Synthesis, Structure, and Reactivity of Four-, Five-, and Six-Coordinate Ruthenium Carbyne Complexes

Abstract

Square-planar carbyne complexes of the form Ru(⋮CR)(PCy 3 ) 2 X (X = F, Cl, Br, I, O 3 SCF 3 ) are prepared by net dehydrohalogenation of the Grubbs catalysts Ru( CHR)(PCy 3 ) 2 Cl 2 followed by substitution of the chloride ligand (when X ≠ Cl). The dehydrohalogenation can be effected in one step (R = n -Bu, Ph, p -C 6 H 4 Me) by Ge(CH[SiMe 3 ] 2 ) 2 or in two steps via treatment with excess aryloxide such as NaO- p -C 6 H 4 - t -Bu followed by SnCl 2 . The latter route gives greater yields but is more restricted in scope. Addition of HCl (1 equiv) to Ru(⋮CR)(PCy 3 ) 2 X (X = Cl, Br, I) affords Ru( CHR)(PCy 3 ) 2 ClX; those with mixed halide ligand sets undergo rapid halide exchange in solution. Upon treatment with the appropriate oxidant, each Ru(⋮C- p -C 6 H 4 Me)(PCy 3 ) 2 X complex undergoes two-electron oxidation. Oxidation of Ru(⋮C- p -C 6 H 4 Me)(PCy 3 ) 2 X (X = F, Cl, Br, I) by XeF 2, C 2 Cl 6, Br 2, and I 2, respectively, yields either six-coordinate bis-phosphine complexes Ru(⋮C- p -C 6 H 4 Me)(PCy 3 ) 2 X 3 (X = F, Cl) or square-pyramidal mono-phosphine complexes Ru(⋮C- p -C 6 H 4 Me)(PCy 3 )X 3 (X = Br, I) depending on the size of the halide ligands. Cationic square-pyramidal complexes of the form [Ru(⋮C- p -C 6 H 4 Me)(PCy 3 ) 2 X 2 ] + (X = Cl, I) can be prepared from Ru(⋮C- p -C 6 H 4 Me)(PCy 3 ) 2 Cl 3 by chloride abstraction using [Ph 3 C]BF 4 and from Ru(⋮C- p -C 6 H 4 Me)(PCy 3 )X 3 by addition of PCy 3 . Hydride addition to Ru(⋮C- p -C 6 H 4 Me)(PCy 3 ) 2 Cl 3 yields the carbene complex Ru( CHR)(PCy 3 ) 2 Cl 2, whereas fluoride addition affords the carbyne complex Ru(⋮C- p -C 6 H 4 Me)(PCy 3 ) 2 Cl 2 F, results with important implications for metathesis of vinyl fluorides. X-ray structures of Ru(⋮C- p -C 6 H 4 Me)(PCy 3 ) 2 X 2 F (X = F, Cl), [Ru(⋮C- p -C 6 H 4 Me)(PCy 3 ) 2 Cl 2 ]BF 4, and Ru(⋮C- p -C 6 H 4 Me)(PCy 3 )I 3 reveal short Ru⋮C bonds in the 1.670(5)−1.714(3) Å range; when two PCy 3 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 -C 6 H 4 Me)(PCy 3 ) 2 X 2 F (X = F, Cl) display reactivity toward alkynes, serving as alkyne dimerization catalysts.