New principle for palladacycle resolution: diastereoselective monomer to dimer conversion

Dunina, V. V.; Razmyslova, Elena D.; Gorunova, O. N.; Ливанцов, М. В.; Grishin, Yuri K.

doi:10.1016/j.tetasy.2004.12.019

Cited by 10 publications

(2 citation statements)

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“…Resolving phosphines that contain no organic functional groups is often tedious and, on the laboratory scale, palladium-based reagents are frequently employed. ,, Obvious constraints mean that such protocols are rarely employed on larger batches but the well-documented − poor compatibility of relatively “hard” palladium(II) centers with “soft” 1,1′-diphosphaferrocene donors of the type implicated here allows a straightforward and economical resolution . Otsuka’s naphthyl-1-ethylamine-derived complex 10 ,, is unreactive toward phosphaferrocenes 6 in donor solvents; however, it shows weak coordination in dichloromethane that can be driven to completion by the addition of silver tetrafluoroborate .…”

Section: Introductionmentioning

confidence: 99%

“…9,37,38 Obvious constraints mean that such protocols are rarely employed on larger batches but the well-documented [39][40][41][42][43][44][45] poor compatibility of relatively "hard" palladium(II) centers with "soft" 1,1′-diphosphaferrocene donors of the type implicated here allows a straightforward and economical resolution. 46 Otsuka's naphthyl-1-ethylamine-derived complex 10 37,38,47 is unreactive toward phosphaferrocenes 6 in donor solvents; however, it shows weak coordination in dichloromethane that can be driven to completion by the addition of silver tetrafluoroborate. 48 The product diastereomers, which show an Fe:Pd stoichiometry of 1:2, are quite easily separated by washing with ethylacetate and the less soluble complex 8 was obtained in monocrystalline form, suitable for a diffraction study, through vapor diffusion of pentane into its dichloromethane solution (Figure 2).…”

Section: Introductionmentioning

confidence: 99%

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Concise Synthesis of Enantiopure (S)-(+)-2,2′-Bis(tert-butyldimethylsilyl)-1,1′-diphosphaferrocene: Anion-Dependence of Its Coordination to Palladium(II) Centers

2008

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Concise Synthesis of Enantiopure (S)-(+)-2,2′-Bis(tert-butyldimethylsilyl)-1,1′-diphosphaferrocene: Anion-Dependence of Its Coordination to Palladium(II) Centers

2008

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Asymmetric exchange of cyclopalladated ligands: A new route to optically active phosphapalladacycles

et al. 2006

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An asymmetric version of the cyclopalladated ligand exchange reaction was developed. This procedure involves the use of prochiral phosphines in an aprotic medium. A benzylaminate palladacycle bearing the primary amino group and the bulky Bu t substituent at the C* stereo center serves as a chirality inductor.Key words: asymmetric induction, C-H bond activation, cyclopalladated ligand exchange, optically active phospha and azapalladacycles, X ray diffraction analysis.Although the idea of asymmetric C-H bond activa tion by transition metals is attractive, examples of this process are scarce. In a special case of cyclopalladation, two versions of asymmetric C-H bond activation under control of either external sources of chirality (bases) 1-7 or inner sphere sources are known. Bidentate N,N 8,9 and P,P donor 10,11 ligands were tested as the latter sources. The chirality transfer from chelated ligands proved to be highly efficient in the closure of C*O 9 and C*C palladacycles (see Refs 8, 10, and 11), whereas an attempt to generate planar chirality upon the formation of a CN palladacycle with the use of an optically active monodentate S* donor ligand (sulfoxide) in a metallating agent failed. 12 Chelation of phosphino P ylides giving rise to PC* palladacycles with diastereoselectivity of ~70% de (see Refs 13 and 14) is the only example of the use of CN palladacycles as chirality inductors. However, con figurational lability of such systems substantially limits their use.The aim of the present study was to develop a new method of asymmetric C-H bond activation based on cyclopalladated ligand exchange (CLE ) 15,16 (Scheme 1). Scheme 1Although the starting palladacycle in the CLE reac tion can serve not only as the metallating agent but also as the source of chirality, only achiral versions of this reac tion have been examined. The only attempt to perform asymmetric CLE has been unsuccessful. 17 High efficiency of cyclopalladated complexes in optical resolution 18,19 and enantioselective catalysis, 20-23 as reagents for the enantiomeric purity determination, 24,25 and as matrices for asymmetric synthesis 26-28 was documented. This stimulated the estimation of their potential as chirality inductors in CLE reactions. The preliminary results of our investigations in this field have been published re cently. 29 Results and DiscussionWe chose a series of benzylaminate CN dimers (1a,b and 2a-7a), which differ in the nature of the amino The asymmetric atom directly bound to the metal atom is marked with an asterisk.The more laconic term transcyclometallation has been pro posed 16 for the description of such reactions; however, this term does not reflects the essence of the process, in which ligands rather than metal atoms (transmetallation) are exchanged.The number of the complex corresponds to the superscript n in the code of the starting ligand HL n , and the letters stand for different derivatives of this palladacycle.

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First optically active PC-palladacycle bearing a phosphorus atom in an axially chiral environment

et al. 2009

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Direct aromatic C-H bond activation in the (S a ) BINOL derived phosphite (S a ) HL afforded the dimeric cyclopalladated complex (S a ,S a ) {Pd(η 2 L)(μ Cl)} 2 (2) which is the first optically active PC palladacycle bearing a phosphorus atom in an axially chiral environment. ortho Palladated structure of dimer 2 was confirmed by spectral ( 1 H and 31 P NMR) examina tion of its mononuclear derivatives and by X ray diffraction analysis of the phosphine adduct (η 2 L)PdCl(PPh 3 ) (4). The enantiomeric purity of the starting ligand remained unchanged in the PC palladacycle under the thermal conditions used for the cyclopalladation (∼110°C); this fact was confirmed by the 31 P NMR spectroscopy after chiral derivatization in situ of dimer (S a ,S a ) 2 with the (R C ) valinate chiral auxiliary (Val). trans(N,C) Configuration of the valinate complex (η 2 L)Pd(Val) (5) was established by 1 H NMR and supported by DFT calculations. The chirality transfer in the new PC palladacycle was discussed on the basis of X ray diffrac tion data for the phosphine adduct rac 4 and DFT calculations performed for both phosphine and valinate mononuclear derivatives.Transition metal coordination complexes with mono 1 and bidentate 2 P donor ligands, atropoisomeric or bear ing axially chiral moieties, are widely known as highly effective enantioselective catalysts. In particular, phos phites, 3 phosphoramidites 3e,4 and other P donor ligands 5 derived from commercially available enantiomerically pure diol BINOL 6 or its analogs provide up to 99.9% ee selectivity in the asymmetric catalysis of various transfor mations including palladium catalyzed reactions. 3h,4d,5c,7 Monodentate ligands of the above type often prove more effective than bidentate ones, affording optical yields exceeding 99% ee. 3a,b,d,e,k-m,4a,b,5b,7e A number of processes catalyzed by coordination compounds of iridium and palladium were found 8a,b or supposed 8с to be mediated by the appropriate phosphametallacycles. In particular, for the allylic amination involving phosphoramidite HL´, the cyclometalated derivative of the latter, I formed in situ under catalysis conditions was shown 8a,b to be a true catalyst (Scheme 1). These results may contribute to the explanation of the high enantioselectivity exhibited by monodentate P donor ligands of this type.Despite the high catalytic activity of achiral phosphite palladacycles 9 and the excellent results achieved in asym metric catalysis with the BINOL derived transition metal complexes with monodentate phosphites, 3 cyclopalladated derivaives of such chiral ligands remained unknown until this time. Only recently there have emerged the reports 10 on synthesis and application in catalysis of several РСP Scheme 1 B is base, cod is cycloocta 1,5 diene

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New principle for palladacycle resolution: diastereoselective monomer to dimer conversion

Cited by 10 publications

References 77 publications

Concise Synthesis of Enantiopure (S)-(+)-2,2′-Bis(tert-butyldimethylsilyl)-1,1′-diphosphaferrocene: Anion-Dependence of Its Coordination to Palladium(II) Centers

Concise Synthesis of Enantiopure (S)-(+)-2,2′-Bis(tert-butyldimethylsilyl)-1,1′-diphosphaferrocene: Anion-Dependence of Its Coordination to Palladium(II) Centers

Asymmetric exchange of cyclopalladated ligands: A new route to optically active phosphapalladacycles

First optically active PC-palladacycle bearing a phosphorus atom in an axially chiral environment

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