Synthesis, Characterization, and Reactivity of a (PPP) Pincer-Ligated Manganese Carbonyl Complex: Polarity Reversal Imparted by the Electrophilic Nature of a Planar Mn-P(NR) Fragment.

The bonding interactions of a synthesized pincer-ligated manganese dicarbonyl complex featuring an N-heterocyclic phosphenium (NHP) central moiety are explored. The pincer ligand [PPP]Cl was coordinated to a manganese center using Mn(CO)Br and 254 nm light to afford the chlorophosphine complex (PPP)Mn(CO)Br () as a mixture of halide exchange products and stereoisomers. The target dicarbonyl species (PPP)Mn(CO) () was prepared by treatment of with 2 equiv of the reductant KC. Computational investigations and analysis of structural parameters were used to elucidate multiple bonding interactions between the Mn center and the P atom in . The generation of a product of formal H addition, (PPP)Mn(CO)H (), was achieved through the dehydrogenation of NHBH, affording a 2:1 mixture of : stereoisomers. The nucleophilic nature of the Mn center and the electrophilic nature of the P moiety were demonstrated through hydride addition and protonation of to produce K(THF)[(PPP)Mn(CO)] () and (PPP)Mn(CO)H (), respectively. The observed reactivity suggests that is best described as a Mn/NHP complex, in contrast to pincer-ligated dicarbonyl manganese analogues typically assigned as Mn species.