Xantphos trans complexes

Phosphacyclic diphosphines (73a) and (73b) with wide natural bite angles were synthesized and the effect of the phosphacyclic moieties on the coordination chemistry in the [(diphosphine) Rh(CO)2H] complexes was studied. Both NMR and IR spectroscopy showed that the phosphacyclic xantphos ligands exhibit an enhanced preference for diequatorial chelation compared to the diphenylphosphino-substituted parent compound. In the hydroformylation of 1-octene the introduction of the phosphacyclic moieties leads to higher reaction rates. The dibenzophospholyl- and phenoxaphosphino-substituted xantphos ligands exhibit a high activity and selectivity in the hydroformylation of trans-2- and 4-octene to linear nonanal. CO dissociation rates from the... 

These conclusions confirm the results with Ir(Xantphos) complexes by Eisenberg s group from 2006 [11]. For some of these H2lr complexes, a trans coordination of the diphosphine was found. The hydrido complexes HIr(CO)2(Xantphos) and H3lr(CO)(Xantphos) exhibited only modest hydroformylation activity for the transformation of 1-hexene and styrene (Hj/CO = 2 1, 3 atm 75 °C). The aldehydes were produced in a yield of 10%. More than 50% 1-hexene isomerization was observed. Complete inhibition of the reaction took place in the presence of a twofold excess of the bidentate ligand. It was speculated that in some cases dissociation of Xantphos could be a precondition for catalysis to occur. 

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