Complexes of (Arylimido)vanadium(V). Synthetic, Structural, Specroscopic, and Theoretical Studies of V(Ntol)Cl3 and Derivatives

Article abstract of DOI:10.1021/ja00258a026

The reactions of VOCl3 with various para-substituted aryl isocyanates, p-XC6H4NCO (X = CH3, CF3, OCH3, F, Cl, Br), afford the corresponding (arylimido)vanadium(V) trichloride species, V(NC6H4X)Cl3.The p-tolylimido complex, V(Ntol)Cl3, 1, displays an extensive derivative chemistry.The reaction of 1 with Lewis bases affords monoaddition products such as V(Ntol)Cl3(THF) and V(Ntol)Cl3(PPh3).The chloride ligands of 1 readily participate in nucleophilic substitution reactions, affording a range of alkoxide (V(Ntol)Cl(3-n)(O-t-Bu)n: n = 1, 2; n = 2, 3; n = 3, 4), aryloxide (V(Ntol)Cl(3-n)(OAr)n: n = 1, 5; n = 2, 6; n = 3, 7; Ar = 2,6-C6H3(CH3)2), and organometallic (V(Ntol)Cl(3-n)(CH2SiMe3)n: n = 1, 8; n = 2, 9; n = 3, 10; (η⁵-C5H5)V(Ntol)Cl2, 11) derivatives.The electronic spectra of complexes 1-10 each display an absorption in the near-IR region at ca. 1000 nm.Complexes 1-7 also display a second absorption in the visible region of the spectrum, and the energy of this absorption increases with increasing electronegativity of the basal ligand donor atoms.The 51V NMR spectra of these (arylimido)vanadium(V) complexes have been determined; 51V chemical shifts in this series span a range of 1700 ppm.The 51V chemical shifts also correlate with the electronegativity of the basal ligand donor atoms.The lowest field position is observed for 10(δ(51V) = +1048), and a regular progression of δ(51V) to higher field occurs as the purely ?-donating alkyl groups are replaced by ligands of increased elecronegativity and increased ?-donating ability.The observed correlations of the electronic and 51V NMR spectra with the chemical constitutions of complexes 1-10 are explained in terms of a dominating paramagnetic shielding contribution.Extended Hueckel calculations on several model complexes are used to provide an explanation of the electronic factors underlying the disparate 51V hemical shifts observed for complexes 1-10 and related vanadium(V) complexes bearing oxo and alkylimido ligands.An X-ray crystal structure determination reveals that complex 6 possesses a dimeric structure in the solid state.Each vanadium atom in the centrosymmetric dimer is coordinated in a trigonal-bipyramidal geometry, with a terminal tolylimido ligand and a bridging aryloxide group occupying the apical sites. There is a decided asymmetry in the V-O-V bridge bonding.Crystal data for 6: monoclinic, I2/c; a = 24.937 (5), b= 10.790 (2), c = 16.662 (3) Angstroem; β = 97.18 (2)deg; Z = 8.