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 = 6kex[Lu{OC(NMe2)2}63+] with kex(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.