Synthesis, structure, and reactivity of four-, five-, and six-coordinate ruthenium carbyne complexes

Square-planar carbyne complexes of the form Ru(CR)(PCy3)(2)X (X = F, Cl, Br, I, O3SCF3) are prepared by net dehydrohalogenation of the Grubbs catalysts Ru(CHR)(PCy3)(2)Cl-2 followed by substitution of the chloride ligand (when X not equal Cl). The dehydrohalogenation can be effected in one step (R = n-Bu, Ph, p-C6H4Me) by Ge(CH[SiMe3](2))(2) or in two steps via treatment with excess aryloxide such as NaO-p-C6H4-t-Bu followed by SnCl2. The latter route gives greater yields but is more restricted in scope. Addition of HCl (1 equiv) to Ru(CR)(PCy3)(2)X (X = Cl, Br, I) affords Ru(CHR)(PCy3)(2)ClX; those with mixed halide ligand sets undergo rapid halide exchange in solution. Upon treatment with the appropriate oxidant, each Ru(C-p-C6H4Me)(PCy3)(2)X complex undergoes two-electron oxidation. Oxidation of Ru(C-p-C6H4Me)(PCy3)(2)X (X = F, Cl, Br, I) by XeF2, C2Cl6, Br-2, and I-2, respectively, yields either six-coordinate bis-phosphine complexes Ru(C-p-C6H4Me)(PCy3)(2)X-3 (X = F, Cl) or square-pyramidal mono-phosphine complexes Ru(C-p-C6H4Me)(PCy3)X-3 (X = Br, I) depending on the size of the halide ligands. Cationic square-pyramidal complexes of the form [Ru(C-p-C6H4Me)(PCy3)(2)X-2](+) (X = Cl, I) can be prepared from Ru(C-p-C6H4Me)(PCy3)(2)Cl-3 by chloride abstraction using [Ph3C]BF4 and from Ru(C-p-C6H4Me)(PCy3)X-3 by addition of PCy3. Hydride addition to Ru(C-p-C6H4Me)(PCy3)(2)Cl-3 yields the carbene complex Ru(CHR)(PCy3)(2)Cl-2, whereas fluoride addition affords the carbyne complex Ru(C-p-C6H4Me)(PCy3)(2)Cl2F, results with important implications for metathesis of vinyl fluorides. X-ray structures of Ru(C-p-C6H4Me)(PCy3)(2)X2F (X = F, Cl), [Ru(C-p-C6H4Me)(PCy3)(2)Cl-2]BF4, and Ru(C-p-C6H4Me)(PCy3)I-3 reveal short RuC bonds in the 1.670(5)-1.714(3) A range; when two PCy3 ligands are present, they are mutually trans. The benzylidyne ligands occupy the apical sites in the two square-pyramidal complexes. Of the five- and six-coordinate complexes, only the two fluoride-containing complexes Ru(C-p-C6H4Me)(PCy3)(2)X2F (X = F, Cl) display reactivity toward alkynes, serving as alkyne dimerization catalysts.