Synthesis and structure of an unusual di-rhodium diarylbutadiyne π-complex featuring a μ-(1,2-η2):(3,4-η2)-p-CF3C6H4–Ctriple bond; length of mdashC–Ctriple bond; length of mdashC–C6H4-p-CF3 moiety

Reaction of the salt [Rh(PMe3)4]Cl (1) with p-F3C–C6H4–Ctriple bond; length of mdashC–Ctriple bond; length of mdashC–C6H4-p-CF3 (2) in THF gives a mixture of two related neutral π-bound diyne complexes of [Rh(PMe3)3Cl], each having two distinct CF3 resonances of equal intensity in the in situ 19F{1H} NMR spectrum. The ratio of the two products can be varied by varying the stoichiometry of the reagents. On the basis of the spectroscopic data and literature precedent, we propose Rh(PMe3)3(Cl)((1,2-η2)-p-F3C–C6H4–Ctriple bond; length of mdashC–Ctriple bond; length of mdashC–C6H4-p-CF3) (3a) and [Rh(PMe3)3(Cl)]2(μ-(1,2-η2):(1,2-η2)-p-F3C–C6H4–Ctriple bond; length of mdashC–Ctriple bond; length of mdashC–C6H4-p-CF3) (3b) as the most likely structures of the species in solution. However, upon standing overnight, single crystals of the unusual, dinuclear complex [Rh(PMe3)3(Cl)]2(μ-(1,2-η2):(3,4-η2)-p-F3C–C6H4–Ctriple bond; length of mdashC–Ctriple bond; length of mdashC–C6H4-p-CF3) (4), an isomer of 3b, form reproducibly and in good yield as two different solvates from THF/C6D6 solution. The centrosymmetric structure of 4, obtained from single-crystal X-ray diffraction data, displays a transoid orientation of the bridging diarylbutadiyne ligand.