Carbonylhydridonitrosyltris(trimethylphosphine)molybdenum(0):  An Activated Hydride Complex

The synthesis of the mer -Mo(CO)H(NO)(PMe 3 ) 3 complex 3 is described, which is obtained from Mo(CO) 4 (NO)AlCl 4 via the isolable intermediates MoCl(CO)(NO)(PMe 3 ) 3 ( 1 ) and the borohydride complex Mo(η 1 -BH 4 )(CO)(NO)(PMe 3 ) 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)(PMe 3 ) 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 CO 2 and metal carbonyl compounds. The conversion of 3 with CO 2 leads to the formato-O-complex Mo(CO)(NO)(PMe 3 ) 3 (OCHO) ( 5 ), while CO induces PMe 3 substitution with formation of the nonisolable Mo(CO) 2 (NO)(PMe 3 ) 2 H compound ( 6 ). Fe(CO) 5 readily inserts to yield the dinuclear formyl species (Me 3 P) 3 (ON)(OC)Mo(μ-OCH)Fe(CO) 4 ( 7a ), and Re 2 (CO) 10 is transformed to the related μ-formyl complex (Me 3 P) 3 (ON)(OC)Mo(μ-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 Δ H = −46.5 ± 0.6 kJ/mol and Δ 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 isolable chelate complex ( 8 ). The structures of complexes 2, 3, 4b, 7a, 7b, and 8 were studied by X-ray diffraction.