Hydride transfer reactivity of tetrakis(trimethylphosphine)(hydrido)(nitrosyl)molybdenum(0)

Abstract

The tetrakis(trimethylphosphine) molybdenum nitrosyl hydrido complex trans-Mo(PMe₃)₄(H)(NO) (2) and the related deuteride complex trans-Mo(PMe₃)₄(D)(NO) (2a) were prepared from trans-Mo(PMe₃)₄(Cl)(NO) (1). From ²H T_{1 min} measurements and solid-state ²H NMR the bond ionicities of 2a could be determined and were found to be 80.0% and 75.3%, respectively, indicating a very polar Mo–D bond. The enhanced hydridicity of 2 is reflected in its very high propensity to undergo hydride transfer reactions. 2 was thus reacted with acetone, acetophenone, and benzophenone to afford the corresponding alkoxide complexes trans-Mo(NO)(PMe₃)₄(OCHR′R″) (R′ = R″ = Me (3); R′ = Me, R″ = Ph (4); R′ = R″ = Ph (5)). The reaction of 2 with CO₂ led to the formation of the formato-O-complex Mo(NO)(OCHO)(PMe₃)₄ (6). The reaction of 2 with HOSO₂CF₃ produced the anion coordinated complex Mo(NO)(PMe₃)₄(OSO₂CF₃) (7), and the reaction with [H(Et₂O)₂][BAr^F₄] with an excess of PMe₃ produced the pentakis(trimethylphosphine) coordinated compound [Mo(NO)(PMe₃)₅][BAr^F₄] (8). Imine insertions into the Mo–H bond of 2 were also accomplished. PhCHNPh (N-benzylideneaniline) and C₁₀H₇CHNPh (N-1-naphthylideneaniline) afforded the amido compounds Mo(NO)(PMe₃)₄[NR′(CH₂R″)] (R′ = R″ = Ph (9), R′ = Ph, R″ = naphthyl (11)). 9 could not be obtained in pure form, however, its structure was assigned by spectroscopic means. At room temperature 11 reacted further to lose one PMe₃ forming 12 (Mo(NO)PMe₃)₃[N(Ph)CH₂C₁₀H₆)]) with agostic stabilization. In a subsequent step oxidative addition of the agostic naphthyl C–H bond to the molybdenum centre occurred. Then hydrogen migration took place giving the chelate amine complex Mo(NO)(PMe₃)₃[NH(Ph)(CH₂C₁₀H₆)] (15). The insertion reaction of 2 with C₁₀H₇NCHPh led to formation of the agostic compound Mo(NO)(PMe₃)₃[N(CH₂Ph)(C₁₀H₇)] (10). Based on the knowledge of facile formation of agostic compounds the catalytic hydrogenation of C₁₀H₇NCHPh and PhNCHC₁₀H₇ with 2 (5 mol%) was tested. The best conversion rates were obtained in the presence of an excess of PMe₃, which were 18.4% and 100% for C₁₀H₇NCHPh and PhNCHC₁₀H₇, respectively.