Rhodium(I) complexes of the type [TpRh(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 TpRh(CO)2

Three seriesof Rh(I) complexes of the type Tp^3R,5RRh(LL), with LL = 2 CO (1), norbornadiene (NBD) (2) and 1,5-cyclooctadiene (COD) (3) and the tris (pyrazolyl)borate (Tp) ligands 3R=5R=Me (a), 3R=CF₃5R=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 κ²-Tp³R,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 κ³, Tp³R,5R ligand (type C). In the carbonyl complexes 1 the dynamic equilibria between these isomers are solvent dependent. Interestingly, solutions of complex 1c contained all three isomers simultaneously. ¹⁰³Rh and ¹³C 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,MeRh(CO)₂ (1b) was determined (spacce group C2/ c,a = 21.271(9), B = 11.004(3), C = 21.563(9) Å, β = 114.93(3)°, V=4577(3) ų, 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.