Chemistry of N,S-heterocyclic carbene and metallaboratrane complexes: a new η³-BCC-borataallyl complex

Abstract

A high-yielding synthetic route for the preparation of group 9 metallaboratrane complexes [Cp*MBH(L)₂], 1 and 2 (1, M=Rh, 2, M=Ir; L=C7H₄NS₂) has been developed using [{Cp*MCl₂}₂] as precursor. This method also permitted the synthesis of an Rh–N,S-heterocyclic carbene complex, [(Cp*Rh)(L₂)(1-benzothiazol-2-ylidene)] (3; L=C₇H₄NS₂) in good yield. The reaction of compound 3 with neutral borane reagents led to the isolation of a novel borataallyl complex [Cp*Rh(L)₂B{CH₂C(CO₂Me)}] (4; L=C₇H₄NS₂). Compound 4 features a rare η₃-interaction between rhodium and the B-C-C unit of a vinylborane moiety. Furthermore, with the objective of generating metallaboratranes of other early and late transition metals through a transmetallation approach, reactions of rhoda- and irida-boratrane complexes with metal carbonyl compounds were carried out. Although the objective of isolating such complexes was not achieved, several interesting mixed-metal complexes [{Cp*Rh}{Re(CO)₃}(C₇H₄NS₂)₃] (5), [Cp*Rh{Fe₂(CO)₆}(μ-CO)S] (6), and [Cp*RhBH(L)₂W(CO)₅] (7; L=C₇H₄NS₂) have been isolated. All of the new compounds have been characterized in solution by mass spectrometry, IR spectroscopy, and ¹H, ¹¹B, and ¹³C NMR spectroscopies, and the structural types of 4–7 have been unequivocally established by crystallographic analysis.