Synthesis, characterization and coordination chemistry of a new phosphite–ether ligand: The effects of alkali metal salts and the ligand/Rh molar ratio on the catalytic activity and regioselectivity of a Rh(I) complex of this ligand in the hydroformylation of styrene

Metallacrown ethers with a symmetric bis(phosphite) ligand derived from 1,2-bis-(2-hydroxyethoxy)benzene: Synthesis, characterization and hydroformylation of styrene

“…The 31 P{ 1 H} NMR resonance is a singlet. The chemical shift of the 31 P { 1 H} NMR resonance is close to those of other phosphite and bis(phosphite) ligands [2,32,33] derived from the 2,2 0 -biphenylylenephosphochloridite ester. The 1 H NMR spectrum of the ligand exhibits two resonances in the 4.09e4.30 ppm region, indicating that the protons attached to each methylene carbon are chemically equivalent.…”

“…It is also interesting that the addition of LiBPh 4 has quite different effects on the catalytic activities and regioselectivities of a Rh(I) complex of the phosphite ligand 7 [2]. At a 7:Rh ratio of 2.5:1, which gives essential the same Rh to phosphite donor group ratio as does the 1.2:1 ratio used with the bis(phosphite) ligands, the addition of LiBPh 4 (8:1 LiBPh 4 :Rh) increases both the activity (the pseudo first order rate constant increases 3.5 Â 10 À4 to 6.7 Â 10 À4 ) and the regioselectivity (% iso/% n increases from 76/24 to 85/15) [2].…”

“…At a 7:Rh ratio of 2.5:1, which gives essential the same Rh to phosphite donor group ratio as does the 1.2:1 ratio used with the bis(phosphite) ligands, the addition of LiBPh 4 (8:1 LiBPh 4 :Rh) increases both the activity (the pseudo first order rate constant increases 3.5 Â 10 À4 to 6.7 Â 10 À4 ) and the regioselectivity (% iso/% n increases from 76/24 to 85/15) [2]. Although the increase in regioselectivity for the Rh(I) complex of 7 is similar to that seen with the Rh(I) complex of 1 at 8:1 LiBPh 4 :Rh, the increase in the pseudo first order rate constant is quite different.…”

“…We have recently demonstrated that both the rates and regioselectivities of alkene hydroformylation reactions catalyzed by phosphite and bis(phosphite) ligands can be affected by the presence of alkali metal salts [1,2]. The mechanism by which this occurs is not currently known.…”

“…The first reason is that in recent years, rhodium complexes of rigid and sterically constrained bis(phosphite) ligands and phosphine-phosphite hybrid ligands have receive considerable attention due to their remarkable activities and selectivities [16e25]. The second reason is the ligand has similar phosphite groups to those used in our previously reported hydroformylation results that were carried out either with a Rh(I) catalyst containing a sterically constrained bis(phosphite) ligand derived from tartaric acid [1] or with monodentate phosphite-ether ligands [2] under reactions identical conditions as shown in Fig. 1.…”