Synthesis and characterization of bis- and tris-carbonyl Mn(I) and Re(I) PNP pincer complexes

A series of neutral bis- and cationic tris-carbonyl complexes of the types cis-[M(P-3,N,P-PNP)(CO)(2)Y] and [M(P-3,N,P-PNP)(CO)(3)](+) was prepared by reacting [M(CO)(5)Y] (M=Mn, Re; Y=Cl or Br) with PNP pincer ligands derived from the 2,6-diaminopyridine, 2,6-dihydroxypyridine, and 2,6-lutidine scaffolds. With the most bulky ligand PNPNH-tBu, the cationic square-pyramidal 16e bis-carbonyl complex [Mn(PNPNH-tBu)(CO)(2)](+) was obtained. In contrast, in the case of rhenium, the 18e complex [Re(PNPNH-tBu)(CO)(3)](+) was formed. The dissociation of CO was studied by means of DFT calculation revealing in agreement with experimental findings that CO release from [M(P-3,N,P-PNP)(CO)(3)](+) is in general endergonic, while for [Mn(P-3,N,P-PNPNH-tBu)(CO)(3)](+), this process is thermodynamically favored. X-ray structures of representative complexes are provided. [GRAPHICS] .