Synthesis and Characterization of Some Ru(tmeda) Complexes Containing Chloride, Hydride, and Vinylidene Ligands

Summary.  The polymeric compound Ru(cod)Cl₂] _x (cod = cyclooctadiene) reacts with 2 equivalents of tmeda (N,N,N′,N′-tetramethylethylenediamine) in refluxing MeOH to afford trans-Ru(cod)(tmeda)(Cl)(H)] (1), which upon treatment with CHCl₃ is readily converted to the dichloro complex trans-Ru(cod)(tmeda)Cl₂] (2). When Ru(cod)Cl₂] _x is reacted with tmeda under an atmosphere of H₂ (3 bar), the bis-tmeda complex trans-Ru(tmeda)₂Cl₂] (3) is obtained in 80% yield. DFT calculations revealed that 3 is by 52 kJ/mol more stable than the corresponding cis isomer. Attempts to prepare the coordinatively unsaturated complex Ru(tmeda)₂Cl]⁺ by reacting 1 with TICF₃SO₃ were unsuccessful. According to DFT calculations, however, such a complex should be stable and, interestingly, should adopt a square pyramidal rather than a trigonal bipyramidal structure. If halide abstraction of 3 is performed in the presence of terminal alkynes HC*CR (R*t-Bu, n-Bu), the cationic vinylidene complexes Ru(tmeda)₂(Cl)(*C*CHR)]⁺ (4a,b) are obtained. Received March 26, 2001. Accepted April 26, 2001