Multinuclear ( 31P, 195Pt) magnetic resonance and electrospray mass spectrometric studies of the reactions between platinum bis(dithiolates) and two potentially tetradentate phosphine ligands

Abstract

The reactions of platinum(II) bis(dithiolates) Pt(SS) 2 ((SS)=S 2P(OEt) 2 (dtp), S 2CO nPr (xan), S 2CNEt 2 (dtc)) with two potentially tetradentate phosphine ligands have been investigated by multinuclear magnetic resonance spectroscopy and electrospray mass spectrometry (ESMS). The phosphines used were P(CH 2CH 2PPh 2) 3 (P 3P′) and Ph 2PCH 2CH 2P(Ph)CH 2CH 2P(Ph)CH 2CH 2PPh 2 (P 2P′ 2). 31P and 195Pt NMR spectroscopies show that P 3P′ reacts in dichloromethane solution with Pt(dtp) 2 and Pt(xan) 2 to give five-coordinate [(η 4-P 3P′)Pt(η 1-SS)] + and with Pt(dtc) 2 to give a temperature dependent mixture of [(η 4-P 3P′)Pt(η 1-dtc)] + and [(η 3-P 3P′)Pt(η 2-dtc)] +. All these formulations were confirmed by observation of the intact ions in the ES mass spectra directly from the solutions. [(η 4-P 3P′)Pt(η 1-xan)] + slowly reacts with the free xan ion to give the dithiocarbonate complex (η 3-P 3P′)Pt(η 2-S 2CO). The pendant phosphine in [(η 3-P 3P′)Pt(η 2-dtc)] + undergoes various chemical reactions such as methylation and reaction with sulfur, and the cation behaves as a monodentate phosphine towards Pt(dtp) 2 to give [(η 1-dtp)(η 2-dtp)Pt(η 1-μ 2-η 3-P 3P′)Pt(η 2-dtc)] + which was fully characterised by multi-NMR spectroscopy and confirmed by observation of the intact ion by ESMS. P 2P′ 2 reacts with Pt(dtp) 2 to give [(P 2P′ 2)Pt] 2+, but with Pt(xan) 2 and Pt(dtc) 2 the products are [(η 4-P 2P′ 2)Pt(η 1-SS)] +, but the xanthate complex slowly de-alkylates to give (η 3-P 2P′ 2)Pt(η 2-S 2CO). The identities of the cationic P 2P′ 2 species in solution were confirmed by direct observation of the intact ion by ESMS.