Cobalt alkylphosphine modified

Cobalt carbonyls are the oldest catalysts for hydroformylation and they have been used in industry for many years. They are used either as unmodified carbonyls, or modified with alkylphosphines (Shell process). For propene hydroformylation, they have been replaced by rhodium (Union Carbide, Mitsubishi, Ruhrchemie-Rhone Poulenc). For higher alkenes, cobalt is still the catalyst of choice. Internal alkenes can be used as the substrate as cobalt has a propensity for causing isomerization under a pressure of CO and high preference for the formation of linear aldehydes. Recently a new process was introduced for the hydroformylation of ethene oxide using a cobalt catalyst modified with a diphosphine. In the following we will focus on relevant complexes that have been identified and recently reported reactions of interest. 

Cobalt was the first catalyst used in commercial applications of the oxo-synthesis. In order to stabilize the HCo(CO)4 catalyst, high pressures are necessary with a maximum n/i ratio of 80/20. In the Shell process,324,325,393 cobalt catalysts modified with alkylphosphines e.g. ( )3 ( 4 9) are more selective towards linear products but exhibit high hydrogenation activity and are therefore mainly used for the direct synthesis of long chain alcohols. 

As mentioned above, most published papers and patent applications deal with ligands and their influence on activity and selectivity in the oxo synthesis. When alkylphosphine-modified cobalt catalysts were introduced by Shell [135], high n/i selectivities were reported. However, coordination of phosphine ligands makes the metal-hydrogen bond more hydridic, therefore leading to substantial formation of hydrogenation products. Hydroformylation of 1-pentene yielded hex-anol with 91 % linearity. 

The second generation processes use rhodium as the metal and the first ligand-modified process came on stream in 1974 (Celanese) and more were to follow in 1976 (Union Carbide Corporation) and in 1978 (Mitsubishi Chemical Corporation), aU using triphenylphosphine (tpp). The UCC process has been licensed to many other users and it is often referred to as the LPO process. Not only are rhodium catalysts much faster - which is translated into milder reaction conditions -, but also their feedstock utilization is much better than that of cobalt catalysts. For example, the cobalt-alkylphosphine catalyst may give as much as 10% of alkane... 

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