UC Berkeley

Chapter 1: The syntheses of neutral (halide and aryl) and cationic vanadium bisimides are described. Characterization of the complexes by X-ray diffraction, 13C NMR, 51V NMR, and V L2,3-edge NEXFAS provide a description of the electronic structure in comparison to group 6 bisimides and the bent metallocene isolobal analogs.

Chapter 2: Under 1 atm of H2, [V(NtBu)2(PMe3)3][Al(PFTB)4], 1.10, (PFTB = perfluoro-tert-butoxide), was shown to catalytically semihydrogenate alkynes to (z)- alkenes. Synthetic and DFT studies, in combination with H2/D2 crossover and PHIP NMR experiments, indicate that H2 is activated by [1,2]-addition to 1.10 and upon the insertion of alkyne into the V-H bond of the vanadium hydrido amide A, the product alkene and 1.10 are generated by the [1,2]-α-NH-elimination of the alkenyl ligand.

Chapter 3: A series of carbon monoxide, isocyanide, and nitrile complexes of [V(PR3)2(NtBu)2][Al(PFTB)4], (R = Me, Et) were prepared. [V(PMe3)3(NtBu)2][Al(PFTB)4], (PFTB = perfluoro-tert-butoxide) reacts with 2,6- xylylisocyanide (CNXyl) or acetonitrile to afford complexes 3.1 and 3.2. Complex 3.1 was crystallographically characterized revealing a C-N bond length of (1.152(4) Å), and IR studies showed a C-N stretching frequency of 2164 cm-1. Treatment of [V(PEt3)2(NtBu)2][Al(PFTB)4] with CNXyl yielded the desired isocyanide complex in 60% yield with a C-N stretching frequency of 2156 cm-1. The desired d0 vanadium bisimido, carbonyl complex was achieved via the exposure of 1.11 to 1 atm of CO. Complex 3.4 has a C-O stretching frequency of 2015 cm-1 (CaF2 solution cell). Isotopic labeling with 13CO reveals a stretching frequency of 1970 cm-1, which confirms the assignment of the complex as a terminal η1-CO complex and which is also implied by its NMR data in comparison to the other crystallographically characterized compounds presented here. The 13C{31P}{1H} NMR spectrum of 3.4-13C reveals a broad singlet at 228.36 ppm implying deshielding of the carbonyl carbon. This datum, in conjunction with the shielded vanadium NMR shift of -843.71 ppm, suggests π back-bonding is operative in the bond between carbon monoxide and 1.11. This model was further confirmed by DFT analysis of the model complex [V(η1-CO)(PMe3)2(NtBu)2]+, 3.5, which reveals that the basis of the reduced stretching frequency in 3.4 is π back-bonding from the 2b1 and 1b2 orbitals of 1.11.