PREPARATION AND REACTIVITY OF 5-MEMBERED PHOSPHONICKELOCYCLES

The complexes trans-[NiCl(P-C)L] [L = PMe2Ph 1a, PEt3 1b, P(CH2Ph)3 1c or PPh3 1d], and [{NiCl(P-C)}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 P2(1)/c, a = 20.641(6), b = 9.794(3), c = 17.047(5) angstrom, beta = 102.05(3)-degrees 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 [NiX(P-C)L] compounds by NMR spectroscopy, depending on the size of the phosphine and the anionic ligands. With [Ni(C6H2Me3-2,4,6)(P-C){P(CH2Ph)3}] only the cis product is obtained. The ionic compounds [Ni((P-C)(PMe2Ph)2]BF4 and [Ni(P-C)(MeCN){P(CH2Ph)3}]BF4 were synthesised by reaction of [NiCl(P-C)L] with 1 equivalent of TlBF4 in the presence of free ligand. The five-co-ordinate compound [NiCl(P-C)(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 [NiCl(o-COC6H4CH2PPh2)L] (L = PEt3 or P(CH2Ph)3] and [NiCl(o-SO2C6H4CH2PPh2){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 [NiCl{cis-(CPh=CPh)(C6H4CH2PPh2}L] [L = PEt3 or P(CH2Ph)3] and [NiCl{2-(CPh=CCO2Et)C6H4CH2PPh2}{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 P2(1)/c, a = 11.386(3), b = 14.715(3), c = 26.000(5) angstrom, beta = 90.03(4)-degrees and Z = 4. Decomposition products after insertion of ethylene under pressure in 1c and [Ni(C6H2Me3-2,4,6)(P-C){P(CH2Ph)3}] were also observed. No evidence of insertion reactions was obtained with CS2 and CO2 even under pressure.