Synthesis and electrospray mass spectrometry of platinum(II) complexes of 5,5-diethylbarbituric acid (Hdebarb); crystal structure of cis-[PtCl(debarb)(PPh3)2]·CH2Cl2

Abstract

The reactions of 5,5-diethylbarbituric acid (Hdebarb; 1H,3H,5H-5,5-diethylpyrimidine-2,4,6-trione), either as the monosodium salt or free acid in the presence of ancillary base (silver oxide or triethylamine), with platinum(II) halide complexes yielded mono(barbiturato) complexes cis-[PtX(debarb)L₂][X = Cl, Br or I; L = PPh₃; L₂= 1,2-bis(diphenylphosphino)ethane (dppe) or 1,1′-bis(diphenylphosphino)ferrocene (dppf)]. A single-crystal structure determination of cis-[PtCl(debarb)(PPh₃)₂]·CH₂Cl ₂ showed that the plane of the N-bonded barbiturate ligand is approximately perpendicular to the platinum co-ordination square plane, rendering the two ethyl substituents inequivalent. Electrospray mass spectrometry has also been used to study these complexes, with the major ions for cis-[PtX(debarb)L₂] being [Pt(debarb)L₂]⁺ and [Pt(debarb)(NCMe)L₂]⁺, though molecular ions [M + H]⁺ are also observed for all complexes. A number of cationic derivatives of the type [Pt(debarb)L₂L′]⁺(L = PPh₃ or L₂= dppe; L′= pyridine or PPh₃) are also reported.