NMR, IR and DFT studies of phenylplatinum complexes with O-monodentate coordinated silsesquioxanate and auxiliary phosphine ligands

Abstract

The molecular structure and spectroscopic properties of a series of phenylplatinum complexes containing silsesquioxanate and phosphine ligands with general formula trans-[Pt{O 10Si 7(R) 7(OH) 2}(Ph)(L) 2] ( 1: R = cyclo-C 5H 9, L = PEt 3; 2: R = iso-C 4H 9, L = PEt 3; 3: R = CH 3, L = PEt 3; 4: R = cyclo-C 5H 9, L = PMe 3; 5: R = cyclo-C 5H 9, L = PMe 2Ph; 6: R = cyclo-C 5H 9, L = PPh 2Me; 7: R = cyclo-C 5H 9, L = PPh 3) have been investigated by DFT/OPW91/6-31G(d) calculations, 1H, 13C, 29Si and 31P NMR and IR spectroscopy. DFT molecular modeling based on available X-ray and NMR data for complexes 1 and 2 allowed deriving structure-NMR spectra correlations. It was found that the alkyl substituents (R) attached to Si atoms, cyclo-C 5H 9, iso-C 4H 9 and CH 3, slightly influence the geometry and multinuclear NMR parameters of the complexes in the series studied. The molecular structures of the Pt(II) complexes with R = cyclo-C 5H 9 ( 4– 7) were predicted by DFT calculations of their simplified models with R = CH 3 ( 4′ −7′). The geometry optimizations of 4′ −7′ showed square-planar configuration of Pt(II) center bonded to two trans phosphine ligands, a phenyl group and an O-monocoordinated silsesquioxanate. The structures 4′ −6′ are stabilized by two intramolecular hydrogen bonds similar to 1 and 2. A fast conformer exchange process A↔B and switching of H-bonds in solution of 1– 6 were suggested based on (i) the calculated conformer energies and small barrier of the process, and (ii) the observed single 1H NMR signal at low magnetic field. The stability of the Pt(II) complexes depends on the nature of the phosphine ligands and decreases in the order PMe 2Ph > PMe 3 > PPh 2Me > PEt 3 > PPh 3. The PPh 3 ligands attached to Pt(II) in 7 cause the largest geometry changes and a new set of weaker hydrogen bonds. The comparison of the calculated NMR and IR parameters with the experimental spectroscopic data reveals good coincidence and thus confirmed the suggested molecular structures.