Hydroformylation Phosphinine-rhodium

The most significant results were obtained by the group of Breit who demonstrated that phosphinine rhodium(I) complexes behave as very efficient catalysts. In the first two reports, most efforts focused on the hydroformylation of styrene and important conversion yields and interesting selectivities in favour of the branched aldehyde were obtained by using derivatives of 2,4,6-triphenylphosphin-ine 1 [51]. Importantly, reactions could be carried out under mild conditions in toluene at 25 °C using [Rh(acac)(CO)2] complex as catalytic precursor with a Rh phosphinine substrate ratio of 1 5 280 and a CO/H2 (1 1) pressure of 20 bars. With the triphenyl derivative, a Turn Over Frequency (TOF) of 28.7 mol sub-strate/mol catalyst/h was obtained, the conversion yield reaching 30.8%. Theses... 

Rhodium complexes of phosphorus based ligands are of considerable importance as (pre-)catalysts in hydroformylation which has developed into one of the most important homogeneous catalytic processes [57]. A recent advantage in this field involved the use of phosphinines as ligands whose low-lying r -orbitals provide for similar r-acceptor qualities as for phosphites [13, 58]. 

The electronic properties of phosphinines are located between those of phosphines and phosphites, with somewhat more similarity to phosphites. In general, phosphinines are characterized by considerable it-acceptor properties and thus beneficial for several catalytic applications [32]. A theoretical study on Rh-phosphinine complexes provided evidence that the directionality of the ir-backdonation rather than the overall acceptor ability was responsible for the high catalytic activity [33]. In the rhodium-catalyzed hydroformylation of styrene with phosphinines as ligands, superior results in terms of conversion and TOP (turnover frequency) were noted in comparison to the use of PPhj or standard mono-triarylphosphites [34]. Atropisomeric 2-arylphosphmines have been prepared by Muller s group [35]. In the hydroformylation of trans-2-octene, a clear preference for the formation of 2-methyloctanal was noted. 

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