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Fun with ferrocene : synthesis of polyiron complexes using 1,1'-diaminoferrocene based ligands Pick, Fraser Stanley 2017

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Fun With FerroceneSynthesis of Polyiron Complexes Using 1,1’-Diaminoferrocene BasedLigandsbyFraser Stanley PickB.Sc.(H) Chemistry, University of Alberta, 2010A THESIS SUBMITTED IN PARTIAL FULFILLMENTOF THE REQUIREMENTS FOR THE DEGREE OFDoctor of PhilosophyinTHE FACULTY OF GRADUATE AND POSTDOCTORALSTUDIES(Chemistry)The University of British Columbia(Vancouver)July 2017© Fraser Stanley Pick, 2017AbstractReactions of an amidophosphine supported ditantalum tetrahydride, ([NPNSi]Ta)2(µ-H)4 and COx (x = 1, 2) were studied and all products were fully characterized. Se-lective deuteration allows for the production of two deuterated isotopomers whichwere used in low temperature NMR and GC-MS experiments in order to support acomputationally determined mechanism.Iron and cobalt complexes of a ferrocene linked bis(phosphinoamide) weresynthesized and characterized by X-ray crystallography and Mo¨ssbauer spectroscopy.The cobalt complex contains a Co–Fe bond that was absent in the all-iron complex.The Co–Fe bond was further studied using DFT calculations, which suggest thatthe bond is comprised of donation from the iron center to the cobalt center (Fe→Co) and back donation from the cobalt center to antibonding orbitals in the fer-rocene backbone (Co → fc*). A putative nickel complex supported by the samebis(phosphinoamide) ligand underwent a reductive elimination of the amidophos-phine groups forming a new P-N bond.Reactions between the aforementoned iron complex and H2, CO2 and otherelectrophiles were studied and the products of these reactions were fully charac-terized. The products of these reactions show that the iron phosphinoamides cancooperativley activate a variety of bonds without changing the oxidation state atiiiron. Upon reduction, the iron complex forms an Fe–Fe bond while remaining in ahigh spin state. The cleavage of the N=N double bond of azobenzene was achievedunder photolytic conditions using the same iron phosphinoamide and is thought toinvolve formation of a putative iron imido which migrates to the phosphinoamidegroups. Due to the tendency of iron phosphinoamides to activate substrates us-ing ligand cooperativity, an alternative ligand using amidophosphine donors wassyntheisized and initial coordination studies were performed.iiiLay SummaryCoordination chemistry is the study of metal complexes containing a metal centerand a ligand. A ligand is a molecule which protects and supports the metal center.Some of these metal-ligand complexes function as catalysts, which make chemi-cal transformations more energy efficient and in some cases reduce the amount ofwaste produced in certain chemical reactions. Enzymes found in all living things,are biological catalysts and typically they contain more than one metal center. Of-ten those metal centers are iron. These enzymes can perform impressive chemicaltransformations beyond the abilities of metal-ligand complexes made by scientists.In this dissertation we attempt to simulate some of the chemical transformations fa-cilitated by enzymes in nature by designing new iron complexes that contain morethan one iron center.ivPrefaceSection 2.1 is from Ballmann, J.; Pick, F. S.; Castro, L.; Fryzuk, M. D.; Maron, L.Organometallics 2012, 31, 8516. My contributions were the design and executionof the isotopic labeling studies, characterization of 2.1-d12 and complete character-ization of 2.4. The original discovery of 2.4 was made by Dr. Joachim Ballmann,the manuscript was written by Prof. Michael Fryzuk and the DFT calculationswere performed by Ludovic Castro under the supervision of Prof. Laurent Maron.Section 2.2 is from Ballmann, J.; Pick, F. S.; Castro, L.; Fryzuk, M. D.; Maron, L.Inorg. Chem. 2013, 52, 1685. My contributions were completing the characteriza-tion of 2.5, and attempting to observe predicted intermediates by low temperatureNMR monitoring. The inital discovery of 2.5 was made by Dr. Joachim Ballmann,the manuscript was written by Prof. Michael Fryzuk and the DFT calculationswere preformed by Ludovic Castro under the supervision of Prof. Laurent Maron.The computational details for sections 2.1 and 2.2 are available at pubs.acs.org.Section 3.1 is from Pick, F. S.; Thompson, J. R.; Savard, D. S.; Leznoff, D. B.;Fryzuk, M. D. Inorg. Chem. 2016, 55, 4509. J. R. Thompson and D. S. Savardrecorded the Mo¨ssbauer and VT-SQUID data respectively for compounds 1.50,3.2, 3.3 and 3.4. All synthesis and DFT calculations were preformed by F. S. Pick.The manuscript was written by F. S. Pick with contributions from M. D. FryzukvSection 4.2 is a manuscript which will be submitted for publication. All syn-thesis were preformed by F. S. Pick and the manuscript was written by F. S. Pickwith contributions from M.D. Fryzuk. The syntheses of 4.8 and 4.9 in section4.3 were performed by an undergraduate student, Garrion Hicks, under the directsupervision of F. S. Pick.viTable of ContentsAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiLay Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ivPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vTable of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiList of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiiList of Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvList of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviiAcknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Base Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 Economic and Biological Motivations . . . . . . . . . . . 11.1.2 Iron Complexes: Catalysis and Small Molecule Activation 61.2 Ligand Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151.2.1 Ligand Design in the Fryzuk Group . . . . . . . . . . . . 151.2.2 Phosphinoamides as Ligands . . . . . . . . . . . . . . . . 171.2.3 Tethered Phosphinoamides . . . . . . . . . . . . . . . . . 24vii1.3 Scope of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Reduction of Carbon Monoxide and Carbon Dioxide by a Ditanta-lumtetrahydride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282.1 Complete Reduction of Carbon Monoxide . . . . . . . . . . . . . 282.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 282.1.2 Results and Discussion . . . . . . . . . . . . . . . . . . . 292.1.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 452.2 Reduction of Carbon Dioxide Promoted by a Dinuclear TantalumTetrahydride Complex . . . . . . . . . . . . . . . . . . . . . . . 462.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 462.2.2 Results and Discussion . . . . . . . . . . . . . . . . . . . 472.2.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 523 Synthesis of Base Metal Complexes of the Type [fc(NP)]M . . . . . . 543.1 Synthesis of Iron and Cobalt Complexes of a Ferrocene-LinkedDiphosphinoamide Ligand and Characterization of a Weak Iron-Cobalt Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . 543.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 543.1.2 Results and Discussion . . . . . . . . . . . . . . . . . . . 563.1.3 Magnetic Measurements . . . . . . . . . . . . . . . . . . 683.1.4 DFT Calculations . . . . . . . . . . . . . . . . . . . . . . 703.1.5 Summary and Conclusions . . . . . . . . . . . . . . . . . 733.2 Attempted Synthesis of Group 10 Phosphinoamides . . . . . . . . 743.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 743.2.2 Attempted Synthesis of Group 10 Complexes . . . . . . . 753.2.3 Nickel Complexes of Unlinked Phosphinoamides . . . . . 823.3 Conclusions and Future Directions . . . . . . . . . . . . . . . . . 854 Small Molecule Activation with an Iron Phosphinoamide Dimer . . 874.1 Reactions with Hydrogen and Carbon Monoxide . . . . . . . . . 874.1.1 Reaction with Hydrogen . . . . . . . . . . . . . . . . . . 874.1.2 Reactions with Carbon Monoxide . . . . . . . . . . . . . 90viii4.2 Redox Behaviour of ([fc(NPiPr2)2]Fe)2, Formation of a Fe-Fe Bondand Cleavage of Azobenzene . . . . . . . . . . . . . . . . . . . . 954.3 Cooperative Activation of Polar Multiple Bonds . . . . . . . . . . 1035 Future Work and Conclusions . . . . . . . . . . . . . . . . . . . . . 1105.1 Thesis Synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105.2 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . 1135.2.1 Re-Designing the 1,1’-diphosphinoamide Ligand for Poly-metallic Complex Formation . . . . . . . . . . . . . . . . 1135.2.2 More Ligands Based on 1,1’-diaminoferrocene . . . . . . 1175.2.3 Future Work with Iron Compounds . . . . . . . . . . . . 1195.3 Final Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 1236 Experimental Details . . . . . . . . . . . . . . . . . . . . . . . . . . 1246.1 General Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 1246.1.1 Laboratory Equipment and Procedures . . . . . . . . . . . 1246.1.2 Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . 1246.1.3 Starting Materials . . . . . . . . . . . . . . . . . . . . . . 1256.1.4 Instrumentation and Methods of Analysis . . . . . . . . . 1256.1.5 Computational Details for Chapter 3 . . . . . . . . . . . . 1276.2 Synthesis of Compounds . . . . . . . . . . . . . . . . . . . . . . 1286.2.1 Complexes Pertaining to Chapter 2 . . . . . . . . . . . . 1286.2.2 Complexes Pertaining to Chapter 3 . . . . . . . . . . . . 1326.2.3 Complexes Pertaining to Chapter 4 . . . . . . . . . . . . 1366.2.4 Complexes Pertaining to Chapter 5 . . . . . . . . . . . . 140Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142A Crystallographic Appendix . . . . . . . . . . . . . . . . . . . . . . . 161B Computational Appendix . . . . . . . . . . . . . . . . . . . . . . . . 175C Mo¨ssbauer Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 190D SQUID Magnetometry . . . . . . . . . . . . . . . . . . . . . . . . . . 193ixE Cyclic Voltammetry . . . . . . . . . . . . . . . . . . . . . . . . . . . 194F Gas Chromatography Mass Spectrometry . . . . . . . . . . . . . . . 195xList of TablesTable 1.1 Prices of group 8, 9 and 10 transition metals . . . . . . . . . . 2Table 3.1 Mo¨ssbauer parameters for 3.2, 3.3, 3.4 and related compounds. 68Table 3.2 Computed and experimental bond metrics for 3.2 and 3.4. . . . 71Table A.1 Crystal data and refinement details for 2.5 . . . . . . . . . . . 166Table A.2 Crystal data and refinement details for 1.50 and 3.1 . . . . . . 167Table A.3 Crystal data and refinement details for 3.2 and 3.3 . . . . . . . 168Table A.4 Crystal data and refinement details for 3.4 and 3.7 . . . . . . . 169Table A.5 Crystal data and refinement details for 3.11 and 4.1 . . . . . . 170Table A.6 Crystal data and refinement details for 4.2 and 4.3 . . . . . . . 171Table A.7 Crystal data and refinement details for 4.4 and 4.5 . . . . . . . 172Table A.8 Crystal data and refinement details for 4.7 and 4.8 . . . . . . . 173Table A.9 Crystal data and refinement details for 4.9 . . . . . . . . . . . 174Table B.1 Optimized xyz coordinated for 3.2 . . . . . . . . . . . . . . . 175Table B.2 Optimized xyx coordinates for 3.4 . . . . . . . . . . . . . . . 179Table B.3 Calculated and experimental bond metrics for 3.2 and 3.4 . . . 183Table B.4 Second order perturbation theory analysis of 3.4 . . . . . . . . 189xiList of FiguresFigure 1.1 First generation ligand design in the Fryzuk group . . . . . . 15Figure 1.2 Second generation ligand design in the Fryzuk group . . . . . 17Figure 1.3 Resonance forms, stereoisomers and common binding modesof amidophosphines . . . . . . . . . . . . . . . . . . . . . . 19Figure 1.4 Phosphinoamide complexes of rare earth metals . . . . . . . . 20Figure 1.5 Coordination modes of alkyl linked phosphinoamides . . . . . 26Figure 2.1 ORTEP diagram of 2.4 . . . . . . . . . . . . . . . . . . . . . 32Figure 2.2 Computed structure of 2.1 . . . . . . . . . . . . . . . . . . . 35Figure 2.3 Schematic depiction of the HOMO for complex 2.1 . . . . . . 36Figure 2.4 Gibbs free energy profile of the reaction between 2.1 and CO . 37Figure 2.5 Schematic depiction of the HOMO for Ta2H4•CO . . . . . . 38Figure 2.6 Three proposed pathways to produce 2.4 . . . . . . . . . . . . 40Figure 2.7 Gibbs free energy profile of pathway A . . . . . . . . . . . . 43Figure 2.8 HOMO of putative intermediate Ta2O . . . . . . . . . . . . . 44Figure 2.9 ORTEP diagram of 2.5 . . . . . . . . . . . . . . . . . . . . . 49Figure 2.10 Gibbs free energy profile for the reaction of 2.1 with CO2 . . . 50Figure 3.1 ORTEP diagram of 3.2 . . . . . . . . . . . . . . . . . . . . . 58Figure 3.2 Cp tilt and bite angle . . . . . . . . . . . . . . . . . . . . . . 59Figure 3.3 1H NMR spectra of 3.2 in varying solvents . . . . . . . . . . 60Figure 3.4 ORTEP diagram of 3.3 . . . . . . . . . . . . . . . . . . . . . 62Figure 3.5 57Fe Mo¨ssbauer spectra of 3.2 and 3.3 . . . . . . . . . . . . . 63Figure 3.6 ORTEP diagram of 3.4 . . . . . . . . . . . . . . . . . . . . . 65xiiFigure 3.7 PXRD of 3.4 . . . . . . . . . . . . . . . . . . . . . . . . . . 66Figure 3.8 57Fe Mo¨ssbauer spectrum of 3.4 . . . . . . . . . . . . . . . . 67Figure 3.9 VT-Magnetometry for 3.2, 3.4 and 3.3 . . . . . . . . . . . . 70Figure 3.10 HOMO-9 of 3.4 . . . . . . . . . . . . . . . . . . . . . . . . . 72Figure 3.11 NLMO of 3.4 . . . . . . . . . . . . . . . . . . . . . . . . . . 73Figure 3.12 31P{1H} and 1H NMR spectra of compound 3.7 . . . . . . . . 78Figure 3.13 ORTEP diagram of 3.7 . . . . . . . . . . . . . . . . . . . . . 79Figure 3.14 VT-31P NMR spectra of 3.7 . . . . . . . . . . . . . . . . . . 81Figure 3.15 ORTEP diagram of 3.11 . . . . . . . . . . . . . . . . . . . . 84Figure 4.1 TEM images . . . . . . . . . . . . . . . . . . . . . . . . . . 90Figure 4.2 ORTEP diagram of 4.1 . . . . . . . . . . . . . . . . . . . . . 92Figure 4.3 1H NMR spectra of 4.2 . . . . . . . . . . . . . . . . . . . . . 92Figure 4.4 ORTEP diagram of 4.2 . . . . . . . . . . . . . . . . . . . . . 94Figure 4.5 ORTEP diagram of 4.3 and anionic portion of 4.4 . . . . . . . 98Figure 4.6 1H NMR spectra of PhNNPh Isomerization by 3.2 . . . . . . 100Figure 4.7 ORTEP diagram of 4.5 . . . . . . . . . . . . . . . . . . . . . 101Figure 4.8 1H NMR spectra of 4.7 . . . . . . . . . . . . . . . . . . . . . 105Figure 4.9 ORTEP diagram of 4.7 . . . . . . . . . . . . . . . . . . . . . 106Figure 5.1 1H NMR (400 MHz) spectra of compound 5.2 . . . . . . . . . 117Figure A.1 ORTEP plot of 2.1 . . . . . . . . . . . . . . . . . . . . . . . 161Figure A.2 ORTEP diagram of 1.50 . . . . . . . . . . . . . . . . . . . . 162Figure A.3 ORTEP diagram of 3.1 . . . . . . . . . . . . . . . . . . . . . 162Figure A.4 ORTEP diagram of 4.8 . . . . . . . . . . . . . . . . . . . . . 163Figure A.5 ORTEP diagram of 4.9 . . . . . . . . . . . . . . . . . . . . . 164Figure A.6 ORTEP plot of 5.3 . . . . . . . . . . . . . . . . . . . . . . . 165Figure B.1 Comparison of calculated and experimental geometry for 3.2 . 182Figure B.2 Comparison of calculated and experimental geometry for 3.4 . 183Figure B.3 LUMOα and LUMO+1α for 3.2 . . . . . . . . . . . . . . . . 184Figure B.4 LUMOβ and LUMO+1β for 3.2 . . . . . . . . . . . . . . . . 184Figure B.5 HOMOα to HOMO-7α for 3.2 . . . . . . . . . . . . . . . . . 185xiiiFigure B.6 HOMOβ and HOMO-1β for 3.2 . . . . . . . . . . . . . . . . 186Figure B.7 LUMOα and LUMO+1α for 3.4 . . . . . . . . . . . . . . . . 186Figure B.8 LUMOβ and LUMO+1β for 3.4 . . . . . . . . . . . . . . . . 187Figure B.9 HOMOα and HOMO-1α for 3.4 . . . . . . . . . . . . . . . . 187Figure B.10 HOMOβ and HOMO-1β for 3.4 . . . . . . . . . . . . . . . . 188Figure B.11 HOMO-6α for 3.4 . . . . . . . . . . . . . . . . . . . . . . . 188Figure C.1 Zero field 57Fe Mo¨ssbauer spectra of 1.50 . . . . . . . . . . . 190Figure C.2 Zero field 57Fe Mo¨ssbauer spectra of 3.4. . . . . . . . . . . . 191Figure C.3 Zero field 57Fe Mo¨ssbauer spectra of 4.2. . . . . . . . . . . . 192Figure D.1 VT-Magnetometry fit of 3.4 . . . . . . . . . . . . . . . . . . 193Figure E.1 Cyclic voltammogram of complex 3.2 . . . . . . . . . . . . . 194Figure F.1 Adapter used for head space analysis . . . . . . . . . . . . . 195xivList of Schemes1.1 Selected cofactors from metalloenzymes . . . . . . . . . . . . . . 41.2 Selected alkene hydrogenation catalysts . . . . . . . . . . . . . . 71.3 Catalysts for asymmetric hydrogenation . . . . . . . . . . . . . . 81.4 Selected carbonyl hydrogenation catalysts . . . . . . . . . . . . . 91.5 Selected iron dinitrogen complexes with tetrahedral coordinationgeometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.6 Low coordinate iron complexes cleave dinitrogen with alkali metalpromoters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.7 Polynuclear iron complexes through ligand design . . . . . . . . . 141.8 Dinitrogen functionalization with hybrid ligands . . . . . . . . . . 161.9 Synthesis of phosphinoamides . . . . . . . . . . . . . . . . . . . 181.10 Phosphinoamide complexes of the mid to late transition metals . . 211.11 Early/late heterobimetallic complexes of phosphinoamide ligands 231.12 Heterobimetallic complexes of phosphinoamide ligands. . . . . . 241.13 Hydrogenation of a scandium alkyl . . . . . . . . . . . . . . . . . 262.1 Analogous N2 and CO activation modes . . . . . . . . . . . . . . 302.2 Proposed mechanism for CO reduction by 2.1 . . . . . . . . . . . 332.3 Solvent effects of D2 addition to [NPN]TaMe3 . . . . . . . . . . . 412.4 N2 and CO2 reactivity with 2.1 . . . . . . . . . . . . . . . . . . . 472.5 Reduction of CO2 using 2.1 . . . . . . . . . . . . . . . . . . . . . 482.6 Summary of CO2 reduction using 2.1 . . . . . . . . . . . . . . . 533.1 Ligand motifs in the Fryzuk group . . . . . . . . . . . . . . . . . 553.2 Synthesis of 3.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 57xv3.3 Synthesis of 3.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . 613.4 Attempted synthesis of ([fc(NPiPr2)2]M)2 where M = Pd, Pt . . . 763.5 Synthesis of 3.7. . . . . . . . . . . . . . . . . . . . . . . . . . . . 803.6 Proposed mechanism of exchange in 3.7. . . . . . . . . . . . . . . 823.7 Attempted synthesis of asymmetric P,N ligands. . . . . . . . . . . 833.8 Reaction between 3.10 and NiBr2. . . . . . . . . . . . . . . . . . 854.1 Reaction of phosphinoamide salts with various solvents . . . . . . 884.2 Reaction of phosphinoamide salts with dihydrogen . . . . . . . . 894.3 Reactions of compound 3.2 with carbon monoxide . . . . . . . . 934.4 Polyiron Complexes . . . . . . . . . . . . . . . . . . . . . . . . . 964.5 Reactivity of 3.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 994.6 Reactions between metal-bound amidophosphines and CO2 . . . . 1044.7 Reactions between compound 3.2 and electrophilic carbon centers 1085.1 Synthesis of a ferrocene-linked bis(amidophosphine) . . . . . . . 1145.2 Installing multiple metals in the ferrocene-linked bis(amidophosphine)1155.3 Proposed synthesis of macrocyclic ligands . . . . . . . . . . . . . 1185.4 Ligands designed for bimetallic coordination . . . . . . . . . . . 1205.5 Formation of an FeBr2 cluster . . . . . . . . . . . . . . . . . . . 122xviList of AbbreviationsCp CyclopentadienylDFT Density Functional TheoryECP Effective Core Potentialfc ferroceneGC-MS Gas Chromatography Mass SpectrometryHMDSO HexamethyldisiloxaneHOMO Highest Occupied Molecular OrbitalHS High SpinIRC Intrinsic Reaction CoordinateLS Low SpinLUMO Lowest Unoccupied Molecular OrbitalORTEP Oak Ridge Thermal Ellipsoid PlotNBO Natural Bond OrderNMR Nuclear Magnetic Resonanceppm Parts Per MillionTEM Transmission Electron TomographyxviiTOF Turnover FrequencyVT Variable TemperaturexviiiAcknowledgmentsFirst and foremost I would like to thank Prof. Mike Fryzuk for allowing me theopportunity to work in his lab and for the guidance he has provided throughoutmy degree. To all of the group members I have crossed paths with, Kyle, Nathan,Brian, Truman, Lee, Alyssa, Nick and Amanda, it has been a pleasure workingalongside you. In addition I have had the pleasure of working with many outstand-ing post-doctoral fellows Yogi, Dominik, Thomas, Vince, Rich and Tiko. You haveall a taught me a great deal.The work herein would not have been possible without the excellent supportstaff at the University of British Columbia. In particular Dr. Brian Patrick (X-ray),Ms. Anita Lam (PXRD), Ms. Maria Ezhova (NMR), Dr. Paul Xia (NMR), Mr.Marshal Lapawa and Mr. Ken Love have been generous with their time throughoutmy degree.I have become a practitioner of density functional theory, and a small fractionof that work is included in this thesis. I am indebted to JM, Aleks, Eric, and Damonfor their never ending patience answering all of my questions.Finally I would like to thank my family for their continual support of my ed-ucation. To my parents Heather and Gary, grandparents Phyllis and Brian andsiblings Petrina, Jolleen, Matthew, Trevor, and Kathleen thank you for you supportand confidence in me. To Sonia, you have provided me with the love and strengthto complete this chapter of my life and I will forever be thankful that you werethere to support me. I could not have done it without you.xixChapter 1IntroductionIf I have seen farther it is by standing on the shoulders of Giants.— Sir Isaac Newton1.1 Base Metals1.1.1 Economic and Biological MotivationsSmall molecule activation and catalysis reside at the heart of synthetic inorganicchemistry. While noble metals (Ru, Os, Rh, Ir, Pd, Pt) have revealed tremendouscapabilities that have revolutionized a variety of chemical based industries, thebase metals (Fe, Co, Ni) have, until recently, received less attention.1–6 The costdifferential between the base metals and their heavier congeners, the noble metals,is striking. For example, iron is more than 2000 times cheaper than ruthenium,one of the least expensive noble metals (Table 1.1). In addition to their economicadvantages, base metals have lower toxicity than the heavy metals of groups 8,9 and 10. This is particularily useful in the pharmaceutical industry, as catalystrecovery does not have to be as rigorous when using the less toxic base metals.7With these advantages in mind, it is clear that replacing noble metal catalysts with1base metal catalysts is a worthwhile pursuit.Table 1.1: Prices of group 8, 9 and 10 transition metalsMetal Price ( $ / kg)a Abundance (ppm)bIron Ore 0.05 56 300Ruthenium 1 350.00 0.001Osmium 12 860.00 0.0015Cobalt 23.76 25Rhodium 23 467.46 0.001Iridium 22 089.48 0.001Nickel 8.83 24Palladium 22 039.96 0.015Platinum 31 342.77 0.005aThree month averages in USD from the London Metal Exchange for base metals and the EngelhardIndustrial Bullion Prices for noble metals (September 10th - December 10th 2016)bMass abundance taken from the CRC Handbook8While the utilization of base metals offers substantial benefits in terms of bothcost and environmental impact, noble metals continue to dominate in many streamsof synthetic methodology, and with good reason. Catalysts based on noble met-als are the gold standard in transformations such as C-H activation,9–11 alkenemetathesis,12,13 hydrosilylation,14,15 and a variety of cross-coupling reactions.16,17Precious metals offer numerous advantageous over base metal complexes: (i) No-ble metals readily undergo 2e- reduction and oxidation events and many catalyticcycles18–20 involve oxidative addition and reductive elimination steps, therefore,these cycles are readily accessed using noble metals. The tendency for iron andcobalt complexes to undergo one-electron redox events has traditionally impededthe utilization of their complexes in such catalytic cycles;21 (ii) Noble metals formstronger metal-ligand bonds, when compared to base metals.22–27 This allows formore stable complexes that are less prone to ligand redistribution, and eventual de-2composition; (iii) Noble metals are usually found in Low Spin (LS) electron con-figurations resulting in diamagnetic compounds for the common oxidation states,which allows characterization by routine Nuclear Magnetic Resonance (NMR)spectroscopy. In addition, some of the noble metals (195Pt, 103Rh) are spin active,providing additional spectroscopic handles. The paramagnetic nature of base metalcomplexes combined with their relative instability leads to a situation where basemetal complexes are often very difficult to characterize, requiring multiple tech-niques and large amounts of material. It should be noted that paramagnetic NMRspectroscopy is available for some base metal complexes, however, the amount ofinformation provided is limited; (iv) Finally, the dearth of soluble starting materi-als, both commercially available and reported in the literature, presents a challengewhen synthesizing base metal complexes.28,29 For these reasons the chemistry ofthe base metals is less developed than that of the noble metals.Considering the limitations previously mentioned it may seem like folly tothink iron, cobalt, and nickel could replace many of the noble metal systems wecurrently utilize. Indeed, the goals of exploring base metal chemistry should bemore than simply replicating established reaction manifolds with base metals, butin addition, finding new reaction pathways that offer access to new transforma-tions or selectivities. As is often the case, nature provides insight into what canbe accomplished with these metals. Many impressive enzymatic transformationsoccur in enzymes containing a metallic cofactor and most often these cofactorscontain multiple base metal centers. Examples include the [FeFe]hydrogenasefamily, the cytochrome P450 family, and [FeMo]nitrogenase whose principal co-factors contain 2, 1, and 7 iron atoms respectively (Scheme 1.1). The family of[FeFe]hydrogenases are excellent catalysts for proton reduction, out performing3platinum in terms of required overpotential and TON.30 Cytochrome P450 is ableto oxidize unactivated C-H bonds in hydrocarbons,31 and [FeMo]nitrogenase isable to perform the complete reduction of dinitrogen to ammonia under mild con-ditions.32,33 Clearly, in the enzymatic environment base metals can be used to per-form complex and valuable transformations.Fe FeS[Fe4S4]OCNCS SNHCNCOCONN NNFeOOOOFe(Cys)SSSSFeFeSSFeFeSSMoSFe FeCSN(His)OOORR'H22 H+ 2 e-+N2 8 e-++ 8 H+ H2 + 2 NH32 e-+RH H2OROH2 H+ + +O2 +Scheme 1.1: (Top) Active site of [FeFe]Hydrogenase. (Middle) Heme co-factor, active site of cytochrome P450. (Bottom) Iron molybdenum cofactor(FeMoco), site of N2 reduction in [FeMo]nitrogenase.Enzymes with iron cofactors can be divided into two categories, heme andnon-heme. Both types of cofactors illustrate biological examples of ligand designstrategies, vide infra. Heme cofactors contain iron centers imbeded in porphyrinmacrocycles like the cofactor for cytochrome P450 in Scheme 1.1. These non-innocent heme ligands allow the complex to take on a higher oxidation state thanwould normally be stable under biological conditions.31 The non-heme cofactors4display a wide variety of structural motifs and supporting ligands but they typicallycontain multiple iron centers. One advantage of assembling multiple iron centersis the wide range of redox potentials available to the cluster in comparison to anisolated iron center. For example, the family of iron-sulfur clusters, which facilitateelectron transfer in many proteins, is ubiquitous in biological systems and will notbe reviewed here other than to point out that the [4Fe-4S] clusters have redox po-tentials ranging from -650 mV to +450 mV.34 A second advantage of polynuclearsystems is an increase in the number of possible coordination modes. For example,site-directed mutagenesis studies have suggested that the site of N2 binding is atetra-iron face of FeMoco.35 This advantage of polymetallic binding has also beenrealized in synthetic molecular systems, vide infra. Nature assembles clusters ofbase metals or monomeric cofactors with redox active ligands to tune redox poten-tials, transfer electrons, and activate substrates; these concepts of polynuclearityand redox active ligands should be used as a guide for designing ligands for basemetals.Drawing on the insights provided by nature, discrete polynuclear base metalcomplexes are worthwhile synthetic targets. In the next sections we will look atsome examples of mononuclear and polynuclear base metal complexes, however,it should be mentioned that heterogeneous catalysts containing base metals are alsopoised to utilize these same polynuclear advantages. Many researchers have beenworking on heterogeneous systems in recent years and, while difficult to study,these systems are typically more robust than their soluble molecular cousins. Inorder to gain insights about how polynuclear base metal complexes bind substrateswe have chosen to study discrete homogeneous systems that are more amenable tocharacterization.51.1.2 Iron Complexes: Catalysis and Small Molecule ActivationDiscrete homogeneous complexes of iron have been shown to catalyze many im-portant reactions including ethylene polymerization, alkene hydrogenation, ketonehydrogenation and transfer hydrogenation, and carbon-carbon cross coupling reac-tions. These systems contain a diverse array of ligand sets not so different fromligand sets employed by the 2nd and 3rd row transition metals. In this section, wewill survey a few notable iron complexes suitable for catalysis and small moleculeactivation, finding commonalities that will guide future ligand design.Hydrogenation of alkenes and ketones using base metals was reported as earlyas the 1960’s using metal carbonyls such as Fe(CO)5 and Co2(CO)8.36–39 A fewyears later, transfer hydrogenations with complexes of the form MX2(PPh3)2 werediscovered40 where M = Fe, Co, Ni and X = Cl, Br, I. However, all of these sys-tems suffer from harsh reaction conditions, poor chemoselectivity and substratescope. A breakthrough was made by Bianchini and co-workers when they foundthat they could catalyze the hydrogenation of terminal alkynes to alkenes undermild conditions (1 atm H2 RT) using a tetraphosphine ligated iron(II) center, 1.1 inScheme 1.2.41,42 Years later, the same complex was shown to be active in transferhydrogenation of arylalkynes producing styrene derivatives using cyclopentanol asthe hydrogen source.43 The Peters group modified the tetraphosphine ligand frame-work by removing one P-donor and replacing it with a borane, producing a neutraltriphosphinoborane ligand and corresponding iron complex, 1.2. This complex wasable to hydrogenate alkenes to alkanes under mild conditions (1 atm H2 RT) withTurnover Frequency (TOF) up to 15 h−1.44A major step forward in iron catalysis was the development of the bisiminopyri-6dine ligand. First reported by the Brookhart group, these ligands were coordinatedto Fe(II) salts and the resulting complexes were the first iron based homogeneouscatalysts for ethylene polymerization.45 The Chirik group has since developedmany iron complexes using these ligands. In regards to alkene hydrogenation, thereduced dinitrogen complex 1.3 is a hydrogenation catalyst with TOF up to 1814h−1 for 1-hexene .46,47 Not only was compound 1.3 a catalyst for direct alkene hy-drogenation, it was also shown to oxidatively add carbon-carbon bonds using oneelectron from the metal one from the ligand.48 A recent review sumarizes the reac-tivity of base metal complexes of bisiminopyridine ligands.3 The bisiminopyridineligand represents a synthetic example of a biological design strategy discussed insection 1.1.1, that is, pairing base metals with redox active ligands.NN NAr ArFeAr = 2,6-diisopropylphenylN2 N21.3PPh2FePPh21.1P LPh2P H1.2BPiPr2PiPr22iPrP FeN2BPh4L = H2 or N2Scheme 1.2: Selected alkene hydrogenation catalystsSelective hydrogenation and hydrogen transfer reactions of ketones and aldehy-des are important reactions for both bulk and fine chemical processes.49 In recog-nition of their contributions to the field, half of the 2001 Nobel prize was splitbetween Professor Ryoji Noyori and Professor William Knowles for their work oncatalytic asymmetric hydrogenation reactions, with the other half awarded to Pro-fessor Barry Sharpless for his work on catalytic asymmetric oxidations. Profes-sor Knowles pioneered the use of rhodium complexes containing chiral auxiliary7phosphines. In particular compound 1.4 catalyzes the asymmetric alkene hydro-genation step for the production of L-DOPA.50 Professor Noyori pioneered theuse of a ruthenium catalyst (1.5) containing asymmetric phosphines as auxiliaryligands and a diamine ligand which acts cooperatively in the outer-sphere hydro-genation of ketones.51 Efforts toward using iron in place of ruthenium in thesetransformations have been ongoing for a number of years. Beller and co-workersfound that by adding phosphine ligands, the in situ iron carbonyl catalysts weremuch more effective in transfer hydrogenation.52 The groups of Casey and Bellermade significant improvements to the selectivity, functional group tolerance andreaction conditions by using Kno¨lker-type complexes,53,54 compounds 1.6 and 1.7in Scheme 1.4, which are closely related to the organoruthenium Shvo complex.551.5PPOOP PRhPPBF4 Ph2PPPh2RuClCl NH2H2N1.4Scheme 1.3: Catalysts for asymmetric hydrogenationMorris and co-workers have recently developed a family of tetradentate lig-ands containing phosphine, amine, and imine functionalities. These ligands areactive catalysts for asymmetric hydrogenation of ketones.56–58 A representitive ex-ample, 1.8, is shown in Scheme 1.4. These complexes are reminiscent of 1.5 withtwo phosphine and two amine donors. In the case of 1.8, all four donors are teth-ered producing a very stable compelx. In the Morris and Noyori systems previ-8ously mentioned, the dihydrogen molecule (or dihydrogen equivalent in the caseof transfer hydrogenation) is split between the nitrogen donor and the iron centercreating an Fe–H, N–H pair which then interacts with the incoming ketone.59 Wecan see from these examples that when ligand cooperativity is a key componentof the reaction mechanism iron can substitute for ruthenium quite readily, how-ever, for the highly active species (1.8 and 1.9), tri- and tetradentate ligands mustbe used to overcome the lower stability of iron complexes. A new form of ligandmetal cooperativity has recently been reported by the Milstein group. This new co-operativity is proposed to be driven by an aromatization-dearomatization cycle60and complexes including 1.9 (Scheme 1.4) are active catalysts for the hydrogena-tion of ketones61 and carbon dioxide.62 Deprotonation of these complexes occursat the benzyl linker, to generate systems that can cleave dihydrogen between theiron center and the backbone of the ligand producing an Fe–H, C–H pair, like theone shown in compound 1.9.FeOSiMe3SiMe31.6 1.7FePCy2PCy2N NHPh Ph1.8NPiPr2PiPr2Fe COHBr1.9OCOC HOHSiMe3SiMe3 FeOCOC H COClHScheme 1.4: Selected carbonyl hydrogenation catalystsThere has been increasing interest in using iron-based systems for activationand functionalization of small molecules including NO,63 O2,64 and CO2.65 Ofparticular interest to the Fryzuk research group is the activation of N2. The earliestreport of an iron dinitrogen compound is from 1976.66 Over the next two decades9additional examples were sparsely reported.67–71 Only a few of these compoundswere structurally characterized and for all examples the N-N bond lengths (1.102A˚- 1.139 A˚) are not substantially elongated compared to free dinitrogen (1.0975A˚), indicating minimal activation upon binding to the metal center.72 Another com-monality between these early examples is that all of these species are LS with co-ordination numbers of 5 or 6. In the last two decades a number of High Spin (HS)iron dinitrogen complexes were reported with coordination numbers less than 5.We will now examine several examples of these low valent iron dinitrogen com-plexes and illustrate how they have led to progressively more activated dinitrogenand stoichiometric functionalization of the N2 unit.1.10 1.11 1.12 1.13PhBiPr2PPiPr2PiPr2FeNN[BPPP]FePhBiPr2PPiPr2PiPr2FeNNB2iPrPPiPr22iPrPFeNNSiSiNSiMe2NiPr2PiPr2PFeNNFe[P2N2]MgCl(THF)2Scheme 1.5: Selected iron dinitrogen complexes with tetrahedral coordina-tion geometriesThe first tetrahedral iron compounds containing a dinitrogen ligand were re-ported in 2003 by Peters and co-workers (1.10) using the tripodal ligand [PhB(CH2-PiPr2)3]−.73 In contrast to previously reported iron N2 complexes, compound 1.10displays a bridging end-on coordination mode for the N2 ligand, and moderate ac-tivation (N–N = 1.171 A˚). Interestingly, while 1.10 forms upon reduction of theiron chloride complex [PhB(CH2PiPr2)3]FeCl with sodium, reduction with mag-10nesium leads to a monomeric end-on ate complex, 1.11. This report represents abreakthrough in iron dinitrogen activation because treating compound 1.11 withMeOTf results in the formation of a nitrogen-carbon bond. A few years later aneutral ligand with ortho-phenylene linkers, B(C6H4PiPr2)3, was utilized to formanother dinitrogen compound, [B(C6H4PiPr2)3]Fe(N2), which, when treated with1,2-(dimethylchlorosilyl)ethane results in N2 functionalization producing 1.12.74Unfortunately, total N-N bond cleavage could not be achieved by further reductionof 1.12. It should be noted that the Arnold group also developed an anionic tri-dentate ligand that showed a similar tetrahedral iron center and N2 activation via adiiron system, compound 1.13.75 However, functionalization of the N2 unit has notbeen reported for this system.Moving to even lower coordination numbers, the Holland group has been de-veloping iron complexes that bind, activate, and in some cases cleave N2.5 The lig-and framework used in all of this chemistry contains a 1,3-diketiminato, NacNac,system, which can be sterically tuned by appropriate choice of N-aryl substituent.76Utilizing salt metathesis, three coordinate complexes of the type (NacNac)FeClhave been reported for a variety of NacNac derivatives. Upon reduction, these com-plexes bind dinitrogen in a bridging end-on coordination geometry illustrated by1.14 in Scheme 1.6.77 Interestingly, further reduction of this neutral complex yieldsthe dianionic ate complex 1.15, which shows even greater N-N bond elongation.77Attempts to functionalize the N2 unit in 1.14 or 1.15 were unsuccessful as the com-plexes react by displacing N2 and binding other neutral ligands such as PR3, COand C6H6.78 Modifying the ligand architecture by reducing the steric bulk led to adifferent product. When complex 1.16 was reduced with potassium graphite, thetrinuclear complex 1.17 was formed. In compound 1.17, the N–N bond has been11completely cleaved by a 6-electron reduction, resulting in two nitrido ligands.79The first nitrido is bound by three (NacNac)Fe moieties and the second bridgestwo of the aforementioned centers and two potassium ions. A fourth equivalent of(NacNac)Fe is bound through chloride bridges to the potassium promoters; com-putational studies suggest that the potassium atoms play a role in the dinitrogenactivation.80 This result is hugely important as it shows that by tuning the stericprofile of the supporting ligands, cluster formation can be encouraged and in thesehigh nuclearity complexes the N-N bond of dinitrogen can be cleaved.2 KC8NNFeNNFeN NiPriPriPriPriPr iPriPriPrKKNNFeNNFe 2 KC8ClClNNFeClClKKNNFeNNFeN NiPriPriPriPriPr iPriPriPrN NFeN NFeN NNNArFeN2N21.14 1.151.16 1.17ArArArArArScheme 1.6: Low coordinate iron complexes cleave dinitrogen with alkalimetal promoters12To examine the effect of the reductant, MC8 reagents were used where M = Rb,and Cs. These reagents have similar reduction potentials to KC8 so the analogoustrinuclear clusters would have been expected. For Rb, the analogous complex isobtained, however, using CsC8 no N-N bond cleavage is observed and the productis a trinuclear dinitrogen complex with three equivalents of dinitrogen bridging themetal centers.5 The different outcomes of reactions of 1.16 with MC8 (M = K, Rb,Cs) suggest that these alkali cations play a crucial role in assembling the unob-served (NacNac)Fe(I) intermediates into polynuclear reaction sites. These reportsfrom the Holland group show that high spin iron complexes with low coordinationnumber and low oxidation states should be targets for dinitrogen activation. Thefortuitous cluster formation templated by alkali metal cations suggests that polynu-clear reaction sites are another fruitful avenue for investigation, and construction ofmore complex ligand sets could alleviate the need for spontaneous self assembly.Recently, ligand scaffolds specifically designed for coordinating multiple metalcenters have been gaining attention. These ligand sets have been used to system-atically study metal metal bonding,81–84and to activate small molecules.85–89 Mostrelevant to iron dinitrogen activation are the ligand sets developed by the Betley andMurray research groups. Both ligand sets consist of three donor pockets bound to-gether such that the open coordination sites of each metal are pointed towards thecenter of the ligand scaffold. In the Betley system the ligand is hexaanionic andwhen three Fe(II) ions are installed the neutral compound displays short iron–irondistances, which are best described as weak interactions (1.18 in Scheme 1.7).Compound 1.18 does not spontaneously react with N2. However, treatment of 1.18with azobenzene results in cleavage of the N–N double bond, producing compound1.19 with two phenyl imido ligands.9013NNFe FeN NFeNSiSiNSiONNPh Ph80oCNN NNSiNSiNSiFe FeFeNNBetley 2013Murray 2015NNFeNNFeBrNNFe BrBrNNFeNNFeNNFe NHNHNHC7H8, RTN2 , 6 KC81.18 1.191.20 1.21Scheme 1.7: Polynuclear iron complexes through ligand designIn contrast, the ligand set developed by the Murray group is a trianionic ligandthat effectively tethers three NacNac ligands into a trigonal array. Based on reportsfrom the Holland group, vide supra, this trigonal system should be competent in N2reduction. Indeed, reducing the iron bromide complex, 1.20, results in completeN–N bond cleavage and formation of a complex containing three bridging imidos,1.21.91 While the H atom source and mechanism of formation remain unclear, la-beling studies have shown that these imidos originate from atmospheric nitrogen.91Both of the examples shown in Scheme 1.7 illustrate the utility of polynuclear com-14plexes.Examining some of the iron complexes from above, a few design features arecommon: i) low-coordinate complexes allow for stronger substrate activation; ii)high-spin complexes display higher degrees of N-N bond elongation, although low-spin complexes are excellent hydrogenation catalysts; iii) non-innocent ligands canbe helpful when promoting 2-electron chemistry in base metal complexes; and iv)polymetallic clusters are crucial for the cleavage of strong bonds such as the N-Ntriple bond in dinitrogen. When designing new ligands to be used for iron-basedsmall molecule activation, these design features should be kept in mind. In thefollowing sections we will look at previous ligand design in the Fryzuk group andintroduce the phosphinoamide ligand.1.2 Ligand Design1.2.1 Ligand Design in the Fryzuk GroupMNNMe2SiMe2SiSiMe2SiMe2P PR RMNNMe2Si ArArSiMe2PRGeneration 1:MNMe2SiMe2SiP PR RR R[P2N2][NPNSi] [PNP]Figure 1.1: First generation ligand design in the Fryzuk groupLigands designed in the Fryzuk group typically combine “hard” amido and“soft” phosphine donors into chelating arrays.92 The central hypothesis is that us-15ing a mixed donor system allows for the formation of hard-soft acid-base mis-matches, which affords a more reactive metal complex. For example, these hybridligands (Figure 1.1) have been coordinated to early and late transition metals andhave resulted in the first examples of early metal-phosphine and late metal-amidolinkages.93,94 The first generation of hybrid ligands utilized silyl methylene linkersto connect the disparate donor environments. Three versions of the first genera-tion ligands were investigated: a dianionic pincer [NPNSi], a monoanionic pincer[PNP], and a dianionic macrocycle [P2N2]. Early transiton metal complexes of[NPNSi] and [P2N2] have shown remarkable N2 activation and the N2 units canbe hydrogenated95 and functionalized96–98 (Scheme 1.8). A problem with the firstgeneration ligands was that the N-Si linkers in the the ligand backbone were labileand in many cases the ligand as well as the dinitrogen units were functionalized.[P2N2]ZrClCl[P2N2]ZrNNZr[P2N2]KC8N2H2N2[P2N2]ZrHNZr[P2N2]NH[NPN]Ta Ta[NPN]HHHH[NPN]Ta Ta[NPN]HHNN[NPN]Ta Ta[NPN]NNSiH2BuSiH2Bu2 nBuSiH3Scheme 1.8: Dinitrogen functionalization with hybrid ligandsTo avoid ligand rearrangments, modifications were made to the linkers of thefirst generation [NPNSi] ligands. Aryl [ArNPN∗],99–101 alkenyl [NPNcp],102,103 ando-thiophene [NPNS]104 linked amidophosphine ligands have been synthesized andcoordinated to a variety of transition metals (Figure 1.2). In some cases dinitrogencomplexes have been made, however, none of these complexes have been able tofunctionalize dinitrogen like the complexes of the first generation ligands. More-16over, none of these second generation ligands allowed for any kind of catalyticfunctionalization of dinitrogen. More recently, linkerless donor sets were studiedin our lab. In particular, complexes of the group 3 and 4 metals were investigatedfor a variety of transformations. The following section will explore the history ofthe linkerless ligand sets and their incorporation into larger ligand scaffolds.[NPNcp][ArNPN*] [NPNS]PN NAr ArMRPN NAr ArMRPN NAr ArMRS SFigure 1.2: Second generation ligand design in the Fryzuk group1.2.2 Phosphinoamides as LigandsNeutral phosphine (P-C) and phosphite (P-O) ligands are ubiquitous P donors inorganometallic chemistry, both as monodentate donors, and as part of a largerchelating ligand set. A new class of phosphine donor that is gaining increased at-tention is the phosphinoamine ligand containing a P-N bond.105 These P-N bondsare relatively easy to construct from the appropriate amine and chlorophosphinein the presence of an external base (Scheme 1.9). For some sterically demandingderivatives an alkali amido precursor may be required.105 These phosphinoamineshave been used as ligands for late transition metals including a rhodium complexcapable of catalytic hydroformylation.106 Asymmetric phosphinoamines have beensynthesized and the resulting copper complexes catalyze enantioselective nucle-ophilic addition to enones.10717NHR'H PClRR+NEt3NHR'PRRNHR'Li PClRR+-LiCl- NEt3HClNHArPPhPhNArPPhPhLiOEt2OEt2Ar = 2,4,6-tBu3C6H2 nBuLiEt2O(1.22) (1.23)Scheme 1.9: Synthesis of phosphinoamidesMore relevant to this thesis, phosphinoamines serve as precursors to the anionicphosphinoamide functional group. Treatment of the phosphinoamine (1.22) withalkyl lithium reagents generates the lithium phosphinoamide (1.23) as shown inScheme 1.9. The amidophosphine anion has several important structural features.The first feature is the short P-N bond length in the [RNPR’2]− anion. The shortbond is due to a combination of phosphinoamide (A) and iminophosphide (B) res-onance forms (see Figure 1.3). Computational modeling suggests that the phosphi-noamide resonance structure (A) is the major contributor, except when particularlyelectron withdrawing groups are attatched to phosphorus.108 The delocalization isbest described as a nitrogen based lone pair donating into the σ∗PR orbital. The N–Pbond length in phosphinoamides (∼ 1.70 A˚) is substantially longer than the P=Ndouble bond (∼ 1.60 A˚) in phosphinimines (also known as iminophosphoranes).18Due to the partial double bond character between the nitrogen and phosphorusatoms, cis and trans stereoisomers are possible (Figure 1.3). Computational stud-ies suggest that the two stereoisomers are nearly degenerate when all steric bulk isremoved, however, there is a significant barrier to interconversion (7.4 kcal/mol forH2PNH−).108 There are four binding modes which have been observed for phos-phinoamides. Both κ1 - (N) and κ1 - (P) coordination modes are possible. In ad-dition η2 - (NP) is common109 and phosphinoamides have the potential to bridgetwo metal centers in the µ binding mode.110,111NR'PRR N PRRR'cis transNR'PRRMNR'PRRMκ1 − (N) κ1 − (P)NR'PRRMη2 − (ΝP)NR'PRRMM'µNR'PRR NR'PRRA BFigure 1.3: Resonance forms, stereoisomers and common binding modes ofamidophosphinesPhosphinoamide complexes of rare earth metals have been reported by ourgroup and others. Anionic ’ate’ complexes can be formed by salt metathesis oflithium phosphinoamides with MCl3 (M = Y, Yb, Lu),112 however, neutral com-plexes are more easily accessed by protonolysis of metal alkyl precursors M(CH2-SiMe3)3 (M = Sc, Y) with phosphinoamines (See Figure 1.4).109 Based on thehighly symmetric 31P NMR spectrum displaying a small 2JPY coupling, complex1.24 is thought to have all four phosphinoamides bound κ1 - (N) in solution. The19neutral compounds 1.25 and 1.26 were found to undergo deleterious ligand ex-change reactions and therefore were not suitable for small molecule activationstudies.YPPh2PhNNPhPPh2PhNPh2P PPh2PhNLi(THF)4 MNArPiPr2OArNiPr2PArNiPr2PAr = 3,5-dimethylphenylM= Sc (1.25); Y (1.26)1.24Figure 1.4: Phosphinoamide complexes of rare earth metalsPhosphinoamide complexes of the mid to late transition metals are more com-monly dinuclear, displaying the µ-(NP) binding mode. Phosphinoamide com-plexes of chromium have been synthesized and can be dinuclear (1.27), or tetranu-clear (1.28) depending on the stoichiometry of the reaction (Scheme 1.10). Thesechromium complexes are active catalysts for ethylene oligermization.113 Reductionof the tetramer leads to a dinuclear Cr(I)/Cr(II) complex 1.29, which is an ethylenetrimerization catalyst.114 Recently the Thomas group has extended the use of phos-phinoamides, making dinuclear complexes of iron (1.30) and manganese (1.31).111The iron complex, 1.30, can be reduced to give a mixed valent Fe(I/II) system,1.32, which is best described as a delocalized [Fe2]3+ unit. Compound 1.32 reactswith organic azides to produce the C3 symmetric iron imido (1.33), however, nogroup transfer reactivity has been reported.115Utilizing the disparate phosphine and amido donors, heterobimetallic com-plexes have been constructed using phosphinoamides. The Nagashima group pi-oneered the strategy of using phosphinoamide complexes of group IV transition20Cr CrP NP NP NPNPhPhPhPh PhPhPhPhtButButButBuN PHtBu PhPh2 i) 2 nBuLiii) CrCl2(THF)2Cr CrP NP NPNPhPhPhPhPhPhtButButBui) 2 nBuLiii) 2 CrCl2(THF)2ClCrCrPNPNPNPhPhPhPhPhPhtButButBuCl1) PMe32) KC8Cr CrP NP NP NPhPhPhPhPhPhtButButBuPMeMeMe(1.27)(1.29)(1.28)Fe FeNNNPPh2PPh2PPh2NiPr iPriPrPPh2iPrMn MnNNNPPh2PPh2PPh2NiPr iPriPrPPh2iPr1) 1.5 Na/Hg2) PMe3Fe FeNNNPPh2PPh2PPh2iPr iPriPrPMe32 RN3, THF-RN=PMe3-2 N2Fe FeNNNPPh2PPh2PPh2iPr iPriPrN R(1.30) (1.31)(1.33)(1.32)Scheme 1.10: Phosphinoamide complexes of the mid to late transition metals21metals as ‘metalloligands’(ligands containing a metal atom) for late transtion met-als. The first example of this strategy utilized the metalloligand (tBuNPPh2)2TiCl2(1.34) to coordinate Pt(II) precursors forming heterobimetallics containing a Pt→Ti interaction, compound 1.35 in Scheme 1.11.116 Later work from the Nagashimagroup extended this methodology to ruthenium, copper and molybdenum.117,118They were able to synthesize a platinum allyl complex, 1.36, and show that the da-tive Pt→ Ti interaction generates increased electrophilicity at the pi-allyl moiety,trans to the titanium center.119 Building off this methodology, the Thomas grouphas examined early-late heterobimetallics containing Co → Zr interactions 1.37.This open shell system contains three amidophosphine ligands and binds dinitro-gen to the cobalt center upon reduction, forming 1.38.110 If the reduction of 1.37 isperformed under argon, compound 1.39 is obtained, which upon exposure to CO2,cleaves one of the carbon oxygen bonds forming compound 1.40.120–122 It shouldbe noted that 1.38 is a catalyst for the hydrosilyation of ketones.123 The work bythe Nagashima and Thomas groups illustrates the utility of phosphinoamides inconstructing heterobimetallic complexes across the periodic table.It is clear from the examples in Scheme 1.11 that phosphinoamides can be usedto build early/late heterobimetallic frameworks. As discussed previously, we wouldlike to be able to build polymetallic base metal complexes. Recently the Thomasgroup has shown that not only can these ligands form homobimetallic compoundsof iron, vide supra, but heterobimetallics can be formed between iron and othermid transition metals.124–126 These complexes are formed with control over thebinding site for each metal, and there are no reports of metal or ligand scramblingwithin theses complexes. The Cr/Fe and V/Fe (1.41 and 1.42) complexes allowedfor detailed study of the metal-metal multiple bond upon reduction and oxidation22TiNNPPClCltButBuPhPhPhPh(1.34)ClTiClNN PtBuPtBuPtMe-OTf(1.36)PhPhPhPhNZrClNN PArPArCoiPriPriPriPr(1.37)PiPr iPrArIxs Na/HgNZrNN PArPArCoiPriPriPriPr(1.38)PiPr iPrArN NNaClbNZrNN PArPArCoiPriPriPriPr(1.40)P2iPrArC OONZrTHFNN PArPArCoiPriPriPriPr(1.39)PiPr iPrArNa/HgArCO2ClTiClNN PtBuPtBuPt(1.35)PhPhPhPhMeMeaN2Scheme 1.11: Early/late heterobimetallic complexes of phosphinoamideligands. Ar = 2,4,6-trimethylphenyl. a: ((PtMe2)(µ - SMe2))2, b:[((CH3)2CO)2Pt(C4H8)]OTf23(1.43, 1.44, 1.45).122 This work provides an excellent comparison to the Cr/FeV/Fe heterobimetallics (amongst others) that have been developed in the Lu lab(See Scheme 1.12). We will not explore the systems developed by the Lu lab indetail because they do not employ phosphinoamide ligands.NCrNN PiPrPiPrFePhPhPhPh(1.41)PPh PhiPrIxs KC8PMe3NCrNN PiPrPiPrFePhPhPhPh(1.43)PPh PhiPrPMe3NVNN PiPrPiPrFePhPhPhPh(1.42)PPh PhiPrIxs KC8PMe3NVNN PiPrPiPrFePhPhPhPh(1.45)PPh PhiPrPMe3[fc][PF6]NVNN PiPrPiPrFePhPhPhPh(1.44)PPh PhiPrIFScheme 1.12: Heterobimetallic complexes of phosphinoamide ligands.1.2.3 Tethered PhosphinoamidesPhosphinoamide ligands are typically labile, easily interconverting between bind-ing modes. This lability creates a situation where control of stoichiometry inM(R2PNR)x compounds is difficult, and ligand redistribution is common.109 Inan effort to control the coordination modes and number of bound ligands, re-searchers have begun designing multidentate ligands containing multiple phosphi-noamide groups. The Stephan group has developed bis(phosphinoamide) ligandswith aliphatic linkers (R2PNH(CH2)nNHPR2) where n = 2 or 3. When mixed withnickel halides these ligands were found to coordinate nickel in the aminophos-24phine/phosphinoamide (κ3-P,η2-N,P; 1.46) or bis(aminophosphine) (κ3-P,C,P; 1.47)coordination modes (Figure 1.5).127 A second generation of these ligands were de-signed with a neutral amine donor tethering three aminophosphine donors. Ruthe-nium complexes of this tris(phosphinoamine) were synthesized and deprotonationof the complex leads to compound 1.48 containing one η2 phosphinoamide andtwo phosphinoamine donors. This complex was shown to activate CO2 coopera-tively between the nucleophilic phosphorus atom and the electrophilic rutheniumcenter, and is an active catalyst for the hydroboration of CO2.128 A third itera-tion, again pioneered by the Stephan group, contained two phosphinoamine donorsflanking a central thiol donor. Protonolysis with Hf(CH2Ph)4 led to the formationof compound 1.49, which is the first example of a tethered bis(phosphinoamide)complex. This complex was found to activate CO2 cooperatively, analogous to theruthenium system.129 However, no catalytic hydroboration was reported for thiscomplex, presumably due to the stronger M-O bond in the hafnium system. Thehigh degree of flexibility in the backbone of the ligands developed by the Stephangroup has led to C-H bond activation in the case of nickel, and ligand dissocia-tion in the case of ruthenium. However, an interesting feature of these systems isthe nucleophilicity of the P atom in the phosphinoamides, and their ability to actcooperatively with a metal center to activate CO2.Our group has investigated the use of phosphinoamide ligands with rare earthelements and discovered that ligand redistribution was common.109 In order toavoid this challenge we searched for an appropriate linker. Our attention soonturned to work done by the Arnold and Diaconescu groups which utilized 1,1’-diaminoferrocene based ligands such as fc(NH2)2,130,131 fc(NHSiR3)2132–135 andfc(NHAr)2.136 Using these ligands, complexes of zirconium and ruthenium could252tBuPNNi PtBu2ClNH(1.46)PtBu2NiPtBu2ClHNNHn =1, 2(1.47)PiPr2NHNHNN PiPr22iPrP RuHBPh4(1.48)NHfNS(1.49)PPh2PPh2PhPhFigure 1.5: Coordination modes of alkyl linked phosphinoamidesbe developed, which were active catalysts for olefin polymerization and transferhydrogenation, respectivley.131,136 Utilizing the same ferrocene (fc) linker we con-structed the bis(aminophosphine) ligand 1,1’-fc(NHPiPr2)2 (1.50). With 1.50 inhand, a scandium alkyl complex, 1.51, could be formed, via protonolysis. Unlikeprevious scandium alkyls supported by phosphinoamide ligands, compound 1.51cleanly reacts with dihydrogen to produce a rare scandium hydride, 1.52.137 Wewondered whether this bis(phosphinoamide) ligand set would be a good candidatefor supporting polymetallic complexes of the base metals.FeNNPPScFeNNPPScFeNNPPScCH2SiMe3THFHHH2(1.51) (1.52)FeNHHNPP(1.50)aScheme 1.13: Hydrogenation of a scandium alkyl. a: Sc(CH2SiMe3)3(THF)3261.3 Scope of ThesisExamining the bis(phosphinoamine), 1.50, while considering the design featuresmentioned in section 1.1.2, we thought that this ligand would be useful for syn-thesizing polynuclear base metal complexes. Phosphinoamide donors have beenshown to bridge multiple metal centers, including iron. The ferrocene linker pro-vides a rigid backbone that will enable the controlled assembly of metal complexescontaining only two phosphinoamide donors, yielding low coordinate complexes.In addition the ferrocene backbone is potentially redox non-innocent.138 A directN–M bond between this ligand set and an appropriate metal has the potential toreact with hydrogen in a cooperative fashion, similar to the Noyori and Morrissystems (Scheme 1.4).This thesis will discuss the coordination chemistry of hybrid amidophosphinedonors with transition metals. Chapter 2 contains mechanistic studies of reactionsbetween a tantalum tetrahydride supported with the 1st generation [NPNSi] lig-ands and C1 sources, CO2 and CO. Chapter 3 focuses on the synthesis of basemetal complexes supported by the new ferrocene linked bis(phosphinoamide) lig-and, 1.50. Chapter 4 examines the reactivity of a dimeric iron complex with a widearray of small molecules. Chapter 5 discusses future directions for the compoundsreported in this thesis as well as new ligand designs.27Chapter 2Reduction of Carbon Monoxideand Carbon Dioxide by aDitantalumtetrahydrideEducation is what remains after one has forgotten what one haslearned in school — Albert Einstein2.1 Complete Reduction of Carbon Monoxide2.1.1 IntroductionThe analogy between carbon monoxide (CO) and dinitrogen (N2) is often made torationalize their relative abilities to be activated by transition metal complexes.139Even though these molecules are isoelectronic, the more polar CO is a much betterligand than N2 largely because of the smaller energy gap between the HighestOccupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital(LUMO) for CO as compared to N2, which allows better overlap of these orbitalswith appropriate transition metal d-orbitals. In addition, unlike dinitrogen, carbon28monoxide undergoes migratory insertion processes, which are key to a number ofindustrial catalytic processes such as hydroformylation, Fischer Tropsch, and theacetic acid synthesis;140 by comparison, the only industrial process that utilizes N2as a feedstock is the Haber-Bosch ammonia synthesis,141 which does not involveany migratory insertion steps with intact dinitrogen.142We recently described the facile activation of dinitrogen (N2) by a dinucleartantalum tetrahydride, ([NPN]Ta)2(µ−H)4 2.1 to generate the side-on end-on di-tantalum dinitrogen complex, ([NPN]Ta)2(µ−η2 : η1−N2)(µ−H)2 2.2.143,144 Asthis N2 complex displays a rich reactivity that results in E-N bond formation (E= B, C, Al, Si) and even N-N bond cleavage,143 we wondered if a similar kind ofactivation process could be realized for carbon monoxide (CO) by reaction withtetrahydride 2.1 (i.e., formation of 2.3 in Scheme 2.1). What we discovered wasthat CO can be activated by an apparent series of migratory insertion processesinvolving 2.1 in a manner quite different from its isoelectronic analogue, N2.2.1.2 Results and DiscussionWhile the reaction of 2.1 with N2 proceeds smoothly with excess N2,144,145 thecorresponding reaction of 2.1 with CO requires stoichiometric addition of CO asexcess carbon monoxide results in a complicated mixture of products. Addition ofexactly 1 equiv of CO to 2.1 results in the formation of a dark brown solution fromwhich red crystals could be obtained in reasonable yield (54%). The spectroscopiccharacteristics of the isolated material show that it is an unsymmetrical specieswith inequivalent phosphorus-31 nuclei (two sharp singlets at δ 20.2 and 12.1 inthe 31P{1H}NMR spectrum) and a very complicated 1H NMR spectrum with eightdistinct silyl methyl groups, consistent with C1 symmetry. These patterns alone29Scheme 2.1made it clear that this product was not 2.3 (Scheme 2.1), the anticipated analogueof the side-on end-on N2 complex 2.2, as both species would have Cs symmetry.In particular, no peaks were observed in the 1H NMR spectrum of the product inthe downfield region between δ 8-18, which is diagnostic for a bridging hydrideof the type Ta2(µ-H)x. Moreover, the aromatic protons displayed a complicatedupfield-shifted pattern of four coupled resonances in the range of δ 4.8−6.4. Theuse of carbon-13 labeled carbon monoxide (13CO) was confusing as the isolatedproduct did not display any isotope-enhanced peaks in the 13C NMR spectrum.However, we did observe an intense peak at δ -4.5 when the solution and gas phasewere carefully analyzed by 13C NMR spectroscopy before separation of the productfrom the crude reaction mixture; this peak corresponds to 13CH4. The reaction of30the polydeuteride (2.1-d12, vide infra) with 1 equiv of CO resulted in the formationof an isotopologue of the final product, whose upfield 1H NMR resonance at δ4.98 is absent. While a number of possible structures were considered, particularlyin light of previous studies wherein upfield shifted aromatic proton resonances ofa cyclometalated N-Ph unit were observed,146 the isolation of suitable crystals forX-ray analysis provided an unequivocal answer.As shown in Figure 2.1, the product 2.4 has a dinuclear structure and there isboth a bridging hydride unit and a bridging oxo. Also interesting is the pi-boundcyclometalated N-C6H4 group of one of the amido donors; this feature in 2.4 ra-tionalizes the upfield shifted proton resonances observed as they are due to thisunique cyclometalated ring. As a resonance for the bridging hydride was not de-tected in the range from δ -20 to +50 in the 1H NMR spectrum, we suggest that itis buried under the aromatic resonances. Attempts to confirm this using the variousdeuterated forms of 2.1 (cf., 2.1-d12 or 2.1-dx) were inconclusive.A mechanism for the formation of 2.4 is proposed in Scheme 2.2 that takesadvantage of previous studies on the reaction of carbon monoxide with tantalumhydrides.147–149 The structure of the initial adduct of CO with the tetrahydride,Ta2H4•CO, could not be detected and therefore its formulation is speculativelyshown as a simple end-on CO bound to one of the Ta centers of the dinucleartetrahydride. Subsequent migratory insertion generates the bridging η2-formyl,Ta2H3•CHO, which is then converted to the methylene-oxy species,Ta2H2•CH2O, via migratory insertion. The next step is a reductive ring opening ofa ditantalamethylene oxy 4-membered ring to generate a coordinated methylideneand tantalum-oxo species. Another migratory insertion of the methylidene and oneof the hydrides generates the methyl-µ-oxo hydride, Ta2H•CH3O, which upon31Figure 2.1: ORTEP diagram of 2.4 (silylmethyls omitted and only ipsocarbons of the N- and P-phenyls are shown, except for the cyclometal-lated phenyl). Selected bond lengths (A˚) and bond angles (°): Ta1-Ta22.7240(6), Ta1-C18 2.095(4), Ta2-C18 2.399(4), Ta-C17 2.501(4), Ta1-O1 1.925(3), Ta2-O1 2.009(3), Ta1-H1 1.96(5), Ta2-H1 1.92(5), Ta1-N12.127(3), Ta1-N2 2.081(4), Ta1-P1 2.6706(12), Ta2-N3 2.043(4), Ta2-N42.068(3), Ta2-P2 2.6154(12), Ta1-N1-C13 94.8(2), N1-C13-C18 104.4(3),Ta1-C18-C13 95.0(3), C18-Ta1-N1 64.81(14), C17-C18-Ta1 143.2(3), Ta1-C18-Ta2 74.29(13), Ta1-O1-Ta2 87.60(11), O1-Ta1-N1 107.72(12), O1-Ta1-N2 126.07(13), O1-Ta1-C18 100.74(14), N2-Ta1-C18 116.15(15), N2-Ta1-N1 122.77(13), N3-Ta2-N4 113.35(13), N3-Ta2-C18 102.07(14), N4-Ta2-C18 144.54(14), O1-Ta2-N3 91.87(12), O1-Ta2-N4 88.40(12), O1-Ta2-C1888.85(13)reductive elimination of CH4 would generate the highly coordinatively unsaturatedspecies Ta2O; it is this species that we propose undergoes activation of the N-Phmoiety to generate the observed cyclometalated derivative 2.4.Carbon monoxide can be cleaved by both mononuclear and multinuclear earlytransition metal150 and lanthanide complexes.151 In certain cases, the systems uti-lized are low oxidation early transition metal complexes, such as Ta(silox)315232Scheme 2.2: Proposed mechanism for CO reduction by 2.1or W2(silox)4Cl2153 (where silox = OSiBut 3), and the cleavage process operatesvia reduction of the CO.154 Other examples include multistep processes involvingmigratory insertion,147–149 sometimes through the intermediacy of a coordinatedformyl unit. As proposed above in Scheme 2.2, the dinuclear ditantalum systemcleaves CO by a combination of migratory insertion steps and a reductive cleavagestep. In an effort to better understand the mechanism of the reaction of tetrahydride2.1 with CO, we examined possible intermediates and transition states computa-tionally.33Computational DetailsTantalum atoms were treated with the small core Stuttgart-Dresden relativisticEffective Core Potential (ECP) in combination with its adapted basis set.155,156Carbon, oxygen, nitrogen and hydrogen atoms have been described with a 6-31G(d,p) double-ζ basis set.157 Silicon and phosphorus atoms were treated withthe Stuttgart-Dresden ECP in combination with its adapted basis set and additionald polarization functions.158,159 Calculations were carried out at the Density Func-tional Theory (DFT) level of theory using the hybrid functional B3PW91.160,161Geometry optimizations were performed without any symmetry restrictions andthe nature of the extremes (minima and transition states) was verified with ana-lytical frequency calculations. Gibbs free energies were obtained at T = 298.15K within the harmonic approximation. Intrinsic Reaction Coordinate (IRC) cal-culations were performed to confirm the connections of the optimized transitionstates. DFT calculations were carried out with the Gaussian09 suite program.162The electronic density (at the DFT level) has been analyzed using the Natural BondOrder (NBO) technique.163 Calculations have been realized in the gas-phase andthe real NPN ligands have been computed.To begin, we computed the structure of the ditantalum tetrahydride 2.1 andcompared it to an incomplete X-ray crystal structure (see Appendix, Figure A.1).The computed structure is presented in Figure 2.2 with selected bond lengths andangles. It confirms the presence of four bridging hydrides and the global structurematches the structure observed experimentally164 for the complex ([P2N2]Ta)2(µ-H)4. The NBO analysis is consistent with the presence of the Ta(IV) oxidationstate and the presence of a Ta-Ta bond. This is further confirmed by analyzingthe molecular orbitals. Indeed, the HOMO of this complex corresponds to the σ -34interaction of two d orbitals of tantalum (Figure 2.3), suggesting that the electronsstored in the Ta-Ta bond can be used to reduce substrates.Figure 2.2: Computed structure of complex 2.1. NPN ligands have been sim-plified for clarity. Selected bond distances (A˚), bond angles (deg) and torsionangles (deg) ; comparisons to the incomplete structure of 2.1 (see SupportingInformation) are given where applicable in brackets: Ta1-Ta2 2.589 [2.57],Ta-P 2.605, Ta1-N1 2.104 [2.08], Ta1-N2 2.124 [2.09], Ta2-N3 2.124 [2.09],Ta2-N4 2.104 [2.08], Ta1-H1 1.965, Ta1-H2 1.918, Ta1-H3 1.978, Ta1-H41.909, Ta2-H1 1.918, Ta2-H2 1.965, Ta2-H3 1.909, Ta2-H4 1.978, P1-Ta1-P2154.57, Ta2-Ta1-P1 128.97, Ta2-Ta1-N1 122.69, Ta1-H1-Ta2 83.61, P1-Ta1-Ta2-P2 179.99 [180], N1-Ta1-Ta2-N4 179.98.The reaction between 2.1 and CO is complex. The first part of the Gibbs freeenergy profile of the reaction between 2.1 and CO is presented in Figure 2.4. Eachminimum of the profile has been optimized in its singlet and triplet spin-states andthe singlet spin-states are also found to be the most stable for all minima, by 8∼30kcal/mol. Thus, the reactivity takes place on the singlet potential energy surface.The first step of the reaction is the coordination of CO to 2.1 involving bothTa centers. Interestingly, two of bridging hydride groups have become terminal in35Figure 2.3: Schematic depiction of the HOMO for complex 2.1, correspond-ing to the metal-metal overlap.order to allow the coordination; this was not considered in the original proposedmechanism shown in Scheme 2.2. The coordination mode shows the CO to beunsymmetrically bridging in a µ-η1-η1 mode with quite different Ta1-C and Ta2-C distances of 2.08 A˚and 2.43 A˚, respectively. The C-O bond length is 1.19 A˚,which is elongated with respect to free CO (1.13 A˚), which supports some pi-back-donation from the two tantalum centers. The HOMO of this system corresponds tothe interaction between the Ta centers and CO and is depicted in Figure 2.5. Thecoordination of CO is exergonic by -7.8 kcal/mol. Interestingly, this resembles theaforementioned product of CO activation shown in Scheme 2.1, by analogy to the36Figure 2.4: Gibbs free energy profile of the reaction between the tetrahydride complex 2.1 and CO. NPN ligands havebeen simplified for clarity. Atoms colors: Ta: green, P: orange, N: blue, O: red, C: black, H: white. For atom numbering,Ta1 is on the left while Ta2 is on the right.37Figure 2.5: Schematic depiction of the HOMO for Ta2H4•CO, correspond-ing to the metal-CO overlaps; the bridging hydrides are not shown and mostof the ligands except for the two amido donors on each tantalum are omitted.N2 activation; however, in this calculation the side-on, end-on CO species, lossof H2 does not occur as in the case of dinitrogen activation. Rather, the adductTa2H4•CO easily undergoes migratory insertion of CO into a terminal Ta-H bond.Indeed, the transition state of insertion lies at only +1.9 kcal/mol above the adduct,and the formation of the corresponding formyl, Ta2H3•HCO, is exergonic by -8.2kcal/mol with respect to Ta2H4•CO. The structure of the first transition state, TS1-CO, has the hydride poised for migratory insertion to generate the formyl group ina µ-η1-η2 coordination mode.The next step of the reaction is the facile migration of the other terminal hy-dride (transition state TS2-CO at +11.4 kcal/mol), which generates Ta2H2•H2COthat contains a coordinated formaldehyde unit, whose formation is slightly ender-38gonic by +5.0 kcal/mol with respect to the formylTa2H3•HCO. The formaldehydegroup is unsymmetrically bridging the two Ta centers, with the Ta1-C, Ta2-C, Ta1-O, and Ta2-O distances being 2.16 A˚, 2.41 A˚, 2.24 A˚, and 2.16 A˚, respectively.At this point, the Ta-Ta distance is equal to 2.66 A˚, consistent with the presenceof a Ta-Ta bond and the Ta(IV) formal oxidation state. This intermediate can fur-ther react by breaking the C-O bond of the formaldehyde moiety with concomitantoxidation of both Ta(IV) centers to Ta(V). Overcoming this third transition state,TS3-CO, is the most difficult part of the reaction since the activation barrier isequal to +19.2 kcal/mol with respect to Ta2H2•H2CO; interestingly, the overallbarrier can be defined as the conversion of Ta2H3•HCO to TS3-CO, and requires+24.2 kcal/mol. However, the next intermediate is Ta2H2•(CH2)O, which is exer-gonic by -23.5 kcal/mol with respect to Ta2H2•H2CO. Ta2H2•(CH2)O displaysa bridging µ-oxo group as well as a bridging hydride, a terminal methylene groupon Ta1 and a terminal hydride on Ta2. From this point on, different pathways havebeen examined computationally in order to generate the experimentally observedproduct 2.4, but only three were found to be competitive and these are summarizedschematically in Figure 2.6.The three pathways A, B, and C, in Figure 2.6, differ in the order of the mi-gratory insertion of the methylene unit and the activation of the N-phenyl moiety,which results in differences on where the ortho proton of the activated N-phenylgroup ends up. In path A, the ortho-C-H ends up as the bridging hydride, whereasin paths B and C, one of the original bridging hydrides of 2.1 remains in the bridg-ing position. We anticipated that testing this would be straightforward based onour earlier report144 on the preparation of ([NPN]Ta)2(µ-D)4, 2.1-d4 which shouldgenerate CD4 via path A, whereas both paths B and C generate CD3H. However,39Figure 2.6: Starting with the putative tetradeuteride, ([NPN]Ta)2(µ−D)4;three proposed pathways leading to the experimental product with concomi-tant release of deuterated methane from Ta2H2•(CH2)O. In pathways B andC, CD3H is produced whereas in path A, CD4 would result.we have since discovered that the preparation of 2.1-d4 by addition of excess D2to the precursor trimethyl [NPN]TaMe3 is more complicated and actually resultsin the formation of 2.1-d12, wherein all eight of the ortho-C-H units on the N-Phmoieties have also been deuterated, in addition to formation of the four bridgingdeuterides (Scheme 2.3). None of ortho-C-Hs of the phenyl on the phosphine moi-ety are exchanged. To distinguish paths A-C in Figure 2.6, the use of 2.1-d12 wouldnot be useful as CD4 would result in all cases.However, we have determined that the deuteration of the trimethyl complex inhexanes results in less deuterium incorporation; this arises from precipitation of the40Scheme 2.3partially deuterated complex, which presumably intercepts the isotopic incorpora-tion process. By 1H NMR spectroscopy, there is no incorporation of deuteriuminto the ortho-C-H positions of the N-Ph groups, and partial deuteration of thebridging tantalum hydrides (Scheme 2.3). In fact, the formation of a mixture ofisotopologues ([NPN]Ta)2(µ-D)4−x(µ-H)x (x = 0-4) can easily be determined bythe isotopically perturbed signals in the 1H NMR spectrum in the tantalum hydrideregion.144,148 While the mechanism of this process is currently under investigation,by correlating the number of deuterium atoms of the partially deuterated dinuclear41hydride 2.1-dx to the amount of deuterium contained in the methane product, weare able to provide some support for one of the pathways. By Gas ChromatographyMass Spectrometry (GC-MS) analysis, we observe the formation of approximatelyequal amounts of CD4 and CD3H from the reaction of 2.1-dx with CO; CD2H2 isalso likely produced but its parent ion overlaps with CD +3 ions from CD4. Thedeuteration of the trimethyl complex in Et2O is homogeneous throughout, whichlikely promotes exchange of both the bridging hydrides and the ortho-C-H bonds(Scheme 2.3). Reaction of CO with the fully deuterated material 2.1-d12 results inthe formation of CD4 exclusively as expected.While the other pathways are found to be energetically accessible, only theGibbs free energy profile for path A is shown in detail. The Gibbs free energyprofile of pathway A is presented in Figure 2.7. It begins by the migration of thebridging hydride group of Ta2H2•(CH2)O to the carbene group in order to formTa2H•(CH3)O. The activation barrier is equal to +16.1 kcal/mol with respect toTa2H2•(CH2)O and the energetic gain is only 2.3 kcal/mol. The Ta-Ta distancehas decreased from 3.15 A˚ in Ta2H2•(CH2)O to 2.83 A˚ in Ta2H•(CH3)O which isconsistent with the passage from Ta(V) to Ta(IV). The terminal hydride becomes abridging hydride in order to slightly stabilize the complex. Then, this new bridginghydride can also migrate towards the methyl group in order to release a methanemolecule and form the Ta(III) µ-oxo complex Ta2O. This latter complex presentsa bent Ta-O-Ta angle of 89.1° allowing the formation of a double Ta-Ta bond.This is confirmed by analyzing the HOMO and HOMO-1 of the complex, whichcorrespond respectively to one pi and one σ orbital arising from the overlap of thed orbitals of the metal centers (Figure 2.8).42Figure 2.7: Gibbs free energy profile of pathway A. NPN ligands have been simplified for clarity. Atoms colors: Ta:green, P: orange, N: blue, O: red, C: black, H: white. For atom numbering, Ta1 is on the left while Ta2 is on the right.43Figure 2.8: The calculated HOMO (top) and HOMO-1 (bottom) for theTa=Ta of the putative intermediate Ta2OThe activation barrier corresponding to its formation is equal to +27.9 kcal/moland the reaction is exergonic by -14.2 kcal/mol, both with respect toTa2H•(CH3)O.This thermodynamic gain is mainly due to the formation of the stable methanemolecule along with the entropic gain due to the release of a small molecule (T∆Sestimated to 10∼15 kcal/mol at room temperature).165 Thus, the formation of thecoordinately unsaturated Ta2O complex itself is not a favorable process, otherwisethe energetic gain would be much larger than the 14.2 kcal/mol calculated. In orderto stabilize the complex, the last step of the reaction is the C-H activation of theortho C-H bond of an N-phenyl group of the NPN ligand, leading to the observedproduct 2.4. The transition state lies only at +2.1 kcal/mol above the oxo complexand the reaction is exergonic by -22.9 kcal/mol with respect to Ta2O, which is con-sistent with the low stability of Ta2O. The product exhibits a bridging oxo group(Ta1-O bond length of 2.02 A˚ and Ta2-O bond length of 1.95 A˚, versus 2.009(3)and 1.925(3) exp.), a bridging hydride (Ta1-H bond length of 2.02 A˚ and Ta2-H44bond length of 1.92 A˚, versus 1.92(5) and 1.96(5) exp.) and a phenyl bridgingligand, coordinated by the ortho-carbon (Ta1-C bond length of 2.42 A˚ and Ta2-Cbond length of 2.11 A˚ versus 2.399(4) and 2.095(4) exp.). It is thus a Ta(IV) com-plex, which is confirmed by the short Ta-Ta bond distance (2.75 A˚ versus 2.7240(6)exp.). It is noteworthy that the quintet spin-state of the Ta(III) µ-oxo complex ismore stable than the singlet spin-state by 3.6 kcal/mol, but in the first case, theTa-O-Ta angle becomes linear, which would make the last reaction step forbidden.We can thus assume without risk that there is equilibrium between the singlet andthe quintet spin-states, and that the singlet spin-state complex Ta2O reacts directlyto generate ConclusionsThe reaction of CO with the highly reducing ditantalum tetrahydride complex 2.1proceeds by a series of migratory insertion reactions. Of particular interest forthis process is how CO interacts with the starting hydride. By using a computa-tional approach, an adduct structure is proposed that involves CO interacting withtetrahydride 2.1 wherein two of the bridging hydrides isomerize to terminal hy-drides, presumably to open up a coordination site. In fact, one of the interestinginsights that is suggested from these calculations is the importance of the terminalhydride unit in the migratory insertion processes documented in this work. Whilethe starting tetrahydride 2.1 contains four bridging hydrides in its ground state,each insertion process involves a terminal hydride interacting with a small organicmoiety in a bridging position. While dinuclear complexes have offered unique ac-tivation modes for small molecules, mainly by invoking simultaneous interactionswith two metal centers,154,166,167 in this work, we show that a strongly reducing45dinuclear center in concert with available hydrides for migratory insertion can con-vert an important C1 molecule, CO, into CH4 via complete utilization of the fourbridging hydrides.2.2 Reduction of Carbon Dioxide Promoted by aDinuclear Tantalum Tetrahydride Complex2.2.1 IntroductionCarbon dioxide (CO2) is potentially a plentiful C1 source that continues to occupydiscussions related to climate change.168 While conversion of CO2 to higher-valuecarbon-based materials is a worthy goal, it is clear that these kinds of approachesare not realistic as a way to sequester this greenhouse gas,169 particularly if dihy-drogen (H2) derived via steam reforming is involved. Nevertheless, from a funda-mental point of view, discovering systems that can transform CO2 with170–172 orwithout H2173 is of considerable interest174–176 and may provide hints on ways tobetter utilize this ever-more-abundant resource.177We have described the facile activation of dinitrogen (N2) by dinuclear tanta-lum tetrahydride, ([NPN]Ta)2(µ-H)4 (2.1, where NPN = PhP(CH2SiMe2NPh)2), togenerate the side-on end-on ditantalum dinitrogen complex ([NPN]Ta)2(µ-η2:η1-N2)(µ-H)2 (2.2;143,144 Scheme 2.4). Given that N2 is a very stable, inert molecule,the question arose as to what the outcome would be in the reaction of tetrahydride2.1 with the very stable CO2 molecule. Herein we report our efforts to examinethe reactivity of CO2 with the strongly reducing ditantalum tetrahydride complex2.1. What emerges from this work is a rare example of a dinuclear metal hydridesystem that functionalizes CO2 and retains its dinuclearity.46Scheme Results and DiscussionOur initial inspiration to examine the activation of CO2 was based on the report thatcertain zirconium and hafnium dinitrogen complexes react productively with CO2to generate new N-C bonds and regiospecific hydrazides.178 However, the reactionof CO2 and the tantalum side-on end-on N2 complex 2.2 led to the formation of amultitude of products even when the stoichiometry of added CO2 was controlled.Undaunted, we turned to the reaction of the ditantalum tetrahydride 2.1 with CO2and discovered that a single product could be obtained provided that strict con-trol of the stoichiometry was followed. For example, if excess CO2 is used, verycomplicated spectra are obtained, indicative of a mixture of products, perhaps aconsequence of migratory insertion of CO2 in the tantalum-amido linkages of theNPN ligand. However, if exactly 1 equiv of CO2 is employed, a clean reaction en-sues with the formation of only one very symmetrical product (60% recrystallizedyield) on the basis of a singlet at δ -13.1 observed in the 31P NMR spectrum. Thecorresponding 1H NMR spectrum shows a triplet resonance downfield at δ 6.81,which simplifies to a singlet upon 31P decoupling and integrates to two H atoms.47Analysis by heteronuclear single quantum coherence indicates that these H atomsare not C-bound, consistent with the presence of bridging tantalum hydrides, andare likely a Ta2(µ-H)2 moiety. Also diagnostic in the 1H NMR spectrum is a sin-glet at δ 6.11 that again integrates for two H atoms. That these two sets of protonresonances are derived from the bridging hydrides of 2.1 was confirmed by the useof 2.1-d12, in which all four bridging hydrides and all eight of the o-NPh protonsare deuterated (See Scheme 2.3); in this reaction, the peaks at δ 6.81 and 6.11 bothdisappear in the 1H NMR spectrum, as does a peak at δ 6.89 due to the o-H atomsof the NPh moiety of the NPN ligand. When 13C-labeled CO2 was utilized, theresonance at δ 6.11 becomes a doublet with 1JCH = 110 Hz. Given our earlier pub-lication179 of the complete disassembly of CS2 to generate the ditantalum specieswith a bridging methylene, an analogous structure was considered. However, thereare no bridging hydrides in the CS2 disassembly product, and the chemical shift ofthe resonance due to the bridging methylene of this material occurs at δ 4.5 in the1H NMR spectrum, which is considerably upfield of the methylene resonance ob-served for the CO2 product 2.5. In fact, a recent report of the reaction of CO2 witha mononuclear tantalum hydride to generate a ditantalum species with a methylenediolate fragment proved to be a better analogy.180Scheme 2.5: Reduction of CO2 using 2.148Figure 2.9: Selected bond lengths (A˚) and bond angles (deg) for 2.5: Ta1 -N1 2.091(7), Ta1 - N2 2.062(6), Ta1 - P1 2.628(2), Ta1 - O1 1.980(5), Ta1 -Ta1 2.7688(7), N1 - Si1 1.742(7), N2 - Si2 1.739(7), C1 - O1 1.384(7); O1 -C1 - O1 117.0(9), Ta1 - O1 - C1 126.4(5), O1 - Ta1 - O1 117.0(9), O1 - Ta1- N1 91.6(2), O1 - Ta1 - N2 91.6(2), N1 - Ta1 - N2 118.2(3), O1 - Ta1 - P1160.99(15), N1 - Ta1 - P1 77.82(19), N2 - Ta1 - P1 79.08(19), O1 - Ta1 - Ta183.45(14).The solid-state structure of this complex (2.5) is shown in Figure 2.9, alongwith the transformation in Scheme 2.5; the most notable feature of 2.5 is the bridg-ing methylene diolate unit between the two Ta centers. The Ta1-O1 bond length of2.5 of 1.980(5) A˚ is slightly longer that the Ta-O bonds of 1.929(5) and 1.917(2)A˚ found in two dinuclear methylene diolate complexes formed via intermolecularprocesses.180 The other parameters of this µ-OCH2O unit compare unremarkablyto other examples of this rare kind of fragment with the exception that the O-C-Oangle in 2.5 of 117.0(9)° is larger than the aforementioned dinuclear systems [cf.49111.4(7) and 109.7(3)°]180 and a tetrayttrium cluster [cf. 107.6(3)°]181 that containthis unit.The formation of 2.5 likely involves hydride addition reactions most probablythrough a formate-type intermediate.62,170 In an effort to shed light on this pro-cess, possible structures of intermediates and transition states were examined com-putationally. DFT [B3PW91//SDDALl(Ta,P)/6-31G** (other atoms)] calculationswere carried out on the full system.The Gibbs free-energy profile of the reaction between 2.1 and CO2 is presentedin Figure 2.10. For each minimum, singlet and triplet spin states have been con-sidered, and the singlet spin states are always the most stable, by 20-50 kcal/mol.Thus, the reactivity takes place on the singlet potential energy surface.Figure 2.10: Gibbs free-energy profile of the reaction between the tetrahy-dride complex 2.1 and CO2. NPN ligands have been simplified for clarity.Atoms colors: Ta, green; P, orange; N, blue; O, red; C, black; H, white. Foratom numbering, Ta1 is on the left, while Ta2 is on the right.50The first step of the reaction is coordination of CO2 to 2.1, involving the twoTa centers. In Ta2H4•CO2, two bridging hydride groups have become terminalin order to liberate one coordination site on each Ta center and thus allow the µ-η2:η2-coordination mode of CO2, all of which happens in a concerted fashion.The computed O-C-O angle is 132.8° and both C-O bonds are equal to 1.26 A˚,suggesting that CO2 has been reduced by 2.1. The Ta-Ta distance has increasedfrom 2.59 to 3.01 A˚ so that the Ta-Ta bond has been broken. This is confirmedby NBO analysis, which gives an oxidation state of +5 for each Ta, suggestive ofthe presence of CO22−, at least formally. NPA charges show that the C atom ofCO2 is strongly positively charged (+0.70). The formation of this adduct is slightlyexergonic by -3.4 kcal/mol, but it readily transforms to give the dinuclear µ-η2:η2-formato Ta2H3•HCO2. Indeed, the transition state corresponding to the hydrogentransfer from one Ta center to CO2 lies at only +10.7 kcal/mol with respect toTa2H4•CO2, while the formation of Ta2H3•HCO2 is exergonic by -11.4 kcal/molwith respect to the adduct. The geometry of the first transition state is standardbecause one O atom of CO2 has just moved away from the Ta-Ta-CO2 plane ofTa2H4•CO2 in order to allow the terminal hydride to bridge from the Ta center tothe C atom of CO2. All other bond lengths or angles are mostly unchanged.The intermediate Ta2H3•HCO2 presents a nearly symmetrical µ-η2:η2-HCO2moiety. The Ta-Ta distance is 2.95 A˚, which is not consistent with a formate unitbetween two Ta(IV) centers unless the two d electrons remain unpaired. NBOanalysis shows that there are no unpaired electrons in the d orbitals of the Ta cen-ters or the presence of a Ta-Ta bond. The Lewis configuration extracted from theNBO shows a covalent bond between Ta1 and the C atom and two dative bondsfrom both negatively charged O atoms to each Ta center. The system can thus be51described with two electrons delocalized between both Ta-C bonds and formallyTa(V) centers. The formation of the experimental product involves the transitionstate TS2-CO2, which corresponds to the transfer of the second terminal hydrideto the C atom of the HCO2 unit. The activation barrier is calculated to be +20.5kcal/mol, which is high but still kinetically accessible. The geometry of this tran-sition state looks like that of TS1-CO2, discussed above. The formation of 2.5 iscalculated to be exergonic by -17.4 kcal/mol with respect to the dinuclear formatecomplex Ta2H3•HCO2. The computed structure of 2.5 is similar to the experimen-tal one, for example, with C-O, Ta-O, and Ta-Ta bond lengths of 1.40 [1.388(10)A˚ exp], 1.95 A˚ [1.982(8) A˚ exp], and 2.80 A˚ [2.7693(9) A˚ exp], respectively. TheHOMO still corresponds to the σ interaction of the two d orbitals of Ta, confirmingthe Ta(IV) oxidation state. The importance of the metal is clearly evident becausecalculations using copper surfaces detail quite different intermediates.182The reaction of CO2 with the highly reducing ditantalum tetrahydride complex2.1 proceeds by a migratory insertion process followed by reductive elimination,as summarized in Scheme ConclusionsOf particular interest is how CO2 interacts with the starting hydride. By using acomputational approach, a low-energy structure emerged, wherein CO2 binds re-ductively with tetrahydride 2.1 to generate Ta2H4•CO2, wherein two of the bridg-ing hydrides become terminal and the CO2 unit is formally a CO22− moiety. Oneof the interesting insights that result from these calculations is the importance ofthe terminal hydride unit in the transformation documented in this work. While thestarting tetrahydride 2.1 contains four bridging hydrides in its ground state, each52Scheme 2.6step in the process involves a terminal hydride interacting with a small organicmoiety in a bridging position. In the first transfer, the µ-η2:η2-formato complexTa2H3•HCO2 is generated and finally the methylene diolate product 2.5; this latterprocess is formally a dinuclear C-H reductive elimination, wherein the two Ta(V)centers of Ta2H3•HCO2 are converted to Ta(IV) moieties in 2.5.While dinuclear complexes offer unique activation modes for small molecules,mainly by invoking simultaneous interactions with two metal centers, in this work,we show that the strongly reducing ditantalum complex in concert with availablehydrides can convert the important C1 source CO2 to a reduced form, in this case,a methylene diolate fragment.53Chapter 3Synthesis of Base MetalComplexes of the Type [fc(NP)]MThe only place where success comes before work is in the dictionary— Vince Lombardi3.1 Synthesis of Iron and Cobalt Complexes of aFerrocene-Linked Diphosphinoamide Ligand andCharacterization of a Weak Iron-Cobalt Interaction3.1.1 IntroductionThe recent interest in the use of earth abundant or base metals (e.g. Fe, Co, Ni) inlieu of precious metals (e.g., Ru, Rh, Pd) in homogeneous catalysis is due to lowercost, higher availability and decreased environmental and health issues, especiallywith Fe-based systems.183 From a burgeoning spate of publications,3,57,81,90,184–196it has emerged that the chemistry of the base metals can be more complicated thanthat of the precious metals. This is particularly the case because paramagneticcomplexes are often found for these elements, especially with Fe and Co,197–20154and simple two-electron oxidative addition and reductive elimination processes,which are a staple for precious metal catalytic cycles, are not as common for basemetal catalyst precursors.1,202FeNNPPRRRRFeEMNNMe2SiMe2SiSiMe2SiMe2P PR RAMNNMe2Si ArArSiMe2PRBMNNArArPRDMNNArArPRCSSScheme 3.1The kinds of ligand environments used to generate base metal complexes arenot too different from those found for the precious metals.198,203,204 To promoteversatility we have been exploring ligand sets that incorporate amido and phos-phine donors into chelating arrays.92,205 We have already shown that these kinds ofdonors can stabilize complexes of the early and late transition metal elements92–94,206including a number of the aforementioned base metals.198,199 Ongoing efforts inour group have focused on the effect of the linkers that connect the disparatedonor environments on the structures and reactivity of the resultant metal com-plexes. We have previously reported (Scheme 3.1) metal complexes stabilizedby diamido donors with one or two phosphine units connected in macrocyclic55(A)207–210 or chelating arrays using o-phenylene (P−C6H4−N: C),99–101,211 2,3-thiophenyl (P−C4H2S−N:) D:143 or methylene-dimethysilyl (P−CH2SiMe2−NA,B)207–210,212 linkers. More recently, we have investigated109,137 phosphinoamidedonors110,111,213 in which there is no linker between the amido and the phosphinedonor, and have the general formula [R2P−NR′]−. Of particular interest is theuse of a ferrocenediamine scaffold to generate a diphosphinoamido donor set asdepicted in E137 in Scheme 3.1. One intriguing feature of this system is the pres-ence of the ferrocene unit that can undergo redox chemistry and therefore act in anon-innocent fashion.214In this contribution we outline the coordination chemistry of 1,1’-ferrocenebis-(diisopropylphosphinoamide) with Fe(II) and Co(II) precursors, which generatenew structural motifs in base metal chemistry that result from this linkerless donorset. What emerges from this study is that a weak metal-metal bond can arise fromthe interaction of the closed-shell iron center of ferrocene with an open-shell basemetal center.3.1.2 Results and Discussion1,1’-Ferrocenediamine130 is easily converted to 1,1’-ferrocenebis(diisopropylphos-phinoamine), fc(NHPiPr2)2, 1.50, as previously reported.137 Deprotonation of 1.50with KH leads to formation of the dipotassium derivative, K2[fc(NPiPr2)2], 3.1,which can be stored under nitrogen as a solid for several weeks without significantdegradation. An X-ray single crystal structural analysis (See Figure A.3) of thismaterial indicates that it is polymeric in the solid state; nevertheless, it serves as auseful metathesis reagent as described below.The reaction of 3.1 with FeBr2(THF)2 results in the formation of a species that56has the empirical formula, Fe[fc(NP)2], 3.2, as a red brown solid. Complex 3.2 isparamagnetic, and assuming a monomeric structure, exhibits a lower than expectedeffective magnetic moment (µeff Evans Method: 3.3 µB, Gouy: 3.2 µB), and givesrise to an NMR spectrum that contains 10 paramagnetically-shifted singlets overthe range of δ +120 to −80.FeNNPPFeFeNNPPFe3.2FeNHHNPP1.50FeN NP P3.1•1.25 THFKKn2 KHTHFFeBr2(THF)2THFScheme 3.2From the NMR evidence alone, it is clear that 3.2 cannot be a mononuclearcomplex with a geometry similar toE in Scheme 3.1 (M = Fe), as one would predictonly five resonances in the 1H NMR spectrum on the basis of C2v symmetry. Inaddition the µeff value does not match simple spin-only values expected for a highspin (HS) or low spin (LS) monomeric Fe(II) complex. Fortunately, single crystals57can be grown by slow evaporation of hexanes; the solid-state molecular structureis shown in Figure 3.1, along with selected bond lengths and angles.Fe2Fe1N2P2P1N1P1iFe1iFigure 3.1: ORTEP diagram of 3.2 with ellipsoids drawn at 50% proba-bility. All H atoms and iPr methyl groups have been omitted for clarity.Selected bond lengths (A˚) and angles (deg): Fe2-Fe1 3.5341(4); Fe1-Fe1i3.9241(5); Fe1-P1 2.4443(4); N1-Fe1 1.9459(12); N2-Fe1 1.9217(12); N1-P11.6692(13); N2-P2 1.6993(12); N2-Fe1-N1 123.47(5); N1-Fe1-P1 115.71(4);P1-Fe1-N2 120.81(4).In the solid state, 3.2 is dimeric with bridging and terminal phosphine donorsgenerating two three-coordinate Fe(II) centers, in addition to the ferrocene Fe(II)units. Complex 3.2 displays Ci symmetry where the inversion center of the molec-ular structure sits in the middle of an elongated six-membered heterocyclic ringmade up of two Fe(II) centers and two phosphinoamide moieties. The bridgingphosphinoamides in 3.2, (N1-P1 ≈ 1.67 A˚), are similar to other iron N-Aryl phos-phinoamide complexes,111 all of which are longer than typical N-alkyl substitutedphosphinoamides111,215 due to competing delocalization of the nitrogen based lonepair into pi∗ orbitals of the arene rings. The trigonal planar coordination geometry58of 3.2 results in an unstrained ligand backbone characterized by the tilt angle of0.13°216–219 and bite angle of 107.34° (See Figure 3.2 for depiction of Cp tilt (α)and bite (δ ) angles). Other examples of trigonal planar iron phosphinoamide com-plexes have been reported by the Thomas group111,115 and in all cases the N-P axesare perpendicular to the donor atom plane.Feα Fe δFigure 3.2: Cp tilt angle (left) and bite angle (right).Using a dimeric structure, the room temperature effective magnetic moment of3.2 was determined to be 6.7 µB by the Evans method, and 6.6 µB using a Gouy bal-ance; the agreement between methods indicates that the dimer formulation existsin both the solution and solid state. As already mentioned, the paramagneticallyshifted 1H NMR spectrum of 3.2 displays 10 shifted singlets in C6D6 as shown inFigure 3.3. In d8-THF, a slightly shifted set of 10 singlets is again observed, in-dicating that the dimeric structure is maintained in the presence of excess etherealdonors. However, when 3.2 is dissolved in d5-pyridine, a simplified spectrum isobserved in which 5 signals can be detected (Figure 3.3). When the pyridine solu-tion is evaporated to dryness and the residue dissolved in C6D6, the original 10 linepattern is again observed, indicating that in the presence of pyridine, a differentstructure is generated, but reversion to the dimer 3.2 occurs when the pyridine isremoved.59120 110 100 90 7080 60 50 40 30 20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 -90(ppm)1 23457689 101 2344556789 10321******†††Figure 3.3: 300 MHz 1H NMR spectra of 3.2 in C6D6 (top), d8 -THF (mid-dle), d5 - pyridine (bottom): * denotes residual proton peak(s) of the NMRsolvent; † denotes protonated ligand, 1.50.In an effort to investigate this apparent change in symmetry, the reaction of3.2 with p-dimethylaminopyridine (DMAP) was examined, which resulted in theisolation of the mononuclear complex 3.3. This mononuclear derivative can alsobe accessed by direct reaction of the potassium salt 3.1 with FeBr2(THF)2 in thepresence of a slight excess of DMAP and the NMR spectrum of 3.3 is similar tothat of 3.2 in d5 - pyridine. The effective magnetic moment of 3.3 in solution (5.1µB) is within the range expected for a HS Fe(II) center (Scheme 3.3).The single crystal X-ray structure of 3.3 is shown in Figure 3.4, along withselected bond lengths and angles. The iron center in 3.3 displays a distorted tetra-hedral geometry, with a large N1-Fe2-N1i angle for the ferrocene based nitrogendonors (120.66°) and a more constricted N2-Fe2-N2i angle for the DMAP donors60FeNNPPFeFeNNPPFe3.2FeN NP P3.1•1.25 THFKKnFeNNPPFe3.3DMAPFeBr2(THF)2DMAP NNNMe2NMe2Scheme 3.3(91.55°). This type of distortion is common in four-coordinate complexes with1,1’-diaminoferrocene based ligands132,220 due to the large bite angle imposed.The N-P bond lengths are very typical of an aryl-phosphinoamide and similar tothat found for the unbound N-P unit in the dimer 3.2. Upon changing the coor-dination geometry from trigonal planar in 3.2 to tetrahedral in 3.3 we observe anelongation of the Fe-Fe distance to 3.60 A˚ which is typical for tetrahedrally boundsystems displaying no interaction with the ferrocene backbone.132,133,220,221The 57Fe Mo¨ssbauer spectra of 3.2 and 3.3 are shown in Figure 3.5; each com-pound displays two doublets arising from the two unique Fe(II) centers. The spec-trum of 3.2 was fit as a pair of quadrupolar doublets. Based on the isomer shiftand quadrupolar splitting of 1.50 (See Figure C.1) and other ferrocene based lig-61Fe1 Fe2N1C1P1N1iP1iC1iN2N2iFigure 3.4: ORTEP diagram of 3.3 with ellipsoids drawn at 50% probability.All H atoms and iPr methyl groups have been omitted for clarity. Selectedbond lengths (A˚) and angles (deg): Fe2-Fe1 3.6059(5); Fe1-N1 1.9650(15);Fe1-N2 2.1223(14); N1-P1 1.6855(15); N1-Fe1-N1i 120.66(8); N2-Fe1-N2i91.55(8); N1-Fe1-N2 106.15(6).ands221–224 the doublet with ∆Eq = 2.34 mm/s was assigned to the ferrocene ironcenter. The doublet with ∆Eq = 1.02 mm/s, assigned to the trigonal planar Fe(II)center, displays an isomer shift value of 0.43 mm/s consistent with a HS Fe(II) ion.Trigonal planar iron complexes with a diamido phosphine donor set are relativelyuncommon,78,225,226 and to our knowledge, only one other has been characterizedby Mo¨ssbauer spectroscopy (See Table 3.1).111 While the quadrupolar splitting(1.02 mm/s) of the trigonal planar iron in 3.2 is substantially smaller than that of[Fe(NP)2(NP)FeCl], there is some ambiguity in the latter as to whether the tetra-hedral or trigonal planar iron center is being observed. However, the quadrupolar62Absorption (%)V e l o c i t y  ( m m / s )Absorption (%)v e l o c i t y  ( m m / s )Velo i  (mm/s)Absorption (%)Figure 3.5: Zero field 57Fe Mo¨ssbauer spectra of 3.2 (top) and 3.3 (bot-tom) recorded at room temperature. Black diamonds are data points fromthe Mo¨ssbauer experiment, green curves are fits for the ferrocene iron (δ =0.43 mm/s, ∆Eq = 2.34 mm/s for 3.2; δ = 0.45 mm/s, ∆Eq = 2.36 mm/s for3.3), blue curves are fits for the non-ferrocene iron centers (δ = 0.43 mm/s,∆Eq = 1.02 mm/s for 3.2; δ = 0.71 mm/s, ∆Eq = 2.22 mm/s for 3.3), and redcurves are fits for total contributions.63splitting of 3.2 is consistent with other trigonal planar species227,228 particularly theelectron-rich, dimeric [Fe(N(SiMe3)2)2]2.229 Not surprisingly, in the mononuclearcomplex 3.3 the ferrocene iron displays nearly identical Mo¨ssbauer parameters tothe ferrocene iron in 3.2. The second doublet, attributed to the tetrahedral Fe(II)center, displays a typical isomer shift and quadrupolar splitting for HS tetrahedralFe(II).190,230–232To further investigate the coordination chemistry of K2[fc(NP)2], 3.1, we per-formed a salt metathesis with CoCl2(py)4. We were able to isolate a solid by con-ducting the reaction of 3.1 and CoCl2(py)4 in a hydrocarbon solvent such as pen-tane or toluene, to precipitate the product (compound 3.4) directly. If the reactionis conducted in a more polar solvent the product rapidly decomposes. Fortunately,single crystals could be obtained by performing the metathesis in toluene at highconcentration; the solid-state molecular structure is shown in Figure 3.6 along withselected bond lengths and angles. In order to confirm that the solid state molec-ular structure was consistent with the bulk sample we performed a powder X-raydiffraction analysis, see Figure 3.7.The overall dimeric structure of 3.4 is similar to that of the iron-based 3.2, butwith one striking difference: whereas in 3.2 the non-ferrocene iron adopts a trigonalplanar geometry, the cobalt center of 3.4 adopts a nearly square planar geometry asa result of an interaction with the iron of the ferrocene backbone. While the Co-Febond length in 3.4 is very similar to the sum of the van der Waals radii, the dramaticdifference in Fe-M distances between 3.2, 3.5341(3) A˚ and 3.4, 2.8451(10) A˚,suggests an electronic interaction is responsible for this nearly 0.7 A˚ contraction,as steric effects should be similar between the two complexes. One of the furtherconsequences of this Fe-Co interaction in 3.4 is the disposition of the nitrogen64Fe1C1C6Co1N1N2P2P1iP1Co1iFigure 3.6: ORTEP diagram of 3.4 with ellipsoids drawn at 50% probability.All H atoms and iPr methyl groups have been omitted for clarity. Selectedbond lengths (A˚) and angles (deg): Fe1-Co1 2.8451(10); N1-Co1 1.854(2);N2-Co1 1.877(2); N1-P1 1.676(2); N2-P2 1.697(2); Co1-P1 2.1562(11); N1-Co1-N2 159.64(9); P1-Co1-Fe1 166.90(2); N1-Co1-Fe1 80.50(7); N1-Co1-P1 96.19(6); C1-N1-Co1 95.64(15).atoms, N1 and N2, in the 1,1’-diaminoferrocene backbone. The C1-N1-Fe1 angleof 115.12(2)° in 3.2 shows a relatively strain-free sp2-hybridized nitrogen atom,in contrast to the more acute C1-N1-Co1 angle of 95.64(15)° in 3.4. In addition,the Cp plane angle of the ferrocene backbone increases from 0.1° in 3.2 to 6.9°in 3.4, which indicates more strain of the rigid backbone in the latter complex.Interactions between the iron of ferrocene and a metal bound by donor atoms inthe 1,1’ position are known including Fe-Pd233–238 and Fe-Pt239,240 interactions.Outside of the two aforementioned metals, only a few examples133,134,221,241 ofthis kind of interaction have been reported. To our knowledge, 3.4 represents thefirst example of a ferrocene-stabilized group 9 metal. It is only the second example6510 20 30 40Normalized Intensity2  (degrees) PXRD ProjectionKCl (200)KCl (220)Figure 3.7: PXRD for bulk 3.4 compared to a projection obtained from singlecrystal X-ray diffraction data of 3.4.with a 1st row transition metal, the other being a titanium complex which can bethought of as a Lewis acid Lewis base interaction (d6 Fe(II)→ d0 Ti(IV)).133While the ferrocene iron centers in 1.50, 3.2 and 3.3 display similar isomer shiftand quadrupole splitting values, the Mo¨ssbauer spectrum of 3.4 displays a singlequadrupole doublet for the ferrocene center, which has a contracted quadrupolarsplitting of 2.01 mm/s. Figure 3.8 shows the overlay of the fits for the ferrocenecenters in 3.2 and 3.4 illustrating the smaller quadrupolar splitting of the dicobaltderivative, 3.4, compared to the diiron, 3.2. A similar ferrocene-metal interac-tion has been recently characterized221 for a closed-shell ruthenium complex of a66Figure 3.8: Zero field 57Fe Mo¨ssbauer spectrum of 3.4 collected at roomtemperature fit as a quadrupolar doublet; δ = 0.42 mm/s, ∆Eq = 2.01 mm/s(top) and an overlay of the ferrocene center fits for 3.2 in black and 3.4 in red,showing the contraction of the latter (bottom).67ferrocene diamide ligand. While the fc-M bond lengths are similar (Fe-Ru: 2.80A˚; Fe-Co: 2.84 A˚), the ruthenium complex displays an even smaller quadrupolarsplitting, 1.81 mm/s, possibly due to greater orbital overlap with the larger 4d metalruthenium.Table 3.1: Mo¨ssbauer parameters for 3.2, 3.3, 3.4 and related compounds.Compound Isomer Shift (mm/s) Quadrupolar Splitting (mm/s)1 0.48 2.523.2a 0.43 2.340.43 1.023.3a 0.45 2.360.71 2.223.4 0.42 2.01[Fe(NP)2(NP)FeCl]b 0.60 1.80(Fe(N(SiMe3)2)2)2 0.58 1.02a The iron of the ferrocene moiety is listed above; b (NP) : NiPrPiPr23.1.3 Magnetic MeasurementsIn an effort to determine the spin states and gain insight into the electronic struc-ture of 3.2, 3.3 and 3.4 we performed Variable Temperature (VT)-magnetometry.Figure 3.9 shows the plots of effective magnetic moment (µeff) vs. T for 3.2, 3.3and 3.4. The monomeric 3.3 displays a fairly constant µeff value from 300 K downto 55 K, with an average value of 5.1 µB. After 55 K the data undergo a brief riseto a maximum of 5.3 µB at 22 K before falling steeply to a minimum of 4.2 µB at1.8 K. This data can be fit with a Curie-Weiss Law with parameters of C = 3.222(4)cm3 K mol−1 and Θ = -1.89(6) K (see Figure D.1 for fit). The room temperatureµeff value for 3.3 is higher than the spin only value of 4.9 µB expected242 for highspin d6; however, this is common with tetrahedral Fe(II) centers due to spin-orbit-coupling.243 Examining 3.2 we see a room temperature magnetic moment of 6.6 µB68per dimer that slowly begins to decrease until∼125 K at which point µeff decreasesto a minimum of 1.4 µB at 1.8 K. The gradual decrease of µeff with decreasing tem-perature is consistent with an antiferromagnetic exchange between the two trigo-nal planar iron centers. The combination of weak anti-ferromagnetic coupling andzero-field splitting creates a situation where modelling is not of significant valueand was not pursued. We tentatively assign 3.2 as having two central HS Fe(II)centers (spin only: 9.8 µB) with weak antiferromagnetic coupling between the twotrigonal planar iron centers. It should be noted that performing Evans method244,245on a C6D6 solution of 3.2, yields a room temperature magnetic moment of 6.7 µB.The agreement between room temperature measurements in the solid state and insolution indicates that the dimeric nature of 3.2 is maintained in solution. The pro-posed antiferromagnetic exchange is likely intramolecular mediated through theN-P bridges or by direct exchange and not by intermolecular exchange processes.Due to a large Fe-Fe distance of 3.9241(5) A˚, we prefer magnetic exchange throughthe amidophosphine bridges as a rationale for the low magnetic moment.In Figure 3.9, the overall shape of the µeff vs T curves for 3.2 and 3.4 are sim-ilar; however, the most striking difference is the low µeff for 3.4 throughout theentire temperature range. Starting at 4.2 µB at 300 K (confirmed by Gouy balance)µeff gradually decreases to 3.0 µB at 16 K, indicative of weak antiferromagneticcoupling. Below 16 K µeff sharply falls to a value of 1.2 µB at 1.8 K, which is at-tributed to a combination of Zeeman and zero field splitting; again modelling wasnot pursued. The low room temperature value of µeff is higher than the spin onlyvalue but consistent with other LS square planar Co(II) centers with some second-order spin-orbit coupling.199,242,246 Based on structural and magnetic analysis of3.2 and 3.4 it is evident that the electronic structures of these two compounds are69012345670 50 100 150 200 250 300µeff (µB)Temperature (K) 3.9: Variable-temperature effective magnetic moment (µeff) for 3.2,3.3 and 3.4 collected under an applied DC field of 1 T.drastically different. The observation of LS Co(II) centers in the dimer further sup-ports a Fe-Co interaction in 3.4, as the additional donor interactions would resultin a stronger ligand field and therefore a low spin complex.3.1.4 DFT CalculationsIn order to confirm the spin state assignments obtained from VT-magnetomerty,and investigate the Fe-Co interaction in 3.4 we turned to DFT methods. We per-formed geometry optimizations on the full molecules of 3.2 and 3.4 using theatomic coordinates obtained from the solid-state molecular structures as an initialgeometry. Both LS and HS configurations for 3.2 (S = 0 and S = 4) and 3.4 (S = 1and S = 3) were evaluated at the BP86247,248 level of theory using triple-ζ -valence70basis sets. The HS (S = 4) and LS (S = 1) spin states were found to be more stablefor 3.2 and 3.4 respectively, supporting the spin state assignments made based onVT-magnetometry. In both cases, the geometry obtained in silico for the more sta-ble spin state is very similar (See Figure B.1 and Figure B.2 in Appendix B) to thegeometry obtained by single crystal diffraction studies; the less stable spin statesshow large distortions from the experimentally determined coordinates. A few ofthe observed and calculated bond metrics are compared in Table 3.2, for a moreexpansive set see Table B.3.Table 3.2: Computed and experimental bond metrics for 3.2 and 3.4.Bond Metric 3.2 3.4expt S = 0 S = 4 expt S = 1 S = 3Fe – M (A˚) 3.5341(4) 2.914 3.522 2.845(1) 2.871 3.203M – P (A˚) 2.4442(4) 2.160 2.439 2.156(1) 2.182 2.403N–M–N (°) 123.47(5) 157.17 124.85 159.64(9) 158.90 139.97With the spin states confirmed we examined the bonding between Fe and Coin 3.4. Through NBO analysis, the Mayer bond order249,250 for the Fe-Co unit wascalculated to be 0.21, indicative of a weak but significant bonding interaction. Incomparison, 3.2 displays a Fe-Fe Mayer bond order of 0.04. Due to the scarcity ofweak M-M bonds between 3d metals that have been characterized using the Mayerbond order, direct comparison is difficult. The carbonyl cluster Fe3(CO)12 anddimeric [CpCoH(CO)]2 display bond orders of 0.42251 and 0.342252 respectively,and are described as single bonds. However, other complexes of 1,1’-substitutedferrocene based ligands, which display a Fe-M interaction have been studied. Forcomplexes with Pd(0.26), Pt(0.31) and Ru(0.26) the Mayer bond order is typicallyless than other metal metal single bonds.134,22171Gratifyingly, three of the high lying molecular orbitals show bonding interac-tions between the iron and cobalt centers. HOMO-6 in 3.4 is a highly delocalizedorbital (See Figure B.11) which displays an Fe-Co σ interaction. In addition a pairof pi bonding orbitals can be found, HOMO - 9/10 see Figure 3.10. For 3.2 the highlying orbitals, HOMO→ HOMO-20, were examined for similar interactions andnone were found; a complete set of frontier molecular orbitals for 3.2 and 3.4 areshown in Figure B.3 to Figure B.11.Figure 3.10: HOMO-9α for 3.4. HOMO-10α , HOMO-7β and HOMO-8β aresimilar.The optimized coordinates of 3.4 were then used in subsequent analysis usingNBO 6.0.253 Analysis of the natural bond orbitals reveals a sigma overlap betweena filled valence orbital on iron and an empty σ∗ orbital between cobalt and phos-phorus, as shown in Figure 3.11. The natural localized molecular orbitals generatedfrom these natural bond orbitals are predominately iron based with a 2.2% contri-bution from cobalt.Furthermore, NBO second order perturbation analysis of donor-acceptor inter-72Figure 3.11: Contour plots of Left: NBO 91 (Fe) and NBO 250 (Co-P∗)overlap. Right NLMO 91.actions reveals several stabilizations from filled orbitals on cobalt to empty orbitalsin the ferrocene unit (11.41 kcal/mol) and vice versa (7.79 kcal/mol). In addition todirect interactions, there are several donations from filled cobalt-ligand bonding or-bitals to empty orbitals on iron (10.42 kcal/mol) for a total of 29.62 kcal/mol. Notethat these energy values are described for only one Fe-Co pair. For a detailed listof relevant second order interactions see Table B.4 The nearly equal energy con-tributions of Fe → Co and Co → Fe are surprising given that a recently reportediron-ruthenium interaction221 showed only donation from filled ferrocene-basedorbitals to empty ruthenium-based orbitals.3.1.5 Summary and ConclusionsUsing the dianionic ferrocene-based diphosphinoamide ligand precursor, we havebeen able to prepare dimeric base metal complexes that incorporate iron(II) andcobalt(II) centers symmetrically bridged by phosphinoamide units. Each of thesedimers exhibits similar structures that involve a central six-membered heteroatom73ring flanked by closed shell ferrocene units that also display uncoordinated phos-phine moieties. The key difference in these structures is evident in the geome-tries of the open-shell iron and cobalt centers. In the diiron dimer 3.2, each ironis trigonal planar, while in the dicobalt dimer 3.4, each cobalt displays a squareplanar geometry, due to a significant interaction with each ferrocene iron center.This interaction has been confirmed by DFT analysis showing bonding orbitals en-compassing the iron and cobalt centers and NBO analysis suggesting that a filledvalence orbital on ferrocene donates to an low-lying σ∗Co−P orbital.Other ferrocene→ M bonding interactions are well known and have been re-ported for M = Pd, Pt, Ru and Ti, all of which display closed-shell configurations.To our knowledge, this is the first example of a ferrocene→ M bond to an open-shell metal ion. A rationale for the difference in the interaction of the two dimericcomplexes reported here is likely that the HS Fe(II) centers in 3.2 do not haveavailable orbitals for donation from the ferrocene unit, whereas in 3.4 the low-spinCo(II) centers mimic closed-shell Pd(II) and Pt(II) ions with available metal-basedorbitals for interaction with the ferrocene Fe centers. Chapter 4 will focus on thereactivity of these structurally unique dimers.3.2 Attempted Synthesis of Group 10 Phosphinoamides3.2.1 IntroductionIn the previous section we examined the coordination chemistry of a bisamidophos-phine ferrocene ligand by performing salt metathesis reactions of 3.1 with iron andcobalt halides to produce metal complexes of the type ([fc(NPiPr2)2]M)2. Duringthese syntheses, we discovered that the iron center of the ferrocene backbone can74act as a donor to the cobalt center, yielding the square-planar coordination environ-ment observed in 3.4. While square planar Co(II) complexes like 3.4 are becom-ing more common because of their potential application in catalysis ,3,254–263 thenumber of square planar d7 metal complexes pales in comparison to the plethoraof square planar d8 complexes based on group 10 metals. For this reason, wewondered if the group 10 metal complexes would be more stable than the cobaltderivative 3.4. Therefore, we endeavoured to synthesize compounds of the type([fc(NPiPr2)2]M)2 where M = Ni, Pd, Pt. If indeed these diamagnetic complexeswere more stable than 3.4, this would allow us to characterize the Fe→M donationin solution and examine any potentially non-innocent effects this interaction wouldhave on small molecule activation.3.2.2 Attempted Synthesis of Group 10 ComplexesInitial synthetic efforts were directed toward platinum in order to take advantageof the NMR spectroscopic handle provided by the spin-active 195Pt nucleus. Weinitially tried the same salt metathesis methodology, shown to be successful withiron and cobalt. However, using the dipotassium salt 3.1 and a variety of PtL2X2(Scheme 3.4) metathesis reagents resulted in intractable mixtures, which, whenanalyzed by solution phase 31P NMR spectroscopy, did not display any evidence ofphosphorus-platinum coupling. Salt metathesis with Pd(II) sources (Scheme 3.4)resulted in similarly intractable mixtures. In addition, based on the observationof black precipitate in both the Pd and Pt reaction mixtures, we concluded thatreductive elimination to Pt0 was too facile with this electron rich ligand set.An alternative synthetic strategy was attempted involving a two step coordina-tion and deprotonation protocol using PtCl2(PPh3)2 as the metal precursor. Stirring75FeN NP P3.1•1.25 THFKKnFeNHHNPP1.50MX2L2aTHF-2 KX- M0Intractable MixtureEt2O0.5 [PtMe2(u−SMe2)]2FeNHNHPPPtMeMeheat3.6FeNHNHPPPtClCl3.5toluenePtCl2(PPh3)2KHTHFb-SMe2-2 PPh3a:When M=Pd,Pt X = Cl,I L = PPh3, SMe2 b: NEt3, KOtBu, LiHMDS, KHMDS, KHScheme 3.4: Attempted synthesis of ([fc(NPiPr2)2]M)2 where M = Pd, Pta solution of the diphosphinoamine 1.50 with PtCl2(PPh3)2 and monitoring by 31PNMR spectroscopy leads to a spectrum with two new resonances correspondingto a major and minor product. Both resonances display coupling to platinum andare separated by a mere 0.71 ppm. The 1JP,Pt coupling constants for the major andminor products are 2547 Hz and 2565 Hz, respectively, consistent with a platinum-phosphorus bond. Due to the similar chemical shifts and coupling constants wetentatively assigned these resonances to cis/trans isomers of [fc(NHPiPr2)2]PtCl2.The 1H NMR spectrum displays two N-H resonances at 5.64 and 5.95 ppm, withthe major N-H resonance split into a virtual triplet, which, upon 31P decouplingcollapses to a singlet. Virtual coupling requires strong coupling between the equiv-alent phosphorus nuclei suggesting that the major product is the species with thetrans arrangement of the phosphorus atoms, shown for 3.5 in Scheme 3.4. Unfor-76tunately, deprotonation of this complex with a wide variety of bases led to eitherno reaction (NEt3, KOtBu) or decomposition to an intractable mixture (KHMDS,LiHMDS, KH, MeLi). As we were unable to generate ([fc(NPiPr2)2]Pt)2 using thisroute, complete characterization of 3.5, including determination of the solid statemolecular structure, was not pursued.A third synthetic route was envisioned whereby a platinum alkyl complex of1.50 could undergo alkane elimination to generate the desired ([fc(NPiPr2)2]Pt)2.After converting PtCl2(SMe2)2 to (Pt(µ-SMe2)Me2)2264 addition of 1.50 resultedin conversion, as evidenced by 31P NMR spectroscopy, to a single product 3.6,with 1JP,Pt = 2029 Hz. Characterization by 1H NMR spectroscopy reveals the samepattern as 3.5 with one additional resonance for the methyl groups at 0.97 ppm.Gentle heating (50°C) of 3.6 results in no reaction and more aggressive heating(100°C) results in decomposition of 3.6 and formation of a platinum mirror on theinside of the NMR tube. No resonances are observed in the 1H NMR spectrum formethane or ethane, however, several low intensity signals were observed between0 and 1 ppm.Our inability to synthesize phosphinoamide complexes of platinum and palla-dium led to investigations of the coordination chemistry of Ni(II), another d8 metalion, unique from its heavier congeners due to its ability to adopt both square pla-nar and tetrahedral coordination geometries.265,266 We began by performing saltmetathesis between 3.1 and a variety of NiX2L2 compounds where X = Cl, Br andL = DME, THF, PPh3. In all of the reactions a new diamagnetic compound, 3.7 inScheme 3.5, was observed by 31P NMR spectroscopy in varying purity.The original synthesis of 3.7 was performed using NiCl2(PPh3)2, however,subsequent syntheses have utilized the much cheaper and more atom economical77Figure 3.12: 31P{1H} (162 MHz, insert) and 1H NMR (400 MHz) spectra ofcompound 3.7 in C6D6NiBr2. Examination of the 31P and 1H NMR spectra of 3.7, shown in Figure 3.12,suggested that we had indeed synthesized the desired ([fc(NPiPr2)2]Ni)2 complex.The 31P NMR spectrum displays two resonances coupled to one another (3JP,P =40.7 Hz) with very similar chemical shifts (∆δ = 1.16 ppm). The 1H NMR spec-trum is consistent with inequivalent ligand arms, displaying 4 sets of resonancesfor the iso-propyl protons, as would be expected for a complex with an analogousstructure to 3.4. The stability of 3.7 was demonstrated by multiple heating andcooling cycles from 25°C to 80°C followed by 1H NMR analysis, showing no sig-nificant compound degradation.Single crystals of 3.7 were grown by cooling a toluene/hexanes solution to -40°C, and the solid-state molecular structure was established by single-crystal X-raydiffraction, and shown in Figure 3.13. Surprisingly, the structure shows a com-pound containing no nickel and a new P-N bond formed between the phosphorusof one phosphinoamide and the nitrogen of the other ligand arm, a completely un-expected result. Examination of the bond lengths obtained from the solid-state78molecular structure shows that the N1-P1 bond length (1.565(3) A˚) is substantiallyshorter than the other two P-N distances (> 1.7 A˚) suggesting that an oxidation ofone amidophosphine has occurred and there is now a formal double bond betweenN1-P1. The N1-P1 distance of 3.7 is comparable to other phosphinimines from ourgroup (1.5594(1) A˚) and others (∼1.58 A˚).267Figure 3.13: ORTEP diagram of 3.7 with ellipsoids drawn at 50% probability.All H atoms and iPr methyl groups have been omitted for clarity. Selectedbond lengths (A˚) and angles (deg): N1-P1 1.565(3); N2-P2 1.750(3); P1-N21.720(3) C1-N1 1.391(5); C6-N2 1.443(5); Fe1-P1 3.5182(12); N1-P1-N2114.95(16); P1-N1-C1 126.4(3); P1-N2-C6 119.4(2); P1-N2-P2 1.479(5); Cptilt angle 9.40(17).The salt metathesis reaction with nickel is more complicated than with ironor cobalt. Balancing the equation, Ni0 and KBr must be produced in the reac-tion. We attempted to identify a putative Ni intermediate in the reaction by trap-ping with PMe2Ph. Adding 5 eq of PMe2Ph to the reaction of the dipotassiumsalt 3.1 and NiBr2 yields a reaction mixture with a resonance at -9.5 ppm in the31P NMR spectrum, attributed to Ni(PMe2Ph)4. All other resonances in the spec-trum could be attributed to compound 3.7 and excess PMe2Ph.268 The addition ofPMe2Ph did not allow us to observe a Ni intermediate, however, the observation ofNi(PMe2Ph)4 is evidence for the production of Ni0 during the course of the reac-79tion. We propose that a Ni(II) intermediate like (fc(NPiPr2)2Ni)2 (or a monomericcomplex fc(NPiPr2)2NiLx) is initially formed before rapid reductive eliminationoccurs to yield 3.7 (Scheme 3.5). All attempts to isolate or characterize the pro-posed (fc(NPiPr2)2Ni)2 intermediate, including low temperature 31P and 1H NMRstudies, were unsuccessful.FeN NP P3.1•1.25 THFKKnFeNNPPNiFeNNPPNi2 NiBr2THFFeNNPP3.7-4 KX-2 Ni0Scheme 3.5: Synthesis of 3.7.The similar chemical shifts of the two phosphine environments (Figure 3.12)in 3.7 was surprising given that one is a P(V) phosphinimine and one is a P(III)phosphinoamine. We undertook VT-NMR spectroscopy studies to identify anyexchange processes and, under gentle heating (328 K), observed the coalescenceof the phosphorus resonances (Figure 3.14). This was surprising as the exchangeof the inequivalent phosphorus atoms requires cleavage and formation of a P-Nbond on the NMR time scale. Repeating this experiment with multiple heating and80cooling cycles does not result in product decomposition; the original spectra areobserved every time upon returning to room temperature. Unfortunately, we werenot able to fully resolve the two signals at low temperature because at temperaturesbelow 209 K solubility issues prevent the collection of quality data. There is noindication from Figure 3.14 that the signals are fully separated even at 209 K.Figure 3.14: VT-31P (162 MHz) NMR spectra of compound 3.7 in d8-tolueneTo the best of our knowledge compounds like 3.7 where a R2P−NR−PR2−NRlinkage is present are virtually unknown, with only one report of the protonatedcation R2P−NR−PR2−NHR+.269 However, aryl phosphoramidines ArNHPR2NArand the deprotonated phosphoaramidinates are known and the latter have beenshown to stabilize copper(I) carbenes270 and zirconium complexes competent inethylene polymerization.271 In these systems, no ligand rearrangements are re-81ported even at elevated temperatures up to 353 K, indicating that the phospho-ramidinate linkage is not inherently labile. We suggest that the chemical exchangein 3.7 is triggered by a delocalization of electron density from the Cp ring into theaminophosphine arm of the ligand, breaking the P-N single bond (A in Scheme 3.6).The iminophosphoranide produced (B) can attack the phosphorus atom resulting ina rearomatization of the Cp ring (C). However, the lone pair of the phosphorus(III)center could also trigger the same P-N bond cleavage and this possibility can notbe ruled out.Fe2+NNPP Fe2+NNPPNNPPFe2+NNPPFe2+A B C DScheme 3.6: Proposed mechanism of exchange in Nickel Complexes of Unlinked PhosphinoamidesAs previousely mentioned, compounds of the type RN=PR′2-NR-PR′2 are unknown.If the reaction between NiBr2 and 3.1 could be generalized to unlinked phosphi-noamides this reaction could provide a simple route to neutral unsymmetric imine/ phosphine ligands like compound 3.8 in Scheme 3.7. A potential reaction schemeis shown in Scheme 3.7, whereby unsymmetric ligands could be constructed in twosteps starting from anilines and chlorophosphines. In order to investigate this pos-sibility we began by synthesizing a monomeric phosphinoamine that we had previ-ously used,109 ArNHPiPr2, where Ar = 3,5-dimethylphenyl, 3.9. Subsequently, 3.982was treated with potassium hydride and the resulting phosphinoamide, 3.10, wasfully characterized.R' NH2 NEt3PR2ClR' HNPR2 i) KHii) NiX2NR2P NPR2R'R'3.8Scheme 3.7: Attempted synthesis of asymmetric P,N ligands.Treating 3.10 with NiBr2 results in an immediate reaction to form a new com-pound. While the symmetry displayed in the 1H and 31P NMR spectra is consistentwith coupled phosphinoamides, the chemical shifts of the phosphorus resonanceswere highly separated (68.8 ppm and 29.9 ppm) in contrast to that observed for 3.7.In addition, the integration of aryl and iso-propyl proton resonances indicates thatthere are twice as many PiPr2 groups as NAr groups. Again, clarity was establishedonly after single crystals were grown for X-ray diffraction. The solid-state molec-ular structure is shown in Figure 3.15, and shows a very strange and unexpectedcompound, 3.11, which contains two nickel ions, two bridging phosphinoamideligands and two terminal phosphide ligands. The Fenske group has previouslyreported salt metathesis of Li[PhNPPh2] with NiCl2(PPh3)2 and have found thatduring salt metathesis ligand rearangments are common,272 however, neither of thecompounds reported are analogous to compound 3.11.Examining the solid-state molecular structure more closely we see that thenickel atoms have adopted a square planar geometry (sum of internal angles 359.7°,τ4273 = 0.25) involving a Ni-Ni bond. Metal-metal interactions are known innickel(II) dimers,274,275 however, in these cases the square-pyramidal nickel atom83Figure 3.15: ORTEP diagram of 3.11 with ellipsoids drawn at 50% prob-ability. All H atoms and iPr methyl groups have been omitted for clar-ity. Selected bond lengths (A˚) and angles (deg): Ni1-Ni1i 2.4741(6); Ni1-N1 1.9008(5); Ni1-P1 2.5983(7); Ni1-P1i 2.1239(5); Ni1-P2 2.1952(5);N1-P1 1.6402(4); P2-Ni1-N1 100.12(2); P2-Ni1-P1i 102.78(2); P1-N1-Ni194.121(18); 109.08(2).is surrounded by 4 donor atoms from the ligands and the metal-metal interactionis normal to the donor plane. In contrast, the Ni(II) ions in 3.11 are bound byonly three donor atoms and the metal-metal bond is in the donor plane. Anotherinteresting structural feature of 3.11 is the short N1-P1, P1-Ni1i and long N1-Ni1distances. As discussed in Chapter 1, the N-P bond length of phosphinoamine lig-ands can be invaluable in characterizing the ligand as one of two possible resonancestructures (see Figure 1.3): phosphinoamide or iminophosphoranide. In this case,the contracted P-N bond in combination with a weaker and longer N-Ni, comparedto 3.2 and 3.4, bond suggests that the iminophosphoranide resonance structure is abetter description of this compound.Although 3.11 is structurally interesting it seems as though our goal of a gen-eral methodology for the coupling of amidophosphines is not possible by thisroute. The product obtained, 3.11, clearly does not account for all the startingmaterials and by mass balance the by-product should be ArNNAr where Ar = 3,5-84NPiPr2NiBr2THFK2.11NiN PiPr2NiiPr2P NiPr2P PiPr2- ArNNAr ?2.10Scheme 3.8: Reaction between 3.10 and NiBr2.dimethylphenyl. However, we were unable to detect this byproduct using GC-MSor 1H NMR spectroscopy.3.3 Conclusions and Future DirectionsThe diphosphinoamide ligand, compound 1.50, has been successfully installed oniron(II) and cobalt(II) using a salt metathesis methodology. While both compoundsdisplay the same overall dimeric structure, the cobalt(II) complex shows an addi-tional interaction with the iron atom in the ferrocene backbone. This interaction hasbeen characterized using X-ray crystallography and 57Fe Mo¨ssbauer spectroscopy,and studied using DFT. The iron compound, 3.2, has been shown to maintain itsdimeric structure in solution until a significantly strong donor such as pyridine orp-dimethylaminopyridine is added. On the other hand, 3.4 undergoes rapid decom-position in solution before it can be characterized. Attempts at forming complexesof group 10 metals led to a reductive elimination and formation of 3.7 in the case ofnickel. Attempts to generalize this reaction to intermolecular coupling of phosphi-noamides were unsuccessful. Moving forward, 3.2 will be subjected to a battery of85experiments with the aim of characterizing how this polyiron system behaves un-der reducing and oxidizing conditions as well as its binding and activation modesfor a variety of small molecules. It is impractical to study the reactivity of 3.4 dueto it’s instability in solution and while the reactivity of 3.3 could be interesting it isbeyond the scope of this thesis.86Chapter 4Small Molecule Activation withan Iron Phosphinoamide DimerSuccess consists of going from failure to failure without loss ofenthusiasm. — Winston Churchill4.1 Reactions with Hydrogen and Carbon Monoxide4.1.1 Reaction with HydrogenAs discussed in Chapter 1, iron complexes containing amido and imine donors cancatalyze hydrogenation/dehydrogenation and transfer hydrogenation reactions.57,58,60,61Unfortunately we quickly discovered that compound 3.2 is not an appropriatecatalyst for acceptorless alcohol dehydrogenation or transfer hydrogenation re-actions. Compound 3.2 reacts rapidly with alcohols producing the protonatedbis(phosphinoamine) ligand, 1.50, as evidenced by 1H NMR spectroscopy. Noadditional products are observed by 1H NMR spectroscopy and a likely end-statefor the iron is the insoluble material, isolated from the reaction mixture. Interest-ingly, reaction of compound 3.2 or 3.1 with acetonitrile also produces compound871.50. The fact that compound 3.2 reacts with acetonitrile but not toluene allows usto put limits on the pKa of compound 1.50 (31.3 – 41).276,277Scheme 4.1: Reaction of phosphinoamide salts with various solventsIn order to investigate whether compound 3.2 could catalyze hydrogenationreactions we examined reactions of 3.2 with H2. When a toluene solution of 3.2was exposed to H2 gas, a color change was observed from dark brown to lightorange, along with concomitant formation of a dark precipitate. When the volatileswere removed and the residue was redissolved in C6D6 a crude NMR spectrumwas obtained that contains resonances attributed to 1.50 in the diamagnetic regionof the spectrum and no major resonances in the paramagnetic regions. In order todetermine whether adventitious water was responsible for the formation of 1.50,side by side hydrogenations of 3.2 and the potassium salt 3.1 were performed,as shown in Scheme 4.2. While hydrogenation of the iron dimer (3.2) producedprotonated ligand, no reaction was observed in the hydrogenation of compound3.1, thus eliminating the possibility of any trace H2O.The production of compound 1.50 suggests a heterolytic cleavage of H2 oc-curs over the Fe–N bonds in compound 3.2. We propose that once all the Fe–N88Scheme 4.2: Reaction of phosphinoamide salts with dihydrogenbonds are hydrogenated, the resulting ”[fc(NHPiPr2)2]FeH2” intermediate decom-poses via reductive elimination forming H2, Fe0 and 1.50. We were able to supportthis proposal by observing that the solids produced in the reaction mixture are at-tracted to a bar magnet and are therefore ferromagnetic, consistent with Fe0 forma-tion. Simultaneous to our investigation, the Morris group reported that asymmetrictransfer hydrogenation reactions of ketones using iron complexes thought to behomogeneous278 were actually catalyzed by Fe0 nanoparticles formed in situ.279Interestingly, these nanoparticles were able to catalyze enantioselective transferhydrogenation and the authors suggest that chirality of the ligand is imparted viacoordination to the surface of the nanoparticle. We attempted transfer hydrogena-tion and direct hydrogenation of ketones using compound 3.2 as a precatalyst butno conversion was observed.89Figure 4.1: Selected TEM images of a carbonized reaction mixture of 3.2 andH2 showing inconsistent morphologies and particle sizesWe sought to evaluate the morphology of the Fe(0) produced in the hydrogena-tion of compound 3.2 for comparison to the active Fe(0) nanoparticles reported byMorris and coworkers. After exposing 3.2 to 4 atm of H2 for 12 h the volatileswere removed in vacuo and the resulting residue was heated to 700 °C in a tubefurnace for 16 h to remove the organic residues. The resulting solids were analyzedby Transmission Electron Tomography (TEM) and some representative images areshown in Figure 4.1. The TEM images show inhomogeneous particles with a widerange of diameters (100 nm - 2000 nm) and inconsistent morphologies. No furtherstudy of these particles was undertaken.4.1.2 Reactions with Carbon MonoxideThe iron catalysts for ketone hydrogenation (compound 1.6 - 1.9 in Scheme 1.4)have higher coordination numbers and lower spin states (HS vs LS) than com-90pound 3.2 and contain one or more CO ligand. We hypothesized that addition ofCO ligands to compound 3.2 would increase the ligand field enough to create alow spin complex, similar to compound 1.8. Exposing a toluene solution of 3.2to 1 atm of carbon monoxide for 16 h produces an intractable mixture of param-agnetic materials. If the reaction mixture is left under a carbon monoxide atmo-sphere for several days without stirring, low yields (2 - 5%) of dark red crystalsof a new compound, 4.1, are obtained. The solid state molecular structure shownin Figure 4.2 depicts a surprising disassembly of the ferrocene-based ligand. Theshort C1-N1, C2-C3, C4-C5 and long C1-C2 and C1-C5 bond lengths indicatethat each iPr2PNC5H4 fragment has been oxidized by two electrons producing aneutral cyclopentadieneimine fragment. These ligands coordinate to the iron cen-ters in a µ(η4Cp - P) coordination mode, yielding a dimeric piano stool complexreminiscent of the Kno¨lker complexes discussed in Chapter 1. It should be notedthat the reaction between compound 3.2 and excess carbon monoxide (shown inScheme 4.3) is completely atom economical and can be thought of as a reductionof the iron atoms by the iPr2PNC5H4 fragment, however, due to the low yields ofthis compound complete characterization was not pursued.If the amount of carbon monoxide is limited to one equivalent, a new highlyasymmetric species, 4.2, is observed by 1H NMR spectroscopy in the crude reac-tion mixture. After purification, black crystals of compound 4.2 can be obtained.Redissolving these crystals produces the same 1H NMR spectrum (Figure 4.3) asthe crude reaction mixture. Single crystals of compound 4.2 can be grown by slowevaporation of hexanes and the solid-state molecular structure is shown in Fig-ure 4.4. One carbon monoxide ligand is bound to one of the non-ferrocene ironcenters and one of the ligand arms has reversed its coordination geometry from91Fe1C1C5 C4C3C2N1P1C12C13O2O1Fe1 iFigure 4.2: ORTEP diagram of 4.1 with ellipsoids drawn at 50% prob-ability. All H atoms and iPr methyl groups have been omitted for clar-ity. Selected bond lengths (A˚) and angles (deg): Fe1i-C2 2.1443(12);Fe1i-C3 2.0748(13); Fe1i-C4 2.0742(14); Fe1i-C5 2.1317(12); Fe1i-C12.3636(12); C1-N1 1.3252(15); C2-C3 1.4291(16); C4-C5 1.4152(16); C1-C2 1.4527(16); C1-C5 1.4668(16) N1-P1 1.6642(11); C12-O1 1.1532(15);C1-N1-P1 123.78(9); Fe1-C12-O1 176.45(10).		Figure 4.3: 300 MHz 1H NMR spectra of 4.2 in C6D692µ-N,P to µ-P,N, as shown in Scheme 4.3. As a result, the non-ferrocene iron cen-ters are formally Fe(I)/Fe(III). It is tempting to suggest that the binding of carbonmonoxide results in an electron transfer and ligand rearrangement between the in-terior iron centers. 57Fe Mo¨ssbauer spectra of compound 4.2 were collected atroom temperature and 77 K in order to help assign the oxidation states of the ironcenters, see Figure C.3. The data collected was fit with four doublets, however,the data quality is low enough that other fits are possible and conclusive oxidationstates could not be assigned.FeNNPPFeFeNFeNNPPFe3.24 atm COtoluene1eq COtoluenePFeNPCOOCOCCOFeNNP PFeCOPFeNNFeP4.24.1Scheme 4.3: Reactions of compound 3.2 with carbon monoxideThe IR stretching frequency of the CO ligand in compound 4.2 is 1880 cm−1.Direct comparison of this stretching frequency is difficult because, to the best ofour knowledge, no high spin iron complexes containing CO ligand(s) have beenreported. Octahedral low-spin iron complexes reported by the Morris (1.8) andMilstein (1.9) group both contain carbonyl ligands with similar stretching frequen-93cies to the CO ligand in 4.2, µIR = 1894 and 1865 respectively. Therefore the COligated iron center in 4.2 is consistent with a low spin iron carbonyl.56,62 To answerthe original question, whether addition of a CO ligand would produce a more stablehydrogenation catalyst, compound 3.2 was exposed to one atmosphere of hydrogenand again we observed decomposition to insoluble material and protonated ligand,1.50.C45O1Fe1Fe2Fe3Fe4N2P2N1P1P3N3N4P4Figure 4.4: ORTEP diagram of 4.2 with ellipsoids drawn at 50% prob-ability. All H atoms and iPr methyl groups have been omitted for clar-ity. Selected bond lengths (A˚) and angles (deg): C45-O1 1.162(3); N1-P11.6726(19); N2-P2 1.6659(17); N3-P3 1.6617(17); N4-P4 1.6886(19); Fe2-N2 1.8559(15); Fe2-P2 2.2321(8); Fe2-P1 2.2441(10); Fe2-P3 2.2432(9);Fe3-N1 2.0033(16); Fe3-N3 1.9968(18); Fe3-N4 1.9287(17); Fe2-C45-O1 169.79(18) P1-Fe2-P3 96.59(3); P1-Fe2-C45 97.23(9); N1-Fe3-N3108.48(7); N1-Fe3-N4 131.24(7); N3-Fe3-N4 120.16(7).The above results suggest that phosphinoamide ligands are not suitable for co-operative activation of dihydrogen due to complex instability. Modifications tothe ligand scaffold providing a larger chelate ring, vide infra could help remediate94these issues by keeping the Fe–H N–H pair stable long enough to react with an in-coming substrate. Moving forward we will investigate the oxidation and reductionof compound 3.2 and investigate its reactivity with various small molecules.4.2 Redox Behaviour of ([fc(NPiPr2)2]Fe)2, Formation ofa Fe-Fe Bond and Cleavage of AzobenzeneThe impressive transformations facilitated by heterogeneous catalysts280–285 andmultimetallic co-factors in metalloenzymes, such as nitrogenase,286–289 have ledto interest in the study of polynuclear molecular systems.142,290–292 The ability ofmetalloenzymes to perform multielectron reductions293,294 using iron-based cofac-tors is particularly noteworthy considering the conditions of the intracellular en-vironment. Despite significant efforts, the binding and activation of substrates bythese polynuclear sites remain poorly understood.294–298 Attempts to create syn-thetic models of these polyiron sites has been of increasing interest,295,299–304 assuch studies may reveal insights into complex redox processes. Of particular note,recent reports of polyiron complexes supported by abiological ligands detail theactivation of substrates relevant to nitrogen fixation.90,115,305–307 Such studies areimportant because these synthetic systems can be more easily studied than the nat-urally occurring enzymes, which allows for a more detailed description of theirelectronic structures, factors affecting metal-metal bonding, and substrate bind-ing.308,309Betley and coworkers have contributed to this area with the isolation of thetrinuclear, high-spin cluster of Fe(II) centers (A in Scheme 4.4), which is capableof cleaving the N-N bond of azobenzene (PhN=NPh) with no external reductant.90We have previously reported the tetrairon dimer 3.2 that contains two ferrocenyl95diphosphinoamides supporting two high spin Fe(II) ions; this ancillary ligand sys-tem also can be used to generate a mixed tetranuclear Fe2-Co2 system that displaysinteresting Fe–Co interactions (compound 3.4).310 Based on reports from our groupand others that show how dinitrogen can be activated and functionalized by dinu-clear or trinuclear complexes,5,89,91,95,96,144,191 we investigated the redox reactivityof 3.2 to examine structural changes, as well as interaction with small moleculesrelated to dinitrogen fixation. In this section, we report the oxidation and reductionof 3.2, and the cleavage of azobenzene by 3.2.FeNNPPFeFeNNPPFe3.2NNFe FeN NFeNSiSiNSiOAScheme 4.4: Polyiron ComplexesInitially, we sought to use cyclic voltammetry to study the redox behaviourof 3.2 but the results were poor, with multiple irreversible waveforms observed inboth the reductive and oxidative regimes (see Figure E.1 in Appendix E) suggestingthat compound 3.2 undergoes a chemical reaction following reduction or oxidation.We then examined chemical oxidants and reductants. Although 3.2 reacts rapidlywith numerous oxidants of the type Ag(Y) and X2 (Y= OTf−, Cl−, BPh−4 , X =Br, I) the cleanest reactions were obtained using the molecular iodine equivalent1,2-diiodoethane. Treatment of 3.2 with four equivalents of 1,2-diiodoethane re-96sulted in conversion to a new paramagnetic product. Limiting the equivalents of1,2-diiodoethane simply results in partial conversion to the same product. The sto-ichiometry of the reaction suggested that the oxidation was more than a simpleFe(II)/Fe(III) event. Recrystallization from toluene/hexanes mixture results in theformation of dark red crystals of a new paramagnetic product, 4.3, with an empir-ical formula of [fc(NPiPr2)2]FeI4 (56 %). X-ray analysis of 4.3 revealed the solidstate molecular structure, shown in Figure 4.5. The P-N bond shortens from 3.2(1.6993(12) A˚) to 4.3 (1.603(7) A˚) demonstrating that the electron-rich phosphi-noamide arms of the ligand have been oxidized while both iron atoms remain inthe Fe(II) oxidation state. We suggest that irreversible oxidation of the P-N bondis contributing to the poor quality of CV data in the oxidative regime.Attempts to generate a dinitrogen complex by reduction of 3.2 under mild con-ditions (Na/Hg or cobaltacene under 4 atm N2) were unsuccessful. Upon reductionwith excess KC8 3.2 does not coordinate dinitrogen but rather undergoes a rear-rangement to form an iron-iron bond between the two internal iron centers (Fig-ure 4.5). The Fe1-Fe2 distance decreases from 3.9241(5) A˚ in 3.2 to 2.4760(6)A˚ in 4.4, similar to the diiron (FeI/FeII) trisphosphinoamide complex reported bythe Thomas group (2.4645 A˚).115 In order for the iron centers in 4.4 to get closeenough to form a bond, the ferroceene backbones of the ligand must twist to be-come perpendicular to each other (cp plane to cp plane angle = 84.75°- 86.05°).The iron-iron bond, formed upon reduction of 3.2 illustrates the potential for thestorage of reducing equivalents in this system. Compound 4.4 is stable as a solidin the glovebox freezer for up to a week; however, in a C6D6 solution 4.4 revertsback to over 50% compound 3.2 in less than 48 hours. The magnetic moment of4.4 (7.8 µB) indicates that the complex maintains a maximally high spin S=7/297Figure 4.5: ORTEP diagram of 4.3 (left) and anionic portion of 4.4 (right)with ellipsoids drawn at 50% probability. All H atoms and iPr methylgroups have been omitted for clarity. Selected bond lengths (A˚) and angles(deg) of 4.3: Fe1-Fe2 3.4836(17); N1-P1 1.607(7); N2-P2 1.603(7); Fe1-I1 2.6889(13); Fe1-I2 2.6428(13); P1-I3 2.408(3); P2-I4 2.409(3); I1-Fe-I2 104.97(4); N1-Fe-N2 115.7(3); cp tilt[216, 219] 2.78; and 4.4: Fe1-Fe23.7016(10); Fe2-Fe3 2.4755(7); Fe3-Fe4 3.6954(10); N1-P1 1.690(3); N2-P2 1.651(3); Fe2-N2 1.975(3); Fe2-N1 1.983(3); Fe2-P2 2.7252(11); Fe3-P2 2.3607)10); N1-Fe2-N2 11.49(11); N2-Fe2-P4 110.22(8); N1-Fe2-Fe3136.97(8); cp tilt216,219 for Fe1 1.18 and Fe4 0.88.ground state. It has been observed that diiron systems displaying a M-M bondcontract upon oxidation311 with the rationale being a depopulation of the M-Manti-bonding orbitals. However, in a recent contribution, Betley and coworkers re-port that the same triiron system that activates PhNNPh (A in Scheme 4.4) displaysa contracted Fe-Fe distance (0.13 A˚) upon reduction.309 Compound 3.2, 1.30 andA in Figure Scheme 4.4 represent rare examples of polyiron compounds that dis-play increased iron-iron interactions upon reduction while maintaining a high-spinstate, and therefore population of metal-metal anti-bonding orbitals. The reactivityof 4.4 with nitrogen rich substrates such as PhNNPh has so far led to complicated98mixtures, no doubt due to the high reactivity of this complex.FeNNPPFeFeNNPPFe3.2FeNNPPFeIIII24 ICH2CH2IKC8PhNNPhUVFe NNPPFeFeNNPPFe-K+(THF)FeNNPPFe2NN4.34.4 4.5Scheme 4.5: Reactivity of 3.2While 3.2 was unable to coordinate dinitrogen even under reducing conditions,we wondered how 3.2 would react with the N=N double bond in azobenzene.Cleavage of PhNNPh is known for iron312 and ruthenium313 carbonyl clusters,which involve transfer of the putative metal imidos to CO to form isocyanates.More recently, a trinuclear ruthenium hydride314 and a trinuclear iron complex90were shown to cleave PhNNPh into metal imido fragments. We thought that com-plex 3.2, containing four iron(II) centers, would also have the available reducingequivalents to cleave the PhNNPh bond.Exposing compound 3.2 to azobenzene does not result in a reaction as evi-denced by 1H NMR spectroscopy. Even heating the mixture to 70 °C for 12 hours99Figure 4.6: 1H NMR spectra (400 MHz, 298 K) of A: (left and right) Initialsolution of trans-PhNNPh; B: (left) Solution after irradiation at 350 nm for 25min (right) Solution after irradiation at 350 nm for 60 min; C: 30 minutes aftermixing with (left) and without (right) compound 3.2. Green: trans-PhNNPhand red:cis-PhNNPhdoes not result in any new signals in either the paramagnetic or diamagnetic 1HNMR spectra. However, when a solution of 3.2 and PhNNPh in C6D6 was irradi-ated with UV light (350 nm) a reaction was observed by NMR spectroscopy to anew paramagnetic product, 4.5. Initially we hypothesized that 3.2 could only reactwith cis-PhNNPh due to steric congestion. To test this we produced a mixture ofcis/trans-PhNNPh by photolysis and added compound 3.2 in the absence of UVlight. No reaction was observed, however, 3.2 does seems to catalyze the cis/transisomerization of azobenzene (See Figure 4.6). Compound 4.5 could only be pro-duced when both reactants are exposed to UV light together, indicating that the100role of UV radiation is more than isomerization of azobenzene. Single crystals of4.5 were obtained by cooling a solution of pentane, and the solid state structure isshown in Figure 4.7.Figure 4.7: ORTEP diagram of 4.5 with ellipsoids drawn at 50% prob-ability. All H atoms and iPr methyl groups have been omitted for clar-ity. Selected bond lengths (A˚) and angles (deg): Fe1-Fe2 4.0103(4); N1-P1 1.6142(13); P1-N3 1.6260(14); N1-Fe1 2.0558(13); P1-Fe1 2.7176(5);N3-Fe1 2.0634(14); N1-P1-N3 96.90(7); N1-Fe1-N2 98.04(5); N1-Fe1-N372.13(5); N3-Fe1-N4 118.01(5).Unexpectedly two new P-N bonds were formed and the resulting N–P–N frag-ment has similar P1-N1 and P1-N3 bond lengths of 1.6119(14) A˚ and 1.6260(14) A˚respectively, indicate a delocalized diiminophosphorinato anion. Interestingly theferrocene linker forces the iron center to adopt a distorted square-planar geometry(τ4273 = 0.19). Compound 4.5 displays a room temperature magnetic moment of2.9 µB, consistent with the spin only value of two unpaired electrons (S = 1) andother square planar Fe(II) complexes.232 Replacing PhNNPh with tolNNtol (tol =4-methylphenyl) results in conversion to a new paramagetic product, 4.6, which101displays a very similar 1H NMR spectrum to compound 4.5. Using a 50:50 mix-ture of PhNNPh and tolNNtol in a reaction with compound 3.2 and analysis bymass spectrometry allowed us to observe the parent peak for the ”mixed” species,[fc(NPiPr2NPh)(NPiPr2Ntol)]Fe, suggesting that the reaction is not a concertedreaction between ArNNAr and [fc(NPiPr2)2]Fe.Diiminophosphinato ligands have been used to support metal metal bonds inalkali earth metals,315–317 rare earth element polymerization catalysts318–322 andgroup 10 cross-coupling catalysts.323–325 To the best of our knowledge, this is thefirst report of a bis(diiminophosphorinato)iron complex, however, a diiron sys-tem with a bridging diiminophosphorinato backbone has been reported.215 Whilediiminophosphorinatos are most commonly synthesized from phosphines and or-ganic azides, synthesis from azobenzene is precedented. Recently, a reaction be-tween the Ti/Co phosphinoamide complex, (THF)Ti(ArNPR2)3Co(N2) (Ar = 2,4,6-trimethylphenyl , R = iPr), and azobenzene has been reported to result in cleavageof azobenzene and formation of one diiminophosphorinato and one bridging metalimido.326 We suggest that an iron imido is produced in the reaction between PhN-NPh and compound 3.2, but this imido quickly reacts with a phosphinoamide armof the ligand. The complex most similar to 3.2 is Fe(iPrNPPh2)3Fe(PMe3),115which reacts with organic azides to produce an iron imido. However, this imido isnot reported to react with the bound amidophosphine ligands and we suggest thatthe geometric differences between the two complexes, namely the presence of anη1-N phosphinoamide in compound 3.2, is responsible for the divergent reactionprofiles of these complexes.In this report, we present a polyiron complex that, under photolytic condi-tions, cleaves azobenzene through a proposed but undetected iron imido. We also102note that 3.2 undergoes a ligand rearrangement forming a metal-metal bond uponreduction while maintaining a high-spin S = 7/2 state. From a ligand design per-spective, it appears that amidophosphine donors are too electron-rich to study ox-idation of high-spin iron clusters. Further work will involve determining whetherthe proposed imido, generated during the reaction of 3.2 with PhNNPh, can betrapped before transfer to the phosphine. New ligand designs will focus on scaf-folds that can support higher nuclearity iron systems that are more redox-innocent,and stay dimeric throughout redox processes and reactions with nitrogen-rich smallmolecules.4.3 Cooperative Activation of Polar Multiple BondsIn the previous section we described the redox behavior of compound 3.2 andshowed that the site of oxidation is the phosphinoamide arms. Based on this ob-servation we investigated the reactivity of 3.2 with electrophilic carbon centersof CO2, PhCHO and PhCN to determine whether the phosphinoamide would bethe most nucleophilic site. Metal-bound phosphinoamides react with carbon-basedelectrophiles as initially reported for zirconium phosphinoamides and nitriles.327Later, reports of CO2 activation by (CO)2CpM(R2PNR’) (M = Fe,Ru) emerged;328however, in all of the aforementioned cases, the [R2PNR’]− anion is best describedby the iminophosphide resonance structure (See Figure 1.3). A better comparisonto compound 3.2 can be found in a report from the Stephan group,128 where aruthenium amidophosphine complex (B in Scheme 4.6) was found to insert CO2between the metal phosphorous bond forming a 5-membered ring from the metal,amidophosphine and CO2 molecule. The ruthenium amidophosphine complex re-ported by the Stephan group is an active (albeit poor) catalyst for the hydroboration103of CO2. We wondered if our iron complex featuring four amidophosphines and amore ridgid ferrocene-backbone, 3.2, would activate CO2 using the same metal-ligand cooperativity observed for compound B.FeNNPFeFeNNPFe4.7POOPOOFeNNPFeFeNNPFe3.2PPN PRuHN NHPHNP N RuONNHPHNPPOBPh4 BPh4B C2 CO2CO2Scheme 4.6: Reactions between metal-bound amidophosphines and CO2Treatment of a solution of 3.2 with excess carbon dioxide results in decompo-sition to an intractable mixture of diamagnetic and paramagnetic materials. How-ever, when the equivalents of CO2 are limited, a light orange solution was observedfrom which light yellow crystals, 4.7, were isolated. A solution made from thesecrystals shows 15 paramagnetically shifted peaks in the 1H NMR spectrum (SeeFigure 4.8), 5 more than the would be expected for a dimeric structure similar tocompound 3.2.The solid state molecular structure of 4.7 is shown in Figure 4.9 and reveals theexpected asymmetric dimeric structure, shown in Scheme 4.6, which clearly shows104Figure 4.8: 300 MHz 1H NMR spectrum of 4.7 in C6D6that a cooperative CO2 binding event has taken place utilizing the electron-richamidophosphine as a Lewis base. In addition, one equivalent of 1.50 is present inthe lattice, bound by hydrogen bonding between the phosphinoamine N–H groupsand the oxygen atoms of 4.7, which explains the 5 extra signals observed in the 1HNMR spectrum. When ultra-pure CO2 was used under rigorously dry conditionsthe same color change was observed, however, these reaction mixtures failed toyield crystalline material. We propose that the activation of CO2 occurs regardlessof whether adventitious water is present or not, but that crystallization requiresan appropriate hydrogen bond donor. From the bond length contraction of N2–P2 from 1.6993(12) A˚ in 3.2 to 1.617(4) A˚ in 4.7 and concomitant elongation ofthe Fe-N2 bond from 1.9218(12) A˚ in 3.2 to 2.061(3) A˚ in 4.7, it is clear that theCO2 activation proceeds via oxidation of the phosphinoamide unit. The solutionmagnetic moment of 4.7 (5.9 µB) was measured by the Evans method and is lowerthan the expected spin-only value for two high-spin Fe(II) centers (9.8 µB). Fromthe magnetic moment, we conclude that the dimeric structure remains intact insolution and suggest that an increase in antiferromagnetic coupling is responsible105for the decreased magnetic moment in 4.7 compared to the starting material (µe f f =6.7 µB). Although compound 3.2 is able to cooperatively activate two equivalentsof CO2, neither 3.2 nor 4.7 catalyze the hydroboration of CO2, as observed by 11BNMR spectroscopy.Fe1Fe2Fe2'N1P1C12O1N2P2O2N3P3H1P2'Figure 4.9: ORTEP diagram of 4.7 and co-crystallized protonated ligand,1.50, with ellipsoids drawn at 50% probability. All H atoms and iPr methylgroups have been omitted for clarity. Selected bond lengths (A˚) and an-gles (deg): Fe1-Fe2 3.6854(9); Fe2-Fe2’ 3.5592(11); Fe2-N1 2.061(3); Fe2-N2 1.956(3); Fe2-P2’ 2.4635(11); Fe2-O1 2.084(3); N1-P1 1.617(4); N2-P2 1.673(3); N3-P3 1.695(4); P1-C12 1.857(5); C12-O1 1.262(6); C12-O21.221(6); O2-H1 2.04(6); N3-H1 0.84(6); N1-Fe2-N2 114.24(13); N2-Fe2-P2’ 109.32(10); N1-Fe2-O1 85.99(13).After observing that the outer sphere cooperative activation of CO2 is morefavorable than a direct, exclusive interaction with the iron centers, we turned ourattention to another substrate with an electrophilic carbon center, benzaldehyde.In order to determine the stoichiometry of the reaction between benzaldehyde andcompound 3.2 we performed small scale reactions with 1, 2, 4 and ∼100 equiv-106alents of benzaldehyde in deuterated solvent and monitored the reactions by 1HNMR spectroscopy. Addition of 1 or 2 equivalents of benzaldehyde resulted ina mixture of products evidenced by the numerous peaks in the 1H NMR spectra.When 4 or ∼100 equivalents were added to compound 3.2, conversion to one ma-jor product, compound 4.8, was observed suggesting that all four amidophosphinearms had been substituted (Scheme 4.7). In order to investigate whether a coop-erative activation would occur with a less electrophilic substrate we examined thestoichiometry of the reaction between 3.2 and benzonitrile in an identical mannerto the reaction with benzaldehyde. Treatment of 3.2 with benzonitrile provided asimilar 1H NMR spectrum of a new paramagnetic compound, 4.9, regardless ofthe stoichiometry of benzonitrile (1,2,4 or 100 equiv.) suggesting only a singlephosphinoamide arm was functionalized. While 4.9 does not react with additionalequivalents of benzonitrile, a reaction can be observed by 1H NMR spectroscopyupon addition of a more electrophilic substrate like benzaldehyde or methyl ben-zoate, however these products could not be characterized. It is interesting to notethat unlike the addition of excess CO2, addition of excess benzaldehyde (> 4 eq)or benzonitrile (> 1 eq) does not result in further reaction. We hypothesize thatthe small steric profile of CO2 allows for further deleterious reactions.Single crystals of both 4.8 and 4.9 were grown and the solid state molecularstructures are show in Figure A.4 and Figure A.5 respectively. The relevant N–Pbond lengths in compounds 4.7 - 4.9 are contracted by ∼ 0.1 A˚ compared to thestarting material, compound 3.2, indicating that the phosphinoamides have beenconverted to iminophosphoranes. The intrairon distance between the non-ferroceneirons has decreased for compounds 4.7 - 4.9 by 0.36, 0.61, and 1.03 A˚ respectively,however, only the Fe–Fe distance of compound 4.9 (2.8932(13) A˚) is below the107FeNNPPFeFeNNPPFeOOPhPhFeNNPPFeFeNNPPFe3.22 CO 2FeNNPFeFeNNPFe4.7POOPOOFeNNPPFe4.8OOPhPh4.9FeNNPPFeNPh4 PhCHO1 PhCNScheme 4.7: Reactions between compound 3.2 and electrophilic carbon cen-terssum of the covalent radii (3.06(8) A˚).329It appears that amidophosphines are not suitable ligands for the study of theinteraction of polyiron systems with CO2 due to the propensity of these complexesto activate polar unsaturated bonds in a cooperative fashion. Future work shouldlook at modified ligand designs without the electron-rich amidophosphine donors,therefore avoiding this type of metal-ligand cooperativity. This could be done byintroducing electronic spacers between the nitrogen and phosphorus atom, or byremoving the phosphorus donor entirely, vide infra. Further study of the reactionsbetween compound 3.2 and polar unsaturated molecules could investigate the po-108tential application of these complexes as catalysts in functionalization reactionssuch as hydrosilyation.109Chapter 5Future Work and ConclusionsI was taught that the way of progress is neither swift nor easy—Marie Curie5.1 Thesis SynopsisThis thesis is divided into two distinct branches, one focused on an amidophosphine-supported ditantalum tetrahydride, and the other focused on the synthesis and re-activity of polyiron complexes. The goal of the first branch was to investigate thetransformations of carbon monoxide and carbon dioxide by the ditantalum tetrahy-dride, 2.1. This work was preceded by two discoveries by Dr. Joachim Ballmann.First, that compound 2.1 can completely reduce carbon monoxide to methane, re-sulting in an oxo bridged ditantalum species, 2.4. Second, when compound 2.1 isexposed to carbon dioxide, two hydrides are transfered resulting in a bridging di-olate. The second branch involved investigating the coordination chemistry of the1,1’-bis(phosphinoamide)ferrocene, 1.50 with base metals and probing the abilityof these complexes to activate small molecules with a focus on dinitrogen. Thisligand set had been previously developed by Dr. Nathan Halcovitch to prevent110ligand redistribution in early transition metal phosphinoamide complexes.Chapter 2 covers all of the tantalum amidophosphine chemistry, and consists oftwo publications. Based on our previous reports of a ditantalum tetrahydride, 2.1,which spontaneously activates dinitrogen in a side-on-end-on binding mode,144 weexamined the reaction between 2.1 and isoelectronic carbon monoxide. We found,however, that instead of a side-on-end-on activation product, we obtained a newditantalum species containing no new carbon atoms, and a bridging oxide, com-pound 2.4. The fate of the carbon atom was identified as methane based on anexperiment using labeled 13CO. After consulting with our computational collab-orators they suggested three separate mechanistic pathways for the reaction. Allthree have energy barriers that are within the error of the calculations and thus,experimental evidence was required to reveal the operative mechanism. The criti-cal difference between the mechanisms is that in one, all 4 tantalum hydrides areused to produce the methane, while in the others, a proton from one of the N-Phrings is removed by a Ta-CH3. An isotopic labeling study reveals two different iso-topologues of compound 2.1, one where only the hydrides are deuterated and onewhere all hydrides and all ortho N-Ph protons were deuterated. Using these twoisotopologues in reactions with carbon monoxide we trapped the product methaneand analyzed its mass by GC-MS. These results support a mechanism that involvesa transient Ta(III)=Ta(III) double bond, which rapidly cyclometalates the N-Ph ringby oxidative addition of a C-H bond. To probe the catalytic potential of these trans-formations, regeneration of the tetrahydride 2.1 was pursued through treatment of2.4 with E-H reagents (Et3SiH, nBuSiH3, LiAlH4, NaBH4, THF·BH3). However,in all cases either no reaction was observed or many phosphorus containing specieswere observed by 31P NMR spectroscopy, none of which were compound 2.1.111Section 2.2 details the reaction of tetrahydride 2.1 with carbon dioxide. In thiscase, retention of the O–C–O framework is observed after two hydride transfersresulting in a diolate-bridged ditantalumdihydride, 2.5. My main contributions tothis publication were finishing the characterization of compound 2.5 and using d4-2.1 to prove that the hydrogen atoms of the methylene diolate originate from thehydrides of 2.1. In addition to the published material, we sought to observe re-action intermediates consistent with the minima suggested by DFT calculations.Regardless of temperature, the product and starting material were observed exclu-sively.Chapter 3 details the coordination chemistry of the 1,1’-bis(phosphinoamide)fe-rrocene ligand, 1.50, with base metals. We isolated complexes of iron(II) (3.2) andcobalt(II) (3.4), which exist in a dimeric form. Interestingly the cobalt complex,which is only stable in the solid state, displays weak bonding interactions betweenthe iron of the ferrocene backbone and the cobalt center. This interaction was char-acterized by 57Fe Mo¨ssbauer spectroscopy, SQUID magnetometry and modeledwith DFT calculations. The calculations suggest that this interaction is comprisedof donation from the iron center to the cobalt center (Fe→ Co) and back donationfrom the cobalt center to antibonding orbitals in the ferrocene backbone (Co →fc*). We sought to synthesize the analogous nickel(II) complexes, however, elim-ination of Ni(0) and oxidation of the dianionic ligand to compound 3.7 was toofacile.Chapter 4 covers a selection of reactions between the dimeric iron phosphi-noamide 3.2 and various small molecules. Treatment with dihydrogen led to het-erolytic cleavage of H2 across the Fe–N bond, which unfortunately results in de-composition to Fe(0) and compound 1.50. Addition of carbon monoxide to com-112pound 3.2 is more complicated than originally imagined and resulted in a ligandrearrangement. This illustrates the reluctance of compound 3.2 to break apart intomonomers. Reactions with polar unsaturated organic molecules led to nucleophilicattack of the organic substrate by the phosphorus atom of the ligand, forming met-allocycles. To our dismay, compound 3.2 does not react with N2 when reducedwith KC8 under 4 atmospheres of dinitrogen. Instead, reduction of compound 3.2results in formation of a metal-metal bond between the iron centers resulting in abimetallic Fe-Fe unit with an average formal oxidation state of +1.5 for each ironcenter, [Fe2]3+. Reaction of 3.2 with ArNNAr under photolytic conditions led tothe cleavage of the N=N double bond. We propose that an unobserved iron imidointermediate is formed prior to imido transfer to the phosphorus atom, resultingin two [NPNAr]− ligand arms on the 1,1’ferrocene backbone in compound 4.5and 4.6. Reactions between compound 3.2 and oxidants generally afford multipleproducts, however, using the iodine equivalent ICH2CH2I conversion to a singleproduct is observed where both phosphinoamide arms have been oxidized, 4.3.Throughout Chapter 4 the phosphinoamide arms of compound 3.2 were found tobe non-innocent, often acting as nucleophilic iminophosphide, which complicatedinvestigation of small molecule activation by two iron centers.5.2 Future Directions5.2.1 Re-Designing the 1,1’-diphosphinoamide Ligand forPolymetallic Complex FormationThe ferrocene-linked phosphinoamide ligand undergoes bond-forming reactionsand displays redox non-innocence in many of the reactions performed with com-pound 3.2. Typically the phosphinoamide functions as a nucleophile, leaving the113oxidation state of the iron unchanged, which illustrates the metal ligand coop-erativity in these iron phosphinoamide complexes. However, due to the strongP–C bond formed when reacting with organic electrophiles, the ability of thesecomplexes to catalytically functionalize organic electrophiles is likely unrealistic.Unfortunately, the observed ligand cooperativity precluded reactivity at the metalcenter and/or the ferrocene backbone. In order to eliminate phosphinoamide in-volvement we redesigned the ligand by placing an electronic spacer between thenitrogen and phosphorus atoms. Initially we decided to keep the spacer as shortas possible to encourage short intermetallic distances and thus chose a methylenelinker. Professor Connie Lu has recently pioneered the use of methylene linkedtris(amidophosphine) as ligands for homo- and heterobimetallic base metal com-plexes. Highlighting their successes with these ligands is a dicobalt complex capa-ble of catalytic silyation of dinitrogen.892.1 HPtBu22.1 p-formaldehydeFeNH2NH2130oCFeNHNHPPFeNNM M'PPN N5.1 AScheme 5.1: Synthesis of ferrocene-linked bis(amidophosphine)Starting from 1,1’-diaminoferrocene we envisioned a reaction with ditertbutyl-phosphine and p-formaldehyde producing a novel tetradentate ligand set 5.1. RNH–CH2–PR2 linkages can be formed by a condensation reaction between a primaryamine and a dialkylphosphinomethanol,330 which can be generated from secondaryphosphines and p-formaldehyde. Using this methodology we developed a melt pro-cedure for the synthesis of compound 5.1 depicted in Scheme 5.1. Upon toluene ex-114traction and precipitation from pentane, an orange semi-solid was isolated. Charac-terization by 1H NMR spectroscopy and elemental analysis confirmed the identityas the desired bis(aminophosphine), compound 5.1. With the bis(aminophosphine)now available, we anticipate that a variety of bimetallic compounds of the form Ain Scheme 5.1 can be synthesized and evaluated as catalysts for dinitrogen func-tionalization.FeNHNHPP5.1i) 2.2 nBuLi tolueneii) FeBr2(THF)20.5 (Fe(Mes)2)2FeNNFePP5.2FeNNM M'PPBM'X2FeNNM M'PPN NAKC8N2XXScheme 5.2: Installing multiple metals in the ferrocene-linkedbis(amidophosphine)After succesfully synthesizing the neutral form of the methylene-linked ligand,we turned our attention to installing base metals into the donor pockets. Takingcues from the Lu group, we decided to install the first metal center by a deprotona-tion / salt metathesis route, shown in Scheme 5.2 (top). We began by deprotonat-ing compound 5.1 with nBuLi; monitoring the reaction by 1H NMR we observedthe disapearence of the N–H resonance after 1 hour. Removing the volatiles, andwashing with pentane afforded a red powder, which was immediately redissolved115in THF and treated with FeBr2(THF)2 resulting in a dark red solution. After allow-ing the salt metathesis reaction to proceed for 16 hours, the paramagnetic complex5.2 was isolated as dark red needles. Unfortunately this compound persistentlycrystallizes with a fine needle morphology, which is not suitable for X-ray diffrac-tion. However, using elemental analysis we were able to confirm that the needleshave the expected empirical formula C28H48N2P2Fe2. The1H NMR spectrum of5.2 displays 5 signals, which are assigned as 1 very broad methylene resonance,2 Cp resonances, and 2 tert-butyl resonances based on integration, see Figure 5.1.Inequivalency in the tert-butyl resonances is inconsistent with a C2v symmetricstructure like the one shown in Scheme 5.2 and led to uncertainty in our assign-ment.To support our characterization we investigated an alternative synthetic routeto compound 5.2. A protonolysis reaction between 5.1 and Fe2Mes4 (Mes = 2,4,6-trimethylphenyl) was examined. Treatment of 5.1 with Fe2Mes4 results in an im-mediate color change to a dark red solution and after 4 hours the volatiles wereremoved in vacuo yielding a dark red powder. This powder displayed a similar setof 5 signals as was previously observed for the material obtained by salt metathesis.Crude spectra for both syntheses of compound 5.2 are shown in Figure 5.1.The convergence of the salt metathesis and protonolysis reactions to a singleproduct, strongly supports the identity of those products being compound 5.2. Forcomparison, the Lu lab does not attempt to isolate the ”metalloligand”, rather asecond metal is added in situ, which improves the crystallinity. Considerable ef-forts are still required to uncover the potential of this ligand set, including instal-lation of a second metal, proving that 5.1 is a suitable pro-ligand for constructionof bimetallic complexes of the type [fc(NCH2PiPr2)2]FeMXn. Additionally, us-116*****0 -20 -40 -60 -80204060Figure 5.1: 1H NMR (400 MHz) spectra of compound 5.2 in C6D6 fromprotonolysis reaction between 5.1 and Fe2Mes4 (top) salt metathesis reac-tion between 5.1, nBuLi and FeBr2(THF)2 (middle) and after recrystallization(bottom). The peaks attributed to 5.2 are indicated with a *ing a different base metal for the initial protonolysis with compound 5.1 such asCo(py)2(CH2SiMe3)2 could offer access to a new set of bimetallic combinations.Following synthesis and isolation of bimetallic compounds, reduction under ni-trogen could offer insight into the effect of different electronic configurations ondinitrogen coordination complexes.5.2.2 More Ligands Based on 1,1’-diaminoferroceneThe 1,1’-diaminoferrocene scaffold has been employed by the Arnold and Dia-conescu groups in dianionic bidentate ligands bearing silane and arene substituentsas a means to tune the electronic and steric environments.131–134,136,220 However,117ligands synthesized from this backbone with higher denticities (1.50 and 5.1) arerare. For example, the bis(salen) ligand developed by Arnold and coworkers331demonstrates a tetradentate ligand environment with group 4 metals. These salencomplexes have application in catalytic ring-opening polymerization of lactones,as reported by Diaconescu and coworkers. Interestingly, the authors showed thatsubstrate selectivity was oxidation state dependent with regards to the ferrocenescaffold.214 The ligands synthesized in this thesis were designed in pursuit of poly-metallic systems, but many other ligands based on the 1,1’diaminoferrocene scaf-fold have intriguing potential. We will now present a variety of ligand designs thatoffer promising reactivity potential.FeNH2NH2FeNHNHMe2SiClMe2SiClFeNNMe2SiSiMe2P PhCl SiCl2i) 2  nBuLiii)i) PhPH2   4 nBuLiFeNH2NH2AFeNNi) PhPH22 CH2OP Phii) nBuLiBii) MCl2Miii) MCl2MScheme 5.3: Proposed synthesis of novel cyclic ligands with 1,1’diaminofer-rocene backbonesAs discussed in Chapter 1, the tridentate amidophosphine, [NPN]Si, has al-lowed us to uncover unprecedented reactivity in tantalum complexes. By replacingthe N-Ph groups of [NPN]Si with the Cp rings of 1,1’-diaminoferrocene, a macro-cyclic [NPN] ligand (A in Scheme 5.3) can be envisioned. This macrocyclic de-118sign, which has a small internal binding pocket would likely coordinate faciallyto large transition metals like tantalum, similar to the coordination geometry ob-served in [NPN]SiTaMe3, the precursor to the side-on-end-on dinitrogen complex,compound 2.2. An even smaller macrocycle (B in Scheme 5.3) could be accessedby employing a simple CH2 linker. This smaller macrocycle would further reducethe steric projection of the ligand, allowing for more unencumbered dimerization.A proposed synthesis of each ligand set is shown in Scheme 5.3 based on previoussynthetic reports from our group144 and others.332The Meyer group uses pyrazole backbones for tethering two coordination pock-ets, which are typically polydentate ligands that have been previously reported tosupport monometallic complexes. These pyrazole-tethered ligands have been co-ordinated to a variety of transition metals including a diruthenium water oxidationcatalyst.85 Building from this idea we suggest the 1,1’diaminoferrocene backbonecould serve a similar role as the pyrazole backbone. For example, establishedligands like [NPN]Si, α-diimines, bisiminopyridine, aminopyridines could be teth-ered producing ligands A - D in Scheme 5.4. These ligands would be well suitedfor bimetallic coordination and potentially allow for detailed study of multimetallictransformations in situ. In addition, having two metal centers in close proximetycould allow for novel activation modes for dinitrogen and other small molecules.This concept of using 1,1’diaminoferrocene backbone to tether previously estab-lished ligands is currently being explored by members of our group.5.2.3 Future Work with Iron CompoundsAfter discovering compound 3.2, we imagined a wide array of small moleculesthat could be activated by the two Fe(II) centers. We intended to systematically119FeN N ArABCFeNMe2SiPSiMe2NArPhMNMe2SiPSiMe2N ArPhMFeN NNArMNNN ArMNNArMMDFeN NPR2MNNPR2MScheme 5.4: Ligands designed for bimetallic coordination with 1,1’-diaminoferrocene backbones based on previously established ligands.study reactions between compound 3.2 and various small molecules, oxidants andreductants, but unfortunately most reactions led to inconclusive results. For exam-ple, a systematic study of different oxidation reactions similar to the reaction of3.2 with diiodoethane was undertaken to see the effects of adding elemental oxy-gen, sulfur, as well as one electron oxidants like silver(I) and ferrocinium salts. Inall cases compound 3.2 undergoes a reaction but crystalline material could not beisolated from the reaction, and the paramagnetic nature of the product(s) precludesstructural characterization by NMR spectroscopy. Paramagnetic 1H NMR spectraare particularly difficult to analyze in this case because the putative Fe(III) formedin these reaction typically displays line broadening that is 10-1000 times widerthan Fe(II).333 In addition to the oxidants mentioned, activation of P4, NO and CS2120appeared promising but the reaction mixtures failed to yield crystalline material.Employing 3.2 as a metalloligand we exposed compound 3.2 to additionalequivalents of FeBr2(THF)2 in an effort to synthesize compound A (Scheme 5.5),which led to the observation of an unusual reaction. The results of this reactionlooked initially promising based on the 1H NMR spectrum containing 5 peaks,consistent with C2v symmetric coordination of [fc(NPiPr2)2]2−. Single crystalssuitable for X-ray diffraction were isolated in low yields ( ≤ 10 %) and, to oursurprise, the solid state molecular structure reveals a compound with 10 new ironcenters (5.3 in Scheme 5.5); multiple views of the solid state molecular structureare shown in Figure A.6. Along with the iron centers there are 16 bromide ligands(all but two are bridging) and two oxide ligands. Balancing the charges all ironcenters remain Fe(II), however, the source of the µ–oxo ligands is troubling. Hy-pothesizing that adventitious water was causing the formal elimination of HBr weattempted to increase the yield of this reaction by adding stoichiometric amountsof water to the solvent; the presence of water proved ineffective. Characterizationof this compound beyond X-ray crystallographic analysis is difficult. TraditionalC,H,N elemental analysis is consistent with the the expected empirical formulaC44H72Br16Fe14N4O2P4, however the solution molecular structure can not be con-firmed by this route as the 1H NMR spectrum is broad and very symmetric. Itis easy to imagine various cluster formulations that would give rise to similar 1HNMR spectra. We attempted to characterize this cluster using mass spectrometry,however, no parent ions were detected. Reassuringly, this synthesis is reproducible,and additional trials afforded crystals with unit cell parameters consistent with 5.3.To date, characterization of 5.3 and associated byproducts necessary for mass bal-ance remains elusive.121FeNNPPFeFeNNPPFe3.2FeNNPPFe FeBrBrFeNNFe FeBrPPFeFeBrBrOFe BrBr BrOFeBr BrBr BrOFe FeNNFeFeBrPPFeFeBrBrOFeBrBrBr5.3AScheme 5.5: Formation of an FeBr2 clusterIn 5.3, the bis(phosphinoamide)ferrocene ligand appears to cap a FeBr2 clusterwhich resembles an ionic lattice of FeBr2. The striking symmetry of this clusteris illustrated with multiple views of the solid state molecular structure shown inAppendix A. As emphasized in Chapter 1, polyiron complexes are found as activesites in nitrogenase as well as all-iron compounds capable of cleaving the N-Nbond of dinitrogen. In the context of N2 reduction, the existence of compound5.3 is intriguing due to the large number of metal centers. Controlled synthesisand potential for homogenous catalysis remain unanswered questions, however,the number of coordination sites and reducing equivalents is enticing.1225.3 Final ConclusionsThis dissertation is the result of countless hours spent coaxing compounds intocrystallization and staring at very broad NMR spectra. As outlined in Chapter 1,iron is a versatile metal, with economic and environmental benefits, but using itcomes with a host of issues, the most noticeable being the intense reliance on crys-tallography, which impedes rapid progress. The phosphinoamide functional groupplays a feature role in this dissertation. While unlinked phosphinoamides have beenused to form polyiron complexes in the Thomas lab,115 which form iron imidos, thesusceptibility for the N–P units to undergo redox or bond forming transformationsprecluded diverse reactivity at the metal center. We attribute this non-innocenceto the coordination mode of the phosphinoamide, specifically, the η1-N bindingresulting in a dissociated phosphine. Phosphinoamide ligands are intriguing fortheir simplicity and wide array of coordination modes. However, as we have seenrepeatedly they are often non-innocent, especially when exposed to oxidants andelectrophiles. Harnessing the cooperative activation illustrated in section 4.3 couldresult in cooperative catalysis, analagous to the ruthenium tris(phosphinoamine)system developed by the Stephan group.128 Alternatively, modifications to the lig-and arms of compound 1.50, as detailed in section 5.2, could alleviate these prob-lems and allow for the study of polymetallic systems unimpeded by ligand coop-erativity. Construction of trimetallic systems based on the methylene-linked ami-dophosphine 5.1 show promise, and as a linear M-M-M-N-N unit has never beensynthesized there is potential for a highly activated N2 unit.89123Chapter 6Experimental Details6.1 General Procedures6.1.1 Laboratory Equipment and ProceduresUnless otherwise noted all procedures were performed using standard Schlenktechnique or inside a glovebox (MBraun) equipped with a freezer (-40 °C) underan atmosphere of dry dinitrogen using oven-dried (200 °C) glassware and cooledunder dynamic vacuum. A ”bomb”, as referenced in the experimental proceduresbelow, is a thick-walled glass reactor fitted with a Kontes needle valve.6.1.2 SolventsAnhydrous hexanes, toluene, diethyl ether and tetrahydrofuran were purchasedfrom Aldrich, sparged with dinitrogen and dried further by passage through towerscontaining activated alumina and molecular sieves. Pentane and Hexamethyldis-iloxane (HMDSO) were refluxed over sodium benzophenone ketal, distilled un-der positive N2 pressure and degassed via several freeze-pump-thaw cycles. C6D6was stirred over sodium benzophenone ketal, vacuum transferred and freeze-pump-124thaw degassed; toluene-d8, THF-d8 and and pyridine-d5 were stirred over activatedmolecular sieves and freeze-pump-thaw degassed. Gaseous reagents (H2, D2, CO2,CO) were dried by passage through a trap containing activated molecular sievesprior to use.6.1.3 Starting MaterialsParaformaldehyde, tolNNtol, PhNNPh and nBuLi (1.6 M in hexanes) were pur-chased from commercial suppliers and used as received. KH was purchased fromAldrich, placed on a glass frit, washed with anhydrous pentane under dinitrogenand dried in vacuo. NiBr2 was purchased from Aldrich, oven-dried and cooledunder dynamic vacuum. DMAP and ICH2CH2I were purchased from Aldrich andrecrystallized from diethyl ether/hexane and diethyl ether respectively. PhCHOand PhCN were purchased from Aldrich, fractionaly distilled and stored over ac-tivated molecular sieves. FeBr2(THF)2 was preparred by Soxhlet extraction ofFeBr2 with anhydrous THF under dinitrogen and recrystallized from the THF so-lution. tBu2PH was prepared by reducing tBu2PCl with lithium aluminum hydrideand fractional distillation of the reaction mixture. [P(CH2SiMe2NPh)2]TaMe3,145fc(NHPiPr2)2,137 CoCl2py4,28 ArNHPiPr2,109 KC8,334 and 1,1’-diaminoferrocene130were prepared according to literature methods.6.1.4 Instrumentation and Methods of Analysis1H, 13C and 31P NMR spectra were recorded on a Bruker Avance 300 or 400 MHzspectrometer. 1H and 13C NMR chemical shifts were referenced to residual sol-vents signals from the deuterated solvents. 31P NMR chemical shifts were refer-enced to external samples of phosphoric acid (85 % in aqueous solution) at δ = 0125ppm.Elemental analyses (EA) determinations were performed using a Carlo ErbaElemental Analyzer 1108, and were performed in the Department of Chemistry atthe University of British Columbia by Mr. Derek Smith.Suitable single crystals were selected in a glovebox, coated in STP motor oiland mounted on a glass loop. Single crystal X-ray data sets were collected on aBruker DUO Apex II diffractometer with graphite-monochromated Mo Kα radia-tion (λ = 0.71073 A˚) at a temperature of 90 K. Data were collected and integratedusing the Bruker SAINT software package.335 Absorption corrections were per-formed using the multiscan technique (SADABS).336 The structures were solvedby direct methods and refined using all reflections with the SHELX-2013337 pro-gram package. All non-hydrogen atoms were refined anisotropically. All structureswere solved and refined using the WinGX (version 1.80.05)338 or Olex2 (version1.2.5)339 software packages. Crystallographic tables containing unit cell and re-finement information are located in Appendix A.Powder X-ray diffraction experiments were performed on a Bruker Apex IIdiffractometer with Cu Kα radiation (λ = 1.54184 A˚) using an area detector. Pow-der samples were packed in a borosilicate glass capillary (0.7 mm diameter, fromCharles Supper Company) under nitrogen and then flame sealed. Two measure-ments were taken on the sample, centering the X-ray beam on two different posi-tions of the capillary to ensure reproducibility.57Fe Mo¨ssbauer spectra were recorded using a W.E.B. Research Mo¨ssbauerspectroscopy system at room temperature. A 57Co (in rhodium matrix) source witha strength of 25 mCi was used. The detector was a Reuters-Stokes Kr/CO2 propor-tional counter. The sample powders were loaded in a high-density polyethylene flat126washer, wrapped in parafilm and secured with Kapton tape. The sample chamberwas evacuated to -28 ”Hg and back filled to -25 ”Hg with He. The velocity wasscanned between 4 and −4 mms−1 using a constant acceleration triangle wave-form, and calibrated against a Fe foil measured at 295 K in zero magnetic field.All isomer shifts (δ ) are relative to Fe foil. Fitting of the data was performed usingWMOSS software, which is available free of charge at http://wmoss.org/.Magnetic susceptibility data were acquired in the solid state using a QuantumDesigns MPMS5 SQUID magnetometer for VT measurements, or Mk 1 JohnsonMatthey magnetic susceptibility balance at room temperature. Magnetic momentsin solution were obtained using Evans NMR method.244,245GC-MS analysis of head space gases was performed on a Agilent Technologies5975B instrument. The ionization was done by electron impact at 1494 EMV. TheColumn used was a HP5MS - 5 % phenyl methyl siloxane. The program was asfollows: 3 minutes at 50 °C ramp at 10 °C/min to 180 °C, hold at 180 °C for 5 min.The elution time for head space gases was 1.9 min. A image of the apparatus usedis provided in Figure F.16.1.5 Computational Details for Chapter 3DFT Calculations were carried out using the Gaussian 09162 package. Calculationswere performed at the BP86 level of theory,247,248 using triple- -potential (TZP)basis sets and effective core potentials on Fe and Co. Calculation of NBOs,340NLMOs,341 and Mayer Bond Order was performed using NBO 6.0.253 Images oforbitals were generated using NBOPro6,253 as well as Chemcraft.3421276.2 Synthesis of Compounds6.2.1 Complexes Pertaining to Chapter 2PhP(CH2SiMe2NPh)2Ta(µ-O)(µ-H)Ta(κ-o-C-C6H4-NSiMe2CH2)PhP(CH2Si-Me2NPh) (2.4)A pale yellow solution of [NPN]TaMe3 (600 mg, 0.908 mmol) in Et2O (50 ml)was transferred into a thick-wall glass vessel equipped with a Teflon valve andthoroughly degassed via three freeze-pump-thaw cycles. The vessel was immersedin liquid dinitrogen, filled with H2 gas and sealed under atmospheric pressure. Thereaction mixture was allowed to warm to room temperature, while the pressureinside the vessel slowly rose to approximately four atmospheres. After stirringat room temperature overnight, a deep purple solution of ([NPN]Ta)2(µ-H)4 (2.1)was obtained. The vessel was cooled in liquid nitrogen, the headspace evaporatedand the solution thoroughly degassed at -78°C. The vessel was immersed in liq-uid dinitrogen and carbon monoxide (10 mL, 0.409 mmol, 0.9 eq) condensed intothe vessel from a calibrated glass bulb. Note that exposure to dinitrogen has to beavoided during this procedure, due to the N2-sensitivity of 2.1. The vessel was thensealed under static vacuum and the reaction mixture slowly warmed to room tem-perature. Within 30 min the purple solution turned brown-orange. After stirringfor another 15 min, all volatiles were removed in vacuum. Hexamethyldisiloxane(approx. 10 mL) was added to the tacky residue, resulting in the precipitation ofthe product as a brown powder, which was filtered off, rinsed with hexamethyl-disiloxane (2 x 2 ml) and dried in vacuum. Yield: 310 mg, 0.249 mmol, 61%.31P{1H} NMR (δ in ppm, C6D6 293 K, 162 MHz) 20.2 (s), 12.1 (s); 1H NMR (δin ppm, C6D6 293 K, 400 MHz) 7.93 (m, 2H), 7.74 (m, 2H), 7.31 (m, 4H), 7.05128(m, 8H), 6.85 (m, 4H), 6.72 (m, 3H), 6.59 (t, 1H, J = 7.2 Hz), 6.47 (d, 2H, J = 7.3Hz), 6.34 (dd, 1H, J = 5.3Hz, 7.8Hz), 6.04 (t, 1H, J = 7.3Hz), 5.48 (app t, 1H, J =5.8Hz), 4.98 (d, 1H, J = 6.5 Hz), 1.57 (m, 5H), 1.27 (m, 1H), 1.06 (m, 1H), 0.81(m, 1H), 0.45 (s, 3H), 0.41 (s, 3H), 0.35 (s, 3H), 0.08 (s, 3H), -0.07 (s, 3H), -0.10(s, 3H), -0.20 (s, 3H), -0.29 (s, 3H); 13C{1H} NMR (δ in ppm, C6D6 293 K, 101MHz) 163.5 (d, 2JCP = 12.7 Hz), 160.8 (d, 2JCP = 8.62 Hz), 156.4 (d, 3JCP = 7.27Hz), 155.2 (d, 3JCP = 5.61 Hz), 154.8 (d, 3JCP = 6.31 Hz) 138.24 (d, 1JCP = 28.12Hz), 136.5 (d, 1JCP = 27.58 Hz), 133.8 (d, 3JCP = 13.63 Hz) 131.8 (d, 3JCP = 11.50Hz) 130.4 (s), 129.1 (s), 129.0 (s), 129.0 (s), 128.7 (s), 128.6 (s), 127.6 (s), 127.3(s), 127.2 (s), 127.1 (s), 126.0 (s), 125.3 (s), 122.6 (s), 122.2 (s), 121.5 (s), 107.2(s), 98.1 (s), 19.5 (d, 2JCP = 3.64 Hz), 17.7 (s), 14.8 (s), 13.9 (s), 5.21 (s), 3.56 (d,3JCP = 4.42 Hz), 3.03 (s), 2.49 (d, 3JCP = 7.07 Hz), 2.38 (s), 2.09 (s), 1.12 (d, 3JCP= 10.6 Hz) 0.53 (d, 3JCP = 5.69 Hz). MS (EI) m/z (%) 1246 (100%) [M+]. Anal.Calcd. for C48H62N4O1P2Si4Ta2: C, 46.22; H, 5.01; N, 4.49. Found: C, 46.17; H,5.24; N, 4.33Reaction of 13CO with (PhP(CH2SiMe2NPh)2Ta)2(µ−H)4A pale yellow solution of [NPN]TaMe3 (53 mg, 0.0401 mmol) in C6D6 (5 ml) wastransferred into a thick-wall glass vessel equipped with a Teflon valve and thor-oughly degassed via three freeze-pump-thaw cycles. The vessel was immersed inliquid dinitrogen, filled with H2 gas and sealed under atmospheric pressure. The re-action mixture was allowed to warm to room temperature, while the pressure insidethe vessel slowly rose to approximately four atmospheres. After stirring at roomtemperature overnight, a deep purple solution of [([NPN]Ta)2(µ-H)4 (2.1) was ob-tained. After removing the over-pressure of hydrogen the solution was cannulatransferred to an NMR tube equipped with a Teflon valve and the tube was filled129with C6D6 ( 3 mL) until 1 mL of headspace remained. The NMR tube was im-mersed in liquid nitrogen and the volatiles were removed under high vacuum. 13CO(1 mL, 0.409 mmol) was condensed into the NMR tube from a break seal flask. TheNMR tube was sealed and allowed to warm to room temperature. Within 30 minthe solution had turned brown-orange, indicative that the reaction was complete.The reaction mixture was characterized by NMR spectroscopy. 31P{1H} NMR (δin ppm, C6D6 293 K, 162 MHz) 20.2 (s), 12.1 (s);1H NMR (δ in ppm, C6D6 293K, 400 MHz) 7.93 (m, 2H), 7.74 (m, 2H), 7.31 (m, 4H), 7.05 (m, 8H), 6.85 (m,4H), 6.72 (m, 3H), 6.59 (t, 1H, J = 7.2 Hz), 6.47 (d, 2H, 7.3 Hz), 6.34 (dd, 1H, J= 5.3Hz, 7.8Hz), 6.04 (t, 1H, J = 7.3Hz), 5.48 (app t, 1H, J = 5.8Hz), 4.98 (d, 1H,J = 6.5 Hz), 1.57 (m, 5H), 1.27 (m, 1H), 1.06 (m, 1H), 0.81 (m, 1H), 0.45 (s, 3H),0.41 (s, 3H), 0.35 (s, 3H), 0.08 (s, 3H), -0.07 (s, 3H), -0.10 (s, 3H), -0.20 (s, 3H),-0.29 (s, 3H); 13C{1H} NMR (δ in ppm, C6D6 293 K, 101 MHz) 133.8 (d, 3JCP= 13.63 Hz), 131.8 (d, 3JCP = 11.50 Hz), 130.4 (s), 129.1 (s), 129.0 (s), 129.0 (s),128.7 (s), 128.6 (s), 127.6 (s), 127.3 (s), 127.2 (s), 127.1 (s), 126.0 (s), 125.3 (s),122.6 (s), 122.2 (s), 121.5 (s), 17.7 (s), 14.8 (s), 13.9 (s), 5.21 (s), 3.56 (d, 3JCP =4.42 Hz), 3.03 (s), 2.49 (d, 3JCP = 7.07 Hz), 2.38 (s), 2.09 (s), ), 1.12 (d, 3JCP =10.6 Hz) 0.53 (d, 3JCP = 5.69 Hz), -4.26 (s).[PhP(CH2SiMe2NPh)2Ta(µ−H)]2(µ−OCH2O) (2.5)A solution of [PhP(CH2SiMe2NPh)2Ta]2(µ−H)4 (2.1) in Et2O (50 ml) was pre-pared from [PhP(CH2SiMe2NPh)2]TaMe3 (600 mg, 0.908 mmol) and thoroughlydegassed. Subsequently, the thick-wall glass vessel was immersed in liquid dini-trogen and carbon dioxide (10 mL, 0.409 mmol, 0.9 eq) condensed in from a cali-brated glass bulb. The vessel was sealed under static vacuum and warmed to roomtemperature. A brown solution was obtained after stirring at room temperature for1301 h. The solvent was evaporated to afford a brown residue, which was recrystal-lized from a minimum amount of pentane (approx. 10 ml) at -40°C. The productwas collected on a sintered glass frit, washed with cold pentane (2 x 1 ml) anddried under vacuum. Yield: 345 mg, 0.22 mmol, 60%. 1H NMR (C6D6, 400 MHz): δ 0.12 (s, 12H, SiCH3), 0.15 (s, 12H, SiCH3), 1.18 (m, 8H, SiCH2P), 6.11 (s,2H, OCH2O), 6.81 (t,2JH,P = 4.8 Hz, 2H, TaH2Ta), 6.89 (d,3JH,H =7.4 Hz, 8H, o-NPh), 6.96 (t, 3JH,H = 7.3 Hz, 4H, p-NPh), 7.03 - 7.14 (m, 6H, m-PPh and p-PPh),7.18 (t, 3JH,H = 7.6 Hz, 8H, m-N-Ph), 7.74 (m, 4H, o-PPh). 1H{31P}NMR (C6D6),selected peaks only: 1.18 (m, 8H, SiCH2P), 6.81 (s, 2H, TaH2Ta), 7.74 (d,3JH,H= 7.0 Hz, 4H, o-PPh). 31P{1H} NMR (C6D6, 161 MHz): δ 13.1 (s). 13C APTNMR (C6D6, 101 MHz): δ 2.4 (s, SiCH3), 16.2 (s, SiCH2P), 110.6 (s, OCH2O),122.7, 128.4, 129.7, 130.2, 132.4 and 132.7 (o-, m- and p-Ph carbons), 138.9 (d,1JC,P = 25 Hz, ipso-PPh carbon), 153.9 (s, ipso-NPh carbon). MS (EI) m/z (%):1278 (100%) [M]+. Elemental Anal.: Calcd. for C49H64N4O2P2Si4Ta2: C 46.01;H 5.20 N 4.38. Found: C 45.36; H 5.19; N 4.20[PhP(CH2SiMe2-o-D2-NPh)2Ta(µ−D)]2(µ−OCD2O) (d12-2.5)A sample of d12-2.5 was prepared in a manner identical to that for 2.5 using D2gas. 1H NMR (C6D6, 400 MHz): δ 0.12 (s, 12H, SiCH3), 0.15 (s, 12H, SiCH3),1.18 (m, 8H, SiCH2P), 6.96 (t,3JH,H = 7.3 Hz, 4H, p-NPh), 7.03 - 7.14 (m, 6H,m-PPh and p-PPh), 7.18 (d, 3JH,H = 7.6 Hz, 8H, m-N-Ph), 7.74 (m, 4H, o-PPh).31P{1H} NMR (C6D6, 400 MHz): δ 13.1 (s). 2H NMR (Et2O, 61.4 MHz): δ 6.2(sbr, OCD2O), 6.6 - 8.0 (sbr, TaD2Ta and o-D2-NPh).[PhP(CH2SiMe2NPh)2Ta(µ−H)]2(µ−O13CH2O) (12C-2.5)A sample of 13C-2.5 was prepared in a manner identical to that for 2.5 using 13C-enriched carbon dioxide. 1H NMR (C6D6, 400 MHz), selected peaks only: δ 6.11131(d, 1JC,H = 164 Hz, 2H, OCH2O).13C{1H} NMR (C6D6, 400 MHz), selectedpeaks only: δ 110.6 (s, OCH2O), 13C NMR (gated-decoupling, C6D6, 101 MHz),selected peaks only: δ 110.6 (t, 1JC,H = 164 Hz OCH2O).6.2.2 Complexes Pertaining to Chapter 3[fc(NPiPr2)2]K2(THF)1.25 (3.1)To an oven-dried Schlenk flask was added fc(NHPiPr2)2 (2.563 g, 5.717 mmol)and KH (1.829 g, 45.74 mmol). THF (100 mL) was added via cannula resulting inan orange suspension that was stirred for 16 hours resulting in a deep red solutionwith white precipitate. The solution is filtered through Celite, to remove excessKH, and reduced to dryness in vacuo resulting in a red sticky solid. The red solidis suspended in pentane, filtered with a glass frit, washed with pentane (3 x 15 mL)and dried in vacuo. Yield: 2.93 g, 4.767 mmol, 83%. 31P{1H} NMR (δ in ppm,DMSO-d6, 293 K, 162 MHz) 70.1 (s); 1H NMR (δ in ppm, DMSO-d6, 293 K, 400MHz) 3.60 (s, 5H, THF), 3.18 (s, 4H, Cp), 2.96 (s, 4H, Cp), 1.76 (s, 5H, THF),1.29 (broad sept, 4H, J = 5.4 Hz, iPr CH), 1.01 (d, 12H, J = 5.4 Hz, iPr CH3), 0.86(d, 12H, J = 4.7 Hz, iPr CH3); 13C{1H} NMR (δ in ppm, DMSO-d6 , 293 K, 101MHz, ipso-Cp carbon not found) 66.97 (s, THF O−CH2), 58.76 (s, Cp), 56.65 (d,3JC,P = 17.17 Hz, Cp), 27.99 (d, 1JC,P = 15.31 Hz, P-CH), 25.09 (s, CH2 THF),20.14 (d, 2JC,P = 18.81 Hz, CH3), 18.59 (d,2JC,P = 10.52 Hz, CH3). Anal. Calcdfor C108H184O5N8P8Fe4K8: C, 52.76; H, 7.54; N, 4.56. Found: C, 52.64; H, 7.61;N, 4.60.([fc(NPiPr2)2]Fe)2 (3.2)To an oven-dried Schlenk flask containing K2[fc(NHPiPr2)2](THF) (2.50 g, 4.07mmol) and FeBr2(THF)2 (1.50 g,4.17 mmol) was added THF (100 mL), resulting132in a brown slurry that was allowed to stir for 12 hours. The resulting solution wasfiltered through Celite, reduced to dryness and washed with cold pentane (3 x 5mL). The resulting brown solids were isolated and further dried in vacuo. Yield:1.48 g, 1.47 mmol, 72%. 31P{1H} NMR (δ in ppm, C6D6, 293 K, 121 MHz):962.0 (s). 1H NMR (δ in ppm, C6D6, 293 K, 300 MHz) 109.51 (s), 76.95 (s),62.13 (s), 12.98 (s), -2.08 (s), -3.73 (s), -13.12 (s), -13.42 (s), -74.46 (s), -77.70(s).MS (EI) m/z (%): 1004 (14%) [M]+. Anal. Calcd for C44H72N4P4Fe4: C, 52.62;H, 7.23; N, 5.58. Found: C, 52.39; H, 7.36; N, 5.40. µeff (solution 25 °C ) 6.7 µB.µeff (solid, Gouy balance, 25°C) 6.6 µB.[fc(NPiPr2)2]Fe(DMAP)2 (3.3)Synthesis A: To an oven-dried Schlenk flask containing ([fc(NPiPr2)2]Fe)2 (0.452g, 0.45 mmol) and 4-dimethylaminopyridine (0.220 g, 1.80 mmol) was added Et2O(50 mL) via cannula at room temperature. After stirring for 16 hours, the volatileswere removed in vacuo and the resulting solids were suspended in Et2O (10 mL)and filtered to give yellow powder. Yield: 0.430 g, 0.576 mmol, 64%. 1H NMR(δ in ppm, C6D6, 293 K, 300 MHz): 57.82 (s), 31.76 (s), 15.90 (s), 12.13 (s), 0.44(s), -1.34 (s), -26.91 (s), -56.99 (s). Anal. Calcd for C36H56N6P2Fe2: C, 57.92; H,7.56; N, 11.26. Found: C, 57.61; H, 7.52; N, 11.28. µeff (solution 25°C) 4.9 µB.µeff (solid, Gouy balance, 25°C) 5.1 µB.Synthesis B: To an oven-dried Schlenk flask containing K2[fc(NPiPr2)2](THF)(0.100 g, 0.167 mmol), FeBr2(THF)2 (0.060 g, 0.167 mmol) and 4-dimethylamino-pyridine (0.040 g, 0.327 mmol) was added THF (25 mL) via cannula at room tem-perature. After 16 hours, the volatiles were removed in vacuo and the resultingorange-red solids were extracted with toluene (15 mL), filtered through Celite andreduced to dryness. The resulting orange-yellow solids were suspended in Et2O (5133mL), filtered, and dried in vacuo resulting in a fine yellow powder. Yield: 0.088 g,0.117 mmol, 71%.([fc(NPiPr2)2]Co)2 (3.4)To an oven-dried Schlenk flask containing K2[fc(NPiPr2)2] (0.200 g, 0.335 mmol)and CoCl2(py)4 (0.152 g, 0.341 mmol) was added pentane (50 mL) via cannula.The resulting slurry was allowed to stir at room temperature for 16 hours at whichpoint the resulting dark brown solids were filtered away from the light orange su-pernatant and dried in vacuo. Due to solubility and stability issues, the resultingKCl cannot be separated from the product therefore all calculations are based ona molecular formula including four equivalents of KCl and the characterization isall performed in the solid state. Yield: 82%. Very small quantities of X-ray qualitycrystals can be obtained by performing the reaction in saturated toluene, withoutstiring and decanting the supernatant away from the crystals which grow on theside of the vial. To confirm that the solid state molecular structure is representativeof the bulk powder isolated; a PXRD analysis was performed. MS (EI) m/z (%):1010.2081 (100%) [M]+. Anal. Calcd for C44H72N4P4Fe2Co2K4Cl4: C, 40.38; H,5.55; N, 4.28. Found: C, 40.15; H, 5.34; N, 3.97. µeff (solid, Gouy balance, 25°C)2.7 µB.fc(NPiPr2−N(PiPr2) (3.7)To an oven-dried Schlenk flask containing H2[fc(NPiPr2)2] (0.050 g, 0.11 mmol)and KH (0.030 g, 0.75 mmol) was added THF (5 mL) and the solution was allowedto stir for 16 hours. The solution was filtered through Celite into an oven driedSchlenk flask containing NiBr2 (29 mg, 0.13 mmol) suspended in THF (1 mL)and allowed to stir for 2 hours, turning the red solution dark brown. The volatileswere removed in vacuo and the resulting solids were extracted with toluene (3 x1341 mL). The toluene solutions were combined, reduced to 2 mL, and cooled to -40°C, resulting in crystallisation of the product. The toluene solution was decantedfor successive crystallization and the black crystals were dried in vacuo. Yield: 43mg, 86% . 31P{1H} NMR (δ in ppm, C6D6, 293 K, 162 MHz): 69.2 (d, 2JP,P =40.7 Hz, PA), 68.1 (d, 2JP,P = 40.7 Hz, PB); 1H NMR (δ in ppm, C6D6, 293 K, 400MHz): 4.03 (m, 2H, fcC−H), 4.00 (m, 4H, fcC−H), 3.70 (m, 2H, fcC−H), 2.50(sept, 2H, 3JH,H = 7.0 Hz, iPr C-HA), 1.89 (sept, 2H, 3JH,H = 6.9 Hz, iPr C-HB),1.33 (dd, 6H, 3JH,P = 15.0 Hz, 3JH,H = 7.1 Hz iPr CH3A), 1.26 (dd, 6H,3JH,P = 15.5Hz, 3JH,H = 7.2 Hz iPr CH3A), 1.12 (dd, 6H,3JH,P = 17.0 Hz, 3JH,H = 7.4 Hz iPrCH3B), 0.78 (dd, 6H,3JH,P = 11.5 Hz, 3JH,H = 7.0 Hz iPr CH3B);13C APT NMR(δ in ppm, C6D6, 101 MHz): δ , 106.31 (d, 2JC,P = 13.4 Hz, ipso cp), 91.66 (d,2JC,P = 6.0 Hz,ipso cp), 69.20 (s, cp ), 67.89 (d, 3JC,P = 6.7 Hz, cp), 66.71 (s, cp),66.52 (s, cp), 28.85 (dd, J = 77.8, 9.7 Hz, CH or CH3), 27.04 (d, J = 20.4 Hz, CHor CH3), 22.18 (d, J = 24.9 Hz, CH or CH3), 18.28 (t, J = 3.2 Hz, CH or CH3),17.94 (dd, J = 5.3, 3.2 Hz, CH or CH3), 17.77 (d, J = 12.2 Hz, CH or CH3). Anal.Calcd for C22H36FeN2P2: C, 59.20; H, 8.13; N, 6.28. Found: C, 58.91; H, 8.11;N, 5.96.K[ArNPiPr2] (3.10)To an oven-dried Schlenk flask containing ArNHPiPr2 (Ar = 3,5-dimethylphenyl)(0.500 g, 2.11 mmol) and KH (0.210 g, 5.24 mmol) was added THF (50 mL),resulting in a colorless solution, and allowed to stir at room temperature. After16 hours, the excess KH was filtered off through a Celite plug, and the volatileswere removed in vacuo yielding a white solid. The white solids were suspended inbenzene (20 mL) and stirred for 30 min yielding a white suspension. Filtration ofthis suspension yields a crystalline white powder. Yield: 0.520 g, 90%. 31P{1H}135NMR (δ in ppm, THF-d8, 293 K, 162 MHz) 56.2 (s); 1H NMR (δ in ppm, THF-d8, 293 K, 400 MHz) 6.21 (s, 2H, o-Ar), 5.54 (s, 1H, p-Ar), 1.95 (s, 6H, Ar-CH3),1.47 (sept, 3JH,H = 7.0 Hz, 2H, iPr-CH), 0.94 (dd, 3JH,H = 7.0 Hz,3JH,P = 10.3 Hz,12H, iPr-CH3). 13C APT NMR (δ in ppm, THF-d8, 101 MHz, ipso-Ar carbon notfound) 137.60 (s, Ar C-CH3), 116.87 (s, o/pAr C-H), 116.69 (s, o/pAr C-H), 29.03(d, 1JC,P = 16.2 Hz, iPr CH), 27.17 (s, Ar CH3), 20.50 (d, 2JC,P = 21.3 Hz, iPrCH3), 18.90 (d, 2JC,P = 9.84 Hz, iPr CH3). Anal. Calcd for C14H23KNP: C, 61.50;H, 8.42; N, 5.09. Found: C, 61.22; H, 8.65; N, 4.75.([ArNPiPr2]Ni(PiPr2))2 (3.11)To a slurry of NiBr2 (20 mg, 0.092 mmol) in THF (2 mL) was added dropwisea solution of K[ArNPiPr2] (Ar = 3,5-dimethylphenyl) (0.050 g, 0.182 mmol) inTHF (2 mL) and the solution was allowed to stir at room temperature for 2 hours.The solution was reduced to dryness and the red/orange residue was extracted withpentane (2 x 3 mL) and filtered through Celite yielding an intense orange solution.This solution was concentrated to (∼1 mL) and cooled to -40°C resulting in theformation of dark red crystals. Yield (0.018 g, 46 %). 31P{1H} NMR (δ in ppm,C6D6, 293 K, 162 MHz) 68.8 (d,2JP,P = 44.8 Hz ), 29.9 (d, 2JP,P = 44.8 Hz ); 1HNMR (δ in ppm, C6D6, 293 K, 400 MHz) 6.71 (s, 2H, o-Ar), 6.42 (s, 1H, p-Ar),2.10 (s, 6H, Ar-CH3), 1.47 (sept, 3JH,H = 7.0 Hz, 2H, iPr-CH), 1.29 (sept, 3JH,H =7.0 Hz, 2H, iPr-CH), 0.99 (dd, 3JH,H = 7.0 Hz,3JH,P = 9.8 Hz, 12H, iPr-CH3) 0.96(dd, 3JH,H = 7.0 Hz,3JH,P = 10.7 Hz, 12H, iPr-CH3).6.2.3 Complexes Pertaining to Chapter 4((C5H4NPiPr2)Fe(CO)2)2 (4.1)To an oven dried bomb was added a solution of ([fc(NPiPr2)2]Fe)2 (0.100 g, 0.0996136mmol) in toluene (5 mL). The solution was degassed via 3 freeze-pump-thaw cy-cles and then exposed to 1 atm of CO at 77 K. The flask was allowed to warm toroom temperature without stirring for 14 days resulting in the formation of darkred crystals. Yield 0.006 g, 0.01 mmol, 5%.fc(NPiPr2)2Fe(CO)fc(NPiPr2)2Fe (4.2)To an oven dried bomb was added a solution of ([fc(NPiPr2)2]Fe)2 (0.100 g, 0.0996mmol) in toluene (5 mL). The solution was degassed via 3 freeze-pump-thaw cy-cles and then exposed to CO (2.4 mL, 0.1 mmol) at 77 K. The flask was allowed towarm to room temperature with stirring for 16 hours. The volatiles were removedin vacuo and the resulting solids were extracted with a 3:1 hexanes:toluene mixture(4 mL) filtered through Celite and recrystallized at -40 °C, resulting in dark browncrystals. Yield 0.085 g, 0.083 mmol, 83%. 1H NMR (δ in ppm, C6D6, 293 K, 400MHz) 51.86 (s), 29.23 (s) 28.73 (s), 27.16 (s), 24.23 (s), 23.38 (s), 22.39 (s), 20.19(s), 17.30 (s), 14.89 (s), 13.33 (s), 10.08 (s), 1.04 (s), -0.24 (s), -2.81 (s), -5.60 (s),-8.40 (s), -12.16 (s), -13.30 (s), -20.22 (s), -33.88 (s), -61.15 (s), -75.86 (s). Anal.Calcd for C45H72Fe4N4OP4: C, 52.35; H, 7.03; N, 5.43. Found: C, 51.98; H, 6.85;N, 5.71. µCO = 1880cm−1. µe f f = 5.3 µB.fc(NPiPr2I)2FeI2 (4.3)To an oven-dried Schlenk flask was added ([fc(NPiPr2)2]Fe)2 (0.100 g, 0.0996mmol) and toluene (5 mL). A solution of ICH2CH2I (0.118 g, 0.419 mmol) intoluene (5 mL) was added dropwise and the resulting solution was allowed to stirfor 16 h. The volatiles were removed in vacuo and the resulting solids were re-crystallized from a 50/50 mixture of toluene and hexanes resulting in dark redcrystalline solids, which were dried in vacuo. Yield 0.112 g, 55.7 %. 1H NMR (δin ppm, C6D6, 293 K, 400 MHz) 18.36 (s), 4.74 (s), 3.19 (s), 0.88 (s), -9.33 (s).137Anal. Calcd for C29H44Fe2I4N2P2: C, 31.61; H, 4.02; N, 2.54. Found: C, 31.94;H, 4.12; N, 2.50. µeff (solution 25 °C ) 5.4 µB.[(fc(NPiPr2)2Fe)2][K(THF)6] (4.4)To an oven-dried Schlenk flask was added ([fc(NPiPr2)2]Fe)2 (0.100 g, 0.0996mmol) and toluene (5 mL) and chilled to -30 °C. In a separate Schlenk flask KC8was suspended in toluene (5 mL) and chilled to -30 °C. The ([fc(NPiPr2)2]Fe)2solution was cannula transferred to the KC8 slurry and allowed to warm to roomtemperature with stirring for 6 h. The resulting slurry is filtered through Celite andand the volatiles were removed in vacuo leaving a black residue. The residue wasdissolved in a minimal amount of THF, layered with hexanes and cooled to -35 °Cresulting in the formation of black crystals which were filtered and dried in vacuo.Yield: 0.094 g, 0.064 mmol, 64%. 1H NMR (δ in ppm, C6D6, 293 K, 400 MHz)188.42 (s), 36.80 (s), 34.10 (s), 25.32 (s), 15.14 (s), 12.08 (s), 11.51 (s), -2.75 (s),-17.86 (s), -29.72 (s). Anal. Calcd for C68H120Fe4KN4O6P4: C, 55.33; H, 8.19; N,3.80. Found: C, 55.11; H, 7.82 ; N, 3.98. µeff (solution 25 °C ) 7.8 µB.fc(NPiPr2NPh)2Fe (4.5)An oven dried bomb was loaded with (Fe[fc(NPiPr2)2])2 (0.100 g, 0.0996 mmol),PhNNPh (0.020 g, 0.110 mmol) and toluene (10 mL). The bomb was sealed, re-moved from the glovebox and irradiated with UV-light (350 nm) for 20 hours. Thesolution was then filtered, removing minimal solids, and reduced in vacuo to 1 mL.Pentane (1 mL) was added and the solution was cooled to -40 °C resulting in for-mation of an orange powder. Yield: 0.057 g, 0.083 mmol, 83 %. 1H NMR (δ inppm, C6D6, 293 K, 400 MHz) 98.3 (s), 30.2 (s), 28.9 (s), 8.0 (s), 0.32 (s), -0.6 (s),-10.7 (s), -13.6 (s). Anal. Calcd for C68H120Fe4KN4O6P4: C, 55.33; H, 8.19; N,3.80. Found: C, 54.98 ; H, 8.36 ; N, 4.11. µeff (solution 25 °C ) 2.9 µB.138fc(NPiPr2Ntol)2Fe (4.6)An oven dried NMR tube was loaded with (Fe[fc(NPiPr2)2])2(0.010 g, 0.0099 mmol), tolNNtol (0.004 g, 0.019 mmol) and toluene (10 mL). TheNMR tube was sealed, removed from the glovebox and irradiated with UV-light(350 nm) for 20 hours. The solution was then filtered, removing minimal solids.1H NMR (δ in ppm, C6D6, 293 K, 400 MHz) 98.9 (s), 30.1 (s), 28.3 (s), 25.9 (s),8.1 (s), 0.6 (s), -0.51 (s), -13.4 (s).((fc(NPiPr2)(NPiPr2CO2))Fe)2 (4.7)To an oven dried bomb was delivered a solution of ([fc(NPiPr2)2]Fe)2 (0.061 g,0.0607 mmol) in THF (∼ 10 mL). The solution was degassed via 3 freeze-pump-thaw cycles and CO2 (3 mL, 0.12 mmol) was delivered at 77 K. The solution wasallowed to warm to room temperature and stirred for 4 hours. The resulting yellowsolution was reduced in vacuo and the resulting yellow-brown solids were recrys-talized from toluene (∼ 1 mL) at -40 °C. Yield: 0.047 g, 0.0430 mmol, 64 %. 1HNMR (δ in ppm, C6D6, 293 K, 400 MHz) 90.2 (s), 72.3 (s), 47.3 (s), 34.3 (s), 24.1(s), 16.0 (s), 11.1 (s), 9.8 (s), -2.8 (s), -23.2 (s), -27.2 (s), -30.6 (s), -36.5 (s), -41.9(s), -84.1 (s). Anal. Calcd for C46H72Fe4N4O4P4 • C22H38FeN2P2 C, 53.01; H,7.20; N, 5.45. Found: C, 53.33 ; H, 7.46 ; N, 5.02. µeff (solution 25 °C ) 5.9 µB.(fc(NPiPr2CHPhO)2Fe)2 (4.8)To an oven-dried vial containing ([fc(NPiPr2)2]Fe)2 (100 mg, 0.0996 mmol) andtoluene (2 mL) was added benzaldehyde (40 mg, 0.38 mmol), resulting in an or-ange solution that was allowed to stir for 30 min. The solution was reduced todryness in vacuo resulting in an orange-yellow solid. The orange-yellow solid wasdissolved in minimal hexanes, and the solution was filtered through Celite. Theorange filtrate was allowed to recrystallize at -40 °C, resulting in the formation ofa yellow solid, which was filtered through a glass frit and dried in vaccuo. Yield:13969 mg, 0.048 mmol, 48% yield. 1H NMR (δ in ppm, C6D6, 293 K, 400 MHz) 94.6(s), 68.1 (s), 35.3 (s), 34.1 (s), 18.6 (s), 15.7 (s), 13.4 (s), 12.6 (s), 10.6 (s), 10.1 (s),2.8 (s), -6.6 (s), -7.1 (s), -21.1 (s), -29.4 (s), -32.8 (s), -39.4 (s), -43.9 (s), -82.0 (s).Anal. Calcd for C72H96Fe4N4O4P4: C, 60.52; H, 6.77; N, 3.92 Found: C, 60.04 ;H, 6.56 ; N, 4.11. µeff (solution 25 °C ) 5.8 µB.(fc(NPiPr2)(NPiPr2CPhN))Fefc(NPiPr2)2Fe (4.9)To an oven-dried 50 mL round bottom flask containing ([fc(NPiPr2)2]Fe)2 (200mg, 0.199 mmol) and toluene (2 mL) was added benzonitrile (20 mg, 0.19 mmol),resulting in a dark purple solution that was allowed to stir for 30 min. The solutionwas reduced to dryness in vacuo, resulting in a black solid. The black solid wassuspended in hexane, filtered through a glass frit, washed with hexane (3 x 2 mL)and dried in vacuo, resulting in a red powder. Yield 145 mg, 0.131 mmol, 69%yield. 1H NMR (δ in ppm, d8-THF, 293 K, 300 MHz) 18.99 (s), 18.52 (s), 18.06(s), 17.57 (s), -3.40 (s). -4.54 (s), -34.24 (s). Anal. Calcd for C51H77Fe4N5P4: C,55.31; H, 7.01; N, 6.32 Found: C, 55.11 ; H, 6.81 ; N, 6.87. µeff (solution 25 °C )6.4 µB.6.2.4 Complexes Pertaining to Chapter 5fc(NHCH2PtBu2)2 (5.1)To an oven-dried Schlenk flask containing fcNH2 (2.9 g, 0.013 mol) and p-CH2O( 0.80 g, 0.027 mol) was added tBu2PH (5.0 mL, 3.9 g, 0.027 mol). The flask washeated to 110 °C under a dinitrogen atmosphere for 2.5 h until the formation ofwater vapor had stopped. The resulting orange-brown solids were extracted withtoluene filtered through Celite, and the resulting solution was cooled to -40 °C,forming a waxy orange solid. Yield 4.01 g, 0.0076 mmol, 58.5% yield. 31P{1H}140NMR (δ in ppm, d8-toluene, 293 K, 162 MHz) 28.3 (s); 1H NMR (δ in ppm, d8-toluene, 293 K, 400 MHz) 3.94 (s, 4H), 3.89 (s, 4H), 3.18 (d, 4H, 2JHP = 5.9 Hz),2.42 (broad s, 2H), 1.17 (d, 36 H, 3JHP = 10.9 Hz); 13C{1H} NMR (δ in ppm,d8-toluene, 293 K, 101 MHz) 112.4 (d, 3JCP = 13.5 Hz), 63.4 (s), 56.1 (s), 42.2 (d,1JCP = 14.8 Hz), 31.2 (d, 1JCP = 21.0 Hz), 29.9 (d, 2JCP = 13.3 Hz) Anal. Calcd.for C28H50FeN2P2: C, 63.15; H, 9.46; N, 5.26. Found: C, 63.21; H, 9.49; N, 5.22.fc(NCH2PtBu2)2Fe (5.2)Synthesis A: To a solution of fc(NCH2PtBu2)2 (0.25g, 0.47 mmol) in ether (15mL) was added 1.6 M nBuLi in hexanes (0.57 mL, 0.91 mmol) at -78 °C. Thesolution was allowed to warm to room temperature over 3 h. This solution wasadded dropwise to an oven dried Schlenk containing FeBr2(THF)2 (0.16 g, 0.44mmol) suspended in THF (5 mL). The reaction was allowed to stir for 16 h atwhich point the volatiles were removed in vacuo. The resulting red solids wereextracted with hexanes, filtered through Celite and recrystallized from hexanes at-40 °C affording red needle-shaped crystals. Yield 0.088 g, 0.15 mmol, 32% yield.1H NMR (δ in ppm, C6D6, 293 K, 400 MHz) 53.1 (s), 16.8 (s), -5.7 (s), -14.9 (s),-66.1 (s). Anal. Calcd. for C28H48N2P2Fe2: C 57.36; H, 8.25; N, 4.78. Found: C,57.55, 8.31, 4.44.Synthesis B: To an oven dried Schlenk containing fc(NCH2PtBu2)2 (0.050 g, 0.094mmol) in toluene (5 mL) was added dropwise a solution of Fe2Mes2 (0.027 g,0.045 mmol) in toluene (5 mL). The resulting red solution was allowed to stir atroom temperature for 2.5 h. The solution was reduced to dryness in vacuo and theresulting solids were recrystallized from hexanes. Yield 0.026 g, 0.044 mmol, 47%yield.141Bibliography(1) Chirik, P. J.; Wieghardt, K. Science 2010, 327, 794.(2) Chirik, P. J. In Catalysis without Precious Metals; Wiley-VCH VerlagGmbH & Co. KGaA: 2010, pp 83–110.(3) Chirik, P. J. Acc. Chem. 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Silyl-methyl and ligand N,P-phenyl-ringcarbons (except ipso positions) have been omitted for clarity. Selected bondlengths (A˚, rounded to two decimal places) and angles (°, rounded to integervalues): Ta1-Ta1′ 2.57; Ta1-N1 2.08; Ta1-N2 2.09; Ta1-P1 2.56; Ta-H rang-ing from 1.87 to 1.92; N1-Ta1-N2 113; H-Ta-H (cis) 61 to 64; H-Ta-H (trans)91 to 94; P1-Ta1-Ta1-P1 180; H1-H1-H2-H2 0.161Fe1N1P1C1Figure A.2: ORTEP diagram of 1.50 with ellipsoids drawn at 50% probabil-ity. All H atoms have been omitted for clarity. elected bond lengths (A˚) andangles (deg): C1-N1 1.4021(4); N1-P1 1.7130(3). Cp plane angle = 0° due toinversion center at Fe1Fe1K1O1N1N2P1P2K2Figure A.3: ORTEP diagram of 3.1 with ellipsoids drawn at 50% probability.All H atoms, iPr methyl groups and carbons from the THF molecules havebeen omitted for clarity. The figure represents 1/3 of the asymmetric unit withan extra Cp ring shown to illustrate connectivity. Refinement not complete.162Fe1Fe2N1N2P1O1P2O2Fe3Fe4O4C12Figure A.4: ORTEP diagram of 4.8 with ellipsoids drawn at 50% probability.All H atoms and iPr methyl groups have been omitted for clarity. Selectedbond lengths (A˚) and angles (deg): Fe1-Fe2 4.0122(11); Fe2-Fe3 3.3087(11);N1-P1 1.607(4); N2-P2 1.618(4); P1-C12 1.857(5); Fe2-N1 2.239(4); Fe2-N2 2.108(4); Fe2-O1 1.987(4); Fe2-O2 2.132(4); Fe3-O2 2.040(3); Fe2-O32.077(3); Fe3-O3 2.177(4); P1-C12-O1 105.7(4); N1-Fe2-O1 81.13(15); O2-Fe2-N1 170.87(14); O2-Fe2-O1 91.90(14); Fe2-O2-Fe3 104.92(15); Fe2-O3-Fe3 102.09(14).163Fe1Fe2N1N2P1P2P4N4N3P3Fe3Fe4N5C12Figure A.5: ORTEP diagram of 4.9 with ellipsoids drawn at 50% probability.All H atoms and iPr methyl groups have been omitted for clarity. Selectedbond lengths (A˚) and angles (deg): Fe1-Fe2 3.4980(14); Fe2-Fe3 2.8932(13);Fe3-Fe4 3.7358(14); N1-P1 1.600(5); N2-P2 1.656(5); N3-P3 1.682(5); N4-P4 1.656(5); Fe2-N1 2.017(5); Fe2-N2 1.935(5); Fe2-P4 2.4187(19); Fe2-N5 2.008(5); Fe3-N3 1.972(5); Fe3-N4 2.021(5); Fe3-P2 2.5703(19); Fe3-N52.011(5); Fe2-N5-Fe3 92.1(2); N1-Fe2-N2 112.7(2); N1-Fe2-N5 87.6(2); N2-Fe2-P4 109.56(14); N3-Fe3-N4 112.0(2); N3-Fe3-N5 122.8(2); N3-Fe3-P2120.85(6).164Figure A.6: ORTEP plot (30% thermal ellipsoids) of 5.3 All H atoms and iPrmethyl groups have been omitted for clarity.165Table A.1: Crystal data and refinement details for 2.5Compound 2.5empirical formula C49H64N4O2P2Si4Ta2formula weight 1277.24crystal size [mm] 0.18 x 0.16 x 0.10crystal system monoclinicspace group C2/c (No. 15)a [A˚] 22.1884(16)b [A˚] 11.7359(9)c [A˚] 25.096(2)α [°] 90β [°] 97.377(2)γ [°] 90V [A˚3] 6480.9(9)ρ [g cm3] 1.309Z 4F(000) 2356µ [mm−1] 3.531 (Mo-Kα)Tmin/Tmax 0.431/0.702hkl range -22 – 26, ±13, ± 29θ range [°] 1.64 – 25.02meassured refl. 21114unique refl. 5695refined parameters 285completeness to θ [%] 99.9goodness-of-fit 0.966R1, wR2 (I > 2σ(I)) 0.0519, 0.1245R1, wR2 (all data) 0.0737, 0.1328res. el. dens. [e- A˚3] 4.172/-1.544166Table A.2: Crystal data and refinement details for 1.50 and 3.1Compound 1.50 3.1empirical formula C22H38FeN2P2 C26H36FeK2N2OP2formula weight 448.34 588.58crystal size [mm] 0.44 x 0.20 x 0.18 0.17 x 0.16 x 0.08crystal system monoclinic triclinicspace group C2/c (No. 15) P−1 (No. 2)a [A˚] 18.063(5) 16.608(4)b [A˚] 14.407(4) 16.689(3)c [A˚] 10.848(3) 19.732(2)α [°] 90.00 112.329(11)β [°] 122.754(5) 106.485(3)γ [°] 90.00 106.206(4)V [A˚3] 2374.0(12) 5147.9(11)ρ [g cm3] 1.254 1.138Z 4 8F(000) 960 1846µ [mm−1] 0.779 (Mo-Kα) 0.789 (Mo-Kα)Tmin/Tmax 0.3763 / 0.7452 0.6120 / 0.7460hkl range ± 21, ± 17, ± 12 ± 23, -23 – 25, ± 27θ range [°] 1.95 – 25.10 1.242 – 30.149meassured refl. 14339 27690unique refl. 1858 27690refined parameters 132 848completeness to θ [%] 98.6 91.1goodness-of-fit 1.091 1.024R1, wR2 (I > 2σ(I)) 0.0737, 0.2029 0.1165, 0.2644R1, wR2 (all data) 0.0786, 0.2084 0.1452, 0.2771res. el. dens. [e- A˚3] 1.586/-0.891 3.3284/-2.43167Table A.3: Crystal data and refinement details for 3.2 and 3.3Compound 3.2 3.3empirical formula C22H36Fe2N2P2 C36H56Fe2N6P2formula weight 502.17 746.51crystal size [mm] 0.22 x 0.20 x 0.14 0.14 x 0.10 x 0.05crystal system monoclinic monoclinicspace group P21/n (No. 14) C2/c (No. 15)a [A˚] 10.3912(8) 21.5781(11)b [A˚] 12.2273(10) 10.6543(5)c [A˚] 19.1171(15) 17.4825(8)α [°] 90.00 90.00β [°] 96.112(2) 112.2320(10)γ [°] 90.00 90.00V [A˚3] 2415.1(3) 3720.4(3)ρ [g cm3] 1.381 1.333Z 4 4F(000) 1056 1584µ [mm−1] 1.344 (Mo-Kα) 0.900 (Mo-Kα)Tmin/Tmax 0.6139 / 0.7456 0.6633 / 0.7459hkl range -12 – 13, -15 – 10, ± 24 ± 29, ± 14, ± 24θ range [°] 1.98 – 27.59 2.04 – 29.45meassured refl. 21051 19671unique refl. 5580 5155refined parameters 253 215completeness to θ [%] 99.6 99.5goodness-of-fit 1.026 1.023R1, wR2 (I > 2σ(I)) 0.0237, 0.0599 0.0348, 0.0785R1, wR2 (all data) 0.0292, 0.0634 0.0568, 0.0872res. el. dens. [e- A˚3] 0.521 / -0.266 0.710 / -0.313168Table A.4: Crystal data and refinement details for 3.4 and 3.7Compound 3.4 3.7empirical formula C22H36CoFeN2P2 C22H36FeN2P2formula weight 505.25 446.32crystal size [mm] 0.10 x 0.08 x 0.07 0.25 x 0.11 x 0.05crystal system monoclinic monoclinicspace group P21/n (No. 14) P21 (No. 4)a [A˚] 9.969(5) 9.745(2)b [A˚] 12.244(5) 10.920(3)c [A˚] 19.170(5) 10.448(3)α [°] 90.00 90.00β [°] 98.468(5) 91.151(5)γ [°] 90.00 90.00V [A˚3] 2314.4(16) 1111.7(5)ρ [g cm3] 1.450 1.333Z 4 2F(000) 1060 476µ [mm−1] 1.492 (Mo-Kα) 0.832 (Mo-Kα)Tmin/Tmax 0.6585 / 0.7456 0.6435 / 0.7453hkl range ± 12, ± 15 , ± 24 -11 – 12, ± 13, ± 12θ range [°] 1.98 – 27.52 1.95 – 26.14meassured refl. 18977 15384unique refl. 5307 4391refined parameters 253 252completeness to θ [%] 99.5 99.5goodness-of-fit 1.014 1.065R1, wR2 (I > 2σ(I)) 0.0354, 0.0674 0.0338, 0.0807R1, wR2 (all data) 0.0601, 0.0751 0.0373, 0.0824res. el. dens. [e- A˚3] 0.618 / -0.359 0.776 / -0.321169Table A.5: Crystal data and refinement details for 3.11 and 4.1Compound 3.11 4.1empirical formula C20H37NNiP2, 0.5(C5H12) C26H36Fe2N2O4P2formula weight 444.19 614.21crystal size [mm] 0.31 x 0.09 x 0.06 0.10 x 0.10 x 0.05crystal system monoclinic monoclinicspace group P21/n (No. 14) C2/c (No. 15)a [A˚] 15.919(5) 23.955(5)b [A˚] 8.787(3) 11.231(4)c [A˚] 17.620(6) 9.830(4)α [°] 90.00 90.00β [°] 97.814(8) 90.664(5)γ [°] 90.00 90.00V [A˚3] 2441.9(14) 2644.5(19)ρ [g cm3] 1.208 1.543Z 4 4F(000) 956 1280µ [mm−1] 0.933 (Mo-Kα) 1.254 (Mo-Kα)Tmin/Tmax 0.761/0.946 0.6617/0.7460hkl range ± 19, ± 10, -21 – 19 ± 33, ± 15, ± 13θ range [°] 1.854 – 26.234 1.700 – 30.026meassured refl. 18629 27810unique refl. 4872 3855refined parameters 243 163completeness to θ [%] 99.1 99.8goodness-of-fit 1.028 1.045R1, wR2 (I > 2σ(I)) 0.0411, 0.0912 0.0228, 0.0592R1, wR2 (all data) 0.0663, 0.1014 0.0269, 0.0610res. el. dens. [e- A˚3] 0.840/-0.510 0.486/-0.267170Table A.6: Crystal data and refinement details for 4.2 and 4.3Compound 4.2 4.3empirical formula C45H72Fe4N4OP4 0.5(C29H44Fe2I4N2P2)formula weight 1032.34 550.95crystal size [mm] 0.18 x 0.15 x 0.12 0.06 x 0.06 x 0.02crystal system triclinic monoclinicspace group P−1 (No. 2) Cc (No. 9)a [A˚] 13.920(3) 14.8284(13)b [A˚] 14.903(7) 17.0000(15)c [A˚] 16.3381(11) 14.5439(13)α [°] 109.772(4) 90β [°] 101.935(4) 90.654(2)γ [°] 106.720(5) 90V [A˚3] 2884.3(17) 3666.0(6)ρ [g cm3] 1.189 1.996Z 2 8F(000) 1084 2104µ [mm−1] 1.128 (Mo-Kα) 4.268 (Mo-Kα)Tmin/Tmax 0.6980/0.7458 0.6284/0.7453hkl range ± 18, ± 20, ± 22 -18 – 10, ± 20, ± 17θ range [°] 1.751 – 28.729 1.822 – 26.099meassured refl. 56376 26127unique refl. 14822 6304refined parameters 548 302completeness to θ [%] 99.2 99.8goodness-of-fit 1.007 1.136R1, wR2 (I > 2σ(I)) 0.0317, 0.0719 0.0243, 0.0572R1, wR2 (all data) 0.0534, 0.0811 0.0252, 0.0575res. el. dens. [e- A˚3] 0.443/-0.443 0.564/-0.507171Table A.7: Crystal data and refinement details for 4.4 and 4.5Compound 4.4 4.5empirical formula C68H120Fe4KN4O6P4 C34H46Fe2N4P2formula weight 1475.24 684.39crystal size [mm] 0.23 x 0.05 x 0.05 0.12 x 0.11 x 0.08crystal system monoclinic monoclinicspace group P21/c (No. 14) P21/n (No. 14)a [A˚] 14.292(3) 13.6777(7)b [A˚] 21.153(5) 13.5134(6)c [A˚] 24.731(6) 17.7979(8)α [°] 90 90β [°] 91.213(5) 94.0140(10)γ [°] 90 90V [A˚3] 7475(3) 3281.6(3)ρ [g cm3] 1.311 1.385Z 4 4F(000) 3145 1440µ [mm−1] 0.951 (Mo-Kα) 1.011 (Mo-Kα)Tmin/Tmax 0.6530/0.7456 0.6760/0.7456hkl range -18 – 17, -26 – 27, ± 32 ± 17, ± 17, ± -23 – 15θ range [°] 1.720 – 27.548 1.818 – 27.503meassured refl. 68997 30760unique refl. 17128 7523refined parameters 792 563completeness to θ [%] 99.5 99.9goodness-of-fit 0.985 1.022R1, wR2 (I > 2σ(I)) 0.0482, 0.0958 0.0279, 0.0638R1, wR2 (all data) 0.0917, 0.1123 0.0372, 0.0675res. el. dens. [e- A˚3] 0.980/-1.005 0.421/-0.236172Table A.8: Crystal data and refinement details for 4.7 and 4.8Compound 4.7 4.8empirical formula C34H55N3P3Fe2.5 C73.5H99.5Fe4N4O4P4formula weight 770.34 1450.85crystal size [mm] 0.29 x 0.18 x 0.08 0.24 x 0.11 x 0.07crystal system Monoclinic Triclinicspace group C2/c (No. 15) P−1 (No. 2)a [A˚] 18.292(3) 13.1417(11)b [A˚] 28.392(4) 23.350(2)c [A˚] 18.367(4) 27.418(2)α [°] 90 88.065(2)β [°] 116.591(2) 76.473(2)γ [°] 90 81.651(3)V [A˚3] 8530(2) 8093.3(12)ρ [g cm3] 1.200 1.191Z 8 4F(000) 3248 3060µ [mm−1] 0.985 (Mo-Kα) 0.826 (Mo-Kα)Tmin/Tmax 0.6054/0.7452 0.6368/0.7452hkl range -21 – 22, -34 – 20, -22 – 20 ± 15, ± 27, ± 32θ range [°] 1.490 – 25.390 1.166 – 25.159meassured refl. 22830 103776unique refl. 7774 28748refined parameters 418 1633completeness to θ [%] 99.1 99.0goodness-of-fit 1.163 0.981R1, wR2 (I > 2σ(I)) 0.0584, 0.1569 0.0645, 0.1259R1, wR2 (all data) 0.0895, 0.1740 0.1384, 0.1516res. el. dens. [e- A˚3] 1.134/-0.584 0.666/-0.479173Table A.9: Crystal data and refinement details for 4.9Compound 4.9empirical formula C57H91Fe4N5P4formula weight 1193.62crystal size [mm] 0.18 x 0.11 x 0.07crystal system monoclinicspace group P21/c (No. 14))a [A˚] 14.1719(3)b [A˚] 31.7623(6)c [A˚] 13.7659(3)α [°] 90β [°] 110.7260(10)γ [°] 90V [A˚3] 5791.7(2)ρ [g cm3] 1.369Z 4F(000) 2528µ [mm−1] 9.225 (Cu-Kα)Tmin/Tmax 0.4185/0.7530hkl range ± 16, ± 37, -15 – 16θ range [°] 2.782 – 67.860meassured refl. 43002unique refl. 10186refined parameters 649completeness to θ [%] 97.2goodness-of-fit 1.007R1, wR2 (I > 2σ(I)) 0.0722, 0.1731R1, wR2 (all data) 0.1239, 0.2045res. el. dens. [e- A˚3] 0.948/-0.858174Appendix BComputational AppendixTable B.1 Optimized xyz coordinated for 3.2C -3.69183100 -3.04030900 3.61032100H -4.43243700 -3.63115700 3.04283000C -3.76036400 -3.44043100 5.09624600H -3.66095200 -4.52693500 5.24577400H -4.72679500 -3.13343900 5.53263300H -2.96350700 -2.94465700 5.67778200C -4.00660600 -1.54569500 3.43233300H -3.90886100 -1.22990800 2.38124300H -3.32081200 -0.92358600 4.03254200H -5.03605200 -1.32183200 3.76285900Fe -1.10130300 -1.57670500 0.52167400Fe -3.52181300 -3.08340100 -1.54606500P -1.96076900 -3.40926900 2.91340300P 1.04009300 -0.91509700 1.48280100N 1.46852000 0.71745700 1.17848500N -2.05902400 -3.08290000 1.21595000C -4.93221900 -4.34630400 -0.77496800H -5.97120500 -4.39475800 -1.09676900C 2.46372900 1.35023000 1.96680900C 1.02704500 -1.22659100 3.34458900H 0.58351800 -2.24026900 3.37963600C -2.97589500 -3.71423100 0.34859200175C 3.89670200 1.12201300 1.95155400H 4.41763200 0.43471500 1.28821900C 4.50212400 1.96443900 2.94669200H 5.56602800 2.02912200 3.16878700C -1.88690200 -5.30495000 3.12753900H -1.76998800 -5.38885100 4.22589100C -4.40487000 -3.48797700 0.24945400H -4.97125100 -2.77156600 0.83999000C -3.11505700 -6.13148600 2.70829600H -4.03902700 -5.79085000 3.20095400H -2.96755200 -7.19112200 2.98550900H -3.27918800 -6.09156500 1.62115500C -2.63734200 -4.69948300 -0.66029000H -1.63077600 -5.06114300 -0.86094100C 3.46262600 2.74652000 3.56167600H 3.60510500 3.50647400 4.32812800C 2.21467000 2.38390600 2.95119700H 1.23706400 2.81076700 3.16535900C 2.37892700 -1.24454300 4.07870600H 3.10748300 -1.92236800 3.60764400H 2.22147200 -1.60222400 5.11165100H 2.83188000 -0.24485300 4.13765200C 2.46149800 -1.99392000 0.85392500H 3.37237000 -1.67200000 1.38927400C 0.01918700 -0.28438000 4.02231200H -0.96464700 -0.32662800 3.52778300H 0.37135000 0.75752900 4.01199900H -0.12608700 -0.58654800 5.07335900C 2.64962200 -1.75550800 -0.65218600H 2.83833400 -0.69122000 -0.87532700H 1.75152300 -2.06416800 -1.21365200H 3.50702300 -2.33671100 -1.03250500C 2.18189300 -3.47457800 1.15621700H 2.17142100 -3.68594300 2.23651500H 2.95483800 -4.11417600 0.69661400H 1.20301600 -3.77707800 0.74642200C -0.59849600 -5.84730700 2.48675200H 0.29220200 -5.30623500 2.84279100H -0.63197700 -5.75437200 1.38987300H -0.46614500 -6.91613600 2.72897300176C -3.83998500 -5.09442900 -1.33754900H -3.90989500 -5.80777400 -2.15706200C 3.69183100 3.04030900 -3.61032100H 4.43243700 3.63115700 -3.04283000C 3.76036400 3.44043100 -5.09624600H 3.66095200 4.52693500 -5.24577400H 4.72679500 3.13343900 -5.53263300H 2.96350700 2.94465700 -5.67778200C 4.00660600 1.54569500 -3.43233300H 3.90886100 1.22990800 -2.38124300H 3.32081200 0.92358600 -4.03254200H 5.03605200 1.32183200 -3.76285900Fe 1.10130300 1.57670500 -0.52167400Fe 3.52181300 3.08340100 1.54606500P 1.96076900 3.40926900 -2.91340300P -1.04009300 0.91509700 -1.48280100N -1.46852000 -0.71745700 -1.17848500N 2.05902400 3.08290000 -1.21595000C 4.93221900 4.34630400 0.77496800H 5.97120500 4.39475800 1.09676900C -2.46372900 -1.35023000 -1.96680900C -1.02704500 1.22659100 -3.34458900H -0.58351800 2.24026900 -3.37963600C 2.97589500 3.71423100 -0.34859200C -3.89670200 -1.12201300 -1.95155400H -4.41763200 -0.43471500 -1.28821900C -4.50212400 -1.96443900 -2.94669200H -5.56602800 -2.02912200 -3.16878700C 1.88690200 5.30495000 -3.12753900H 1.76998800 5.38885100 -4.22589100C 4.40487000 3.48797700 -0.24945400H 4.97125100 2.77156600 -0.83999000C 3.11505700 6.13148600 -2.70829600H 4.03902700 5.79085000 -3.20095400H 2.96755200 7.19112200 -2.98550900H 3.27918800 6.09156500 -1.62115500C 2.63734200 4.69948300 0.66029000H 1.63077600 5.06114300 0.86094100C -3.46262600 -2.74652000 -3.56167600H -3.60510500 -3.50647400 -4.32812800177C -2.21467000 -2.38390600 -2.95119700H -1.23706400 -2.81076700 -3.16535900C -2.37892700 1.24454300 -4.07870600H -3.10748300 1.92236800 -3.60764400H -2.22147200 1.60222400 -5.11165100H -2.83188000 0.24485300 -4.13765200C -2.46149800 1.99392000 -0.85392500H -3.37237000 1.67200000 -1.38927400C -0.01918700 0.28438000 -4.02231200H 0.96464700 0.32662800 -3.52778300H -0.37135000 -0.75752900 -4.01199900H 0.12608700 0.58654800 -5.07335900C -2.64962200 1.75550800 0.65218600H -2.83833400 0.69122000 0.87532700H -1.75152300 2.06416800 1.21365200H -3.50702300 2.33671100 1.03250500C -2.18189300 3.47457800 -1.15621700H -2.17142100 3.68594300 -2.23651500H -2.95483800 4.11417600 -0.69661400H -1.20301600 3.77707800 -0.74642200C 0.59849600 5.84730700 -2.48675200H -0.29220200 5.30623500 -2.84279100H 0.63197700 5.75437200 -1.38987300H 0.46614500 6.91613600 -2.72897300C 3.83998500 5.09442900 1.33754900H 3.90989500 5.80777400 2.15706200178Table B.2 Optimized xyx coordinates for 3.4Co 1.19084800 1.75658600 -0.35145100Fe 3.16981200 2.88394300 1.39634600P 0.61484800 -1.06375300 1.36118100P 1.92220200 3.60908000 -3.11667800N 1.86988400 3.13178300 -1.44631300N 1.08396100 0.56378000 1.07649400C 2.07394200 1.16603600 1.86466300C 2.76536000 3.65374300 -0.50686700C 1.84929100 2.23851000 2.82256500H 0.88037500 2.68640600 3.02921300C 4.17312400 3.32184400 -0.33012700H 4.72634900 2.60411500 -0.93018000C -0.34165800 -0.32236200 3.90192500H -1.30242000 -0.27636200 3.36768800H -0.54429100 -0.65363900 4.93490400H 0.07574300 0.69438500 3.94778800C 1.83577200 -3.60619200 1.05520700H 1.72567700 -3.80903000 2.13147400H 0.91508100 -3.95275600 0.55885900H 2.68179300 -4.20899300 0.68158500C 2.07260200 -2.11780200 0.76077900H 2.94738000 -1.77022500 1.33927600C 1.98701200 -1.34797700 3.95555400H 2.69167600 -2.06031300 3.49989700H 2.47566400 -0.36448700 4.00200800H 1.81580800 -1.68175700 4.99446400C 1.93919500 5.52052000 -3.15064600H 1.93063700 5.70003600 -4.24381400C 3.14263900 6.27057400 -2.55432500H 4.10187800 5.93298700 -2.97596900H 3.05522000 7.35191500 -2.76584600H 3.19464800 6.15128600 -1.46200200C 3.10064500 2.58480600 3.42166300H 3.26024300 3.35789800 4.17136100C 0.61161300 6.06134200 -2.59396200H -0.25524000 5.58018600 -3.07376800179H 0.53351300 5.88537200 -1.50950700H 0.53404800 7.14948100 -2.76371400C 0.63230900 -1.30146700 3.22665800H 0.16785300 -2.30286800 3.30851600C 2.43156200 4.59983700 0.55040500H 1.44003500 5.01574800 0.71354500C 3.70466600 3.25298400 -3.68746800H 4.40762400 3.75995500 -3.00276100C 3.51251500 0.92356900 1.84554700H 4.01958500 0.20966600 1.20080700C 4.68979500 4.09564800 0.75725000H 5.70983900 4.06453800 1.13671300C 4.12608700 1.77058800 2.82295800H 5.19066300 1.82383800 3.04486700C 3.91350800 3.79911500 -5.11307900H 3.87028600 4.89853400 -5.15790300H 4.90038200 3.49113000 -5.50073200H 3.14929400 3.40259500 -5.80437200C 2.33450900 -1.87043000 -0.73182700H 2.46456100 -0.79664800 -0.94703400H 3.24348400 -2.40783100 -1.05396600H 1.48661700 -2.22622300 -1.33889800C 3.61464800 4.88231100 1.30264100H 3.68490800 5.54548100 2.16328800C 3.97212900 1.73942400 -3.64549600H 3.74970700 1.31028000 -2.65571500H 3.34439400 1.21105600 -4.38213500H 5.02748600 1.52392400 -3.88914500Co -1.19084800 -1.75658600 0.35145100Fe -3.16981200 -2.88394300 -1.39634600P -0.61484800 1.06375300 -1.36118100P -1.92220200 -3.60908000 3.11667800N -1.86988400 -3.13178300 1.44631300N -1.08396100 -0.56378000 -1.07649400C -2.07394200 -1.16603600 -1.86466300C -2.76536000 -3.65374300 0.50686700C -1.84929100 -2.23851000 -2.82256500H -0.88037500 -2.68640600 -3.02921300C -4.17312400 -3.32184400 0.33012700H -4.72634900 -2.60411500 0.93018000180C 0.34165800 0.32236200 -3.90192500H 1.30242000 0.27636200 -3.36768800H 0.54429100 0.65363900 -4.93490400H -0.07574300 -0.69438500 -3.94778800C -1.83577200 3.60619200 -1.05520700H -1.72567700 3.80903000 -2.13147400H -0.91508100 3.95275600 -0.55885900H -2.68179300 4.20899300 -0.68158500C -2.07260200 2.11780200 -0.76077900H -2.94738000 1.77022500 -1.33927600C -1.98701200 1.34797700 -3.95555400H -2.69167600 2.06031300 -3.49989700H -2.47566400 0.36448700 -4.00200800H -1.81580800 1.68175700 -4.99446400C -1.93919500 -5.52052000 3.15064600H -1.93063700 -5.70003600 4.24381400C -3.14263900 -6.27057400 2.55432500H -4.10187800 -5.93298700 2.97596900H -3.05522000 -7.35191500 2.76584600H -3.19464800 -6.15128600 1.46200200C -3.10064500 -2.58480600 -3.42166300H -3.26024300 -3.35789800 -4.17136100C -0.61161300 -6.06134200 2.59396200H 0.25524000 -5.58018600 3.07376800H -0.53351300 -5.88537200 1.50950700H -0.53404800 -7.14948100 2.76371400C -0.63230900 1.30146700 -3.22665800H -0.16785300 2.30286800 -3.30851600C -2.43156200 -4.59983700 -0.55040500H -1.44003500 -5.01574800 -0.71354500C -3.70466600 -3.25298400 3.68746800H -4.40762400 -3.75995500 3.00276100C -3.51251500 -0.92356900 -1.84554700H -4.01958500 -0.20966600 -1.20080700C -4.68979500 -4.09564800 -0.75725000H -5.70983900 -4.06453800 -1.13671300C -4.12608700 -1.77058800 -2.82295800H -5.19066300 -1.82383800 -3.04486700C -3.91350800 -3.79911500 5.11307900H -3.87028600 -4.89853400 5.15790300181H -4.90038200 -3.49113000 5.50073200H -3.14929400 -3.40259500 5.80437200C -2.33450900 1.87043000 0.73182700H -2.46456100 0.79664800 0.94703400H -3.24348400 2.40783100 1.05396600H -1.48661700 2.22622300 1.33889800C -3.61464800 -4.88231100 -1.30264100H -3.68490800 -5.54548100 -2.16328800C -3.97212900 -1.73942400 3.64549600H -3.74970700 -1.31028000 2.65571500H -3.34439400 -1.21105600 4.38213500H -5.02748600 -1.52392400 3.88914500Figure B.1 Overlay of solid state molecular structure (red) and calculatedgeometry (green) for 3.2182Figure B.2 Overlay of solid state molecular structure (red) and calculatedgeometry (green) for 3.4Table B.3 Comparison of calculated and experimental bond metrics for 3.2and 3.4. Bond lengths in A˚ and angles in °Complex Bond Metric Calculated ExperimentalN - Pi 1.72 1.67N - Pt 1.73 1.70Fe - Ni 1.94 1.95Fe - Nt 1.91 1.923 Fe - P 2.44 2.44Fe f c Fe 3.52 3.53Fe Fe 3.98 3.92N - Fe - N 124.8 123.5Cp Plane Angle 2.1 0.1N - Pi 1.72 1.68N - Pt 1.74 1.70Co - Ni 1.86 1.85Co - Nt 1.88 1.885 Co - P 2.18 2.16Fe f c Co 2.87 2.84Co Co 4.30 4.23N - Co - N 158.9 159.6Cp Plane Angle 8.2 6.9183Molecular Orbitals of 3.2Figure B.3 LUMOα (left) and LUMO+1α (right) for 3.2 (Isosurface value =0.02)Figure B.4 LUMOβ (left) and LUMO+1β (right) for 3.2 (Isosurface value =0.02)184Figure B.5 HOMOα to HOMO-7α for 3.2 (Isosurface value = 0.02)185Figure B.6 HOMOβ (left) and HOMO-1β (right) for 3.2 (Isosurface value =0.02)Molecular Orbitals of 3.4Figure B.7 LUMOα (left) and LUMO+1α (right) for 3.4 (Isosurface value =0.02)186Figure B.8 LUMOβ (left) and LUMO+1β (right) for 3.4 (Isosurface value =0.02)Figure B.9 HOMOα (left) and HOMO-1α (right) for 3.4 (Isosurface value =0.02)187Figure B.10 HOMOβ (left) and HOMO-1β (right) for 3.4 (Isosurface value =0.02)Figure B.11 HOMO-6α for 3.4 (Isosurface value = 0.02)188Table B.4 Second order perturbation theory analysis of 3.4Spin Donor Acceptor Energy (kcal/mol)α 86. LP ( 2)Co 1 247. LV ( 1)Fe 2 1.84β 85. LP ( 1)Co 1 246. LV ( 1)Fe 2 3.00α 88. LP ( 4)Co 1 389. 3C*( 1)Fe2-C7-C8 3.18β 87. LP ( 3)Co 1 389. 3C*( 1)Fe2-C7-C8 3.39β 88. LP ( 1)Fe 2 245. LV ( 1)Co 1 1.16α 89. LP ( 1)Fe 2 249. BD*( 1)Co 1- N 6 0.99β 88. LP ( 1)Fe 2 249. BD*( 1)Co 1- N 6 0.94α 89. LP ( 1)Fe 2 250. BD*( 1)Co 1- P 67 2.33β 88. LP ( 1)Fe 2 250. BD*( 1)Co 1- P 67 2.37α 107. BD ( 1)Co 1- N 6 247. LV ( 1)Fe 2 3.58β 105. BD ( 1)Co 1- N 6 246. LV ( 1)Fe 2 2.37α 107. BD ( 1)Co 1- N 6 389. 3C*( 1)Fe2-C7-C8 3.15β 105. BD ( 1)Co 1- N 6 389. 3C*( 1)Fe2-C7-C8 3.52α 108. BD ( 1)Co 1- P 67 247. LV ( 1)Fe 2 3.00β 106. BD ( 1)Co 1- P 67 246. LV ( 1)Fe 2 3.39189Appendix CMo¨ssbauer Appendix-4 -2 0 2 4-5.0-4.5-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.50.0Absorption (%)Velocity (mm/s)Figure C.1 Zero field 57Fe Mo¨ssbauer spectra of 1.50. See Table 3.1 forisomer shifts and quadrupole splittings.190-4 -2 0 2 4-4-3-2-101Absorption (%)velocity (mm/s)Figure C.2 Zero field 57Fe Mo¨ssbauer spectra of 3.4. δ = 0.42mm/s; ∆Eq =2.01mm/s.191Figure C.3 Zero field 57Fe Mo¨ssbauer spectra of 4.2. Fits of the four ironcenters (purple) δ = 0.45 mm/s, ∆Eq = 2.31 mm/s; (green) δ = -0.08 mm/s,∆Eq = 1.29 mm/s; (orange) δ = 0.76 mm/s, ∆Eq = 1.89 mm/s; (blue) δ = 0.45mm/s, ∆Eq = 0.66 mm/s.192Appendix DSQUID MagnetometryFigure D.1 Plot of χMT vs T for 3.4 fit with a Curie-Weiss law, C = 3.222(4)cm3 K mol−1 and Θ = -1.89(6) K.193Appendix ECyclic Voltammetry-4.000-3.500-3.000-2.500-2.000-1.500-1.000-0.5000.0000.5001.0001.500Potential (V vs fc/fc+) Figure E.1 Cyclic voltammogram of complex 3.2 (in 0.1 M [nBu4N][PF6] inTHF; scan rate = 100 mv s−1194Appendix FGas Chromatography MassSpectrometryFigure F.1 Adapter used for head space analysis195


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