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Issue 12, 2013
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Radical-chain oxidative addition mechanism for the reaction of an [Re(CO)5] anion with α-bromostilbene

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Abstract

E-α-Bromostilbene spontaneously reacts with Na[Re(CO)5] at 22 °C in THF to give Na[ReBr(CO)4{Z-C(Ph)[double bond, length as m-dash]CHPh}] and Na[Re2(CO)9{Z-C(Ph)[double bond, length as m-dash]CHPh}] as the main products. Z-α-Bromostilbene is less reactive, but gives the same products. The reaction is stimulated by visible light or a source of solvated electrons (NaK2.8) and can be inhibited by a quinomethide radical trap. With an excess of Na[Re(CO)5] one can observe the initial formation of Na[ReBr(CO)4{Z-C(Ph)[double bond, length as m-dash]CHPh}] and its complete transformation into Na[Re2(CO)9{Z-C(Ph)[double bond, length as m-dash]CHPh}]. Treatment of Na[ReBr(CO)4{Z-C(Ph)[double bond, length as m-dash]CHPh}] with CO almost quantitatively converts it to [Re(CO)5{Z-C(Ph)[double bond, length as m-dash]CHPh}], the structure of which is established by a single-crystal X-ray diffraction study. A radical-chain mechanism is proposed for the reaction comprising the following steps: (a) coupling of a Vin˙ radical with Na[Re(CO)5], (b) CO-dissociation from the formed 19-electron radical-anion and (c) bromine atom abstraction by [Re(CO)4{Z-C(Ph)[double bond, length as m-dash]CHPh}]˙ from α-bromostilbene. The mechanism is confirmed by the formation of the same Na[ReBr(CO)4{Z-C(Ph)[double bond, length as m-dash]CHPh}] product in the presence of NaI. When the radical-chain process is inhibited, a slow halogenophilic reaction is observed, mainly giving the Z and E-isomers of the acylrhenate Na[Re2(CO)9{C(O)C(Ph)[double bond, length as m-dash]CHPh}].

Graphical abstract: Radical-chain oxidative addition mechanism for the reaction of an [Re(CO)5]− anion with α-bromostilbene

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Publication details

The article was received on 24 Oct 2012, accepted on 06 Dec 2012 and first published on 06 Dec 2012


Article type: Paper
DOI: 10.1039/C2DT32552G
Dalton Trans., 2013,42, 4223-4232

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    Radical-chain oxidative addition mechanism for the reaction of an [Re(CO)5] anion with α-bromostilbene

    P. K. Sazonov, D. S. Ptushkin, V. N. Khrustalev, N. G. Kolotyrkina and I. P. Beletskaya, Dalton Trans., 2013, 42, 4223
    DOI: 10.1039/C2DT32552G

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