Synthesis and dynamic NMR studies of Pt(η 5-C 5Me 5)(CO){C(O)NR 2} complexes

Abstract

The formation of Pt(η 5-C 5Me 5)(CO){C(O)NR 2} (R = Me, Et) complexes was established by spectroscopic analysis. The infrared spectra of these complexes showed a sharp absorption due to the presence of coordinated carbonyl group in the region 2017–2013 cm −1. The N, N-dialkylcarbamoyl ligands showed a characteristic C O stretching absorption in the range 1609–1616 cm −1. The proton NMR spectra of these complexes revealed the expected singlet arising from five equivalent methyl groups on the cyclopentadienyl ring with satellites due to coupling to 195Pt. The N-methyl and N-ethyl protons exhibited very broad resonances due to restricted rotation about the N–C bond at room temperature. On cooling to −30 °C, the N, N-dimethyl protons for complex Pt(η 5-C 5Me 5)(CO){C(O)NMe 2} showed two sharp singlets at δ 2.86 and 3.09 ppm as expected for the static structure. For the N, N-diethyl derivative, Pt(η 5-C 5Me 5)(CO){C(O)NEt 2}, the methyl protons exhibited only a single triplet at δ 1.06 ppm at −10 °C due to coupling with the methylene protons. This single resonance arises through accidental overlap as the methylene protons of the ethyl groups are inequivalent at this temperature and each exhibited a quartet at δ 3.33 and 3.70 ppm due to coupling with the methyl protons. The singlet resonances for the methyl and ring carbons of the η 5-C 5Me 5 group found in 13C{ 1H} NMR spectra are illustrative of the chemical equivalence of all the carbon atoms caused by free rotation of the ring in these complexes. The signals attributable to the carbonyl and carbamoyl carbon atom resonances are found downfield as two singlets each with a large coupling constant to platinum. The platinum coupling constants of the downfield resonances could not be identified for Pt(η 5-C 5Me 5)(CO){C(O)NMe 2} due to presence of impurities.