Reaction of Heterotrinuclear Vinylacetylide Complexes Cp*WRe₂(CO)₉(C≡CR) with Alcohol and Dihydrogen. Formation of WRe₂ Allenylidene and Metallacyclopentadienyl Derivatives

Heterometallic vinylacetylide clusters with the structural formula Cp*WRe₂(CO)₉(C≡CR) were obtained in high yields from condensation of mononuclear tungsten acetylide complexes Cp*W(CO)₃(C≡CR) and rhenium carbonyl complex Re₂(CO)₈(NCMe)₂. The acetylide ligand in these WRe₂ clusters is coordinated perpendicular to the unique Re—Re bond which also supports a bridging CO ligand. Treatment of the vinylacetylide complex Cp*WRe₂(CO)₉[C≡CC-(Me)=CH₂] (1a) with alcohols in refluxing toluene solution afforded complexes Cp*WRe₂(CO)₈(μ-OR)(C=C=CMe₂) (2a, R = Me; 2b, R = Et; 2c, R = Ph), which contain an unusual μ₃-η³-allylidene ligand and a bridging alkoxide ligand. The fluxional behavior of allenylidene complexes 2 in solution was confirmed by ¹H NMR measurements. When 1a was heated in the presence of hydrogen, the metallacyclopentadienyl complex Cp*WRe₂(CO)₇(μ-H) [CHCHC-(Me)CH] was formed, as a mixture of two noninterconvertible isomers (3a and 3b). Hydrogenation of 1b under similar conditions initially produced a dihydride cluster Cp*WRe₂(CO)₈(μ-H)₂- [C≡C(C₆H₉)] (4b). Crystals of 4b are orthorhombic of space group Pna2₁ with a = 20.170(6) Å, b = 16.854(3) Å, c = 9.320(3) Å, Z = 4, R = 0.035, and R_w = 0.031 for 2537 observed reflections with I > 2σ(I). Upon extending the reaction time to 1 h, complex 1b produced two metallacyclopentadienyl clusters 3c and 5, and their distinction lies in the location of the cyclohexenyl ring and the arrangement of the metal cluster skeleton. Elaborate structural analysis reveals the complex 3c adopts a triangular arrangement with a metal—metal double bond which is essentially identical to that of 3a and 3b, whereas complex 5 is best considered as a M₃C₄ pentagonal-bipyramidal cluster with a W atom and one Re atom at the axial positions and the second Re atom in the equatorial plane. Crystal data for 3c: space group P1‾, a = 10.947(1) Å, b = 11.074(1) Å, c = 11.167(2) Å, α = 101.38(1)°, β = 104.10(1)°, γ = 94.65(1)°, Z = 2, R = 0.020, R_w = 0.020 for 3045 observed reflections with I > 2σ(I). Crystal data for 5: space group P2₁/c, a = 12.359(5) Å, b = 9.814(4) Å, c = 25.372(8) Å, β = 97.85(3)°, Z = 4, R = 0.036, R_w = 0.033 for 2654 observed reflections with I > 2σ(I).