Preparation of new acetylide and vinylidene complexes of ruthenium

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Abstract

Monoacetylide RuCl(CCR)P4 complexes (R=Ph, 4-MeC6H4, 1,4-C6H4CCH, SiMe3, But or COOMe; P=P(OEt)3 or P(OMe)3) were prepared by allowing RuCl2P4 to react with terminal alkynes RCCH in the presence of an excess of NEt3. Dinuclear compounds [{Ru[P(OEt)3]5}2(μ-1,4-CCC6H4CC)]Y2 (Y=PF6 or BPh4) were also prepared from the reaction of RuCl2P4 with 1,4-HCCC6H4CCH. Treatment of RuCl2P4 with Li+[1,4-HCCC6H4CC] afforded bis(alkynyl) Ru(1,4-CCC6H4CCH)2P4 [P=P(OEt)3, P(OMe)3 or PPh(OEt)2] derivatives. Protonation reactions of monoacetylides RuCl(CCR)P4 with CF3SO3H led to vinylidene [RuCl{CC(H)R}P4]CF3SO3 [R=Ph, 4-MeC6H4 or 1,4-C6H4CCH; P=P(OEt)3 or P(OMe)3] complexes, which were fully characterised by IR and 1H-, 31P- and 13C-NMR spectra.

Introduction

The chemistry of acetylide and vinylidene organometallic complexes continues to attract interest, due to their potential use in several stoichiometric or catalytic transformations, such as dimerisation of alkynes to enynes or butatrienes [1], formation of unsaturated carbene complexes [2] and metallocumulenes [3], and other C–C coupling reactions [4]. In addition, carbon-rich organometallic compounds are also attractive, due to their potential for granting non-linear optical [5], liquid crystal [6], mixed-valence or conducting [7] properties.

These properties motivate constant studies on the synthesis of mono- and dinuclear σ-acetylide derivatives and their chemical reactivity [1], [2], [3], [4], [8]. Important in this context is the influence of the ancillary ligands, generally mono-, bi- and polydentate phosphine, cyclopentadienyl or arene rings. In contrast, very few reports refer to phosphite P(OEt)3, substituted-phosphite PR(OR′)2 or PR2(OR′) ligands, and only recently some studies [9] on acetylide, vinylidene and enynyl derivatives of iron(II), ruthenium(II) and osmium(II) with these ligands have been reported by our research group. Following this initial work, we now report the synthesis and characterisation of new mono- and dinuclear acetylide complexes of ruthenium, together with their reactivity studies, which yielded new vinylidene derivatives.

Section snippets

General considerations and physical measurements

All synthetic work was carried out in an inert atmosphere (argon, N2) using standard Schlenk techniques or a Vacuum Atmosphere dry-box. Once isolated, the complexes turned out to be quite air-stable and were stored at −20°C. All solvents used were dried over appropriate drying agents, degassed on a vacuum line, and distilled into vacuum-tight storage flasks. Diethoxyphenylphosphine was prepared by the method of Rabinowitz and Pellon [10]; trimethyl- and triethylphosphite were Aldrich products

Preparation of acetylide derivatives

Dichloro complexes RuCl2P4 react with terminal alkynes in the presence of an excess of NEt3 to give the mono-acetylide complexes RuCl(CCR)P4, which were isolated in good yield and characterised (Scheme 1). The reaction also proceeds with 1,4-diethynylbenzene to afford the corresponding mono-acetylide containing the acetylenic end-group.

Studies on the reaction course in the absence of NEt3 indicate (by NMR, see below) the formation of vinylidene intermediates [RuCl{CC(H)R}P4]+ which, by

Conclusions

The present investigations show that the use of monodentate phosphite as ancillary ligand allows the preparation of new monoacetylide RuCl(CCR)P4 derivatives, including 1,4-diethynylbenzene as an alkyne. Dinuclear complexes [{RuP5}2(μ-1,4-CCC6H4CC)](PF6)2 and bis(alkynyl) Ru(1,4-CCC6H4CCH)2P4 derivatives were also synthesised. Among the properties shown by the monoacetylides, we emphasise the fact that protonation reactions are easy, yielding new stable vinylidene [RuCl{CC(H)R}P4]CF3SO3

Acknowledgements

This work was supported by the Ministero della Ricerca Scientifica e Tecnologica (MURST), Rome. We thank Dr Giuseppe Balacco (Menarini Ricerche S.p.A.) for permission to use his swan-mr software. We also thank Daniela Baldan for technical assistance.

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