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

Abstract

The reaction of the alkali metal salt of several hydrotris(pyrazolyl)borate anions (Tp 3R,4R,5R) with RhCl 3·3H 2O in MeOH gave complexes of the type [Tp 3R,4R,5RRhCl 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 [RhCl 3(MeCN) 3] in MeCN gave [Tp Me2RhCl 2(Pz Me2H)] ( 18), that of Na[Tp CF3,Me] gave [Tp CF3,MeRhCl 2(MeCN)]. The X-ray crystal structure of 18 (space group P 1 ̄ , a = 10.949(8), b = 11.415(8), c = 24.16(2) Å; α = 95.40(7), β = 91.39(7), γ = 115.37(5)°; 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 RhCl 3·3H 2O or [RhCl 3(MeCN) 3] gave mer-[RhCl 3(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,5RRhCl 2(L)] (L = MeOH and MeCN) react with Cl − in CHCl 3 forming the corresponding [Tp 3R,4R,5RRhCl 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 [PPh 4][Tp Me2RhCl 3] ([ PPh 4 ] [ 25]) (space group P2 1/ c, a = 16.301(1), b = 9.9830(6), c = 26.337(1) Å; β = 101.97(3)°; 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 CF 3-substituents in position 5 on the pyrazolylborate and (b) the CF 3-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.