C−H Activation and C−C Coupling Reactions in 2-Vinylpyridine Cationic Complexes of Iridium

Abstract

The complex [IrH2(NCCH3)3(PiPr3)]BF4 (1) reacts with 2-vinylpyridine to form the hydride [IrH{NC5H4-2-Z-(CHCH)-κ-N,C}(NCCH3)2(PiPr3)]BF4 (3) in a reaction that likely involves the observed dihydride [IrH2(NC5H4-2-CHCH2-κ-N)(NCCH3)2(PiPr3)]BF4 (2). Crystallization of the C−H activation product 3 affords the dicationic derivative [IrH{μ-η2-NC5H4-2-(Z-CHCH)-κ-N,C}(NCCH3)(PiPr3)]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 [Ir(NC5H4-2-(Z-CHCH)-κ-N,C)(NC5H4-2-CH2CH2-κ-N,C)(NCCH3)(PiPr3)]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 [Ir{C(Ph)CH2}{NC5H4-2-Z-(CHCH)-κ-N,C}(NCCH3)2(PiPr3)]BF4 (9) and [Ir(E-CHCHtBu){NC5H4-2-Z-(CHCH)-κ-N,C}(NCCH3)2(PiPr3)]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)-κ-N,C}{NC5H4-2-Z-(CHCH)CH(R)CH2-κ-N,C}(NCCH3)(PiPr3)]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){NC5H4-2-Z-(CHCH)-κ-N,C}(NCCH3)2(PiPr3)] BF4 (7) and the diphenylacetylene derivative [Ir{Z-C(Ph)CHPh}{NC5H4-2-Z-(CHCH)-κ-N,C}(NCCH3)2(PiPr3)]BF4 (11) form the compound [Ir{NC5H4-2-Z-(CHCH)-κ-N,C}2(NCCH3)(PiPr3)]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.

Gold(III) adducts of 2-vinyl- and 2-ethylpyridine and cyclometallated derivatives of 2-vinylpyridine: Crystal structure of the cyclometallated derivative [Au(k2-C,N–CH2CH(Cl)–C5H4N)(PPh3)Cl][PF6]

“…Cyclometallation reactions of 2-vinylpyridine, or its derivatives, have been reported previously with metal complexes of Pd [9], Pt [9a,10], Co [11], Rh [12], Ir [13], Ru [14], Os [14d,e,15] and Re [16]. In most cases C(sp 2 )-H activation of 2-vinylpyridine occurs with formation of the cyclometallated derivatives [M ].…”

An exhibition of different coordination modes displayed by 2-vinylpyrazine and 2-vinylpyridine at triosmium centres

“…The chemistry of transition metals with 2-vinylpyridines has been widely investigated in recent years in order to develop new catalysts for selective olefinic C-H bond activation via cyclometallation which is an importent process in catalysis and also in the synthesis of organometallic compounds [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Most of these studies have utilised mononuclear complexes in which chelation of 2-vinylpyridines occurs either through π-complexation of the alkene functionality or activation of a β-C-H alkenyl bond in addition to coordination of pyridinyl nitrogen [6][7][8][9][10][11][12][13][14][15]. In contrast, surprisingly little attention has been paid to related reactions of 2-vinylpyridines with polynuclear centres [16][17][18][19][20][21][22].…”

Dirhenium carbonyl complexes bearing 2-vinylpyridine, morpholine and 1-methylimidazole ligands

“…The reactivity of 2-vinylpyridine with a variety of mononuclear complexes has been studied extensively in recent years [9][10][11][12][13][14][15][16][17]. In particular C-H oxidative-addition reaction of both vinyl and pyridyl functionalities in the ligand has been observed.…”