Structural and electronic features of Group 8 metal complexes containing one α-diiminobenzene chelate ligand

Abstract

Known complexes of general formula L n M( diim), where diim=C 6H 4(NH) 2- o, α-diiminobenzene, n=3, 4 and M is a metal of Group 8 (Ru(II), in particular) are analyzed in terms of their electronic structure and associated energetics. The newly synthesized compound [(CO) 2(PPh 3)BrRu(C 6H 4(NH) 2- o)]Br, 1, is a new member of the category. This is confirmed by the X-ray structure of 1 that is presented together with electrochemical measurements and other spectroscopic characterization. At variance with the isoelectronic L 4M( o-phenylenediamido) compounds (M=Group 6 metal) that are affected by structural deformations, 1 and similar complexes have a regular pseudo-octahedral structure. Density functional theory calculations and qualitative MO arguments provide an explanation for the different electronic trends as well as for the diimino/diamido dichotomy of the non-innocent chelate ligand. The latter is affected, not only by the nature of the metal (energy of d orbitals), but also by the surrounding environment (three or four coligands). Moreover, the calculations allow to outline the stability trends for the loss of one coligand from L 4M( diim) systems when the Ru(II) complexes are chemically or electrochemically reduced.