| Abstract
| - Iridium complexes containing the large bite angle bisphosphine ligand xantphos have been synthesized and theirreactivity studied. Several of these complexes are the first reported Ir(xantphos) systems to be characterized byX-ray diffraction. Variable-temperature NMR spectroscopic studies of IrI(CO)2(xantphos) (1-I) and Ir(COEt)(CO)2(xantphos) (8) show two separate dynamic processes in which the phosphorus donors and the backbone methylgroups of the xantphos ligand are exchanged. The addition of parahydrogen (p-H2) to 1-I leads to the formation oftwo dihydride isomers including one in which both hydride ligands are trans to the phosphorus donors, suggestiveof an Ir(I) xantphos intermediate with the ligand chelated in a trans-spanning fashion (2b). The bromide and chlorideIr(I) analogues (1-Br and 1-Cl) also form this isomer upon reaction with parahydrogen, with 1-Cl yielding only thisdihydride species. The trihydride complex IrH3(CO)(xantphos) (7) has been prepared, and its exchange with freehydrogen at elevated temperature is confirmed by reaction with p-H2. The hydride complexes IrH(CO)2(xantphos)(6) and IrH3(CO)(xantphos) (7), as well as the propionyl complex 8, are modest catalysts for the hydroformylationof 1-hexene and styrene under mild conditions. The addition of p-H2 to 8 permits direct observation of the propionyldihydride species IrH2(COEt)(CO)(xantphos) (9) under both thermal and photolytic conditions, as well as unusualbut weak polarization of the aldehydic proton of the propanal product that forms upon reductive elimination from9.
- A series of new iridium complexes containing the wide bite angle ligand xantphos has been synthesized and characterized. The complexes react with dihydrogen to form different kinetic dihydrides as seen using para-hydrogen induced polarization. A key model hydroformylation intermediate has been characterized, and unusual oneH−PHIP is seen in the generation of aldehyde product from this species.
|
