Reactions of triphenylcyclopropenyl bromide with [Mo(CO)4L2][L2= 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), or 2,2′-dipyridylamine (dpa)] yield the two series of products [MoBr(CO)2(η3-C3Ph3)L2] and [MoBr(CO)2(η3-C4Ph3O)L2]. The cyclopropenyl complexes were also prepared from [MoBr(CO)2(η3-C3Ph3)(NCMe)2] by reaction with L2 in MeCN, which yielded crystalline solvates suitable for an X-ray structure determination. Crystals of [MoBr(CO)2(η3-C4Ph3O)(bipy)]·thf, (1), are monoclinic, a= 9.87(1), b= 20.36(1), c= 16.23(1)A, β= 92.2(1)°, Z= 4, space group P21/c. Crystals of [MoBr(CO)2(η3-C3Ph3)(bipy)]·MeCN, (2), are triclinic, a= 10.552(8), b= 11.607(9), c= 13.801(11)A, α= 67.1(1), β= 100.4(1), γ= 89.5(1)°, Z= 2, space group P. 2 832 and 1 804 above background reflections were collected on a diffractometer and refined by full-matrix least squares to R 0.072 and 0.082 for (1) and (2) respectively. In both structures the molybdenum atoms are in octahedral environments, with the mutually cis carbonyl groups and the bipy ligand occupying an equatorial plane. In trans positions are a bromine atom and in (1) a η3-oxocyclobutenyl group and in (2) a η3-cyclopropenyl group.