Publication detail

Facile activation of alkynes with a boraguanidinato-stabilized germylene: a combined experimental and theoretical study

Year: 2017

Type of publication: článek v odborném periodiku

Name of source: Dalton Transactions

Publisher name: Royal Society of Chemistry

Place: Cambridge

Page from-to: 12339-12353

Titles:

Language	Name	Abstract	Keywords
cze	Aktivace alkynu amidoboránových komplexů germania	Byly studována aktivace alkynů amidoboránových komplexů germania.
eng	Facile activation of alkynes with a boraguanidinato-stabilized germylene: a combined experimental and theoretical study	A boraguanidinato-stabilized germylene, [(i-Pr)(2)NB(N-2,6-Me2C6H3)2] Ge, reacts with alkynes RC CR selectively in a 2 : 1 molar ratio to afford 3,4-R, R'-1,2-digermacyclobut-3-enes 1a-e as the products of formal [2 + 2 + 2] cyclization [R/R' = Me/Me (1a), Ph/Ph (1b), Ph/H (1c), t-Bu/H (1d) and Cy/H (1e)]. Ferrocenyl-substituted alkynes react similarly, yielding the corresponding ferrocenylated 3,4-R, R'-1,2-digermacyclobut-3-enes 2a-d [where R/R' = Fc/H (2a), Fc/Me (2b), Fc/Ph (2c), and Fc/Fc (2d); Fc = ferrocenyl]. By contrast, only one of the triple bonds available in conjugated diynes RC CC CR is activated with the germylene, while the second one remains intact even in the presence of an excess of the germylene. The exclusive formation of 3,4-R,(C CR)-1,2-digermacyclobut-3-enes 3a-c [R = Ph (3a), t-Bu(3b), and Fc (3c)] was ascribed to a steric repulsion around the second triple bond. On the other hand, the reaction of the germylene with more flexible dialkyne fc(CuCPh)(2) (fc = ferrocene-1,1'-diyl) proceeded in the expected manner, producing compound 4, where both triple bonds are transformed into 1,2-digermacyclobut- 3-ene rings by reaction with four equivalents of the germylene. All compounds were characterized by multinuclear NMR spectroscopy, Raman and IR spectroscopy, and in the case of 1a-c, 2a, 2c, 3a, 3b and 4, also by single-crystal X-ray diffraction analysis. The ferrocenyl substituted compounds were studied by cyclic voltammetry (CV). Finally, the plausible reaction pathway was studied for a model reaction of [(i-Pr)(2)NB(N-2,6-Me2C6H3)(2)] Ge with MeC CMe using DFT computations.	bond covalent radii; n-heterocyclic germylene; c-h activation; vibrational frequencies; cycloaddition reactions; molecular-interactions; arene elimination; transition-states; crystal-structure; carbene analogs

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