Crystal structure and reactivity of mononuclear cationic palladium(II) and platinum(II) triphos complexes with phenyltin(IV) anions. The formation of polynuclear platinum–triphos ionic and covalent complexes

Abstract

The ionic complexes [M(triphos)Cl]X [M=Pd, X=Cl ( 1), SnCl 3 ( 1a), SnPh 2Cl 3 ( 1c); M=Pt, X=Cl ( 3), SnCl 3 ( 3a), SnPh 2Cl 3 ( 3c)], [M(triphos)Cl] 2X [X=SnPh 2Cl 4, M=Pd ( 1b), Pt ( 3b); X=PtCl 4, M=Pt ( 3d)] and [M(triphos) 2]X 2 [X=SnPh 2Cl 3, M=Pd ( 2), Pt ( 4)] where triphos=bis(2-diphenylphosphinoethyl)phenylphosphine, were synthesised and characterised by microanalysis, mass spectrometry, IR, 119Sn Mössbauer, NMR ( 31P, 195Pt and 119Sn) spectroscopies and conductivity measurements. The X-ray crystal structures of compounds 1b, 3b and 3c, where tetrachlorodiphenylstannate(IV) and trichlorodiphenylstannate(IV) act as counterions stabilising cationic metal complexes, are reported. These compounds contain the cation [M(triphos)Cl] + with distorted square-planar geometry at palladium or platinum, triphos acting as a tridentate chelating ligand. The anions [SnPh 2Cl 4] 2− ( 1b, 3b) and [SnPh 2Cl 3] − ( 3c) have trans-octahedral and distorted trigonal-bipyramidal environments for the metal, respectively. Although the dinegatively charged [SnPh 2Cl 4] 2− is counteracted by the presence of two singularly positively charged [M(triphos)Cl] + species, interanion contacts via hydrogen bonds were found for 1b and 3b but were absent for compound 3c. The crystalline solids [M(triphos) 2][SnPh 2Cl 3] 2 [M=Pd ( 2), Pt ( 4)] were formed via a chelate ring-opening reaction of [M(triphos)Cl] + induced by triphos. The formation of heterometallic complexes by reaction of AgCl or Au(I) with the complex [Pt(triphos) 2][SnPh 2Cl 3] 2 ( 4), followed by 31P NMR in solution, did not take place. The presence of dangling arm phosphine oxide groups, on oxidation of complex 4 with H 2O 2, was detected. Other ring-opening reactions were observed by 31P NMR and conductivity measurements when solutions containing PtCl 2(PhCN) 2 and triphos in a molar ratio 3:2 were refluxed C 6H 6. Besides [Pt(triphos)Cl] 2[PtCl 4] ( 3d) and the ionic complex with a dinuclear anion, [Pt(triphos)Cl][Pt 2(triphos)Cl 5] ( 5), the covalent trinuclear complexes [{PtCl 2(Ph 2PCH 2CH 2) 2PPh-P 1,P 2} 2(P 3,P 3)PtCl 2] ( 6a, 6b) were formed as minor products. These latter diastereomeric species become the dominant species upon heating, being thermodynamically controlled complexes. Mixtures of 3d, 5, 6a and 6b converted to complex [Pt(triphos)Cl]Cl ( 3) by addition of triphos, chelate ring-closure reactions of 6a, 6b and the complex anion 5 occurring. With an excess of triphos (Pt:triphos=3:4 or higher ratio), broad peaks reflecting fast equilibria between ring-opened and ring-closed products were found.