Treatment of [NnBu4][OsVI(N)Cl 4] with a stoichiometric amount of H2L (L = N,N′-bis(salicylidene)-o-cyclohexylenediamine dianion) in the presence of PF6- or ClO4- in MeOH affords [OsVI(N)(L)(OH2)](PF6) 1a and [Os VI(N)(L)(CH3OH)](ClO4) 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 CH3CN, 1a reacts at room temperature to afford the mixed-valence μ-N2 (salen)osmium species [(X)(L)OsIII-NN-Os II(L)(X)](PF6), 2-14 (X = py 2; 4-Mepy 3; 4- tBupy 4; pz 5; 3-Mepz 6; 3,5-Me2pz 7; Im 8; 1-MeIm 9; 2-MeIm 10; 4-MeIm 11; 1,2-Me2Im 12; 2-Meozl 13; 4-MeTz 14). These complexes are formed by ligand-induced N⋯N coupling of two [Os VIN]+ to give initially [OsIII-N 2-OsIII]2+, which is then reduced to give the more stable mixed-valence species [OsIII-N2-Os II]+. Cyclic voltammograms (CVs) of 2-14 show two reversible couples, attributed to OsIII,III/OsIII,II and OsIII,II/OsII,II. The large comproportionation constants (Kcom) of (5.36-82.3) × 1013 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 [Cp2Fe](PF 6) afford the symmetrical species [(X)(L)OsIII-NN-Os III(L)(X)](PF6)2 (X = 4-tBupy 15; 4-MeTz 16). These are the first stable μ-N2 diosmium(iii,iii) complexes that have been characterized by X-ray crystallography.
Scopus Subject Areas
- Inorganic Chemistry