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)A, 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)A, 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.