General Route to Cyclobutadiene Rhodium Complexes

Cyclobutadiene rhodium complexes bear high potential for applications in organometallic synthesis and catalysis. We have found that the cyclobutadiene complexes with substitutionally labile p-xylene ligands [(C4R4)Rh(p-xylene)](+) can be synthesized in one step from the commercially available bis(ethylene) complex [{(C2H4)(2)RhCl}(2)], p-xylene, and internal alkynes. The replacement of p-xylene by various ligands provides a general access to other [(C4R4)Rh] compounds, such as [(C4R4)RhCl](x), [(C4R4)RhL3](+), [(C4R4)Rh(C5H5)], and [(C4R4)Rh(arene)](+). Complex [(C4Et4)Rh(p-xylene)](+) also catalyzes an unusual cycloisomerization of a 1,11-dien-6-yne into a bicyclic diene.