Rhodium vinylidene and alkyne complexes containing a pendant uracil group

Reaction of HCtriple bond; length of mdashCUr (Ur = uracil) with [RhCl(PiPr3)2] results in the formation of the vinylidene complex [RhCl(PiPr3)2(double bond; length as m-dashCdouble bond; length as m-dashC{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-PhCtriple bond; length of mdashCUr)] and [Rh(η5-C5H5)(PiPr3)(η2-PhCtriple bond; length of mdashCUr)] have also been prepared. In contrast to the behaviour of [Rh(η5-C5H5)(PiPr3)(η2-PhCtriple bond; length of mdashCUr)], [RhCl(PiPr3)2(η2-PhCtriple bond; length of mdashCUr)] 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.