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)(kappa(2)-o-C6H4NCH=NAr) (1a Ar = 4-C6H4-OMe; 1b Ar = 2,6-C6H3-Me-2; 1c Ar = 2,6-C6H3-Et-2; 1d Ar = 2,6-C6H3-i-Pr-2). 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 la afforded the corresponding rhodium(III) complex trans-Rh(kappa(2)-o-C6H4NCH=NAr)(CHCl2)(Cl)(acac) (2). Addition of B(2)cat(3) (cat = 1,2-O2C6H4) to 1 gave zwitterionic Rh(eta(6)-catBcat)(kappa(2)-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 eta(6)-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.