Physical, Spectroscopic, and Structural Properties of the Various Group 4B Metallocene Dicarbonyls

PHYSICAL, SPECTROSCOPIC, AND STRUCTURAL PROPERTIES OF THE VARIOUS GROUP 4B METALLOCENE DICARBONYLS 

Because of the low oxidation state of the metal [M(II)] in the group 4B metallocene dicarbonyl compounds, all of them, perhaps with the exception of (17—C5Me5)2Ti(CO)2 (27), are very air sensitive and decompose rapidly on exposure to air, forming a yellow solid for the titanium compounds and cream-colored solids for the zirconium and hafnium analogs. While the dicarbonyl 27 is indeed air sensitive, its decomposition appears qualitatively to be much slower relative to the other related complexes. 

The group 4B metallocene dicarbonyls exhibit excellent solubility in aromatic and ethereal solvents and very good solubility in aliphatic solvents. In most cases the dicarbonyls can be purified by recrystallization from aliphatic solvents at about -20°C (58,59) and/or by sublimation at 70-80°C and 10 1 2-10 3 mm Hg (6-8,24). 

All the group 4B metallocene dicarbonyl complexes exhibit two strong metal carbonyl stretching frequencies (Ax and Bf) with the exception of bis(i7-indenyl)dicarbonyltitanium (34) and bis(i7-tetrahydroindenyl)dicar-bonyltitanium they exhibit three frequencies due to splitting of the Bt 

The chemical shifts and multiplicities of the various metallocene dicarbonyl compounds are listed in Table I. 

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