Clusters Containing Ynamine Ligands. 6. Transformations of an Ynamine Ligand in a Dirhenium Complex. Synthesis and Structural Characterization of Re₂(CO)₈[μ-H₂CCHCNMe₂], Re₂(CO)₇[μ-H₂CCCNMe₂](μ-H), and Re₂(CO)₈[μ-H₂C=CCNMe₂](μ-H)

The complex Re₂(CO)₈(μ-MeC₂NMe₂) (1) was transformed into three new compounds, Re₂(CO)₇(μ-η³-H₂CCCNMe₂)(μ-H) (2; 17%), Re₂(CO)₈(μ-H₂CCHCNMe₂) (3; 25%), and Re₂(CO)₈(μ-H₂C=CCNMe₂)(μ-H) (4; 0.5%), when heated to 80 °C for 2 h. Compounds 2–4 were characterized by IR, ¹H NMR, and single-crystal X-ray diffraction analyses. Compound 2 is a hydride-containing decarbonylation product of 1 formed by a shift of one of the hydrogen atoms on the C-methyl group to the metal atoms. It also contains a η³ bridging (dimethylamino)allenyl ligand that exhibits carbene-like character at the amine-substituted carbon atom. Compounds 3 and 4 are isomers of 1 formed by a shift of one of the hydrogen atoms on the C-methyl group of 1 to one of the alkynyl carbon atoms. Compound 3 contains a bridging vinyl(dimethylamino)carbene ligand in which the vinyl group is π-bonded to one metal atom and the carbene is terminally coordinated to the other metal atom. Compound 4 contains a η² bridging (dimethylamino)allenyl ligand in an unusual coordination in which the two coordinated carbon atoms lie parallel to the metal-metal bond. The amine-substituted carbon shows a pronounced carbene-like character. Addition of CO to 2 at 25 °C/1 atm yielded compound 4 (79%) and only a trace 3 (1%). At 75 °C 4 was slowly converted to 3 (54% in 18 h) and the new compound 5 (39% in 18 h). Although it was not possible to isolate 5, it was unambiguously identified as Re₂(CO)₈[μ-η²-C₃H₃NMe₂] on the basis of its ¹H NMR spectrum and comparison with the known compound Mn₂(CO)₈(μ-η²-C₃H₃NEt₂). Over a period of 35 h at 100 °C compound 5 was decarbonylated to yield the new compound Re₂(CO)₇(μ-η⁴C₃H₃NMe₂) (6; 53%). Compound 6 is assigned a structure analogous to that of the known compound Mn₂(CO)₇(μ-η⁴-C₃H₃NEt₂) on the basis of its spectral similarities. Crystal data: for 2, space group PĪ, a = 9.572 (2) Å, b = 9.922 (2) Å, c = 9.193 (2) Å, α = 107.91 (2)°, β = 101.25 (1)°, γ = 92.63 (2)°, Z = 2, 1912 reflections, R = 0.021; for 3, space group P2₁/a, a = 15.428 (4) Å, b = 16.047 (6) Å, c = 15.341 (4) Å, β = 115.03 (2)°, Z = 8, 3256 reflections, R = 0.038; for 4, space group P2₁/n, a = 9.268 (2) Å, b = 18.652 (4) Å, c = 10.276 (2) Å, β = 101.24 (1)°, Z = 4, 1738 reflections, R = 0.029.