Formation and molecular structure of (η5-cyclopentadienyl)-(η4-cyclobuta-[l]phenanthrene)rhodium: a cyclobutadiene–metal complex derived from the intramolecular cyclodimerization of an acyclic diacetylene

Abstract

Interactions of the diacetylene 2,2′-bis(phenylethynyl)biphenyl with the metal carbonyls [(η⁵-C₅H₅)-Co(CO)₂], [(η⁵-C₅H₅)Rh(CO)₂], and [Fe(CO)₅] proceed via intramolecular cyclodimerization to form the respective η⁴-1,2-diphenylcyclobuta[l]phenanthrene complexes in each case; for the rhodium analogue, a cyclobutadiene-type structure containing a unique trapezoidal η⁴-C₄-ring has been unequivocally established by means of X-ray diffraction techniques.