Chemistry of N,S-Heterocyclic Carbene and Metallaboratrane Complexes: A New η³-BCC-Borataallyl Complex

A high-yielding synthetic route for the preparation of group9 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 13CNMR spectroscopies, and the structural types of 4-7 have been unequivocally established by crystallographic analysis. New group9 metallaboratranes: Addition of a monoborane reagent to an Rh-N,S-heterocyclic carbene complex led to the formation of rhodaboratrane and a rare η3-BCC-borataallyl complex (see scheme).