Chemistry of diruthenium and dirhodium analogues of pentaborane(9): synthesis and characterization of metal N,S-heterocyclic carbene and B-agostic complexes

Abstract

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)₂B₃H₇] (1) with 2-mercaptobenzothiazole (2-mbtz) and 2-mercaptobenzoxazole (2-mboz) led to the isolation of Cp*-based (Cp*=η⁵-C₅Me₅) borate complexes 5 a,b [Cp*RuBH₃L] (5 a: L=C₇H₄NS₂; 5 b: L=C₇H₄NOS)) and agostic complexes 7 a,b [Cp*RuBH₂(L)₂], (7 a: L=C₇H₄NS₂; 7 b: L=C₇H₄NOS). In a similar fashion, a rhodium analogue of pentaborane(9), nido-[(Cp*Rh₂B₃H₇] (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)(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-[(Cp*RuCO₂B₂H₆] (3), in which the metal center possesses different ancillary ligands.