Hydroformylation, asymmetric pressure

Alkane dehydroeyelization with Pt-Sn-alumina catalysts—Continued pressure effect, 120 PtSn alloy formation, 117-118 role of Sn, 117 Sn vs. carbon deposition, 120 Sn vs. coking, 118-119 Sn vs. n-octane conversion, 120-122 Sn vs. selectivity, 118 temperature effect, 119 Alkene hydroformylation, asymmetric catalysis, 24... 

MeOBIPHEP is the atropisomeric diphosphine 2,2,-bis(diphenylphosphino)-6,6 -dimethoxy-l,-l -biphenyl (100), has been synthesized. In the presence of SnCl2, this species is an efficient catalyst for the asymmetric hydroformylation of styrene. Asymmetric inductions are higher than those attainable using the system [PtCl2 (i )-(+)-BINAP ]/SnCl2, where BINAP is 2,2 -bis(di-phenylphosphino)-l,l,-binaphthyl. The influence of CO and H2 partial pressures on the catalytic activity of the (99)/SnCl2 system has also been studied.328 Complexes [PtMeCl(P-P)][(101), P-P = (5)-6,6,-(dimethoxybiphenyl)-2,2,-diylbis(diphenylphosphine) ((5)-MOBIPH) (102),... 

A chiral diphosphite based on binaphthol, coordinated with rhodium (I) forming a nine-member ed ring, led to an efficient hydroformylation of vinylarenes, although moderate ees were obtained (up to 46%) at mild pressure and temperature reaction conditions.364 Chiral diphosphites and phosphinite-phosphites derived from spiro[4.4]nonane-l,6-diol were synthesized. Using these catalysts in the asymmetric hydroformylation of styrene, high regioselectivity (97%) and... 

Effects of GO and H2 partial pressures on the reaction rate and selectivity of asymmetric hydroformylation of 1-hexene and styrene are examined using (7 ,A)-BINAPHOS-Rh catalyst system. For both substrates, high GO partial pressure tends to retard the reaction the partial pressure of H2 hardly affects the reaction rate (Phz -5 MPa). In most cases, the regio- and enantioselectivities are independent of H2 and GO pressure. Deuterioformylation experiments clearly demonstrate the irreversibility of the olefin-insertion step at total pressures of 2-10MPa (D2/G0=I/I). This fact proves that the regio- and enantioselectivity of the present hydroformylation should be controlled by the olefin-insertion step. Herrmann reported the theoretical calculation of the olefin coordination step, explaining selectivity obtained with (i ,A)-BINAPHOS/Rh system for the hydroformylation of styrene. 

As in the previous section, this section deals with two topics (i) high-pressure NMR study on unmodified catalyst system and (ii) high-pressure NMR study on norma/sckctivc or asymmetric hydroformylation. 

Asymmetric hydrocarbalkoxylation of alkenes has been studied since the early 1970s, but the number of papers published on this subject is much less than that of asymmetric hydroformylation. This difference is mainly due to the fact that these reactions catalyzed by palladium complexes with chiral phosphine ligands usually require a very high pressure of carbon... 

ESPHOS (178), a chiral bis(diazaphospholidine) ligand developed by the Wills group, has been found to be active in the asymmetric hydroformylation of vinyl acetate.231 (This ligand system is being commercialized by Stylacats.) Enantioselectivities of 87-89% ee and regioselectivities of 95/5 (b/1) have been obtained at 120 psig pressure of syn gas.232 Unfortunately, the substrate scope is not as broad as BINAPHOS. 

Hydroformylation in SCFs was first studied by Rathke and Klingler from 1991 (114—116), with the first asymmetric examples being reported by Leitner s group in 1998 (117). They noted that enantioselectivity for the hydroformylation of styrene with an in situ catalyst formed from [Rh(CO)2(a-cac)] and 7 ,5 -BINAPHOS [L in Eq. (23) and Scheme 1] was far worse in SCCO2 than in a liquid phase under a lower pressure of CO2 gas ... 

The presence of gaseous (subcritical) CO2 above a solid compound can cause the compound to melt at a temperature 20 or more degrees below its normal melting point. This phenomenon can make it possible to perform solventless reactions at temperatures at which the substrate would normally be solid (132). The method, which requires much less CO2 pressure than supercritical techniques, has been used for nonasymmetric hydrogenations and hydro-formylations (132) and for an asymmetric hydroformylation (101). 

Acetoxypropanal [Asymmetric Hydroformylation of a Vinyl Ester under Homogeneous Conditions]. " A solution of vinyl acetate (532.3 mg, 6.19 mmol), Rh(acac)(CO)2 (4.0 mg, 1.55 X 10 mmol), and (/ ,5 )-BINAPHOS (89) (17.7 mg, 3.34 X 10 mmol) in benzene (10 mL) placed in a Schlenk tube was degassed by freeze-thaw cycles. It was then transferred into a 50 mL autoclave, and the mixture was stirred at 60° for 36 hours under hydrogen and carbon monoxide pressure (1 1 ratio, total 100 atm). H NMR analysis of the reaction mixture showed that the conversion was >99% and the branched and normal aldehydes (2-acetoxypropanal and 3-acetoxypropanal) were formed in 86 14 ratio. The enantiomeric excess of (5)-2-acetoxypropanal (92%) was determined by GC using a chiral capillary column. 

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