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Structural and reactivity insights in Mg Zn hybrid chemistry: Zn-I exchange and Pd-catalysed cross-coupling applications of aromatic substrates

Lookup NU author(s): Emeritus Professor Bill CleggORCiD, Dr Luca Russo


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Expanding the synthetic potential of Mg-Zn hybrid organyl reagents (generated via transmetallation reactions), this study uncovers a versatile approach, involving a sequence of direct Zn-I exchange and Pd catalysed cross-coupling reactions which grants access to a wide range of asymmetric bis(aryls). By combining X-ray crystallography with ESI-MS and non-deuterium NMR spectroscopic studies, new light is shed on the heterobimetallic constitution of the intriguing organometallic species [(THF)(4)MgCl2Zn(tBu)Cl] (1) and [{Mg2Cl3(THF)(6)}(+){ZntBu(3)}(-)] (2), formed through transmetallation of tBuMgCl with n equivalent amounts of ZnCl2 (n = 1 and 3 respectively). Operating by cooperative effects, alkyl-rich hybrid 2 can effectively promote direct Zn-I exchange reactions with aromatic halides in short periods of time at room temperature in THF solution. The structural elucidation of key organometallic intermediates involved in some of these Zn-I exchanges, provides new reactivity insights into how these bimetallic systems operate. Thus, while the reaction of 2 with 3 equivalents of 2-iodoanisole (3b) gives magnesium dizincate [{Mg(THF)(6)}(2+)(Zn(o-C6H4-OMe)(3))(2)(-)] (4) which demonstrates the 3-fold activation of the tBu groups attached to Zn in 2, using 2-iodobenzonitrile (3I), only two tBu groups react with the substrate, affording [(THF)(4)MgCl(NC-o-C6H4)ZnI(o-C6H4-CN)(THF)] (7). In 7 Mg and Zn are connected by an aryl bridge, suggesting that the formation of contacted ion-pair hybrids may have a deactivating effect on the outcome of the Zn-I exchange process. A wide range of homoleptic tris(aryl) zincate intermediates have been prepared in situ and used as precursors in Pd catalysed cross-coupling reactions, affording bis(aryls) 6a-s in excellent yields under mild reaction conditions without the need of any additive or polar cosolvent such as NMP or DMI.

Publication metadata

Author(s): Bluemke TD, Clegg W, Garcia-Alvarez P, Kennedy AR, Koszinowski K, McCall MD, Russo L, Hevia E

Publication type: Article

Publication status: Published

Journal: Chemical Science

Year: 2014

Volume: 5

Issue: 9

Pages: 3552-3562

Print publication date: 01/09/2014

Online publication date: 16/06/2014

Acceptance date: 13/06/2014

ISSN (print): 2041-6520

ISSN (electronic): 2041-6539

Publisher: RSC Publications


DOI: 10.1039/c4sc01263a


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