Carbonylhydridonitrosyltris(trimethylphosphine)molybdenum(0): An activated hydride complex

The synthesis of the mer-Mo(CO)H(NO)(PMe3)(3) complex 3 is described, which is obtained from Mo(CO)(4)(NO)AlCl4 via the isolable intermediates MoCl(CO)(NO)(PMe3)(3) (1) and the borohydride complex Mo(eta(1)-BH4)(CO)(NO)(PMe3)(3) (2). The reactivity of 3 with respect to insertions has been probed. 3 thus reacts with benzaldehyde, benzophenone, acetophenone, and acetone to afford the corresponding alkoxide complexes Mo(CO)(NO)(PMe3)(3)(OCHR'R") (R' = H, R" = Ph (4a); R', R" = Ph (4b); R' = Me, R" = Ph (4c), and R', R" = Me (4d)). A high propensity of 3 to undergo carbonyl insertion was also manifested in its transformations with CO2 and metal carbonyl compounds. The conversion of 3 with CO2 leads to the formato-O-complex Mo(CO)(NO)(PMe3)(3)(OCHO) (5), while CO induces PMe3 substitution with formation of the nonisolable Mo(CO)(2)(NO)(PMe3)(2)H compound (6). Fe(CO)(5) readily inserts to yield the dinuclear formyl species (Me3P)(3)(ON)(OC)Mo(mu-OCH)Fe(CO)(4) (7a), and Re-2(CO)(10) is transformed to the related mu-formyl complex (Me3P)(3)(ON)(OC)Mo(mu-OCH)Re-2(CO)(9) (7b) in an equilibrium reaction lying far to the formyl side. Temperature-dependent NMR measurements allowed us to derive equilibrium constants and Delta H = -46.5 +/- 0.6 kJ/mol and Delta S = -103 +/- 2 eu. These values for 7b were approximately reproduced by accurate DFT calculations and investigated further via an incremental analysis of bond dissociation energies. Finally insertion reactions of 3 with various imines were studied. Only in the case of a bisdihydroproline ester did an insertion take place, however, across the ester carbonyl group. Concomitant elimination of a phosphine moiety was observed with formation of the I isolable chelate complex trans-Mo[OCH(OCH3)(C4H6N)](CO)(NO)(PMe3)(2) (8). The structures of complexes 2, 3, 4b, 7a, 7b, and 8 were studied by X-ray diffraction.