- A Zinc Catalyzed C(sp3)?C(sp2) Suzuki–Miyaura Cross-Coupling Reaction Mediated by Aryl-Zincates
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The Suzuki–Miyaura (SM) reaction is one of the most important methods for C?C bond formation in chemical synthesis. In this communication, we show for the first time that the low toxicity, inexpensive element zinc is able to catalyze SM reactions. The cross-coupling of benzyl bromides with aryl borates is catalyzed by ZnBr2, in a process that is free from added ligand, and is compatible with a range of functionalized benzyl bromides and arylboronic acid pinacol esters. Initial mechanistic investigations indicate that the selective in situ formation of triaryl zincates is crucial to promote selective cross-coupling reactivity, which is facilitated by employing an arylborate of optimal nucleophilicity.
- Procter, Richard J.,Dunsford, Jay J.,Rushworth, Philip J.,Hulcoop, David G.,Layfield, Richard A.,Ingleson, Michael J.
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supporting information
p. 15889 - 15893
(2017/10/24)
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- Zinc-zinc bonded zincocene structures. Synthesis and characterization of Zn2(η5-C5Me5)2 and Zn2(η5-C5Me4Et)2
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While, in general, decamethylzincocene, Zn(C5Me 5)2, and other zincocenes, Zn(C5Me 4R)2 (R = H, But, SiMe3), react with dialkyl and diaryl derivatives, ZnR′2, to give the half-sandwich compounds (η5-C5Me4R) ZnR′, under certain conditions the reactions of Zn(C5Me 5)2 with ZnEt2 or ZnPh2 produce unexpectedly the dizincocene Zn2(η5-C 5Me5)2 (1) in low yields, most likely as a result of the coupling of two (η5-C5Me 5)Zn. radicals. An improved, large scale (ca. 2 g) synthesis of 1 has been achieved by reduction of equimolar mixtures of Zn(C 5Me5)2 and ZnCl2 with KH in tetrahydrofuran. The analogous reduction of Zn(C5Me 4R)2 (R = H, SiMe3, But) yields only decomposition products, but the isotopically labeled dimetallocene 68Zn2(η5-C5Me5) 2 and the related compound Zn2(η5-C 5Me4Et)2 (2) have been obtained by this procedure. Compound 2 has lower thermal stability than 1, but it has been unequivocally characterized by low-temperature X-ray diffraction studies. As for 1 a combination of structural characterization techniques has provided unambiguous evidence for its formulation as the Zn-Zn bonded dimer Zn 2(η5-C5Me4Et)2, with a short Zn-Zn bond of 2.295(3) A indicative of a strong Zn-Zn bonding interaction. The electronic structure and the bonding properties of 1 and those of related dizincocenes Zn2(η5-Cp′)2 have been studied by DFT methods (B3LYP level), with computed bond distances and angles for dizincocene 1 very similar to the experimental values. The Zn-Zn bond is strong (ca. 62 kcal-mol-1 for 1) and resides in the HOMO-4, that has a contribution of Zn orbitals close to 60%, consisting mostly of the Zn 4s orbitals (more than 96%).
- Grirrane, Abdessamad,Resa, Irene,Rodriguez, Amor,Carmona, Ernesto,Alvarez, Eleuterio,Gutierrez-Puebla, Enrique,Monge, Angeles,Galindo, Agustin,Del Rio, Diego,Andersen, Richard A.
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p. 693 - 703
(2007/10/03)
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