Highly Enantioselective Hydroformylation of Olefins Catalyzed by Rhodium(I) Complexes of New Chiral Phosphine-Phosphite Ligands

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• 作者：Kyoko Nozaki ; Nozomu Sakai ; Tetsuo Nanno ; Takanori Higashijima ; Satoshi Mano ; Toshihide Horiuchi ; and Hidemasa Takaya
• 刊名：Journal of the American Chemical Society
• 出版年：1997
• 出版时间：May 14, 1997
• 年：1997
• 卷：119
• 期：19
• 页码：4413 - 4423
• 全文大小：490K
• 年卷期：v.119,no.19(May 14, 1997)
• ISSN：1520-5126

文摘

A new chiral phosphine-phosphite ligand,(R)-2-(diphenylphosphino)-1,1'-binaphthalen-2'-yl(S)-1,1'-binaphthalene-2,2'-diyl phosphite[(R,S)-BINAPHOS,(R,S)-2a], was synthesized. Its Rh(I)complex was prepared,and its structure has been characterized by ¹H and³¹P NMR spectroscopy. Using Rh(I) complexes of(R,S)-2a andits enantiomer, highly enantioselective hydroformylation of styrene hasbeen performed (94% ee, iso/normal = 88/12). The catalyst system was also effective for a variety of otherolefins. Some other phosphine-phosphite ligandsbearing 1,1'-binaphthyl and biphenyl backbones, such as(S)-3,3'-dichloro-6-(diphenylphosphino)-2,2',4,4'-tetramethylbiphenyl-6'-yl (R)-1,1'-binaphthalene-2,2'-diyl phosphite[(S,R)-BIPHEMPHOS, (S,R)-5a],(R,R)-2a, (R,S)-2b,(R)-2c, and (R)-5b, were tested forasymmetric hydroformylation. The results indicate that the senseof enantiofaceselection for the prochiral olefins is mainly determined by theabsolute configuration of the phosphine site, forexample, the(R)-2-(diphenylphosphino)-1,1'-binaphthalen-2'-yl group in(R,S)-2a. The relative configurationsofthe two biaryl groups in the phosphine-phosphites play crucial rolesin the degree of the enantioselectivities, thatis, the (R*,S*)-isomer generally gives products in highee's and the (R*,R*)-isomer does in low ee's.Treatment ofRh(acac)[(R,S)-2a] with a 1:1 mixtureof carbon monoxide and hydrogen gave a hydridorhodium complex,RhH(CO)₂[(R,S)-2a], as a singlespecies. Trigonal bipyramidal structure is suggested for thiscomplex, in which thehydride and the phosphite moiety are located at the apical positionsand the phosphine and the two carbonyls occupythe equatorial positions. The interchange of the phosphine and thephosphite sites with each other through rapidpseudorotations has not been observed inRhH(CO)₂[(R,S)-2a].The structural deviations of the monohydridecomplexes from an ideal trigonal bipyramid seem to be larger in(R*,R*)-isomers than in the corresponding(R*,S*)-isomers. The existence of only one active species involved in theRh(I)-(R,S)-2a-catalyzed hydroformylationhasbeen manifested by the plot ofln([R]/[S]) of the hydroformylationproduct vs the reciprocals of the reactiontemperatures. The higher thermodynamic stability ofRh(acac)[(R,S)-2a] than itsdiastereomerRh(acac)[(R,R)-2a]is demonstrated in relation to the restricted configuration of(R)-2c to (R,S)-2c in itscomplex formation with Rh(I).