Preparation and reactivity of five-membered phosphonickelocycles

Abstract

The complexes trans-[[graphic omitted])L][L = PMe₂Ph 1a, PEt₃1b, P(CH₂Ph)₃1c or PPh₃1d], and [{[graphic omitted])}₂] containing the bidentate anionic ligand o-C₆H₄CH₂PPh₂(P–C) have been prepared. The molecular structure of 1c has been determined by single-crystal X-ray crystallographic methods: space group P2₁/c, a= 20.641(6), b= 9.794(3), c= 17.047(5)Å, β= 102.05(3)° and Z= 4. Complexes 1 showed a conformational interconversion of the metallocyclic ring. Different amounts of cis and trans isomers were observed in the solutions of [[graphic omitted])L] compounds by NMR spectroscopy, depending on the size of the phosphine and the anionic ligands. With [[graphic omitted]){P(CH₂Ph)₃}] only the cis product is obtained. The ionic compounds [[graphic omitted])(PMe₂Ph)₂]BF₄ and [[graphic omitted])(MeCN){P(CH₂Ph)₃}]BF₄ were synthesised by reaction of [[graphic omitted]] with 1 equivalent of TIBF₄ in the presence of free ligand. The five-co-ordinate compound [[graphic omitted])(PMe₂Ph)₂] was obtained from 1a and PMe₂Ph. The reactivity of the Ni–C bond of compounds 1 in the presence of CO, SO₂, CS₂, CO₂, alkynes and olefins was studied. Acyl or S-sulfinate compounds containing six-membered rings [[graphic omitted]Ph₂)L][L = PEt₃ or P(CH₂Ph)₃] and [[graphic omitted]Ph₂){P(CH₂Ph)₃}] were obtained from the reactions with CO and SO₂. The reaction with diphenylacetylene or ethyl phenylpropiolate of compounds 1a and 1c gave one isomer of [[graphic omitted]Ph₂}L][L = PEt₃ or P(CH₂Ph)₃] and [[graphic omitted]Ph₂}{P(CH₂Ph)₃}], with the alkenyl fragment cis with respect to the substituents of the alkyne. The geometry of the latter was confirmed by single-crystal X-ray structure determination: space group P2₁/c, a= 11.386(3), b= 14.715(3), c= 26.000(5)Å, β= 90.03(4)° and Z= 4. Decomposition products after insertion of ethylene under pressure in 1c and [[graphic omitted]){P(CH₂Ph)₃}] were also observed. No evidence of insertion reactions was obtained with CS₂ and CO₂ even under pressure.