Synthetic, Structural, Spectroscopic, and Theoretical Studies of Decamethylvanadocene Arylnitrenes

Article abstract of DOI:10.1021/ja00312a024

The reaction between Cp^*2V * = η-C5(CH3)5> and N3R (R = 2,6-(CH3)2C6H3, C6H5, 2-(C6H5)C6H4, and Cp^*2VN3 yields Cp^*2VNR (I, II, III, and IV, respectively).When the bulky azides, R = SiMe3, SiPh3, and CPh3, were employed in the reaction, Cp^*2VN3 was produced.Complexes I-IV are formally 19e V(IV) complexes and exhibit solution μ_eff = 1.56-1.79 μ_B consistent with the presence of one unpaired electron.These nitrene complexes display isotropic EPR spectra in solution at room temperature (g = 1.986-1.988, a_V = 4.6-9.8, a_N = 4.6-4.9 * 1E-4 cm^-1).The vanadium hyperfine splitting is ca. 1/10 that in typical V(IV) complexes, suggesting covalent V-N bonding.Crystals of I belong to the space group P1, Z = 2, a = 8.584(2) Angstroem, b = 9.607(3) Angstroem, c = 15.899(4) Angstroem, α = 93.67(3) deg, β = 95.18(3) deg, and γ = 110.17(4) deg.Of the 2989 unique reflections collected, 2541 with F_o > 2.5?(F_o) were used in the solution and refinement of the structure, R_F = 0.0642, R_wF = 0.0794, and GOF = 2.034.The structure exhibits a linear V-N-C fragment <179.7(5) deg>, short V-N bond <1.707(6) Angstroem>, and small Cp (centroid)-V-Cp (centroid) angle <135.8(3) deg>.For the model complex Cp2VN(C6H5), SCF-Xα-DV calculations show two strong V-N ? bonds in addition to the ? bond.Spin-polarized SCF-Xα-DV calculations predict an a_V/a_N ratio in close agreement with the experimental ratio.The calculated highest occupied molecular orbital is nonbonding and localized on V with an exchange splitting of 1.52 eV.Cyclic voltammograms of complexes I-IV in CH2Cl2 show quasi-reversible oxidations to 18e vanadium(V) complexes at potentials ca. 750 mV more negative than ferrocene.