Preparation and reactivity of germyl complexes of ruthenium and osmium stabilised by cyclopentadienyl, indenyl and tris(pyrazolyl)borate fragments
Graphical abstract
The preparation of trichlorogermyl complexes of ruthenium and osmium, stabilised by cyclopentadienyl, indenyl and tris(pyrazolyl)borate ligands, is described. Their reactions with LiAlH4 and NaBH4, affording trihydridogermyl and triethoxygermyl derivatives, is also reported.
Introduction
The chemistry of transition metal complexes containing trichlorogermyl GeCl3 or triorganogermyl GeR3 as ligands has been extensively studied over several decades [1], [1](a), [1](b), [2], [2](a), [2](b), [2](c), [2](d), [2](e), [2](f), [2](g), [2](h), [2](i), [2](j), [2](k), [2](l), [2](m), [2](n), [2](o), [2](p), [2](q), [2](r), [2](s), [3], [3](a), [3](b), [3](c), [3](d), [3](e), [3](f), [3](g), [3](h), [3](i), [3](j), [3](k), [3](l), [3](m), [3](n), [3](o), [3](p), [3](q), [3](r), both from a fundamental point of view and because these complexes are regarded as intermediates in a number of transition metal-catalysed transformations of group-14 element compounds [4], [4](a), [4](b), [4](c), [4](d), [5], [5](a), [5](b), [5](c), [5](d), [5](e), [5](f). A number of germyl complexes of several metals have thus been prepared, containing both mononuclear GeCl3 and GeR3 and polynuclear [GeR2GeR2GeR2] germyl groups, but relatively few have been reported with trihydridogermyl GeH3 as ligand [6], [6](a), [6](b), [6](c), [6](d).
We are interested in the synthesis and reactivity of germyl complexes of transition metals and have recently reported [7], [8] the synthesis and reactivity of trihydrido- [M]–GeH3 and organo-germyl [M]–GeR3 (R = Me, OEt, PhC
C) derivatives of Mn and Re, and the preparation of osmium complexes containing an oxo-germanium cluster as ligand. We have now extended these studies to both half-sandwich and tris(pyrazolyl)borate complexes of the iron triad of the types MCl(η5-C5H5)PPh3L, MCl(η5-C9H7)PPh3L, and MCl(Tp)PPh3L [M = Ru, Os; Tp = tris(pyrazolyl)borate; L = phosphite] and this paper reports the preparation and characterisation of new germyl complexes, including the first trihydridogermyl derivatives of ruthenium and osmium.
Section snippets
General comments
All synthetic work was carried out in an appropriate inert atmosphere (Ar, N2) using standard Schlenk techniques or an inert atmosphere dry-box. Once isolated, the complexes were found to be relatively stable in air, but were stored under nitrogen at −25 °C. All solvents were dried over appropriate drying agents, degassed on a vacuum line, and distilled into vacuum-tight storage flasks. RuCl3·3H2O and OsO4 were obtained from Pressure Chemical Co. (USA) and used as received. Phosphonite PPh(OEt)2
Cyclopentadienyl and indenyl complexes
Half-sandwich trichlorogermyl complexes of the types Ru(GeCl3)(η5-C5H5)(PPh3)L (1) and Ru(GeCl3)(η5-C9H7)(PPh3)L (2) were prepared by reacting chloro complexes RuCl(η5-C5H5)(PPh3)L and RuCl(η5-C9H7)(PPh3)L with GeCl2·dioxane in ethanol, as shown in Scheme 1.
The reaction proceeded with the insertion of GeCl2 into the Ru–Cl bond to afford trichlorogermyl derivatives 1 and 2, which were isolated in good yield and characterised.
Trichlorogermyl derivatives 1 and 2 were reacted with hydride-transfer
Conclusions
This paper reports that both half-sandwich fragments with cyclopentadienyl and indenyl ligands Ru(η5-C5H5)(PPh3)L and Ru(η5-C9H7)(PPh3)L (L = phosphite) can stabilise trichlorogermyl complexes [Ru]–GeCl3. Their reaction with group 13 hydrides, which afforded trihydridogermyl derivatives [Ru]–GeH3 with LiAlH4, was interesting, whereas triethoxygermyl complexes [Ru]–Ge(OEt)3 were only obtained with NaBH4 in ethanol. The tris(pyrazolylborate) ligand (Tp) can also stabilise trichlorogermyl
Acknowledgements
The financial support of MIUR (Rome) - PRIN 2009 is gratefully acknowledged. We also thank Mrs. Daniela Baldan, from the Università Ca’ Foscari Venezia (Italy), for her technical assistance.
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