Novel Amphiphilic Diphosphines:  Synthesis, X-ray Structure, Rhodium Complexes, Use in Hydroformylation, and Rhodium Recycling

Abstract

Three novel amphiphilic diphosphines have been synthesized: bis[2-(phenyl(3-pyridyl)-phosphino)ethyl] ether (POPpy) and bis [2-((4-((diethylamino), and 4,6-bis[bis(4-((diethylamino)methyl)phenyl)phosphino]-10,10-dimethylxanthene (xantham), based on 4,6-bis(diphenylphosphino)-10,10-dimethylxanthene (Xantphos). The crystal structure of xantham has been determined. Solution structures of rhodium xantham complexes have been studied using NMR and IR spectroscopy. When POPam is used in the hydroformylation of oct-1-ene, a linear/branched ratio (l/b) of 7.3 is achieved (88% nonanal) without isomerization to oct-2-ene. The use of POPpy results in an activity that is twice as high, a higher l/b-ratio of 9, and 0.7% isomerization. When xantham is used in the hydroformylation of hex-1-ene, oct-1-ene, and dodec-1-ene (80°C, 20 bar of syngas, toluene), l/b-ratios of 50 have been achieved (94% nonanal) together with 4% of isomerized octenes. The pHdependent distribution characteristics of the free ligands have been determined, and it is shown that POPpy, POPam, and xantham can be extracted for 40% from a Et 2 O solution into an aqueous solution of H 2 SO 4 at pH values of, respectively, 2.5, 5, and 5. Rhodium recycling experiments using POPam and xantham show that rhodium can be extracted into an aqueous layer at pH 5-5.5 for more than 99.95%, as determined by ICP-AES analysis, which allows complete separation of the product aldehydes and catalyst. After neutralization of the aqueous phase containing protonated POPam with an aqueous solution of NaHCO 3 , only 65% of the rhodium can be re-extracted into fresh toluene. In the case of xantham, 98% of the rhodium is re-extracted. Pressurizing the recovered rhodium and excess xantham to 20 bar at 80°C resulted in regeneration of the original active hydride complex, as judged by the retention of activity of up to 86%. POPpy has proved inappropriate for the recycling of rhodium.

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

“…The xanthene backbone is only slightly twisted with an interplanar angle of 8.33(10)8 which is in accordance with the absence of any stacking of the aromatic rings due to steric congestion. [19] X-Ray Crystallographic Study of Ni(II) Complex of Diphosphonite Ligand 1…”

“…All hydrogen atoms are omitted for clarity. Selected bond lengths (ä), angles, and torsion angles (8): NiÀP1 2.1632(7); NiÀP2 2.1848(7); NiÀBr1 2.2886(4); NiÀBr2 2.3110(4); P1 ± O2 1.6020(16); P1 ± O3 1.6060(17); P1 ± C1 1.808(2); P2 ± O4 1.6191(16); P2 ± O5 1.6167(17); P2 ± C10 1.814(2); O1 ± C6 1.393(3); O1 ± C15 1.393(3); NiÀO1 2.6137(16); P1 ± P2 4.2171(9); Br1 ± Ni À Br2 163.073(18); P1 ± Ni À P2 151.81(3); Br1 ± Ni À P1 94.69(2); Br1 ± Ni À P2 98.56(2); Br2 ± Ni À P1 87.68(2); Br2 ± Ni À P2 86.78(2); O2 ± P1 ± O3 96.66(9); O4 ± P2 ± O5 106.55(9); NiÀP1 ± O2 121.41(7); NiÀP1 ± O3 121.38(6); NiÀP2 ± O4 113.46(7); NiÀP2 ± O5 121.14(7); NiÀP1 ± C1 109.00(8); NiÀP2 ± C10 109.24(8); C6 ± O1 ± C15 116.87(16); C5 ± C7 ± C14 108.25 (19); O2 ± P1 ± C1 100.09(9); O3 ± P1 ± C1 105.38(10); O4 ± P2 ± C10 104.89(10); O5 ± P2 ± C10 99.62(10); C1 ± C6 ± C5 ± C7 179.1(2); C10 ± C15 ± C14 ± C7 174.4(2). Species C is highly symmetrical because the two phosphorus atoms of the diphosphonite unit remain equivalent.…”

Bisphosphine ligands containing two o-N,N-dimethylanilinyl substituents at each phosphorus atom

“…The amino-bisphosphine systems, which have been reviewed (6), have been developed mainly with the aim of surmounting the severe problem in homogeneous catalysis of separating the catalyst from the reaction products. Approaches to solving this problem, including representative literature references, have been: (i) to "heterogenize" the homogeneous catalyst by incorporating it into an insoluble polymer via attachment through the N atom (5,(7)(8)(9); (ii) to solubilize the catalyst in water (in which the reactants and products are only slightly miscible) by quaternization of the N atom via protonation or alkylation (10)(11)(12)(13)(14)(15)(16); (iii) to water solubilize the catalyst via incorporation of a sulfonate group within an elaborated N-containing functionality (17); and (iv) to extract the catalyst postreaction with aqueous acid in which the product does not dissolve (18,19).…”

Biphasic and Flow Systems Involving Water or Supercritical Fluids

“…1 Graphs showing the slow rate of alkene hydroformylation in aqueous biphasic systems and the dramatic rate increase effected by adding [Octmim]Br (0.5 mol dm -3 ). After [5] Reproduced with permission Ó Royal Society of Chemistry using basic amine groups on phoshines which protonate on addition of acid to make them water soluble, but deprotonate to become organic soluble on addition of base, but in these cases, salt accumulation becomes a problem in time [17].…”