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

The complex Tp(Ph.Me)Rh(CO)(2) (1) was prepared from the reaction of the ap propriate potassium pyrazolyl borate, Tp(Ph.Me)K, with Rh(acac)(CO)(2) in w arm benzene. Reaction of Rh(acac)(CO)(2) with Tp(Ph.Me)K and PPh3 gave the compound Tp(Ph.Me)Rh(CO)(PPh3) (2). The complexes 1 and 2 were characterize d by elemental analysis and IR, H-1-, C-13-, and P-31-NMR spectroscopies. T he structures of both compounds were determined by X-ray crystallography. T he complex 1 crystallizes in the triclinic space group P (1) over bar with a = 11.227(2), b = 12.219(2). c = 12.262(2) Angstrom, alpha = 63.61(3), bet a = 87.67(3), gamma = 88.17(3)degrees, V = 1505.4(4) Angstrom(3). and Z = 2 . Crystals of 2 are triclinic, space group P (1) over bar. with a = 11.114( 2), b = 11.913(2), c = 18.071(4) Angstrom, alpha = 82.69(3), beta = 82.02(3 ), gamma = 64.01 degrees, V= 2123.9(7) Angstrom(3), Z = 2. The fluxional be havior of 1 and 2 was studied by variable-temperature H-1-NMR spectroscopy. In the case of 1 the kappa(2)<->kappa(3) conversion is fast on the NMR tim e-scale even at - 90 degrees C, whereas complex 2 is a unique example of tw o well-separated kappa(2)<->kappa(3) equilibria (by 21 kJ mol(-1) Delta G* gap). (C) 2000 Elsevier Science S.A. All rights reserved.