A proton magnetic resonance study of ligand exchange on tetrakis(N,N-diethylacetamide)beryllium(II)

Abstract

A ^lH n.m.r. study shows that ligand exchange on tetrakis(N,N-diethylacetamide)beryllium(II) in both CD₃NO₂ and CD₃CN solution is charaterized by the rate law:

Exchange rate = 4(k₁ + k₂[OCMe(NEt₂)]_free)[Be{OCMe(NEt₂)}₄²⁺]

In CD₃NO₂ solution k₁ (340K) is 2.3 ± 0.1 s^-1, ΔH^‡.76.4 ± 2.2 kJ mol^-1, ΔS^‡ -14.6 ± 6.4 JK^-1 mol^-1, k₂ (340K) 19.9 ± 0.3 dm³ mol^-1s^-1, ΔH^‡ 68.5 ± 0.8kJ mol^-1, ΔS^‡ -19.6 ± 2.4 JK^-1 mol^-1, and somewhat different magnitudes are observed in CD₃CN solution. The k₁ term is assigned to a dissociative (D) ligand exchange mechanism, and the k₂ term is assigned to either an associative (A) or an interchange (I) mechanism. These data are discussed in conjunction with ligand exchange data for other beryllium(II) systems.