Rhodium Complexes of Sterically Demanding Diphosphonites:  Coordination Chemistry and Catalysis

Abstract

The coordination chemistry of various sterically constrained diphosphonites 1-6 with rhodium are reported. The stoichiometric reaction of ligand 5 with [Rh(µ-Cl(CO) 2 ] 2 gives rise to the sole formation of trans-[RhCl(CO)(5)] (7), as shown by NMR and IR spectroscopy and X-ray crystallography. The molecular structure reveals a weak interaction between the metal center and the oxygen from the xanthene backbone. This complex serves as a structural model for the first intermediate in the catalytic cycle of rhodium hydroformylation, [Rh(H)-(CO)(PkP)]. A detailed study on the solution structure of the catalyst resting state under catalytic conditions is performed by high-pressure NMR and FT-IR spectroscopy. The spectroscopic data show that under hydroformylation conditions the bidentate ligands form well-defined complexes with the structure [Rh(H)(CO) 2 (PkP)]. All ligands show preference for a bis-equatorial (ee) coordination mode in the trigonal-bipyramidal Rh complexes. These novel sterically constrained diphosphonite ligands are applied in the rhodium hydroformylation of 1-octene and 2-butene, and good activities and regioselectivities are obtained.

Sterically Demanding Diphosphonite Ligands –Synthesis and Application in Nickel‐Catalyzed Isomerization of 2‐Methyl‐3‐Butenenitrile

“…Recently we finished a study on the coordination behaviour of these diphosphonites to various transition metals other than nickel [21] as well as on the application of the diphosphonites in the rhodium-catalyzed hydroformylation of higher alkenes. [36] Experimental Section General All chemicals were purchased from Aldrich Chemical Co., Acros or Merck and used as received. All preparations were carried out under an argon atmosphere using standard Schlenk techniques.…”

Solvent‐Free Olefin Hydroformylation Using Hemispherical Diphosphites

“…Mainly for steric reasons, these intermediates orientate the olefin insertion step towards the formation of a linear alkyl-rhodium complex, which ultimately will then result in formation of a linear aldehyde. [19][20][21] Scheme 2. Equatorial-equatorial configuration of the two phosphorus atoms leading to the formation of the linear aldehyde.…”

Rhodium-catalyzed hydroformylation of olefins: Effect of [bis(2,4-di-tert-butyl) pentaerythritol] diphosphite (alkanox P-24) on the regioselectivity of the reaction

“…High activities were obtained for 1-octene, with good selectivity to the linear aldehyde and for the 2-butene the selectivity for the n-pentanal was 62% [10].…”