Reactivity of [M<inf>2</inf>(μ-Cl)<inf>2</inf>(cod)<inf>2</inf>] (M=Ir, Rh) and [Ru(Cl)<inf>2</inf>(cod)(CH<inf>3</inf>CN)<inf>2</inf>] with Na[H<inf>2</inf>B(bt)<inf>2</inf>]: Formation of Agostic versus Borate Complexes

Treatment of [M2(μ-Cl)2(cod)2] (M=Ir and Rh) with Na[H2B(bt)2] (cod=1,5-cyclooctadiene and bt=2-mercaptobenzothiazolyl) at low temperature led to the formation of dimetallaheterocycles [(Mcod)2(bt)2], 1 and 2 (1: M=Ir and 2: M=Rh) and a borate complex [Rh(cod){κ2-S,S′-H2B(bt)2}], 3. Compounds 1 and 2 are structurally characterized metal analogues of 1,5-cyclooctadiene. Metal–metal bond distances of 3.6195(9) Å in 1 and 3.6749(9) Å in 2 are too long to consider as bonding. In an attempt to generate the Ru analogue of 1 and 2, that is [(Rucod)2(bt)2], we have carried out the reaction of [Ru(Cl)2(cod)(CH3CN)2] with Na[H2B(bt)2]. Interestingly, the reaction yielded agostic complexes [Ru(cod)L{κ3-H,S,S′-H2B(bt)2}], 4 and 5 (4: L=Cl; 5: L=C7H4NS2). One of the key differences between 4 and 5 is the presence of different ancillary ligands at the metal center. The natural bond orbital (NBO) analysis of 1 and 2 shows that there is four lone pairs of electrons on each metal center with a significant amount of d character. Furthermore, the electronic structures and the bonding of these complexes have been established on the ground of quantum-chemical calculations. All of the new compounds were characterized by IR,1H,11B,13C NMR spectroscopy, and X-ray crystallographic analysis.