Zinc-zinc bonded zincocene structures. Synthesis and characterization of Zn2(eta5-C5Me5)2 and Zn2(eta5-C5Me4Et)2.
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 (eta5-C5Me4R)ZnR', under certain conditions the reactions of Zn(C5Me5)2 with ZnEt2 or ZnPh2 produce unexpectedly the dizincocene Zn2(eta5-C5Me5)2 (1) in low yields, most likely as a result of the coupling of two (eta5-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(eta5-C5Me5)2 and the related compound Zn2(eta5-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(eta5-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(eta5-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
A
Instituto de Investigaciones Químicas-Departamento de Química InorgAnica, Universidad de Sevilla-Consejo Superior de Investigaciones Científicas, Américo Vespucio 49, 41092 Sevilla, Spain.
Resa
Irene
I
Rodriguez
Amor
A
Carmona
Ernesto
E
Alvarez
Eleuterio
E
Gutierrez-Puebla
Enrique
E
Monge
Angeles
A
Galindo
Agustín
A
del Río
Diego
D
Andersen
Richard A
RA
D001665:Binding Sites; D002712:Chlorides / Q000737:chemistry; D005663:Furans / Q000737:chemistry; D007553:Isotope Labeling; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000138:chemical synthesis*; D013696:Temperature; D014961:X-Ray Diffraction; D015032:Zinc / Q000737:chemistry*; D017967:Zinc Compounds / Q000737:chemistry
D002712:Chlorides; D005663:Furans; D009942:Organometallic Compounds; D017967:Zinc Compounds; C018674:tetrahydrofuran; C016837:zinc chloride; D015032:Zinc