Photochemical synthesis of a zirconium cyclobutadienyl complex.

Photolysis of (MePMPMe)2ZrBn2 (MePMPMe = 3,5-dimethyl-2-(2-pyridyl)pyrrolide) in the presence of diphenylacetylene yields the first η4-cyclobutadienyl zirconium complex, (MePMPMe)2Zr(η4-C4Ph4), through formal [2+2] cycloaddition of two alkynes at a putative low-valent zirconium intermediate. This unique reactivity expands the scope of alkyne coupling reactions at low-valent zirconium centers that traditionally produce zirconacyclopentadienes.