A series of (butadiene)rhodium(I) complexes with an open-sandwich- or half-sandwich-type structure

A series of mono(diene)- and bis(diene)rhodium(I) compounds (diene = butadi ene, 2-methylbutadiene (isoprene), and 2,3-dimethylbutadiene) was prepared from the triflato-bridged dimer [Rh{mu-O2S(O)CF3}(C8H14)(2)](2) (1) Reactio n of 1 with excess diene affords the monomeric complexes [Rh{eta(1)-OS(O)(2 )CF3}(eta(4)-diene)(2)] (2-4) which, as established by X-ray crystal struct ure analysis of the isoprene derivative 3, possess a sandwich-type structur e with the open site of the two parallel diene units directed towards the m onodentate triflato ligand. Treatment of compounds 2-4 with an equimolar am ount of gives the ionic compounds PiPr(3) [Rh(eta(4)-diene)(2)(PiPr(3))]O3S CF3 (5-7), which can also be prepared from [Rh{eta(2)-O2S(O)CF3}(PiPr(3))(C 8H14)] (9) and excess diene. The arrangement of the two diolefin ligands in the cations of 5-7 is quite similar to that in 2-4, as shown by an X-ray d iffraction study of the butadiene derivative 5. The reaction of 9 with one equivalent of 2,3-dimethylbutadiene affords the mono(diene) complex [Rh{eta (1)-OS(O)(2)CF3}(eta(4)-C6H10)(PiPr(3))] (8). X-ray crystal structure analy sis of this complex reveals that the plane containing the rhodium, the meta l-bound oxygen, and the phosphorus atoms does not lie exactly perpendicular to the plane of the diene. Treatment of 2 and 3 with PiPr(3) (molar ratio = 1:3) leads to ligand displacement and nucleophilic attack of a phosphane on one diene ligand to form the pi-allylphosphonium complexes [Rh{eta(3)-an ti-(iPr(3)PCH(2))CHCRCH2}(PiPr(3))(2)]O3SCF3 (10, 11). The structure of the PF6- salt of the corresponding cation with R=CH3 has been determined by X- ray crystallography.