of these transition metalcompounds should include a quantitive examination of interactions with specific adductsincluding a study of the kinetics of their formation, using a variety of small molecules suchas ammonia, water, oxygen and chlorine, including measurements of absolute reactivityrates. A combination of electron-, proton- and hydrogen atom- (= electron + proton)transfer kinetic studies may enable correlation of the three processes.Some of the new, fairly unreactive cluster cations found in the five metal systemsstudied here may be sufficiently stable for isolation in solution; examples are(CpV)2(C0)3; (CpMn)O) (BzCr)3CO;andBu2Fe3(C0).Other closely-related systems should be examined; for instance, complexes withunstable, or less stable arene ligands than are Cp and benzene, perhaps yielding newevidence of internal restructuring and ligand repositioning for enhancement of stability;complexes of scandium and titanium (‘electron-poor’ transition metals), and nickel andcopper (‘electron-rich’ transition metals) in the first transition series; homologouscomplexes of the second and third transition metal series (i.e., Nb, Mo, Ru, Rh); andfinally, homologous complexes of the present five metals containing NO, 02 and N2ligands rather than carbonyl ligands only.243Catalytic activity of the vanadium-cobalt series of transition metals has been asubject of enormous interest over many Ability to cleave C-Hand C-C bonds varies across the first transition row of transition metals: for example, bothV and Cr cleave C-C bonds in ethane to produce methane and MCH2+; whereas Fe,Q) and Ni preferentially cleave C-H in ethane to produce H2 and MC2H4,reflecting afundamental mechanistic difference in operation between early and late transition metals[3].Other reaction products have been demonstrated to vaiy with transition metal precursors ina similar way[9’1021].Greater insight into these and other differing pathways may becomeaccessible with laser excitation and isotopic labelling studies of the metal intermediates insuch systems.Utilising Marcus’ theory, electron transfer rates in solution can be predicted fromisotope charge exchange reaction rates[41’250].Parallel gas phase rates for the present fivesystems and similar ones could be determined by FT-ICR without the complication ofsolvent interference; and rate constants for electron transfer from any neutral molecule toion would hence be measurable both directly and indirectly. Some self-exchange kineticstudies on metallocene complexes have been performed earlier by Richardson andEyler[501.A comparison of large numbers of such data may enable collision efficiencystudies in the gas phase, as well as enlarging and extending scales of proton affmities andionisation potentials for organometallic molecules.A careful comparison of excited and ground state ion-molecule chemistry over veryshort time-scales would allow better discrimination between mechanisms of reactivity ofions in excited and ground energy states.Instrumentally, implementation of a larger magnetic field will permit easierdiscrimination between closely-spaced, heavier ion masses, such as mono- and di-hydrogenated adducts of multi-nuclear clusters, permitting characterisation of new ionproducts. Narrow-band ionisation energy (laser) sources will permit determination of bonddissociation parameters.244Thermostatted temperature regulation of the entire ion source assembly, within atemperature range compatible with the instrument, would enable experimentaldetermination of thermodynamic parameters (activation energies, entropies, etc.) of thevarious reactive pathways. A comparison of such values with those in solution would be oftheoretical, as well as of practical interest for synthetic and catalytic studies.Tandem methods, with appropriate computer programming instrumentationdesigned to identify and isolate specific secondary ions, followed by laser ionisation of thesecondary (or tertiary) ion beam and detection of subsequent products, will enable moreprecise determination of the fates and the stereochemistries of the larger cluster ionsproduced in these systems.Lastly, collisional relaxation techniques[53]employing dual-cell ion chambers, oruse of high pressure inert gases will lessen complications caused by the presence ofreacting ions in excited states.245V References(1) Allison, J. Prog. Inorg. Chem. 1986,34, 627.(2) Aradi, A. A.; Fehiner, T. P. Adv. Organomet. Chem. 1990,30, 189.(3) Armentrout, P. B.; Halle, L. F.; Beauchamp, J. L. J. Am. Chem. Soc. 1981,103, 6501.(4) Armentrout, P. B. in Gas Phase Inorganic Chemistry; Russell, D. H.; PlenumPress, New York, 1989; pp 1 - 42.(5) Aroney, M. J.; Cooper, M. K.; Pierens, R. K.; Pratten, S. J. J. Organomet.Chem. 1985,295, 333; Aroney, M. J.; Clarkson, R. M.; Klepetko, R. J.;Masters, A. F.; Pierens, R. K. J. Organomet. Chem. 1990, 393, 371.(6) Bartmess, J. E.; Mclver, R. T., Jr. in Gas Phase Ion Chemistry, vol. 2; Bowers,M. T.; Academic Press, New York, 1979; pp 87-121.(7) Bartmess, J. E.; Georgiadis, R. M. Vacuum 1983,33, 149.(8) Beran, J. A.; Kevan, L. J. Phys. Chem. 1973, 73, 3866.(9) Bjarnason, A. Organomet. 1991, 10, 1244.(10) Bjarnason, A. Anal. Chem. 1991, 61, 1889.(11) Bottomley, F.; Grein, F. Inorg. Chem. 1982,21, 4170.(12) Bottomley, F.; Sutin, L. Adv. Organomet. Chem. 1988, 28, 339.(13) Brodbelt-Lustig, J.; van Koppen, P.; Bowers, M.; Dearden, 3.; Beauchamp, J.Ann. Conf. ASMS All. Top. 1989, 37, 830.(14) Chen, S.-P.; Comisarow, M. B. Ann. Conf. ASMS All. Top. 1989, 37, 323.(15) Chen, S.-P. Ph. D. Dissertation 1992.(16) Coliman, J. P.; Hegedus, L. S.; Norton, 3. R.; Finke, R. G. Principles andApplications ofTransition Metal Chemistry; University Science Books: MillValley, California, 1987.(17) Connor, J. A. Top. Curr. Chem. 1977, 71, 71.246(18) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; John Wiley andSons: New York, 1980.(19) Cotton, F. A.; Walton, R. A. Struct. Bond. 1985, 62, 1.(20) Crabtree, R. H. Chem. Rev. 1985, 85, 245.(21) Elkind, J. L.; Armentrout, P. B. Inorg. Chem. 1986,25, 1078;Elkind, J. L.; Armentrout, P. B. J. Chem. Phys. 1987, 86, 1868.(22) Eller, K.; Schwarz, H. Chem. Rev. 1991, 91, 1121.(23) Eyler, 3. R.; Richardson, D. E. J. Am. Chem. Soc. 1985, 107, 6130.(24) Franklin, 3. L.; Dillard, 3. G.; Rosenstock, H. M.; Herron, J. T.; Draxi, K.; Field,F. H. Ionization Potentials, Appearance Potentials and Heats ofFormation ofGaseous Positive Ions; American Chemical Society, American Institute of Physics:Washington, D. C., 1969.(25) Fredeen, D. J. A.; Russell, D. H. J. Am. Chem. Soc. 1985, 107, 3762.(26) Freiser, B. S. in Bonding Energetics in Organometallic Compounds, Marks, T.;American Chemical Society, Washington, D. C., 1990; pp 55-69.(27) Frost, A. A.; Pearson, R. G. Kinetics and Mechanism; John Wiley and Sons,Inc.: New York, 1953.(28) Geusic, M. E.; Morse, M. D.; Smalley, R. E. J. Chem. Phys. 1985, 82, 590.(29) Halpern, 3. Inorg. Chim. Acta 1985, 100, 41.(30) Harrison, A. G. Chemical Ionization; Wiley - Interscience: New York, 1984.(31) Hoffman, R. Science 1981, 211, 995.(32) Jacobson, D. B.; Freiser, B. S. J. Am. Chem. Soc. 1985, 107, 5870.(33) Kaldor, A.; Cox, D. M.; Trevor, D. J.; Zakin, M. R. Metal Clusters; Trager, F.zu Putlitz, G.; Springer: Berlin, 1986.(34) Kan, Z.; Comisarow, M. Ann. Conf. ASMS All. Top. 1991, 39, 461.(35) Kan, Z. private communication 1992.(36) Lane, K. R.; Sallans, L.; Squires, R. R. Organometallics 1985, 4, 408.247(37) Lauher, J. W. J. Am. Chem. Soc. 1978, 100, 5305.(38) Lauher, J. W. J. Am. Chem. Soc. 1979, 101, 2604.(39) Levin, R. D.; Lias, S. 0. Ionization Potential and Appearance PotentialMeasurements; NSRDS-NBS; U. S. Department of Commerce: Washington,D. C., 1982.(40) Lukehart, C. M. Fundamental Transition Metal Organometallic Chemistry;Geoffroy, G. L.; Brooks/Cole Publishing Company: Monterey, California, 1985.(41) Marcus, R. A. J. Phys. Chem. 1963, 67, 853.(42) Marcus, R. A. Ann. Rev. Phys. Chem. 1966, 15, 155.(43) Mingos, D. M. P.; May, A. S. in Structural and Bonding Aspects ofMetal ClusterChemistry; Shriver, D. F.; Kaesz, H. D. Adams, R. D.; VCH Publishers, NewYork, 1990; pp 11 - 119.(44) Mingos, D. M. P.; Slee, T.; Zhenyang, L. Chem. Revs. 1990, 90, 383.(45) Owen, S. M.; Brooker, A. T. A Guide to Modern Inorganic Chemistry; JohnWiley and Sons: New York, 1991.(46) Pan, Y. H.; Ridge, D. P. J. Am. Chem. Soc. 1989, 111, 1150.(47) Pearson, R. G. Inorg. Chem. 1984,23, 4675.(48) Pruchnik, F. P. Organometallic Chemistry of the Transition Elements; Fackler Jr.,J. P.; Plenum Press: New York, 1990.(49) Reents, 3., W. D. ; Strobel, F.; Freas, R. B.; Wronka, J.; Ridge, D. P. J. Phys.Chem. 1985,89, 5666.(50) Richardson, D. E.; Christ, C. S.; Sharpe, P.; Eyler, J. R. J. Am. Chem. Soc.1987, 109, 3894; Richardson, D. E. J. Phys. Chem. 1986, 90, 3697.(51) Ridge, D. P.; Meckstroth, W. K. in Gas Phase Inorganic Chemistry; Russell, D.H.; Plenum Press, New York, 1989; pp 93-113.(52) Russell, D. H.; Fredeen, D. A.; Tecklenburg, R. E. in Gas Phase InorganicChemistry; Russell, D. H.; Plenum Press, New York, 1989; pp 115-135.248(53) Russell, D. H. Ann. Conf. ASMS All. Top. 1990,38, 1261.(54) Sallans, L.; Lane, K. R.; Squires, R. R.; Freiser, B. S. J. Am. Chem. Soc.1987, 107, 4379.(55) Schildcrout, S. J. Chem. Phys. 1969,51, 4055.(56) Schildcrout, S. M. J. Am. Chem. Soc. 1973, 95, 3864.(57) Schultz, R. H.; Elkind, J. L.; Armentrout, P. B. J. Am. Chem. Soc. 1988, 110,411.(58) Simoes, J. A. M.; Beauchamp, J. L. Chem. Revs. 1990, 90, 629.(59) Skinner, H. A.; Connor, J. A. Pure App!. Chem. 1985,57, 79.(60) Squires, R. R. J. Am. Chem. Soc. 1985, 107, 4385.(61) Squires, R. R.; Lane, K. R. in Gas Phase Inorganic Chemistry, Russell, D. H.;Plenum Press, New York, 1989; pp 43-91.(62) Sung, S.-S.; Hoffman, R. J. Am. Chem. Soc. 1985, 107, 578.(63) Teo, B. K.; Longoni, G.; Chung, F. R. K. Inorg. Chem. 1984, 23, 1257.(64) VanOrden, S. L.; Pope, S. M.; Buckner, S. W. Organometallics, 1991, 10,1089.(65) Wronka, J.; Ridge, D. P. J. Am. Chem. Soc. 1984, 106, 67.(66) Wronka, 3.; Forbes, R. A.; Laukien, F. H. mt. J. Mass Spectrom. Ion Proc.1988,83, 23.(67) Zakin, M. R.; Cox, D. M.; Whetten, R. L.; Trevor, D. I.; Kaldor, A. Chem.Phys.Lett. 1987,135, 223.(68) Ziegler, T.; Tschinke, V. in Periodic Trends in the Bond Energies ofTransitionMetal Complexes; Marks, T.; American Chemical Society, Washington, D. C.,1990; pp 279-292.249AppendicesI250Appendix IKinetic DevelopmentFor all five systems reaction rate constants were evaluated by assuming thatconcentrations of the parent neutral molecule, [M], were always much larger than that ofany reacting ion, [1+], generated either during the electron ionisation or by subsequent ion-molecule interactions. In any sequence of ion-molecule reactions involving ion 1+ andneutral molecule M;I + M => A + X (Rate constant kA)I + M => B + Y ( “ kB)1÷ + M => C+ + Z ( H k)where kA,B,C are second-order rate constants for the reactions, A+, B+, C are productions and X, Y, Z are uncharged products. Accordingly, the decay rate of I will be-d[Ii/dt = kA [I][M] + kB [I][M] + ke [I][M]= (kA + kB + k)[I-i-][M]= k [1+1 [M] where k = the overall second order rate constant fordecay of ion 1+.1. Evaluation of Pseudo-First Order Rate Constants (k’)If the concentration of neutral molecules, [M] >> E [Ij, the sum of all the ionfragments generated by electron ionisation, which is assumed to be valid in FT-ICR-MS;then [MJ will remain relatively constant with time.251Therefore letkA[M] = k’A; kB[M] = k’B; and kcjM] =where k’A, k’B, k’ axe pseudo-first order rate constants in the preceding equation, and let(k’A + k’B + k’) = k’where k’ is the total pseudo-first order rate constant for disappearance of [1+1.Then -d[P]/dt = (kA’ + kB’ + ks’) [Ifi = (k’) [IfiIntegrating, -d[I]Idt = (k’) [P] yields a pseudo-first order relationship,[If] = [I] e - k’twhere [I] is the initial concentration of ion [P]. A linear plot results when in [Ilj isplotted against time. Hence monitoring the disappearance of [Ij permits a graphicalevaluation of k’, the total first-order rate constant, from the slope.Estimated values of in k’ were used in the plots of electron deficiencyversus reaction rate constants (k’), in Figures 2.18, 3.11, 4.11, 5.10 and6.9.2. Evaluation of Second Order Rate Constants (k)Recall that for the production of ion A,1÷ + M => A + X (with rate constant kA)Then for ion product A+,d[Afl/dt = kA [Ifl[M] = k’A [1+] = k’A [1fl0 e - k’tIntegrating this equation for ion product A; and integrating parallel equations for ionproducts B and C+[Mj = [Aj0 + (k’A [I] / k’)(l - e - k’t)[Bk] = [Bj0 + (k’B [P]0 / k’)(l - e - k’t[C] = [C]0 + (k’s [P]0 / k’)(l - e - k’t)252If initial concentrations [AJ0 = [B]0 = [Cj0 = 0, a condition which occursdirectly after multiple resonance ejection of all ions except 1+; then these three equationssimplify to become[Ak] I [B9 / [C] = k’A / kB I k’Thus, an individual pseudo-first order rate constant (k’A, k’B, etc.) forthe appearance of a product ion (Ak, B, etc.) will be proportional to its relativeconcentration in a mixture of appearing products. The proportion of any ion product A,B+, etc. present in a product mixture at any time can be used to estimate its rate offormation from the decay rate of the reactant ion, P. Concentration values for each productwere measured at several times on at least three separate temporal plots, then averaged inorder to calculate final k’ values for each ion product.3. Evaluation of Neutral Reactant Gas Pressures, [MlSecond order rate constants kA, kB, etc., were calculated from k’A, k’B, etc., using[M] values calculated from experimental temperature and pressures using the followingprocedure. Since k’A = kA [M], then in order to calculate second order rate constants, therelationship between the molecular neutral concentration [M], which is directly proportionalto the true pressure P(true) and the nominal pressure read from the pressure gauge, isrequired. This is because each gaseous compound affects a pressure gauge differently.According to methods devised by Bartmess et. al., the true pressure, P(true), exerted by asample gas inside an ion chamber can be estimated from the molecular polarisabiity (cv) ofthe neutral sample gas present in the chamber using the following relationship:P(true) = P(gauge) I R where R = (0.36ct + 0.30)253Values of R for each organometallic reactant system were approximated by usingknown or estimated values for the molecular polarisibility and the calculated truepressure for the five complexes listed in Table A.1 on the following page. Because of thelarge molecular polarisability of CpV(CO)4, neutral pressures in the vanadium system areaffected most: nominal (gauge) pressure in the vanadium system must actually bediminished by a factor of 8.35. Polarisibility effects in the other four metal systemsapparently decrease with increasing atomic number of the metal.Since the molecular polarisibility c is a three-dimensional property rather than alinear one, the values given for true pressures in Table A. 1, as determined from nominalion gauge readings are approximate. Consequently, values of k are accurate to within 25-30% only.254Table A. 1Molecular Polarisabilities and PressuresCompound Molecular Gauge Pressure True Pressure bPolarisablity (a) a (torr) (torr)(A)3C p V(C 0)4 22.36 6.OxlO8 7.19x109BzCr(C0)3 21.25 11 7.55x109CpMn(C0)3 19.53 U 8.19x109BuFe(C0)3 18.3C 8.7 x1O9CpCo(C0)2 16.72 9.49x10-a Relative ion gauge sensitivities calculated by method of Bartmess(Bartmess, J. E.; Georgiadis, R. M. Vacuum 1983, 33, 149.)with Chen modification (Chen, S.-P., Ph. D. Dissertation; 1992.)b True pressures estimated from known literature values for a(Handbook of Chemistry and Physics, 72nd ed., CRC;Boca Raton, 199 1-1992, PP. 194-210.) and using extension of Aroney’sapproximation for a of ferrocene. (Aroney, M.; Le Fèvre, R. J. W.;Somasundaram, K. M. J. Chem. Soc. 1960, 1812.)C Data for butacliene iron tricarbonyl estimated by method of Aroney(Aroney, M. J.; Cooper, M. K.; Pierens, R. K.; Pratten, S. 3.;J. Organomet. Chem. 1985,295, 333.)255Approximate absolute second order rate constants (kA, kB, etc.) were calculatedusing P(true) values to obtain concentrations (molecules cm3)of the neutral molecule [M]for each system at experimental pressures.For each reacting ion, sets of relative values of product ions [A+j, [B+j, [C’j, etc.,were determined at several specific times. Setting k’A at some arbitrary value, say k’A =100, then k’B , k’, etc., were assigned values relative to k’A for each time period. Theserate constants were averaged for each product ion. Tables of calculated second orderrate constants (kA, kB, etc.) and relative rate constants ( lOOk’B / k’A ; 100k’ /k’A; etc.) are listed for all reactive cations as follows: Vanadium cations in Table 2.2- 5 inChapter 2; for Chromium cations, Table 3.2 in Chapter 3; for Manganese cations, Table4.2 in Chapter 4; for Iron cations, Table 5.2 in Chapter 5; and for Cobalt cations, Table 6.2in Chapter 6. As well, most of these data are summarised in Tables 7.2 - 4 in Chapter 7.256Appendix IIFigure A.1. Schematic Diagram of FT - ICR Reaction Cell*The cell is composed of six square metal plates. The two Vs are trapping platesto which is applied a direct current voltage, typically + 1 V for trapping positiveions and— 1 V for negative ions; N and S are receiver plates for detection of theion cyclotron motion; E and W are transmitter plates for if excitation for ionexcitation and ejection; F is a thermionic filament for electron ionisation; G is agrid for shielding the cell and contents from the strong ionisation voltage; C isan electron collector for attracting and monitoring the electron current; P is thepreamplifier for ion detection; A is a transmitter amplifier for the if field.; B isthe magnetic field applied across the cubic cell.* Adapted from Chen, S.-P.; Ph.D. Dissertation, 1992.FT- ICR Cubic Reaction Cell* for FT-ICR Studies:257Figure A.2. FT . ICR Mass Spectrometer Instrumentation*A sample contained in a sampling tube is introduced by meansof a roughing valve, then passes through a leak valve into the highvacuum chamber containing the cubic reaction cell. The entiresystem is evacuated by means of the diffusion and mechanicalpumps. Sample pressure is maintained at low, constant dynamicpressure by continuous ion pumping.* Adapted from Chen, S.-P.; Ph.D. Dissertation, 1992.CubicCellSchematic Diagram of the Vacuum Systemof an FT-ICR Mass Spectrometer*258

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