Synthesis and Characterization of Imine-Palladacycles Containing Imidate 鈥淧seudohalide鈥?Ligands: Efficient Suzuki鈥揗iyaura Cross-Coupling Precatalysts and Their Activation To Give Pd0L<

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• 作者：Jos茅 Luis Serrano ; Luis Garc铆a ; Jos茅 P茅rez ; Eduardo P茅rez ; Joaqu铆n Garc铆a ; Gregorio S谩nchez ; Petr Sehnal ; Sara De Ornellas ; Thomas J. Williams ; Ian J. S. Fairlamb
• 刊名：Organometallics
• 出版年：2011
• 出版时间：October 10, 2011
• 年：2011
• 卷：30
• 期：19
• 页码：5095-5109
• 全文大小：1333K
• 年卷期：v.30,no.19(October 10, 2011)
• ISSN：1520-6041

文摘

Dinuclear palladacyclic complexes [{Pd(CN)(渭-NCO)}₂] (CN = N-phenylbenzaldimine, Phbz) containing asymmetric imidato units (鈭扤CO鈥?= succinimidate (succ; 1), phthalimidate (phthal; 2), maleimidate (mal; 3), 2,3-dibromomaleimidate (2,3-diBrmal; 4), glutarimidate (glut; 5)) have been readily prepared by reaction between the di-渭-acetate precursor and cyclic imide ligands in a 1:2 molar ratio. Base treatment of the less acidic ligands 2-oxazolidone and 未-valerolactame with KOH/MeOH was required to give analogous 鈭扤CO鈥?bridged complexes (6 and 7). Reactions of the dinuclear complexes with tertiary phosphines provide novel mononuclear N-bonded imidate derivatives of the general formula [Pd(Phbz)(imidate)(PR₃)] (R = Ph (a), 4-F-C₆H₄ (b), 4-MeO-C₆H₄ (c), CH₂CH₂CN (d)). The application of these novel palladacyclic complexes as precatalysts for the Suzuki鈥揗iyaura cross-coupling reactions of both aryl and benzyl bromides with phenylboronic acid has been examined. The acetate adducts [Pd(Phbz)(CH₃COO)(PR₃)] (8a,c) were prepared to assess the role of imidate ligands in catalyst performance. The mononuclear imidate derivatives possess greater activity than the parent dinuclear complexes, exhibiting comparable performance in the cross-coupling of benzyl bromide with arylboronic acids to the best examples reported in the literature. The mononuclear imidate derivatives give a common Pd⁰L_n intermediate, as inferred by the release of the organic fragment (first reductive elimination product). Catalyst activation occurs by reaction of phenylboronic acid with the palladacycle in the absence of exogenous base (as shown by GC-MS and ESI-MS), with implications for the reliable comparison of catalyst performance across a series of related precatalysts (e.g., how catalyst/reagents are mixed and what is their order of addition). The single-crystal X-ray structures of compounds 4, 7, 1d, 3c, and 8a have been determined.