A comparative study of the reactivity of the lightly stabilized cluster [Os3(CO)8{μ3-Ph2PCH2P(Ph)C6H4}(μ-H)] towards tri(2-thienyl)-, tri(2-furyl)- and triphenyl-phosphine

Abstract

Reactions of the lightly stabilized triosmium cluster [Os3(CO)8{μ3-Ph2PCH2P(Ph)C6H4}(μ-H)] with tri(2-thienyl)phosphine (PTh3) and tri(2-furyl)phosphine (PFu3) are described and compared to analogous reactions with PPh3. At room temperature, a number of products are isolated: [Os3(CO)10(μ-dppm)] from CO addition, [Os3(CO)8(PR3){μ3-Ph2PCH2P(Ph)C6H4}(μ-H)] from phosphine addition, [Os3(CO)9(PR3)(μ-dppm)] from phosphine and CO addition and [Os3(CO)8(PR3)2(μ-dppm)] from addition of two equivalents of phosphine. The latter are shown by NMR and X-ray diffraction to exist as 1,2-isomers, whereby one phosphine is bound to the non-dppm-substituted center and the second shares an osmium atom with one end of the diphosphine. Heating 1,2-[Os3(CO)8(PTh3)2(μ-dppm)] at 100 °C results in its clean isomerization to the 1,1-isomer in which both monodentate phosphines are located on the same osmium atom. Prolonged heating of [Os3(CO)8(PR3)2(μ-dppm)] (R = Th, Ph) at 110 °C gives [Os3(CO)9(PR3)(μ-dppm)] and the new lightly stabilized clusters [Os3(CO)7(PR3){μ3-Ph2PCH2P(Ph)C6H4}(μ-H)], the latter being formed by loss of phosphine and CO with concurrent metalation of a phenyl ring. Heating [Os3(CO)8(PFu3)2(μ-dppm)] at 110 °C gives [Os3(CO)9(PFu3)(μ-dppm)] together with the carbon-phosphorus bond cleavage products [Os3(CO)7(μ-PFu2)(μ3-η2-C4H2O)(μ-H)(μ-dppm)] and [Os3(CO)7(μ-PFu2)(μ3-η2-C6H3CH3)(μ-H)(μ-dppm)]. All new compounds were characterized by analytical and spectroscopic techniques together with single crystal X-ray diffraction analysis of nine clusters. Density functional theory (DFT) calculations have been carried out on isomers of [Os3(CO)8(PR3)2(μ-dppm)] in order to understand the observed isomer ratios.