Speciation and mechanistic studies of chiral copper(I) Schiff base precursors mediating asymmetric carbenoid insertion reactions of diazoacetates into the Si-H bond of silanes

被引:74
作者
Dakin, LA
Ong, PC
Panek, JS
Staples, RJ
Stavropoulos, P
机构
[1] Boston Univ, Dept Chem, Boston, MA 02215 USA
[2] Harvard Univ, Dept Chem & Biol Chem, Cambridge, MA 02138 USA
关键词
D O I
10.1021/om0003786
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
[Cu(CH3CN)(4)](PF6) and the chiral C-2-symmetric diimine ligand (1R,2R)-bis((2,6-dichlorobenzylidene)diamino)cyclohexane (R,R-1) (1.2 equiv) mediate asymmetric carbenoid insertion of aryl diazoesters into the Si-H bond of silanes in good to high yields and levels of enantiocontrol. Dichloromethane solutions of [Cu(CH3CN)4](PF6)/R,R-1 afford yellow crystals of [Cu-I(R,R-1)(CH3CN).Cu-I(R,R-1)(CH3CN)(2).Cu-2(I)(R,R-1)(3)](PF6)(4).2CH(2)Cl(2).3Et(2)O, which feature three distinct copper complexes in the crystal lattice. H-1 NMR and electrospray ionization MS (ESI-MS) studies establish that only [Cu-I(R,R-1)(CH3CN)](+) is present in solution in high yields. Upon addition of stoichiometric PhC(N-2)CO2Me, cations [Cu-I(R,R-1)(C(CO2Me)Ph)](+) and [Cu-I(R,R-1)(C(CO2Me)Ph)(CH3CN)](+) are detected by ESI-MS, consistent with the presence of a copper-carbenoid moiety. The catalytically active precursor is most likely a mononuclear unit of the type [Cu-I(R,R-1)(CH3CN)](+), as suggested by the linearity of plots relating the enantiomeric excess tee) of product to that of the ligand (Kagan's analysis). Hammett plots correlate enhanced catalytic reactivities with stabilization of a sizable positive charge on the carbenoid carbon and a smaller positive charge on the silicon atom, but the corresponding enantioselectivities are insensitive to these electronic properties. The kinetic isotope effect for carbenoid insertion into PhMe2Si-H(D) varies from 2.12 (-40 degrees C) to 1.08 (25 degrees C), in agreement with other small KIE values observed for processes in which Si-H activation is involved in the turnover-limiting step. A linear Eyring plot of In(k(major enantiomer)/k(minor enantiomer)) over a range of 80 K supports the notion of a single step controlling the levels of enantioselection. No H/D scrambling is observed in competitive carbenoid insertions into PhMe2Si-D/Ph2MeSi-H, indicating that the insertion reaction takes place in a concerted fashion. These results are discussed in Light of an early transition state, characterized by hydrogen-first penetration of the Si-H bond into the copper-carbenoid cavity, which is assumed to impart high levels of enantioselectivity due to intrinsic preorganization under the influence of the specific ligand and aryl diazoesters employed.
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页码:2896 / 2908
页数:13
相关论文
共 123 条
[1]   RHODIUM ACETATE CATALYZES THE ADDITION OF CARBENOIDS ALPHA-OXYGENS TO ETHER OXYGENS [J].
ADAMS, J ;
POUPART, MA ;
GRENIER, L ;
SCHALLER, C ;
OUIMET, N ;
FRENETTE, R .
TETRAHEDRON LETTERS, 1989, 30 (14) :1749-1752
[2]  
AMBRAMOVITCH RA, 1965, J CHEM SOC CHEM COMM, P542
[3]   SYNTHESIS OF ALPHA-(ALKOXYSILYL)ACETIC ESTERS - A ROUTE TO 1,2-DIOLS [J].
ANDREY, O ;
LANDAIS, Y ;
PLANCHENAULT, D ;
WEBER, V .
TETRAHEDRON, 1995, 51 (44) :12083-12096
[4]   TRANSITION-STATE STRUCTURE AND THE TEMPERATURE-DEPENDENCE OF THE KINETIC ISOTOPE EFFECT [J].
ANHEDE, B ;
BERGMAN, NA .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1984, 106 (24) :7634-7636
[5]  
APELOIG Y, 1993, ISR J CHEM, V33, P387
[6]   SELECTIVE INTERMOLECULAR CARBON-HYDROGEN BOND ACTIVATION BY SYNTHETIC METAL-COMPLEXES IN HOMOGENEOUS SOLUTION [J].
ARNDTSEN, BA ;
BERGMAN, RG ;
MOBLEY, TA ;
PETERSON, TH .
ACCOUNTS OF CHEMICAL RESEARCH, 1995, 28 (03) :154-162
[7]   CHEMISTRY OF BIVALENT CARBON INTERMEDIATES .6. PHOTOLYSIS OF 2-BUTYLPHENYLDIAZOMETHANE [J].
BAER, TA ;
GUTSCHE, CD .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1971, 93 (20) :5180-&
[8]   A NEW AND GENERAL-SYNTHESIS OF ALPHA-SILYL CARBONYL-COMPOUNDS BY SI-H INSERTION FROM TRANSITION-METAL CATALYZED-REACTIONS OF DIAZO ESTERS AND DIAZO KETONES [J].
BAGHERI, V ;
DOYLE, MP ;
TAUNTON, J ;
CLAXTON, EE .
JOURNAL OF ORGANIC CHEMISTRY, 1988, 53 (26) :6158-6160
[9]   THE EFFECT OF SUBSTITUTIONS ON THE BASICITY OF PHOSPHORUS LIGANDS IN R3P-NI(CO)3 COMPLEXES [J].
BARTIK, T ;
HIMMLER, T ;
SCHULTE, HG ;
SEEVOGEL, K .
JOURNAL OF ORGANOMETALLIC CHEMISTRY, 1984, 272 (01) :29-41
[10]  
BELL RP, 1981, TUNNEL EFFECT CHEM