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Synthesis, characterization and reactivity of Group 6 alkoxo nitrosyl complexes Lundmark, Penelope J. 1993

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SYNTHESIS, CHARACTERIZATION AND REACTIVITY OFGROUP 6 ALKOXO NITROSYL COMPLEXESbyPENELOPE J. LUNDMARKB.Sc., University of Calgary, 1988A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIES(Department of Chemistry)We accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAAugust 1993© Penelope J. Lundmark, 1993In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library 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.(Signature)71",Department of  ti/hey' li Date Az le , 1993The University of British ColumbiaVancouver, CanadaDE-6 (2/88)iiAbstractThree new classes of alkoxo nitrosyl complexes of the type Cp*M(NO)(OR)X (Cp * =C5Me5 ; M = Mo, W; R = alkyl, aryl; X = CI, OR, alkyl), all of which have been fullycharacterized, are prepared by metathesis reactions. The molecular structures ofCp*W(NO)(OCMe3)2 and Cp *W(NO)(OCH2Ph)2 have been established by X-raycrystallographic analyses. While in general the above metathesis reactions are straightforward,two interesting bimetallic complexes, [Cp *W(N0)(CH2 SiMe3)][Cp*W(C1)(0)]-(11 2-il:T12-NC(H)SiMe3) and [Cp*W(N0)(CH2SiMe3)C1][Cp*W(C1)(i2-N{0){H)CH2SiMe3 )]-(1.t-N), areproduced in attempts to prepare alkoxo alkyl complexes using potassium salts. X-raycrystallographic analyses of both products are presented.The reaction chemistry of the three classes of alkoxo complexes, Cp*M(NO)(OR)X, with avariety of reagents such as oxygen, water, phosphines, carbon monoxide, dihydrogen, HCI,isonitriles and isocyanates has been investigated. In general, the 18-electron bis(alkoxo)complexes are chemically inert to most of these reagents; the only exceptions being the reactionsof Cp*M(NO)(OR)2 with H2 and HC1. The inertness of the bis(alkoxo) complexes is attributed todonation of electron density from filled p-type orbitals on the oxygen atoms into empty metalorbitals on the metal center. The reactivity studies of the chloro compounds are limited becauseof their extreme air- and moisture-sensitivity. In contrast, the alkoxo alkyl complexes decomposecleanly to isolable organometallic species when treated with 02 or H2O. In Lewis acid-base typereactions with PMe3, CNCMe3, PhNCO and p-tolylNCO, the Cp *M(N0)(R)(OR') species havesufficiently electron-deficient metal centers to form 1:1 adducts and/or insertion products. Thediamagnetic bimetallic complex, [Cp *Mo(N0)(CH2Ph)(11-0)]2 , is produced whenCp*Mo(NO)(CH2Ph)(OCMe3) is treated with H2 in THF.Earlier work into the reactions of dialkyl complexes, Cp'W(NO)R 2 (Cp' = r15-05H5, is-C5Me5), with carbon monoxide has been extended to permit some general conclusions regardingCO-insertion reactions in these systems. These studies show that the products obtained from thecarbonylation of various Cp'W(NO)R2 complexes are very dependent upon the nature of theancillary ligands. The nature of the cyclopentadienyl ligand determines the extent of thereactivity, with only the Cp complexes inserting a second equivalent of CO. The nature of thehydrocarbyl group influences the rate of the reaction such that the greater Lewis acidity of thediaryl complexes results in their forming monoacyl products faster than do the related dialkylcomplexes. However, only the monoacyl alkyl complexes possess a sufficiently weak M-Cbond to undergo a second insertion of CO to form bis(acyl) species, Cp'W(NO)(C{O}R)2 . Thenature of the hydrocarbyl ligand also plays an influential role in the case when R = CH2Ar in thatputative reductive elimination of ketone occurs from the undetectable monoacyl intermediatecomplexes.TABLE OF CONTENTSAbstract ^ iiTable of Contents ^ ivList of Tables List of Figures ^ xiList of Schemes xiiiList of Abbreviations ^ xivAcknowledgments xviiiCHAPTER 1: General Introduction ^  11.1 Background^  11.1.1 Bonding in Organometallic Complexes^  11.1.2 Bonding in Nitric Oxide^ 21.1.3 Bonding in Transition-Metal-Nitrosyl Complexes^ 31.1.4 Oxidation States and Valence-Electron Count 41.2 Nitrosyl Complexes^ 41.3 Alkoxo Complexes 51.3.1 Bonding in Transition-Metal-Alkoxo Complexes^ 51.3.2 Reactions of Alkoxo Complexes^ 61.3.2.1 Ligand-Based Reactivity of Alkoxo Complexes^ 61.3.2.2 Catalytic Reactivity of Alkoxo Complexes 71.4 Scope and Format of This Thesis^ 81.5 References and Notes^ 9CHAPTER 2: Synthesis, Characterization and Reactivity of Bis(Alkoxo) and AlkoxoChloro Complexes ^  132.1 Introduction  13iv2.2 Experimental Procedures^  152.2.1 Methods^  152.2.2 Reagents  162.2.3 Preparation of LiOCMe3^ 172.2.4 Preparation of NaOPh, NaOCH2Ph and NaOMe^ 172.2.5 Preparation of Bis(Alkoxo) Complexes, Cp *M(N0)(OR)2 (2.1 - 2.4)^ 172.2.6 Preparation of Alkoxo Chloro Complexes, Cp *M(N0)(0R)C1 (2.5 - 2.7)^ 182.2.7 Reactions of Cp*W(N0)(OCMe3 )2 and Cp*W(N0)(OCMe3 )C1 with HCI^ 192.2.8 Reactions of Cp *W(N0)(OCMe3)2 with H2O, 02 , PMe3 , Me2CHCN,PhCCH, acetone, CO, NHPh2 or S8^  192.2.9 Reaction of Cp *W(N0)(OCMe3)2 (2.2) with H2^ 202.2.10 Reactions of Cp *Mo(N0)(OCMe3 )2 and Cp *W(NO)(OCH2Ph)2 with H2^ 212.2.11 Reaction of Cp *Mo(N0)(0CMe3 )C1 (2.5) with H2O^ 202.2.12 Reaction of Cp *W(NO)(OCMe3)C1 (2.6) with H2O 212.2.13 Reaction of Cp *W(NO)(OCMe3)Cl (2.6) with PMe3^ 212.2.14 Synthesis of [Cp *W(N0)(OCMe3 )]2 (2.10)^ 212.3 Characterization Data^ 222.4 Results and Discussion 252.4.1 Synthesis and Characterization of Bis(alkoxo) Complexes, Cp *M(N0)(OR)2^ 252.4.2 Some Chemical Properties of Bis(Alkoxo) Complexes^ 272.4.3 X-ray Crystallographic Analyses of Complexes 2.2 and 2.4 292.4.4 Systems Related to the Bis(alkoxo) Complexes^ 322.4.5 Synthesis and Characteristic Properties of the Alkoxo Chloro Complexes^ 332.4.6 Some Chemical Properties of Cp *M(N0)(OR)Cl Complexes^ 352.4.7 Systems Related to the Alkoxo Chloro Species^ 362.4.8 A Related Reaction with KOCMe 3^ 362.5 Epilogue and Future Work^ 382.6 References and Notes 38viCHAPTER 3: Synthesis and Characterization of Alkoxo Alkyl Complexes^ 433.1 Introduction^ 433.2 Experimental Procedures^ 443.2.1 Methods^ 443.2.2 Reagents 443.2.3 Reaction of Cp *Mo(NO)(OCMe3)C1 and (PhCH2)2MgX(dioxane)^ 453.2.4 Reaction of Cp *Mo(NO)(OCMe3)2 and (PhCH2)2MgX(dioxane) 453.2.5 Preparation of Cp *M(NO)(CH2Ph)(OR) (3.1 - 3.3)^ 453.2.6 Preparation of Cp *W(NO)(CH2SiMe3)(OR) (3.4 - 3.7) 463.2.7 Preparation of[Cp*W(N0)(CH2SiMe3)][Cp *W(C1)(0)]-(1.12-x1 1 :11 2-NC {H} SiMe3)^ 473.2.8 Preparation of[Cp*W(N0)(CH2SiMe3)Cl][Cp *W(C1)(112-N{O} {H}CH2SiMe3 )]-(4-N)^ 473.2.9 Reaction of Cp *W(NO)(CH2SiMe3)(OCMe3) (3.4) with KOCMe3^ 483.2.10 Reaction of Cp*W(N0)(CH2SiMe3)C1 with KOCMe3 in the presence of PPh3^ 493.2.11 Preparation of Cp *W(NO)(CH2SiMe3)(Cl)(PMe3) (3.10)^ 493.2.12 Reaction of Cp *W(NO)(CH2SiMe3 )(Cl)(PMe3) (3.10) with KOCMe3^ 503.2.13 Reaction of Cp *W(NO)(CH2SiMe3)(C1)(PMe3) (3.10) with KOMe^ 503.2.14 Reaction of Cp *W(NO)(CH2SiMe3)C1 with KOCD 3^ 503.3 Characterization Data^ 513.4 Results and Discussion 543.4.1 Synthesis of Alkoxo Alkyl Complexes^ 553.4.2 Characterization of Alkoxo Alkyl Complexes 583.4.3 Related Systems^ 593.4.4 Unique Reactions 613.4.4.1 Synthesis of[Cp*W(N0)(CH2SiMe3)][Cp*W(C1)(0)]-(112 -r1 12 _ NC {II) SiMe3 )^ 623.4.4.2 Characterization of Complex 3.8^ 623.4.4.3 Synthesis of[Cp*W(N0)(CH2S iMe3)C1] [Cp *W(C1)(12 -N ( 0 ) {H}CH2SiMe3)]-(p.-N)^ 683.4.4.4 Characterization of Complex 3.9^ 693.4.5 Trapping Attempts with Phosphines 763.4.6 Deuterium-Labeling Experiments^ 793.4.7 Reactions Resulting in Nitrosyl-Ligand Transformations^ 813.4.8 Mechanistic Considerations^ 833.5 Epilogue and Future Work 883.6 References and Notes^ 88CHAPTER 4: Reactivity of Alkoxo Alkyl Complexes^ 934.1 Introduction^ 934.2 Experimental Procedures^ 954.2.1 Methods^ 954.2.2 Reagents 954.2.3 Reaction of Cp *Mo(N0)(CH2Ph)(OCMe3) (3.1) andCp*Mo(N0)(CH2Ph)(OPh) (3.2) with 02^ 954.2.4 Reactions of Cp *W(NO)(CH2Ph)(OCMe3) (3.3) andCp*W(NO)(CH2SiMe3 )(OPh) (3.5) with 02 and H2O ^ 964.2.5 Preparation of [CpMo(NO)(CH2Ph)]2-(.t-O) (4.1)^ 964.2.6 Preparation of [Cp *Mo(N0)(CH2CMe2Ph)]2-(2-0) (4.2) 964.2.7 Reactions of Cp *Mo(NO)(CH2Ph)(OCMe3) (3.1) andCp*W(NO)(CH2SiMe3)(OPh) (3.5) with HC1^ 974.2.8 Reaction of Cp*W(NO)(CH2SiMe3)(OMe) (3.6) with PhOH^ 974.2.9 Reaction of Cp *W(NO)(CH2 SiMe3 )(OPh) (3.5) with PMe3 984.2.10 Reaction of Cp *W(N0)(CH2 SiMe3)(OPh) (3.5) with CNCMe3^ 984.2.11 Hydrolysis of Cp *W(N0)(0Ph)(71 2-C{NCMe3 }CH2SiMe3) (4.3)to Cp *W(N0)(0Ph)(r12-C {NCMe3 }Me) (4.3') ^ 98viiviii4.2.12 Reaction of Cp *Mo(NO)(CH2Ph)(OCMe3) (3.1) with CO^ 994.2.13 Reaction of Cp *W(NO)(CH2SiMe3)(OPh) (3.5) with CO 994.2.14 Reactions of Cp*W(NO)(CH2SiMe3)(OPh) (3.5) with CO2 or CS2^ 994.2.15 Reaction of Cp *W(NO)(CH2SiMe3 )(OPh) (3.5) with RNCO^ 1004.2.16 Reaction of Cp *Mo(NO)(CH2Ph)(OCMe3) (3.1) with H2  1004.2.17 Magnetic Susceptibility Measurements of [Cp *Mo(N0)(CH2Ph)(p.-0)] 2 ^ 1014.3 Characterization Data^ 1024.4 Results and Discussion  1054.4.1 Reactions of Alkoxo Alkyl Complexes with Oxygen and Water^ 1054.4.1.1 Reactions of Tungsten Alkoxo Alkyl Complexes with Oxygen^ 1054.4.1.2 Reactions of Molybdenum Alkoxo Alkyl Complexes with Oxygen^ 1064.4.1.3 Reactions of Isolated Tungsten Alkoxo Alkyl Complexes with Water ^ 1074.4.1.4 Preparation of [Cp'Mo(NO)R]-(p.-O) Complexes^ 1084.4.2 Reactions of Alkoxo Alkyl Complexes with HC1^ 1094.4.3 Reaction of Cp*W(NO)(CH2SiMe3 )(OMe) with PhOH 1114.4.4 Reactions of Lewis Bases with Alkoxo Alkyl Complexes: AdductFormation or Insertion^  1134.4.4.1 Reaction of Cp*W(NO)(CH2SiMe3)(OPh) with PMe3^ 1134.4.4.2 Insertion Reaction of Cp *W(N0)(CH2SiMe3)(0Ph) and CNCMe3^ 1164.4.4.3 Reactions of Alkoxo Alkyl Complexes with CO^  1184.4.4.4 Reactions of the Heterocumulenes CO 2 , CS2 and RNCO[R = Ph, p-tolyl] with Cp *W(N0)(CH2SiMe3)(0Ph)^ 1214.4.5 Reactions of Alkoxo Alkyl Complexes with Dihydrogen  1254.5 Epilogue and Future Work^ 1344.6 References and Notes  136ixCHAPTER 5: Reactions of Cp'M(NO)R2 Complexes with Carbon Monoxide^ 1395.1 Introduction^  1395.2 Experimental Procedures^  1425.2.1 Methods^  1425.2.2 Reagents  1425.2.3 Reaction of CpW(NO)(p-tolyl) 2 with CO (1 atm)^  1435.2.4 General Synthetic Methodology for High-Pressure Reactions^ 1435.2.5 Reaction of Cp *W(N0)(r12-C{O)CH2CMe2Ph)(CH2CMe2Ph)with CO (30 atm)^ 1445.2.6 Treatment of CpW(N0)(7 -1 2-C{O}p-toly1)(p-toly1) (5.1) with CO (30 atm)^ 1445.2.7 Reactions of Cp'M(NO)(CH2Ph)2 with CO (30 atm)^ 1445.2.8 Reaction of Cp*Mo(N0)(CH2C6H4-4-Me)2 with CO (30 atm)^ 1455.2.9 Preparation of CpW(NO)(C {0 ) {PMe3 }CH2CMe2Ph)(CH2CMe2Ph) (5.4)^ 1465.3 Characterization Data^ 1465.4 Results and Discussion  1495.4.1 Step 1: Formation of the Monoacyl Complexes^  1505.4.1.1 Spectroscopic Properties of the Monoacyl Nitrosyl Complex^ 1515.4.1.2 X-ray Crystallographic Analysis ofCpW(N0)(C{O)CH2CMe2Ph)(CH2CMe2Ph) ^ 1525.4.1.3 The Unique Case of R = CH2Ar^ 1555.4.2 Step 2: Formation of the Bis(acyl) Complexes  1585.4.3 Reactivity Trends^  1625.4.4 Electrochemical Study of CpW(N0)(C {0)CH2CMe2Ph)2^  1625.4.5 Related Systems^ 1635.5 Epilogue and Future Work 1645.6 References and Notes^  165List of TablesTable 2.1.^Numbering Scheme, Color, Yield and Elemental Analysis Datafor Complexes 2.1 - 2.10^ 22Table 2.2.^Mass Spectral and Infrared Data for Complexes 2.1 - 2.10^ 23Table 2.3.^1H and 13 C{ 1H} NMR Data for Complexes 2.1 - 2.10 in C6D6^ 23Table 2.4.^Selected Bond Lengths and Bond Angles for Cp *W(NO)(OCMe 3)2 (2.2) ^ 30Table 2.5.^Selected Bond Lengths and Bond Angles for Cp *W(NO)(OCH2Ph)2 (2.4)^ 31Table 3.1.^Numbering Scheme, Color, Yield and Elemental Analysis Datafor Complexes 3.1 - 3.10^ 51Table 3.2.^Mass Spectral and Infrared Data for Complexes 3.1 - 3.10^ 52Table 3.3.^1H and 13 C ( 111) NMR Data for Complexes 3.1 - 3.10 in C6D6^ 53Table 3.4.^Selected Bond Lengths and Bond Angles for 3.8^ 66Table 3.5.^Selected Bond Lengths and Bond Angles for 3.9 73Table 3.6.^Bond Angle Comparisons between 3.9 and Cp *W(N0)(CH2SiMe3)C1 ^ 74Table 3.7. Product Ratios for the Reactions of Cp*W(NO)(CH 2SiMe3)C1 withKOCH3 and KOCD3^ 81Table 4.1.^Numbering Scheme, Color, Yield and Elemental Analysis Datafor Complexes 4.1 - 4.6^  102Table 4.2.^Mass Spectral and Infrared Data for Complexes 4.1 - 4.6 ^ 102Table 4.3.^1H and 13 C{ 1}1} NMR Data for Complexes 4.1 - 4.6 in C6D6^ 103Table 4.4.^Selected Bond Lengths and Bond Angles for [Cp *W(N0)(CH2Ph)(4-0)]2 ^ 128Table 5.1.^Numbering Scheme, Color, Yield and Elemental Analysis Datafor Complexes 5.1 - 5.4^  146Table 5.2.^Mass Spectral and Infrared Data for Complexes 5.1 - 5.4^ 147Table 5.3.^1H and 13 C{ 111} NMR Data for Complexes 5.1 - 5.4 in C6D6^ 147Table 5.4.^Selected Bond Lengths and Bond Angles forCpW(N0)(ri2-C {0 } CH2CMe2Ph)(CH2CMe2Ph) ^ 154List of FiguresxiFigure 1.1Figure 2.1Figure 2.2Figure 2.3Figure 3.1Figure 3.2Figure 3.3Figure 3.4Figure 3.5Figure 3.6Figure 3.7Figure 4.1Figure 4.2Figure 4.3The molecular-orbital diagram of nitric oxide^ 2Monitoring of the reaction between Cp *W(NO)C12 and 2 equivof LiOCMe3 in THE by IR spectroscopy^ 26ORTEP diagram of Cp *W(NO)(OCMe3)2 (2.2) 30ORTEP diagram of Cp *W(NO)(OCH2Ph)2 (2.4)^ 311H NMR spectrum of Cp *Mo(NO)(CH2Ph)(OCMe3) in C6D6^ 60Nujol mull infrared spectrum (1658 - 490 cm -1) of complex 3.8^ 631IINMR spectrum of[Cp *W(N0)(CH2SiMe3)][Cp *W(C1)(0)]-(12 :11 2-NC(H)SiMe3 ) in C6D6^ 65ORTEP diagram of[Cp*W(N0)(CH2SiMe3 )][Cp *W(C1)(0)]_(µ2 A-1 2-NC(H)SiMe3)^ 66Nujol mull infrared spectrum (1684 - 527 cm -1) of complex 3.9^ 70NIVIR spectrum of [Cp *W(N0)(CH2SiMe3)(C1)][Cp *W(C1)012-N{O} {H}CH2SiMe3)]4.-N) in C6D6^ 71ORTEP diagram of [Cp *W(N0)(CH2SilVle3)(C1)][Cp *W(C1)(i2-N{O} {H} CH2SiMe3)]4-N)^ 731H NMR spectrum of Cp *W(NO)(CH2SiMe3)(C1)(PMe3 ) in C6D6^ 781H NMR spectra in C6D6 of the reaction mixtures of(a) Cp *W(NO)(CH2SiMe3)(C1) and KOCD3(b) Cp*W(NO)(CH2SiMe3)(C1) and KOCH3^ 801H NMR spectrum of Cp *W(N0)(CH2SiMe3)(0Ph) (3.5)and PMe3 at 24 °C in CDC13^ 1141H NMR spectrum of Cp *W(N0)(CH2 SiMe3)(0Ph) (3.5)109and PMe3 at -60 °C in CDC1 3^  115Nujol mull infrared spectrum (1739 - 953 cm -1) ofCp*W(NO)(r1 2-C {NCMe 3 } CH2 S iMe3 )(0Ph) (4.3)^  117Figure 3.8Figure 3.9Figure 4.4Figure 4.5Figure 4.6Figure 4.7Figure 4.8Figure 4.9Figure 4.10Figure 4.11Figure 4.12Figure 5.1Figure 5.2Figure 5.3Figure 5.4Figure 5.5Figure 5.6Partial 1H NMR spectrum (8 3.1 - 0.1 ppm) ofCp*W(NO)(r12-C{NCMe3 }CH2 SiMe3)(OPh) (4.3) and its hydrolysisproduct Cp *W(N0)(11 2-C{NCMe3 }CH3 )(0Ph) (4.3')^ 1191H NMR spectrum of 4.4 in C6D6 ; an equilibrium mixture of 4.4,Cp*W(NO)(CH2SiMe3 )(OPh) (3.5) and PhNCO^ 1231H NMR spectrum of a C6D6 mixture of Cp *W(NO)(CH2SiMe3)(OPh)and excess p-toly1NCO (•)^ 124ORTEP diagram of [Cp *Mo(N0)(CH2Ph)(4-0)}2 (4.6).^ 126A stereoview of [Cp *Mo(N0)(CH2Ph)(1.1-0)12 (4.6).  1281H NMR spectrum of [Cp *Mo(N0)(CH2Ph)(4-0)}2 (4.6) in C6D6^ 129Partial 1H NMR spectrum (8 3.56 - 1.74 ppm) of[Cp*Mo(N0)(CH2Ph)(11,-0)}2 (4.6) in C6D6^ 130Partial 1H NMR spectrum (8 1.64 - 1.36 ppm) of[Cp*Mo(N0)(CH2Ph)(p,-0)} 2 (4.6) in C6D6^ 131Partial 1H NMR spectrum (8 0.6 to -1.9 ppm) of[Cp*Mo(N0)(CH2Ph)(p,-0)}2 (4.6) in C6D6^ 1321H NMR spectrum of CpW(N0)(i 2-C{0}-p-toly1)(p-toly1) in C 6D6^ 152The solid-state molecular structure ofCpW(N0)(11 2-C {0 } CH2CMe2Ph)(CH2CMe2Ph) ^ 153Partial IR spectrum (2195 - 1330 cm -1) of the mixture fromthe reaction between Cp *Mo(N0)(CH2C6H4-4-Me)2 and CO^ 157A partial view of the 11-INMR spectrum (C6D6) ofCpW(NO)(C {0) {PMe 3 }CH2Me2Ph)(CH2Me2Ph) (5.4)in the presence of excess PMe3 ^ 160ORTEP diagram of CpMo(N0)(I)(11 2-C {0) {PMe 3 }-p-toly1)^ 161Ambient temperature cyclic voltammogram ofCpW(N0)(C{O}CH2CMe2Ph)2 in THE (scan rate = 0.10 V/s)^ 163xiiList of SchemesScheme 3.1Scheme 3.2Scheme 3.3Scheme 3.4Scheme 4.1Scheme 4.2Scheme 5.1Routes for Preparing Alkoxo Alkyl Complexes^ 55Treatment of Cp *W(N0)(CH2SiMe3)(C1)(PMe3 ) with KOR^ 79Treatment of Cp *W(NO)(CH2SiMe3)C1 with Various Alkoxo Salts ^ 83Possible Mechanism for the Formation of Complex 3.8^ 86Selected Reactivity of Cp'W(NO)R2^ 94Proposed Mechanism for the Formation of [Cp *Mo(NO)(RA2-(1-0)^ 110Reactivity of Cp'W(NO)R2 complexes with CO^  149List of AbbreviationsThe following list of abbreviations, most of which are commonly used in the chemicalliterature, have been employed in this thesis.A^angstrom, 10-10 ma, b, c, a, A y unit cell dimensions (in X-ray Crystallography)anal.^analysisAPT^attached proton test (in NMR Spectroscopy)Ar^arylatm^atmosphere(s)benzyl^CH2Arbr^broad (spectral)Xg^magnetic susceptibility per gramXm^molar magnetic susceptibility°C^degree centigrade13c^carbon-13' 3COM^proton-decoupled carbon-13 (observe carbon while decoupling proton)Carom^aromatic carboncalcd^calculatedC6D6^benzene-d6CDC13^chloroform-d1c.g.s.^centimeters grams secondscm -1^wavenumbersCOSY^correlation spectroscopyCp^i5-05H5, perhydrocyclopentadienylCp*^ri5-05Me5, pentamethylcyclopentadienylCp'^both Cp and Cp *xivxvCV^cyclic voltammogramCy^cyclohexyl5^chemical shift in ppmd^doublet (in an NMR spectrum); or day(s)A^heat (in thermolysis), or differenceAG°^change in Gibbs free energy at standard conditionsdppe^1,2 bis(diphenylphosphino)ethanedppm^bis(diphenylphosphino)methaneEc"^formal reduction potentialEI^electron-impact (in mass spectrometry)emu^electromagnetic unitsEt^CH2CH3, ethylEt20^(CH3CH2)20, ether, diethyl ethereq^equationequiv^equivalentg^gram(s)GC^gas chromatographyGCMS^gas chromatograpic mass spectroscopyh^hour(s)1 H^protonHOMO^highest occupied molecular orbitalHz^Hertz (s-1 )I^intensity (in X-ray Crystallography)i-Pr^(CH3)2CH, isopropylIR^infraredJ^coupling constant (in NMR spectroscopy)n JAB^n-bond coupling constant between atoms A and BK^equilibrium constantxviLDA^LiN(i-Pr)2, lithium diisopropylamideLUMO^lowest unoccupied molecular orbitalm^multiplet (in NMR spectroscopy)M^Mo and W; or molarm/z^mass-to-charge ratio (in mass spectrometry)Me^CH3, methylmg^milligram(s)min^minute(s)mL^milliliter(s)mmol^millimole(s)MO^molecular orbitalmol^moleMS^mass spectrumMW^molecular weightv^stretching frequency (in IR spectroscopy)neopentyl^CH2CMe3neophyl^CH2CMe2PhNMR^nuclear magnetic resonanceORTEP^Oak Ridge Thermal Ellipsoid Plot31p^phosphorus-3 1[131^parent molecular ion (in mass spectrometry)Ph^C6H5, phenylpiC,^antilog of acid dissociation constant, -log[Ka]ppm^parts per million (in NMR spectroscopy)psig^pounds per square inch at gaugepz^C3H4N2, pyrazoleq^quartet (in an NMR spectrum)R, R'^alkyl and/or arylxviiR^residual index (in X-ray Crystallography)R),„^weighted residual index (in X-ray Crystallography)RT^room temperatures^singlet (in an NMR spectrum)SCE^standard calomel electrodeT^temperaturet^triplet (in an NMR spectrum)o-tolyl^C6H4-2-Me, ortho-tolylp-tolyl^C6H4-4-Me, para-tolylTHE^C4H80, tetrahydrofuranV^voltV/s^scan rateV^volume of the unit cell (in X-ray Crystallography)X^halideX^number of molecules of solvateZ^number of molecules in the unit cell (in X-ray Crystallography)xviiiAcknowledgmentsThere are many people I wish thank for seeing me through the last 5 years.First, I thank the Coffee Club. At 9:30 a.m. and 3:00 p.m., we faithfully gathered to talk, to laughand to share chemistry and our lives. Thank you Peter for your vision and supervision. Thankyou Willy for listening to me and telling me about the Simpsons every Friday morning. Neil, Ithank you for late night advice. Principally, my thanks go to JEV. Although you are not mySaviour, you have often been my Hero. You truly understood and provided practical help andwisdom in times of need. As opposite as we are, you have been a real friend to me.Thank you for roots and wings, Mom and Dad. You have never doubted my abilities.My friends, Roseanne, Sean, Letty, Sarah, Kirsten, Natalia, Liz and Deb; you have all held metogether emotionally and deeply enriched my life. For years you have loved me, listened to me,encouraged me, and prayed for me.My husband, Mr. Love, I thank you for sharing the work (Task number 2).Finally, my thanks go to God, in whom I have found my strength, my value and my hope..^sc),,LDICc\ 4 06M(a)— C(cr)1CHAPTER 1General Introduction1.1 Background^ 11.2 Nitrosyl Complexes 41.3 Alkoxo Complexes^ 51.4 Scope and Format of This Thesis^ 81.5 References and Notes^ 91.1 Background1.1.1 Bonding in Organometallic ComplexesOrganotransition-metal chemistry is concerned with compounds which have an organic group(ligand) attached to a transition metal through a direct M - C bond. Such compounds maycontain purely a-bonded ligands (alkyl, aryl, vinyl, alkynyl and acyl ligands) or ligands that canfunction as a-donors/ut-acceptors (carbene, Cp, arene, olefin, alkyne, allyl and carbonyl ligands).0\6°(DM 2 C -Metal-alkyl bond^M(a-)41— C(a)^M(a)w-- C(a)M(7r) --b" C(X ) M(70-1. C(7c*)Metal-carbene bond^Metal-olefin bond1.1.2 Bonding in Nitric OxideAn understanding of the principles involved in the bonding of free nitric oxide is essential tounderstanding the bonding of nitric oxide to transition metals. 1 Nitric oxide exists as aparamagnetic molecule which is thermodynamically unstable with respect to N2 and 02 . 2 Themolecular-orbital diagram of nitric oxide is shown in Figure 1.1.a2 *.,^•• •••I• I^ ItA%%•^2p + 4_ /--f:: ...."^...%• ' :4 11, ± -14- 2p,^...-" '0^',... Ilr ( --a20 ,, \^,^,I ,,■^,,,^,^, ,4 IV',1, , 7CI i\ ‘i,^i^I 1^I %a *1r^1•2s^ %> 45 2ss'sN atomic orbitals^0 atomic orbitalsFigure 1.1 The molecular-orbital diagram of nitric oxide.The odd electron of NO is based in a it molecular orbital. The bonding in nitric oxide may alsobe understood in terms of a valence-bond description of the major resonance structures of NO,i.e.,•• ••N -=- N 0 +0•• • • -•The NO molecule binds to electropositive transition metals through the nitrogen atom. This canbe rationalized by the second resonance form of NO in which the negative charge is localized on2•3the nitrogen atom. Using a molecular-orbital argument, it is also correct to say that the a2 orbital,which donates electron density to the metal, is predominantly N in character.1.1.3 Bonding in Transition-Metal-Nitrosyl ComplexesAlthough there are nine known modes of nitrosyl bonding to transition metals, 1,3 in this workonly linear, terminal nitrosyl ligands are observed. In valence-bond terms, the linear bondingmode of NO to a transition metal can be represented by several resonance forms, i.e.,-••ME-N=0:^M:ir-N=---0^0^M N— 0:••Molecular orbital theory describes the bonding of NO to a metal as a synergic interaction.Thus, the synergic bonding involved in a linear M-NO fragment is understood as (i) formaltransfer of one electron from NO to the metal (thereby forming an NO ligand), (ii) donation of2 electrons from a a-type orbital on NO to the metal, and (iii) backdonation of electron densityfrom the occupied metal d-orbitals to the n * antibonding orbitals of the NO ligand. The M-NOorbital overlaps commonly invoked to account for this synergic bonding are diagrammed below.cr-donation^M CC>1 0M(a)^N(a)it-backdonationM(thr)^NO(N*)Overall, a linear terminal nitrosyl ligand functions as a 3-electron donor to the central transitionmetal.41.1.4 Oxidation States and Valence-Electron CountIn organometallic chemistry the assignment of oxidation state is a formality and often bearslittle resemblance to the actual charge on the metal. 4 A more useful concept in describingorganometallic species is the number of electrons in the valence shell of the central metal. The18-electron rule arises from the observation that complexes in which the sum of the metal'svalence electrons and the electrons donated from the ligands equals 18 are generally stable. Inmolecular-orbital terms, the rule may be rationalized by means of the formation of 9 bondingmolecular orbitals from the interaction of metal atomic orbitals (i.e., s + 3p + 5d) and ligandorbitals, and the filling of these molecular orbitals by 18 electrons. The existence of a largeHOMO-LUMO energy gap also contributes to the stability of such complexes. 4The electron counting formalism used in this thesis considers all metals and ligands to beneutral, except where there is an overall charge on the complex. For example,CpW(NO)(r1 2-C{0}-p-toly1)(p-toly1) is an 18-electron complex: 5e -(Cp) + 6e-(W) + 3e-(NO) +3 e-(C { 0 }-p-toly1) + le -(p-toly1) = 18e - .1.2 Nitrosyl ComplexesAn extensive review of transition-metal organometallic nitrosyl chemistry appeared in theliterature in 1988. 5 This review describes in detail the preparation and reactivity of transition-metal nitrosyl complexes. Recently, Legzdins and Richter-Addo published a book which providesa more in-depth discussion of metal nitrosyls. 1 In this section, I will not reiterate the extensiveamount of knowledge covered in these two publications; however, there are a few basic conceptsregarding nitrosyl chemistry which should be noted:(a) Terminal nitrosyl ligands are strong it-acids.(b) They can adopt two bonding modes, linear or bent, though all of the complexes prepared inthis thesis contain linear, terminal nitrosyl ligands.(c) The infrared absorption of a nitrosyl ligand is one of the most distinctive physical properties of5nitrosyl complexes, and for this very reason, many of the reactions in this thesis are monitored byIR spectroscopy. The value of vNO reflects the degree of n-backbonding from filled transition-metal d orbitals to the n * acceptor orbitals on the linear nitrosyl ligand. Thus, complexes thathave increased electron density at the metal center exhibit lower vNO values than complexeswhich are relatively electron deficient.(d) In general, nitrosyl ligands are not involved directly in the chemistry of their complexes;however nitrosyl ligands greatly influence the electronic environment of the metal.1.3 Alkoxo Complexes1.3.1 Bonding in Transition-Metal-Alkoxo ComplexesThis thesis describes the preparation of organometallic alkoxo nitrosyl complexes. Alkoxoligands are considered to be hard 7c-donor ligands. They have a formal charge of -1. Oneimportant feature of alkoxo ligands is the presence of lone pairs on oxygen. Alkoxo ligands canprovide additional electron density through a It interaction between these p-type orbitals onoxygen and empty d-orbitals on the metal center. The following diagram depicts the two possiblebonding interactions of an alkoxo ligand with a transition-metal.a donation^MAO—RM(a) ..t— OR(a)it donation^MO— RM(dic) .4i— OR(n )6When only the first interaction occurs, the alkoxo ligand is bent and formally donates 1 electron tothe metal. When both bonding interactions occur, the alkoxo ligand is linear and functions as a3-electron donor. The angle M-O-R has been used to indicate the degree of multiple bondingbetween metals and alkoxo ligands. 6In late-transition-metal complexes, which tend to possess 18 valence electrons and have filledd orbitals, the lone pairs on oxygen weaken the M-0 bond by repelling the filled metal orbitals.?Therefore, in late-transition-metal complexes, the alkoxide ligand donates only one electron to themetal in a a interaction. There are very few examples of isolated late-transition-metal alkoxocomplexes because of the unfavorable interactions between hard alkoxo ligands and soft latetransition metals.Alkoxo coordination and organometallic complexes of the early transition metals are wellknown. 8 These species generally contain robust M-0 bonds as a result of a favorable donor-acceptor interaction between the filled oxygen p-type orbitals and empty metal d-type orbitals. Inthe case of early transition metal complexes, the metal is often d 0 and has less than 18 valenceelectrons. Empty do orbitals available on the metal can accept electron density from the oxygenlone pairs. Overall, the alkoxo ligands donate three electrons to early transition metals; one in thea interaction and two in the it interaction. In this way the M-0 bond is strengthened rather thanweakened as in the case of a late-transition-metal complex. Early metals are said to be oxophilicbecause of this strengthening effect.1.3.2 Reactions of Alkoxo Complexes1.3.2.1 Ligand-Based Reactivity of Alkoxo ComplexesSince alkoxo ligands are very strong 7t-donor ligands, the ligand-based reactivity of alkoxocomplexes is very limited. 9 Alkoxo ligands, considered to be pseudohalide ligands, can beinvolved in metathesis reactions since the driving force for reactions such as that shown in eq 1.1is the formation of strong Li-0 bonds. 107Ce(OAr)3 + LiR RCe(OAr)2 + LiOAr^(1.1)Alkoxo ligands are often introduced into metal systems to stabilize an electronically unsaturatedmetal center. Very bulky alkoxo ligands (e.g. t-butoxide or tri-t-butyl methoxide) are extremelyuseful since they also provide steric protection to a coordinatively unsaturated species.Complexes containing these sterically demanding alkoxo ligands are not prone to dimerizethrough alkoxo bridges in order to alleviate electron deficiency. Metal-alkoxo complexes whichhave 0-hydrogens on the alkoxo ligand have been used to prepare metal-hydride complexes,e.g., 11M-OCHRR'^M-H + RR'CO^ (1.2)Actinide alkoxo complexes have been used as models for the species which are responsible fortransporting actinide elements in ground waters, and volatile uranium alkoxo complexes havebeen prepared for use in the separation and enrichment of isotopes. 121.3.2.2 Catalytic Reactivity of Alkoxo ComplexesOne of the most important applications of organometallic complexes is in catalysis, andalkoxo complexes are involved in many of these catalytic processes. 13 Low-valent Group 6transition-metal alkoxo complexes have been shown to catalyze aldehyde/ketone reductions 14 andmethanol carbonylation. 15 The anionic complexes [M(C0) 5 (OR)) -, prepared by Darensbourg andcoworkers, have been extensively studied, and their systems catalyze the hydrogenation ofketones to alcohols. 16 Schrock's W(CCMe3)(OCMe3)3 will catalytically metathesizedialkylacetylenes (eq 1.3), whereas the carbon analogue, W(CCMe 3 )(CH2CMe3)3, reacts withacetylenes, but does not metathesize them in a catalytic fashion. 13W(CCMe3X0CMe3)32 R 1 0E--_CR2 s^ R 1 C-CR 1 + R2CEECR2 (1.3)8Although the 7r-donor ability of the alkoxide ligands does not seem to be important, 17 the bulkyalkoxide ligands on W(CCMe 3)(OCMe3)3 encourage acetylene dissociation thereby enhancingmethathesis activity.Late-transition-metal alkoxo complexes are believed to be key intermediates in various metal-catalyzed synthetic organic transformations. 18 These reactions include oxidation of alcohols, 19hydrogenation of ketones, 20 condensation of aldehydes, 21 decarbonylation of allylic esters andcarbonates,22 and carbonylation of alcohols. 23 The catalysts involved in these processes areusually Ni, Cu, Rh, Pt or Pd systems.1.4 Scope and Format of This ThesisThe metal-carbon bond has, by definition, been the focus of traditional organometallicchemistry. In our group, a significant amount of effort has been directed into determining arational, reproducible and general synthesis of organometallic complexes of the typeCp *M(NO)R2 (M = Mo, W; R = alkyl, aryl). 24 The synthesis of this large class of complexes hasallowed extensive studies of their reaction chemistry. Similarly, fundamental information on thepreparation of transition-metal alkoxo complexes is required before it is possible to investigatewhether these complexes, which contain strongly 7c-donating alkoxo ligands, exhibit reactivity thatis different from those observed for alkyl (a-donating) complexes.This thesis addresses the synthesis, characterization and reactivity of three new classes ofalkoxo nitrosyl complexes of the type Cp *M(NO)(OR)X, where X is either a chloride, alkoxo oralkyl ligand. These species have been prepared by metathesis reactions and fully characterized byelemental analysis, mass spectrometry, infrared spectrocopy, 1H and 13 C{ 1H} NMR spectroscopy(Chapters 2 and 3). Where appropriate, molecular structures of representative products havebeen confirmed by X-ray crystallographic analyses. This thesis also reports the preparation andcharacterization of two complex bimetallic compounds,[Cp *W(N0)(CH2SiMe3)][Cp*W(C1)(0)]-(p2 -11 1 :112-NC(H)SiMe3 ) and9[Cp*W(N0)(CH2 SiMe3)Cl][Cp*W(C1)(1 2-N{0){H}CH2SiMe3 )]-(g-N), which were producedin the attempts to prepare alkyl alkoxo complexes (Chapter 3).The subsequent reaction chemistry of representative examples of each class of alkoxocomplexes, Cp*M(NO)(OR)X, with a variety of reagents such as 0 2 , H2O, PMe3, CO, H2, HCI,CNMe3 and Me3 CNCO constitutes a large part of this work (Chapters 2 and 4). Alkoxo alkylspecies react with most of these reagents to form isolable organometallic complexes, whereas thebis(alkoxo) complexes are generally chemically inert towards these reagents. Since the alkoxochloro complexes were found to be extremely sensitive to air and moisture, their reactionchemistry has not been explored to any great extent.Chapter 5 discusses the reactions of dialkyl complexes, Cp'M(NO)(R) 2 , with carbonmonoxide. Although the preliminary research in this area was performed by Dr. Neil Dryden ofthese laboratories, this chapter presents the completed research along with the general conclusionsregarding CO-insertion reactions in these systems.This thesis is organized using standard legal outlining procedures. For any given chapter X,the major sections are X.1 Introduction, X.2 Experimental, X.3 Characterization Data, X.4Results and Discussion, and X.5 References and Notes. Subsections are numbered X.1.1, X.1.2,X.1.3, etc. Tables, Figures and Schemes for each chapter are numbered in a similar fashion.General methodologies and experimental procedures used throughout this thesis are located inSections 2.2.1 and 2.2.2.1.5 References and Notes(1) Legzdins, P.; Richter-Addo, G. B. Metal Nitrosyls; Oxford University Press: New York,NY, 1992.(2) Nitric oxide has a MI value of 90.2 kJ mo1 -1 . See reference 1, p 1.10(3) Legzdins, P.; Rettig, S. J.; Veltheer, J. E.; Batchelor R. J.; Einstein F. W. B.Organometallics, in press.(4) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications ofOrganotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987;Chapter 2.(5) Legzdins, P.; Richter-Addo, G. B. Chem. Rev. 1988, 88, 989.(6) Todd, J.; Johnson, J. C.; Caulton, K. G J. Am. Chem. Soc. 1992, 114, 2725.(7) Crabtree, R. H. The Organometallic Chemistry of the Tranisition Metals; John Wiley andSons: New York, NY, 1988; p 51.(8) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Metal Alkoxides; Academic Press: New York,NY, 1978.(9) See reference 4, p 693.(10) Heeres, H. J.; Meetsma, A.; Teuben, J. H. Organometallics 1989, 8, 2637.(11) (a) Chatt, J.; Shaw, B. L. J. Chem. Soc. 1962, 5075. (b) See reference 4, p 90.(12) Van der Sluys, W. G.; Sattelberger, A. P. Chem. Rev. 1990, 90, 1027 and referencestherein.(13) (a) Masters, C. Homogeneous Transition-Metal Catalysis; Chapman and Hall: New York,NY, 1981. (b) Wengrovius, J. H.; Sancho, J.; Schrock, R. R. J. Am. Chem. Soc. 1981,103, 3932.(14) (a) Gaus, P. L.; Kao, S. C.; Youngdahl, K.; Darensbourg, M. Y../. Am. Chem. Soc. 1985,107, 2428. (b) Tooley, P. A.; Ovalles, C.; Kao, S. C.; Darensbourg, D. J.; Darensbourg, M.Y. J. Am. Chem. Soc. 1986, 108, 193. (c) Marks, L.; Nagy-Magos, Z. J. Organomet.Chem. 1985, 285, 193.11(15) (a) Darensbourg, D. J.; Gray, R. L.; Ovalles, C.; Pala, M. J. MoL Catal. 1985, 29, 285. (b)Darensbourg, D. J.; Gray, R. L.; Ovalles, C. J. MoL Catal. 1987, 41, 329.(16) (a) Darensbourg, D. J.; Sanchez, K. M.; Reibenspies, J. H.; Rheingold, A. L. J. Am. Chem.Soc. 1989, 111, 7094. (b) Darensbourg, D. J.; Mueller, B. L.; Reibenspies, J. H.; Bischoff,C. J. Inorg. Chem. 1990, 29, 1789. (c) Darensbourg, D. J.; Mueller, B. L.; Bischoff, C. J.;Chojnacki, S. S.; Reibenspies, J. H. Inorg. Chem. 1991, 30, 2418.(17) Churchill, M. R.; Ziller, J. W.; Freudenberger, J. H.; Schrock, R. R. Organometallics 1984,3, 1554.(18) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163.(19) (a) Sasson, Y.; Blum, J. J. Org. Chem. 1975, 40, 1887 and references therein. (b) Tamaru,Y.; Yamada, Y.; Inoue, K.; Yamamoto, Y.; Yoshida, Z. J. Org. Chem. 1983, 48, 1286. (c)Ishii, Y.; Osakada, K.; Ikariya, T.; Saburi, M.; Yoshikawa, S. Tetrahedron Lett. 1983, 24,2677.(20) (a) Noyori, R.; Ohkuma, T.; Kitamura, M.; Takaya, H.; Sayo, N.; Kumobayashi, H.;Akutagawa, S. J. Am. Chem. Soc. 1987, 109, 5856. (b) Heil, B.; Marko, L.; Toros, S.Homogeneous Catalysis with Metal Phosphine Complexes; Pignolet, L. H., Ed.; Plenum:New York, NY, 1983; p 329 and references therein. (c) See reference 4, p 556.(21) (b) Horino, H.; Ito, T.; Yamamoto, A. Chem. Lett. 1978, 17. (b) Ito, T.; Horino, H.;Yamamoto, A. Bull. Chem. Soc. 1982, 55, 504.(22) (a) Tsuji, J.; Minami, I. Acc. Chem. Res. 1987, 20, 140. (b) Tsuji, J.; Yamada, T.; Minami,I.; Yuhara, M.; Nisar, M. J. Org. Chem. 1987, 52, 2988.(23) (a) Davies, S. G.; Organotransition Metal Chemistry: Applications to Organic Synthesis;Pergamon: Oxford, 1982; p 348. (b) Jolly, P. W. Comprehensive OrganometallicChemistry; Wilkinson, G. W.; Stone, F. G. A.; Abel, E. W., Eds.; Pergamon: Oxford, 1982;Vol. 8, p 348. (c) Alper, H.; Vasapollo, G.; Hartstock, F. W.; Mlekuz, M.; Smith, D. J. H.;12Morris, G. E. Organometallics 1987, 6, 2391. (d) Bryndza, H. E. Organometallics 1985,4, 1686.(24) Legzdins, P.; Veltheer, J. E. Acc. Chem. Res. 1993, 26, 41.13CHAPTER 2Synthesis, Characterization and Reactivity of Bis(Alkoxo) and Alkoxo ChloroComplexes'2.1 Introduction^  132.2 Experimental Procedures ^ 152.3 Characterization Data 222.4 Results and Discussion^  252.5 Epilogue and Future Work  382.6 References and Notes ^ 392.1 IntroductionPrevious work in these laboratories has established that the monomeric, 16-valence-electronCp'M(NO)R2 complexes [M = Mo, W; R = alkyl, aryl] have varied and interesting chemistries. 2A logical extension of this work is the investigation of related compounds containing metal-heteroatom linkages such as metal-alkoxides in place of the metal-alkyl or -aryl groups. Thesecomplexes should possess greater metal-ligand bond polarity than their dialkyl or diaryl congenersand thus should exhibit increased reactivity with polar substrates. Furthermore, they should beweaker Lewis acids at the metal centers than the Cp'M(NO)R 2 systems since the electronicrequirements of the metal centers may be satisfied to some extent by the existence of a degree ofM-0 multiple bonding.There are two primary methods for making transition-metal alkoxo complexes. 3 Theseinvolve the reaction of metal halide complexes with either an alkali-metal alkoxide salt,414M-X + M'OR --,. M-OR + M'X^(2.1)M' = Li, Na, K.or with an alcohol in the presence of a base. 5M-X + HOR base, B______÷^M-OR + BH+X-^(2.2)Some other less-common routes to the desired complexes which have been described in theliterature are as follows:1) Bimolecular elimination of 11 2 , e.g.,6+HOR(Me3CC5H4)3Ce^--* (Me3CC5H4)4Ce2(p.-OR)^(2.3)2) Insertion of a ketone into a metal-hydride bond, e.g., 7Re3 (0-i-Pr)5(H)(p-O-i-Pr)3 + Me2C=O^_______,^Re3(0-i-Pr)6(A-0-i-Pr)3^(2.4)3) Alcohol exchange, e.g.,8Cp*Ir(PPh3)(H)(OR) + HOR'^_______,^Cp*Ir(PPh3)(H)(OR') + HOR^(2.5)4) Oxidative addition of an alcohol, e.g., 9Pt(PCy3)2 + PhOH^Pt(PCY3)2(1 )(0Ph)^(2.6)In our group, previous workers attempted to prepare alkoxo nitrosyl complexes of the typeCp'M(NO)(OR)2 by treatment of Cp *M(NO)I2 with alcohols (cf. equation 2.2). In the case ofmethanol, a insoluble tan solid, formulated as [Cp *M(N0)(0Me)I]2, was isolated. 10 Otheralcohols did not result in any isolable organometallic species. The preparation of alkoxocomplexes via the halide metathesis reaction of the diiodide complexes, Cp 1M(NO)I2 , with15KOCMe3 was also attempted (cf. equation 2.1). Unfortunately, this operation resulted in only thedecomposition of the starting materials. Thus, the desired bis(alkoxo) complexes were notobtained by either of these routes.This chapter summarizes the successful synthesis, characterization, and some characteristicchemistry of representative alkoxo chloro and bis(alkoxo) complexes having the compositionsCp*M(NO)(OR)C1 and Cp*M(NO)(OR)2 (M = Mo, W; R = alkyl, aryl).2.2 Experimental Procedures2.2.1 MethodsThe synthetic methodologies employed throughout this thesis are described in detail in thissection. All reactions and subsequent manipulations involving organometallic reagents wereperformed under anhydrous conditions in an atmosphere of purified dinitrogen. Purification of N2was achieved by passing it through a double-walled glass column (10 x 60 cm) containing MnOand activated 4A molecular sieves. Conventional glovebox and greaseless vacuum line Schlenktechniques were utilized throughout. 11 The specific gloveboxes used in this work were VacuumAtmospheres 1-1E-553-2 and BE-43-2 models. All IR samples were either as THF, Et20,hexanes, pentane or CH2C12 solutions in NaC1 cells or as Nujol mulls sandwiched between NaC1or CsI plates. IR spectra were recorded on a Nicolet 5DX FT-IR instrument, internally calibratedwith a He/Ne laser. All NMR spectra were obtained on a Varian Associates XL-300 or a BrukerAC-200 spectrometer and are reported in parts per million. 1H NMR spectra are referenced tothe residual proton signal of C 6D6 (5 7.15) or CDC13 (5 7.24). 31P{ 11-1} NMR spectra (121.42MHz) are referenced to external P(OMe) 3 set at 5 141.00 ppm relative to 85% H3PO4. 13C{1H)NMR spectra (75.43 MHz) are referenced to the natural abundance carbon signals of the solventemployed: C6D6 (5 128.00). Mrs. M. T. Austria, Ms. L. K. Darge, and Dr. S. 0. Chan assisted inobtaining the NMR data. Mass spectra were recorded by Dr. G. K. Eigendorf and the staff of themass spectrometry laboratory. Low-resolution mass spectra (EI, 70 eV) were recorded on a16Kratos MS50 spectrometer using the direct-insertion method. All elemental analyses wereperformed by Mr. P. Borda of this Department.2.2.2 ReagentsThe organometallic reagents, Cp'M(NO)Cl 2 (M = Mo, W), were prepared by establishedprocedures. 12 Cp'Mo(NO)C12 complexes were further purified by Soxhlet extraction withCH2C12 , and the Cp'W(NO)C1 2 complexes were stored at -30 °C.PMe3 was prepared from P(OMe)3 and MeMgI and was dried over, and transferred from,sodium/benzophenone. 13 Me3 COH (Aldrich) was freshly distilled from CaH2. PhCH 2OH(Matheson) and Me0H (Fisher) were dried over activated 4A molecular sieves (Fisher). PhOH(Mallinckrodt), S 8 (Fisher), NHPh2 (Fisher), acetone (reagent grade, Fisher), CO (Matheson) and02 (Medigas, 99.5 %) were used without any further purification. All other reagents werepurchased from Aldrich Chemical Co. and used as received, unless otherwise specified.Solvents were freshly distilled from appropriate drying agents under a dinitrogen atmosphereand were either purged for 10 min with argon prior to use or were directly vacuum transferredfrom the appropriate drying agent. Dioxane, tetrahydrofuran and diethyl ether were distilled fromsodium/benzophenone; hexanes, benzene and pentane were distilled fromsodium/benzophenone/tetraglyme; dichloromethane was doubly distilled from P205 . 14 C6D6 wasdried over activated 4A molecular sieves and degassed using 3 freeze-pump-thaw cycles. Otherdeuterated solvents were used as received. Filtrations were performed through either Celite 545diatomaceous earth (Fisher), silica gel 60 (230 - 400 mesh, BDH) or Florisil (60 - 100 mesh,Fisher) that had been oven-dried and cooled in vacuo.172.2.3 Preparation of LiOCMe315A fine white precipitate formed as an Et20 solution (20 mL) of n-BuLi (66 mL, 1.6 M inhexanes) was slowly added via an addition funnel to an excess of Me 3 COH (10 mL) in Et20(20 mL). After the addition was complete, the resulting mixture was stirred for 0.5 h and thentaken to dryness in vacuo. The white solid remaining was washed with pentane (2 x 25 mL) andthen redissolved in Et20 (120 mL). The Et20 extracts were filter cannulated into anotherSchlenk tube, and the filtrate was concentrated and cooled to induce the crystallization of[LiOCMe3 ], as large white blocks. 162.2.4 Preparation of NaOPh, NaOCH 2Ph and NaOMeAll the NaOR [R = Ph, CH2Ph, Me] reagents were prepared in a similar fashion. Na metalwas cut into small flakes in a glovebox and then transferred into a three-necked flask. THF(20 mL) was added to the flask via syringe. A THE (10 mL) solution of alcohol (excess) wascannulated into the flask containing the Na. This mixture was stirred for 0.5 h and then taken todryness in vacuo. The remaining white solid was washed with pentane, dried in vacuo, and usedwithout further purification. 162.2.5 Preparation of Bis(Alkoxo) Complexes, Cp *M(NO)(OR)2 [M = Mo, R = CMe3 (2.1);M = W, R = CMe3 (2.2), Ph (2.3), CH2Ph (2.4)]All these complexes were synthesized in a similar manner. The preparation ofCp*W(NO)(OCMe3 )2 (2.2) is described as a representative example.A THF solution (20 mL) of LiOCMe3 (0.58 g, 7.2 mmol) was added slowly via an additionfunnel to a stirred THF solution (20 mL) of Cp *W(NO)C12 (1.5 g, 3.6 mmol). The progress ofthe reaction was monitored by LR spectroscopy. The reaction proceeded in a straightforwardmanner with the initial diminution of the starting nitrosyl absorption band at 1630 cm -1 occurringconcomitantly with the appearance and growth of a new band at 1593 cm -1 . As the addition of18LiOCMe3 continued, a second nitrosyl absorption band at 1557 cm -1 appeared at the expense ofthe band at 1593 cm -1 . During this time the color of the reaction mixture changed from green topurple to deep orange-red. The solvent was removed from the final reaction mixture in vacuo,and the residue was extracted with hexanes (2 x 50 mL). The combined extracts were filteredthrough Celite (3 x 6 cm) supported on a sintered glass frit. The filtrate was concentrated invacuo until incipient crystallization, and the mixture was then cooled at -30 °C overnight. Theorange crystals of Cp*W(NO)(OCMe3 )2 (0.57 g, 32% yield) thus formed were isolated byremoval of the supernatant solution by cannulation and drying of the crystals in vacuo.The numbering scheme, color, yield, and elemental analysis data for complexes 2.1 - 2.4 arecollected in Table 2.1. The mass spectral and IR data for these compounds are compiled in Table2.2, and their 1H and 13 C( 1H) NMR data are presented in Table 2.3.2.2.6 Preparation of Alkoxo Chloro Complexes, Cp *M(N0)(0R)C1 [M = Mo, R =CMe3 (2.5); M = W, R = CMe3 (2.6), Ph (2.7)]Since the synthetic approach to each of these complexes is similar, their syntheses aredescribed in the next paragraph in a generalized manner.In a glovebox, Cp *M(NO)Cl2 (1.00 mmol) and the appropriate alkoxide salt (1.00 mmol)were intimately mixed in a Schlenk tube. The tube was removed from the box, and THE (25 mL)was vacuum transferred onto the solids at -196 °C. The stirred reaction mixture was then allowedto warm slowly to 0 °C, whereupon the color changed from red (M = Mo) or green (M = W) topurple and vNo diminished by approximately 35 cm-1 in the IR spectrum of the mixture. Thesolvent was removed in vacuo, the purple residues were extracted with pentane (2 x 20 mL), andthe extracts were filtered through Celite (2 x 5 cm) supported on a sintered glass frit. The filtratewas concentrated in vacuo until the first signs of crystallization were evident. Additionalcrystallization occurred upon storing these concentrated solutions at -30 °C overnight. Finally,the desired alkoxo chloro complexes were isolated by removal of the supernatant solution bycannulation and drying of the remaining black to purple needle-like crystals in vacuo.19The numbering scheme, color, yield, and elemental analysis data for complexes 2.5 - 2.7 arecollected in Table 2.1. The mass spectral and IR data for these compounds are compiled inTable 2.2, and their 1H and 13 C{ 1H) NMR data are presented in Table 2.3.2.2.7 Reactions of Cp *W(NO)(OCMe3)2 (2.2) and Cp *W(NO)(OCMe3)Cl (2.6) with HClComplexes 2.2 (0.05 mmol) and 2.6 (0.05 mmol) were treated in Et20 (20 mL) with 1 equivof HCI (1.4 M solution in Et20). Work up of the final reaction mixtures involved removing thesolvent in vacuo, extracting the residues with pentane or CH2C12 , and cooling the combinedextracts at -30 °C to obtain crystalline precipitates (80 - 90% yields) of the product complexes.Comparisons with authentic spectral data confirmed that the organometallic products of thesereactions were Cp*W(NO)(OCMe3)Cl (2.6) and Cp*W(NO)C12 , 12 respectively.2.2.8 Reactions of Cp *W(NO)(OCMe3)2 (2.2) with H2O, 02, PMe3 , Me2CHCN, PhCCH,acetone, CO, NHPh 2 or S8The experimental conditions for these experiments are presented here for completeness. Inall cases, no reaction occurred as indicated by IR spectroscopy. In many cases, the reactants wereisolated from the reaction mixture and were characterized by IR, MS, and 1H NMRspectroscopies. The scale of these reactions was 0.50 mmol in the organometallic reagent.Cp*W(NO)(OCMe3)2 was reacted with excess H 2O in THE and with 02 (1 atm) in Et20.Hexanes solutions of complex 2.2 were reacted at ambient temperatures with an excess of PMe3,Me2CHCN, PhCCH, or acetone. CO (600 psig) was reacted with 2.2 overnight in C6H6 .Reactions of 2.2 with NHPh2 and S8 were performed in Et 20 and toluene, respectively, atelevated temperatures.202.2.9 Reaction of Cp *W(NO)(OCMe3)2 (2.2) with H2A THE solution (20 mL) of Cp *W(N0)(0CMe3)2 (0.30 g, 0.61 mmol) was placed in aFischer and Porter pressure vessel, and the vessel was pressurized with H2 (80 prig). After beingstirred overnight, the reaction solution was taken to dryness under reduced pressure. Theremaining orange residue was washed with hexanes (20 mL). The solid was then dissolved in aminimal amount of C6H6 , and an equal volume of hexanes was added. This solution was cooledto -30 °C for 1 week to induce the crystallization of orange crystals.Partial characterization data for the orange crystals: Anal. Found: C, 36.03; H, 4.51; N,1.90. IR (Nujol mull): vNO 1541cm -1 . 1H NMR (C6D6): 5 2.22 (s, 15H, C 5(CH3)5),2.20 (s, 2H), 2.07 (s, 15H, C5(CH3)5), 1.98 (s, 1H), 1.87 (s, 2H). 13 C{ 111} NMR(C6D6): 5 119.9 (C5 (CH3 )5), 119.6 (C5(CH3 )5), 10.9 (C5 (CI13 )5), 10.8 (C5(CH3)5), 10.2, 9.7,9.5. Low-resolution mass spectrum (probe temperature 100 °C): m/z 718. 172.2.10 Reactions of Cp *Mo(NO)(OCMe3)2 (2.1) and Cp *W(N0)(OCH2Ph)2 (2.3) with H2These reactions were performed in a manner similar to that described in the preceedingsection. Solution IR spectra of the resulting reaction mixtures showed only bands due to theorganometallic reactants.2.2.11 Reaction of Cp *Mo(N0)(0CMe3)C1 (2.5) with H2OComplex 2.5 (0.33 g, 1.0 mmol) in Et20 (20 mL) was treated with an excess of deaeratedH2O (50 AL). The stirred reaction mixture turned red-black immediately and was stirred for afurther 2.5 h at room temperature. After this time, the reaction mixture was taken to dryness invacuo, and the residue was redissolved in Et 20 (20 mL). The black Et20 solution was filteredthrough Celite (2 x 5 cm) supported on a medium-porosity frit. Concentration of this filtrate andcooling at -30 °C afforded black crystals (0.11 g, 35% yield) formulated as[Cp*Mo(NO)(OH)(Cl)]2 (2.8).212.2.12 Reaction of Cp *W(N0)(0CMe3)C1 (2.6) with H2OA stirred Et20 solution (15 mL) of complex 2.6 (0.23 g, 0.50 mmol) was treated with anexcess of deaerated H2O (50 !IL). The reaction mixture turned brown immediately. The brownmixture was taken to dryness in vacuo, and Et20 (20 mL) was added to the brown residues. Themixture was filtered through Celite (2 x 5 cm). The filtrate was concentrated under reducedpressure to incipient crystallization and was cooled to -30 °C overnight to obtain brown crystals(0.070 g, 35% yield) of a solid formulated as [Cp *W(NO)(OH)(Cl)]2 (2.9).2.2.13 Reaction of Cp *W(N0)(0CMe3)C1 (2.6) with PMe3A Schlenk tube containing a pentane solution (5 mL) of complex 2.6 (0.23 g, 0.50 mmol)was cooled to -196 °C until its contents had solidified. Excess PMe3 was then vacuumtransferred into the tube. The reaction mixture was allowed to warm to -30 °C over 0.5 h asyellow precipitate formed. At -30 °C, the reaction mixture was taken to dryness in vacuo. Theremaining solid remained yellow at low temperatures, but turned brown and decomposed uponwarming to room temperature.2.2.14 Synthesis of [Cp *W(NO)(OCMe3)]2 (2.10)In a glovebox, Cp*W(NO)C12 (1.00 g, 2.38 mmol) was placed in the bottom of a Fischer andPorter pressure vessel. A vial containing KOCMe3 (0.54 g, 4.8 mmol) was also placed in thevessel. The vessel was removed from the glovebox, and THF (30 mL) was carefully syringed intothe vessel without allowing the KOCMe 3 in the vial to mix with the THF solution ofCp *W(NO)C12. The vessel was charged with H2 (40 psig). The vessel was then shaken to allowthe KOCMe3 to enter into the reaction mixture. The reaction mixture turned from green to red in5 min. After stirring the reaction mixture for a further 30 min, it was taken to dryness in vacuo.The remaining residue was extracted with hexanes (2 x 10 mL), and the extracts were filteredthrough Celite (3 x 5 cm) supported on a sintered glass fit. The amber-red filtrate was22concentrated to 10 mL and chromatographed on Florisil (2 x 5 cm). The column was eluted firstwith hexanes to develop a yellow band which was discarded. A second red-purple band was theneluted with Et20. Concentration and cooling of the Et 20 fraction afforded purple crystals(0.25 g, 25% yield) of complex 2.10.2.3 Characterization DataTable 2.1. Numbering Scheme, Color, Yield and Elemental Analysis Data for Complexes2.1 - 2.10complex compdno.color(yield, %)anal. found (calcd)C H NCp*Mo(NO)(OCMe3 )2 2.1 orange (67) 53.31 (53.07) 8.17 (8.16) 3.35 (3.44)Cp*W(NO)(OCMe3 )2 2.2 orange (32) 43.59 (43.65) 6.66 (6.72) 2.84 (2.83)Cp*W(NO)(OPh)2 2.3 red (20) 49.23 (49.36) 4.80 (4.71) 2.50 (2.62)Cp*W(NO)(OCH2Ph)2 2.4 red (22) 51.06 (51.17) 5.24 (5.19) 2.45 (2.49)Cp*Mo(NO)(OCMe3)C1 2.5 purple (25) 45.09 (45.48) 6.45 (6.54) 3.78 (3.78)Cp*W(NO)(OCMe3)Cl 2.6 purple-black (37) 36.81 (36.74) 5.40 (5.29) 3.00 (3.06)Cp*W(NO)(OPh)Cl 2.7 red black (44) 40.21 (40.23) 4.40 (4.22) 2.70 (2.93)[Cp*Mo(NO)(OH)(Cl)] 2 2.8 black (35) 38.57 (38.30) 5.13 (5.14) 4.50 (4.47)[Cps W(N0)(OH)(0)1 2 2.9 brown (35) 29.72 (29.91) 4.20 (4.02) 3.30 (3.49)[Cp* W(NO)(OCMe3)]2 2.10 purple (25) 39.63 (39.83) 5.71(5.73) 3.50 (3.32)23Table 2.2. Mass Spectral and Infrared Data for Complexes 2.1 - 2.10compdno.MS, m/za tempi', °C ER, cm-1VNO (THF) vNo (Nujol)2.1 409 [P+] 80 1589 16012.2 495 [Pi ]439 [P+- CMe3]80 1557 15502.3 535 [P+]505 [P+- NO]100 1593 15662.4 563 [P+]533 [P+- NO]457 [P+- OCH2Ph]80 1556 15572.5 371 [P+] 100 1622 16132.6 457 [P+] 100 1593 15782.7 477 [P+]447 [P+- NO]80 1595 15892.8 608 [P+- H2O] 80 C 1613 br d2.9 768 [Pt- CI] 120 c 1588 br e2.10 844 [Pt] 80 1555 1543 bra in/z values are for the highest intensity peak of the calculated isotopic cluster,b Probe temperatures.C Not recorded.d VoH = 3642, 3631e V0H = 3641, 3626i.e. 98Mo and 184W.Table 2.3. ill and 13C(111) NMR Data for Complexes 2.1 - 2.10 in C6D6compdno.ill NMR (5, ppm) ugly} NMR (5, ppm)2.1 1.73 (s, 15H, C5 (CH3)5 ) 116.3 (C5 (CH3 )5)1.40 (s, 18H, OC(CH3)3) 81.3 (OC(CH3)3)33.5 (OC(CH3)3)10.0 (C5 (CH3 )5)2.2 1.80 (s, 15H, C5 (CH3)5) 114.6 (C5(CH3)5)1.40 (s, 18H, OC(CH3)3) 81.3 (OC(CH3)3)33.4 (OC(CH3)3)10.0 (C5(CH3)5)242.3 7.30 - 6.85 (m, 10H, 006H5)1.60 (s, 15H, C5(CH3)5)a2.4 7.60 - 7.00 (m, 10H, OCH2C6H5) 142.7, 129.1, 128.6, 127.55.95 (s, 4H, OCH2C6H5) (OCH2C6H5)1.60 (s, 15H, C5 (CH3)5) 114.7 (C5 (CH3)5)84.2 (OCH2C6H5 )9.4 (C5 (CH3)5)2.5 1.67 (s, 15H, C5 (CH3)5) 118.4 (C5 (CH3)5 )1.47 (s, 9H, OC(CH3 )3 ) 32.8 (0C(CH3)3 )b10.1 (C5 (CH3)5)2.6 1.71 (s, 15H, C5 (CH3 )5 ) 116.0 (C5 (CH3 )5 )1.42 (s, 9H, OC(CH3)3) 86.0 (OC(CH3)3)32.7 (0C(CH3 )3 )9.9 (C5 (CH3)5 )2.7 7.22 - 6.85 (m, 5H, 006H5) 129.6, 123.7, 122.5, 118.9 (006H5)1.65 (s, 15H, C5 (CH3 )5) 116.7 (C5 (CH3)5)9.7 (C5 (CH3)5)2.8 1.75 (s, 15H, C5 (CH3 )5) 119.0 (C5 (CH3)5)1.63 (s, 1H, OH) 10.2 (C5 (CH3)5)2.9 1.94 (s, 15H, C5(CH3)5) a1.75 (s, 15H, C5 (CH3)5)1.44 (s, 2H, OH)2.10 2.04 (s, 15H, C 5(CH3) 5) a2.00 (s, 15H, C 5 (CH3)5)1.44 (s, 9H, OC(CH3)3 )1.26 (s, 9H, OC(CH3)3)a Not recorded.b A resonance attributable to OC(CH3)3 was not observed.THFRTRO OR+ 2 M'CI^(2.7)+ 2 M'OR252.4 Results and Discussion2.4.1 Synthesis and Characterization of Bis(alkoxo) Complexes, Cp *M(NO)(OR)2Bis(alkoxo) nitrosyl complexes of the type Cp *M(NO)(OR)2 [R = alkyl, aryl] are preparableby treating Cp *M(NO)C12 with 2 equiv of alkoxide salts such as LiOCMe 3 or NaOR [It = Ph,CH2Ph], i.e.The four Cp *M(NO)(OR)2 complexes synthesized during this work (2.1 - 2.4) are isolable as redto orange crystalline solids in 20 - 67% yields. They are very soluble in common organic solvents.As solids, the bis(alkoxo) complexes are indefinitely stable in air. The bis(alkoxo) complexes arealso thermally stable in solution, as evidenced by the fact that 2.2 persists unchanged in C6D6after 16 h at 120 °C. The spectroscopic properties of 2.1 - 2.4, collected in Tables 2.2 and 2.3,are consistent with their possessing monomeric, three-legged piano-stool molecular structures.The progress of reactions 2.7 can be monitored by observing the changes in the nitrosyl-stretching frequencies evident in the IR spectra of the reaction mixtures (Figure 2.1). Forinstance, the reaction of Cp *W(NO)C12 (vNO = 1630 cm -1 ) with 2 equiv of LiOCMe 3 in THFexhibits first an intermediate nitrosyl-stretching band at 1593 cm-1 (vide infra) which appears atthe expense of the band due to the starting material. As the transformation continues, thisabsorption feature decreases as the 1557 cm -1 band characteristic of the product complex appearsand intensifies. In other words, the vNo is shifted to lower energy as the chloro ligands arereplaced by the more electron-donating alkoxo groups. In general, the nitrosyl-stretchingfrequency18 has proven to be an extremely powerful tool in estimating the Lewis acidity of ametal nitrosyl complex. 2 The nitrosyl-stretching frequencies of the Cp *M(NO)(OR)2 class of26Figure 2.1 Monitoring of the reaction between Cp *W(NO)C12 and 2 equiv of LiOCMe 3 in THEby IR spectroscopy [spectral region 1850 - 1480 cm-I].27complexes (Table 2.2) indicate that the metal is receiving significant donation of it-electrondensity from the alkoxide ligands. For comparison, it may be noted that a THF solution ofCp*W(N0)(CH2CMe3)2 exhibits a v No at 1568 cm -1 , whereas Cp*W(N0)(0CMe3)2 has thesame feature at 1557 cm -1 .2.4.2 Some Chemical Properties of Bis(Alkoxo) ComplexesConsistent with Cp *M(NO)(OR)2 complexes having electron-rich metal centers, they arerelatively inert chemically towards nucleophiles. As noted above, these bis(alkoxo) complexes areextremely air-stable. Furthermore, Cp *W(NO)(OCMe3 )2 (2.2) does not react with 02 (1 atm) inEt20 or with an excess of H2O in THF. The stability of 2.2 towards 02 suggests that complexesof this type are not easily oxidized. Consistent with this, a cyclic voltammogram ofCp*W(NO)(OCMe3)2 in THE shows no oxidation features to the solvent limit of 0.85 V. 19 Thehydrolytic stability is somewhat surprising since the polar W-0 bonds in complex 2.2 would beexpected to be susceptible to nucleophilic attack. 20Complex 2.2 also does not react with typical Lewis bases such as CO and PMe3 .Consequently, I believe that the chemical inertness of the Cp *M(NO)(OR)2 complexes reflectstheir inability to form Lewis acid-base adducts at their relatively electron-rich metal centers. Thisbehavior is in marked contrast to the 16-electron dialkyl and diaryl species, Cp'M(NO)R 2 , whichreadily form 1:1 metal-centered adducts with a variety of Lewis bases. 2 Cp*W(NO)(OCMe3)2(2.2) is also inert to NCCH(Me)2, PhCCH, (Me)2CO, NHPh2 and S8 under the conditionsdescribed in Section 2.2.8. The reaction with S8 with 2.2 was performed since it is known thatsulfur adds across the metal-sulfur bond of CpW(NO)(SCH2SiMe3)(CH2SiMe3) to form theperthiolate species, CpW(NO )(r12 -S {S)CH2SiMe3)(CH2SiMe3).21Bis(alkoxo) complexes react rapidly with HC1 to form first the alkoxo chloro complex andthen the corresponding dichloro species, i.e.,28HaMe3CO'^ OCMe3^Me3CON0Ha--11.Cl^Cl/ :-.^CIN0N0The alkoxide ligands are replaced by chloride ligands with the production of alcohol. This type ofreactivity has been observed previously by McCleverty's group.22Interestingly, Cp*W(NO)(OCMe 3)2 (2.2) does react with H2 (80 psig) in THE to produceorange crystals. The exact nature of this product is uncertain. Partial characterization data forcan be found in Section 2.2.9. The elemental analysis data support a C22H 33N ratio. The massspectrum shows the fragmentation pattern for a common decomposition product,[Cp*W(0)2]2-(4-0). 23 IR data indicate the presence of a nitrosyl ligand in the product(vNQ = 1541 cm -1 ), at lower energy than the starting bis(alkoxo) complex (vNO = 1557 cm -1 ).The 1H NMR data suggest that this complex is a bimetallic species with two inequivalent Cp*ligands whose protons resonate at 8 2.22 and 2.07 ppm. The 13 C{ 111} NMR data support thisconclusion in that there are two signals due to C5(CH3)5 (E• 119.9, 119.6 ppm) and two signalsdue to C5 (CH3 )5 (8 10.9, 10.8 ppm) in the 13 C{ 1H}NMR spectrum of the orange crystals in theC6D6 . Additional signals in the 1H NMR spectra could not be assigned. A solid-statecrystallographic analysis of the orange crystals was attempted by Dr. S. J. Rettig.(2.8)29Due to severe disorder problems, the only information obtained was the identification of a W 202core unit, i.e.,/O\W W\o/A similar core unit is observed in the structure of [Cp *Mo(N0)(CH2Ph)(l1-0)]2 (see Section4.4.5). Surprisingly, Cp*Mo(NO)(OCMe3 )2 (2.1) and Cp*W(NO)(OCH2Ph)2 (2.4) do not reactwith H2 under similar experimental conditions.2.4.3 X-ray Crystallographic Analyses of Complexes 2.2 and 2.4X-ray crystallographic analyses of 2.2 (Figure 2.2)24 and 2.4 (Figure 2.3)25 demonstrate thatthese representative examples of Cp *W(NO)(OR)2 complexes are best viewed as 18-valence-electron species, the ability of the alkoxo ligands to donate 7c-electron density effectivelysatisfying the electronic requirements of the metal centers. Both Cp *W(NO)(OCMe3)2 (2.2) andCp*W(NO)(OCH2Ph)2 (2.4) are monomeric, and some selected bond angles and bond lengths arecollected in Tables 2.4 - 2.5. Their chemically most interesting features are the dimensions aboutthe alkoxide ligands. Since the OCMe3 and OCH2Ph ligands have very different stericrequirements, we believe that the large W-O-C angles (averaging 135.9° for 2.2 and 128.3° for2.4) and short W-0 bond lengths (averaging 1.90 A for 2.2 and 1.91 A for 2.4) are a result ofelectronic rather than steric effects. The increased W-0 bond order likely results from thedonation of electron density from filled p orbitals on oxygen to the empty clxy orbital on the metalcenter. 26 The W-O-C angle of alkoxide ligands can approach linearity as it donation from thealkoxide ligand to the metal increases. 27 The tungsten centers in 2.2 and 2.4 are thus relativelymore electron rich (a fact also indicated by their IR and chemical properties, vide supra) thanthose in their dialkyl or diaryl analogues. 2 Consistent with this, no evidence for the existence ofagostic interactions between the metal and the 0-hydrogens of the alkoxo ligands is revealed bythe crystallographic analysis of 2.4.30Figure 2.2 ORTEP diagram of Cp*W(N0)(OCMe3)2 (2.2). 50% probability thermal ellipsoidsare shown for the non-hydrogen atoms.Table 2.4. Selected Bond Lengths and Bond Angles for Cp*W(NO)(OCMe3)2 (2.2)bond lengths (A) bond angles (°)W - 01 1.890(5) W - 01 -C11 136.2(5)W - 02 1.903 (5) W - 02 - C15 135.6 (5)01 -C11 1.46(1) 01 - W - 02 109.7 (2)W - N 1.758 (7) W - N - 03 168.1 (7)N - 03 1.232 (8)31Figure 2.3 ORTEP diagram of Cp*W(NO)(OCH2Ph)2 (2.4). 50% probability thermal ellipsoidsare shown for the non-hydrogen atoms.Table 2.5. Selected Bond Lengths and Bond Angles for Cp*W(NO)(OCH2Ph)2 (2.4)bond lengths (A) bond angles (°)W - 02 1.910(4) W - 02 - C8 128.3 (4)02 - C8 1.444 (7) 02 - W - 02' 107.6 (3)W - N 1.759 (7) W - N - 03 169.8 (7)N - 01 1.218 (9)32The structure of Cp *W(NO)(OCMe3)2 can be compared to the structure ofCp*W(NO)(OCMe 3)(NHCMe3), which has been recently completed. 28 The metrical parametersof the two compounds are very similar, and the most interesing comparison involves their W-0bond lengths. Whereas the alkoxo amido complex has a W-0 bond length of 1.916 (4) A, theaverage W-0 bond length in the bis(alkoxo) complex is 1.90 A. These findings suggest that thevery slight lengthening of the W-0 bond in Cp*W(N0)(0CMe 3)(NHCMe3) may be a result of theamide ligand (W-N bond length of 1.939 (4) A) have a greater it-donating ability than alkoxideligand.2.4.4 Systems Related to the Bis(alkoxo) ComplexesA bis(alkoxo) chromium complex related to the compounds synthesized during this work hasrecently been described by Hubbard and McVicar. 29 They prepared Cp*Cr(N0)(0-i-Pr)2 bytreatment of Cp*Cr(NO)2(CH2C1) with excess Na(O-i-Pr) in isopropanol, a process which resultsin the formal replacement of NO and CH2C1 ligands by isopropoxide groups. Such chromiumcomplexes cannot be synthesized via a route analogous to that portrayed in eq 2.7 because theCp*Cr(NO)C12 precursor remains unknown. In other work, McCleverty and coworkers haveprepared an extensive series of isoelectronic pyrazolylborate alkoxide compounds,{11B(Me2pz)3 }M(N0)(OR)2 [M = Mo, W] which result from alcoholysis of{HB(Me2pz)3}M(NO)X2 [X = Cl, I].5a,22,26b,30 Interestingly, we find that similar treatment ofCp *M(NO)Cl2 [M = Mo, W] with alcohols does not produce the bis(alkoxo) complexessynthesized during this work, but rather affords intractable materials. Both McCleverty andHubbard have attributed the stability of their Group 6 bis(alkoxo) complexes to the electron-donating ability of the alkoxo ligands.Sulfur analogues of the bis(alkoxo) complexes 2.1 - 2.4 have been prepared by the treatmentof [CpMo(NO)I2]2 with thiolates31 or via direct sulfur insertion into the metal-alkyl bonds ofCpW(NO)(CH2SiMe3)2 to form CpW(N0)(SCH2SiMe3)2 . 21 Ashby and Enemark haveperformed Fenske-Hall molecular-orbital calculations on CpMo(NO)(SPh)2 to Show that theTHE aiN0N0RO C lC l C l+ M'OR + M'Cl (2.9)33stability of the thiolate ligands may be attributed to the pn-dn interaction between the p-typeorbitals on the thiolate ligands and the empty molybdenum d xy orbitals. 32 Consistent with themolecular orbital calculations, CpMo(NO)(SPh) 2 does not react with CO, PPh3 , or 12 . 32Nitrogen analogues of the bis(alkoxo) complexes have been prepared in our group fromCp *W(NO)C12 and an excess of t-butyl amine. 28 In the same way that alkoxide ligands provideextra electron density to stabilize the bis(alkoxo) compounds, Cp *W(NO)(NHCMe3)2 is alsostable due to the electron donating ability of the amide groups.2.4.5 Synthesis and Characteristic Properties of the Alkoxo Chloro Complexes,Cp*M(NO)(OR)ClIn order to explore the reactivity of more electron-deficient Group 6 alkoxo complexes, wedecided to isolate the alkoxo chloro complexes, Cp*M(N0)(0R)C1, which are the intermediateorganometallic species formed during conversions 2.7. The Cp *M(NO)(OR)Cl compounds arebest obtained via metathesis reactions utilizing 1 equiv of an alkoxide salt at low temperatures, i.e.The three such product complexes prepared during this work (2.5 - 2.7) are isolable as black topurple analytically pure needles in moderate yields (25 - 44%). The alkoxo chloro complexes,like the bis(alkoxo) compounds, are very soluble in all common organic solvents. In contrast tocomplexes 2.1 - 2.4, however, the monoalkoxo species are very thermally, oxidatively andhydrolytically sensitive both as solids and in solutions.34The spectroscopic properties (Tables 2.2 - 2.3) of complexes 2.5 - 2.7 are consistent withtheir possessing monomeric, three-legged piano-stool molecular structures. The v No bandsevident in their IR spectra are higher in energy than those exhibited by the correspondingbis(alkoxo) complexes, but lower in energy than those characteristic of the dichloro startingmaterials. For example, the nitrosyl-stretching frequencies decrease in the order Cp *W(NO)C12(1630 cm -1 ) > Cp*W(NO)(OCMe3)Cl (1593 cm-1 ) > Cp*W(NO)(OCMe3 )2 (1557 cm-1 ) for THEsolutions of the various compounds. Such spectroscopic data indicate that the metal centers inthe Cp*M(NO)(OR)Cl complexes are relatively more electron-deficient than in the analogousCp*M(NO)(OR)2 compounds. A similar trend is observed between Cp'M(NO)R 2 andCp'M(NO)(R)Cl complexes. 33 Thus, alkyl chloro complexes are markedly more Lewis acidicthan their dialkyl counterparts.Previous work in our laboratories by Dr. E. C. Phillips has shown that treatment ofCp *M(NO)I2 with Me0H results in insoluble tan powders which are thought to be[Cp *M(NO)(OMe)I]2 complexes. 10 The mass spectral and 1H NMdt data of these speciesindicate that they are dimeric. This dimeric nature may account for the difference in their colorand their solubility from the other alkoxo chloro complex isolated in this work. Dr. Phillips wasnot able to establish unequivocally the dimeric nature of the methoxide complexes because of theirlow solubility in common organic solvents. McCleverty's group were not able to determine theexact natures of [CpMo(NO)(OMe)X]2 (X = I, Br) because of their low solubility. 34 Molecular-weight determinations by the Signer method 35 of Cp *W(NO)(OCMe3)Cl and Cp *W(NO)(OPh)Clin THE are unsuccessful because solutions of the alkoxo chloro complexes decompose slowly toblack, cloudy mixtures.36352.4.6 Some Chemical Properties of Cp*M(N0)(0R)C1 ComplexesConsistent with the greater electron-deficiency at the metal centers of complexes 2.5 - 2.7,the Cp*M(NO)(OR)Cl complexes decompose rapidly both in solution and in the solid state whenexposed to the atmosphere. Indeed, attempts to perform reactivity studies on this class of alkoxochloro complexes has been hampered by their extreme sensitivity to air and moisture.Upon treatment with dry 02 (1 atm), compounds 2.5 - 2.7 decompose to intractable tansolids. Nevertheless, exposure to water results in compounds 2.5 and 2.7 being converted to theisolable [Cp *M(NO)(OH)(Cl)]2 species. The molybdenum and tungsten compounds may becrystallized from diethyl ether as black and brown crystals, respectively. The hydroxo complexesare formulated as dimers for several reasons. The mass spectra of complexes 2.8 and 2.9 showthe parent peak of the dimer, and the v NO's are broad in the Nujol mull IR spectra of thecomplexes. In addition, both 2.8 and 2.9 exhibit two peaks in their Nujol-mull IR spectrabetween 3645 and 3625 cm-1 which are attributable to OH stretches. Finally the 1H NMRspectrum of 2.9 exhibits signals attributable to two inequivalent Cp* ligands (6 1.94 and 1.75ppm). The molybdenum complex (2.8) is either a monomer, or a centrosymmetric dimer insolution since a single Cp* resonance is observed at 6 1.75 ppm in the 1H NMR spectrum of thecomplex. McCleverty's group has prepared the analogous [CpMo(NO)(OH)I]2 complex byhydrolysis of CpMo(NO)(O2CMe)I. 34The monoalkoxo complexes do react with PMe3 presumably to form adducts of the typeCp*M(NO)(OR)(Cl)(PMe3), but these yellow adducts are only stable at low temperatures. Uponattempted work-up these adducts decompose to intractable brown solids and free PMe 3 .362.4.7 Systems Related to the Alkoxo Chloro SpeciesNitrogen-containing analogues the alkoxo chloro complexes have also been prepared by K.Ross from Cp *M(NO)C12 in a two-step procedure (eq 2.10 - 2.11). 28Cp*Mo(NO)C12 + NH2Ar^Cp*Mo(NO)(Cl)2 (NH2Ar)^(2.10)Cp*MO(N0)(C 1)2(NH2Ar) ^Ikkip02Cp*Mo(NO)(NHAr)Cl-HN(i-pr)2 , -Lia(2.11)Alternatively these amido complexes can be made via a metathesis reaction as in eq 2.13. 28Cp*M(NO)C12 + LiNHAr^Cp*M(N0)(NHAr)CI + LiC1^(2.12)The reactions of alkyl amines with Cp*M(NO)C1 2 proceed directly to the amido chlorocomplexes, Cp *M(NO)(NHR)Cl.2.4.8 A Related Reaction with KOCMe 3The reaction of Cp*W(NO)C12 with KOCMe3 in the presence of H2 (40 psig) affords thedimeric alkoxo complex 2.10. This air-sensitive complex is crystallized from Et 20 as purpleneedles in 25% yield.Cp*W(NO)C12 + H2 + KOCMe3^[Cp*W(N0)(0CMe3)12 (2.10) (2.13)The IR spectrum of 2.10 as a Nujol mull exhibits a broad v No, at 1543 cm-1 . The formulation of2.10 as a dimer is based on the observation of the parent mass peak (m/z = 844) in the massspectrum of the complex and on the presence of two Cp* resonances (5 2.04 and 2.00 ppm) andtwo C(CH3 )3 resonances (6 1.44 and 1.26 ppm) in the 1H NMR spectrum of 2.10 in C6D6 . Thetwo sets of peaks in the 1H NMR result from the two isomers in which the Cp * ligands are cis ortrans to each other, i.e.,0R^N^ Rw .4,0 „,...w/ .4, 1„COW .^W/^1:)Ir / .. 0 2r. \N RA metal-metal bond is invoked in [Cp *W(NO)(OCMe3)]2 to account for its apparentdiamagnetism.This type of dimer has precedent since [CpCr(N0)(0R)} 2 (R = Me,37 Et38) dimers have beenisolated previously by others in our group. In these paramagnetic chromium complexes, theheteroatom ligands bridge the two metals and there is no Cr-Cr bond. 37 However, othercomplexes of the type [Cp 1M(NO)X]2 (M = Mo, W; X = OR, SR, SeR, TeR)39 and[CpCr(N0)(NHCMe 3))240 are formulated as diamagnetic, electronically saturated species withM-M bonds.Under the conditions of the experiment outlined in Section 2.2.14, Cp *W(NO)C12 does notreact with H2 in THE until the potassium salt has been added. Consistently, it has also beenshown that Cp *W(NO)C12 has a very low reduction potential of -750 mV (vs SCE in THF). 41Since Cp *W(NO)(OCMe3)2 reacts with molecular hydrogen to form the bimetallic speciesdescribed in Section 2.4.2., H2 most likely reacts with the monoalkoxo species,Cp*W(NO)(OCMe3)Cl. Thus, the first step in the mechanism of reaction 2.13 is the formation ofCp*W(N0)(0CMe3)C1 (eq 2.14).Cp*W(NO)C12 + KOCMe3^Cp*W(NO)(OCMe3)Cl + Ka^(2.14)The subsequent reaction of Cp *W(NO)(OCMe 3 )Cl with molecular hydrogen can then beenvisioned to proceed in two ways. Either Cp *W(NO)(OCMe3)Cl is reduced by H2 to a radicalwhich then couples to form 2.10 (eq 2.15 - 2.16),370 ON 0382 Cp *W(NO)(OCMe3)Cl + H2 ----* 2 [Cp*W(N0)(0CMe3)]* + 2 HC1 (2.15)2 [Cp*W(N0)(0CMe3)r ---' [Cp *W(NO)(OCMe3)]2^(2.16)or 2.10 is produced by a bimolecular reductive elimination of H2 from an intermediate hydridespecies according to equations 2.17 - 2.18.^Cp*W(N0)(0CMe3)C1 + H2 ----• Cp *W(NO)(OCMe3)H + HCl^(2.17)2 Cp*W(NO)(OCMe 3)H --■ [Cp*W(N0)(0CMe3)}2 + H2^2.18)I would suggest utilizing electron spin resonance (ESR) spectroscopy to determine if a radicalmechanism is operative. In addition, the reaction of isolated Cp *W(NO)(OCMe3)Cl with H2would establish if the chloride is indeed the active species.2.6 Epilogue and Future WorkThe work presented in this chapter outlines the synthesis, characterization and some chemicalreactivity of two classes of Group 6 alkoxo nitrosyl complexes. The 18-electron bis(alkoxo)complexes are chemically inert to a wide variety of reagents, whereas the monoalkoxo chlorospecies, Cp *M(NO)(OR)Cl, are highly reactive. The reactivity studies of the chloro compoundshave been limited because of their air- and moisture- sensitivity. For future studies, I wouldrecommend an examination of the reactivity of the second class of alkoxo complexes,Cp*M(NO)(OR)Cl. For example, Cp *M(NO)(OR)Cl [R = CMe3 , Ph] complexes react withprimary amines to afford alkoxo amido complexes, Cp*M(NO)(OR)(NHR).28Clearly, the properties and chemical reactivity patterns of both the mono and bis(alkoxo)complexes are very different from those of the electronically unsaturated dialkyl complexes21 andtherefore the reactivity of the alkoxo complexes with different types of reagents should beexplored. Specifically, I would suggest polar species as reactants to exploit the polarity of theW-0 bond. The possible reactivity patterns of these complexes will probably not proceed via(5 )39initial adduct formation since these species are electronically saturated. Investigations into theinsertion reactions of CO2 , CS2 and RNCO with the related Cp'M(NO)(OR)R, 42Cp'M(NO)(NHR)R and Cp'M(NO)(NHR)(OR) systems have proven to be quite fruitful. 432.7 References and Notes(1) Legzdins, P.; Lundmark, P. J.; Rettig, S. J. Organometallics, accepted for publication.(2) Legzdins, P.; Veltheer, J. E. Acc. Chem. Res. 1992, 26, 41 and references therein.(3) (a) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163. (b) Bradley, D. C. Adv. Inorg.Chem. Radiochem. 1972, 15, 259. (c) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. MetalAlkoxides; Academic Press: New York, NY, 1978.(4) For examples of halide metathesis reactions, see (a) Gomez-Sal, P.; Martin, A.; Mena, M.;Royo, P.; Serrano, R. J. Organomet. Chem. 1991, 419, 77. (b) Rees, W. M.; Churchill,M. R.; Fettinger, J. C.; Atwood, J. S. Organometallics 1985, 4, 2179. (c) Chisholm, M.H.; Huffman, J. C.; Pasterczyk, J. W. Polyhedron 1987, 6, 1551. (d) Hartwig, J. H.;Anderson, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1990, 112, 5670.For examples of alcoholysis reactions, see (a) McCleverty, J. A.; Wlodarczyk, A. J. Chem.Soc., Dalton Trans. 1988, 449. (b) Kresinski, R. A.; Hamor, T. A.; Jones, C. J.;McCleverty, J. A. J. Chem. Soc., Dalton Trans. 1991, 603. (c) O'Regan, M. B.; Vale, M.G.; Payack, J. F.; Schrock, R. R. Inorg. Chem. 1992, 31, 1112.Stults, S. D.; Anderson, R. A.; Zalkin, A. Organometallics 1990, 9, 1623.Hoffman, D. M.; Lappas, D.; Wierda, D. A. J. Am. Chem. Soc. 1989, 111, 1531.Newman, L. J.; Bergman, R. G. J. Am. Chem. Soc. 1985, 107, 5314.Fornies, J.; Green, M.; Spencer, J. C.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1977,1006.(10) Phillips, E. C. Ph.D. Dissertation, The University of British Columbia, 1989.40(11) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-Sensitive Compounds, 2nd ed.;Wiley-Interscience: New York, NY, 1986.(12) Dryden, N. H.; Legzdins, P.; Batchelor, R. J.; Einstein, F. W. B. Organometallics 1991,10, 2077.(13) The method used in preparing PMe 3 is adapted from Wolfsberger, W.; Schmidbaur, H.Synth. React. Inorg. Met.-Org. Chem., 1974, 4, 149.(14) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals, 3rded., Pergamon Press: Oxford, England, 1988.(15) The method used in preparing LiOCMe 3 is adapted from Cetinkaya, B.; Ganytikcia, I.;Lappert, M. F.; Atwood, J. L.; Shakir, R. J. Am. Chem. Soc. 1980, 102, 2086.(16) The compositions of the solids with respect to their active alkoxide equivalents wereestablished by hydrolysis of weighed solid samples and titration of the resulting solutionswith 0.100 N HCl using phenolphthalein as the indicator.(17) The mass spectum can be attributed to [Cp*W(0)2]2-(11-0), a common decompositionproduct of tungsten nitrosyl-containing complexes in our laboratories.(18) For a discussion of the dependence of vNo on electron density at the metal center, see:Richter-Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford University Press: New York,1992; pp 61-68.(19) General electrochemical experimental details are summarized in section 5.2.1. The cyclicvoltammogram of 2.2 was recorded using a Pt-bead electrode in THE and 0.1 M[Bu4N]l3F6 as the support electrolyte and SCE as the reference electrode. Scan ratesranged from 0.2 to 1.0 V s -1 .(20) Bradley, D. C.; Chisholm, M. H. Acc. Chem. Res. 1976, 9, 272.(21) CpW(NO)(CH2SiMe3)2 reacts with elemental sulfur in a stepwise fashion to form firstly thealkylthiolate complex CpW(N0)(SCH 2SiMe3)(CH2SiMe3), then the perthiolate species,41CpW(N0)(ri 2-S {S)CH2SiMe3)(CH2SiMe3). Thermolysis of the perthiolate complexresults in the formation of CpW(NO)(SCH2SiMe3)2 . See Legzdins, P.; Rettig, S. J.;Sanchez, L. Organometallics 1988, 7, 2394.(22) McCleverty, J. A.; Rae, A. E.; Wolochowicz, I.; Bailey, N. C.; Smith, J. M. J. Chem. Soc.,Dalton Trans. 1982, 951.(23) (a) Faller, J. W.; Ma, Y. J. Organomet. Chem. 1988, 340, 59. (b) Legzdins, P.; Lundmark,P. J.; Phillips, E.C.; Rettig, S. J.; Veltheer, J. E. Organometallics 1992, 11, 2991.(24) Crystals of 2.2 are orthorhombic of space group Pbca (#61); a = 23.627 (3) A, b = 15.862(2) A, c = 11.009 (3) A, V= 4126 (1) V, Z = 8. Dr. S. J. Rettig solved the structure usingthe Patterson method and full-matrix least-squares refinement procedures to R= 0.032,Rw = 0.035 for 2473 reflections with / 3a(/).(25) Crystals of 2.4 are orthorhombic of space group Pnma (#62); a = 8.758 (2) A, b = 15.762(1) A, c = 16.352 (2) A, V = 2257.3 (8) A3 , Z = 4. Dr. S. J. Rettig solved the structureusing the Patterson method and full-matrix least-squares refinement procedures toR = 0.031, Rw = 0.034 for 1807 reflections with I ?_ Rya).(26) (a) Lunder, D. M.; Lobkovsky, E. B.; Streib, W. E.; Caulton, K. G. J. Am. Chem. Soc.1991, 113, 1837. (b) McCleverty, J. A.; Seddon, D.; Bailey, N.A.; Walker, N. W. J. J.Chem. Soc., Dalton Trans. 1976, 898.(27) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications ofOrganotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987; p 48.(28) Legzdins, P; Rettig, S. J.; Ross, K. Organometallics, 1993, 12, 2103.(29) Hubbard, J. L.; McVicar, W. K. Inorg. Chem. 1992, 31, 910.(30) (a) McCleverty, J. A.; Denti, G.; Reynolds, S. J.; Drane, A. S.; Rae, A. E.; Bailey, N. C.;Adams, H.; Smith, J. M. J. Chem. Soc., Dalton Trans. 1983, 81. (b) Denti, G.;McCleverty, J. A.; Wolochowicz, I. J. Chem. Soc., Dalton Trans. 1981, 2021. (c)McCleverty, J. A.; Wlodarczyk, A. Polyhedron 1988, 7, 449 and references cited therein.42(31) McCleverty, J. A.; Seddon, D. J. Chem. Soc., Dalton Trans. 1972, 2588.(32) Ashby M. T.; Enemark, J. H. J Am. Chem. Soc. 1986, 108, 730.(33) Debad, J. D.; Legzdins, P.; Rettig, S. J; Veltheer, J. E. Organometallics, in press.(34) Hunt, M. M.; Kita, W. G.; McCleverty, J. A. J. Chem. Soc., Dalton Trans. 1978, 474.(35) Clark, E. P. Ind. Eng. Chem. Anal. Ed. 1941, 13, 820.(36) The decomposition of the sample is due to a small amount of hydrolysis. See Section 2.4.6.(37) [CpCr(N0)(0Me)J 2 has been structurally characterized and shown to have no Cr-Cr bond.See Hardy, A. D. U.; Sim, G. A. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst.Chem. 1979, B35, 1463.(38) (a) Legzdins, P.; Nurse, C. R. Inorg. Chem. 1985, 24, 327. (b) Kolthammer, B. W. S.;Legzdins, P.; Malito, J. T. Inorg. Chem. 1977, 16, 3173.(39) (a) Clark, G. R.; Hall, D.; Marshden, K. J Organomet. Chem. 1979, 177, 411. (b) Alt, H.G.; Freytag, U.; Herberhold, M.; Hayen, H. I. J. Organomet. Chem. 1987, 336, 361. (c)Rott, J.; Guggolz, E.; Rettenmeier, A.; Ziegler, M. L.; Z Naturforsch., B: Anorg. Chem.,Org. Chem. 1982, 37B, 13. (d) James, T. A.; McCleverty, J. A. J. Chem. Soc. A 1971,1068. (e) McCleverty, J. A.; Seddon, D. J. Chem. Soc., Dalton Trans. 1972, 2588.(40) Legzdins, P.; McNeil, W. S. unpublished observations.(41) Debad, J. D.; Legzdins, P.; Rettig, S. J.; Veltheer, J. E. Organometallics 1993, 12, 2714.(42) See section 4.4.4.4.(43) Legzdins, P.; Ross, K. J. unpublished observations.43CHAPTER 3Synthesis and Characterization of Alkoxo Alkyl Complexes3.1 Introduction^ 433.2 Experimental Procedures ^ 443.3 Characterization Data 513.4 Results and Discussion^  543.5 Epilogue and Future Work  883.6 References and Notes ^ 883.1 IntroductionDuring the last few years, research in the Legzdins' group has centered mainly on thesynthesis and reactivity of the 16-electron dialkyl complexes CpM(NO)R 2 . 1 The chemistry ofthese coordinatively and electronically unsaturated complexes is dominated by their ability to form1:1 metal-centered adducts with Lewis bases. 1,2,3 When the Lewis base has an unsaturated link,e.g. CO, CNCMe3 , NO, these adducts often undergo intramolecular insertion of the coordinatedLewis base into the M-C a bond.The research direction of our group has recently moved towards other metal-heteroatomlinkages. The impetus for this shift has been to compare the relative reactivity of alkyl ligands vs.amido4 or alkoxo ligands5 at the same metal center. For example, complexes such asCp*M(N0)(R)(OR') (R, R' = alkyl or aryl) should allow for the direct comparison of R and ORligand reactivities. This chapter describes the successful preparation and characterization of such44alkoxo alkyl complexes. Chapter 4 reports on the reaction chemistry of this class of alkoxocomplexes.The synthetic methodologies used to prepare the alkoxo alkyl compounds are described indetail since any variation of reaction conditions results in significantly different products beingformed. These latter products, [Cp *W(N0)(CH2SiMe3)][Cp*W(C1)(0)]-(112-1) 1 :12-NC{H)SiMe3) and [Cp *W(N0)(CH2SiMe3)Cl][Cp *W(C1)(r1 2-N{0){H}CH2SiMe3)]-(µ-N) areinteresting organometallic bimetallic compounds in their own right. These bimetallic complexeshave been isolated and characterized by conventional spectroscopic techniques as well as by X-raycrystallographic analysis. This chapter also reports some selected experiments, including adeuterium isotopic labeling study and phosphine reactions, conducted in an attempt to explain themechanism of the reactions which led to these bimetallic complexes.3.2 Experimental Procedures3.2.1 MethodsThe synthetic methodologies employed in this chapter are described in detail in Section 2.2.1.3.2.2 ReagentsThe organometallic dichloro complexes, Cp *M(NO)C12, were prepared and handled asdescribed in Section 2.2.2. The preparation of Cp*M(NO)(CH2Ph)2 complexes [M = Mo, W]and their subsequent conversion to Cp *M(NO)(CH2Ph)Cl have been previously reported. 6 '7Alkoxide salts (LiOCMe3, NaOCMe 3 , NaOPh and NaOMe) were prepared as described inSections 2.3.3 - 2.3.4. (Me3 SiCH2)2Mg•(dioxane) 3 and (PhCH2)2MgX(dioxane) 8 wereprepared according to the published procedures. CD3OD (MSD Isotopes) and KOEt (Aldrich)were used as received. PPh3 (Aldrich) was recrystallized from Et20. A 50% xylene dispersion ofKH (Alfa) was washed with hexanes to remove the xylene and afford KH as a white powder.n-BuLi (1.6 M solution in hexanes, Aldrich) was diluted to 0.70 M with hexanes before use.453.2.3 Reaction of Cp *Mo(N0)(0CMe3)C1 and (PhCH2)2Mg•(dioxane)A purple Et20 solution (20 mL) of Cp *Mo(N0)(0CMe3 )C1 (2.5) (0.16 g, 0.50 mmol) wascannulated into a Schlenk tube containing (PhCH2)2MgX(dioxane) (0.50 mmol PhCH2-). Thestirred reaction mixture turned red and deposited a white precipitate over the course of 1 h. Afterthis time, the reaction mixture was filtered through Celite (2 x 5 cm) supported on a sintered glassfrit. The filtrate was concentrated in vacuo, and cooled (-30 °C) to induce the crystallization of0.12 g (62% yield) of orange crystals of Cp *Mo(NO)(CH2Ph)Cl. The spectral data of theproduct were identical to those of an authentic sample.?3.2.4 Reaction of Cp *Mo(NO)(OCMe3)2 and (PhCH2)2Mg•(dioxane)Cp*Mo(NO)(OCMe3 )2 (2.1) (0.063 g, 0.15 mmol) and (PhCH2)2MgX(dioxane) (0.15 mmolPhCH2-) were mixed as solids in a Rotoflo pressure vessel in a glovebox. The vessel wasremoved from the glovebox, and THE (5 mL) was added via syringe. The orange reactionmixture was stirred overnight at 65 °C. No color change was observed, and a solution ERspectrum of the reaction mixture exhibited a single vNO (1589 cm-1) corresponding to that of thestarting material.3.2.5 Preparation of Cp *M(NO)(CH2Ph)(OR) [M = Mo, R = CMe3 (3.1), Ph (3.2); M = W,R = CMe3 (3.3)]All of these complexes were prepared in a similar manner. The synthesis ofCp*W(NO)(CH2Ph)(OCMe3) (3.3) is described in detail as a representative example.Cp*W(N0)(CH2Ph)CI (0.31 g, 0.65 mmol) and LiOCMe 3 (0.050 g, 0.65 mmol) wereintimately mixed in a Schlenk tube. Et20 (20 mL) was transferred to the tube via syringe, and theorange-red reaction mixture was stirred overnight with no apparent color change occurring. Thesolvent was then removed in vacuo, the remaining red residue was extracted with hexanes(2 x 20 mL), and the extracts were filtered through Celite (2 x 5 cm) supported on a medium-46porosity glass frit. The filtered solution was concentrated and cooled at -30 °C overnight toinduce the precipitation of Cp *W(NO)(CH2Ph)(OCMe3) (0.33 g, 45% yield) as red needles whichwere collected by filtration.Physical properties and spectroscopic data of complexes 3.1 - 3.3 are contained in Tables3.1 - 3.3.3.2.6 Preparation of Cp *W(NO)(CH2SiMe3)(OR) [R = CMe3 (3.4), Ph (3.5), Me (3.6), Et(3.7)]A THF solution (30 mL) of Cp *W(NO)(CH2SiMe3)C19 was generated from Cp *W(NO)C12(1.7 g, 4.0 mmol) and (Me3SiCH 2)2MgX(dioxane) (4.0 mmol CH2SiMe3 -) in a Schlenk tube.I 0The THF was removed from the blue reaction mixture in vacuo, and the blue residue wasextracted with pentane (2 x 30 mL). The extracts were filtered through Celite (2 x 5 cm)supported on a sintered glass frit. The filtrate was divided equally into four Schlenk tubes.To each of the blue pentane solutions 11 (vNO = 1616 cm -I) was added the appropriatealkoxide salt (LiOCMe3 , NaOPh, NaOMe or KOEt; 1.0 mmol each, slight excess). The mixtureswere stirred for 2 h and became red for R = CMe 3 (vNO = 1572 cm- I), Me (vNO = 1584 cm - I),and Et (vNO = 1582 cm- I), but purple for R = Ph (vNO = 1597, 1586 cm-I). The final mixtureswere filtered through Celite (2 x 5 cm) supported on sintered glass frits. The filtered solutionswere then concentrated and cooled at -30 °C overnight to induce the deposition of the desiredorganometallic products. Cp *W(NO)(CH2SiMe3)(OCMe3) (3.4) andCp*W(NO)(CH2SiMe3)(OEt) (3.7) were isolated as a red oils, whereasCp*W(NO)(CH2SiMe3)(OPh) (3.5) and Cp*W(N0)(CH2SiMe3)(0Me) (3.6) were isolated aspurple and red crystals, respectively.Physical properties and spectroscopic data of complexes 3.4 - 3.7 are contained in Tables3.1 - 3.3.47Attempts to prepare analogous cyclopentadienyl alkoxide complexes, CpM(NO)(R)(OR'), viamethodology similar to that outlined in Sections 3.2.5 - 3.2.6 have been unsuccessful.3.2.7 Preparation of [Cp *W(N0)(CH2SiMe3)1[Cp *W(C1)(0)]-(µ2-71 1 :i2-NC{H}SiMe3)(3.8)A pentane solution of Cp *W(N0)(CH2SiMe3 )C1 (20 mL) (generated from Cp *W(NO)C12(0.42 g, 1.0 mmol) and (Me3 SiCH2)2Mg•(dioxane) (1.0 mmol CH2SiMe3 -) as in Section 3.2.6)was cooled to -20 °C. This solution (vNO = 1616 cm -1) was then cannulated into a Rotoflopressure vessel containing KOCMe3 (0.11 g, 1.0 mmol). The heterogeneous reaction mixturewas allowed to warm to room temperature and was stirred overnight. After this time, the reactionmixture consisted of a red-purple solution (vNO = 1624, 1570 cm -1 ) and an off-white precipitate.Filtration of the mixture through Celite (2 x 3 cm) afforded a red-purple filtrate. The filtrate wasconcentrated in vacuo and maintained at -30 °C for several days. Purple needles of--[Cp*W(N0)(CH2SiMe3)][Cp*W(C1)(0)]-(42-ri1 -2_ NC{H)SiMe3 ) (3.8) (0.042 g, 9.3% yield)formed and were separated from the mother liquor by cannulation. The physical properties andspectroscopic data for complex 3.8 are collected in Tables 3.1 - 3.3.3.2.8 Preparation of [Cp *W(N0)(C112SiMe3)C11[Cp *W(C1)01 2-N(0){11}CH2SiMe3)]-(µN)(3.9)A cooled (-20 °C) pentane solution of Cp *W(NO)(CH2SiMe3)Cl (20 mL) (generated fromCp*W(NO)C12 (0.42 g, 1.0 mmol) and (Me3 SiCH2)2Mg.X(dioxane) (1.0 mmol CH2SiMe 3 -) as inSection 3.2.6) was cannulated into a Rotoflo pressure vessel containing KOMe (0.070 g,1.0 mmol). The heterogeneous reaction mixture was stirred and allowed to warm slowly to roomtemperature. Over the course of 5 h, the reaction mixture turned from blue to orange, and anorange precipitate formed. The reaction mixture was then taken to dryness in vacuo. The residuewas extracted with pentane (2 x 20 mL). The combined extracts were filtered through Celite(2 x 3 cm) supported on a sintered glass frit, and the yellow filtrate was collected and48concentrated. Cooling the concentrated pentane solution at -30 °C overnight resulted in thecrystallization of Cp*W(0) 2(CH2SiMe3) (0.11 g, 0.25 mmol, 31% yield based onCp*W(NO)Cl2).The remaining residue was also extracted with Et20 (2 x 20 mL). The Et20 extract wasfiltered through Celite (2 x 3 cm) supported on a sintered glass frit, and the filtrate was collectedand concentrated. Maintaining the saturated orange solution at -30 °C overnight resulted in thedeposition of [Cp *W(N0)(CH2SiMe3 )Cl][Cp *W(C1)(71 2-N{0}{H}CH2SiMe3 )]-(4-N) (3.9)(0.097 g, 0.10 mmol, 13% yield based on Cp *W(NO)C12) as orange needles. Physical propertiesand spectroscopic data of complex 3.9 are contained in Tables 3.1 - 3.3.This reaction was also performed on an NMR scale to determine the exact ratio of productcomplexes. For example, Cp *W(NO)(CH2SiMe3)Cl (0.02 g, 0.04 mmol) and KOMe (0.003 g,0.04 mmol) were mixed as solids in a Rotoflo pressure vessel. Pentane (5 mL) was added viasyringe, and the atmosphere of the vessel was removed. Overnight, the stirred reaction mixtureturned from blue to yellow. The reaction mixture was then taken to dryness in vacuo. In aglovebox, the yellow residue was dissolved in C6D6, and the resulting amber-yellow solution wasfiltered through Celite (6 x 20 mm). The filtrate was collected in an NMR tube, and its 1H NMRspectrum exhibited resonances attributable to only Cp *W(0)2(CH2CMe3) and complex 3.9 in a1:0.6 ratio.3.2.9 Reaction of Cp *W(NO)(CH2SiMe3)(OCMe3) (3.4) with KOCMe3A red pentane solution of Cp *W(NO)(CH2SiMe3)(OCMe3) (20 mL) (1.0 mmol prepared asin Section 3.2.6) was cannulated into a Rotoflo vessel containing KOCMe3 (0.11 g, 1.0 mmol).The reaction mixture was stirred overnight, and the mixture was filtered through Celite (2 x 5 cm)supported on a sintered glass frit. The red filtrate was reduced in vacuo to obtain a red oil. TheIR spectrum of this oil exhibited one nitrosyl-stretching frequency attributable toCp*W(NO)(CH2SiMe3)(OCMe3) (3.4). In addition, the 1H NMR spectrum of the oil in C 6D6revealed 3.4 to be the only proton-containing species present.493.2.10 Reaction of Cp *W(N0)(CH2SiMe3)C1 with KOCMe3 in the presence of PPh3A pentane solution of Cp*W(N0)(CH2SiMe3 )CI (20 mL) (1.0 mmol generated as in Section3.2.6) was cannulated into a flask containing KOCMe 3 (0.11 g, 1.0 mmol) and PPh3 (0.36 g,1.5 mmol). The reaction mixture turned red-purple within 5 min. After being stirred for 2 h, thereaction mixture was filtered through a Celite plug (2 x 5 cm) supported on a sintered glass frit.The red-brown pentane filtrate was concentrated and cooled to induce the crystalization of PPh 3(0.19 g). The mother liquor was further concentrated to induce the precipitation of 0.040 g of[Cp*W(N0)(CH2SiMe3)][Cp *W(C1)(0)]-(112-also washed with Et20 (2 x 10 mL), and the purple Et 20 filtrate was collected and concentrated.A further 0.11 g of PPh3 (83% total recovered yield) and 0.060 g of 3.8 (22% total yield) wasisolated from this solution.3.2.11 Preparation of Cp*W(N0)(CH2SiMe3)(CI)(PMe3) (3.10)A pentane solution of Cp *W(NO)(CH2 SiMe3)Cl (20 mL) (2.0 mmol generated as in Section3.2.6) was frozen in liquid N2, and excess PMe3 was vacuum transferred onto the reactionmixture. As the reaction mixture warmed to room temperture, it turned yellow and deposited ayellow precipitate. The mixture was taken to dryness in vacuo, and the remaining yellow residuewas washed with pentane (2 x 5 mL) and then dissolved in Et20 (20 mL). This Et20 solutionwas filtered through Celite (2 x 3 cm), and hexanes (5 mL) were added to the filtrate. Thesolution was then concentrated until the first signs of crystallization were evident. Theconcentrated solution was maintained at -30 °C to induce the crystallization ofCp *W(NO)(CH2SiMe3)(Cl)(PMe3) (3.10) (0.63 g, 58% yield) as golden flakes. Physicalproperties and spectroscopic data of complex 3.10 are contained in Tables 3.1 - 3.3.- - 2_TI 1 :11 NC(H}SiMe3) (3.8). The Celite plug was503.2.12 Reaction of Cp *W(NO)(CH2SiMe3)(CI)(PMe3) (3.10) with KOCMe3Cp *W(N0)(CH2SilVle3)(C1)(PMe3) (3.10) (0.27 g, 0.49 mmol) and KOCMe 3 (0.055 g,0.49 mmol) were mixed as solids in a Rotoflo vessel, and pentane (20 mL) was added via syringe.The pale yellow stirred reaction mixture became red over the course of 2 days. The reactionsolution was taken to dryness in vacuo, and the remaining red-brown oil was redissolved inpentane (15 mL). The pentane solution was filtered through Celite (2 x 5 cm) supported on asintered glass frit. The filtrate was taken to dryness in vacuo to yield a red oil which wasidentified as Cp*W(NO)(CH2SiMe3)(OCMe3) (3.4) from comparison of its spectral data to thoseof an authentic sample.3.2.13 Reaction of Cp *W(NO)(CH2SiMe3)(C1)(PMe3) (3.10) with KOMeCp*W(N0)(CH2SiMe 3 )(C1)(PMe3 ) (0.22 g, 0.40 mmol) and KOMe (0.028 g, 0.40 mmol)were mixed as solids in a Rotoflo vessel, and pentane (20 mL) was added via syringe. Thereaction mixture was stirred for 2 days, and over this time there was no color change. Thereaction mixture was taken to dryness in vacuo, and the remaining residue was extracted withpentane (20 mL). The extract was filtered through Celite (2 x 5 cm). The yellow filtrate wasconcentrated and cooled to induce the crystallization of 0.18 g of the starting material,Cp *W(NO)(CH2SiMe3 )(Cl)(PMe3) (3.10) (82% recovered yield).3.2.14 Reaction of Cp *W(N0)(CH2SiMe3)C1 with KOCD3An excess of CD 3 OD (0.5 mL) in Et20 (10 mL) was slowly cannulated into a Schlenk tubecontaining KH (0.040 g, 1.0 mmol). As the addition proceeded, the KH dissolved and a gasevolved. The solvent was then removed in vacuo to afford a white solid which was washed withpentane (2 x 10 mL). Cp*W(NO)(CH2SiMe3)Cl (1.0 mmol, generated as in Section 3.2.6) inpentane (20 mL) was cannulated onto the white solid, which was assumed to be KOCD 3(1.0 mmol). The heterogeneous reaction mixture was stirred overnight, and the color of the51mixture turned red. The mixture was then filtered through Celite (2 x 5 cm) supported on asintered glass frit. The red pentane filtrate was concentrated and cooled to induce thecrystallization of 0.040 g (9.1% yield based on Cp *W(NO)C12) of Cp*W(0)2(CH2SiMe3) ascolorless crystals. The mother liquor was then taken to dryness to obtainCp*W(NO)(CH2SiMe3 )(OCD3) (3.6-d3) a red oil (-0.2 g, -40% yield).Data for Cp *W(N0)(CH2SiMe3)(0CD3 ). IR (Nujol mull): vc_D 2056, vNO 1574,vsj_c 1244, 1258 cm-1 . 1H NMR (C6D6): 8 1.58 (s, 15 H, C 5(CH3)5), 0.91 (d, 1 H, CHAHB ,JBH = 11.7 Hz), 0.84 (d, 1 H, CHAHB, JHEI = 11.7 Hz), 0.34 (s, 9 H, Si(CH3)3).This reaction was also performed on an NMR scale to determine the exact ratio of productcomplexes. For example, Cp *W(NO)(CH2SiMe3)Cl (0.17 g, 0.36 mmol) and KOCD3 (0.014 g,0.36 mmol) were mixed as solids in a Rotoflo pressure vessel. Pentane (5 mL) was added viasyringe, and the vessel was evacuated. Overnight, the stirred reaction mixture turned from blue toorange-red. The reaction mixture was then taken to dryness in vacuo. In a glovebox, the redresidue was dissolved in C 6D6 , and the resulting red solution was filtered through Celite(6 x 20 mm). The filtrate was collected in an NMR tube, and its 1H NMR spectrum exhibitedresonances attributable to only Cp *W(0)2(CH2SiMe3) and Cp *W(NO)(CH2SiMe3)(OCD 3 )(3.6-d3) in a 1:5 ratio.3.3 Characterization DataTable 3.1. Numbering Scheme, Color, Yield and Elemental Analysis Data for Complexes3.1- 3.10complex compdno.color anal. found (calcd)(yield, %) C H NCp *Mo(NO)(CH2Ph)(OCMe3) 3.1 red (56) 59.49 (59.29) 7.52 (7.34) 3.31 (3.29)Cp *Mo(NO)(CH2Ph)(OPh) 3.2 red (39) 62.22 (62.02) 6.03 (6.11) 3.29 (3.14)Cp*W(N0)(CH2Ph)(0CMe3 ) 3.3 red (45) 49.05 (49.14) 6.05 (6.09) 2.70 (2.73)Cp*W(N0)(CH2SiMe3)(0CMe3) 3.4 red oil (gg30) 41.41 (42.44)° 6.73 (6.92) 2.87 (2.75)52Cp*W(N0)(CH2SiMe3)(0Ph) 3.5 purple (66) 45.58 (45.38) 5.89 (5.90) 2.57 (2.65)Cp*W(NO)(CH2SiMe3)(OMe) 3.6 red (26) 38.68 (38.55) 6.29 (6.25) 2.90 (3.00)Cp*W(N0)(CH2SiMe3)(0Et) 3.7 red oil (ft20) 39.71 (39.92) 6.45 (6.49) 2.79 (2.91)[Cp*W(NO)(CH2SiMe3)][Cp*W(C1)(0)1-(12 -11 1 :11 2 -NC{H} SiMe3)3.8 purple (9.3) 37.19 (37.08) 5.59 (5.67) 3.07 (3.09)[Cp* W(N0)(CH2SiMe3 )C1][Cp*W(C1)(11 2 -N{0 } {H} CH2SiMe3 )]-(µ-N)3.9 orange (13) 35.13 (35.09) 5.77 (5.57) 4.22 (4.38)Cp*W(NO)(CH2SiMe3)(Cl)(PMe3) 3.10 gold (58) 37.68 (37.27) 6.53 (6.44) 2.51 (2.56)a The elemental analysis of C is probably low because of incomplete combustion. Addition of V205 additiveto this oil did not correct this problem.Table 3.2. Mass Spectral and Infrared Data for Complexes 3.1 - 3.10compdno.MS, m/za tempo, °C IR, cm-1 (Nujol)VNO VSi-Me3.1 427 [Pt] 120 1596, 1586c3.2 447 [Pt] 120 1595, 1578c3.3 513 [Pt] 100 1593, 1557c3.4 509 [Pt] 120 1563 1254, 12423.5 529 [Pt] 100 1584, 1545c 1244, 12273.6 467 [P+] 1578 1262, 12463.7 481 [P+] 120 1566 1256, 12443.8 879d 120 1545 1240, 1154,937e3.9 820 100 1571 1251, 12333.10 525d471 [Pt- PMe3]100 1570, 1549 1282, 1236a m/z values are for the highest intensity peak of the calculated isotopic cluster,b Probe temperatures.c vc_c are also observed in this region.d The highest m/z peak reported is not assignable.e vw=0i.e. 98Mo and 184W.53Table 3.3. 1H and 13C{1H} NMR Data for Complexes 3.1 - 3.10 in C6D6compdno.1H NMR (5, ppm) 13C{1H} NMR (5, ppm)3.1 7.42 (d, 2H, o-ArH, 2JHH = 8.4 Hz) 147.3 (ipso C)7.15 (t, 2H, m-ArH, 2JHH = 12.0 Hz) 129.8, 128.4, 124.2 (CH2C6H5)6.98 (t, 1H, p-ArH, J^10 2 Hz)2 HH = _ ._ _ _, 112.8 (C5 (CH3)5)2.86 (d, 1H, CHACHB, 2414 = 8 .4 Hz) 83.0 (OC(CH3)3)2.77 (d, 1H, CHACHB, 24H = 8 .4 Hz) 50.0 (CH2C6H5)1.59 (s, 15H, C 5(CH3)5) 32.0 (OC(CH3)3)1.10 (s, 9H, OC(CH3)3) 9.7 (C5(CH3)5)3.2 7.3 - 6.8 (m, 10H, Ar-H) 167.6, 134.1, 130.2, 128.9, 128.8,3.42 (d, 1H, CHACHB, 2411 = 6 . 0 Hz) 119.9, 118.6 (aryl C)2.59 (d, 1H, CHACHB , 2JHH = 6.0 Hz) 112.3 (C5 (CH3)5)1.58 (s, 15H, C5 (CH3)5 ) 53.9 (CH2C6H5)9.8 (C5(CH3) 5)3.3 7.47 (d, 2H, o-ArH, 2JHH = 8.7 Hz) 147.4 (ipso C)7.20 (t, 2H, m-ArH, 2JHH = 7.5 Hz) 129.6, 128.0, 124.0 (CH2C6H5)6.98 (t, 1H, p-ArH, 2JHH = 7.2 Hz) 111.8 (C5(CH3)5)2.76 (d, 1H, CHACHB , J^11 2 Hz)2 HH =^_.^_^, 83.7 (OC(CH3)3)2.64 (d, 1H, CHACHB, 2JHH = 11.2 Hz) 46.0 (CH2C6H5)1.62 (s, 15H, C5 (CH3 )5) 31.8 (OC(CH3)3)1.08 (s, 9H, OC(CH3)3 ) 9.6 (C5 (CH3 )5)3.4 1.65 (s, 15H, C5 (CH3 )5) 112.5 (C5 (CH3)5)1.40 (s, 9H, OC(CH3)3) 83.2 (OC(CH3)3)0.81 (d, 1H, CHACHB, 2JHH = 12 . 9 Hz) 33.0 (OC(CH3)3)0.49 (s, 9H, Si(CH3)3) 27.4 (CH2)-0.24 (d, 1H, CHACHB, 2JHH = 12 . 9 Hz) 9.9 (C5 (CH3)5 )3.1 (Si(CH3 )3)3.5 7.28 (d, 2H, o-ArH, 2JHH = 7.5 Hz) 129.5, 123.0, 118.2, 100.3 (CH2C6H5)7.18 (t, 2H, m-ArH, 2JHH = 8.4 Hz) 111.9 (C5 (CH3)5)6.84 (t, 1H, p-ArH, 2JHH = 6.9 Hz) 44.4 (CH2)1.60 (s, 15H, C5 (CH3)5 ) 9.9 (C5 (CH3)5)0.25 (s, 9H, Si(CH3)3 )a 2.0 (Si(CH3)3)3.6 4.70 (s, 3H, OCH3) 111.7 (C5(CH3)5)1.59 (s, 15H, C5(CH3) 5) 70.4 (OCH3)0.92 (d, 1H, CHACHB, 2JHH = 12.0 Hz) 35.5 (CH2)0.84 (d, 1H, CHACHB, 2JHH = 12.0 Hz) 9.5 (C5 (CH3) 5)0.35 (s, 9H, Si(CH3 )3) 2.2 (Si(CH3)3)543.7 4.93 (q, 2H, OCH2CH3, 3fii = 6 . 9 Hz)1.53 (s, 15H, C5 (CH3)5)1.17 (t, 3H, OCH2CH3, 3JHH = 6 . 9 Hz)0.76 (d, 2H, CH2SiMe3, 2JHH = 2 .4 Hz)0.30 (s, 9H, Si(CH3 )3)111.8 (C5 (CH3)5)77.9 (OCH2CH3)34.0 (WCH2, Jwc = 55.0 Hz)20.7 (OCH2CH3)9.7 (C5 (CH3)5)2.2 (Si(CH3)3)3.8 2.64 (s, 1H, CH) 117.0 (C5(CH3)5)1.70 (s, 15H, C5(CH3)5) 111.2 (C5(CH3) 5)1.68 (d, CHAHB)b 75.2 (CH)1.65 (s, 15H, C5(CH3)5) 44.1 (CH2)0.68 (s, 9H, CHSi(CH3)3) 11.1 (C5(CH3) 5)0.40 (d, CHAHB)a 10.4 (C5(CH3) 5)0.40 (s, 9H, Si(CH3)3) 4.6 (Si(CH3)3)1.6 (Si(CH3)3)3.9 9.50 (dd, 1H, NH,3JHH = 5 - 4 Hz, 3Jii = 6 . 6 Hz) 115.1 (C5 (CH3)5)2.40 (dd, 1H, N-CHAHBSi(CH3)3, 344H = 5 . 4 Hz,2JHH = 14.6 Hz)c105.5 (C5 (CH3)5)40.1 (CH2)1.90 (s, 15H, C5 (CH3)5 ) 28.2 (CH2)1.76 (s, 15H, C5 (CH3 )5 ) 6.1 (C5 (CH3)5)1.19 (d, 1H, W-CHA,HB,Si(CH3)3, 2JHH = 9.8 Hz,2Jwii = 3.9 Hz)5.6 (C5 (CH3)5)0.3 (Si(CH3 )3)0.69 (s, 9H, Si(CH3 )3 ) -6.7 (Si(CH3 )3)0.10 (s, 9H, Si(CH3)3 )0.45 (d, 1H, W-CHABB,Si(CH3)3 , 2JHH = 9 . 8 Hz)3.10a 1.53 (s, 15H, C5(CH3)5) 108.6 (C5 (CH3)5)1.13 (d, 9H, P(CH3)3 , 2JHp = 9.6 Hz) 26.5 (d, CH2, 2Jcp = 8.3 Hz)0.58 (s, 9H, Si(CH3)3) 12.1 (d, P(CH3)3 , 1../cp = 29.7 Hz)0.34 (d, 1H, CHAHB, 2JHH = 10.8 Hz) 9.9 (C5(CH3) 5)-0.33 (dd, 1H, CHAHB, 2JHH = 10.8 Hz,3./Hp = 2.4 Hz)4.4 (Si(CH3)3)a The signals attributable to CH2Si(CH3)3 were not observed.b Signal was assigned using a COSY spectrum of the sample.C The signal attributable to N-CH AHBSi(CH3)3 was not observed.d The 31P( 1 1.1) NMR (81.015 MHz) spectrum of 3.10 in C6D6 exhibited a signal at 6.88 ppm ( 1Jpw = 191 Hz) dueto coordinated PMe3 .3.4 Results and DiscussionDr. E. C. Phillips of our laboratories previously attempted to prepare alkoxo alkyl complexesby treating dialkyl complexes with alcohols (eq 3.1).6,12Cp'M(NO)R2 + R'OH ----► Cp'M(NO)(R)(OR') + RH (3.1)N N0 0R'0' -'Cl^RON0551 H NMR spectra of these NMR-scale reaction mixtures exhibited signals which were consistentwith the alkoxo alkyl complexes Cp *W(NO)(CH2Ph)(OMe), Cp'W(N0)(CH2SiMe3)(0Me),CpW(NO)(CH2SiMe3)(OCMe3) and CpW(N0)(CH2SiMe3)(0C6H4-p-Me). However, attemptsto isolate these alkoxo alkyl complexes were unsuccessful. From these experiments it wasconcluded that alkoxo alkyl complexes were synthesizable, but not isolable, under theexperimental conditions depicted in equation 3.1. I therefore set out to prepare these complexesby a different synthetic route.3.4.1 Synthesis of Alkoxo Alkyl ComplexesThree different routes to preparing alkoxo alkyl complexes can be envisioned as summarizedin Scheme 3.1.Scheme 3.11^2^3RP\R2Mg/OR' N.WO/ zNO56The first route to the preparation of alkoxo alkyl complexes involves the metathesis of a chlorideligand for an alkyl group. This type of reactivity has precedent in the literature, as the[HB(3,5-Me2C3HN2)2]Ti(OR)C12 species will react with Grignard reagents to form alkoxodialkyl complexes. 13 However, treatment of Cp *Mo(NO)(OCMe3)Cl with(PhCH2)2MgX(dioxane) results in the production of the 18-electron Cp*Mo(NO)(CH2Ph)Clcomplex and not the desired Cp *Mo(NO)(OCMe3)(CH2Ph) species (eq 3.2).2Cp*Mo(NO)(OCMe3)Cl^(PhCE12)mg■ Cp*Mo(N0)(CH2Ph)C1^(3.2)- (PhCH2)Mg(OCMe3)The Et20 reaction mixture turns from the distinctive purple color of the precursor monoalkoxocomplex to orange, characteristic of Cp *Mo(NO)(CH2Ph)Cl, over the course of 1 h. Reaction3.2 is the result of metathesis of an alkoxide ligand rather than a halide ligand, the driving forcelikely being the formation of a very strong magnesium-oxygen bond. 14 This type of reactivity hasprecedent in the literature and, in fact, metathesis of alkoxide ligands is often used to prepare alkylcomplexes in systems where the metal halide complex is prone to reduction by Grignardreagents. 15Since reaction 3.2 demonstrates that alkoxo groups can be replaced by alkyl groups via ametathesis reaction, I attempted to utilize this type of reactivity to prepare alkyl alkoxo complexes(cf. route 2 of Scheme 3.1). Unfortunately, no reaction occurs between Cp *Mo(NO)(OCMe3 )2and (PhCH2)2MgX(dioxane) in THE overnight, even at elevated temperatures.Cp*Mo(NO)(OCMe3)2^(Ph012)2Mg No Reaction^(3.3)THF, 65 °CNo color changes are observed, and the solution IR spectra of aliquots of the reaction mixtureexhibit bands attributable to only the starting material. It has been demonstrated (Chapter 2) thatthe electronically saturated bis(alkoxo) complexes are extremely stable towards a number ofreagents due to ic-electron donation from the alkoxo groups, and so this lack of reactivity is notoverly surprising. The alkoxo chloro species do react with Grignard reagents (eq 3.2),(3.4)•M'OR'-M'ClR^OR'057presumably because the chloro complexes are less sterically crowded and/or less electron rich thanthe bis(alkoxo) complexes.The third route envisioned to alkyl alkoxo complexes is an alkoxide for chloride metathesisreaction. Alkoxo alkyl complexes, Cp *M(N0)(R)(OR') (3.1 - 3.7), are successfully prepared bytreating the appropriate alkyl chloro precursor with an alkali metal alkoxide salt.Reaction 3.4 is conducted in pentane or Et 20. Normally, metathesis reactions are performed inpolar solvents such as THF in order to stabilize ionic intermediates. However, if reaction 3.4 isconducted in THF, the only products are intractable amber oils, and no alkoxo alkyl species areformed. The limiting factor in preparing this family of alkoxo compounds by metathesis reactions(eq 3.4) is the availability of the requisite alkyl chloro precursors. Until very recently, 16 only thebenzyl chloro7 and trimethylsilylmethyl chloro 9,10 complexes, Cp*M(NO)(R)Cl [M = Mo,R = CH2Ph; M = W, R = CH2Ph, CH2 SiMe3] were available. Therefore, the seven alkoxo alkylcomplexes prepared during this work have been made from these starting materials. LiOCMe3,NaOCMe3 , NaOPh, NaOMe and KOEt can be used as alkoxylating reagents. The potassiumalkoxide salts, KOCMe3 and KOMe cannot be used since they do not afford the desired alkoxoalkyl complexes (Section 3.4.4).The desired organometallic products are isolable from reactions 3.4 in yields that range from20 - 67% (Table 3.1). The low isolated yields of complexes 3.4, 3.6 and 3.7 may be attributed totheir high solubility in pentane. Of the complexes 3.1 - 3.7, Cp *W(NO)(CH2SiMe3)(OCMe3)(3.4) and Cp *W(NO)(CH2SiMe3)(OEt) (3.7) are isolated as red oils. Complex 3.6 is thermallysensitive as a solid, its crystals undergoing decomposition to a brown oil if left at roomtemperature overnight.583.4.2 Characterization of Alkoxo Alkyl ComplexesThe spectroscopic properties of complexes 3.1 - 3.7 are collected in Tables 3.2 and 3.3. Inthese systems, the nitrosyl-stretching frequency in the IR spectrum of a given complex isdiagnostic of the electronic environment at the metal. 17 For example, as more electron density isdonated from the ancillary ligands to the metal, the metal has more electron density to donate intothe 7t* orbital of the nitrosyl ligand. As the n* orbital is filled, the N-0 bond lengthens andweakens, and the vm, decreases in frequency. Since alkoxide ligands can donate more electrondensity to the metal (Section 2.4.1) than alkyl ligands, alkoxo complexes generally have lowervN0's than analogous alkyl complexes. As expected, the nitrosyl-stretching frequencies of thealkoxo alkyl complexes lie midway between those for the symmetric bis(alkyl) and the bis(alkoxo)complexes. For instance, the v No exhibited in the IR spectrum ofCp*W(N0)(CH2 SiMe3)(0CMe3 ) as a Nujol mull is 1563 cm -1 , whereasCp*W(NO)(CH2SiMe3) 2 and Cp*W(NO)(OCMe3)2 exhibit nitrosyl-stretching frequencies of1572 and 1550 cm-1 , respectively, in their Nujol mull IR spectra.The formulation of compounds 3.1 - 3.7 as monomeric entities is supported by their low-resolution mass spectral data, since for all of these alkoxo alkyl complexes parent ions areobserved. The C 6D6 1H NMR spectra of 3.1 - 3.7 are straightforward (Table 3.3). The onlyexception to this generalization is the 11-INMR spectrum of 3.5. Although the signals attributableto the methylene protons are not observed in the 1H NMR spectrum, the resonance attributable toCH2 is clearly observed in the 13 C{ 1H) NMR spectrum of 3.5 at 8 44.4 ppm.It is reasonable to assume that the trimethlysilyl complexes 3.4 - 3.7 receive additionalelectron density from their alkoxide ligands in a manner similar to bis(alkoxo) and alkoxo chlorocomplexes (see Chapter 2). However, it has been shown that benzyl complexes can attainelectron sufficiency at their metal centers by coordinating the benzyl ligand in an ri 2 fashion. 6,7As demonstrated by X-ray crystallography, bis(benzyl) complexes, Cp'M(NO)(CH 2Ph)2 ,6 andbenzyl chloro complexes, Cp 1M(N0)(CH2Ph)C1, 7 are 18-electron species by virtue of one benzylligand functioning as a three-electron donor. Therefore, to attain electron sufficiency at their59metal centers, the benzyl alkoxo species, Cp *M(NO)(CH2Ph)(OR), can, in principle, adopt one oftwo bonding modes shown below:The 1H and 13 C { 1H} NMR spectral data of these compounds clearly distinguish between thesetwo structural possibilities. For instance, the ipso carbon chemical shift at 6 147 ppm (Table 3.3)in the 13 C { 1H} NMR spectrum of Cp *Mo(NO)(CH2Ph)(OCMe3) (3.1) in C6D6 is diagnostic foran i 1 -benzyl ligand. 6 An APT experiment confirms the assignment of this resonance as the signalattributable to the ipso carbon. Furthermore, the 1H NMR spectrum of 3.1 in C 6D6 (Figure 3.1)exhibits an AB pattern due to the diastereotopic methylene protons, for which the low-fieldchemical shifts (6 2.86 and 2.77 ppm) and the large 24.11{ coupling constant (8.4 Hz) are typical ofthose displayed by 1 1 -benzyl ligands. 6 It thus appears that the benzyl ligand is functioning as aone-electron donor in complexes 3.1 - 3.3, and it donation from the alkoxide ligand providesadditional electron density to stabilize the metal centers.3.4.3 Related SystemsThere are several related alkoxo alkyl systems reported in the literature. Group 4 alkoxoalkyl complexes, Cp 2Ti(OR)(CH3) [R = alkyl and acylJ, valence isoelectronic analogues ofcomplexes 3.1 - 3.7, are prepared by alcoholysis of Cp 2Ti(CH3)2 18,19 Bergman's group hasobtained two late-transition-metal alkoxo alkyl systems. Cp *Ir(PPh3)(Me)(OR) [R = acetyl,phenyl] complexes were prepared in order to investigate the properties of Ir-O linkages as60JIIIIIIIITIIIIIIIiritimirIIIIIIIIIIIIIIIIIIII1IIIIIirlimillli PPMFigure 3.1 1H NMR spectrum of Cp *Mo(NO)(CH2Ph)(OCMe3) in C 6D6 .6 1compared to Ir-N bonds,20 and the ruthenium system, (PMe3 )4Ru(Me)(OC{CH2 }Me), is knownto exist as an equilibrium mixture of the oxygen- and carbon-bound transition metal enolates. 21Recently our group has published a paper on the synthesis of the alkyl amido complexesCp*M(N0)(R)(NHCMe3 ) {M = Mo, W; R = CH2CMe3 , Me].4 These complexes are prepared bytreating the appropriate alkyl chloro precursor, Cp *M(NO)(R)Cl, with an excess of amine. Likethe alkoxo alkyl complexes, the 18-electron amido analogues are stabilized by donation ofelectron density from the heteroatom to the metal. A sulfur analogue,CpW(N0)(SCH2 SiMe3 )(CH2SiMe3 ), is also preparable from CpW(NO)(CH 2SiMe3 )2 by directinsertion of elemental sulfur into one of the metal-alkyl bonds. 23.4.4 Unique ReactionsThe preparation of alkoxo alkyl complexes requires a sagacious choice of alkoxylatingreagent. As noted above, Cp *W(NO)(CH2 SiMe3 )(OEt) (3.7) is prepared from reaction ofCp*W(N0)(CH2SiMe3)C1 and the potassium salt, KOEt. However, in the synthesis of eitherCp*W(NO)(CH2SiMe3)(OCMe3) or Cp *W(NO)(CH2SiMe3)(OMe), the use of the potassiumreagents, KOCMe3 or KOMe, results in the preparation of the bimetallic complexes[Cp *W(N0)(CH2SiMe3)][Cp *W(C1)(0)]-(22-1 1 :12-NC {H} SiMe3) (3.8) and[Cp *W(N0)(CH2 SiMe3 )Cl][Cp *W(C1)(n 2-N{ 0 } {H}CH2SiMe3)]-(1A-N) (3.9), respectively.2/7\Me3 SiC H2 = Cl0623.4.4.1 Synthesis of [Cp *W(N0)(CH2SiMe3)1[Cp *W(C1)(0)1-(.12-11 1 :112-NC{H}SiMe3)[Cp*W(N0)(CH2SiMe3)][Cp *W(C1)(0)]-(42-11 1 :112-NC(H)SiMe3) (3.8) is produced by theheterogeneous reaction between Cp *W(N0)(CH2SiMe3)CI and KOCMe3, i.e.,C l`2 KOCMe3 , pentane —N—Wt^o^ 3 SiC H2 =^\C4I\ 0N^0^/SiMe3(3.5)Reaction 3.5 can be monitored by IR spectroscopy, since the blue reaction mixture(vN0 1616 cm-1 ) slowly turns red-purple (vNo = 1624, 1570 cm -1 ) as it is warmed to roomtemperature. The product 3.8 is isolated as purple needles in low yields from pentane. The lowyield can be attributed to the extreme solubility of the complex. Complex 3.8 is both air- andtemperature-sensitive. Thus, 1H NMR spectroscopy shows that C 6D6 solutions of 3.8decompose thermally (120 °C) and that 3.8 reacts rapidly with 0 2 , as a solid or in solutions, toform the known Cp *W(0)2(CH2SiMe3 ) complex. 22For the successful synthesis of 3.8, the choice of both the solvent and the cation of thealkoxide salt is crucial. For example, if reaction 3.5 is performed in THE or Et 20,Cp*W(N0)(CH2SiMe3)(OCMe3) (3.4) (-30% yield) is produced rather than the bimetalliccomplex 3.8. Similarily, if the alkoxylating reagent is changed to either the sodium or the lithiumtertiary butoxide salt, 3.4 is also produced.3.4.4.2 Characterization of Complex 3.8The infrared spectrum of 3.8 as a Nujol mull (Figure 3.2) exhibits a low-energy vislo at1545 cm-1 and a vsic at 1240 cm -1 . Typically, terminal W=0 stretches appear between 1058 and922 cm -1 in the infrared spectrum of terminal oxo-containing complexes; 23 therefore, the band atFigure 3.2 Nujol (marked by X) mull infrared spectrum (1658 - 490 cm-I) of complex 3.8.64937 cm-1 in the IR spectrum of complex 3.8 is assigned to the vw.o. The values of vw=0 andvSiC may be compared with those of CpW(0)(CH2SiMe 3)3 which as a Nujol mull exhibits avw=0 at 941 cm -1 and vsi_c's at 1259 and 1240 CM-1 . 24 The band at 1154 cm -1 of the IRspectrum of 3.8 is most probably a N-C stretch,25 but confirmation of this assignment requiresisotopic labeling of the bridging nitrogen.The 1H NMR spectrum of [Cp *W(N0)(CH2SiMe3)][Cp *W(C1)(0)]-(22-1 1 :12-NC{H}SiMe3 ) (Figure 3.3) exhibits two resonances attributable to the Cp* ligands(5 1.70 and 1.65 ppm) and two signals attributable to the SiMe3 groups (5 0.68 and 0.40 ppm).The singlet at 5 2.67 ppm is assigned to the hydrogen of the bridging ligand. Although theinequivalent methylene proton resonances are obscured in the standard 1H NMR spectrum, theycan be observed in the COSY spectrum of 3.8. Thus, the resonances attributable to the methyleneprotons appear as doublets at 5 1.68 and 0.40 ppm in the off-diagonal peaks of the C6D 6 COSYspectrum of 3.8. In addition to the signals due to the two inequivalent Cp* ligands and the twoinequivalent SiMe 3 groups, the 13 C{ 1H} NMR spectrum of 3.8 clearly shows the signalsattributable to the CH of the bridging ligand and the methylene carbon at 5 75.2 and 44.1 ppm,respectively.The structure of complex 3.8 has been determined by X-ray crystallography by Dr. S. J.Rettig. 27 The ORTEP diagram of 3.8 is shown in Figure 3.4 and some selected bond lengths andangles are located in Table 3.4. The bimetallic complex 3.8 possesses a 14e - [Cp*W(CI)(0)]fragment and a normal 15e - Cp *W(NO)(CH2SiMe3) fragment. The two metals are bridged by aNC{H}SiMe3 ligand.651111^It^lit^ ►^!ILI3.0^2.5 2.0^1.5^1.0^0.5 PPM^0.0Figure 3.3 1H NMR spectrum of [Cp *W(N0)(CH2SiMe3)}[Cp*W(C 1)(0)]-(112-11 1 :12-NC(H)SiMe3) in C6D6 .66Figure 3.4 ORTEP diagram of [Cp *W(N0)(CH2SiMe3)][Cp *W(C 1 )(0)] - (1A2 -71 1 : 112-NC(H)SiMe3 ). 33% probability thermal ellipsoids are shown for the non-hydrogen atoms.Table 3.4. Selected Bond Lengths and Bond Angles for 3.8bond lengths (A) bond angles (°)WI - NI 2.004 (7) WI - NI - W2 143.8 (4)W2 - NI 1.969 (7) W1 - NI - C21 74.9 (5)NI -C21 1.44(1) W2-N1-C21 137.8(6)WI - C21 2.14 (1) W2 - N2 - 02 166.4 (8)W1 - 01 1.697 (8)67The [Cp*W(Cl)(0)] fragment has four-legged piano-stool type geometry about Wl, whereas,the Cp *W(NO)(CH2SiMe3 ) fragment has normal intramolecular parameters for a three-leggedpiano stool complex. These geometries are most clearly seen below in the Newman projections ofthe W1 fragment and the W2 fragment of complex 3.8, each looking down the W - Cp * centroidaxis.The W1-01 bond length for complex 3.8 is 1.697 (8) A, well within the typical range for terminaloxo ligands (1.58 - 1.78 A). 28 For comparison, CpW(0)(CH 2SiMe)3 has a W-0 bond length of1.664 (8) A. 24 The typical linear (166.4 (8)°) nitrosyl ligand of W2 has W2 - N2 and N2 - 02bond distances of 1.767 (8) and 1.22 (1) A, respectively. The bridging ligand, NC{H)SiMe3 , is1 2 to WI and ill to W2, thereby acting as a two-electron donor to WI and a one-electron donorto W2. In this way, each metal center attains a 16-valence-electron configuration. The geometryabout C21 is approximately tetrahedral, i.e., W1 - C21 - Sil = 120.0 (5)° and N1 - C21 - Sil =123 (2)°.Overall, the structure indicates there is a formal loss of HC1 and no incorporation ofKOCMe3 in reaction 3.5. For a discussion on the possible mechanism of this reaction, seeSection 3.4.8.683.4.4.3 Synthesis of [Cp *W(N0)(CH2SiMe3)C1][Cp *W(C1)(92-1■1{0}{H)CH2SiMe3)1-(L-N)To determine if reaction 3.5 is independent of the type of potassium alkoxide salt used,Cp*W(NO)(CH2SiMe3)Cl was treated with potassium methoxide in pentane, i.e.,CW N EEWOW'^',"oR = `Cl0^R = CH2 S1Me31 KOMe, pentaneR CI-- —H-- 1\T\RThe heterogeneous reaction mixture turns from blue to orange over the course of 5 h, and thebimetallic complex 3.9 is isolated as orange crystals from Et20 in 13% yield (based onCp*W(NO)C12). Complex 3.9 is thermally sensitive and decomposes readily to the known oxocomplex, Cp *W(0)2(CH2 SiMe3),22 in the presence of oxygen.Reaction 3.6 does not occur in solvents other than pentane, nor with other methoxide salts.For instance, treatment of Cp *W(NO)(CH2SiMe3)Cl with KOMe in THE or with NaOMe inpentane, results in the formation of Cp*W(NO)(CH 2SiMe3)(OMe) (3.6) (vide supra).An important feature of reaction 3.6 is that Cp *W(0)2(CH2SiMe3) is also produced (31%isolated yield based on Cp*W(NO)C1 2). An NMR-scale reaction showed that the final reactionmixture contained a ratio of Cp *W(0)2(CH2SiMe3) to 3.9 of 1:0.6. The Cp*W(0)2(CH2SiMe3 )produced in reaction 3.6 is not a result of the decomposition of the air-sensitive product complex.Cp*W(0)2(CH2SiMe3) was originally prepared from the dialkyl complex according toequation 3.7. 22Cp*W(NO)(CH2SiMe3)2 + 02^CP*W(0)2(CH2SiMe3)^(3.7)To date, the mechanism of reaction 3.7 is uncertain; however, one of the by-products of thisreaction is thought to be the powerful oxidizing agent, Me 3 SiCH2NO. It has been established69independently that PhNO in Et 20 converts the dialkyl complex to the dioxo species in low yields(20 - 25%).12,22Cp *W(N0)(CH2SiMe3)2 + PhNO^Cp*W(0)2(CH2SiMe3)^(3.8)In reaction 3.6, the by-products from the production of Cp *W(0)2(CH2SiMe3) may be reactingwith Cp *W(NO)(CH2SiMe3 )Cl to produce complex 3.9. This type of rationale may account forthe extra nitrogen atom in the product.3.4.4.4 Characterization of Complex 3.9The Nujol mull 1R spectrum of complex 3.9 (Figure 3.5) exhibits a broad vNo band at1571 cm -1 and two absorptions due to Si-C stretches at 1252 and 1233 cm -1 . The nitrosyl-stretching frequency is lowered by 28 cm -1 from that of the starting material, a feature consistentwith the tungsten center (W1) in 3.9 being more electron-rich than in the precursor complex. Inunsymmetrically bridging transition-metal nitrides of the type M=N-M, the absorption due to theM-N bond is found in the range 948 - 1125 cm-1 . 23 In this region, and in the terminal oxo region(960 - 885 cm-1 ), there are a number of bands in the IR spectrum of 3.9, so neither of thesestretching frequencies could be assigned unambiguously.The 1 H NMR spectrum of [Cp *W(N0)(CH2SiMe3)Cl][Cp *W(C1)01 2-N{O} (H)CH2 SiMe3 )]-(11-N) in C6D6 (Figure 3.6) exhibits two inequivalent Cp * resonances andtwo inequivalent SiMe3 resonances. The diastereotopic methylene protons of the simple alkylgroup resonate at 5 1.19 (2J = 9.8 Hz, Jwii = 3.9 Hz) and -0.45 ppm (2JHH = 9.8 Hz). Thesignal at low field (5 9.50 ppm) is attributable to the hydrogen of the N(0){11}CH 2 SiMe3 ligand(Figure 3.6 inset). The coupling pattern of this signal ( 3JRxiim = 5.4, 3.41xNa = 6.6 Hz) is a resultof coupling to the diastereotopic methylene protons of the N-bound alkyl group. The signals dueto the diastereotopic methylene protons of the N-bound alkyl group should appear as twodoublets of doublets. Only one of these doublet of doublets is observed at 5 2.40 ppm (2JHaFli„ =14.7 Hz, 3J}ixilm = 5.4 Hz). The other methylene-proton signal, probably obscured in the Cp*IO.1*I I•ar\,t/11 I^1^11395^1105 816 527wavenumbers (cm -1 )rN\ I•C)^warpMN001...170Figure 3.5 Nujol (marked by X) mull infrared spectrum (1684 - 527 cm - 1 ) of complex 3.9.71Figure 3.6 1 H NMR spectrum of [Cp*W(N0)(CH2SiMe3)(C1)][Cp*W(C1)(r12-N{0}{H)CH2SiMe3)]-(i-N) in C6D6. Insets show the spectral regions 5 9.64 - 9.36 ppm and5 2.48 - 2.12 ppm.3JH„H. = 6.6 Hz 2jHan =14.7 Hz 2jHan = 14.7 Hz3JR,H,„ = 5.4 Hz 3JR,,Hm = 5.4 Hz^3JR,fla = 6.6 Hz72resonances, should show couplings of 2JHailin = 14.7 Hz and 3JR,dia = 6.6 Hz. A representationof the coupling in this three-spin system is depicted below.An X-ray crystallographic analysis was performed by Dr. S. J. Rettig on a single crystal of3.9. 29 Selected bond lengths and angles for this complex are located in Table 3.5. A view of 3.9(Figure 3.7) shows the four-legged piano-stool molecular geometry about each electronicallysaturated tungsten center.The W1 moiety is essentially a 1:1 adduct of Cp*W(NO)(CH2SiMe3)Cl with the nitridoligand of the W2 fragment acting as a Lewis base. Surprisingly, the bridging nitrido ligand issituated cis to the nitrosyl ligand and trans to the alkyl ligand. This is not expected sincemolecular orbital calculations and X-ray crystallographic analyses have indicated that the vacantcoordination site in 16-electron complexes of the type Cp'M(NO)(Y)(Z) [Y, Z = 1-electronligand] is located trans to the NO ligand. 30 The solid-state molecular structure ofCp*W(N0)(CH2SiMe3)CI has been previously reported and the angle between the alkyl groupand the chloride ligand (C - W - Cl) is 109.9°, thereby indicating this is the most accessible site atthe W atom (Table 3.6). 9 Chemically, it has also been demonstrated thatCp*W(NO)(CH2SiMe3)Cl (Section 3.4.6) and Cp *M(N0)(CH2CMe3)C1 16 form 18-electronmetal-centered phosphine adducts in which the phosphine coordinates trans to the nitrosyl group.73Figure 3.7 ORTEP diagram of [Cp *W(N0)(CH2SiMe3)(C1)][Cp *W(C1)(i2-N{0}(H}CH2SiMe3 )]-(1-N) with 20% probability thermal ellipsoids.Table 3.5. Selected Bond Lengths and Bond Angles for 3.9bond lengths (A) bond angles (°)W1 - N3 2.10 (1) WI - N3 - W2 168.0 (7)W2 - N3 1.72(1) N2 - W2 - 02 41.6(4)W2 - 02 1.93 (I) W2 - 02 - N2 75.7 (6)W2 - N2 2.10 (I) W2 - N2 - 02 62.7 (6)NI -01 1.22(I) 02 - N2 - C25 117(1)N2 - 02 1.44 (1) W1 -N1 -01 175 (1)C11 -H1 2.29 N2 - HI -C11 144.974Table 3.6. Bond Angle Comparisons between 3.9 and Cp*W(NO)(CH2SiMe3)Clbond angles (°)3.9bond angles (°)Cp*W(NO)(CH2SiMe3)ClC11 - W1 - Ni 129.3 (5) Cl - W - N 102.0 (3)Cll - W1 - C11 75.8 (4) C - WI - Cl 109.9 (3)Ni -W1 -C11 166.6 N - WI - Cl 94.4(4)The novel N{0}{H}CH2SiMe3 ligand is bound in an 12 fashion to W2. The geometry aboutN2 is approximately trigonal planar, with H1/C25/02 defining the plane. Thus, H1 - N2 - 02 =119.9°, C25 - N2 - 02 = 117 (1)° and C25 - N2 - HI = 107.7°. The bond distances W2 - N2(2.10 A) and N2 - 02 (1.93 A) suggest single bonds between these atoms; whereas, the distancebetween W2 and 02 (1.93 A) indicates there is some degree of multiple bond character in thislink. 31 Several resonance structures could be drawn for this ligand. Overall, the712-N{0} {H}CH2 SiMe3 ligand must donate a total of three electrons to W2 to satisfy the 18-electron rule. The bonding of this ligand could be viewed as first involving formal transfer of oneelectron to the metal (thereby forming a [N{0}{H}CH2SiMe3r ligand), then donation of 2electrons from a it-type molecular orbital on [N{0}{H}CH2SiMe31 + to empty d orbitals ontungsten. In this way, the bonding of [N{0}{H}CH 2SiMe3 r would be similar to the bonding ofan ri2-ketone to a transition metal. Molecular orbital calculations on this type of ligand arerequired to fully explain how N{O} {H}CH2SiMe3 binds to this metal center.75The intramolecular dimensions of the N{0}{H)CH2SiMe3 ligand in 3.9 can be compared tothose of the nitrosobenzene ligand in Cp *W(112 -N{O}Ph)(NPh)(Ph), 32 i.e.,The bond lengths of the nitrosobenzene ligand in Cp*W(1 2-N(0)Ph)(NPh)(Ph) are similar to thatfound in the N{0}{H)CH2 SiMe3 ligand in 3.9. Whiler12-N{O}Ph is a two-electron donor totungsten, N{0}{}1}CH2SiMe3 provides three electrons to the tungsten in 3.9.The bridging nitrido ligand is essentially linear with a W1 - N3 - W2 angle of 168.0°. Thedistance between WI - N3 (2.10 (1) A) indicates a single bond, whereas the distance betweenW2 - N3 (1.72 (1) A) suggests N3 is triply bonded to W2. 33 These distances can be compared tothose between W2 - N2 (2.10 (1) A) and W1 - N1 (1.77 (1) A). The bridging nitrogen functionsas a three-electron donor to W2 and a two-electron donor to Wl, thereby satisfying each metal'selectronic requirements. In other words, the nitrido ligand acts as a simple Lewis base to the16-electron Cp *W(NO)(CH2 SiMe3)Cl fragment (vide supra). There are very few examples ofthis kind of nitrido bridging group, and most of them are found in polymeric species. 23 Thus,comparisons can be made between (W(1-N)(0CMe3)3 ). and 3.9.34 For instance,{W(µ-N)(0CMe3)3} 0, contains the same type of bridging unit as complex 3.9 (i.e., WEN-4W).In this polymer, the WEN bond length is 1.740 (15) A, and the dative N-4W bond distance is2.661 (15) A, barely short enough to call a bond. 35An interesting feature of complex 3.9 is that it contains an intramolecular hydrogen bondbetween HI located on the N(0) {H}CH 2SiMe3 ligand of W2 and the chloride ligand on W1 .The hydrogen-chlorine bond distane (2.29 A) is in the range expected for hydrogen bonding.3676The N-H•••C1 angle is 144.9°. Hydrogen bonding is common in organic 37 and inorganicchemistry.38 Some of the most common types of inorganic complexes that contain hydrogenbonds are amine complexes of Co(III), Rh(III), Ru(III), and Cr(III). In these species thehydrogen bond is between the N-H moiety and the halide counteranion. 39a-d[Ir2(C0)2(p-OH•C1)(dppm)2] contains a hydrogen bond between the bridging hydroxide ligandand the chloride counteranion, 39e (Ph4C4CO)(CO)2Ru(NHEt2) has a hydrogen bond between thecarbonyl oxygen and the amide hydrogen, 39f and a seven-coordinate tungsten(II) metallacyclecomplex contains both inter- and intramolecular bonds between chloride ligands and amidehydrogens. 39g Intermolecular hydrogen bonding has been invoked to explain the rate accelerationof carbonylation reactions involving manganese a-hydroxyacyl complexes. 39h Fryzuk andcoworkers have attributed the stereoselective formation of octahedral Ir(III) and Rh(III)complexes to an intermediate involving a H-bond. 39 i3.4.5 Trapping Attempts with PhosphinesTo gain some insight into the above-mentioned complicated reactions, selected experimentswere performed in an attempt to trap any possible intermediates of reactions 3.5 and 3.6.Since PPh3 does not coordinate to the precursor complex, Cp *W(N0)(CH2 SiMe3)C1, thereaction of Cp*W(NO)(CH2SiMe3)Cl with KOCMe 3 was performed in the presence of PPh 3 .Cp*W(N0)(CH2 SiMe3)C1 + KOCMe3 + PPh 3^3.8^(3.9)Since the reaction proceeds to form the bimetallic complex 3.8 despite the presence of PPh3 , it ispossible that PPh3 is also too large to coordinate to any intermediate species.The smaller phosphine, PMe3, reacts readily with 16-electron alkyl chloro complexes to formmetal-centered adducts, Cp *M(NO)(R)(Cl)(PMe3). 16 In this work,Cp*W(NO)(CH2SiMe3)(Cl)(PMe3) (3.10) was prepared in a similar fashion fromCp*W(N0)(CH2SiMe3)CI and an excess of PMe3.PMe3ON 7 ClMe3 SiCH2^ClN Me3SiCH2 PMe30(3.10)77Like the other yellow 1:1 metal-centered adducts previously prepared,Cp*W(NO)(CH2SiMe3)(C1)(PMe3 ) (3.10) is an air- and temperature-stable complex which showsno tendency to undergo isomerization or phosphine dissociation. Complex 3.10 exhibits twovNO's (1570, 1549 cm-1) in its Nujol mull IR spectrum. Each of these stretches are significantlylower than the vNo of the starting alkyl chloro complex (1599 cm-1), thus indicating that themetal center in 3.10 becomes more electron rich with the addition of the Lewis base. The 1HNMR spectrum for 3.10 (Figure 3.8) exhibits signals that are diagnostic for a 4-legged piano-stoolmolecular structure having the phosphine trans to the nitrosyl ligand. 2,16 The stereochemistry atthe metal is clearly seen in the Newman projection of Cp *W(N0)(CH2SiMe3 )(C1)(PMe3 ) (3.10)down the W - Cp* centroid axis, i.e.,The methylene protons of the alkyl group are positioned such that HA is transoidal to the PMe3ligand (3./Hp = 2.4 Hz) and HB is cisoidal (3JHp = 0 Hz). The 31P{ 111} NMR spectrum of 3.10exhibits a signal at 5 6.88 ppm (Jpw = 95.3 Hz) due to coordinated PMe3 . The coupling totungsten is clear evidence for a metal-centered adduct.Complex 3.10 was made to be used as a reagent in subsequent reactions that attempted totrap intermediate complexes on the way to complexes 3.8 and 3.9.78Figure 3.8 1H NMR spectrum of Cp *W(N0)(CH2SiMe3)(CI)(PMe3 ) in C6D6 . Inset shows thespectral region 5 -0.29 to -0.39 ppm.Scheme 3.279pentaneON^ClMe3 SiC H2 PMe3KOCMe3-PMe3KOMe/WiMe3 SiCH2^OCMe303.4No ReactionIt was hoped that complex 3.10 would react with the potassium alkoxide salts to produce anintermediate species of reactions 3.5 and 3.6. However, Cp *W(NO)(CH2SiMe3)(Cl)(PMe3)(3.10) reacts with KOCMe3 to produce Cp *W(NO)(CH2 SiMe3 )(OCMe3) (3.4), and the18-electron phosphine adduct does not react at all with KOMe in pentane (Scheme 3.2).3.4.6 Deuterium-Labeling ExperimentsIn an attempt to determine the source of the hydrogen involved in H-bonding in compound3.9, Cp *W(N0)(CH2 SiMe3 )C1 was treated with KOCD3. Under the same experimentalconditions as reaction 3.6, KOCD3 effects the metathesis of the chloride ligand to formCp *W(NO)(CH2SiMe3)(OCD3) (3.6-d3).Cp*W(NO)(CH2SiMe3)Cl^i Cp *W(NO)(CH2SiMe3)(OCD3) +Cp*W(0)2(CH2SiMe3)^(3.11)In this reaction, Cp *W(0)2(CH2SiMe3) is also isolated in low yields (9.1%), and there is noevidence for the formation of a bimetallic complex such as 3.9. 1H NMR spectroscopy(Figure 3.9) shows a ratio of 1:5 of the dioxo alkyl species and complex 3.6-d3 with no bimetallicspecies present. In comparison, a similar NMR tube experiment of reaction 3.6 demonstrated the•(a)IIIIIIIIIIIII^li I IIIIIII[IIIIIIIIIIIIIIr (11111111111d10^8 4 ^PPM(b)XX•_^■ If milittreiliiiitIliiriiiiIIIIII^diiiitiiirtiliiiiitMil10^ PP80Figure 3.9 1H NMR spectra in C6D6 (•) of the reaction mixtures of (a)Cp*W(N0)(CH2SiMe3)(C1) and KOCD 3 (b) Cp*W(NO)(CH2SiMe3)(Cl) and KOCH3 . Theresonances attributable to Cp *W(0)2(CH2SiMe3) are marked with x's.81ratio of the dioxo alkyl species to 3.9 of 1:0.6. In this case no signals due to the alkoxo alkylcomplex were observed. For clarity, these product ratios are tabulated below.Table 3.7. Product Ratios for the Reactions of Cp *W(NO)(CH2SiMe3)Cl with KOCH3 andKOCD3Reactants Cp*W(0)2(CH2SiMe3) 3.6 (or 3.6-d3) 3.9Cp *W(NO)(CH2SiMe3)Cl + KOCH3 1 0 0.6Cp*W(NO)(CH2SiMe3)Cl + KOCD3 1 5 0Clearly, there is a very large isotope effect which results in different mechanistic pathways beingfavored, and therefore different products are formed. Since C-D bonds are stronger than C-Hbonds,40 this result suggests that 13-H elimination may be operative in reaction 3.6. With thesubstitution of deuteriums for the hydrogens 13 to the metal, the 13-elimination is slowed to thepoint where no bimetallic product is formed. To establish if two independent pathways are inoperation, I would suggest reacting 1 equiv Cp*W(N0)(CH2SiMe3)C1 with a mixture of 0.5equiv of KOCH3 and 0.5 equiv of KOCD3 . Given independent pathways, I would expect amixture of Cp *W(0)2(CH2SiMe3 ), 3.6-d3 , and 3.9 to be formed in this reaction.3.4.7 Reactions Resulting in Nitrosyl-Ligand TransformationsUntil very recently, nitrosyl ligands were considered to be innocent spectator ligands by ourgroup, affecting only the electronic environment of their complexes. Over the last two years, inaddition to reactions 3.5 and 3.6, our group has discovered several other reactions in which thenitrosyl ligand is modified. For example, treatment of the diaryl complex, CpW(NO)(o-tolyl) 2with water induces a formal isomerization to the oxo imido complex, i.e., 41Pte//^ /17\0Ph^Ph Ph 0N Ph(3.14)H2 (1 atzn), benzene  10.-2 RHR= CH2 SiMe3/0Mc:F*11=N =--MoR /N02 (3.15)82 H2Os(j.DRO 4\0R(3.12)R = R0R= o-tolyland a similar chromium complex is obtained according to equation 3.13.42C=-----f - ^C-------)I^1) 2 RMgBr^ICr .^/ \^2) trace 02R/C1.\0THE E I'I■1 R= mesityl^N0 R(3.13)Cp*W(N0)(Ph)2 undergoes a unique thermal reaction to afford Cp *W(r12-N{O)Ph)(NPh)(Ph)and Cp*W(0)2Ph (eq. 3.15). 32OReactions of C6H6 solutions of Cp*Mo(NO)(CH2SiMe3)2 with hydrogen afford the bimetallicspecies shown in equation 3.15. 4383Similar tungsten complexes, [Cp *W(N0)(R)][Cp*W(0)R](µ-N) (R = CH2CMe3, Ph) result whenCp*W(N0)(R)C1 is reacted with Zn. 44Cp*W(N0)(R)C1 + Zn^[Cp*W(N0)(R)][Cp*W(0)1q(p.-N)^(3 . 16)In addition, 1:1 mixtures Cp *W(NO)C12 and Cp *W(NO)(R)Cl are reduced with to produce[Cp *W(N0)(R)][Cp *W(0)C1](p.-N). This indicates that initial reduction must occur atCp*W(NO)C12 (which is more easily reduced than Cp*W(NO)(R)C1 complexes)45 and thisreduction must somehow induce the cleavage of the nitrosyl ligand.3.4.8 Mechanistic ConsiderationsThe role of KOCMe3 and KOMe in reactions 3.5 and 3.6 is not clear, and to date, there areno reagents which effect similar chemical transformations. The potassium cation must play animportant function in these reactions since simple metatheses occur if K+ is replaced by Li+ orNa+.M =Li, Na^ 1.R = CMe3 , Ph, MeMe3 SiCH2^ORN0Complexes 3.4 - 3.6M =K; R = CMe 3 Complex 3.8M = K, R =MeComplex 3.9Scheme 3.3 MOR pentaneMe3 SiCH2 z `ClN-OIt is also evident that the alkoxide anion (0CMe 3 - or OMe-) also influences the pathway of thesereactions. The three obvious functions of alkoxide salts are as reducing, metathesis anddeprotonating reagents.843.4.8.1 Reduction MechanismsAnions of potassium salts are often potent reducing agents. As stated in Section 3.4.7,reducing reagents such as zinc metal affect nitrosyl cleavage of Cp *W(NO)(R)Cl complexes;however, reduction leads to bridging nitrido complexes of the type [Cp *W(N0)(R)][Cp *W(0)12]-(4-N) (eq 3.16) and not bimetallics such as 3.8 and 3.9. It is therefore improbable that reactions3.5 and 3.6 occur via initial reduction, since there is nothing to indicate thatCp*W(NO)(CH2SiMe3)Cl would react differently than its neopentyl analogue under reducingconditions.3.4.8.2 Metathesis MechanismsIt is unlikely that the KOCMe3 is reacting further with the Cp *W(NO)(CH2SiMe3)(OCMe3)complexes, since it has been shown that Cp *W(NO)(CH2SiMe3 )(OCMe3) is stable to excessKOCMe3 (Section 3.2.9). However, the deuterium labeling studies of reaction 3.6 indicate thatthere is a very large isotope effect which results in different products (Section 3.4.7). From thoseexperiments, it follows that the initial step in the reaction to form 3.9 is probably metathesis toform Cp*W(NO)(CH2SiMe3 )(OCH3 ). This alkoxo alkyl complex is isolable, but under theseexperimental conditions this species must undergo further reaction. It is possible that at somepoint in the mechanism of reaction 3.6, 13-H elimination occurs. This would be consistent with theobservations that (1) no alkoxo ligand is found in the product, (2) there is an extra hydrogenincorporated in 3.9, and (3) Cp*W(NO)(CH2SiMe 3)(OCD3), having strong C-D bonds, is notlikely to undergo [3-D elimination. It is very difficult to account for the mass balance of this low-yielding reaction. However, it is important to remember that in reaction 3.6Cp*W(0)2(CH2SiMe3) is produced, and the by-products of this reaction may be participating inthe reaction to form complex 3.9.853.4.8.3 Deprotonation MechanismsLiterature indicates potassium salts may also react as deprotonating agents. 46 For example,Ir(CH3 )(I)(PH2Ph)[N(SiMe2CH2PPh2)2] undergoes loss of KI and HOCMe3 to affordIr(CH3)(PHPh)[N(SiMe2CH2PPh2)2) when treated with KOCMe 3 .47 I propose that the reactionto form complex 3.8 occurs by initial deprotonation of the alkyl chloride complex by KOCMe 3 .Thus, the most plausible mechanism for reaction 3.5 is outlined in Scheme 3.4. Deprotonation ofCp*W(NO)(CH2SiMe3)Cl with KOCMe 3 results in loss of alcohol and formation of an 18-electron anion (A). This species has a localized negative charge at the a-C, and nucleophilicattack of this carbon upon the nitrosyl leads to intermediate B. Intermediate B then attacks asecond equivalent of Cp*W(NO)(CH2SiMe3)Cl to displace a chloride ligand. Finally, the neutralintermediate C undergoes an intramolecular rearrangement to form the final product. Overall thismechanism indicates loss of HOCMe 3 and KCl and is consistent with the experimental data athand.Reaction 3.5 is very low yielding (9.3%), and therefore it is not unreasonable to envision asecond pathway where intermediate A loses KCl to form the 16-electron alkylidene[Cp *W(NO)(CHSiMe3)] species. (3.17)6.^decomposition- KClI would expect this intermediate to be thermally unstable under the reaction conditions anddecompose in a manner similar to the analogous [CpMo(NO)(CHCMe3)] species, which can betrapped by Lewis bases (L) to form CpMo(NO)(CHCMe3)L or, in the absence of a trappingligand, forms the asymmetric dimer [CpMo(NO)](.t-1 1 :?1 2-NO)(µ-CHCMe3 ) [CpMo(CHCMe3)].480•N—WC-.11 CIS iMe3B0N—WMe3SCH2 c.-11 Cl0 S iMe30/N—WC.I1 CIS Me/CScheme 3.486 KOCMe3Me3SiCH2 -N-ci0- HOCMe3A+ Cp *W (NO)(CH2S iN1 e3 )C1-KC187Reaction 3.5 is solvent dependent. Thus, when reaction 3.5 is performed in pentane complex3.8 is formed; however, in THF, the alkoxo alkyl complex is produced. Ionic species may bestabilized in THF making the metathesis reaction a more favorable pathway. In addition, THF isalso a very good donor ligand, and in the presence of donors such as THE or PMe 3 onlyCp*W(NO)(CH2SiMe3)(OCMe3) is produced. Apparently, the electronics ofCp *W(N0)(CH2SiMe3 )C1 may be sufficiently altered by coordination of a base, such that themechanism outlined in Scheme 3.4 is not followed. The reaction of Cp*W(NO)(CH2SiMe3)Clwith KOCMe3 was also performed in the presence of PPh3 . Since complex 3.8 was formeddespite the presence of the phosphine, this indicates that either the concentrations of theintermediate species are very low at any given time or PPh3 is simply too large (cone angle145°)49 to coordinate to any intermediates present.Although the most likely mechanism for the formation of 3.8 is by initial deprotonation, otherdeprotonating reagents do not effect a similar transformation. As with the relatedCp *M(N0)(CH2CMe3 )C1 16 complexes, I have shown that Cp *W(NO)(CH2SiMe3)Cldecomposes to a plethora of products when treated with classic deprotonators such as n-BuLi orLDA. It is likely that for steric and electronic reasons KOCMe 3 is the most effectivedeprotonating reagent for this transformation.I would suggest three additional experiments that may give more mechanistic insight into thisreaction. (1) Determine the correct stoichometry for the reaction, since Scheme 3.4 indicates only0.5 equiv of KOCMe3 is required. (2) Use intermediate-sized phosphines such as PMe2Ph (coneangle 122°), PEt3 (cone angle 132°) or PMePh2 (cone angle 136°), since PMe3 (cone angle 118°)coordinates to the alkyl chloride starting reagent and PPh3 (cone angle 145°) is too large to trapany intermediate present. 49 (3) Eliminate the possibility that this reaction proceeds via a radicalmechanism by performing the reaction in the presence of a radical trapping reagent such asTEMPO (2,2,6,6-tetramethyl-l-piperidinyloxy).883.5 Epilogue and Future WorkThis chapter has presented the synthesis and characterization of alkoxo-containing complexesof the type Cp*W(N0)(R)(011 1). The characteristic chemistry of these complexes and futureresearch suggestions can be found in Chapter 4.The nitrosyl-altering reactions constitute the newest research interests of these laboratories.To date, the mechanisms of all of these "nitrosyl-cleavage" reactions are unknown; however, thecurrent working hypothesis is that each of these processes at some point may proceed via anintermediate containing a i2-NO group. As shown, nitrosyl-containing complexes are beginningto show interesting ligand-based chemistry, and these reactive NO ligands are proving to be morethan just good n-acceptor ligands. For future studies of the nitrosyl altering reactions involvingthe potassium alkoxide salts, I have recommend several key experiments in Section 3.4.8. Inorder to elucidate the mechanisms of these reactions, an understanding of the role of the KORsalts and the apparent dependency of these reactions on the alkoxo group are essential.3.6 References and Notes(1) Legzdins, P.; Veltheer, J. E. Acc. Chem. Res. 1993, 26, 41.(2) Legzdins, P.; Rettig, S. J.; Sanchez, L. Organometallics 1988, 7, 2394.(3) Dryden, N. H.; Legzdins, P.; Rettig, S. J.; Veltheer, J. E. Organometallics 1992, 11, 2583.(4) Legzdins, P; Rettig, S. J.; Ross, K. Organometallics, 1993, 12, 2103.(5) Legzdins, P.; Lundmark, P. J.; Rettig, S. J. Organometallics, in press.(6) Legzdins, P.; Jones, R. H.; Phillips, E. C.; Yee, Y. C.; Trotter, J.; Einstein, F. W. B.Organometallics 1991, 10, 986.(7) Dryden, N. H.; Legzdins, P.; Trotter, J.; Yee, Y. C. Organometallics 1991, 10, 2857.89(8) (PhCH2)2MgX(dioxane) was prepared in a manner similar to that outlined for(Me3 SiCH2)2MgX(dioxane) in reference 3.(9) Debad, J. D.; Legzdins, P.; Batchelor, R. J.; Einstein, F. W. B. Organometallics 1992, 11,6.(10) Debad, J. D.; Legzdins, P.; Batchelor, R. J.; Einstein, F. W. B. Organometallics, 1993, 12,2094.(11) This pentane solution can be concentrated in vacuo and cooled to induce the crystallizationof pure Cp*W(NO)(CH2SiMe 3 )Cl in —80% yield.(12) Phillips, E. C. Ph.D. Dissertation, University of British Columbia, 1989.(13) Ipaktschi, J.; Sulzbach J. Organomet. Chem. 1992, 426, 59.(14) Mg-0 bond strength is 94.1 ± 8.4 kcal mo1 -1 . See The CRC Handbook of Chemistry andPhysics, 62nd Edition; Weast, R. C., Astle, M. J., Eds.; CRC Press, Inc.: Boca Raton,Florida, 1982.(15) For an example of alkoxide for alkyl metathesis see: Heeres, H. J.; Meetsma, A.; Teuben, J.H.; Rodgers, R. D. Organometallics 1989, 8, 2637.(16) A series of Cp'M(NO)(R)(Cl) complexes has been prepared in our laboratories. ForM = W, see reference 10. For M = Mo, see: Debad, J. D.; Legzdins, P.; Rettig, S. J.;Veltheer, J. E. Organometallics 1993, 12, 2714.(17) Legzdins, P.; Richter-Addo, G. B. Metal Nitrosyls; Oxford University Press: New York,NY, 1992.(18) Darr, S.; 116holein, U.; Schobert, R. Organometallics 1992, 11, 2950.(19) Schobert, R. J. Organomet. Chem. 1991, 405, 201.(20) Glueck, D. S.; Bergman, R. G. Organometallics 1991, I 0 , 1479.(21) Hartwig, J. F.; Anderson, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1990, 112, 5670.90(22) Legzdins, P.; Phillips, E. C.; Rettig, S. J.; Sanchez, L. Organometallics 1989, 8, 940.(23) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds; John Wiley & Sons, Inc.:New York, NY, 1988; p 116.(24) Legzdins, P.; Rettig, S. J.; Sanchez, L. Organometallics 1985, 4, 1470.(25) The N-C vibration of an imide ligand is expected in the range of 1300 - 1100 CM- 1 ,26whereas W-N stretches can be found at lower energies (1125 - 948cm -1 ).23(26) Osborn, J. H.; Trogler, W. C. Inorg. Chem. 1985, 24, 3098.(27) Crystals of 3.8 are triclinic of space group P1 (#2); a = 12.140 (2) A, b = 13.334 (2) A, c =11.627 (1) A, a = 90.54 (1)°, r3 = 103.30 (2)°, y = 76.06 (1)°, V= 1742.8 (4) A3 , Z = 2.Dr. S. J. Rettig solved the structure using the Patterson method and full-matrix least-squares refinement procedures to R= 0.042, Rw = 0.041 for 4300 reflections with I ?_ 3o(1).(28) See reference 23 pp 172-173.(29) Crystals of 3.9 are monoclinic of space group P2 1/n (#14); a = 9.948 (2) A, b = 20.118 (5)A, c = 19.002 (5) A, 13 = 103.30 (2)°, V= 3701 (3) A3 , Z = 4. Dr. S. J. Rettig solved thestructure using the Patterson method and full-matrix least-squares refinement procedures toR = 0.038, R,,„= 0.034 for 2595 reflections with I ?_. 3a(1).(30) Legzdins, P.; Rettig, S. J.; Sanchez, L.; Bursten, B. E.; Gatter, M. G. J. Am. Chem. Soc.1985, 107, 1411.(31) (a) For N-0 bond distances see reference 14. (b) For W-0, W-N single bond lengths see:Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, 0.; Watson, D. G. J. Chem. Soc.,Dalton Trans. 1989, 51. (c) The covalent radii of W, C, N, and 0 are 1.30, 0.77, 0.75, and0.73 A, respectively. 14(32) Cp*W(NO)(Ph)2 undergoes a thermal reaction to afford the 16-electronCp*W(712-N{O}Ph)(NPh)(Ph) complex. The dihapto linkage in this complex is described91as a metallaoxaziridine. See Brouwer, E. B. M.Sc. Dissertation, University of BritishColumbia, 1992.(33) W-N bond distances average 1.952 A (see reference 31b), W=N bond distances range from1.78 - 1.61 A, and WEN bond distances range from 1.74 - 1.55 A (see reference 23).(34) Chisholm, M. H.; Hoffman, D. M.; Huffman, J. C. Inorg. Chem. 1983, 22, 2903.(35) For comparison, the W-N(py) bond distance is 2.323 (7) A in (Me3C0)3W(N0)(py) see:Chisholm, M. H.; Cotton, F. A.; Extine, M. W.; Kelly, R. L. Inorg. Chem. 1979, 18, 116.(36) Hamilton, W. C.; Ibers, J. A. Hydrogen Bonding in Solids; W . A. Benjamin: New York,NY, 1968; pp 14-16.(37) (a) Pimentel, G. C.; McClellan, A. L. The Hydrogen Bond; W . H. Freeman: San Francisco,CA, 1960. (b) Joesten, M. D.; Schaad, L. J. Hydrogen Bonding; Marcel Dekker: NewYork, NY, 1974. (c) The Hydrogen Bond; Schuster, P., Zundel, G., Sandorfy, C., Eds.;North Holland: Amsterdam, 1976. (d) Novack, A. Structure Bonding 1974, 18,177 . (e)Allen, L. C.; Kollman, P. A. Chem. Rev. 1972, 72, 283. (f) Joesten, M. D. J Chem. Ed.1982, 59, 362.(38) Emsley, J. Chem Soc Rev. 1980, 9, 91.(39) For examples of intramolecular hydrogen bonds in organometallic complexes see: (a)Fujita, J.; Kobayashi, M.; Nakamoto, K. J. Am. Chem. Soc. 1956, 78, 3295. (b) Osborn, J.A.; Powell, A. R.; Thomas, K.; Wilkinson, G. J. Chem. Soc. A 1968, 1801. (c) Chatt, J.;Leigh, G. J.; Thankarajan, N. J. Chem. Soc. A 1971, 3168. (d) Bronty, C.; Spinat, P.;Whuler, A. Acta. Crystallogr., Sect. B 1980, 36, 1967. (e) Sutherland, B. R.; Cowie, M.Organometallics 1985, 4, 1637. (f) Abed, M.; Goldberg, Z.; Stein, Z.; Shvo, Y.Organometallics 1988, 7, 2054. (g) Poss, M. J.; Atta, M. A.; Richmond, T. G.Organometallics 1988, 7, 1669. (h) Vaughn, G. D.; Gladys; J. A. Organometallics 1984,3, 1596. (i) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem. Soc. 1987, 109,2803.92(40) More energy (1.2 kcal/mol) is required to break a C-D bond than a C-H bond, seeFessenden, R. J.; Fessenden, J. S. Organic Chemistry, 3rd ed.; Brooks/Cole PublishingCo.: Monterey, CA, 1986; p 200.(41) Legzdins, P.; Rettig, S. J.; Ross, K. J.; Veltheer, J. E. J. Am. Chem. Soc. 1991, 113, 4361.(42) Shaw, M. J. Ph.D. Dissertation, University of British Columbia, 1993.(43) Legzdins, P.; Young, M. A., unpublished observations.(44) Debad, J. D; Legzdins, P., unpublished observations.(45) Debad, J. D.; Legzdins, P.; Rettig, S. J.; Veltheer, J. E. Organometallics 1993, 12, 2714.(46) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 4th ed.; John Wiley & Sons,Inc.: New York, NY, 1980; p 258.(47) Fryzuk, M. D.; Joshi, K.; Chadha, R. K.; Rettig, S. J. J. Am. Chem. Soc. 1991, 113, 8724.(48) Legzdins, P.; Rettig, S. J.; Veltheer, J. E. J. Am. Chem. Soc. 1992, 114, 6922.(49) Tolman, C. A. Chem. Rev. 1977, 77, 313.93CHAPTER 4Reactivity of Alkoxo Alkyl Complexes4.1 Introduction^ 934.2 Experimental Procedures ^ 954.3 Characterization Data  1024.4 Results and Discussion^  1054.5 Epilogue and Future Work  1344.6 References and Notes^  1364.1 IntroductionWith any new class of organometallic complexes, it is important to determine characteristicphysical and chemical properties of the compounds; therefore, this chapter describesinvestigations into the chemical reactivity patterns of alkoxo alkyl complexes,Cp*M(N0)(R)(0R). These complexes provide a system in which it is possible to comparedirectly the reactivity of a metal-carbon bond versus a metal-oxygen bond at the same metalcenter.Alkoxo complexes which undergo ligand-based reactions are fairly rare. 1 However, alkoxocomplexes are known to undergo insertion of polar substrates into the M-0 bond, and they havebeen postulated as intermediates in some important catalytic processes.' The alkoxo complexesCp*M(NO)(OR)2 prepared in Chapter 2 are extremely inert evidently because electron density isdonated from the alkoxo ligands to the formally unsaturated metal center. In comparison, therelated and truly 16-electron dialkyl complexes, CpM(NO)R2, have a rich reaction chemistry withi COPMe3vacuumN01/8 S8SR94Lewis bases. 2,3 For instance, the reactions of Cp'M(NO)R2 complexes with Lewis bases proceedby initial adduct formation followed by subsequent intramolecular insertion into the metal-carbonbonds, as depicted in Scheme 4.1.Scheme 4.101`111/ \ "i1 —RR 0ON E / \ tillR PMe3Since alkoxo ligands are generally unreactive towards Lewis bases, the reactivity ofCp*M(N0)(R)(OR') complexes was expected to involve primarily the metal-carbon bonds. It washoped that some interesting intermediate complexes could be isolated by virtue of the stabilizingeffect of the alkoxo ligand.954.2 Experimental Procedures4.2.1 MethodsThe synthetic methodologies employed throughout this thesis are described in detail inSections 2.2.1.4.2.2 ReagentsThe organometallic alkoxo alkyl complexes Cp *M(N0)(R)(OR') were prepared as describedin Sections 3.2.5 - 3.2.6. LiOCMe3 was synthesized as in Section 2.2.3.(PhMe2CCH2)2MgX(dioxane)4 and CpMo(N0)(CH2Ph)C15 were prepared according topublished procedures. CS 2 (99+%, Aldrich) was distilled from P20 5 . 02 (Medigas, 99.5 %),CO (Linde), CO2 (99.999%, Matheson), H2 (Linde), CNCMe3 (Aldrich), PhNCO (Aldrich),p-tolylNCO (Aldrich), LDA (LiN(i-propyl) 2 , Aldrich) and PhOH (Mallinckrodt) were used asreceived.The numbering scheme, color, yield and elemental analysis data for all new complexes(4.1 - 4.6) are collected in Table 4.1, while their mass spectral and infrared data are compiled inTable 4.2. The 1H and 13 C{ 1}1} NMR data for 4.1 - 4.6 can be found in Table 4.3.4.2.3 Reaction of Cp *Mo(NO)(CH2Ph)(OCMe3) (3.1) andCp*Mo(NO)(CH2Ph)(OPh) (3.2) with 02Treatment of complexes 3.1 and 3.2 (0.50 mmol each) in Et20 (10 mL) with 02 (1 atm)resulted in a color change from red to yellow over the course of several hours at roomtemperature. The solvents were removed in vacuo, the residues were extracted with Et 20(4 x 20 mL), and the extracts were filtered through Celite (2 x 5 cm). The filtrates wereconcentrated in vacuo and cooled at -30 °C overnight to induce the precipitation of small amountsof [Cp*Mo(0)2]2-(p-0) (-20% yield).6964.2.4 Reactions of Cp *W(N0)(CH2Ph)(OCMe3) (3.3) and Cp *W(N0)(CH2SiMe3)(0Ph)(3.5) with 02 and H2OStirred Et20 solutions (10 mL) of complexes 3.3 and 3.5 (1.0 mmol each) were exposed to02 (1 atm) or deaereated H2O (50 AL). The colors of the reaction mixtures immediately turnedfrom red (3.3) or purple (3.5) to yellow. The final reaction mixtures were taken to dryness invacuo, and the residues were extracted with Et 20 (2 x 10 mL) and filtered through Celite(2 x 5 cm). The filtrates were concentrated in vacuo and cooled at -30 °C to induce thedeposition of colorless crystals of the dioxo alkyl complexes, Cp*W(0) 2(CH2Ph) andCp *W(0)2(CH2SiMe3),7 respectively, in virtually quantitative yields.4.2.5 Preparation of [CpMo(N0)(CH2Ph)1 2-(1-0) (4.1)CpMo(N0)(CH2Ph)CI (0.64 g, 2.0 mmol) and LiOCMe3 (0.16 g, 2.0 mmol) were mixed assolids in a Schlenk tube in a glovebox. The tube was removed from the glovebox, and Et 20(30 mL) was added to the solids via syringe. The reaction mixture was stirred for 1.5 h, duringwhich time it turned red. The solvent was removed in vacuo from the reaction mixture to obtain ared oil. The oil was dissolved in pentane/Et20 (1:1, 20 mL). Over the course of the work-up thissolution continued to darken. 8 The solution was filtered through Celite (2 x 5 cm). Uponconcentrating and cooling the solution, crystals formed. [CpMo(NO)(CH 2Ph)]2-(.t-O) (4.1)(0.30 g, 42% yield) was isolated by cannulation as black needles.4.2.6 Preparation of [Cp *Mo(N0)(CH2CMe2Ph)12-(1-0) (4.2)Cp*Mo(NO)Cl2 (0.66 g, 2.0 mmol) and (PhMe 2CCH2)2Mg.X(dioxane) (2.0 mmolMe3CCH2 -) were combined as solids in a Schlenk tube contained in a glovebox. The tube wasremoved from the glovebox and cooled to -80 °C. THE (20 mL) was added slowly to the solidsvia syringe. As the solution warmed to -40 °C, it turned purple (v NO = 1618 cm-1 ). 9 The solventwas then removed in vacuo without allowing the reaction mixture to warm above -30 °C. The97remaining purple residue was extracted with Et20 (2 x 20 mL), and the extracts were filteredthrough Celite (2 x 5 cm). The purple filtrate was taken to dryness in vacuo and redissolved inTHF (20 mL). The THF solution was cannulated into a Schlenk tube containing LiOCMe 3(0.16 g, 2.0 mmol). The reaction mixture turned red within 0.5 h. After this time the solvent wasremoved in vacuo, and the remaining residue was extracted with hexanes (2 x 20 mL). Over thecourse of the work-up this solution continued to darken. 8 The extracts were filtered throughCelite (2 x 5 cm). The filtrate was concentrated and cooled to induce the crystallization of 0.80 g(50% yield) of [Cp *Mo(N0)(CH2CMe2Ph)]2-(A-0) (4.2) as red-black needles. 104.2.7 Reactions of Cp *Mo(NO)(CH2Ph)(OCMe3) (3.1) and Cp *W(NO)(CH2SiMe3)(OPh)(3.5) with HCIComplexes 3.1 and 3.5 were treated in Et20 with 1 equiv of HCI (as a 1.4 M solution inEt20). The workup of the final reaction mixtures involved removing the solvent in vacuo,extracting the residues with Et20 (for 3.1) or pentane (for 3.5), and cooling the combinedextracts at -30 °C to obtain crystalline precipitates (80 - 90% yields) of the product complexes.Comparisons with authentic spectral data confirmed that the organometallic products of thesereactions were Cp*Mo(N0)(CH2Ph)C1,5 and Cp*W(N0)(CH2SiMe3 )C1, 11 respectively.4.2.8 Reaction of Cp *W(N0)(CH2SiMe3)(0Me) (3.6) with PhOHExcess PhOH was vacuum transferred onto a red pentane solution ofCp*W(NO)(CH2SiMe3)(OMe) (3.6) (0.086 g, 0.18 mmol) (vNO = 1584 cm -1). The mixture wasstirred for 2 d after which time the IR spectrum of an aliquot of the red-purple reaction solutionexhibited a new band at 1597 cm -1 . The reaction mixture was taken to dryness in vacuo and theremaining residue was extracted with pentane (2 x 10 mL). The extracts were filtered throughCelite (2 x 5 cm), and the filtrate was concentrated and cooled to induce the crystallization of0.060 g (60% yield) of Cp *W(NO)(CH2SiMe3)(OPh) (3.5).98Pentane solutions of Cp *W(NO)(CH2SiMe3)(OPh) did not react with excess Me0H at roomtemperature overnight.4.2.9 Reaction of Cp*W(N0)(CH2SiMe3)(0Ph) (3.5) with PMe3An excess of PMe3 was vacuum transferred from sodium/benzophenone into an NMR tubecontaining a CDC1 3 solution of 3.5. Variable-temperature 1H NMR spectra from 24 °C to -60 °Cof the reaction mixture were recorded.On a larger scale, Cp *W(NO)(CH2SiMe3)(OPh) (0.24 g, 0.46 mmol) was reacted neat withPMe3 to form a yellow precipitate. The excess PMe 3 was removed under reduced pressure toobtain a yellow solid. Under dynamic vacuum, this solid reverted to the distinctive purple color ofthe starting organometallic species over the course of 0.5 h.4.2.10 Reaction of Cp *W(NO)(CH2SiMe3)(OPh) (3.5) with CNCMe3Complex 3.5 (0.10 g, 0.19 mmol) was dissolved in CNCMe 3 (0.20 mL, excess). The purplesolid turned yellow as it dissolved. After the reaction mixture had been stirred for 5 min, theexcess CNCMe3 was removed in vacuo to obtain a yellow oil. This oil was dissolved in pentane(20 mL), and the resulting yellow solution was filtered through Celite (2 x 5 cm). The yellowfiltrate was collected and concentrated in vacuo. Maintaining the concentrated solution at -30 °Cresulted in the deposition of 0.092 g (80% yield) of Cp *W(N0)(0Ph)(n 2-C{NCMe3}CH2SiMe3 )(4.3) as yellow nuggets.4.2.11 Hydrolysis of Cp *W(N0)(0Ph)(712-C{NCMe3}CH2SiMe3) (4.3) toCp*W(N0)(0Ph)(71 2-C{NCMe3}Me) (4.3')1H NMR spectroscopy established that Cp *W(N0)(0Ph)(11 2-C{NCMe3}CH2SiMe3) (4.3)was easily hydrolyzed by trace H2O in C6D6 to form Cp*W(N0)(0Ph)(r1 2-C{NCMe3 }Me)(4.3'). 1H NMR data for 4.3' can be found in Table 4.3.994.2.12 Reaction of Cp*Mo(NO)(CH2Ph)(OCMe3) (3.1) with COThe high-pressure treatment of Cp *Mo(N0)(CH2Ph)(OCMe3 ) (0.17 g, 0.40 mmol) in C6H6with CO was carried out in a Parr reactor (see section 5.2.4). The resulting amber solution wasreduced to a red-amber oil in vacuo. This oil was redissolved in pentane, and then transferred tothe top of a silica gel column (2 x 8 cm) made up in pentane. The column was eluted withpentane, resulting in the elution of a single orange band which was collected and concentrated invacuo. Cooling of this concentrated solution in a freezer (-10 °C) overnight resulted in thedeposition of orange crystals of Cp *Mo(NO)(CO)2 (0.034 g, 27% yield). 12 Subsequent elutionof the column with Et20 developed an amber band which was also collected and reduced in vacuoto afford a small amount (<5% yield) of an amber oil. The spectroscopic properties of this oilwere identical to those exhibited by an authentic sample of 1,3-diphenylacetone. 13Complex 3.1 was reacted with CO (1 atm) in C6D6 . After several hours, the 1H NMRspectrum of this reaction mixture exhibited a large number of peaks in the region of Cp*resonances, thereby indicating a plethora of products.4.2.13 Reaction of Cp *W(N0)(CH2SiMe3)(0Ph) (3.5) with COComplex 3.5 was reacted with CO either at 1 atm in C 6D6 or at higher pressures (600 psig)in C6H6 . A large number of unidentified products were formed as evidenced by the 1H NMRspectra (C6D6) of the reaction mixtures which exhibited many peaks in the region of Cp *resonances.4.2.14 Reactions of Cp *W(NO)(CH2SiMe3)(OPh) (3.5) with CO2 or CS2A pentane solution (10 mL) of Cp *W(N0)(CH2SiMe3)(0Ph) (0.23 g, 0.43 mmol) wasexposed to CO2 (1 atm). The solution was stirred overnight with no color change beingobserved. An IR spectrum of the reaction mixture exhibited one vNo which was attributable toCp*W(NO)(CH2 SiMe3)(OPh).100An excess of CS2 (-2 mL) was vacuum transferred to a pentane solution (10 mL) ofCp*W(N0)(CH2SiMe3)(0Ph) (0.26 g, 0.50 mmol). The reaction mixture was stirred overnightwith no color change being observed. The mixture was taken to dryness in vacuo, and the purpleresidue was extracted with pentane. Cp *W(NO)(CH2SiMe3 )(OPh) (0.22 g, 85% recovered yield)was crystallized from the pentane extracts.4.2.15 Reaction of Cp *W(NO)(CH2SiMe3)(OPh) (3.5) with RNCO [R = Ph, p -tolyl]Crystals of Cp *W(NO)(CH2SiMe3)(OPh) (0.16 g, 0.30 mmol) were treated with an excess ofPhNCO orp-tolylNCO (-0.5 mL). The purple crystals immediately turned orange upon theaddition of the isocyanate reagent. Pentane (10 mL) was added to the mixtures to induce theprecipitation of orange solids. The supernatant pentane solutions were discarded, and theremaining solids were washed with pentane (10 mL). The orange solids were dried in vacuo for2 h, and recrystallized from Et20. Orange crystals of Cp *W(NO)(CH2SiMe3)(OPh)(PhNCO)(4.4) (0.065 g, 33% yield) and Cp*W(N0)(CH2SiMe3)(0Ph)(p-toly1NCO) (4.5) (0.064 g,26% yield) were isolated by cannulation.4.2.16 Reaction of Cp *Mo(NO)(CH2Ph)(OCMe3) (3.1) with H2An infrared spectrum of a THE solution (40 mL) of complex 3.1 (0.57 g, 1.3 mmol) exhibitedseveral absorption bands in the nitrosyl region (1611, 1580, 1578 cm -1). This solution waspressurized to 40 psig with H2 in a Fischer-Porter high-pressure vessel. The reaction mixture wasleft to stir for 4 d. After this time an IR spectrum of the reaction solution exhibited a single bandat 1618 cm -1 . The solution was taken to dryness in vacuo, and the residue remaining wasextracted with Et20 (2 x 10 mL). The extracts were filtered over Celite, combined andconcentrated. Amber crystals of [Cp *Mo(N0)(CH2Ph)(1-0)J2 (4.6) (0.092 g, 19% yield) formedwhen the saturated solution was cooled to -30 °C for 2 days. Complex 4.7 can be recrystallizedfrom CH2Cl2/hexanes solutions.101The alkoxo alkyl complexes Cp *W(NO)(CH2Ph)(OCMe3) (3.3),Cp*W(N0)(CH2SiMe3)(0CMe3) (3.4) and Cp*W(N0)(CH2SiMe3)(0Ph) (3.5) were treatedwith H2 in fashion similar to that described above. In all cases, only the organometallic startingmaterial was isolated.4.2.17 Magnetic Susceptibility Measurements of [Cp*Mo(N0)(012Ph)(11-0)12 (4.7)Crystals of [Cp*Mo(N0)(CH2Ph)(11-0)12 (4.7) (0.0748 g) were ground into a powder with amortar and pestle in a glovebox. This powder was packed firmly into a capillary tube. Amagnetic susceptibility measurement of this sample was recorded on a Johnson-Matthey magneticsusceptibility balance at room temperature. 14 The susceptibility per gram of sample, xg, wasmeasured directly by the Johnson-Matthey magnetic susceptibility balance according to thefollowing formula: YA.g = CBOXR-ROY(M)( 1 09), where CBai was the balance calibration constant(1.006), e was the length of the sample (1.5 cm), R was the reading of the tube plus the sample(-55), R0 was the reading of the empty tube (+15) and m was the mass of the sample (0.0748 g).From this formula xg was calculated to be -1.4 x 10 -6 c.g.s emu for complex 4.6. The molarsusceptibility for the monomer is -520 x 10 -6 cm3mo1-1 , since xm = xg x MW of monomer. Thevalue of xm obtained by summing Pascal's constants was estimated at -260 x 10 -6 cm3mol- 1 . 151024.3 Characterization DataTable 4.1. Numbering Scheme, Color, Yield and Elemental Analysis Data for Complexes4.1 - 4.6complex compdno.color anal. found (calcd)(yield, %) C H N[CpMo(N0)(CH2Ph)1 2-(1-0) 4.1 black (42) 49.95(49.67) 4.28(4.17) 5.00(4.82)[Cp*Mo(N0)(CH2CMe2Ph)12-(4-0) 4.2 red-black(50)59.33(59.69) 7.15(7.01) 3.23(3.48)Cp*W(N0)(0Ph)(n 2-C{NCMe3 }CH2 SiMe3)4.3 yellow (80) 49.19(49.02) 6.59(6.58) 4.49(4.57)Cp*W(NO)(CH2SiMe3 )(OPh)(PhNCO) 4.4 orange (33) 50.01(50.00) 5.59(5.66) 4.32(4.40)Cp*W(N0)(CH2SiMe3)(0Ph)(p-tolyINCO)4.5 orange (26) 50.76(50.63) 5.78(5.67) 4.32(4.01)[Cp*Mo(N0)(CH2Ph)O-L-0)]2 4.7 amber (19) 55.41(55.51) 6.22(6.02) 3.79(3.80)Table 4.2. Mass Spectral and Infrared Data for Complexes 4.1 - 4.6compdno.MS, m/za tempo, °C IR, cm -1 (Nujol)vNO other bands4.1 284 [CpMo(N0)(CH2Ph)l 100 1597, 1574 698e4.2 805 [Pt] 100 1578, 1564 764a4.3 612 [P+] 200 1585 1670d4.4 529 [P+- PhNC0] 120 1597, 1543 br 1263, 1241e4.5 529 [P+- p-toly1NCO] 120 1554, 1539 1259, 1245e4.7 526f 120 1599, 1588, 1568 756sh, 748, 700ca m/z values are for the highest intensity peak of the calculated isotopic cluster, i.e. 98Mo and 184W.b Probe temperatures.C vx4,0d VCNe VSi-Mef The mass of the parent ion can be attributed to [Cp *Mo(0)2] 2-(4-0), a common decomposition product ofmolybdenum nitrosyl-containing complexes.103Table 4.3. 114 and 13C{1H} NMR Data for Complexes 4.1 - 4.6 in C6D6compdno.1H NMR (5, ppm) 13C{111} NMR (8, ppm)4.1 7.15 - 6.90 (m, 10 H, ArH) 130.5 (Cips.)5.10 (s, 10 H, C5H5) 128.2 (aryl C)2 HH = 12.0 Hz)3.38 (d, 2 H, CH2, J 126.8 (aryl C)3.28 (d, 2 H, CH2 , 2JHH = 12.0 Hz) 125.7 (aryl C)104.6 (C5H5)46.2 (CH2)4.2 7.71 (d, 4 H, o-ArH, 2JHH = 7.4 Hz) 155.42 (Cipso)7.32 (t, 4 H, m-ArH, 2JHH = 8 .2 Hz) 128.40 (aryl C)7.10 (t, 2 H,p-ArH, 2JHH = 7.3 Hz) 125.91 (aryl C)2.18 (d, 2 H, CHACHB, 2JHH = 12.4 Hz) 125.34 (aryl C)2.04 (d, 2 H, CHACHB, 2JHH = 12.4 Hz) 112.83 (C5 (CH3)5)1.84 (s, 6 H, CH2C(CH3)A(CH3)BPh) 69.91 (CH2C(CH3 )2Ph)1.78 (s, 6 H, CH2C(CH3)A(CH3 )BPh) 43.78 (CH2C(CH3)2Ph)1.56 (s, 30 H, C5 (CH3)5 ) 32.02 ((CH3 )A)30.77 ((CH3)B)9.76 (C5 (CH3 )5)4.3 7.43 - 7.32 (m, 4 H, ArH) 216.9 (CNCMe3)6.87 - 6.74 (m, 1 H, ArH) 168.3, 129.5, 120.7, 117.1 (aryl Cs)2.94 (d, 2 H, JHH = 11.1 Hz, CHAHB) 110.9 (C5 (CH3 )5)2.45 (d, 2 H, JHH = 11.1 Hz, CHAHB) 29.8 (C(CH3 )3)1.73 (s, 15 H, C 5 (CH3)5) 27.4 (CH2)1.18 (s, 9 H, NC(CH3 )3) 9.8 (C5 (CH3 )5 )0.21 (s, 9 H, SiC(CH3 )3 ) 0.5 (Si(CH3)3 )4.3'a 7.42 - 7.32 (m, 4 H, ArH) 216.8 (CNCMe3)6.87 - 6.80 (m, 1 H, ArH) 168.2, 129.5, 120.6, 117.1 (aryl C's)2.08 (s, 3 H, CH3) 110.8 (C5 (CH3)5)1.71 (s, 15 H, C5 (CH3)5 ) 59.5 (CNC(CH3)3)1.05 (s, 9 H, NC(CH3)3 ) 29.1 (C(CH3)3)19.1 (CH3 )9.6 (C5 (CH3)5)4.4b 7.84 - 6.54 (m, ArH) c1.54 ( s, 15 H, C5 (CH3)5 )0.49 (d, 1 H, JHH = 11.1 Hz, CHAHB)0.41 (s, 9 H, SiC(CH3)3)-0.27 (d, 1 H, JHH = 11.1 Hz, CHAHB)1044.5d 7.75 - 6.75 (m, ArH)2.10 (s, 3 H, PhCH3 )1.57 (s, 15 H, C 5 (CH3)5 )0.46 (d, 1 H, JHH = 12.0 Hz, CHAHB)0.39 (s, 9 H, SiC(CH3)3)-0.29 (d, 1 H, Jim = 12.0 Hz, CHAHB)c4.7e 7.82 - 6.99 (m, 50 H) c3.36-3.28 (m, 2 H)3.25 (d, 2 H, J= 11.1 Hz)3.05 (d, 2 H, J= 9.6 Hz)2.86 (d, 2 H, J= 11.1 Hz)2.71 (d, 2 H, J= 9.6 Hz)2.14 (d, 4 H, J= 8.1 Hz)2.02 (d, 4 H, J= 8.7 Hz)1.90 (d, 4 H, J = 8.7 Hz)1.82 (d, 4 H, J= 8.1 Hz)1.61 (s, 8 H)1.49 (s, 8 H)1.48 (s, 22 H)1.42 (s, 45 H)0.42 (d, 2 H, J= 1.2 Hz)-0.17 (s, 1 H)-1.74 (d, 2 H, J = 1.2 Hz)a Cp *W(N0)(0Ph)(1 2-C{NCMe3 }Me) (4.3') is derived in situ by hydrolysis of 4.3. See Section 4.4.4.2b Crystals of 4.4 partially dissociate in C 6D6 to Cp *W(NO)(CH2SiMe3)(OPh) (3.5) and PhNCO such that 4.4 and3.5 exist in a 1:2.7 ratio. 4.4 exists in a 3.5:1 ratio with 3.5 in the presence of excess PhNCO.C Not recorded.d Crystals of 4.5 partially dissociate in C 6D6 to Cp*W(N0)(CH2SiMe3)(0Ph) (3.5) and p-tolylNCO such that 4.5and 3.5 exist in a 1:6 ratio. 4.5 exists in a 2.3:1 ratio with 3.5 in the presence of excess p-tolylNCO [5 6.68 (d,2 H, JHH = 8.4 Hz, ArH), 6.56 (d, 2 H, JHH = 8.4 Hz, ArH), 1.95 (s, 3 H, C6H4CH3) ppm].e The 1 H NMR data for complex 4.7 was not assigned. See Section 4.4.5 for a discussion of this data.1054.4 Results and DiscussionThe investigation into the chemical reactivity patterns of alkoxo alkyl complexes involved thetreatment of representative Cp*M(N0)(R)(011. 1) species with a variety of reagents such asoxygen, water, HCI, phenol, trimethylphosphine, carbon monoxide, tert-butyl isocyanide, CO2 ,CS2 , isocyanates, and dihydrogen. The reactions of the alkoxo alkyl species are not easilygeneralized. The outcomes of these reactions are sensitive to changes in the metal, the alkoxoligand, the alkyl ligand, and the reaction conditions employed. Diverse reactivity patternsincluding an insertion reaction, a dimerization, and the formation of several Lewis acid-baseadducts are observed for the family of alkoxo alkyl complexes, Cp*M(N0)(R)(OR').4.4.1 Reactions of Alkoxo Alkyl Complexes with Oxygen and WaterMost organometallic complexes are sensitive to the atmosphere, with oxygen and water beingthe key reactive components of the atmosphere. Organometallic complexes are prone tooxidation by oxygen, and undergo hydrolysis reactions with water because of their polar M-Cbonds. Not surprisingly, therefore, the alkoxo alkyl complexes Cp *M(N0)(R)(01V) decomposewhen exposed to the atmosphere. However, when Cp*M(N0)(R)(01t) complexes are treatedwith pure 02 or H2O under controlled conditions, they afford isolable organometallic compoundswhich in several cases retain their metal-carbon bonds.4.4.1.1 Reactions of Tungsten Alkoxo Alkyl Complexes with OxygenBoth in solutions and in the solid state, Cp*M(N0)(R)(01t) complexes react rapidly whenexposed to oxygen. Interestingly, the products of these oxygen reactions are dependent on themetal of the starting alkoxo alkyl species. Thus, in the case of M = W, 0 2 effects thetransformations depicted in eq 4.1.7106Cp*W(N0)(R)(01V)02Cp*W(0)2R^(4.1) R = CH2Ph; R' = CMe3R = CH2SiMe3 ; R' = PhReactions 4.1 afford the organometallic dioxo products in high yields. These products can beidentified by the presence of two strong vw_c • bands in their Nujol mull IR spectra.? However, aGCMS trace of the remaining reaction mixture shows at least 9 organic byproducts. The parention masses of these products range from m/z = 59-223. The large number of organic speciesindicates that reaction 4.1 probably proceeds via a complex mechanism. As with the relateddialkyl and diary] complexes of tungsten, which undergo a similar type of reaction with oxygen(eq 4.2),7 a considerable amount of effort has been expended in attempting to identify the organiccomplexes produced in these transformations.Cp*W(N0)R202Cp*W(0)2R^(4.2)The most important aspect of reactions 4.1, is that reactivity occurs at the M-0 bond, while theM-C bond remains intact. This is most certainly not a thermodynamic affect, since group 6 metal-oxygen bonds are stronger than M-C bonds.4.4.1.2 Reactions of Molybdenum Alkoxo Alkyl Complexes with OxygenMolydenum alkoxo alkyl species react with 02 to form the known complex[Cp*Mo(0)2]2 -( 1-0), i.e.,6Cp*Mo(N0)(R)(011. 1)02[Cp *M0(0)2i2-(.1-0)^(4.3)R = CH2Ph; R' = CMe3R = CH2Ph; R' = PhReactions 4.3 demonstrate that the molybdenum species are more reactive than their tungstencongeners (eq 4.1). It has been shown in our laboratories previously that the thermodynamicallyH2O(4.6)W/ i \0^0RR' E^OR'N0107stable [Cp*Mo(0)2]2-(1-0) species is a ubiquitous decomposition product of molybdenumnitrosyl complexes. 6 [Cp*Mo(0)2]2-(1-0) is easily identified by its Nujol IR spectrum whichexhibits two strong terminal oxo stretches at 910 and 878 cm -1 as well as a broad absorption dueto the bridging oxo ligand at 762 cm -1 . 6 Additionally, the 1H NMR spectrum of[Cp*Mo(0)2]2-(g-0) in C6D6 displays a single signal at 5 1.78 ppm due to the protons of thepermethylcyclopentadienyl ligands.4.4.1.3 Reactions of Isolated Tungsten Alkoxo Alkyl Complexes with WaterIt has been previously shown that Cp *W(NO)R2 species are inert with respect to hydrolysiswhen R = alkyl, but react with H2O to form Cp *W(0)2(aryl) when R = aryl. 6bCp*W(N0)(alkY1)2Cp*W(N0)(ary1)2 H2ONo Reaction^(4.4)Cp *W(0)2(aryl)^(4.5)H2OThe tungsten alkoxo alkyl compounds 3.3 and 3.5 resemble the diaryl systems in that they bothreact with H2O to produce the known Cp *W(0)2(CH2Ph) and Cp*W(0)2(CH2 SiMe3)complexes, respectively (eq 4.6).R = CH2SiMe3 , R' = PhR = CH2Ph, R' = CMe30N RR0108In reactions 4.6 the yield of the dioxo alkyl complexes is high. As for any of these dioxoproducing reactions, a GCMS trace of the reaction mixture indicates a large number of organicbyproducts (Section 4.4.1.1).4.4.1.4 Preparation of [Cp'111(N0)(R)1 2-(g-0) Complexes: Reactions of In Situ GeneratedMolybdenum Alkoxo Alkyl Complexes with Trace WaterThe molybdenum alkoxo alkyl complexes CpMo(NO)(CH2Ph)(OCMe3) andCp*Mo(NO)(CH2CMe2Ph)(OCMe3 ) have not been isolated to date. However, in attempts toprepare these species, [CpMo(NO)(CH2Ph)]2-(p.-O) (4.1) and [Cp*Mo(N0)(CH2CMe2Ph)12-(A-0) (4.2) have been isolated.Cp' = Cp, R= CH2Ph;Cp' = Cp * , R = CH2CMe2PhIn these experiments, Cp'Mo(N0)(R)CI is generated in situ from an equimolar solution ofCp'Mo(NO)C12 and the appropriate magnesium dialkyl reagent. 9 The reaction mixtures arefiltered to remove MgC12•X(dioxane) and cannulated to a flask containing the lithium alkoxidesalt. The reaction mixtures turn the characteristic red color of the alkoxo alkyl species; however,as these solutions are worked up they darken to a deep red-black color. Presumably, themolybdenum alkoxo species are extremely water sensitive and are easily hydrolyzed by tracewater present in the solvents used to work-up these complexes. From these solutions, purecrystalline samples of complexes 4.1 and 4.2 are isolated in moderate yields. These[Cp'Mo(NO)(R)] 2-(.t-O) complexes are moderately air-stable as solids, but in solution they areair-sensitive and decompose to [Cp'Mo(0) 2]2-(.i-O). 6 The infrared spectra of 4.1 and 4.2 each109exhibit two nitrosyl stretches between 1600 and 1560 cm -1 . Diagnostic Mo-O-Mo vibrations areobserved at 698 cm -1 for complex 4.1 and 764 cm-1 for complex 4.2.6b The 1H NMR spectra ofthese bimetallic species indicate only one isomer is present in solution (Table 4.3). 16,17Previous work has shown that analogous bimetallic complexes can be produced by treatingmolybdenum dialkyl or diaryl complexes with water, i.e.,6b2 Cp'Mo(NO)(R)2 H2O [CpsMo(N0)(R)]2-(11-0)^(4.7) R = alkyl, aryl[Cp*Mo(N0)(CH2CMe2Ph)] 2-(p.-0) is more easily crystallized from the reaction mixture ofwater and the alkoxo alkyl complex than from the reaction mixture of water and the bis(neophyl)complex. This is because the byproduct of the latter reaction is Me 3CPh which is not easilyseparated from the product due to its low volatility. The byproduct of the alkoxo alkyl reaction isbelieved to be Me3 COH which can be easily removed in vacuo.We believe that the most plausible mechanism for the formation ofg-oxo bimetalliccomplexes from the alkoxo alkyl complexes is similar to the mechanism proposed for thehydrolysis of molybdenum dialkyl complexes. 6b Thus, the putative alkoxo alkyl complex ishydrolyzed to form a hydroxide complex and t-butanol. In turn, the hydroxide intermediate reactswith a second equivalent of the alkoxo alkyl to eliminate alcohol and produce the bimetallicspecies (Scheme 4.2). The products obtained from the hydrolysis of the alkoxo alkyl complexesindicate reaction occurs preferentially at the alkoxo ligand rather than the alkyl ligand.4.4.2 Reactions of Alkoxo Alkyl Complexes with HClIt has been established previously that the bis(benzyl) complexes, Cp *M(NO)(CH2Ph)2 , reactwith HCl to produce Cp *M(N0)(CH2Ph)C1. 5 We have found that similar treatment ofC 10N1 .....,,,RMo=0- --9vloR iN01)LiOR'2)H2O110Scheme 4.2PhO'^ CH2S11\ile3N03.5(4.9)PhOH-Me0HCH2SiMe33.6111Cp*W(NO)(OCMe3)2 with HCI provides first the monoalkoxo complex, Cp *W(NO)(OCMe3)Cl,and then the dichloro compound, Cp *W(NO)Cl2 (Section 2.4.2).The reactions of Cp*M(N0)(R)(01V) with HC1 provide some insight into the relativereactivities of M-C versus M-0 bonds in these systems. As expected, the alkoxo alkyl complexesCp*W(N0)(CH2Ph)(0CMe 3 ) (3.3) and Cp*W(NO)(CH2SiMe3 )(OPh) (3.5) react with HC1 toproduce exclusively the corresponding alkyl chloro species (eq 4.8).Cp*M(N0)(R)(OR') + HCI^Cp*M(N0)(R)(C1) + HOR'^(4.8)Thus, the preferred site of reactivity of the Cp *M(N0)(R)(01V) complexes with the polar reagentHCI is the more polar M-0 bond rather than the M-C linkage.4.4.3 Reaction of Cp *W(NO)(CH2SiMe3)(OMe) with PhOHCp*W(NO)(CH2SiMe3 )(OMe) reacts cleanly with PhOH to produceCp*W(NO)(CH2SiMe3)(OPh) in moderate isolated yield (60%).The reaction mixture turns from red to red-purple over the course of 2 d, and the progress of thereaction can be easily monitored by IR spectroscopy. For instance, the IR spectrum of thepentane solution of Cp *W(NO)(CH2SiMe3)(OMe) exhibits a v NO of 1584 cm-1 , and as it reactswith PhOH, the band at 1584 cm -1 is slowly replaced by two bands at 1597 and 1586 cm -1 . Thisalcohol exchange reaction is favored (AG° < 0) since the pK a of PhOH is 10 and the pKa ofMe0H is 15.2. 18 This reaction is driven by the formation of a strong H-OMe bond.112Reaction 4.9 is not reversible; thus, Cp*W(NO)(CH2SiMe3 )(OPh) does not react withMe0H to reform the methoxy species. It is also interesting to note that the metal-alkyl link isstable to excess phenol. It is not cleaved to form the bis(phenoxide) complex, Cp*W(NO)(OPh) 2 ,which can be prepared via a metathesis reaction (Section 2.2.5).Cp*W(NO)(CH2SiMe3)(OPh) + excess PhOH ^ Cp*W(NO)(OPh)2 (4.10)Several mechanisms for alcohol exchange reactions have been postulated. 1 In alkoxidetransfer between coordinatively unsaturated metal centers exchange is thought to occur in aconcerted, associative manner. Caulton and coworkers have suggested that the coordinativelysaturated species Ir(H)2(0R)(PCy3 )2 undergoes alcohol exchange first via formation of ahydrogen bond to the uncoordinated alcohol, then through a four-centered transition state, i.e., 19 0 RzIT HOR'0••Jr '^• 'H'0 °R.',HOR- Ow Jr — 0'R.'(4.11)Alternatively, the coordinated alkoxo ligand could reversibly dissociate from the metal to give analkoxide anion and a metal cation, and exchange could occur between free ions in solution. L20Exchange reactions are important since they indicate the potential for replacing alkoxoligands with other heteroatom groups. 21 Reagents with acidic protons such as chelating alcohols,carboxylic acids, alkyl and arylthiols may be prone to exchange reactions with these alkoxo alkylspecies given their low pKa values. 18 Consistently, the alkoxo alkyl complexes are converted toalkyl chloride species upon treatment with HCl (Section 4.4.2).1134.4.4 Reactions of Lewis Bases with Alkoxo Alkyl Complexes: Adduct Formation orInsertionThe dialkyl and diaryl complexes, Cp*M(NO)R2, are known to react with Lewis bases toform either 1:1 adducts (e.g. PMe 3)2 or insertion products in which the base has inserted into themetal-carbon bond (e.g. CO). 22 Currently, there is no clear way to predict whether a certainLewis base will form an adduct complex or insert into the metal-carbon bond.4.4.4.1 Reaction of Cp *W(NO)(CH2SiMe3)(OPh) (3.5) with PMe3Cp*W(NO)(CH2SiMe3)(OPh) (3.5) is a sufficiently potent Lewis acid to form an adduct withPMe3 at low temperatures as evidenced by variable-temperature 1H NMR spectroscopy from24 °C to -60 °C. At 24 °C, a purple CDC1 3 solution of 3.5 and excess PMe3 exhibits signals dueto the starting reagents (Figure 4.1). At -60 °C this solution is yellow, and all signals in the1H NMR spectrum are broad (Figure 4.2). Nevertheless, new resonances consistent with theadduct complex are evident at this temperature, most notably a doublet at 8 1.42 ( 2JpH = 6 Hz)attributable to coordinated PMe 3 . When the sample is warmed to room temperature, its colorreverts to purple, and its 1H NMR spectrum is identical to the original spectrum, therebyindicating that this adduct formation is a reversible process (eq 4.12).PMe3Nr uP^12 J ilvie30vacuum ON'^ CH2SiMe3PhO PMe3(4.12)On a larger scale, a yellow solid formulated as Cp*W(NO)(CH 2SiMe3)(OPh)(PMe3) is formed bythe treatment of Cp *W(NO)(CH2SiMe3)(OPh) with neat PMe3. In the presence of excess PMe3this solid is stable at low temperatures. However, it is not possible to isolate and further114__LA^triiiiiiriiiirtipliiiiilmitillimplimpilirinilimilltillô PPM -IFigure 4.1 1H NMR spectrum of Cp *W(NO)(CH2SiMe3 )(OPh) (3.5) and PMe3 at 24 °C inCDC13 .115PPM 1Figure 4.2 1H NMR spectrum of Cp *W(NO)(CH2 SiMe3)(OPh) (3.5) and PMe3 at -60 °C inCDC13 .116characterize this complex since at room temperature, under vacuum or in solution, the yellowadduct loses PMe3 .4.4.4.2 Insertion Reaction of Cp *W(NO)(CH2SiMe3)(OPh) and CNCMe3Tert-butyl isocyanide forms stable inserted products with dialkyl complexes 2 and alkylchloride complexes. 9 In a similar fashion, Cp*W(NO)(CH2SiMe3)(OPh) (3.5) reacts cleanly withCNCMe3 to provide the yellow iminoacyl complex, Cp *W(N0)(112-C{NCMe3 }CH2SiMe3)(0Ph)(4.3), in high yield (eq 4.13).CNCMe3 31 / ^// M**--- NC e 3^PhO =^PhO = CN N I0 0 RR= CH2 S2v1e3(4.13)Purple crystals of complex 3.5 readily react with an excess of CNCMe3 to form a yellow oilymixture. Excess CNCMe3 can be removed in vacuo to afford complex 4.3 as yellow oil, whichcan be easily crystallized from pentane to afford yellow nuggets of analytically pureCp*W(N0)(12-CfNCMe3 1CH2 SiMe3 )(0Ph). Reaction 4.13 demonstrates the Lewis acidicnature of 3.5 and lends more credence to the proposed PMe 3 adduct proposed in the previoussection.Consistent with other iminoacyl complexes that we have previously isolated, 2,9Cp*W(N0)(0Ph)(712-C{NCMe3 }CH2SiMe3) (4.3) contains a dihapto iminoacyl ligand. 23 Thus,the Nujol mull IR spectrum (Figure 4.3) of complex 4.3 exhibits two strong bands attributable tovCN and vNO at 1670 and 1585 cm-1 , respectively. The 1H NMR spectrum of 4.3 isstraightforward. The signals attributable to the diastereotopic methylene protons appear as twodoublets at 5 2.94 and 2.45 ppm.117N0NMi —MMa)mr: ^i 1739. 3N00rf).-4INsrg...•1582. 1 1424. 2 1287. 7 1110. 4wavenumbers (cm-1 )$I $IItomcoON8N0a;Irl04M4m1It)MM0NFigure 4.3 Nujol mull infrared spectrum (1739 - 953 cm -1) ofCp*W(N0)(1 2-C{NCMe3}CH2SiMe3)(0Ph) (4.3).H2O-Me3SiOHW"---NCMe3^PhO -^CN^I0 CH3(4.14). "1----- NCMe3PhO =^-^CN^ I0 CH2 SRVIe34.3118Like the related iminoacyl complex CpW(N0)(1 2-C{NCMe3 }CH2SiMe3 )(CH2SiMe3),2Cp*W(N0)(11 2-C{NCMe3 }CH2SiMe3)(0Ph) is unstable to water. Thus, the phenoxo complexundergoes hydrolysis to form Cp *W(N0)(712-C{NCMe3 }CH3)(0Ph) as evidenced by 1H NMRspectroscopy (Figure 4.4).4.3'The most notable difference in the 1FINMR spectra of 4.3 and 4.3' is the appearance of a singletat 5 2.08 ppm at the expense of two doublets (5 2.94 and 2.45 ppm) attributed to the methyleneprotons of the CH2 SiMe3 group in 4.3.4.4.4.3 Reactions of Alkoxo Alkyl Complexes with COCoordinatively unsaturated Cp'M(NO)R2 complexes form adducts with carbon monoxidewhich undergo intramolecular insertion of the coordinated carbon monoxide into the metal-carbonbond to form acyl species. 22 In contrast, the reactions of the 18-valence-electron dibenzylcomplexes Cp'M(NO)(CH2Ph)2 with CO, described in detail in Section 5.4.1.3, result in theproduction of Cp 1M(N0)(C0)2 and (PhCH2)2CO. In a similar fashion, the benzyl alkoxocomplex Cp *Mo(NO)(CH2Ph)(OCMe3) (3.1) reacts with an excess of carbon monoxide(600 psig) in benzene to form Cp *Mo(NO)(CO)2 (27% yield) and small amounts of1,3-diphenylacetone, i.e.,119Figure 4.4 Partial 1H NMR spectrum (5 3.1 - 0.1 ppm) of Cp sW(N0)(i2-C{NCMe3 )CH2SiMe3)(OPh) (4.3) and its hydrolysis product Cp *W(N0)(712-C{NCMe3)CH3)(0Ph) (4.3')marked with (•) in C 6D6 .0 0+ (4.15)CO(1 atm)OCMe3 Ph PhNOC CO120The reaction mixture contains at least six other organic products as evidenced by a GC trace ofthe reaction mixture after it has been filtered through alumina (I). In attempts to isolate theseorganic products, the reaction mixture was chromatographed on silica gel. The fractions that canbe separated by chromatography are inherently unstable and continue to decompose over time.Cp*Mo(NO)(CO)2 and (PhCH2)2C0 are both air- and moisture-stable complexes, so it wasnot unreasonable to assume that workup of the reaction mixture from equation 4.15 could bedone in the atmosphere in a traditional organic sense. It was soon discovered that mixtures ofpentane or Et20 solutions of Cp*Mo(NO)(CO)2 and (PhCH2)2C0 decompose over the course ofhours when they are exposed to the atmosphere. Therefore, isolation of the product complexesmust be performed under anaerobic and anhydrous conditions.The treatment of 3.1 with lower pressures of CO results in a mixture of organometallicproducts as evidenced by numerous resonances in the Cp * region of a 1H NMR spectrum of thereaction mixture. Cp *W(NO)(CH2SiMe3)(OPh) (3.5) also reacts with CO in C 6H6 to afford amixture of unisolable products.Reaction 4.15 is thought to proceed first by initial adduct formation, then subsequentinsertion of coordinated CO into the molybdenum-carbon bond. However, it is not possible torule out the insertion of CO into the molybdenum-oxygen link. 24 For a more complete discussionof reactions of this type, see Section 5.4.1.3. In the case of the alkoxo alkyl complex 3.1, if anintermediate acyl complex is formed [i.e. Cp*Mo(NO)(r1 2-C{O)CH2Ph)(0CMe 3)], reductiveelimination of the acyl and the alkoxo ligand from this intermediate would produceCp*Mo(NO)(CO)2 and the ester (PhCH2)C(0)OCMe3. There is no obvious reason why this121product would be unstable, but for some reason it is not isolated from the reaction mixture. It ispossible that (PhCH2)2C0 is formed by either a radical coupling process or via a bimolecularreductive elimination reaction of Cp*Mo(N0)(/2-C{O}CH2Ph)(0CMe3) andCp*Mo(N0)(0CMe3)(CH2Ph). In order to distinguish between these two mechanisms, I wouldsuggest the addition of a radical trap such as TEMPO to the reaction mixture or a crossoverexperiment (e.g. treatment of a 1:1 mixture of Cp *Mo(NO)(OCMe3)(CH2Ph) andCp*Mo(N0)(0CMe3)(CH2C6H4-4-Me) with CO). In such an experiment, the asymmetricketone, 4-Me-C6H4CH2C(0)CH2Ph, would be formed if bimolecular processes are in operation.Carbon monoxide induces a complicated sequence of reactions with the alkoxo alkylcompounds 3.1 and 3.5 providing a number of organometallic and organic products. In contrast,CNCMe3 , valence isoelectronic with CO, cleanly forms a stable insertion product with complex3.5. There is no obvious explanation why the alkoxo complexes react differently with CO thanwith CNCMe3 , since presumably both of these reagents form initial Lewis acid-base adducts withthe alkoxo alkyl species.4.4.4.4 Reactions of the Heterocumulenes CO 2 , CS2 and RNCO [R = Ph,p-toly11 withCp*W(NO)(CH2SiMe3)(OPh)Alkoxo complexes are known to undergo insertion of CO 2 and CS2 . 25 However,Cp *W(NO)(CH2SiMe3)(OPh) does not react with CO2 (1 atm) or with excess CS2 in pentane. Incontrast, the related isocyanates PINCO and p-tolylNCO react instantly with solidCp*W(NO)(CH2SiMe3)(OPh) to form the orange complexes 4.4 and 4.5, respectively.RNODCp*W(NO)(CH2SiMe3)(OPh)^Cp*W(N0)(CH2SiMe3)(0Ph)(RNCO) (4.16)The product complexes are markedly less soluble in organic solvents than their precursor,therefore excess RNCO can be washed away with pentane to leave analytically pure samples ofcomplexes 4.4 and 4.5. These complexes are relatively air-stable as solids and decompose slowlyas solutions when exposed to the atmosphere.122In contrast to the diaryl compounds which form inserted products, Cp*M(N0)(ary1)(1 2-N{p-toly1}C {0 } ary1), 26 complexes 4.4 and 4.5 have been formulated as adduct complexes for tworeasons. The Cp*M(N0)(ary1)0-1 2-N{p-toly1}C{O)aryl) species are stable in solution, showingno tendency to liberate PhNCO; whereas, adducts of the type Cp'M(NO)(alkyl)2(PMe3) undergoloss of PMe3 in solution. 3 The 1H NMR data for 4.4 and 4.5 indicate that the isocyanate ligandsare labile in solution. Thus, the 1H NMR spectum of an isolated sample of crystalline 4.4(Figure 4.5) partially dissociates in C 6D6 to Cp*W(NO)(CH2SiMe3 )(OPh) (3.5) and PhNCO suchthat complexes 4.4 and 3.5 exist in a 1:2.7 ratio. Addition of excess PhNCO changes this ratio to3.5:1. In a similar manner, 4.5 dissociates into a 1:6 equilibrium mixture, and this equilibrium canbe changed to 2.3:1 with the addition of excess p-tolyINCO (Figure 4.6). Further evidence forthe lability of the RNCO ligands in these adducts is found in the mass spectral data. Thus, thehighest m/z peak observed for 4.4 and 4.5 is [Pt-RNCO] whereas [Pt] and [Pt-NO] are observedfor the inserted species Cp *M(N0)(ary1)(1 2-N{p-toly1}C{O)ary1). 26The infrared spectra of the adducts as Nujol mulls exhibit two strong bands (1597, 1543cm-1 ) for complex 4.4 and 1554 and 1539 cm -1 for 4.5) in the nitrosyl region. The assignment ofthese bands is very difficult since nitrosyl, carbonyl, C-N and aryl stretches are commonlyobserved in this region. For comparison, the known Cp *W(N0)(Ph)(i2-N{p-toly1}C{O}Ph)complex exhibits three bands (vcN = 1601, vNo= 1576 and vco 1397 cm-1) in this region.261233.54.44.4!III II II I i I Idi I I I II I I III !III ii i 11111111111Hr13^ 2^ 16 PPM3.5Figure 4.5 1H NMI. spectrum of 4.4 in C6D6 ; an equilibrium mixture of 4.4,Cp*W(NO)(CH2SiMe3)(OPh) (3.5) and PhNCO.1244.54.53.53.54.5L )t jl kk^111111111IIIIIIiIIIIIIIIrlf1111111IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIi 1111 1 1111ti PPMFigure 4.6 1 H NMR spectrum of a C6D6 mixture of Cp *W(N0)(CH2SiMe3 )(0Ph) (3.5) andexcess p-tolyINCO (•).4.7Ph^0N.10,.. M°•ON'^O(PhH2, THE (4.17)1254.4.5 Reactions of Alkoxo Alkyl Complexes with DihydrogenWhen Cp *Mo(N0)(CH2Ph)(OCMe3) (3.1) reacts with H2 (40 psig), it is the metal-alkoxidelinkage that is the preferred site of reactivity as the unusual bimetallic complex[Cp *Mo(N0)(CH2Ph)(11-0)]2 (4.6) is isolable from the final reaction mixture in 19% yield (eq4.17). This reaction, as written, implies the cleavage of O-C bonds of alkoxo ligands.PhCH2^OCMe3N0In a typical experiment, a THE solution of complex 3.1 is pressurized to 40 psig with H2 in ahigh-pressure vessel. An initial IR spectrum of this red-orange solution exhibits two bands in thenitrosyl region (1595, 1585 cm -1 ). Over the course of several days, the IR spectrum changes andfinally exhibits a broad band in the nitrosyl region at 1618 cm -1 . No color changes accompanythis transformation. The amber product complex 4.7 is initially formed from diethyl ether in lowyields (19%), and it is easily recrystallized from CH 2C12/hexanes solutions. Compound 4.6 is anair-sensitive complex, and it decomposes thermally (>60 °C) in C6D6 solution.The identity of complex 4.7 was determined by X-ray crystallography. An ORTEP diagramof [Cp*Mo(N0)(CH2Ph)(11-0)] 2 is shown in Figure 4.7, and selected bond lengths and bondangles are presented in Table 4.4. 27 Complex 4.7 is a dimeric species with each molybdenumcenter in a four-legged piano-stool-type geometry. The nitrosyl ligands are essentially linear withMo-N-O bond angles of 168.9 (4)° and 168.1 (4)°. The crystallographic analysis reveals only oneisomer in the solid state. The Cp * ligands are trans to each other, and it is possible toapproximate the configuration as R,R if the oxo bridges are designated together as a 0 2 ligand.126Figure 4.7 ORTEP diagram of [Cp *Mo(N0)(CH2Ph)(µ-0)]2 (4.6). 33% probability thermalellipsoids are shown for the non-hydrogen atoms.127The metals are bridged by two oxo ligands. The slightly asymmetric Mo20 2 core unit of 4.7is clearly seen in the stereoview (Figure 4.8), and its dimensions are depicted pictorally below. 28Bond Lengths (A)^Bond Angles (°)^Intramolecular Distances (A)01^ 01 0168 Mot^3 54  :i 2X2.15^4^Z111NMol Mo2^Mol 67^ Mol^Mo22.12 72 N1137 i Z02^ 02 02The Mo-O bond distances are typical for single Mo-0 bonds. 29 A metal-metal bond is notinvoked for this complex, since the Mol-Mo2 separation is very long at 3.5407 (9) A. 3° 01 and02 are also not close enough (2.380 (5) A) to indicate a bond between these two atoms. 31Considering that there is no metal-metal bond in complex 4.7, and that the benzyl ligands andthe bridging oxo ligands are involved in simple sigma bonds, the electron count at each metalcenter in [Cp *Mo(N0)(CH2Ph)(1A-0)] 2 is 17e- as determined below:Cp*^ 5-electron donorMo 6 electrons in its valence shellNO 3-electron donorCH2Ph 1-electron donor2 x 11.-0^ 2 electrons (one from each bridging oxo ligand)Cp*Mo(N0)(CH2Ph)(1A-0)^17 electronsFrom this simple electron count, one might expect complex 4.7 to be paramagnetic. Therefore, amagnetic susceptibility measurement of [Cp *Mo(N0)(CH2Ph)(p.-0)] 2 was recorded(xm = -520 x 10 -6 cm3mo1 -1 ) on a Johnson-Matthey magnetic susceptibility balance at roomtemperature (Section 4.2.17). Hence overall, complex 4.7 is diamagnetic. This is consistent withthe fact that the 1H NMR spectrum of 4.7 exhibits no unusual chemical shifts or line widthbroadening as is normally expected for paramagnetic species. To account for[Cp*Mo(N0)(CH2Ph)(11-0)]2 being diamagnetic, it is possible that there is through-spaceMo-Mo coupling. 32 However, it is more likely that coupling of the unpaired electrons through128Figure 4.8 A stereoview of [Cp *Mo(N0)(CH2Ph)(1.1-0)}2 (4.6). 33% probability thermalellipsoids are shown for the non-hydrogen atoms.Table 4.4. Selected Bond Lengths and Bond Angles for [Cp *Mo(N0)(CH2Ph)(11-0)]2 (4.6)bond lengths (A) bond angles (°)Mol - 01 2.154 (3) Mol - 01 - Mo2 111.1 (1)Mol - 02 2.122 (3) Mol - 02 - Mo2 113.3 (1)Mo2 - 01 2.140 (3) 01 -Mol - 02 67.6 (1)Mo2 - 02 2.118 (3) 01 - Mo2 - 02 68.0 (1)Mol - Mo2a 3.5407 (9) Mol - C21 - C22 115.2 (3)01 -02a 2.380(5) Mo2 - C28 - C29 116.4(3)a Intermolecular distance. 11r^i^!lir^lir it^1^III!^111111111111111^!III^iir^r^III^!fill^r^18 6 4^2 0 PPM130liiiimpilliiIIIIIIIIIIIITIIIIIIIllipittlitruriiiiiiiiimilititilliwiliiIIIIIIItyll3.4^3.2^3.0^2.8^2.6^2.4^2.2^2.0 PPM 1.8Figure 4.10 Partial 1H NMR spectrum (8 3.56 - 1.74 ppm) of [Cp *Mo(N0)(CH2Ph)(11-0)]2(4.6) in C6D6 .131IIIIIIIi^III -111111111i^I^I^I ^ti^►1.bo^i.55^i.bo^i.45^1.40 PPMFigure 4.11 Partial 1H NMR spectrum (5 1.64 - 1.36 ppm) of [Cp *Mo(N0)(CH2Ph)(11-0)12(4.6) in C6D6 .132Figure 4.12 Partial 1H NMR spectrum (5 0.6 to -1.9 ppm) of [Cp*Mo(NO)(CH2Ph)(1-1-0)}2(4.6) in C6D6 .133the oxygen bridges is occurring. 33 This phenomenon is commonly called superexchange, 34 and inthis case the unpaired electrons are very strongly antiferromagnetically coupled.The spectral data are not very informative in elucidating the identity of[Cp*Mo(N0)(CH2Ph)(p.-0)]2. The mass spectrum of [Cp *Mo(NO)(CH2Ph)(1-0)]2 is attributedto [Cp*M0(0)2]2-(11-0), a common decomposition product of molybdenum nitrosyl-containingcomplexes, and the IR spectrum of 4.7 exhibits a number of bands (1599, 1588, 1568 cm -1 ) in thenitrosyl region as well as several absorptions (756, 748, 700 cm -1) in the region expected forMo-O-Mo stretches. 35 The 1H NMR spectrum of [Cp*Mo(NO)(CH2Ph)(1-0)]2 in C 6D6(Figures 4.9 - 4.12) is extremely complex and has not been assigned to date. Most notably in the1H NMR spectrum of 4.6 there are at least four different resonances (5 1.61, 1.49, 1.48, 1.42ppm) in the Cp * region. Signals that may be attributable to methylene protons occur at 5 0.42 and-1.74 ppm (J= 1.2 Hz). In addition, the 1H NMR spectrum of 4.6 exhibits two other complexpatterns between 5 3.25 - 2.71 ppm and 5 2.14 - 1.82 ppm. It is clear from this data that[Cp*Mo(N0)(CH2Ph)(1A-0)]2 does not retain the observed solid-state bimetallic structure insolution. Complex 4.6 most likely exists as a mixture of isomers in solution. The crystal structureindicates the Cp* ligands are trans to each other; however, there are no steric reasons why thiscomplex could not also exist in the cis configuration. It is also possible to envision diastereomersfor each of these geometric isomers.An alternative formulation of complex 4.6 is as [Cp *Mo(N0)(CH2Ph)(11-0H)12. This18-valence-electron species is analogous to complexes of the type [Cp *M(N0)(C1)(4-0H)] 2which were prepared in Chapter 2. [Cp*Mo(N0)(CH2Ph)(g-OH)]2 has a C/H/N ratio consistentwith the data from elemental analysis, and the hydroxide complex would be expected to bediamagnetic. However, no hydroxide stretches (vOH = 3650 - 3584 cm -1)36 or bends (50H =1420 - 1330 cm -1 )36 are observed in the infrared spectrum of 4.6.134The final difference map showed peaks of 0.30 - 0.35 e/A3 that could correspond to hydrogenatoms associated with the bridging oxygen atoms. Attempts to refine these peaks as H atomsgave ambiguous results: one refined to a reasonable position and the other did not. Inclusion ofthe "µ-OH" protons in the model did not lead to any improvement of the residuals. 1H NMRspectroscopy, mass spectrometry and elemental analysis cannot distinguish between the twopossible formulations. If the 1H NMR spectrum was not so complex, it would be possible tocarry out labeling studies (e.g. 180 and 2H) and 2-D NMR experiments to determine if there arehydroxide ligands present in complex 4.6. Attempts were made to prepare[Cp*Mo(N0)(CH2Ph)(pt-OH)] n by reacting Cp *Mo(N0)(CH2Ph)Cl with 1 equiv of NaOH inpentane, but these reaction mixtures decomposed to insoluble tan solids. Another possibleindependent route to [Cp *Mo(N0)(CH2Ph)(1..t-OH)] n could be by the treatment of[Cp*Mo(N0)(CI)(p.-OH)]2 with Mg(CH2Ph)2 .Attempts to extend this chemistry to related alkoxo complexes have to date beenunsuccessful. Thus, no reaction occurs between Cp *Mo(N0)(OCMe3 )2 (2.1),Cp*Mo(N0)(CH2Ph)2 , Cp *W(N0)(CH2Ph)2 , Cp*W(N0)(CH2Ph)(OCMe3) (3.3),Cp*W(N0)(CH2SiMe 3 )(OCMe3) (3.4), and Cp*W(N0)(CH2SiMe3)(OPh) (3.5) with H2(40 psig) in THE under similar experimental conditions. Since none of these analogues react withdihydrogen, the reaction between 3.1 and H2 is quite possibly unique.4.5 Epilogue and Future WorkSelected alkoxo alkyl complexes were reacted with a variety of reagents such as 0 2 and H2O,HCI, alcohols and H2. In Lewis acid-base type reactions with PMe 3 , CNCMe3 , PhNCO andp-tolylNCO, the alkoxo alkyl species were shown to be sufficiently electron deficient to form 1:1adducts or insertion products. In the case of CO, subsequent reaction of the adduct occurs toproduce a multitude of products. Many of the reactions described in this chapter cannot begeneralized to other alkoxo alkyl complexes. This work has established that the reaction135chemistry of alkoxo alkyl complexes of the type Cp *M(N0)(R)(01V) is diverse; however it isunpredictable and not well-behaved.The prototypal alcohol exchange reaction (eq 4.9) indicates that Cp *M(N0)(R)(OR')complexes may be utilized as synthetic reagents for preparing compounds with heteroatomgroups. Chelating alcohols, carboxylic acids, alkyl and arylthiols may react with these alkoxospecies to afford new alkoxo alkyl, alkyl amido and alkyl thiolate complexes.An interesting diamagnetic bimetallic complex, [Cp *Mo(N0)(CH2Ph)(1.1-0)]2, was producedwhen Cp*Mo(NO)(CH2Ph)(OCMe3) (3.1) was treated with H2 in THF. Elucidating the complexnature of the product in solution is essential before an investigation of its potentially rich reactionchemistry can be undertaken. Future work in this area may also include establishing the role ofH2 in this oxygen-carbon bond cleavage reaction.In general, reactivity studies of these three classes of alkoxo complexes, Cp *M(NO)(OR)Rhave shown that the alkoxo ligands either stabilize their complexes as in the case of thebis(alkoxo) complexes or the alkoxo ligands themselves are the site of reactivity.1364.6 References and Notes(1) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Metal Alkoxides; Academic Press: New York,1978.(2) Legzdins, P.; Rettig, S. J.; Sanchez, L. Organometallics 1988, 7, 2394.(3) Legzdins, P.; Veltheer, J. E. Acc. Chem. Res. 1992, 26, 41.(4) Dryden, N. H.; Legzdins, P.; Rettig, S. J.; Veltheer, J. E. Organometallics 1992, 11, 2583.(5) Dryden, N. H.; Legzdins, P.; Trotter, J.; Yee, V. C. Organometallics 1991, 10, 2857.(6) (a) [Cp*M0(0)2]2-(p.-0) was first synthesized by Faller's group. See Faller, J. W.; Ma, Y.J. Organomet. Chem. 1988, 340, 59. (b) Legzdins, P.; Lundmark, P. J.; Phillips, E.C.;Rettig, S. J.; Veltheer, J. E. Organometallics 1992, 11, 2991.(7) Legzdins, P.; Phillips, E. C.; Sanchez, L. Organometallics 1989, 8, 940.(8) Presumably the complex is undergoing decomposition to the bridging oxo bimetallic as aresult of residual water in the solvents.(9) At this point the flask contains Cp *Mo(NO)(CH2CMe2Ph)Cl (vNO = 1618 cm-1 ), seeVeltheer, J. E. Ph.D. Dissertation, The University of British Columbia, 1993.(10) [Cp *Mo(N0)(CH2CMe2Ph)]2-(1.1-0) (4.2) can also be prepared by the treatment ofCp*Mo(NO)(CH2CMe2Ph)2 with H20. 6b The route described in section 4.2.6 leads to aless oily product, presumably because the byproduct is HOCMe 3 rather than Me3 CPh, andthus is more easily removed in vacuo.(11) Debad, J. D.; Legzdins, P.; Batchelor, R. J.; Einstein, F. W. B. Organometallics 1992, 11,6.(12) See Section 5.2.4 for the characterization data of Cp*Mo(NO)(CO)2.(13) See Tables 5.1 - 5.3 for the characterization data of 1,3-diphenylacetone.(14) Chem 310 -335 Laboratory Manual, University of British Columbia, 1992, pp 71-73.137(15) The diagmagnetic contributions of Cp *, Mo, CH2Ph, 0, NO were estimated at -108 x 10 -6 ,-56 x 10 -6 , -63 x 10-6 , -10 x 10-6 and -20 x 10-6 cm3mo1-1 , respectively. See: KOnig, E.Landolt-Bornstein Numerical Data and functional Relationships in Science andTechnology. New Series; Vol.11/2. Hellwege, K.H.; Hellwege, A. M., Eds.; Springer-Verlag: Berlin, 1966.(16) Some [Cp'Mo(NO)(R)] 2-(t-O) complexes exist as a mixture of diastereomers, seereference 6b.(17) The structure of [Cp*Mo(N0)(CH2SiMe3 )}2-(4-0) has been published, see reference 6b.(18) (a) Fessenden, R. J.; Fessenden, J. S. Organic Chemistry, 3rd ed.; Brooks/Cole PublishingCo.: Monterey, CA, 1986; p 281. (b) March, J. Advanced Organic Chemistry, 3rd ed.;John Wiley & Sons: New York, 1985; p 221.(19) Ludner, D. M.; Lobkovsky, E. B.; Streib, W. E.; Caulton, K. G. J. Am. Chem. Soc. 1991,113, 1837.(20) Simpson, R. D.; Bergman, R. G. Organometallics 1993, 12, 781.(21) (a) Newman, L. J.; Bergman, R. G. J. Am. Chem. Soc. 1985, 107, 5314. (b) Michelman,R. I.; Anderson, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1991, 113, 5100.(22) Dryden, N. H.; Legzdins, P.; Lundmark, P. J.; Riesen, A.; Einstein, F. W. B.Organometallics 1993, 12, 2085.(23) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 1059.(24) (a) Bryndza, H. E. Organometallics 1985, 4, 1686. (b) Rees, W. M.; Atwood, J. D.Organometallics 1985, 4, 402.(25) (a) Simpson, R. D.; Bergman, R. G. Agnew Chem. Int. Ed. Eng11992, 31, 209. (b)Simpson, R. D.; Bergman, R. G. Organometallics 1992, 11, 4306. (c) Darensbourg, D. J.;Sanchez, K. M.; Rheingold, A. L. J. Am. Chem. Soc. 1987, 109, 290.138(26) (a) Brouwer, E. B. M.Sc. Dissertation, The University of British Columbia, 1992. (b)Brouwer, E. B.; Legzdins, P.; Rettig, S. J.; Ross, K. J. Organometallics, in press.(27) Crystals of 4.7 are monoclinic of space group P2 1/c (#14); a = 15.822 (4) A, b = 12.660 (4)A, c = 16.657 (2) A, r3 = 91.70 (2)°, V= 3335 (1) A3 , Z= 4. Dr. S. J. Rettig solved thestructure using the Patterson method and full-matrix least-squares refinement procedures toR = 0.039, R. = 0.042 for 4156 reflections with I 3a(/).(28) A similar W202 core unit was observed in the partial X-ray structure determination for theproduct from the reaction of Cp *W(N0)(OCMe3)2 and H2 (Section 2.4.2).(29) The average value for single Mo-O bonds is 1.900 A, see Orpen, A. G.; Brammer, L.;Allen, F. H.; Kennard, 0.; Watson, D. G. J. Chem. Soc., Dalton Trans. 1989, Si.(30) A bond is usually invoked if the distance between two atoms is less than 1.25 times the sumof the covalent radii. The covalent radii of Mo is 1.30 A, therefore a Mo-Mo bond wouldbe invoked if the Mo-Mo distance was less than 3.25 A.(31) For comparison [0 212- has an 0-0 bond distance of 1.49 A, see The CRC Handbook ofChemistry and Physics, 62nd Edition; Weast, R. C., Astle, M. J., Eds.; CRC Press, Inc.:Boca Raton, Florida, 1982. The covalent radii of 0 is 0.73 A.(32) Rohmer, M. M.; Benard M. Organometallics 1991, 10, 157.(33) (a) Vincent, J. B.; Olivier-Lilley, G. L.; Averill, B. A. Chem. Rev. 1990, 90, 1447.(b)Holtzelmann, R.; Wieghardt, K.; Floerke, U.; Haupt, H. J.; Weatherburn, D. C.Bonvoisin, J.; Blondin, G.; Girerd, J. J. J. Am. Chem. Soc. 1992, 114, 1681.(34) See, for example, Hatfield, W. E.; Paschal J. S. J. Am. Chem. Soc. 1964, 86, 3888.(35) Nakamoto, K Infrared and Raman Spectra of Inorganic and Coordination Compounds,4th ed.; John Wiley and Sons: New York, NY, 1986.(36) Silverstein, R. M.; Bassel, G.C; Morrill, T. C. Spectroscopic Identification of OrganicCompounds, 4th ed.; John Wiley and Sons: New York, NY, 1981, p 112 - 114.139CHAPTER 5Reactions of Cp'M(NO)R2 Complexes with Carbon Monoxide5.1 Introduction^  1395.2 Experimental Procedures ^  1425.3 Characterization Data  1465.4 Results and Discussion^  1495.5 Epilogue and Future Work  1645.6 References and Notes ^ 1655.1 IntroductionThe migratory insertion of carbon monoxide into metal-carbon a bonds is one of the mostextensively studied reactions in organotransition-metal chemistry. The principal reason for thisconsiderable expenditure of effort is the practical importance of both stoichiometric and catalyticcarbonylation reactions in which migratory insertion is the means by which the CO becomesactivated by the transition-metal center. 1The prototypical example of migratory insertion of carbon monoxide is the conversion of analkyl carbonyl complex into an acyl complex with concomitant incorporation of an external ligand,L, i.e.R-M-CO + L L-M-C{O}R^(5.1)A number of mechanistic pathways are available for reaction (5.1), the dominant path often beingcontrolled by the nature of the solvent. 2 Much less common examples of carbon monoxide140insertions are systems in which an external CO molecule is the source of the inserted CO and noincorporation of a trapping ligand is necessary for the insertion to occur, i.e. 2M-R + CO M-C{O}R^(5.2)The interest in the organometallic chemistry of CO is largely centered on attempts to findnew catalytic processes for the conversion of CO into useful organic chemicals or to clarify thesteps of CO reduction in the Fischer-Tropsch process (eq. 5.3). 3catalystCO ± H2 heat, pres sure CH3(CH2)nCH2OH + CH3(CH2)nCH=CH2 + CH3(CH2)nCH3 (5.3)Bidentate (1 2) acyls are believed to be kinetically important species in the C-0 bond cleavage stepof Fischer-Tropsch catalysis. 4 However, most acyl ligands reported in the literature adopt an1 1 -coordination.It has been shown that the reactivity of 16-electron Cp'M(NO)R2 complexes is dominated bytheir ability to form 1:1 adducts with small Lewis bases; these adducts are either isolable as suchor undergo subsequent intramolecular transformations involving the hydrocarbyl ligands. 5 NeilDryden initially investigated some reactions of selected Cp'W(NO)R2 [R = alkyl, aryl] complexeswith carbon monoxide. 6 He expected that the Cp'W(NO)R 2 compounds would react with CO toproduce stable insertion products such as the acyl alkyl complexes, Cp'M(NO)(C{O}R)R. Indeedthis was the case, and in some instances treatment with additional CO resulted in stable bis(acyl)complexes, CpW(N0)(C{O}R)2. The following charts summarizes the research completed priorto this work. The ^is indicate the successful synthesis of the complex, whereas the x's indicatethat an attempt was made but the complex was not synthesizable. The blanks in the chartsindicate that the synthesis was not attempted.Cp'W(NO)(C{O}R)(R)R = alkyl R = arylCp' = CpCp' = Cp *Cp' = CpCp' = Cp *Cp'W(NO)(C{O}R)2R = alkyl R = arylx141This chapter reports the extension of these CO reactions to include the four possible variantsof Cp'W(NO)R2, namely where Cp' = Cp or Cp * , R = alkyl or aryl. The charts presented belowsummarizes the research now completed.Cp'W(NO)(C{O}R)(R)R = alkyl R = arylCp' = CpCp' = Cp *Cp' = CpCp' = Cp*Cp'W(N0)(C{0}R)2R = alkyl R = arylxx^xFrom this completed set of reactions, it is now possible to draw some general conclusions aboutCO insertion reactions in Cp'M(NO)R2 systems. It has been found that the outcome of theseinsertion reactions is profoundly dependent on the natures of Cp' and R. The formation of themonoacyl species occurs for all four variants. Only when Cp' = Cp and R = alkyl does a secondinsertion occur to form the bis(acyl) products.This chapter also reports on the reactions of Cp'M(NO)(CH2Ar)2 complexes with CO toform both ketones and the corresponding Cp'M(NO)(CO)2 species. The 18-electron 7 dialkylcomplexes Cp'M(NO)(CH2Ar)2 presumably undergo insertion of carbon monoxide into a metal-benzyl bond to form, transiently, the monoinserted products. These products are not thermallystable and reductively eliminate the ketones, (ArCH2)2CO. The remaining organometallicfragment is trapped by excess CO.142Finally, the reaction of CpW(N0)(C{O)CH2CMe2Ph)(CH 2CMe2Ph) with PMe3 isdescribed. This reaction results not in the expected metal-centered adduct but rather an ylidecomplex where PMe 3 is attached to the acyl carbon.5.2 Experimental Procedures5.2.1 MethodsThe synthetic methodologies employed in this chapter are described in detail in Section 2.2.1.The customary methodology employed during cyclic voltammetry (CV) studies has beendescribed in detail previously. 8 The potentials were supplied by a BAS CV27 voltammograph,and the resulting cyclic voltammograms were recorded on a Hewlett-Packard Model 7090A X-Yrecorder in the buffered recording mode. The three-electrode cell consisted of a Pt-bead workingelectrode (-1 mm diameter), a coiled Pt-wire auxiliary electrode, and a Ag-wire referenceelectrode. THF solutions were prepared in a glovebox to 0.10 M in the [n-Bu4N]PF6 supportelectrolyte and —6 x 10 -4 M in the organometallic complex to be studied. Ferrocene was used asan internal reference, with the redox couple Cp2Fe/Cp2Fe+occuring at E" = 0.53 V versus Agwire in THF over the scan range used (0.10 - 0.80 V/s).5.2.2 ReagentsCp'M(NO)(CH2Ph)2 [M = Mo, W], 7 '9 CpW(NO)R2 [R = CH2CMe3 , CH2CMe2Ph], 5Cp*W(NO)R2 [R = p-tolyl, CH2CMe2Ph], 10 Cp*Mo(N0)(CH2C61-14-4-Me)2 11 andMg(p-toly1)2X(dioxane) 1 ° were synthesized by the published procedures. The derivativemonoacyl compounds CpW(N0)(112-C{O}R)(R) [R = CH2CMe2Ph, CH2CMe3 ],Cp*W(N0)(12-C{0}11)(R) [R =p-tolyl, CH2CMe2Ph], and the bis(acyl) complexesCpW(NO)(r1 2-C{O}R)2 [R = CH2CMe2Ph, CH2CMe3] were prepared as previouslyreported. 6,12 CO (Matheson CP grade) was used as received.1435.2.3 Reaction of CpW(NO)(p-tolyl)2 with CO (1 atm)A blue solution of CpW(NO)(p-tolyl)2 was generated from CpW(NO)C1 2 (0.70 g, 2.0 mmol)and Mg(p-toly1)2•(dioxane) 10 (2.0 mmol) in THE (25 mL) at -60 °C. The reaction solution waswarmed to -10 °C and exposed to CO (1 atm) whereupon the solution quickly turned orange.The solvent was removed in vacuo, and the orange residue was extracted with CH2Cl2(4 x 50 mL). The combined CH2Cl2 extracts were filtered through Florisil (2 x 8 cm) supportedon a sintered-glass frit. The filtrate was taken to dryness and the remaining residue was extractedwith Et20 (2 x 20 mL). These Et20 extracts were subsequently filtered through Celite (2 x 8 cm)supported on a sintered-glass frit. The Et 20 filtrate was concentrated in vacuo and cooled to-10 °C to induce the crystallization of 0.038 g (4% yield based on CpW(NO)C12) ofCpW(N0)(i2-C{0}-p-toly1)(p-toly1) (5.1) as orange microcrystals. Spectroscopic data forcomplex 5.1 are contained in Tables 5.1 - 5.3.5.2.4 General Synthetic Methodology Employed for High-Pressure Carbon MonoxideReactionsAll high-pressure CO reactions were performed under similar reaction conditions.Specifically, in an inert atmosphere glovebox, a solution of the organometallic reactant in C6H6(20 mL) was prepared in a Pyrex liner for a 300-mL Parr pressure reactor. The reactor was thenassembled, removed from the glovebox, pressurized to 30 atm of CO, and left with its contentsunstirred for 24 h. Excess CO pressure was then vented to a fumehood, and the reactor wastaken back into the glovebox and disassembled. The final reaction solution was transferred into aflask and removed from the glovebox. The specific details of the workup of the individualreaction solutions are presented in the following sections.1445.2.5 Reaction of Cp *W(N0)(112-C{O}CH2CMe2Ph)(CH2CMe2Ph) with CO (30 atm)The reaction of Cp*W(N0)(r12-C{O}CH2CMe2Ph)(CH2CMe2Ph) with CO was performedas described in Section 5.2.4. The solvent was removed from the final orange reaction solutionunder reduced pressure. The IR spectrum of the remaining red-orange solid as a Nujol mullexhibited bands at 2000 (s), 1733 (m), and 1606 (br) cm -1 in the region between 2200 and1500 cm -1 . All attempts to crystallize this new material afforded only the initial reactant. Forcomparison, the IR spectrum of the Cp *W(N0)(r12-C{O)CH2CMe2Ph)(CH2CMe2Ph) reactant asa Nujol mull exhibited vNo = 1561 cm -1 and vco = 1537 cm-1 .5.2.6 Treatment of CpW(N0)(71 2-C{0} -p-toly1)(p-toly1) (5.1) with CO (30 atm)The treatment of 5.1 with CO was effected in the manner described in Section 5.2.4.Removal of solvent from the final reaction solution in vacuo afforded an orange solid. A Nujolmull IR spectrum of this solid in the region 2200 - 1500 cm -1 exhibited features diagnostic onlyof the organometallic reactant, i.e. 1603, 1580, 1568, and 1524 cm -1 .5.2.7 Reactions of Cp'M(NO)(CH2Ph)2 [Cp = Cp, Cp * ; M = Mo, W] with CO (30 atm)These reactions were all effected under similar experimental conditions. The reaction ofCp*Mo(NO)(CH2Ph)2 with CO is described below as a representative example.The high-pressure treatment of Cp*Mo(NO)(CH2Ph)2 (1.32 g, 3.00 mmol) with CO wascarried out in a Parr reactor (see Section 5.2.4). The resulting amber solution was reduced to ayellow-brown, oily solid in vacuo. This solid was redissolved in pentane, and then transferred tothe top of a silica gel column (2 x 8 cm) made up in pentane. The column was eluted withpentane, resulting in the elution of a single orange band which was collected and concentrated invacuo. Cooling of this concentrated solution in a freezer (-10 °C) overnight resulted in thedeposition of orange crystals (0.30 g, 32% yield) of Cp*Mo(NO)(CO)2.145Anal. Calcd for C 1 2H15NO3Mo: C, 45.44; H, 4.77; N, 4.42. Found: C, 45.45; H, 4.80; N,4.50. IR (Nujol mull): vco 2000 (s), 1927 (s) cm-1 , vNo 1661 (s) cm-1 . 1H NMR (C6D6):8 1.62 (s, C 5(CH3)5). 13 C{ 11-1} NMR. (C6D6): 8 220.0 (CO), 106.1 (C5(CH3)5 ,10.4 (C5(CH3)5)• Low-resolution mass spectrum (probe temperature 80 °C): m/z 319 [Pt].Subsequent elution of the silica column with Et 20 developed an amber band which was alsocollected and reduced to an amber oil 5.2 in vacuo. The spectroscopic properties of this oil(-0.15 g, —24% yield) were identical to those exhibited by an authentic sample of1,3-diphenylacetone (Tables 5.1 - 5.3).The other Cp'M(NO)(CH2Ph)2 complexes also converted to 1,3-diphenylacetone and theappropriate Cp'M(NO)(CO) 2 complex when exposed to CO under the experimental conditionsdescribed above.5.2.8 Reaction of Cp *Mo(N0)(CH2C61114-4-Me)2 with CO (30 atm)The high-pressure treatment of Cp *Mo(N0)(CH2C6H4-4-Me)2 (0.60 g, 1.3 mmol) with COwas effected in the manner described in Section 5.2.4. The final amber solution was reduced toan amber-red oil in vacuo. An IR spectrum of the oil as a Nujol mull exhibited bands at 2000 (s),1930 (m), 1726 (m), 1713 (m), 1663 (s), and 1515 (m) cm-1 in the region 2200-1500 cm -1 . Theoil was dissolved in pentane and transferred to the top of a silica gel column (2 x 20 cm) made upin pentane. Elution of the column with pentane developed an orange band which was collectedand concentrated in vacuo. Orange crystals (0.10 g, 25% yield) of Cp *Mo(NO)(CO)2 (videsupra) were deposited from this solution upon cooling to -10 °C overnight.Further elution of the column with Et20/pentane (1:1) afforded a pale yellow band which wascollected and taken to dryness in vacuo. The resulting pale yellow residue was recrystallized frompentane to obtain analytically pure (4-Me-C 6H4CH2)2C0 (5.3) (0.06 g, 20% yield) as a white,crystalline solid. Spectroscopic data for complex 5.3 are contained in Tables 5.1 - 5.3.1465.2.9 Preparation of CpW(NO)(C{O}{PMe3)CH2CMe2Ph)(CH2CMe2Ph) (5.4)Excess PMe3 was vacuum transferred into an orange CH 2C12 (10 mL) solution ofCpW(NO)(r1 2-C{O}CH2CMe2Ph)(CH2CMe2Ph) (0.10 g, 0.17 mmol). The reaction mixture wasstirred for 0.5 h by which time the solution was pale yellow. The final solution was taken todryness in vacuo. The resulting solid was redissolved in 1:1 CH2C12/hexanes (20 mL) and filteredthrough Celite (2 x 4 cm) supported on a medium-porosity glass frit. The filtrate wasconcentrated under reduced pressure and was placed in the freezer at -30 °C overnight to inducethe precipitation of CpW(N0)(C{0){PMe 3 }CH2CMe2Ph)(CH2CMe2Ph) (5.4) as pale yellowflakes (0.07 g, 63% yield). Spectroscopic data for complex 5.4 are contained in Tables 5.1 - 5.3.5.3 Characterization DataTable 5.1. Numbering Scheme, Color, Yield and Elemental Analysis Data for Complexes5.1 - 5.4complex compdno.anal. found (calcd)C H NCpW(N0)(C{0}-p-toly1)(p-toly1) 5.1 48.82 (48.10) 3.91 (3.91) 2.79 (2.86)(PhCH2)2C0a 5.2(4-MeC6H4CH2)2C0 5.3 85.68 (85.67) 7.66 (7.61) 0.00 (0.00)CpW(NO)(C{O}{PMe3 }CH2CMe2Ph)(CH2CMe2Ph)5.4 53.53 (53.63) 6.10 (6.20) 2.10 (2.16)°Elemental analysis of this compound was not obtained due to its oily nature.147Table 5.2. Mass Spectral and Infrared Data for Complexes 5.1 - 5.4compdno.MS, m/za temp,b °C IR, cm-1VN 0 (CH2 C12) vco(CH2C12) other5.1 461 [131 120 1592 15355.2 210 [P+] 150 1717C 754, 733, 6985.3 238 [Pt] 180 1726, 1713d 15155.4 649 [P+]621 [P+ - CO]545 [P ' - CO -PMe3 ]100 1493a m/z values are for the highest intensity peak of the calculated isotopic cluster, i.e. 98m 0 andb Probe temperatures.° IR spectrum is recorded neat.d IR spectrum is recorded as a Nujol mull.Table 5.3. 1H and 13C{ 1H} NMR Data for Complexes 5.1 - 5.4 in C 6D6compdno.1H NMR (8, ppm) 130{1H} NMR (8, ppm)5.1 8.23 (d, 2H, o-ArH, 3./Fni = 9 Hz)7.77 (d, 2H, o-ArH, 3Jnn = 9 Hz)7.35 (d, 2H, m-ArH, 3J/in = 9 Hz)6.85 (d, 2H, m-ArH, 3J/in = 9 Hz)5.22 (s, 5H, C5H5)2.34 (s, 3H, C(0)ArCH3)1.93 (s, 3H, WArCH3)5.2 7.20 - 6.90 (m, C6H5) 204.8 (CO)3.34 (s, CH2). 135.7 (C tpse)129.9 (Cpm.)128.9 (Cmet.)127.0 (Ceram)49.0 (CH2).5.3 6.92 (s, 8H, C6H4) 204.0 (CO)3.39 (s, 4H, CH2) 136.4, 131.8 (Gip.° and Cp.)2.10 (s, 6H, CH3) 129.7, 129.5 (Cmet. and Ceram)48.6 (CH2)21.0 (CH3).7.90 (d, 2H, o-ArH, 3JHH = 7.5 Hz)7.81 (d, 2H, o-ArH, 3.4m = 7.5 Hz)7.42-7.01 (m, 6H, ArH)5.19 (s, 5H, C5H5)2.68 (d, 1H, WCH2, 2jHH = 12.9 Hz)2.37 (d, 1H, WCH2, 2JH = 12.9 Hz)2.20 (dd, 1H, C(0)CH2, 2JHH = 15.6 Hz, 3JHp =30.9 Hz)2.09 (dd, 1H, C(0)CH2, 2.1mi 15.6 Hz , 3JHP10.8 Hz)2.00, 1.98, 1.57, 1.31 (s, 4 x 3H, C(CH3))0.640 (d, 9H, PMe3 , 2.4/1 = 9.6 Hz)155.41 (Cis)149.67 (Cm.)128.33 (Carom)128.06 (Carom)127.90 (Carom)127.02 (Carom)126.26 (C om)124.73 (C )rm58.14 (d, Jcp = 45.1 Hz,C(0)(PMe3))49.89 (d, 2Jcp = 26.8 Hz,C(0)(PMe3)CH2)44.61 (Clue)44.41 (Com)40.21 (WCH2)36.53, 32.79, 31.21, 29.69 (4 x CH3)16.40 (P(CH3), 1Jcp= 13.2 Hz)5.4aa The 3113 { 1 H) NMR spectrum exhibits a singlet at 6.88 ppm ( 1,/pw = 95.3Hz) attributable to coordinated PMe 3 .48CO R = CH2Ar^0'rit)CRs........... ,2:5CO1)PC152)R2MgOC1495.4 Results and DiscussionThe reactions of the various Cp'W(NO)R 2 complexes with carbon monoxide proceed in thestep-wise fashion summarized in Scheme 5.1. The first step involves the conversion of the16-electron bis(alkyl) or bis(aryl) complex to the corresponding 18-electron monoacyl species,probably via an initially formed carbonyl adduct. 5 The /2-acyl-containing complex may beisolable as such or may undergo spontaneous reductive elimination of the symmetrical ketone ifR = CH2Ar. The second step involves the uptake of a second equivalent of CO and the formationof the 18-electron bis(acyl) complex, again via an initially formed carbonyl adduct. Exactly whichpath is followed in a particular instance is dependent upon both the natures of Cp' and R and theexperimental conditions employed. These features are emphasized in the discussion that follows.Scheme 5.1.c.....j.?.t'5^ R'SICO^zW^-a..^., ,'WR ^R^kill Vp^N N C^0 0^IRCO R' = H(5.5)N R01505.4.1 Step 1: Formation of the Monoacyl ComplexesNeil Dryden observed that the treatment of Cp*W(N0)(p-toly1) 2 with 1 atm of CO in Et20 at-38 °C resulted in the formation of a yellow-green precipitate which was formulated as the18-electron, terminal carbonyl adduct of the starting complex (eq 5.4). 6 I.^.RV \ " CO (5.4)N0N R0R = p-tolylThis formulation of the product is based on the presence of a distinctive IR absorption at2014 cm -1 in the Nujol mull IR spectrum of the green solid attributable to a terminal CO ligand.Conversion 5.4 is also consistent with the documented ability of Cp'M(NO)R2 complexes(M = Mo, W) to form 1:1 adducts with small Lewis bases. 5,13 As the terminal carbonyl adduct,Cp *W(N0)(C0)(p-toly1)2, warms to room temperature the coordinated CO inserts into one of thetungsten-aryl bonds to form the corresponding red-orange acyl aryl complex (eq 5.5).R =p-tolylWhile there are no CO adducts observed during the carbonylations of the other Cp'W(NO)R2complexes, it is likely that all the Cp'W(N0)(1 2-C(0)R)(R) complexes synthesized during this151work result from initially formed terminal CO adducts. Carbonylation of the bis(hydrocarbyl)complexes, Cp'W(NO)R2 , occurs irreversibly under very mild conditions in a variety of solventsto afford the monoacyl complexes (eq 5.6).Cp'W(NO)(R)2 + CO (1 atm) Cp'W(N0)(112-C{O}R)R^(5.6)These Cp'W(NO)(r12-C{O}R)R product complexes [Cp' = Cp *, R = CH2CMe2Ph, p-tolyl;Cp' = Cp, R = CH2CMe2Ph, CH2CMe3 , p-tolyl] constitute a new family of thermally stablemonoacyl organometallic compounds. The reactions of the thermally-sensitive diaryl complexeswith CO are best performed at lower temperatures since they are much more reactive than theircongeneric dialkyl complexes. This higher reactivity has been attributed to the greater Lewisacidity of the diary] species relative to the dialkyl complexes. 6,13 The yellow acyl alkyl complexesand the red-orange acyl aryl complexes show reduced solubility in aliphatic hydrocarbon solventswhen compared to their 16-electron precursors, but they are very soluble in aromatic and polarorganic solvents.5.4.1.1 Spectroscopic Properties of the Monoacyl Nitrosyl ComplexThe IR spectrum of complex 5.1 in CH2C12 (Table 5.2) exibits two strong bands at 1592 and1535 cm -1 due to the vibrations of the nitrosyl and 71 2-acyl ligands. The 1535 cm -1 band isassigned to the vco of CpW(N0)(7-1 2-C{0}-p-toly1)(p-toly1) by analogy to the labeling studiesdone by Neil Dryden. 6 The vco value falls well within the range generally observed for i2-acyls(1625-1453 cm-1 ), 1 and thus 5.1 is formulated as the 18-electron species,CpW(NO)(r12-C {0} -p-toly1)(p-toly1).The 1H NMR spectroscopic properties of 5.1 (Figure 5.1) are also consistent with itsformulation as a singly-inserted species. As expected, there are two different hydrocarbyl groupenvironments for the complex corresponding to the aryl and acyl ligands, with the set ofhydrocarbyl signals shifted to lower field being assigned to the acyl ligand due to the deshieldingeffect of the electron-withdrawing carbonyl group.1411111171111118 111111111F111111-11111-11-111111111-11-11r-1141TIT1,11T-111-111111111119^ 7^8^ 2 PPM152Figure 5.1 300 MHz 1H NMR spectrum of CpW(N0)(i2-C{0}-p-toly1)(p-toly1) (5.1) in C6D6.5.4.1.2 X-ray Crystallographic Analysis of CpW(NO)(C{O} CH2CMe2Ph)(CH2CMe2Ph)A number of stable transition-metal acyl complexes have been synthesized and structurallycharacterized, and the acyl ligand has been found to coordinate to the metal in either amonohapto, M(ril-C{O}R), or a dihapto, M(r1 2-C{O}R), fashion. 15 In order to establish thenature of the acyl linkage in CpW(N0)(C{O}CH2CMe2Ph)(CH2CMe2Ph), the complex wassubjected to a single-crystal X-ray crystallographic analysis. 16 Regrettably, two overlappingchemically equivalent, but crystallographically independent, molecules caused severe refinementproblems of the molecular structure. Consequently, the most reliable information that can beextracted from the X-ray crystallographic study is the atom connectivity which establishes(Figure 5.2) that the acyl ligand is indeed coordinated to the tungsten atom in an i2 fashion.153Figure 5.2 The solid-state molecular structure of CpW(N0)(i 2-C{O)CH2CMe2Ph)(CH2CMe2Ph). Atoms are refined isotropically and drawn as open circles; H atoms are omittedfor clarity. Only one view of the disordered overlapping molecules is shown.The intramolecular metrical parameters (Table 5.4) of CpW(N0)(1 2-C(0)CH2CMe2Ph)(CH2CMe2Ph) generally resemble those determined for other r1 2-acyl complexes of the Group 6metals. It has a short W-Caryl bond of 2.01 A. The W-0 separation of 2.21 A is indicative of asingle bond. Since the acyl group functions as a three-electron donor ligand through its C and 0atoms, the complex is best viewed as an 18-electron electronically and coordinatively saturatedspecies.154Table 5.4. Selected Bond Lengths and Bond Angles forCpW(N0)(92-C(0)CH2CMe2Ph)(CH2CMe2Ph).abond lengths (A) bond angles (deg)W - C(30) 2.01 0(2) - W - C(30) 33W - C(19) 2.25 0(2) - W - C(19) 79W - 0(2) 2.21 C(19) - W - C(30) 111C(30) - 0(2) 2.21 C(19) - W - N 96W - N 1.85 C(30) - W - N 93N - 0(1) 1.20 0(2) - W - N 960(1) - N - W 170a These parameters were all subject to restraints during refinement and therefore noe.s.d.s are given.MoC1(r1 2-C{O}CH2SiMe3)(C0)(PMe3)3 has been prepared by Carmona's group , not by COinsertion, but by the nucleophilic attack of Me3 SiCH2- on a terminal CO ligand ofMoC12(C0)2(PMe3)3. 17 The dihapto acyl species has been structurally characterized. Carmonacalculates a value of A mo_oxmo_c) in MoC1(r12-C{O}CH2 SiMe3)(C0)(PMe3)3 of O. 30 A whichhe compares to the value of 0 (mo..0) ..(mo_c) found in other /12-acyl organometallic co mpounds.The values range from 0.44 A for Ru(7-1 2-C{O}CH3)(I)(C0)(PPh3 )2 18 to 0.09 A for Cp2Zr(i2-C(0)CH3)(CH3). 19 Carmona believesthat this value is an indicator of the strength of thei2 interaction. If Nmo_oxmo..c) is high, the 1 2interaction is weak and the reverse migrationreaction may occur. On the other hand, if.0/0 \M—C—R^M4—:C—RI IIA040_,Dxmo-C) is small, as in Cp*2ThCI(C{O}CH2CMe3) (0.07 A), there is a larger contributionfrom the oxycarbene resonance structure (II). Early-transition metals are oxophilic and therefore0^(5.7)+ )CCO R ROCN0155the M-0 interaction is strong enough to make the acyl ligand more like an oxycarbene than an-r 2 ..i acyi. The value of Nmo_oxmo_c) for CpW(N0)(C{O)CH2CMe2Ph)(CH 2CMe2Ph) is0.20 A; therefore we would expect the interaction between the metal and acyl to be strong, andthe resonance form I to dominate.It is important to note from this structure that the oxygen of the acyl ligand is positionedtrans to the NO ligand. This configuration stablilizes the interaction between the a-donating acyland the strongly ic-accepting NO ligand.5.4.1.3 The Unique Case of R = CH 2ArThe reactions of the bis(benzyl) complexes, Cp'M(NO)(CH2Ar)2 [Ar = C6H5 , C6H4-4-Me],with CO do not proceed as depicted in eq 5.6, but rather lead to the reductive elimination ofketone and formation of the well-known dicarbonyl nitrosyl products as summarized in eq 5.7.R = CH2ArThese conversions occur slowly in benzene at 1 atm and ambient temperatures, but are quite rapidat higher pressures of CO (e.g. 30 atm). The workup of the reactions where R = CH 2Ph areparticularily difficult for three reasons. Firstly, the dicarbonyl nitrosyl complex is extremelysoluble in 1,3-diphenylacetone. Secondly, (PhCH2)2C0 is a pale yellow liquid that is difficult topurify. Finally, mixtures of the two independently air-stable product complexes are notthemselves air-stable. 20 The work-up of the reaction solutions resulting from the treatment ofCp*Mo(N0)(CH2C6I-14-4-Me)2 with CO is significantly easier because the resulting ketone,(4-Me-C6H4CH2)2CO, can be crystallized from pentane.156The organometallic dicarbonyl nitrosyl products and 1,3-diphenylacetone have been identifiedby comparison of their spectroscopic properties to those exhibited by authentic samples. Theidentity of (4-Me-C 6H4CH2)2C0 has been established by IR, MS, 1H and 13 C ( 11-1) NMRspectroscopies and by elemental analysis (Tables 5.1 - 5.3). A partial IR spectrum of the reactionmixture of Cp*Mo(NO)(CH2C6H4-4-Me)2 and carbon monoxide is shown in Figure 5.3. Itclearly shows the vNo (1663 cm -1 ) and two vco's (2000 cm -1 and 1930 cm -1) of the dicarbonylnitrosyl complex, as well as weaker bands at 1726, 1713, and 1515 cm -1 due to(4-Me-C6114012)2CO.We believe that reaction 5.7 proceeds via an intermediate acyl alkyl complex. However,unlike the other Cp'W(N0)(1 2 -C(0}R)(R) complexes isolated, the transientCp'M(N0)(C (0}CH2Ar)(CH2Ar) species evidently eliminate (ArCH2) 2C0 spontaneously in thepresence of excess CO. Since the Cp'M(NO)(CH2Ar) 2 reagent complexes are prepared fromCp'M(NO)(CO)2 ,4 '7 reactions 5.7 may be incorporated into a stoichiometric synthetic cycle asshown in Scheme 5.1.The reductive elimination of ketone in this system is significant because organometallicreactions leading to the formation of new carbon-carbon bonds have an important place insynthetic organic chemistry. 21 Reductive elimination is one of the most common ways toconstruct carbon-carbon bonds. The increasing importance of catalytic C-C bond-formingreactions between acyl and alkyl moieties makes the understanding of the fundamental couplingstep important.r Pi2000.0^1700.0^1400.0wavenumbers (cm -1)/( I157Figure 5.3 Partial IR spectrum (2195 - 1330 cm-1 ), as a Nujol mull, of the mixture from thereaction between Cp*Mo(N0)(CH2C61-14-4-Me)2 and CO.1585.4.2 Step 2: Formation of the Bis(acyl) ComplexesNeil Dryden6 showed that exposure of a C 6H6 solution of Cp*W(NO)(r12-C{0}-p-toly1)(p-tolyl) to elevated pressures (e.g. 30 atm) of CO results in the formation of an 18-electron1:1 adduct, i.e.,CO (30 atm)Cp*W(NO)(r1 2-C{O}R)(R) Cp*W(N0)(C{O}R)(R)(CO)^(5.8)R =p-tolylThe formulation of the red-orange product of reaction 5.8 as the CO adduct is based on a terminalCO stretch at 1970 cm -1 evident in its Nujol mull IR spectrum. 22 This adduct is only stable underCO pressure, otherwise it slowly reverts to Cp*W(N0)(71 2-C{0}-p-toly1)(p-toly1). The currentwork has shown that Cp *W(N0)(1-12-C{O}CH2CMe2Ph)(CH2CMe2Ph) also forms an adductunder CO pressure. The IR spectrum of a Nujol mull of a sample of the reaction mixture taken todryness in vacuo exhibits a terminal CO stretch at 2000 cm -1 . A strong band at 1733 cm -1 isattributed to the vNo, and the existence of the il-acyl ligand in the 1:1 adduct is indicated by aCO stretch at 1606 Cm-1 . 4, 23 The terminal CO is labile and, as a result, all attempts to crystallizethis new material afford only the organometallic reactant.In order to confirm the hypothesis that the monoacyl complexes were sufficiently electron-deficient to form a 1:1 adduct with Lewis bases, I investigated the possibility of forming aphosphine adduct with one of the acyl alkyl compounds. Interestingly, treatment ofCpW(N0)(112-C{0}CH2CMe2Ph)(CH2CMe2Ph) with an excess of PMe 3 does not produce themetal-centered adduct, CpW(N0)(1 1 -C{O}CH2CMe2Ph)(CH2CMe2Ph)(PMe3), but rather theylide complex, CpW(N0)(C{0} (PMe3}CH 2CMe2Ph)(CH2CMe2Ph) (5.4). The ylide ligand in5.4 may be described as the acyl phosphonium ion (Me3P)C{0}(CH2CMe2Ph)+. 159exess PMe3Re/ \))N C0 /R PMe3(5.9)R = CH2CMe2PhReaction 5.9 is rapid in CH2C12 . Although the reaction is quantitative, the yields of 5.4 aremoderate (63%) because of the lability of the PMe 3 ligand in solution (vide infra). Complex 5.4,having less solubility in organic solvents than its precursor complex, is best crystallized fromCH2C12/hexanes mixtures.The mass spectrum of complex 5.4 shows first loss of CO, and then loss of CO and PMe3 .The IR spectrum of 5.4 as a Nujol mull is complex. The assignment of vw, is difficult because ofthe presence of phenyl stretching bands. It is taken to be at 1493 cm -1 because of the strength ofthis band and because it is expected to be significantly lower than the v No of 1582 cm -1 inCpW(NO)(r12-C {0 ) CH2Me2Ph)(CH2Me2Ph).The existence of the ylide ligand in 5.4 is indicated by two spectroscopic features, namely asinglet (no W satellites observed) at 22.3 ppm in the 31P NMR spectrum due to the ylide PMe 3fragment, and a doublet at 58.14 ppm ( 1./cp = 45.1 Hz) in the 13 C { 1H} NMR spectrum of thecomplex due to the ylide carbon (Table 5.3). In solution, complex 5.4 exists in equilibrium (K =0.43 at 23 °C in C6D6) with CpW(N0)(C{O}CH2Me2Ph)(CH2Me2Ph)24 and free PMe3 asevidenced by the 1 H NMR spectrum of isolated 5.4. If the reaction is performed in an NMR tubewith an excess of PMe3, the 1H NMR spectrum exhibits peaks due to only 5.4 (quantitative) andthe excess PMe3 (Figure 5.4). A similar spectrum results if a sample of 5.4 is dissolved in C6D6and then excess PMe 3 is added. Thus, in solution, under conditions of excess PMe 3 the ylide is160iiiiiiympiliptimivilipilipmpuirlipmripmiimiliiipiiiimpiiipliiiimputimiiii2.6^2.4^2.2^2.0^1.8^1.6^1.4^1.2^1.0^0.8^0.6 PPMFigure 5.4 A partial view of the 300 MHz 1H NMR spectrum (C6D6) ofCpW(N0)(C{0}{PMe3}CH2Me2Ph)(CH2Me2Ph) (5.4) in the presence of excess PMe3 .161stable. Thus, the tendency for dissociation of the PMe3 from complex 5.4 lowers the yield of thisquantitative reaction.This type of reactivity for an electrophilicdihaptoacyl group has been observed previously forthe related CpMo(N0)(I)(12-C{0}-p-toly1)complex.25 Hersh finds that this acyl species reactswith PMe3 highly stereospecifically to formCpMo(N0)(00-1 2-C {0} {PMe3}-p-toly1). Heobtained an X-ray crystal structure of this complexto confirm the structure of the r1 2-ylide ligand. It isnot unreasonable to assume, based on thespectroscopic data of 5.4, that the geometry of itsylide ligand is similar to that inCpMo(N0)(I)(1 2 -C { 0 } {PMe3 } -p-tolyl).Upon exposure to CO at higher pressures, the perhydrocyclopentadienyl tungsten monoacylalkyl complexes undergo insertion of a second equivalent of CO, thereby affording novel bis(acyl)complexes (eq 5.10). 12CO (30 atm) (5.10)R = CH2CMe2Ph, CH2CMe3162The bis(acyl) complexes probably result from initially formed CO adducts of the type,CpW(N0)(ril-C{O}alkyl)(alkyl)(C0), undergoing insertion into the remaining M-C allcy1 bond.5.4.3 Reactivity TrendsWith the completed set of reactions we can make some generalizations about these COinsertion reactions. The fact that only the cyclopentadienyl alkyl complexes undergo multipleinsertions of CO can be rationalized on both steric and electronic grounds. For steric reasons,CpW(NO)(CH2CMe2Ph)2 will insert two equivalents of CO and Cp *W(NO)(CH2CMe2Ph)2 willnot, presumably because the W center is more sterically accessible in the former compound. Forelectronic reasons, M-C alkyi bonds are weaker than M-Caryl linkages and can thus be more readilycleaved during migratory insertion reactions. 26 Unlike the first insertion of CO (eq 5.6) which isdriven primarily by the Lewis acidity of the starting bis(hydrocarbyl) complex, the secondinsertion evidently depends on the relative bond strengths of the remaining W-C bond since the18-electron monoacyl reactant is not particularly Lewis acidic. In other words, the rate of thesecond insertion reaction (eq 5.10) depends principally on the relative bond strengths of a W-sp 2vs a W-sp3 carbon bond and not on the relative Lewis acidities of the monoacyl reactants.Consistent with this view is the fact that we have been able to isolate CpW(N0)(C {0}alky1) 2complexes but no CpW(NO)(C{O}aryl)2 species during this work.5.4.4 Electrochemical Study of CpW(NO)(C{O}CH2CMe 2Ph)2A cyclic voltammogram of CpW(NO)(C{O}CH2CMe2Ph) 2 in THE (Figure 5.6) exhibits oneirreversible reduction wave at -1.83 V vs. Ag wire. This indicates that some structural changeoccurs upon the addition of an electron. The CV of CpW(NO)(C{O}CH2CMe2Ph) 2 shows nooxidation features to the solvent limit, however a peak at +0.36 V appears after the potential hasbeen scanned past the reduction peak. This return oxidation peak is presumably due to theoxidation of the product obtained from the reduction of CpW(NO)(C{O}CH2CMe2Ph)2.163Figure 5.6 Ambient temperature cyclic voltamrnogram of CpW(NO)(C{O)CH 2CMe2Ph)2 inTHE (scan rate = 0.10 V/s).In attempts to induce the reductive elimination of a diketone,CpW(N0)(C(0)CH2CMe2Ph)2 was treated with Na/Hg in THF. The result of this reaction wasthe decomposition of the starting material to an number of unidentifiable products.5.4.5 Related SystemsStable acyl alkyl complexes are rare. The paucity of isolated acyl alkyl complexes is due tothe strong tendency for these species to undergo reductive elimination of the acyl and alkylligands to form ketones. For instance, the rhenium acyl complex, CpRe(C0)2(C(0)Me)(Me)undergoes reductive elimination of acetone thermally. 27 Cp *Ta(Me)4 reacts with CO to affordthe 71 2-acetone complex, Cp *Ta(Me)2(712-C(0)Me2), which releases acetone under oxidizingconditions. 28 Cp *Rh(CO)(Ph)(Me) reacts with CO to produce acetophenone and the rhodiumdicarbonyl complex. 29 (dppe)FeR2 reacts with CO to produce (dippe)Fe(CO) 3 and R2CO. 4 The164carbonylation of many late transition-metal alkyl complexes also leads to the formation ofaldehydes, ketones and diketones. 21 The classic experiments of catalytic C-C bond-formingreactions between acyl and alkyl groups have been carried out by Yamamoto and involve the latetransition-metal complexes, L2MR2 (M = Pd, Pt). 30 It is speculated that bis(acyl) intermediatesare involved when diketones are formed since CO insertion into acyl-metal bonds are energeticallyunfavorable. 31 Eisenberg has reported that an A-frame Rh complex upon carbonylation produceseither acetone or 2,3-butanedione depending on the pressure of carbon monoxide (i.e. doublecarbonylation is possible). 32The closest analogues to CpM(N0)(112-C{0}R)R are the valence isoelectronicCp2M'(12-C{O)R)R (M' = Zr, Hf) complexes. 19 Unlike our monoacyl complexes, the Group 4species undergo rapid decarbonylation processes. Cp2M 1 (r12-C{O}CH2Ph)(CH2Ph) (M' = Zr, Hf)have been isolated, however Cp 2Ti(CH2Ph)2 reacts with CO to produce Cp 2Ti(CO)2 and1,3-diphenylacetone. 33 It has also been recently reported that pentane solutions ofCp2Zr(CH2Ph)2 react with CO to produce Cp 2Zr(C0)2 and 1,3-diphenylacetone throughCp2M(r12-C(0)CH2Ph)(CH2Ph) intermediates. 345.5 Epilogue and Future WorkThese studies have shown that the products obtained from the carbonylation of variousCp'W(NO)R2 complexes are very dependent upon the nature of the ancillary ligands and theexperimental conditions employed. The nature of the cyclopentadienyl ligand determines theextent of the reactivity, with only the Cp complexes inserting a second equivalent of CO. Thenature of the hydrocarbyl group influences the rate of the reaction such that the greater Lewisacidity of the diaryl complexes results in their forming monoacyl products faster than do therelated dialkyl complexes. However, only the monoacyl alkyl complexes possess a sufficientlyweak M-C a bond to undergo a second insertion of CO to form bis(acyl) species. The nature ofthe hydrocarbyl ligand also plays an influential role in the case when R = CH 2Ar in that putativereductive elimination of ketone occurs from the undetectable monoacyl intermediate complex.165The steric and electronic factors mitigating this set of reactions allows us, in principle, theopportunity to fine tune the reaction conditions so as to obtain specific carbonylation products.The first step towards attaining this goal was achieved when we determined that the insertions ofCO into the asymmetric complexes Cp *W(NO)(R)(R) occur regioselectively. 26 We have nowbegun investigating the reactions of CO analogues such as CNCMe 3 with these dialkyl and acylalkyl systems.5.6 References and NotesDurfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059 and references therein.Coltman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications ofOrganotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987;Chapter 6.Gladysz, J. A. Adv. Organomet. Chem. 1982, 20, 1.Hermes, A. R.; Girolami, G. S. Organometallics 1988, 7, 394.Legzdins, P.; Rettig, S. J.; Sanchez, L. Organometallics 1988, 7, 2394.Dryden, N. H. Ph.D. Dissertation, The University of British Columbia, 1990.One benzyl ligand functions as a three electron donor to the metal center, see: Legzdins, P.;Jones, R. H.; Phillips, E. C.; Yee, V. C.; Trotter, J.; Einstein, F. W. B. Organometallics1991, 10, 986.(8) (a) Legzdins, P.; Lundmark, P. L.; Phillips, E. C.; Rettig, S. J.; Veltheer, J. E.Organometallics 1992, 11, 2991. (b) Herring, F. G.; Legzdins, P.; Richter-Addo, G. B.Organometallics 1989, 8, 1485 and references cited therein.(9) Legzdins, P.; Phillips, E. C.; Sanchez, L. Organometallics 1989, 8, 940.(10) Dryden, N. H.; Legzdins, P.; Rettig, S. J.; Veltheer, J. E. Organometallics 1992, 11, 2583.166(11) Dryden, N. H.; Legzdins, P.; Trotter, J.; Yee, V. C. Organometallics 1991, 10, 2857.(12) Dryden, N. H.; Legzdins, P.; Lundmark, P. J.; Riesen, A.; Einstein, F. W. B.Organometallics 1993, 12, 2085.(13) Legzdins, P.; Veltheer, J. E. Acc. Chem. Res. 1993, 26, 41.(14) (a) Curtis, M. D.; Shiu, K. B.; Butler, W. M. J. Am. Chem. Soc. 1986, 108, 1550.(15) (a) Churchill, M. R.; Chang, S. W. Y. Inorg. Chem. 1975, 14, 1680. (b) Fachinetti, G.;Floriani, C.; Marchetti, F.; Merlino, J. J. Chem. Soc., Chem. Commun. 1976, 522.(16) The X-ray crystallographic analysis of CpW(NO)(r1 2-C{O}CH2CMe2Ph) (CH2CMe2Ph)was performed by Drs. A. Riesen and F. W. B. Einstein at Simon Fraser University,Burnaby, B.C., Canada. Crystal data for CpW(NO)(1 2-C{O}CH2CMe2Ph)(CH2CMe2Ph):orthorhombic, space group P2 1 2 1 2 1 , a = 9.158 (3) A, b = 14.603 (4) A, c = 17.230 (6) A,Z = 4, R = 0.068.(17) Carmona, E.; Sanchez, L.; Marin, J. M.; Poveda, M. L.; Atwood, J. L.; Priester, R. D.;Rogers, R. D. J. Am. Chem. Soc. 1984, 106, 3214.(18) Roper, W. R.; Taylor, G. E.; Waters, J. M.; Wright, L. J. J. Organomet. Chem. 1979, 182,C46.(19) Fachinetti, G.; Fochi, G.; Floriani, C.; Stoeckli-Evans, H. J. Chem. Soc., Dalton Trans.1977, 1946.(20) It was found that a Et20 solution of authentic Cp*Mo(NO)(CO)2 and authentic(ArCH2)2C0 decomposed to insoluble tan solids upon exposure to air.(21) Brown, J. M.; Cooley, N. A. Chem. Rev. 1988, 88, 1031 and references therein.(22) In the IR, terminal CO stretches range from 2100 - 1800 cm-1 . Nakamoto, K. Infraredand Raman Spectra of Inorganic and Coordination Compounds; John Wiley and Sons,Inc.; New York, NY, 1986; p 261.(23) Reference 2, p 107.167(24) 1H NMR data for CpW(NO)(C{O}CH 2Me2Ph)(CH2Me2Ph) in C6D6 : 5 7.66 (d, 2H,o-ArH, 3.4.114 = 7.5 Hz), 7.27 (d, 2H, o-ArH, 3JBH = 7.5 Hz), 7.25 (t, 2H, m-ArH, 3.4ili =7.5 Hz), 7.15 (t, 2H, m-ArH, 3.41}1 = 7.5 Hz), 7.09 (t, 2H, p-ArH, 3JBH = 7.5 Hz), 7.00 (t,2H, p-ArH, 3.4.11.1 = 7.5 Hz), 4.53 (s, 5H, C5H5), 3.21 (d, 1H, C(0)CHAHX, 2.4111 =15.0 Hz), 2.71 (d, 1H, WCHAHB, 24in = 12.9 Hz), 2.69 (d, 1H, C(0)CHAHX, 2JHEI =15.0 Hz), 2.65 (d, 1H, WCHAHB, 2JHEI = 12.9 Hz), 1.89, 1.80, 1.30, 1.13 (s, 4 x 3H,C(CH3)2Ph)(25) Bonneson, P. V.; Yau, P. K. L.; Hersh, W. H. Organometallics 1987, 6, 1587.(26) Debad, J. D.; Legzdins, P.; Batchelor, R. J.; Einstein, F. W. B. Organometallics 1993, 12,2094.(27) Goldberg, K. I.; Bergman, R. G.; Organometallics 1987, 6, 430.(28) Wood, C. D.; Schrock, R. R. J. Am. Chem. Soc. 1979, 101, 5421.(29) (a) Sunley, G. J.; Fanazzi, F. P.; Saez, I. M.; Maitlis, P. M. J. Organomet. Chem. 1987,330, C27. (b) Fanazzi, F. P.; Sunley, G. J.; Maitlis, P. M. J. Organomet. Chem. 1987, 330,C31.(30) Ozawa, F.; Yamamoto, A. Chem. Lett. 1981, 289.(31) Sheridan, J. B.; Johnson, J. R.; Handwerker, B. M.; Geoffroy, G. L.; Rheingold, A. L.Organometallics 1988, 7, 2404.(32) Kramarz, K. W.; Eisenschmid, T. C.; Deutsch, D. A.; Eisenberg, R. J. Am. Chem. Soc.1991, 113, 5090.(33) Fachinetti, G.; Floriani, C. J. Chem. Soc., Chem. Commun. 1972, 654.(34) Via CA Selects: Wang, J.; Wang, Y.; Wang, Q. Gaodeng Xueriao Huaxue Xuebao 1990,11(10), 1076.

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