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 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)2B3H7] (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∗RuCO)2B2H6] (3), in which the metal center possesses different ancillary ligands. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.