A "dendritic effect" in homogeneous catalysis with carbosilane-supported arylnickel(II) catalysts: Observation of active-site proximity effects in atom-transfer radical addition

被引:192
作者
Kleij, AW
Gossage, RA
Gebbink, RJMK
Brinkmann, N
Reijerse, EJ
Kragl, U
Lutz, M
Spek, AL
van Koten, G
机构
[1] Univ Utrecht, Debye Inst, Dept Metal Mediated Synthesis, NL-3584 CH Utrecht, Netherlands
[2] Forschungszentrum Julich, Inst Biotechnol, D-52425 Julich, Germany
[3] Univ Utrecht, Dept Crystal & Struct Chem, Bijvoet Ctr Biomol Res, NL-3584 CH Utrecht, Netherlands
[4] Univ Nijmegen, Dept Mol Spect, NL-6525 ED Nijmegen, Netherlands
关键词
D O I
10.1021/ja0026612
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
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.
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页码:12112 / 12124
页数:13
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