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Zinc−Zinc Bonded Zincocene Structures. Synthesis and Characterization of Zn 2 (η 5 -C 5 Me 5 ) 2 and Zn 2 (η 5 -C 5 Me 4 Et) 2

2006; American Chemical Society; Volume: 129; Issue: 3 Linguagem: Inglês

10.1021/ja0668217

1943-2984

Abdessamad Grirrane, I. Resa, Amor Rodríguez, Ernesto Carmona, Eleuterio Álvarez, Enrique Gutiérrez‐Puebla, Ángeles Monge, Agustı́n Galindo, Diego del Rı́o, Richard A. Andersen,

Organoboron and organosilicon chemistry

While, in general, decamethylzincocene, Zn(C5Me5)2, and other zincocenes, Zn(C5Me4R)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(C5Me5)2 with ZnEt2 or ZnPh2 produce unexpectedly the dizincocene Zn2(η5-C5Me5)2 (1) in low yields, most likely as a result of the coupling of two (η5-C5Me5)Zn• radicals. An improved, large scale (ca. 2 g) synthesis of 1 has been achieved by reduction of equimolar mixtures of Zn(C5Me5)2 and ZnCl2 with KH in tetrahydrofuran. The analogous reduction of Zn(C5Me4R)2 (R = H, SiMe3, But) yields only decomposition products, but the isotopically labeled dimetallocene 68Zn2(η5-C5Me5)2 and the related compound Zn2(η5-C5Me4Et)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 Zn2(η5-C5Me4Et)2, with a short Zn−Zn bond of 2.295(3) Å 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%).