Chemistry of group 5 metallaboranes with heterocyclic thiol ligands: a combined experimental and theoretical study

Thermolysis of [(Cp*Nb)(2)(B2H6)(2)], 1b (Cp* = eta(5)-C5Me5), with 2-mercaptobenzothiazole, C6H4NSCSH (MBT), and 2-mercaptobenzoxazole, C6H4NOCSH (MBO), yielded hydrogen substituted compounds 2 and 3 with a general formula [(Cp*Nb)(2)(B2H6)(B2H5L)] (2: L = C6H4NSCS and 3: L = C6H4NOCS). A similar reaction of 1b with Ph2Se2 yielded the monosubstituted derivative [(Cp*Nb)(2)(B2H6){B2H5(PhSe)}], 4. All further efforts towards persubstitution of 1b under 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*TaCl4 was 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*TaCl3{kappa(2)-N,S-C6H4NSCS}], 5, containing a heterocyclic thiol ligand. Using an alternative method complex 5 was isolated in good yield when Cp*TaCl4 was treated with the potassium salt of 2-mercaptobenzothiazole K[C6H4NSCS]. All the compounds were characterized by H-1, B-11{H-1}, and C-13{H-1} NMR spectroscopy, and their structures were unequivocally established by crystallographic analysis.

Automated summary

Thermolysis and reactions yielded a series of new hydrogen-substituted compounds, but attempts at persubstitution were unsuccessful. Additionally, in the synthesis of the Ta-aziridine complex, a new complex containing a heterocyclic thiol ligand was unexpectedly obtained using an alternative method.