Rhodium vinylidene and alkyne complexes containing a pendant uracil group

Reaction of HCCUr (Ur = uracil) with RhCl(PiPr₃)₂] results in the formation of the vinylidene complex RhCl(PiPr₃)₂(CC{H}Ur)]. In the solid state this complex forms a hydrogen bonded network which consists of complementary interactions between uracil groups on neighbouring rhodium complexes and with the methanol of crystallisation. The η²-alkyne complexes RhCl(PiPr₃)₂(η²-PhCCUr)] and Rh(η⁵-C₅H₅)(PiPr₃)(η²-PhCCUr)] have also been prepared. In contrast to the behaviour of Rh(η⁵-C₅H₅)(PiPr₃)(η²-PhCCUr)], RhCl(PiPr₃)₂(η²-PhCCUr)] shows little evidence for the formation of hydrogen bonded aggregates in solution. The difference in behaviour between the two species is rationalised on the basis of steric effects.