Synthesis, structures and 31P NMR studies of bis(diphenylphosphino)methane adducts of copper and silver thiocarboxylates †

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Abstract
The compounds [Cu3(μ-dppm)3(SC{O}Me)2][PF6] 1, [Cu3(μ-dppm)3(SC{O}Ph)2][X] (X = ClO42 or PF62a) were synthesized by treating Na+R{O}CS− (R = Me or Ph) with a mixture of [Cu(MeCN)4]X (X = PF6 or ClO4) and bis(diphenylphosphino)methane (dppm) in stoichiometric ratios. The structures of 1 and 2 have been determined by single crystal X-ray crystallography. The trinuclear core is held intact by the three bridging dppm ligands and two capping thiocarboxylate anions. One of the thiocarboxylate anions triply bridges to the Cu3(μ-dppm)3 core through a μ3-S and the other by a μ3-S,O bonding mode. Compounds [Ag3(μ-dppm)3(SC{O}Me)2][X] (X = NO33 or ClO43a) and [Ag3(μ-dppm)3(SC{O}Ph)2][ClO4] 4 were prepared by treating Na+R{O}CS− (R = Me or Ph) with dppm and the corresponding silver salt. The structures of 3 and 4 were determined by X-ray crystallography. Both the thiocarboxylate anions bond in μ-S fashion, thereby stabilizing the trinuclear core. In all the four crystal structures C–H O hydrogen bonding is present between one of the methylene hydrogen atoms and the carbonyl oxygen of the thiocarboxylate ligand. 31P NMR studies in solution at low temperatures reveal that all the compounds retain their trinuclear core in solution, while intramolecular exchange involving dppm does not cease even at lower temperatures. Attempts to prepare monocapped trinuclear cations, [M3(μ-dppm)3(SC{O}R)]2+, and binuclear neutral compounds, [M2(μ-dppm)2(SC{O}R)2], yielded only the corresponding bicapped trinuclear compounds.

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