Nuclear magnetic resonance study of ligand exchange on Hexakis(1,1,3,3-tetramethylurea)lutetium(III)

Abstract

A 270-MHz ^lH n.m.r. study shows the rate of 1,1,3,3-tetramethylurea exchange on [Lu{OC(NMe₂)₂}₆]²⁺ in CD₃CN solution to be independent of [OC(NMe₂)₂]_free consistent with the operation of either a dissociative mechanism or an interchange mechanism characterized by an encounter complex stability constant ≥ 400. For this study

ligand exchange rate = 6k_ex[Lu{OC(NMe₂)₂}₆³⁺]

with k_ex(298.2 K) = 41.9 ± 2.7 s^-l, ΔH^‡ = 41.7 ± -0.6 kJmol^-1 and ΔS^‡ = -74 ± JK^-1 mol^-l. These data are compared with those for the analogous scandium(III) and yttrium(III) systems and also those for some eight-coordinate trivalent lanthanide systems. The preparations of [LuL₆] (ClO₄₎₃, where L = OC(NMe₂)₂, OCMe(NMe₂) and OCMe(Net₂), are reported.