CO Fourier-transform infrared study of metallocenes on silica gel and AlPO4

Abstract

Metallocenes of vanadium, manganese, cobalt, iron and nickel have been reacted with silica gel and AlPO₄. The samples were studied with CO FTIR spectroscopy. Vanadocene on AlPO₄ gave a band at 1869 cm^–1, interpreted as VCp₂CO, and two bands from a more stable species at 2046 and 1992 cm^–1, which are due to a [VCp₂(CO)₂]⁺ surface compound. Manganocene produced small amounts of a manganese carbonyl compound only after heating to 200 °C.

Ferrocene reacted with the AlPO₄ surface only at elevated temperatures (300 °C) giving weak CO IR bands at 2065 and 2023 cm^–1. These are interpreted as due to a [FeCp(CO)₂]⁺ species. Cobaltocene reacted similarly on both SiO₂ and AlPO₄. CO IR bands [from CoCp(CO)₂] were observed at 2032 and 1964 cm^–1(SiO₂) and at 2018 and 1950 cm^–1(AlPO₄).

Nickelocene reacted very easily with the surface of both supports. It decomposed at room temperature forming C₁₀H₁₂ and Ni⁰. At low temperatures (–80 °C) a band at 2103 (AlPO₄) or 2094 cm^–1(SiO₂) was the main absorption band found, which is interpreted as arising from [CpNiCO]⁺, bonded to the surface via P—O^– groups. At room temperature Ni(CO)₄(CO IR band at 2056 cm^–1) was formed. Only NiCp₂ and FeCp₂ of the metallocenes studied reacted similarly to chromocene with the two different supports. Ferrocene on the AlPO₄ surface gave much weaker CO IR bands and nickelocene on the supports was less stable at room temperature than chromocene.