Metal complexes of sulphur ligands. Part VII. Reaction of mer-trichlorotris(dimethylphenylphosphine)rhodium(III) with NN-dimethyldithiocarbamate, dimethyl- and diphenyl-phosphinodithioate, and O-ethyl dithiocarbonate (xanthate) ligands

Abstract

Reactions of the complex mer-[RhCl₃(PMe₂Ph)₃], (I), with excess of (S–S)^– ion [(S–S)^–=^–S₂CNMe₂, ^–S₂PMe₂, ^–S₂PPh₂, ^–S₂COEt] have been thoroughly studied. On shaking in methanol for 10 min, the complexes mer-[RhCl₂(S–S)(PMe₂Ph)₃], (IV), are formed which contain a unidentate dithio-acid group. Recrystallisation of complexes (IV) from non-polar solvents gives trans-[RhCl₂(S–S)(PMe₂Ph)₂], (II). For (S–S)^–=^–S₂PMe₂ or ^–S₂PPh₂, further recrystallisation gives small amounts of the cis–cis–cis–isomers (VII). Conversely, for (S–S)^–=^–S₂CNMe₂ or ^–S₂COEt, reaction of complexes (IV) with NaBPh₄ in methanol gives some mer-[RhCl(S–S)(PMe₂Ph)₃]BPh₄, (V), as well as (II). However, reaction of complex (I) with excess of (S–S)^– heated under reflux in ethanol for 60 min, followed by addition of Y (Y = BPh₄^– or PF₆^–) to the filtrate, gives high yields of cis-[Rh(S–S)₂(PMe₂Ph)₂]Y [III; (S–S)^–=^–S₂CNMe₂, ^–S₂PMe₂, or ^–S₂PPh₂]. Reaction of the complex mer-[RhCl₃(PMePh₂)₃] with NaS₂CNMe₂,2H₂O in ethanol gives both cis- and trans-[Rh(S₂CNMe₂)₂(PMePh₂)₂]Y [(III) and (VI) respectively]. In contrast, reaction of complex (I) with KS₂COEt gives mer-[RhCl(S₂CO)(PMe₂Ph)₃](X), K[RhCl₂(S₂CO)(PMe₂Ph)₂](XI), and trans- and cis-[Rh(S₂CO)(S₂COEt)(PMe₂Ph)₂][(XII) and (XIII) respectively], which can be separated by chromatography. The complexes have been characterised by elemental analyses and i.r. and n.m.r. spectroscopy (¹H and ³¹P), and a detailed mechanism for the overall reaction is postulated.