Synthesis of neutral and zwitterionic phosphinomethylpyrrolato complexes of nickel

Potassium salts of the new 2-phosphinomethyl-1H-pyrroles, K[R2PCH2C4H3N] (R = Ph, Cy) react with (η3-allyl)nickel bromide to give the chelate complexes (R2PCH2C4H3N)Ni(allyl), whereas the sterically hindered 2-diphenylphosphinomethyl-5-t-butyl-1H-pyrrole and (η3-allyl)nickel bromide afford a phosphine adduct (HNC4H2-5-But-2-CH2PPh2)Ni(allyl)Br which is stabilized by an intramolecular NH⋯Br hydrogen bond. The addition of B(C6F5)3 to (R2PCH2C4H3N)Ni(allyl) leads to an electrophilic attack in 5-position of the pyrrole ring, to give the thermally unstable zwitterions (η3-C3H5)Ni[NC4H3(2-CH2PR2)-5-B(C6F5)3] which catalyse the isomerisation of 1-hexene. The addition of B(C6F5)3 is reversible, and slow ligand rearrangement to Ni(N-P)2 products appears to be the major catalyst deactivation pathway.