A vibrational investigation of several platinum and palladium cyclopentene complexes

Abstract Complete vibrational assignments of the complexes [Cl 2 Pt(C 5 H 8 )] 2 , [Br 2 Pt(C 5 H 8 )] 2 , [Cl 2 Pd(C 5 H 8 )] 2 and [Br 2 Pd(C 5 H 8 )] 2 have been undertaken from 1500 to 70 cm −1 . A reinvestigation of the cyclopentene spectrum was necessary and a new set of assignments is given. The v (CC) shifts down about 200 cm −1 for all the complexes and represents the largest shift observed for a Pd-mono-olefln complex. The shifts observed for the cyclopentene vibrations upon complexation as well as the fact that there are two platinum-carbon stretching frequencies but only one palladium-carbon stretching frequency is consistent with a strong π interaction in the platinum complexes leading to a bonding scheme and a predominantly σ interaction in the palladium complexes with the bonding scheme being the best description. It appears, however, that the total interaction, i.e. σ + π, is about the same in the complexes studied.