REVERSIBLE SULFUR-DIOXIDE REACTIONS WITH CYCLOPENTADIENYLNICKEL(II) ORGANOCHALCOGENIDE COMPLEXES

A series of cyclopentadienylnickel(II) organochalcogenides containing different phosphines have been prepared by either reacting [CpNi(mu-SC 6H4X-4)](2) (Cp-# = eta(5)-C5H5, (Cp), eta(5)-C5H5Me, (Cp'); X = Cl, B r) with phosphines or Cp#Ni(PR3)Br with HSC6H4X-4 and Et3N or NaSeC6H4 Cl-4. The complexes that were isolated have the general formula CpNi(P R3)(EC6H4X-4), {E = S, X = Cl, R = Ph (1a), Bu (2a), OPh (3a), OEt (4a ), OMe (5a); X = Pr, R = Bu (6a), Ph (7a)}. In addition to spectroscop ic characterisation, the complexes CpNi(PBu3)(SC6H4Cl-4) (2a) and Cp'N i(PPh3)(SeC6H4Cl-4) (9a) were subjected to single-crystal X-ray diffra ction studies. While the solution and solid state structures of CpNi(P Bu3)(SC6H4Cl-4) were found to be the same, that of Cp'Ni(PPh3)(SeC6H4C l-4) were different. The orientation of the methyl group of 9a in the solid state is almost trans to the phosphine, but solution NMR data in dicate that the methyl substituent on the cyclopentadienyl ligand is c is to the phosphorus. All the complexes, 1a-9a, were found to react re versibly with SO2 to form SO2 adducts and the reversibility could be m onitored by visible and H-1-NMR spectroscopy. Electrochemical studies show that 2a and 6a have reversible couples whereas 1a and 7a are only quasi-reversible. The PBu3 complexes are easier to oxidise as compare d with the PPh3 analogues. (C)1998 Elsevier Science S.A. All rights re served.