Vinyl/Phenyl Exchange Reaction within Vinyl Nickel Complexes Bearing Chelate [P, S]-Ligands

Abstract

Three nickel(II) hydrides, [2-Ph2P(4-Me-C6H3)S]NiH(PMe3)2 (1), [2-Ph2P(6-Me3Si-C6H3)S]NiH(PMe3)2 (2), and [2-Ph2P(4-Me3Si -C6H3)S]NiH(PMe3)2 (3), were synthesized via S–H bond activation through the reaction of Ni(PMe3)4 with (2-diphenylphosphanyl)thiophenols. The reactions of nickel(II) hydrides (1–3) with different alkynes were investigated. Although the first step is the insertion of alkyne into the Ni–H bond for each reaction, different final products were isolated. Normal vinyl nickel complex [2-Ph2P(4-Me-C6H3)S]Ni(CPh═CH2)(PMe3) (4) was obtained by the reaction of phenylacetylene with 1. The nickelacyclopropane complexes [2-Ph2P(6-Me3Si-C6H3)S]Ni[Ph(PMe3)C–CH2] (5), [2-Ph2P(4-Me3Si-C6H3)S]Ni[Ph(PMe3)C–CH2] (6), [2-Ph2P(4-Me3-C6H3)S]Ni[Ph(PMe3)C–CHPh] (7), [2-Ph2P(6-Me3Si-C6H3)S]Ni[Ph(PMe3)C–CHPh] (8), [2-Ph2P(4-Me3Si-C6H3)S]Ni[Ph(PMe3)C–CHPh] (9), [2-Ph2P(4-Me-C6H3)S]Ni[Ph(PMe3)C–CHSiMe3] (10) or [2-Ph2P(4-Me-C6H3)S]Ni[Me3Si(PMe3)C–CHPh] (10), [2-Ph2P(6-Me3Si-C6H3)S]Ni[Ph(PMe3)C–CHSiMe3] (11) or [2-Ph2P(6-Me3Si-C6H3)S]Ni[Me3Si(PMe3)C–CHPh] (11), and [2-Ph2P(4-Me3Si-C6H3)S]Ni[Ph(PMe3)C–CHSiMe3] (12) or [2-Ph2P(4-Me3Si-C6H3)S]Ni[Me3Si(PMe3)C–CHPh] (12) containing a ylidic ligand were formed by the reaction of phenylacetylene, diphenylacetylene, and 1-phenyl-2-(trimethylsilyl)acetylene with 1, 2, and 3, respectively. The phenyl/vinyl exchange nickel(II) complexes [2-(Ph(CH2═CSiMe3)P(4-Me-C6H3)S]Ni(Ph)(PMe3) (13), [2-(Ph(CH2═CSiMe3)P((6-Me3Si-C6H3)S]Ni(Ph)(PMe3) (14), and [2-(Ph(CH2═CSiMe3)P((4-Me3Si-C6H3)S]Ni(Ph)(PMe3) (15) could be obtained by insertion of trimethylsilylacetylene into Ni–H bonds of 1, 2, and 3. To the best of our knowledge, this is a novel reaction type between alkyne and nickel hydride. The results indicate that whether increasing the electronegativity on the benzene ring or on the alkyne leads to the instability of the vinyl nickel complex, and is beneficial to the C–P reductive elimination to form nickelacyclopropane complexes or phenyl nickel complexes via vinyl/phenyl exchange reaction in the case of the more electronegative nickel center. All the nickel complexes were fully detected by IR, NMR and the molecular structures of complexes 1, 2, 7, 9, 13, and 14 were confirmed by single crystal X-ray diffraction.