A Proton Magnetic Resonance Study of Ligand Exchange on Tetrakis (N,N‐Dimethylacetamide) Beryllium(II) and its N‐Methylacetamide, and N,N‐Dimethylformamide Analogues

A 1H (90 MHz) NMR study shows that ligand (L) exchange on [BeL4]2+ is characterised by the rate law: exchange rate = 4(k1 + k2[L]free)[BeL2+4] when L = O = CMe(NMe2), O = CMe(NHMe), or O = CH(NMe2) in the non‐coordinating solvents CD3NO2 and CD3CN, and also in CD2Cl2 in the case of O = CH(NMe2). The kinetic parameters observed for these systems are exemplified by those characterising [Be(O = CMe(NMe2))4]2+ in CD3NO2 solution which are: k1 (340 K) = 7.3 ± 0.7 s−1, ΔH#1 = 56.9 ± 1.5 kJ mol−1, ΔS#1 = −62.1 ± 4.6 J K−1 mol−1, k2 (340 K) = 10.5 ± 1.0 dm3 mol−1 s−1, ΔH#2 = 66.7 ± 2.6 kJ mol−1, and ΔS#2 = −30.1 ± 7.4 JK−1 mol−1. The k1 and k2 rate constants are interpreted in terms of dissociative (D) and associative (A) (or interchange (I)) ligand exchange mechanisms and are discussed in conjunction with previously reported data for other beryllium(II) systems.