Dinuclear Mn(I) Complexes with Phosphido and Hydrido Bridges: Synthesis, Reactivity, and Hydrogenative Catalysis.

A class of organomanganese hydrogenation catalysts was recently rediscovered. These are simple dinuclear Mn(I) carbonyl compounds with phosphido (PR2 - ) and hydrido (H- ) bridges. This class of compounds has been known since the 1960's, and they have rich coordination chemistry and reactivity. Given their recently discovered potential for catalytic applications, a fresh look at this class of compounds was necessary. Hence, this Review comprehensively covers the synthesis, reactivity, and catalysis of this interesting class of molecules.

Bench-Stable Dinuclear Mn(I) Catalysts in E-Selective Alkyne Semihydrogenation: A Mechanistic Investigation.

Dinuclear manganese hydride complexes of the form [Mn2 (CO)8 (µ-H)(µ-PR2 )] (R=Ph, 1; R=iPr, 2) were used in E-selective alkyne semi-hydrogenation (E-SASH) catalysis. Catalyst speciation studies revealed rich coordination chemistry and the complexes thus formed were isolated and in turn tested as catalysts; the results underscore the importance of dinuclearity in engendering the observed E-selectivity and provide insights into the nature of the active catalyst. The insertion product obtained from treating 2 with (cyclopropylethynyl)benzene contains a cis-alkenyl bridging ligand with the cyclopropyl ring being intact. Treatment of this complex with H2 affords exclusively trans-(2-cyclopropylvinyl)benzene. These results, in addition to other control experiments, indicate a non-radical mechanism for E-SASH, which is highly unusual for Mn-H catalysts. The catalytically active species are virtually inactive towards cis to trans alkene isomerization indicating that the E-selective process is intrinsic and dinuclear complexes play a critical role. A reaction mechanism is proposed accounting for the observed reactivity which is fully consistent with a kinetic analysis of the rate limiting step and is further supported by DFT computations.