Synthesis and Reactivity of N‐Heterocyclic Carbene‐Phosphinidene Manganese Complexes

The reaction of manganese pentacarbonyl bromide with the N-heterocyclic carbene-phosphinidene adduct (IDipp)PSiMe₃ afforded the tetracarbonyl complex [(IDipp)PMn(CO)₄] (1) with the release of Me₃SiBr and CO (IDipp = 1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene). X-ray crystallographic analysis revealed a trigonal-bipyramidal coordination geometry with a short Mn─P bond, indicative of double bond character. CO substitution with phosphines, NHCs, and isocyanides yielded complexes [(IDipp)PMnL(CO)₃] (2-5) in which the ligands (L) occupy axial positions. Kinetic studies and DFT calculations support an associative substitution mechanism, analogous to the nitrosyl complex [Mn(NO)(CO)₄], demonstrating the ability of (NHC)P and NO ligands to modulate their electronic properties as either one- or three-electron donors. Complex 1 also underwent phosphinidene transfer and chalcogenation reactions along the manganese-phosphorus bond, resulting in metalladiphosphiranes (6, 7) and metallaphospha-chalcogeniranes (8, 9) with three-membered MnPP and MnPE (E = Se, Te) rings.