STEPWISE CONSTRUCTION OF POLYNUCLEAR COMPLEXES OF RHODIUM AND IRIDIUMASSISTED BY BENZIMIDAZOLE-2-THIOL - NMR AND X-RAY-DIFFRACTION STUDIES

Reactions of [M(2)(mu u-Cl)(2)(cod)(2)] (cod = 1,5-cyclooctadiene, M = Rh, Ir) with benzimidazole-2-thiol (H(2)Bzimt) afford the mononuclear complexes [MCl(H(2)Bzimt)(cod)] (M = Rh (1), Ir (2)) for which a S-co ordination of the ligand is proposed based on their spectroscopic data . The dinuclear complexes [M(2)(mu-HBzimt)(2)(cod)(2)] (M = Rh (3), Ir (4)) are isolated from the reaction of [M(acac)(cod)] and benzimidazo le-2-thiol. They contain the monodeprotonated ligand (HBzimt(-)) bridg ing the two metals in a mu(2)-(1 kappa N,2 kappa S) coordination mode and in a relative cis,cis-HT arrangement. Complexes 3 and 4 react with the appropriate species [M(cod)(Me(2)CO)(2)](+) to afford the trinucl ear cationic aggregates [M(3)(mu-HBzimt)(2)(Cod)(3)](+) (M = Rh (5), I r (6)) and with the [M'(2)(mu-OMe)(2)(cod)(2)] compounds to give the h omo- and heterotetranuclear complexes [MM'(mu-Bzimt)(cod)(2)](2) (M = M' = Rh (7), Ir (8); M = Ir, M' = Rh (9)) containing the dideprotonate d ligand (Bzimt(2-)). The trinuclear neutral complexes [M(3)(mu-Bzimt) (mu-HBzimt)(cod)(3)] are intermediates detected in the synthesis of th e tetranuclear complexes. Protonation of 9 with HBF4 gives the unsymme trical complex [Ir2Rh(mu-HBzimt)(2)(cod)(3)]BF4 (10). This reaction in volves the protonation of the bridging ligands followed by the removal of one ''Rh(cod)'' moiety to give a single isomer. The molecular stru cture of [Rh-2(mu-Bzimt)(cod)(2)](2) (7) has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P2(1)/n, a = 20.173(5) Angstrom, b = 42.076(8) Angstrom, c = 10.983(3) Angstrom, b eta = 93.32(2)degrees, Z = 8, 7145 reflections, R = 0.0622, and R(w) = 0.0779. The complete assignment of the resonances of the H-1 NMR spec tra of the complexes 3, 4, and 7-9 was carried out by selective decoup ling, NOE, and H,H-COSY experiments. The differences in the chemical s hifts of the olefinic protons are discussed on the basis of steric and magnetic anisotropy effects.