Chemistry of Diruthenium and Dirhodium Analogues of Pentaborane(9): Synthesis and Characterization of Metal N,S-Heterocyclic Carbene and B-Agostic Complexes

Building upon our earlier results on the synthesis of electron-precise transition-metal-boron complexes, we continue to investigate the reactivity of pentaborane(9) and tetraborane(10) analogues of ruthenium and rhodium towards thiazolyl and oxazolyl ligands. Thus, mild thermolysis of nido-[(Cp*RuH)(2)B3H7] (1) with 2-mercaptobenzothiazole (2-mbtz) and 2-mercaptobenzoxazole (2-mboz) led to the isolation of Cp*-based (Cp*=(5)-C5Me5) borate complexes 5a,b [Cp*RuBH3L] (5a: L=C7H4NS2; 5b: L=C7H4NOS)) and agostic complexes 7a,b [Cp*RuBH2(L)(2)], (7a: L=C7H4NS2; 7b: L=C7H4NOS). In a similar fashion, a rhodium analogue of pentaborane(9), nido-[(Cp*Rh)(2)B3H7] (2) yielded rhodaboratrane [Cp*RhBH(L)(2)], 10 (L=C7H4NS2). Interestingly, when the reaction was performed with an excess of 2-mbtz, it led to the formation of the first structurally characterized N,S-heterocyclic rhodium-carbene complex [(Cp*Rh)(L-2)(1-benzothiazol-2-ylidene)] (11) (L=C7H4NS2). Furthermore, to evaluate the scope of this new route, we extended this chemistry towards the diruthenium analogue of tetraborane(10), arachno-[(Cp*RuCO)(2)B2H6] (3), in which the metal center possesses different ancillary ligands.