Thermolysis of [(Cp*Nb)2(B2H6)2],1b(Cp* = η5-C5Me5), with 2-mercaptobenzothiazole, C6H4NSCSH (MBT), and 2-mercaptobenzoxazole, C6H4NOCSH (MBO), yielded hydrogen substituted compounds2and3with a general formula [(Cp*Nb)2(B2H6)(B2H5L)] (2: L = C6H4NSCS and3: L = C6H4NOCS). A similar reaction of1bwith Ph2Se2yielded the monosubstituted derivative [(Cp*Nb)2(B2H6)B2H5(PhSe)],4. All further efforts towards persubstitution of1bunder various drastic conditions were unfruitful. In parallel, in an effort to find a better synthetic route to the known Ta-aziridine complex [Cp*TaBH(C7H4NS2)CH2S2NC6H4], Cp*TaCl4was treated with a 2-mercaptobenzothiazolyl-based borate ligand Na[H2B(C6H4NSCS)2]. Surprisingly, the reaction led to the formation of the half-sandwich trichloroaryltantalum(v) complex [Cp*TaCl3κ2-N,S-C6H4NSCS],5, containing a heterocyclic thiol ligand. Using an alternative method complex5was isolated in good yield when Cp*TaCl4was treated with the potassium salt of 2-mercaptobenzothiazole K[C6H4NSCS]. All the compounds were characterized by1H,11B1H, and13C1H NMR spectroscopy, and their structures were unequivocally established by crystallographic analysis. © The Royal Society of Chemistry 2021.