Bonding studies of compounds of boron and the group IV elements. Part VIII. Heats of hydrolysis and bond energies for some trimethylmetalyl derivatives Me3M–X(M = Si, Ge, and Sn)

Abstract

The heats of hydrolysis, in aqueous 1 M-hydrochloric acid, of one silicon, five germanium, and eight tin(IV) compounds of type (Me₃M)_nX (where M = Si, Ge, or Sn, n= 1–3, and X is a univalent ligand in which the donor atom adjacent to M is N, O, S, Cl, Br, or I) to give (Me₃Si)₂O, (Me₃Ge)₂O, and (Me₃SnOH)₂ have been measured. From these, standard heats of formation have been calculated as follows: ΔH_f°(Me₃Si·OEt), I =–126·4 ± 0·7; ΔH_f°[(Me₃Ge)₂O], I =–136·0 ± 4·0; ΔH_f°(Me₃GeCl), I =–71·6 ± 2·1; ΔH_f°(Me₃GeBr), I =–62·1 ± 2·1; ΔH_f°(Me₃Ge·OEt), I =–95·8 ± 2·2; ΔH_f°(Me₃Ge·SBuⁿ), I =–64·7 ± 2·1; ΔH_f°(Me₃Ge·NMe₂), I =–37·1 ± 2·2; ΔH_f°(Me₃SnCl), c =–58·4 ± 1·2; ΔH_f°(Me₃SnBr), c =–48·8 ± 1·3; ΔH_f°(Me₃SnI), I =–31·2 ± 1·1; ΔH_f°(Me₃SnOH), c =–90·8 ± 1·2; ΔH_f°(Me₃Sn·OEt), I =–73·1 ± 1·5; ΔH_f°(Me₃Sn·SBuⁿ), I =–47·1 ± 1·6; ΔH_f°(Me₃Sn·NMe₂), I =–13·3 ± 1·4; ΔH_f°[(Me₃Sn)₂NMe], I =–31·5 ± 2·5; ΔH_f°[(Me₃Sn)₃N], c =–29·2 ± 3·6 kcal mol^–1. Gas-phase enthalpies of formation of these compounds and thermochemical bond energy terms E(M–X) have been calculated. Group trends show that, for constant X, E(C–X) < E(Si–X) > E(Ge–X) > E(Sn–X), whereas E(C–Y) > E(Si–Y)(Y = H or Me). Another conclusion is that the ‘softness’(in terms of ΔH of reactions) of the acid Me₃M⁺ increase in the order C < Si < Ge < Sn; several chemical reaction types are examined in this light.