Abstract
Solid‐state route to a cyclobutenone: Ruthenium perchlorocyclobutenonyl complex 2 is obtained by solid‐state photoisomerization of ruthenium trichloroacetyl acetylide complex 1. The four‐membered ring is sufficiently robust that transfer of the intact ligand could be readily achieved in a reaction of 2 with an enyne. Cyclobutenedionyl complex 3 was obtained by hydrolysis of 2 in H~2~O/THF.magnified image
New reactions were observed for the cationic γ‐hydroxyvinylidene complex [Ru^2^]CCHC(OH)(CCl~3~)~2~^+^ (2, [Ru^2^]=CpRu(PPh~3~)~2~). A rare chloroform elimination was observed when 2 was treated with __n__Bu~4~NOH to give neutral acetylide complex [Ru^2^]CCC(O)CCl~3~ (3). Solid‐state photoinduced isomerization of 3 generated ruthenium perchlorocyclobutenonyl complex [Ru^2^]C~4~Cl~3~O (4) in high yield. This transformation was analyzed by DFT calculations, and 4 was found to be 4.22 kcal mol^−1^ more stable in terms of Gibbs free energy than 3. In the coupling reaction of 4 with 2‐methyl‐1‐buten‐3‐yne the four‐membered cyclic ligand is transferred to the enyne to give substituted η^3^‐butadienyl complex 5 containing a cyclobutenonyl group. This coupling product could be removed from the metal by HCl. Deprotonation of 2 gave γ‐hydroxyacetylide complex [Ru^2^]CCC(OH)(CCl~3~)~2~ (9). In the photolysis of 9 phosphine dissociation is followed by addition of HCl to give neutral vinylidene complex Cl[Ru^1^]CCHC(OH)(CCl~3~)~2~ (10, [Ru^1^]=Cp(PPh~3~)Ru). Complex 4 catalyzed the coupling reaction of dimethyl acetylenedicarboxylate with styrene yielding the diene PhCHCHC(CO~2~Me)CHCO~2~Me. Solid‐state structures of 3–6 and 10 were determined by single‐crystal X‐ray diffraction analysis.