Coordination insertion reactions of acrylonitrile into Pd–H and Pd–methyl bonds in a diimine-palladium(II) system

Acrylonitrile (AN) displaces the ethyl ether ligand of the cationic complex [Pd(N-N)Me(Et2O)]+ (N-N = (2,6-(i-Pr)2C6H3)-NCMeCMeN-(2,6-(i-Pr)2C6H3)) to form the N-bonded AN complex [Pd(N-N)Me(AN)]+, which exists as two interconverting rotamers. On standing or heating, [Pd(N-N)Me(AN)]+ undergoes 2,1-insertion to give [Pd(N-N)(CH(CN)CH2Me)(AN)]+, which undergoes β-hydrogen elimination to give the intermediate hydride, [Pd(N-N)H(AN)]+, which in turn inserts AN to give the cyanoethyl complex [Pd(N-N)(CH(CN)Me)]+. Dimerization of the [Pd(N-N)(CH(CN)CH2CH3)]+ moiety via bridging nitrile groups also occurs, giving the dicationic species [Pd(N-N)(CH(CN)CH2Me)]22+. Although [Pd(N-N)Me(AN)]+ does behave as a typical Brookhart ethylene polymerization catalyst, it does not catalyze AN polymerization and in fact added AN suppresses ethylene polymerization.

Graphical abstractAcrylonitrile (AN) coordinates to a cationic diiminemethylpalladium(II) complex to form the N-bonded complex [Pd(N-N)Me(AN)]+ which on standing or heating undergoes 2,1-insertion to give the complex [Pd(N-N)(CH(CN)CH2Me)(AN)]+; the latter also undergoes β-hydrogen elimination to give a hydride, [Pd(N-N)H(AN)]+, which reacts further with AN to give the cyanoethyl complex [Pd(N-N)(CH(CN)Me)]+.Figure optionsDownload full-size imageDownload as PowerPoint slide