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標題: Preparation of cobalt-containing bulky monodentate phosphines with electron-withdrawing/donating substituents on bridged arylethynyl and their applications in Suzuki coupling reactions
作者: Shiu, B.Y.
Huang, P.C.
Huang, Y.L.
Hong, F.E.
關鍵字: Suzuki-Miyaura cross-coupling reaction;DFT methods;ortho-metalation;phosphine ligand;transmetalation;electron-withdrawing substituent;resonance energy-transfer;oxidative addition;cross-couplings;aryl;chlorides;reductive elimination;structural-characterization;palladium(0) complexes;bidentate ligands;bond formation;c-c
Project: Tetrahedron
期刊/報告no:: Tetrahedron, Volume 64, Issue 27, Page(s) 6221-6229.
Several cobalt-containing bulky monodentate phosphines (mu-PPh(2)CH(2)PPh(2))CO(2)(CO)(4)(mu,eta-((t)Bu)(2)PC C (C(6)H(4)R)) (4a: R=H; 4b: R=p-F; 4cp: R=p-CF(3); 4cm: R=m-CF(3): 4d: R=p-OMe) were prepared from the reactions of ((t)Bu)(2)PC C(R-C(6)H(4)) (2a: R=H; 2b: R=p-F; 2cp: R=p-CF(3); 2cm: R=m-CF(3): 2d: R=p-CMe) with CO(2)(CO)(6)(mu-PPh(2)CH(2)PPh(2)) 3. Further reactions of 4a, 4b, 4cp, 4cm, and 4d with Pd(OAc)(2) yielded unique palladium complexes (mu-PPh(2)CH(2)PPh(2))CO(2)(CO)(4)(mu,eta-((t)Bu)(2)PC C(C(6)H(3)R)-kappa C(1))Pd(mu-OAc)(5a: R=H; 5b: R=p-F; 5cp: R=p-CF(3); 5cm: R=m-CF(3): 5d: R=p-OMe, respectively). The strong electron-withdrawing substituents, -F and -CF(3), assist the ortho-metalation process during the formation of 5b, 5cp, and 5cm. The more positively charged palladium center in 5b (or 5cp, 5cm) enhances the probability for PhB(OH)(3)(-) to attack the metal center and the rate of reduction thereafter. DFT studies on the charges of these palladium centers support this assumption. The enhancement of the reaction rates of the Suzuki-Miyaura cross-coupling reactions using 5b, 5cp, and 5cm is thereby attributed to this effect. (C) 2008 Elsevier Ltd. All rights reserved.
ISSN: 0040-4020
DOI: 10.1016/j.tet.2008.04.117
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