Formation of μ-dinitrogen (salen)osmium complexes via ligand-induced N⋯N coupling of (salen)osmium(vi) nitrides

Abstract

Treatment of [N nBu 4][Os VI(N)Cl 4] with a stoichiometric amount of H 2L (L = N,N′-bis(salicylidene)-o-cyclohexylenediamine dianion) in the presence of PF 6 - or ClO 4 - in MeOH affords [Os VI(N)(L)(OH 2)](PF 6) 1a and [Os VI(N)(L)(CH 3OH)](ClO 4) 1b, respectively. The structure of 1b has been determined by X-ray crystallography and the OsN bond distance is 1.627(3) Å. In the presence of a N-donor heterocyclic ligand in CH 3CN, 1a reacts at room temperature to afford the mixed-valence μ-N 2 (salen)osmium species [(X)(L)Os III-NN-Os II(L)(X)](PF 6), 2-14 (X = py 2; 4-Mepy 3; 4- tBupy 4; pz 5; 3-Mepz 6; 3,5-Me 2pz 7; Im 8; 1-MeIm 9; 2-MeIm 10; 4-MeIm 11; 1,2-Me 2Im 12; 2-Meozl 13; 4-MeTz 14). These complexes are formed by ligand-induced N⋯N coupling of two [Os VIN] + to give initially [Os III-N 2-Os III] 2+, which is then reduced to give the more stable mixed-valence species [Os III-N 2-Os II] +. Cyclic voltammograms (CVs) of 2-14 show two reversible couples, attributed to Os III,III/Os III,II and Os III,II/Os II,II. The large comproportionation constants (K com) of (5.36-82.3) × 10 13 indicate charge delocalization in these complexes. The structures of 3 and 14 have been determined by X-ray crystallography, the salen ligands are in uncommon cis-β configuration. Oxidations of 4 and 14 by [Cp 2Fe](PF 6) afford the symmetrical species [(X)(L)Os III-NN-Os III(L)(X)](PF 6) 2 (X = 4- tBupy 15; 4-MeTz 16). These are the first stable μ-N 2 diosmium(iii,iii) complexes that have been characterized by X-ray crystallography. © 2010 The Royal Society of Chemistry.