Thermodynamics of metal-ligand bond formation : XXVII. Reaction of lewis bases with alkylmercury(II) halides

Abstract

Alkylmercury(II) halides, RHgX, form 1 : 1 adducts in benzene solution with heterocyclic bases; the adduct stability is very low ( K < 1), though more stable adducts (10 < K < 100 approximately) are formed with the bidentate bases, 1,10-phenanthroline and N,N,N′,N′-tetramethyl-1,2-diaminoethane. In all cases enthalpies of adduct formation are about −25 kJ mol −1. PBu 3 forms dimeric adducts, (RHgX · PBu 3) 2, of higher stability with enthalpies of formation about −60 kJ(g-at.Hg) −1. The perchloro compounds Cl 3CHgCl and (Cl 3C) 2Hg form more stable adducts with N-bases and also with tetrahydrothiophene and pyridine- N-oxide, but Cl 3CHgCl is symmetrised by phosphines and (Cl 3C) 2Hg reacts slowly with them, depositing mercury. The Lewis acidity of mercury compounds increases in the order: R 2Hg << RHgCl < (Cl 3C) 2Hg < Cl 3CHgCl < HgCl 2.