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-[(CpRuH)2B3H7] (1) with 2-mercaptobenzothiazole (2-mbtz) and 2-mercaptobenzoxazole (2-mboz) led to the isolation of Cp-based (Cp* = η(5)-C5Me5) borate complexes 5 a,b [CpRuBH3L] (5 a: L = C7H4NS2; 5 b: L = C7H4NOS)) and agostic complexes 7 a,b [CpRuBH2(L)2], (7 a: L = C7H4NS2; 7 b: L = C7H4NOS). In a similar fashion, a rhodium analogue of pentaborane(9), nido-[(CpRh)2B3H7] (2) yielded rhodaboratrane [CpRhBH(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 [(CpRh)(L2)(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-[(CpRuCO)2B2H6] (3), in which the metal center possesses different ancillary ligands.