Theoretical Studies of the Additions of Germylenes to Ethylene

Abstract

Complete geometry optimizations were carried out using density functional theory to study the potential energy surfaces for cycloaddition of germylene to the CC double bond of ethylene. The GeX2 + C2H4 (GeX2 = GeH2, Ge(CH3)2, Ge(NH2)2, Ge(OH)2, GeF2, GeCl2, GeBr2, and GeCH2) systems are the subject of the present study. All the stationary points were determined at the B3LYP/6-31G* level of theory. The major conclusions that can be drawn from this work are as follows: (i) In contrast to the case of the carbene additions, a π-complex intermediate is formed between germylene and ethylene, which should play a key role in subsequent polymerization. (ii) On the basis of the results of the present study, it is apparent that germylene cycloadditions occur in a concerted, asynchronous manner. (iii) Germacyclopropanes, unlike cyclopropanes, are quite unstable compounds, reverting thermally to their precursors and then polymerizing rapidly, or even reacting with a second molecule of olefin to yield a cyclic compound. (iv) Considering the effect of substitution at the germanium center, our theoretical findings suggest that the cycloaddition of germylene with electropositive and/or bulky substituents is feasible from both a kinetic and a thermodynamic viewpoint. In contrast, germylenes bearing electronegative and/or π-donating substituents will tend not to undergo cycloadditions. Note that this conclusion is based upon the assumption that three-membered-ring germacyclopropane is the unique end product for germylene additions. (v) The cycloadditions of germylenes to alkenes are more endothermic (or less exothermic) than the same reactions of carbenes, reflecting the weaker Ge−C vs C−C bond.

Gas phase kinetic and theoretical studies of reactions of germylenes and dimethylstannylene

“…72 However, this complex was found in previous quantum chemical studies using MP2 valence only calculations in conjunction with an effective core potential 84 and also in B3LYP/6 31G* calculations. 85 Because the QCISD method provides a better treatment of electron correlation than MP2, its prediction of the existence of the π complex seems reliable, and is in agree ment with the results of DFT calculations.…”

GeCl2 cycloaddition reactions to unsaturated organic compounds taking ethylene, buta-1,3-diene, and hexa-1,3,5-triene as examples: a quantum chemical study

“…15) and the much more reactive GeH 2 (see and GeMe 2 (see Refs 15 and 19 and notes in Ref. 17) proceed in a stepwise manner and begin with a barrierless formation of a π complex, which then undergoes transformation to a germirane (germacyclopropane).…”

“…The salient features of dihalogermylenes include a relatively low exothermicity of the formation of π complexes, high activation energy of the reaction, and endothermicity of formation of the cor responding 1,1 dihalogermirane. 14, 15 The results obtained in Ref. 15 revealed a low probability of the formation of 1,1 dichlorogermirane in the reaction of ethylene with GeCl 2 and suggested that it is π complexes rather than 1,1 dichlorogermiranes that participate as intermediates in the reactions of GeCl 2 with alkenes.…”

“…14, 15 The results obtained in Ref. 15 revealed a low probability of the formation of 1,1 dichlorogermirane in the reaction of ethylene with GeCl 2 and suggested that it is π complexes rather than 1,1 dichlorogermiranes that participate as intermediates in the reactions of GeCl 2 with alkenes. 2 CBS QB3 calculations of the system GeCl 2 + C 2 H 4 (Scheme 1, Tables 1 and 2) predict that the energy released upon the formation of π complex 3 (ΔE 0 = -25 kJ mol -1 ) does not compensate the corresponding decrease in entropy (ΔG°2 98 > 0).…”

Reactions of germylenes with alkynes: A quantum chemical study. Factors determining the stabilities of germacyclopropenes

“…The addition of GeH 2 to the triple bond of acetylene occurs barrierlessly in one step unlike the reactions of germylenes with olefins which usu ally involve formation of a π complex. [18][19][20] Recently, 20 we reported a PBE 21 density functional study of the reactions of GeH 2 and GeMe 2 with olefins and buta 1,2,3 trienes and showed that the overall stabil ity of the product, germacyclopropane (germirane), is de termined by its stability to retrocycloaddition into initial reactants and to a rearrangement similar to rearrange ment (b) in Scheme 1. Taking the stable germirane 10 as an example, we determined the effects of the olefin structure and the nature of the substituents at the Ge atom on the stability of the germacyclopropane system.…”