Catalysis of Organic..

32Halophosphite LigandsIn 1970, Pruett and Smith (2) described a low pressure hydroformylationprocess which utilizes triarylphosphine or triarylphosphite ligands in combinationwith rhodium catalysts. The ligands, although used in many commercial applications,have limitations due to oxidative and hydrolytic stability problems. Since these earlydisclosures, numerous improvements have been made to increase the catalyststability, catalyst activity and the product ratio with a heavy emphasis on yieldinglinear aldehyde product. As a result of many years of research work in academic andindustrial labs, a wide variety of monodentate phosphite and phosphine ligands,bidentate ligands such as bisphosphites and bisphosphines as well as tridentate andpolydentate ligands have been prepared and disclosed in the literature (3,4). Theearly patents are still very significant today as all large scale commercial applicationsof the low pressure hydroformylation reaction are based on the triorganophosphineor triorganophosphite technology that was initially disclosed over thirty years ago.Results and DiscussionThe evaluation of novel trivalent phosphorus compounds as ligands for the lowpressure hydroformylation reaction is an integral part of an ongoing program todevelop and test new hydroformylation catalysts. Thus, when Klender et al. (5) ofAlbemarle Corporation published data demonstrating that the fluorophosphite,Ethanox 398, is surprisingly stable torefluxing aqueous isopropanol, we wereintrigued as to whether or not this materialwould have sufficient stability to serve asa trivalent phosphorus ligand in ahydroformylation catalyst. A search ofthe chemical literature revealed numerousOantioxidant applications but did not revealO Pany use of fluorophosphite compounds asFligands with transition metals. OurEthanox 398 TMpersonal experiences with compounds1containing halogen phosphorus bondswere that these materials are highly reactive, easily hydrolyzed, and subject tosecondary reactions such as disproportionation.The hydrolytic decomposition of a potential fluorophosphite ligand wouldgenerate free fluoride ions which would be expected to be detrimental to the activityof a hydroformylation catalyst. The patent literature contains abundant references tothe detrimental effects of halogens (6) on hydroformylation catalysts, and based onthe patent information, one could not reasonably expect a halophosphite to be asuccessful hydroformylation ligand. However, a second publication by Klender (7)shows that exposure of 1 and other fluorophosphites to moisture at temperatures of250 o C to 350 o C does not generate fluoride, even at part per million levels.Despite our personal skepticism, a sample of 1 was obtained (8) and tested in abench test unit that simulates continuous vapor stripped reactor operation (9). The