Synthetic routes for hydrotris(pyrazolyl)borate complexes of rhodium(III)

The reaction of the alkali metal salt of several hydrotris(pyrazolyl)borate anions (Tp(3R,4R,5R)) With RhCl3. 3H(2)O in MeOH gave complexes of the type [Tp(3R,4R,5R)RhCl(2)(MeOH)] (Tp(3R,4R,5R) = Tp(Me), Tp(Me2),Tp(Me,4Me), Tp(Me2,4Cl), Tp(iPr) and Tp(iPr.4Br)). While the reaction of Na[Tp(Me2)] with [RhCl3(MeCN)(3)] in MeCN gave [Tp(Me2)RhCl(2)(Pz(Me2)H)] (18), that of Na[Tp(CF3.Me)] gave [Tp(CF3.Me)RhCl(2)(MeCN)]. The Xray crystal structure of 18 (space group P (1) over bar, a = 10.949(8), b = 11.415(8), c = 24.16(2) Angstrom; alpha = 95.40(7), beta = 91.39(7), gamma = 115.37(5)degrees; Z = 4, R = 0.032, R-w = 0.035 for 3813 observed reflections) shows that the rhodium atom has an octahedral geometry. The reaction of Na[Tp(Me,Ph)] with RhCl3. 3H(2)O or [RhCl3(MeCN)(3)] gave mer-[RhCl3(Pz(Ph,Me))(3)] while M[Tp(CF3,CF3)] (M = Na or Tl) did not react with either rhodium substrate. The complexes [Tp(3R,4R,5R)RhCl(2)(L)] (L=MeOH and MeCN) react with Cl- in CHCl3 forming the corresponding [Tp(3R,4R,5R)RhCl(3)](-) anions (Tp(3R,4R,5R) = Tp, Tp(Me), Tp(Me2), Tp(Me2,4Me), Tp(Me2,4Cl), Tp(iPr), Tp(iPr.4Br), Tp(CF3,Me)). The X-ray crystal structure of [PPh4][Tp(Me2)RhCl(3)] ([PPh4] [25]) (space group P2(1)/c, a = 16.301(1), b = 9.9830(6), c = 26.337(1) Angstrom; beta = 101.97(3)degrees; Z = 4, R=0.052, R-w = 0.060 for 4264 observed reflections) shows octahedral coordination at rhodium. A molecular modeling study using the structural data for 25 indicates that steric interactions between (a) the CF3-substituents in position 5 on the pyrazolylborate and (b) the CF3-substituents in position 3 and the other ligands present in the coordination sphere, may prevent the formation of rhodium(III) complexes with Tp(CF3,CF3). (C) 1999 Elsevier Science S.A. All rights reserved.