Preparation of half-sandwich ethylene complexes of Osmium(II)
Graphical abstract
Preparation and X-ray crystal structure determination of ethylene complexes of osmium(II) are described.
Highlights
► Synthesis of half-sandwich ethylene complexes of osmium under mild conditions. ► Spectroscopic and crystallographic characterization of η2-ethylene derivatives. ► DFT calculations.
Introduction
The coordination of an alkene to a transition metal fragment occupies an important place in organometallic chemistry [1], [2], not only due to the significant changes in structure and chemical reactivity that the alkene coordination to a central metal may induce [3], [4], but also due to the influence that the metal fragment may have in its catalytic transformations [5]. A number of alkene complexes have been prepared [1], [3], [4], [6] for different central metals with various types of ligands, in order to probe the most important factors which influence the stability of the coordinated alkene and its reactivity in stoichiometric and catalytic organic reactions.
However, the number of reported alkene complexes for the metals of the iron triad is still limited, compared with other metal triads [7] such as those of cobalt and nickel, and the known ethylene complexes for osmium are still few [8].
We have a long-standing interest in the chemistry of arene complexes [9] of the iron triad and, during our studies on the reactivity of p-cymene complexes of osmium, we found that ethylene may coordinate to the metal fragment [OsCl(η6-p-cymene)L]+ (L = phosphite) in very mild conditions.
We report here the results of these studies, including the synthesis and characterization of ethylene complexes of osmium stabilized by the p-cymene ligand.
Section snippets
General comments
All synthetic work was carried out in an appropriate 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, allowing their characterization; nonetheless they 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. OsO4 was a Pressure Chemical Co. (USA) product, used as received.
Results and discussion
Ethylene reacts in mild conditions (1 atm, room temperature) with dichloro complexes OsCl2(η6-p-cymene)L in the presence of NaBPh4 to give η2-ethylene derivatives [OsCl(η6-p-cymene)(η2-CH2CH2)L]BPh4 (1), which were isolated as yellow solids and characterized (Scheme 1).
Important for successful synthesis was the presence of the salt NaBPh4, which probably favors substitution of the chloride ligand in the starting complexes, thus allowing derivatives 1 to be obtained in good yields.
Studies of the
Conclusions
In this paper we report the preparation of ethylene complexes of osmium stabilised by the p-cymene ligand. The facile substitution of the η2-CH2CH2 ligand allowed new half-sandwich derivatives to be obtained. The structural parameters and the nature of the Os–ethylene bond in the ethylene complexes are also discussed.
Acknowledgments
The authors wish to thank MIUR (PRIN2009) for financial support and CINECA Award N. HP10CI3CHF (2010) for making available high-performance computing resources and support. Thanks also go to Mrs. Daniela Baldan, from the Università Ca’ Foscari Venezia (Italy), for technical assistance.
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