Homogeneous catalytic fluorination

Heterogeneously catalysed conversions of CCl2=CCl2 to CCI2FCHCI2 and thence to CF3CHCI2 and of the analogous reaction of CCl2=CHCl 

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Palo, D.R. Erkey, C. Homogeneous catalytic hydroformylation of 1-octene in supercritical carbon dioxide using a novel rhodium catalyst with fluorinated arylphosphine ligands. Ind. Eng. Chem. Res. 1998, 37 (10), 4203-4206. 

Fluorous containing ligands in fluorinated solvents can lead to homogeneous catalytic complexes at moderately high temperature and these separate at room temperature giving a two-phase system from which the catalysts is simply separated by decantation. Horvath, who was the first to develop this concept [82], has reviewed recently the fluorous biphasic chemistry [83], The combination of fluorinated ligands and supercritical carbon dioxide affords a particular efficiency to these systems [84,85]. 

Many different reaction schemes, as described in Figure 7.5, are considered and both homogeneous and heterogeneous catalysts are featured. Fluorinated chromia appears as the catalyst for the catalytic fluorination step that leads to the intermediate, CF3C1C=CH2, HFO-1233xf it is apparent that catalyst deactivation is a problem and for this reason addition of a basic molecule such as di-isopropylamine to the vapor feed is recommended. 

Only a few years after the development of the homogeneous chiral Mn(salen) complexes by Jacobsen and Katsuki, several research groups began to study different immobiUzation methods in both liquid and soUd phases. Fluorinated organic solvents were the first type of Uquid supports studied for this purpose. The main problem in the appUcation of this methodology is the low solubility of the catalytic complex in the fluorous phase. Several papers were pubUshed by Pozzi and coworkers, who prepared a variety of salen ligands with perfluorinated chains in positions 3 and 5 of the saUcyUdene moiety (Fig. 2). 

The oxophilicity and coordination ability of the lanthanide elements turned out to be crucial for the attraction and activation of oxygenated functions which display pivotal components in important condensation and addition reactions [101]. Orga-nometallic systems such as fluorinated )5-diketonate and alkoxide complexes which contain highly polarized Ln-O-C linkages and are soluble in non-oxy-gen-containing solvents seem to be predestined for this type of homogeneous transformation (Structures 20-24). It must be assumed that other precatalysts (Ln"-derivatives or Ln -alkyls) underlie in situ formation of catalytically active Ln-O(alkoxide) moieties such as enolates when substrates such as ketones or aldehydes are involved. 

Parallel to the development of catalysts for olefin metathesis, the first alkyne metathesis catalysts were W and Mo metal oxides or carbonyls suspended on alumina or silica.65 The first homogeneous catalysts were developed by Mortreux and consisted of a mixture of Mo(CO)6 and substituted phenols.66 It was not until the work of Schrock and his collaborators, however, that a well-defined, isolable alkylidyne catalyst (38) was synthesized, characterized, and shown to catalyze alkyne metathesis.67 Later modifications on 38 included substituting the alkoxy groups with fluorinated analogs, and for the corresponding Mo alkylidynes (39), the fluorinated alkoxy groups are essential for catalytic activity.68... 

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