Hydroformylation diphosphine ligands

The results obtained in the biphasic hydroformylation of 1-octene are presented in Table 5.2-1. In order to evaluate the properties of the ionic diphosphine ligand... 

Many chiral diphosphine ligands have been evaluated with regard to inducing enantioselectivity in the course of the hydroformylation reaction [25,26]. However, a real breakthrough occurred in 1993 with the discovery of the BI-NAPHOS ligand by Takaya and Nozaki [65]. This was the first efficient and rather general catalyst for the enantioselective hydroformylation of several classes of alkenes, such as aryl alkenes, 1-heteroatom-functionalized alkenes, and substituted 1,3-dienes, and is still a benchmark in this area [66,67]. But still a major problem in this field is the simultaneous control of enantio-... 

Platinum complexes [PtCl2(diphosphine)] and [PtCl(SnCl3)(diphosphine)] of the ferrocenyl diphosphine ligands (35a), (35b), and (36) have been synthesized. Complexes [PtCl2(35)] and [PtCl2(36)] have been structurally characterized by XRD. Both the preformed and the in situ catalysts have been used in the hydroformylation of styrene.112... 

A water-soluble diphosphine ligand with large bite angle was prepared by controlled sulfonation of XANTHPHOS. The rhodium complex of the resulting (2,7-bis(S03Na)-XANTHPHOS (51) showed a catalytic activity in propene hydroformylation comparable to Rh/TPPTS (TOF 310 vs 500 h" at 120 °C, 9 bar propene and 10 bar CO/H2 = 1/1) [70]. The regioselectivity... 

A family of wide bite angle diphosphine ligands based upon xantphos (8) has been developed and tested in rhodium catalysed hydroformylation. van Leeuwen and co-workers conducted HP IR measurements on a range of Rh/thixantphos... 

Figure 5.2-5 Recycling experiments - Rh-catalyzed, biphasic 1-octene hydroformylation in [BMIMJfPFg] with a guanidinium-modified diphosphine ligand with xanthene backbone.

Kamer. P.C.J.. van Leeuwen, P.W.N.M., Goubitz, K. and Fraanje, J. (1995) New diphosphine ligands based on heterocychc aromatics inducing very high regioselectivity in rhodium-catalyzed hydroformylation - Effect of the bite angle. Organometallics, 14, 3081-3089. 

As a unique medium for asymmetric hydroformylation, supercritical carbon dioxide has recently been examined, which can be carried out in an extremely low catalyst concentration. The reactions of styrene (16a) and pentafluorostyrene (16e) catalyzed by Rh-BINAPHOS appear to give mixed results that are highly dependent on the reaction conditions [77,78], Enantioselectivity up to 92-95% ee for 16a or 85 % ee for 16e has been observed [78]. A biphasic reaction system has also been examined for the reaction using Rh(acac)(CO)2 with a sulfonated diphosphine ligand BINAS [79], The reaction proceeds smoothly at 40°C and 100 atm in high conversion with excellent branched aldehyde selectivity (95%), but enantioselectivity is very low (18% ee). The use of these newer reaction conditions is still in the very early stage and further development is expected in the next decade. 

In Table 6 the results concerning the asymmetric hydroformylation of 1-butene and of styrene with different catalytic systems are reported. When rhodium-containing catalytic systems are used in the presence of several diphosphine ligands, the face of the prochiral unsaturated carbon atom which is preferentially formylated is the same in both substrates for each chiral ligand. 

The phenoxazine-based ligand Nixantphos 8, which was derived from van Leeuwen s initial studies of xanthene-based diphosphine ligands [36], was used as the catalyst in a hydroformylation reaction as well. Nixantphos 8 proved to be a superior ligand with regard to its selectivity towards the linear aldehyde [37]. Moreover, Nixantphos 8 has recently been successfully immobilized on a silica 9 [38-40] and polystyrene 10 [41] matrix. After metal complexation, a catalyst can be obtained that is suitable for recycling by simple filtration (Fig. 4). 

The development of supported aqueous-phase catalysis (SAPC) [275, 276] is a new and efficient way to facilitate the hydroformylation of longer olefins. Most of the SAP catalysts described in the literature use TPPTS as ligand. Only a few sulfonated diphosphine ligands were examined [277]. A water-soluble chelating diphosphine ligand with a wide natural bite angle, based on a xanthene backbone, was studied as a SAP aqueous catalyst. This ligand showed a much better selectivity than the SAP catalysts known so far [278]. 

Electronic effects of diphosphine ligands have been reported by Unruh, Casey and Van Leeuwen [16-18]. Unruh studied the hydroformylation of 1-hexene using substituted ferrocene derived diphosphines Fe(C5H4PR2)2 (Fig. 6.4). 

Extensive mechanistic studies have been performed on reactions catalyzed by rhodium and platinum complexes containing enantiopure C2-symmetric diphosphine ligands.As discussed above, (1) the formation of the Tr-olefin-Rh(H) complex 19, (2) stereospecific cis addition of the hydridorhodium to the coordinated olefin to form the alkyl-Rh complex 20 (and then 2, and (3) the migratory insertion of a carbonyl ligand giving the acyl-Rh complex 17 with retention of configuration, have been established in the hydroformylation of 1-alkenes or substituted ethenes. Thus, it is reasonable to assume that the enantioselectivity of the reaction giving a branched aldehyde is determined at the diastereomeric (1) TT-olefin-Rh complex 19 formation step, (2) alkyl-Rh complex 20 formation step, or (3) acyl-Rh complex 17 formation step. 

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