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(η1-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)2H compound (6). Fe(CO)5 readily inserts
to yield the dinuclear formyl species (Me3P)3(ON)(OC)Mo(μ-OCH)Fe(CO)4 (7a), and Re2(CO)10
is transformed to the related μ-formyl complex (Me3P)3(ON)(OC)Mo(μ-OCH)Re2(CO)9 (7b)
in an equilibrium reaction lying far to the formyl side. Temperature-dependent NMR
measurements allowed us to derive equilibrium constants and ΔH = −46.5 ± 0.6 kJ/mol
and ΔS = −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.