Transition metal nitrosyls as nitrosylation agents. IV. 51V NMR characteristics of dinitrosyl and carbonylmononitrosyl vanadium complexes

The action of Co(X)(NO)₂]₂ (X = Cl, Br, L) on V(H)(CO)_6?nL_n] (L = 1/ndi- and tritertiary phosphine; n = 2, 3) in thf yields V(CO)_5?n(NO)L₂] and V(NO)₂(thf)₄]X as the two main products. Thf is easilty replaced by other ligands L′, leading to the complexes cis-V(NO)₂(thf)_4?nL′_n]X, where n = 1 to 4. In the case of L′= CNR (R = Cy, iPr, tBu), the species VX(NO)₂L′₃] are formed. The presence of X in the first coordination sphere is established by the normal halogen dependence (Cl < Br < I) of ⁵¹V shielding.δ(⁵¹V) values have been obtained for the two series of complexes and compared with δ of other nitrosylvanadium species, including VX(NO)L′₄]X. for V(NO)₂L′₄]br, ⁵¹V shielding increases in the sequence {O} < {S} < NR₃ < NCMe < AsEt₃ < SbEt₃ < PEt₂Ph < P(OMe)₃ < CNR, reflecting a general increase of shielding as the polarizability of the ligand function increases and its electronegativity decreases. Superimposed effects arising from electronic influences (PEtPh₂) < PMe₃ < P(OMe)₃ and steric conditions (chelate-4 ring < 7 ring < 6 ring < 5 ring) are also discussed. Steric factors are especially pronounced in the V(CO)₃(NO)Ph₂P(CH₂)_mPPh₃] series (m = 1–4). The thermo-labile parent compound, V(CO)₅NO], has been characterized by its δ(⁵¹V) = ?1489 ppm at 245 K.