The Discovery of [Ni(NHC)RCN]₂ Species and Their Role as Cycloaddition Catalysts for the Formation of Pyridines

Abstract

The reaction of Ni(COD)2, IPr, and nitrile affords dimeric [Ni(IPr)RCN]2 in high yields. X-ray analysis revealed these species display simultaneous η1- and η2-nitrile binding modes. These dimers are catalytically competent in the formation of pyridines from the cycloaddition of diynes and nitriles. Kinetic analysis showed the reaction to be first order in [Ni(IPr)RCN]2, zeroth order in added IPr, zeroth order in nitrile, and zeroth order in diyne. Extensive stoichiometric competition studies were performed, and selective incorporation of the exogenous, not dimer bound, nitrile was observed. Post cycloaddition, the dimeric state was found to be largely preserved. Nitrile and ligand exchange experiments were performed and found to be inoperative in the catalytic cycle. These observations suggest a mechanism whereby the catalyst is activated by partial dimer-opening followed by binding of exogenous nitrile and subsequent oxidative heterocoupling.

Rational synthesis of normal, abnormal and anionic NHC–gallium alkyl complexes: structural, stability and isomerization insights

“…In order to shed some light on the mechanism involved in this isomerization process, kinetic analysis of a NMR scale reaction ([ 1 ] = 0.22 M) performed at 100 °C in d 8 -THF revealed a pseudo-zeroth-order kinetics over a period of two-half lives (64% conversion). 62 An identical experiment using IPr D ·GaR 3 ( 1 D ) (IPr D = 1,3-bis(2,6-di-isopropylphenyl)-4,5-dideutero-imidazolin-2-ylidene) 68 allowed the comparison of the subsequent zero order rate constants, revealing no observable KIE (see ESI ‡ for details). These findings suggest that the bond cleavage of the C 4 –H in the IPr ligand is unlikely to be rate-determining in the isomerization process.…”

Pyrrolidines and piperidines bearing chiral tertiary alcohols by nickel-catalyzed enantioselective reductive cyclization of N-alkynones

“…T ransition metal-catalyzed coupling of alkynals/alkynones has become a powerful method for efficient construction of allylic alcohol derivatives in current organic chemistry [1][2][3] . Recent development by employing various transition metal catalysts such as Ti 4 , Ni [5][6][7][8][9][10][11][12][13][14][15][16][17][18] , Rh [19][20][21][22][23][24] , Ir 25 , Ru [26][27][28] , and Pd 29,30 in combination with a variety of coupling components and reducing/alkylative agents has greatly expanded its scope and applications. Among them, the nickel-catalyzed coupling of π systems pioneered by Mori 5,8 , Montgomery 6,7,10 , and Jamison 9,15 , is particularly attractive and offers a broad substrate scope and good functional group compatibility.…”

Biodegradation of pyridine‐based polyether polyurethanes by the Alternaria tenuissima fungus

“…The peak at 3431 cm −1 , attributed to the H‐unbonded NH groups, decreased after 60 days of exposure because new hydrogen bonds are made between the macromolecular chains that were broken in the biodegradation process and because a rearrangement of the macromolecular chains occurs, that may have generated new hydrogen connections. It is also important to note that the stretching vibration absorption peaks from 1756 (NC), 1410 (CC), and 1234 cm −1 (NC) that are characteristic of the pyridine group have disappeared after exposure to A. tenuissima . This proves that the pyridine moieties are involved in the biodegradation process.…”