Rhodium(I) complexes of the type [Tp(3R,5R)Rh(LL)] (LL=2 CO, NBD, COD) with trifluoromethyl substituted tris(pyrazolyl) borate ligands and their dynamic behaviour in solution. The X-ray crystal structure of Tp(CF3,Me)Rh(CO)(2)

Three series of Rh(I) complexes of the type Tp(3R),Rh-5R(LL), with LL=2 CO (1), norbomadiene (NBD) (2) and 1,5-cyclooctadiene (GOD) (3) and the tris(pyrazolyl)borate (Tp) ligands 3R=5R=Me (a), 3R=CF3, 5R=Me(b); and 3R=5R=CF3 (c) were synthesized and fully characterized by IR and multinuclear NMR spectroscopy. Three isomeric forms were identified in solutions of these complexes: two square-planar isomers with a kappa(2)-Tp(3R,5R) ligand, the uncoordinated pyrazolyl ring occupying either an equatorial position (type A), or an axial position (type B), and a five-coordinate species with a kappa(3)-Tp(3R,5R) ligand (type C). In the carbonyl complexes 1 the dynamic equilibria between these isomers are solvent dependent. Interestingly, solutions of complex Ic contained all three isomers simultaneously. Rh-103 and C-13 NMR spectral studies indicate that the NBD compounds, 2, preferentially form square-planar complexes when Tp(CF3,Me) and Tp(CF3,CF3) are present, while for the COD complexes, 3, square-planar complexes are preferred for all three Tp-type ligands. The X-ray structure of Tp(CF3,Me)Rh(CO)(2) (1b) was determined (space group C2/c, a=21.271(9), b=11.004(3), c=21.563(9) Angstrom, beta=114.93(3)degrees, V=4577(3) Angstrom(3), Z=8, R=3.41, R(w)=4.70). Its structure is of type B, with the third pyrazolyl ring axially placed, the N(4) being almost directly above the Rh atom but exerting only a weak Rh-N interaction.