Xantphos type ligand

Figure 8.10. Xantphos type ligands and their calculated (V values...

Hydrosilylation of allyl chloride with HSiCl3 leads to Cl(CH2)3SiCl3 that can be used for many surface modifications after substitution of the chlorides by suitable functional groups [5], For instance it can be used to anchor soluble hydroformylation catalysts to a silica surface (Figure 18.3). Many examples have been reported and we present only one example of a selective Xantphos type ligand [6],... 

A transmission cell was used in the studies reported by van Leeuwen [18,21, 30,43]. The autoclave and the transmission cell are only a few millimetres apart and the liquid is pumped with a centrifugal pump from the autoclave to the cell. The time delay between autoclave and cell can be as low as a few milliseconds. The advantage is a higher signal-to-noise ratio. The in-situ measurements on Xantphos type ligand systems showed that the only species that can be observed... 

Scheme 5.3-19 Synthesis of a dicationic phenoxaphosphino-modified xantphos type ligand as used in the hydrofbrmylation ofl-octene in [BMIM][PF6].

An imidazolium-based dicationic phenosaphosphino-modified xantphos type ligand was applied by van Leeuwen et al. for the hydroformylation of 1-octene in [BMIM][PFs] [176]. The ligand was prepared in a six-step synthesis according to... 

The characteristics of the xantphos-type ligands in terms of activity and selectivity were later exploited by Dupont et al. (37). For a better solubility in ILs, sulfonated groups were grafted onto the xanthene backbone (9). Because of the poor natural solubility of this Kgand in I Ls, catalyst formation was achieved by mixing the ligand with (Rh(CO)2(acac)] in a mixture of (BMIM](PFg] and methanol. After evaporation of the methanol under vacuum, a yellow homogeneous IL phase was obtained. 

Two Xantphos-type ligands used in rhodium-catalyzed hydroformylation. 

Pingen D, Eebl T, Vogt D et al (2014) Catalytic activity and fluxional behavior of eomplexes based on RuHCl(CO)(PPh3)3 and Xantphos-type ligands. Organometallics 33(11) 2798 2805... 

Van Leeuwen and the group of Celanese addressed the problem of poor solubility of some phosphine ligands in typical aromatic solvents used for hydroformylation or in the neat olefinic substrate and in the product aldehyde, respectively [71]. For this reason, they linked long-chain alkyl groups to a Xantphos-type ligand. The alkyl groups were introduced by a Friedel-Crafts acylation of 9,9-dimethylxanthene, followed by reduction of the keto group with hydrazine (Scheme 2.26) [72]. 

Van Leeuwen and coworkers [117] prepared a Xantphos-type ligand for application in RTILs (room-temperature ionic liquids) bearing remote imidazolium groups (Scheme 2.34). In the first step, the xanthene-based backbone was functionalized by Friedel-Crafts acylation using 5-bromovaleraldehyde. After reduction of the keto groups, two POP units were introduced. Final incorporation of methyl-imidazolium groups yielded the final ligand. In the first runs of the rhodium-catalyzed hydroformylation of 1-octene in [BMlM][PFg], a diminished activity was noted, obviously due to incomplete conversion of the precatalyst into... 

With the well-known modularity of Xantphos-type ligands in mind. Reek and coworkers [70] developed a chiral phosphine-phosphonite based on this scaffold (Scheme 2.148). 

In the HAM of internal olefins with rhodium Xantphos-type ligands, the same steric dependency on the bite angle concerning the formation of the linear amine as in hydroformylation was observed. An increase in the bite angle up to 125°, which was realized with Nixantphenoxaphos (1), resulted in an increase in n-regioselectivity, whereas with wider angles a reversed tendency was... 

Catalytic hydrocyanation of styrene employing Xantphos-type ligands has been reported previously, but catalyst loading of 5 mol% was necessary to ensure good conversion [18,43]. 

Scheme 5.6 Synthesis of xantphos-type ligand for hydroformylations in scCOa [20].

Phenoxaphosphino-modified xantphos-type ligands in the rhodium-catalyzed hydroaminomethylation of internal olefins were found to give linear amines. Hydro-aminomethylation and each of its individual steps were monitored by high-pressure infrared spectroscopy. The results suggest that hydroaminomethylation takes place by a sequential isomerization/hydroformylation/amination/hydrogenation pathway [170]. 

Experiments showed that both ee and ea isomers are present in solution for xantphos-type ligands and Landis therefore studied a series of 56 isomers and conformers along the reaction pathway by similar ONIOM methods. 

Gompared to other wide-bite-angle diphosphine ligands, xantphos-type ligands can be modified easily while retaining their favorable properties, especially in hydroformylation, and as a result many derivatives have been synthesized by several groups and used in fluorous-phase hydroformylation catalysis, aqueous phase catalysis, one-phase hydroformylation and catalyst extraction, catalysis in ionic liquids, hydroformylation with immobilized catalysts, and catalysis in supercritical G02. ... 

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