Mercapto-benzothiazolyl based ruthenium(ii) borate complexes: synthesis and reactivity towards various phosphines

The synthesis and reactivity of ruthenium complexes containing an anionic boron based ligand, supported by mercapto-benzothiazolyl heterocycles are presented. Specifically, the reaction of [(η⁶-p-cymene)Ru{P(OMe)₂OR}Cl₂], (1a: R = Me; 1b: R = H) with [H₂B(mbz)₂]^- (mbz = 2-mercaptobenzothiazolyl) at room temperature afforded a series of borate complexes, namely [(L)Ru{κ³-H,S,S'-H₂B(L)₂}P(O)(OMe)(HL)], 2, [Ru{κ³-H,S,S'-H₂B(L)₂}₂], 3 and [(κ²-N,S-L)P(OMe)₃Ru{κ³-H,S,S'-H₂B(L)₂}], 4a; (L = C₇H₄NS₂). The pivotal feature of 2 is the coordination of the Ru centre with a phosphorus atom of secondary phosphine oxide and mercapto-benzothiazolyl ligands. On the other hand, 3 features dual RuH-B interactions between Ru and B-H bonds of [H₂B(mbz)₂]^-. Interestingly, along with 3, compound [(κ²-N,S-L)P(OPh)₃Ru{κ³-H,S,S'-H₂B(L)₂}], 4b (L = C₇H₄NS₂), was isolated upon treatment of the same borate with [(η⁶-p-cymene)RuCl₂P(OPh)₃], 1c, which is stabilized by δ-B-H interactions and one phosphite ligand. Furthermore, compound 3 promptly reacts with P(OR)₃ to generate [(OR)₃PRu-{κ²-S,S'-H₂B(L)₂}{κ³-H,S,S'-H₂B(L)₂}], (5a: R = Me, 5b: R = Ph; L = C₇H₄NS₂) by breaking one of the RuH-B interactions. Upon heating, compound 5a converts into [(OMe)₂OPRu{κ²-S,S'-HB(L)₂}{κ³-H,S,S'-H₂B(L)₂}], 6a (L = C₇H₄NS₂) by release of methane gas. Compound 6a is a unique example wherein the boron atom of the borate ligand is bound to an oxygen atom of the phosphite unit. In contrast, the thermolysis of 3 with PR₂R' yielded [Ru{κ³-H,S,S'-H₂B(L₂)}(PR₂R')₂(L)], (7a: R = Me, R' = Ph; 7b: R = Ph; R' = Me; L = C₇H₄NS₂), respectively, revealing the incorporation of two triphosphine ligands in the coordination sphere of ruthenium. Density functional theory (DFT) calculations were undertaken to provide an insight into the electronic structures of the complexes.