Synthesis and structure of Rh(I) tris(pyrazolyl)borate complexes of the type Tp Ph,MeRhL 1L 2

Abstract

The complex Tp Ph,MeRh(CO) 2 ( 1) was prepared from the reaction of the appropriate potassium pyrazolyl borate, Tp Ph,MeK, with Rh(acac)(CO) 2 in warm benzene. Reaction of Rh(acac)(CO) 2 with Tp Ph,MeK and PPh 3 gave the compound Tp Ph,MeRh(CO)(PPh 3) ( 2). The complexes 1 and 2 were characterized by elemental analysis and IR, 1H-, 13C-, and 31P-NMR spectroscopies. The structures of both compounds were determined by X-ray crystallography. The complex 1 crystallizes in the triclinic space group P1̄ with a=11.227(2), b=12.219(2), c=12.262(2) Å, α=63.61(3), β=87.67(3), γ=88.17(3)°, V=1505.4(4) Å 3, and Z=2. Crystals of 2 are triclinic, space group P1̄, with a=11.114(2), b=11.913(2), c=18.071(4) Å, α=82.69(3), β=82.02(3), γ=64.01°, V=2123.9(7) Å 3, Z=2. The fluxional behavior of 1 and 2 was studied by variable-temperature 1H-NMR spectroscopy. In the case of 1 the κ 2↔ κ 3 conversion is fast on the NMR time-scale even at −90°C, whereas complex 2 is a unique example of two well-separated κ 2↔ κ 3 equilibria (by 21 kJ mol −1 Δ G ≠ gap).