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Modeling the platinum-catalyzed intermolecular hydroamination of ethylene: The nucleophilic addition of HNEt2 to coordinated ethylene in trans-PtBr2(C2H4)(HNEt2)статья
Информация о цитировании статьи получена из
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Дата последнего поиска статьи во внешних источниках: 18 марта 2017 г.
- Авторы: Dub Pavel A., Daran Jean-Claude, Levina Vladislava A., Belkova Natalia V., Shubina Elena S., Poli Rinaldo
- Журнал: Journal of Organometallic Chemistry
- Том: 696
- Номер: 6
- Год издания: 2011
- Издательство: Elsevier BV
- Местоположение издательства: Netherlands
- Первая страница: 1174
- Последняя страница: 1183
- DOI: 10.1016/j.jorganchem.2010.09.043
- Аннотация: Compound trans-PtBr2(C2H4)(NHEt2) (1) has been synthesized by Et2NH addition to K[PtBr3(C2H4)] and structurally characterized. Its isomer cis-PtBr2(C2H4)(NHEt2) (3) has been obtained from 1 by photolytic dissociation of ethylene, generating the dinuclear trans-[PtBr2(NHEt2)](2) intermediate (2), followed by thermal re-addition of C2H4, but only in low yields. The addition of further Et2NH to 1 in either dichloromethane or acetone yields the zwitterionic complex trans-Pt(-)Br2(NHEt2)(CH2CH2N(+)HEt2) (4) within the time of mixing in an equilibrated process, which shifts toward the product at lower temperatures (Delta H degrees = -6.8 +/- 0.5 kcal/mol, Delta S degrees 14.0 +/- 2.0 e.u., from a variable temperature IR study). H-1 NMR shows that free Et2NH exchanges rapidly with H-bonded amine in a 4 center dot NHEt2 adduct, slowly with the coordinated Et2NH in 1, and not at all (on the NMR time scale) with Pt-NHEt2 or -CH2CH2N(+)HEt2 in 4. No evidence was obtained for deprotonation of 4 to yield an aminoethyl derivative trans-[PtBr2(NHEt2) (CH2CH2NEt2)](-) (5), except as an intermediate in the averaging of the diasteretopic methylene protons of the CH2CH2N(+)HEt2 ligand of 4 in the higher polarity acetone solvent. Computational work by DFT attributes this phenomenon to more facile ion pair dissociation of 5 center dot Et2NH2+, obtained from 4 center dot Et2NH, facilitating inversion at the N atom. Complex 4 is the sole observable product initially but slow decomposition occurs in both solvents, though in different ways, without observable generation of NEt3. Addition of TfOH to equilibrated solutions of 4, 1 and excess Et2NH leads to partial protonolysis to yield NEt3 but also regenerates 1 through a shift of the equilibrium via protonation of free Et2NH. The DFT calculations reveal also a more favourable coordination (stronger Pt-N bond) of Et2NH relative to PhNH2 to the Pt-II center, but the barriers of the nucleophilic additions of Et2NH to the C2H4 ligand in 1 and of PhNH2 to trans-PtBr2(C2H4)(PhNH2) (1a) are predicted to be essentially identical for the two systems. (C) 2010 Elsevier B.V. All rights reserved.
- Добавил в систему: Шубина Елена Соломоновна