A phosphorus-31 magnetic resonance study of ligand exchange on Hexakis[methyl methyl(phenyl)phosphinate]yttrium(III) ion and the solution chemistry of related yttrium(III) species

Abstract

A ³¹P n.m.r, study shows that the species [YL_n³⁺ where n = 4,5,6 for L = OP(NMe₂), or OPPh₃ n = 5,6 for L = OPMe(0Me)Ph are the major yttrium(III) species formed with these ligands in CD₂CI₂ solution. A detailed ligand exchange study of the latter species shows the rate law to be: exchange rate = 6(k_l+k₂[OPMe(OMe)Ph])[Y(OPMe(OMe)Ph)₆³⁺] where k₁(215 K) = 312±13 s^-1, ΔH₁^‡ = 3l·4 ± 1.4 kJmol^-1, ΔS₁^‡ = -48·4±6.6 J K^-1 mol^-1, k₂(215 K) = 455 ± 31 dm³ mol^-1 s^-1, ΔH₂^‡ = 35·2±2.8 kJmol^-1 and ΔS₂^‡ = -27·6 ± 12·7 JK^-1 mol^-1, where the k¹ and k₂ terms are assigned to D and A mechanisms respectively. The rate of OP(OMe)₃ and OPMe(OMe)₂ exchange on yttrium(III) is found to be in the fast exchange limit of the n.m.r. time scale and thus the coordination numbers of the yttrium(III) species formed with these ligands are not directly determined in solution. Qualitatively it appears that the coordination number and the lability of the yttrium(III) species increases as the size of the ligand decreases. The isolation of the crystalline species [Y(OP(NMe₂)₃)₅ClO₄](ClO₄)₂, [Y(OPPh₃)₄](ClO₄)₃, [Y(OPMe(OMe)Ph)₆] (ClO₄)₃, [Y(OP(OMe)₃)₆](ClO₄)₃ and [Y(OPMe(OMe)₂)₆](ClO₄)₃ is reported.