Journal Article

PreJuSER-26930

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png A 'dendritic effect' in homogeneous catalysis with carbosilane-supported arylnickel(II) catalysts : observation of active-site proximity effects in atom-transfer radical addition

Kleij, A. W. ; Gossage, R. A. ; Klein Gebbink, R. J. M. ; Brinkmann, N. ; Reijerse, E. J. ; Kragl, U.FZJ* ; Lutz, M. ; Spek, A. L. ; van Koten, G.

2000
American Chemical Society Washington, DC

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Please use a persistent id in citations: http://hdl.handle.net/2128/721  doi:10.1021/ja0026612

Abstract: Transmetalation of polylithiated, carbosilane (CS) dendrimers functionalized with the potentially terdentate ligand [C6H2(CH2NMe2)(2)-2,6-R-4](-) ( NCN) with NiCl2(PEt3)(2) produced a series of nickel-containing dendrimers [GO]-N-4 (4), [G1]-Ni-12 (5), and [G2]-Ni-36 (7) in moderate to good yields. The metallodendrimers 4, 5, and 7 are catalytically active in the atom-transfer radical addition (ATRA) reaction (Kharasch addition reaction), viz. the 1:1 addition of CCl4 to methyl methacrylate (MMA). The catalytic data were compared to those obtained for the respective mononuclear compound [NiCl(C6H2{CH2NMe2}(2)-2,6-SiMe3-4)] (2). This comparison indicates a fast deactivation for the dendrimer catalysts beyond generation [GO]. The deactivation of [G1]-Ni-12 (5) and [G2]-Ni-36 (7) is caused by irreversible formation of catalytically inactive Ni(III) sites on the periphery of these dendrimers. This hypothesis is supported by results of model studies as well as ESR spectroscopic investigations. Interestingly, the use of two alternative nickelated [G1] dendrimers [G1]*-Ni-12 (11) and [G1]-Ni-8 (15), respectively, in which the distance between the Ni sites is increased, leads to significantly improved catalytic efficiencies which approximate those of the parent derivative 2 and [GO]-Ni-4 (4). Preliminary membrane catalysis experiments with [GO]-Ni-4 (4) and [G1]-Ni-12 (5) show that 5 can be efficiently retained in a membrane reactor system. The X-ray crystal structure of the Ni(III) complex [NiCl2(C6H2{CH2NMe2}(2)-2,6-SiMe3-4)] (16), obtained from the reaction of 2 with CCl4, is also reported.

Keyword(s): J

Note: Record converted from VDB: 12.11.2012

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Contributing Institute(s):

1. Institut für Biotechnologie (IBT)

Research Program(s):

1. Verfahrenstechnik der Gewinnung (41.45.1)

Appears in the scientific report 2000

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