1981/02/01 by SF Lincoln, DL Pisaniello, TM Spotswood +1
Chemistry · Medicine · #Chemical Reaction Mechanisms #Coordination Chemistry and Organometallics #Metal complexes synthesis and properties
paper · doi:10.1071/ch9810283
openalex publication_date 1981/02/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
31P n.m.r, studies show that the rate of triphenylphosphine oxide exchange on [Zn(O=PPh3)4]2+ in CD2Cl2 solution is independent of [O=PPh3]free. A typical data set is: kex(200 K) = 611 ± 37 s-1, ?H‡ = 32.0 ± 0.7 kJ mol-1 and ?S‡ = -28.3 ± 3.4 J K-1 mol-1 for a solution in which [Zn(O=PPh3)42+] and [O=PPh3]free are 0.163 and 0.639 mol dm-3 respectively, where kex = exchange rate/(4[Zn(O=PPh3)42+]) = (kBT/h)exp(-?H‡/RT)exp(?S‡/R) Similarly the rate of ligand exchange on [Mg(O=PPh3)5]2+ is shown to be independent of [O=PPh3]free and a typical data set is kex'(220 K) = 38 ± 4 s-1, ?H‡ = 73.7 ± 1.8 kJ mol-1 and ?S‡ = 123 ± 8 J K-1 mol-1 for a solution in which [Mg(O=PPh3)52+] and [O=PPh3]free are 0.0813 and 0.276 mol dm-3 respectively. The ligand exchange process on both species is considered to proceed through a D mechanism. The apparent equilibrium constant K = [Mg(O=PPh3)52+]/ ([Mg(O=PPh3)42+][O=PPh3] = 150 dm3 mol-1 but in contrast [Zn(O=PPh3)2+ appears to be the only stable zinc(II) species in solution. It is concluded that these data probably reflect the hard acid character of magnesium(II) and the intermediate acid characteristics of zinc(II).