Competition between Carbon Monoxide and Alkenes in Chloro Complexes of Platinum(II)

ABSTRACT : Mono-olefins (cyclohexene or 1-octene) and di-olefins (cyclo-octadiene, COD, or norbornadiene, NBD) react with cis-PtCl2(CO)2 leading, respectively, to partial and complete displacement of coordinated carbon monoxide. The reactions have been monitored by gasvolumetric methods and by IR and NMR spectra. Equilibrium constants at 21 °C for the monoolefins, as determined by IR spectroscopy in 1,2-dichloroethane are: (2.4 ± 0.5) ́ 10-3 and (2.8 ± 0.4) ́ 10-2 for cyclo-hexene and 1-octene, respectively. Thermodynamic data were obtained by UV spectroscopy between 288 and 313 K, with the following values of DH0 (kJ mol-1) and DS0 (J mol-1 K-1): (30 ± 4) and (51 ± 15) for cyclohexene and (36 ± 2) and (95 ± 8) for 1-octene.