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

摘要

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) ?. 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 ~(VI)N]~+ 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.