Synthesis, Characterization, and Reactivity of Rhodium(I) Acetylacetonato Complexes Containing Pyridinecarboxaldimine Ligands

Addition of o-C6H4NCHNAr to Rh(coe)2(acac) (coe = cis-cyclooctene, acac = acetylacetonato) gave several new iminopyridine rhodium(I) complexes of the type Rh(acac)(κ2-o-C6H4NCHNAr) (1a Ar = 4-C6H4-OMe; 1b Ar = 2,6-C6H3-Me2; 1c Ar = 2,6-C6H3-Et2; 1d Ar = 2,6-C6H3-i-Pr2). All new rhodium complexes have been characterized by a number of physical methods, including multinuclear NMR spectroscopy and X-ray diffraction studies for 1b and 1c. Addition of CHCl3 to 1a afforded the corresponding rhodium(III) complex trans-Rh(κ2-o-C6H4NCHNAr)(CHCl2)(Cl)(acac) (2). Addition of B2cat3 (cat = 1,2-O2C6H4) to 1 gave zwitterionic Rh(η6-catBcat)(κ2-o-C6H4NCHNAr) (3). The molecular structure of 3b has been confirmed by a single crystal X-ray diffraction study and shows that the N2Rh fragment is bound to the catBcat anion via one of the catecholato groups in a η6-fashion. These complexes have also been examined for their ability to catalyze the hydroboration of a series of vinylarenes. Reactions using catecholborane and pinacolborane seem to proceed largely through a dehydrogenative borylation mechanism to give a number of boronated products.