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

ABSTRACT: A series of neutral bis- and cationic tris-carbonyl complexes of the types cis-[M(κ(3)P,N,P-PNP)(CO)(2)Y] and [M(κ(3)P,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 PNP(NH)-tBu, the cationic square-pyramidal 16e bis-carbonyl complex [Mn(PNP(NH)-tBu)(CO)(2)](+) was obtained. In contrast, in the case of rhenium, the 18e complex [Re(PNP(NH)-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(κ(3)P,N,P-PNP)(CO)(3)](+) is in general endergonic, while for [Mn(κ(3)P,N,P-PNP(NH)-tBu)(CO)(3)](+), this process is thermodynamically favored. X-ray structures of representative complexes are provided. GRAPHICAL ABSTRACT: [Image: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00706-018-2307-7) contains supplementary material, which is available to authorized users.