C-H activation and C-C coupling reactions in 2-vinylpyridine cationic complexes of iridium

The complex [IrH2(NCCH3)(3)(PiPr(3))]BF4 (1) reacts with 2-vinylpyridine to form the hydride [IrH{NC5H4-2-Z-(CH=CH)-kappa-N,C}(NCCH3)(2)(PiPr(3))]BF4 (3) in a reaction that likely involves the observed dihydride [IrH2(NC5H4-2-CH=CH2-kappa-N)(NCCH3)(2)(PiPr(3))]BF4 (2). Crystallization of the C-H activation product 3 affords the dicationic derivative [IrH{mu-n(2)-NC5H4-2-(Z-CH= CH)-kappa-N,C}(NCCH3)(PiPr(3))](2)(BF4)(2) (4). 3 reacts with 2-vinypyridine, CH2=CH2, CH=CH, PhC=CH, tBuC=CH, and PhC=CPh to form the corresponding alkyl or alkenyl insertion products. The structure of [lr(NC5H4-2-(Z-CH=CH)-kappa-N,C)(NC5H4-2-CH2CH2-kappa-NC)(NCCH3)(PiPr(3))]BF4 (5), which contains two chelating ligands derived from 2-vinylpyridine, has been determined by X-ray diffraction. The other insertion products 7-11 retain the structure of the precursor 3 even after insertions of different regioselectivity, as evidenced by the 1-alkyne derivatives [IrfC(Ph)=CH2}{NC5H4-2-Z-(CH=CH)-kappa-N,C}(NCCH3)(2)(PiPr(3))]BF4 (9) and [Ir(E-CH=CHtBu) {NC5H4-2-Z-(CH=CH)-K-N,C}(NCCH3)(2)(PiPr(3))]BF4 (10). All obtained insertion products are stable toward the reductive elimination of C - C bonds. However, derivatives 9 and 10 undergo a C-C coupling reaction to form [Ir{NC5H4-2-Z-(CH=CH)-kappa-N,C}{NC(5)H(4-)2-Z-(CH=CH)CH(R)CH2-K-N,C}(NCCH3)(PiPr(3))]BF4 (R = Ph, 12; R = tBu, 13) after treatment with 2-vinylpyridine excess. These latter products are isostructural, despite the different stereochemistry of the alkenyl ligands in the precursors. Under similar conditions, both the alkyl complex [Ir(Et)tNC(5)H(4)-2-Z-(CH=CH)-kappa-N,C}(NCCH3)(2)(PiPr(3))] BF4 (7) and the diphenylacetylene derivative [Ir{Z-C(Ph)=CHPh}{NC5H4-2-Z-(CH=CH)-kappa-N,C}(NCCH3)(2)(PiPr(3))]BF4 (11) form the compound [Ir{NC5H4-2-Z-(CH=CH)-kappa-N,C}(2)(NCCH3)(PiPr(3))]BF4 (15), after elimination of ethane and cis-stilbene, respectively. These latter observations are discussed to conclude that the observed C-C coupling processes comprise the initial generation of an alkene at the coordination sphere of iridium followed by the alkene insertion into an Ir-C bond.