Cyclohexyneplatinum (0) complexes Pt(C6H8)(P~P) [P~P = (Z)-Ph2PCH=CHPPh2, Ph2P(CH2)3- PPh2 or Ph2P(CH2)4PPh2] and Pt(C6H8)(PMePh2)2 have been prepared by displacement of tri- phenylphosphine from Pt(C6H8)(PPh3)2. Like the known compound containing Ph2PCH2CH2PPh2, these complexes are readily protonated by both strong and weak acids (HY) to give η1-cyclohexen-1- yl -platinum(II) complexes PtY (C6H9)(P~P) (Y = Cl , SPh , O2CMe, CH2CN, OMe , OH). An excess of HCl rapidly cleaves the Pt-C6H9 bond giving PtCl2(P~P) complexes identical with those made from PtCl2(cycloocta-1,5-diene) and P~P. The methoxo complexes react rapidly with water to give the hydroxo complexes and with CO to give methoxycarbonyl complexes Pt(CO2Me)(C6H9)- (P~P). The i.r ., 1H and 31P{1H} n.m.r . spectra of the new complexes are reported and trends in the 31P chemical shifts ( δP ) and in the 195Pt-31P coupling constants (1JPt,P) are compared with those reported in the literature for related systems.