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Alkali-metal-mediated manganation(II) of functionalized arenes and applications of ortho-manganated products in Pd-catalyzed cross-coupling reactions with iodobenzene

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

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Abstract

Extending the recently introduced concept of "alkali-metal-mediated manganation" to functionalised arenes, the heteroleptic sodium manganate reagent [(tmeda)Na(tmp)(R)Mn(tmp)] (1; TMEDA = N,N,N′,N′-tetra- methylethylenediamine, TMP = 2,2.6,6-tetramethylpiperidide, R = CH 2SiMe3) has been treated with anisole or N,N-diisopropylbenzamide in a 1:1 stoichiometry in hexane. These reactions afforded the crystalline products [(tmeda)Na(tmp)(o-C6H 4OMe)Mn-(tmp)] (2) and [(tmeda)Na(tmp){o(C(O)N(iPr)2C 6H4)Mn(CH2SiMe3)] (3), respectively, as determined from X-ray crystallography studies. On the basis of these products, it can be surmised that reagent 1 has acted, at least partially and ultimately, as an alkyl base in the first reaction liberating the silane Me 4Si, but as an amido base in the second reaction liberating the amine TMPH. Both of these paramagnetic products 2 and 3 have contacted ion-pair structures, the key features of which are six-atom, five-element (NaNMnCCO) and seven-atom, five-element (NaNMnCCCO) rings, respectively. Manganates 2 and 3 were successfully cross-coupled with iodobenzene under [PdCl2(dppf)] (dppf = 1,1′-bis(diphenylphosphino)ferrocene) catalysis to generate unsymmetrical biaryl compounds in yields of 98.0 and 66.2%, respectively. Emphasizing the importance of alkali-metal mediation in these manganation reactions, the bisalkyl Mn reagent on its own fails to metalate the said benzamide, but instead produces the monomeric, donoracceptor complex [Mn(R) 2{(iPr)2-NC(Ph)(=O)}2] (5), which has also been crystallographically characterised. During one attempt to repeat the synthesis of 2, the butoxide-contaminated complex [{(tmeda)Na(R)(OBu)(o-C 6H4OMe)Mn}2] (6) was obtained. In contrast to 2 and 3, due to reduced steric constraints, this complex adopts a dimeric arrangement in the crystal, the centrepiece of which is a twelve atom (NaOCCMnC)2 ring. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.


Publication metadata

Author(s): Blair VL, Clegg W, Conway B, Hevia E, Kennedy A, Klett J, Mulvey RE, Russo L

Publication type: Article

Publication status: Published

Journal: Chemistry - A European Journal

Year: 2008

Volume: 14

Issue: 1

Pages: 65-72

Print publication date: 01/01/2008

ISSN (print): 0947-6539

ISSN (electronic): 1521-3765

Publisher: Wiley - VCH Verlag GmbH & Co. KGaA

URL: http://dx.doi.org/10.1002/chem.200701597

DOI: 10.1002/chem.200701597


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