CC-Coupling Reactions of Group 6 Allenylidenes with Ynamines: Formation of New Cyclobutenylidene and Pentatrienylidene Complexes

The reaction of the diarylallenylidene complexes [(CO)5MCCC(C6H4R-p)2] (M = Cr (1), W (2); R = H (a), Me (b), OMe (c), NMe2 (d)) with the ynamines MeC⋮CNEt2 and PhC⋮CNEt2 affords two products:  alkenylallenylidene (3, 5) and cyclobutenylidene complexes (4, 6). The alkenylallenylidene complexes [(CO)5MCCC(NEt2)C(R‘)C(C6H4R-p)2] (R‘ = Me, M = Cr (3), W (5), R = H (a), Me (b), OMe (c), NMe2 (d); R‘ = Ph, M = Cr (3), R = OMe (e), NMe2 (f)) are formed via cycloaddition of the C⋮C bond of the ynamine to the C2C3 bond of 1 and 2, respectively, and subsequent cycloreversion. The cyclobutenylidene = Me, M = Cr (4), W (6), R = H (a), Me (b), OMe (c), NMe2 (d); R‘ = Ph, M = Cr (4), R = OMe (e), NMe2 (f)) are formed by cycloaddition of the ynamines to the C1C2 bond of 1 and 2. The compounds 3, 4a−c, 5, and 6a−c are stable at room temperature. In contrast, 4d−f and 6d decompose on contact with air, light, or silica. Complex 3d was characterized by an X-ray structural analysis. The product ratios 3/4 and 5/6 strongly d...