A molybdenum-95 and nitrogen-14 nuclear magnetic resonance study of six-co-ordinate hydrotris(3,5-dimethyl-1-pyrazolyl)borate complexes containing a sixteen-electron {Mo(NO)}4 core

Abstract

The mononitrosyl complexes [Mo{HB(Me₂pz)₃}(NO)XY][HB(Me₂pz)₃^–= hydrotris (3,5-dimethyl-1-pyrazolyl)borate; X = Y = F, Cl, I, OEt, OPh, SPh, or NHPh; X = Cl, Y = SPh, OPh, OEt, NHC₆H₄Br-p, NHC₆H₄Me-p, or NHEt; X = I, Y = OPh, NHC₆H₄Me-p, NHEt, or NHNMe₂] have been studied in solution by ⁹⁵Mo and ¹⁴N n.m.r. spectroscopy. The iodo complex, [Mo{HB(Me₂pz)₃}(NO)I₂], exhibits a ⁹⁵Mo resonance at δ 2 272, the most deshielded monomeric Mo^II resonance reported to date. Replacement of the iodo ligands of [Mo{HB(Me₂pz)₃}(NO)I₂] by other ligands increases the shielding of the ⁹⁵Mo nucleus according to the general trend, I^– < Cl^– < F^– < thiolato < alkoxy < amido. A chemical shift range of δ 161–2 272 was observed for the complexes studied. The complexes exhibit an inverse halogen dependence of the chemical shift. The nitrosyl ligand ¹⁴N chemical shifts follow the same shielding trend as the ⁹⁵Mo chemical shifts.