Photochemical synthesis of a zirconium cyclobutadienyl complex

Photolysis of ((PMPMe)-P-Me)(2)ZrBn2 ((PMPMe)-P-Me = 3,5-dimethyl-2-(2-pyridyl)pyrrolide) in the presence of diphenylacetylene yields the first eta(4)-cyclobutadienyl zirconium complex, ((PMPMe)-P-Me)(2)Zr(eta(4)-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.