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 2 ) 2 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) 5 Br and 254 nm light to afford the chlorophosphine complex (PP Cl P)Mn(CO) 2 Br ( 2 ) as a mixture of halide exchange products and stereoisomers. The target dicarbonyl species (PPP)Mn(CO) 2 ( 3 ) was prepared by treatment of 2 with 2 equiv of the reductant KC 8 . Computational investigations and analysis of structural parameters were used to elucidate multiple bonding interactions between the Mn center and the P NHP atom in 3 . The generation of a product of formal H 2 addition, (PP H P)Mn(CO) 2 H ( 4 ), was achieved through the dehydrogenation of NH 3 BH 3 , affording a 2:1 mixture of 4 syn : 4 anti stereoisomers. The nucleophilic nature of the Mn center and the electrophilic nature of the P NHP moiety were demonstrated through hydride addition and protonation of 3 to produce K(THF) 2 [(PP H P)Mn(CO) 2 ] ( 6 ) and (PP Cl P)Mn(CO) 2 H ( 5 ), respectively. The observed reactivity suggests that 3 is best described as a Mn -I /NHP + complex, in contrast to pincer-ligated dicarbonyl manganese analogues typically assigned as Mn I species.