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.