There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Efficient and reliable amplification of chirality has borne its greatest fruit with transition metal-catalyzed reactions since enantiocontrol may often be imposed by replacing an achiral or chiral racemic ligand with one that is chiral and scalemic While the most thoroughly developed enantioselective transition metal-catalyzed reactions are those involving transfer of oxygen (epoxidation and dihydroxylation)1,2 and molecular hydrogen,3 the focus of this review is on the area of enantioselective transition metal-catalyzed allylic alkylations which may involve C-C as well as C-X (X ) H or heteroatom) bond formation4-9 The synthetic utility of transitionmetal-catalyzed allylic alkylations has been soundly demonstrated since its introduction nearly three decades ago10-21 In contrast to processes where the allyl moiety acts as the nucleophilic partner, we will limit our discussion to processes which result in nucleophilic displacements on allylic substrates (eq 1) Such reactions have been recorded with a broad

http://web4.uwindsor.ca/users/j/jlichaa/reference.nsf/0/10ff8b04ff3a317885256d88005720f6/$FILE/cr-1996-96-395-allylpd-asym.pdf

Asymmetric Transition Metal-Catalyzed Allylic Alkylations.

The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies.1,2 Among all asymmetric catalytic methods, asymmetric hydrogenation utilizing molecular hydrogen to reduce prochiral olefins, ketones, and imines, have become one of the most efficient methods for constructing chiral compounds.3 The development of homogeneous asymmetric hydrogenation was initiated by Knowles4a and Horner4b in the late 1960s, after the discovery of Wilkinson’s homogeneous hydrogenation catalyst [RhCl(PPh3)3]. By replacing triphenylphosphine of the Wilkinson’s catalystwithresolvedchiralmonophosphines,6Knowles and Horner reported the earliest examples of enantioselective hydrogenation, albeit with poor enantioselectivity. Further exploration by Knowles with an improved monophosphine CAMP provided 88% ee in hydrogenation of dehydroamino acids.7 Later, two breakthroughs were made in asymmetric hydrogenation by Kagan and Knowles, respectively. Kagan reported the first bisphosphine ligand, DIOP, for Rhcatalyzed asymmetric hydrogenation.8 The successful application of DIOP resulted in several significant directions for ligand design in asymmetric hydrogenation. Chelating bisphosphorus ligands could lead to superior enantioselectivity compared to monodentate phosphines. Additionally, P-chiral phosphorus ligands were not necessary for achieving high enantioselectivity, and ligands with backbone chirality could also provide excellent ee’s in asymmetric hydrogenation. Furthermore, C2 symmetry was an important structural feature for developing new efficient chiral ligands. Kagan’s seminal work immediately led to the rapid development of chiral bisphosphorus ligands. Knowles made his significant discovery of a C2-symmetric chelating bisphosphine ligand, DIPAMP.9 Due to its high catalytic efficiency in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids, DIPAMP was quickly employed in the industrial production of L-DOPA.10 The success of practical synthesis of L-DOPA via asymmetric hydrogenation constituted a milestone work and for this work Knowles was awarded the Nobel Prize in 2001.3k This work has enlightened chemists to realize * Corresponding author. 3029 Chem. Rev. 2003, 103, 3029−3069

New Chiral Phosphorus Ligands for Enantioselective Hydrogenation

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The Golden Age of Transfer Hydrogenation

The synthesis and properties of palladium(II) and platinum(II) complexes with quadridentate Schiff bases derived from the condensation of salicylaldehyde and (R)-1,2-diamines are described. The ligand conformation of the platinum(II) complexes is discussed on the basis of the circular dichroism and the 1H n.m.r. spectra. The anomalous patterns of the circular dichroism spectra of palladium(II) derivatives are also reported.

Optically active complexes of Schiff bases. Part 6. Palladium(II) and platinum(II) complexes with quadridentate Schiff bases of salicylaldehyde

A facile synthesis of complexes of the type Ru(η5-C5H5)L2H (L2 = chelating phosphine)

The catalytic asymmetric hydrogenation of prochiral ketones was carried out with Ru(II) complexes prepared from new chiral diphosphine ligands, cis-(R,R)-2,5-bis[(diarylphosphino)]-3-hexenes. These new ligands were prepared from enantiomerically pure (R,R) or (S,S)-(Z)-3-hexene-2,5 diol and enantiomeric excesses up to 85% were obtained in the reduction of 2-benzamidomethyl-3-oxobutanoate, starting material for the synthesis of 4-acetoxy-2-azetidinone.

Chiral 1,4-bis-diphosphine ligands from optically active (Z)-olefines

https://air.unimi.it/bitstream/2434/288769/2/c5cc02170g.pdf

VCD spectroscopy as an excellent probe of chiral metal complexes containing a carbon monoxide vibrational chromophore

A complex of the type [Pd(η3-CH2CMeCH2)(P–P′)]+[where P–P′= the chiral chelating ligand (S-)–(N-diphenylphosphino)(2-diphenylphosphinoxymethyl) pyrrolidine, not having C2v symmetry] has been prepared and its 1H, 13C, 31P, and two-dimensional H–X (X =13C or 31P) correlation spectra recorded. On the basis of n.m.r. data the absolute configurations in solution of the major and minor diastereoisomers have been assigned. Proton and 13C n.m.r. data have been discussed in terms of trans influence of the chelating ligand P–P′. Correlations between the n.m.r. parameters of the intermediate η3-allyl diastereoisomers, donor properties of the ligand, and regiochemistry of nucleophilic addition to the allyl termini have been proposed.

Edoardo Cesarotti

Papers

Optically active complexes of Schiff bases. Part 6. Palladium(II) and platinum(II) complexes with quadridentate Schiff bases of salicylaldehyde

A facile synthesis of complexes of the type Ru(η5-C5H5)L2H (L2 = chelating phosphine)

Chiral 1,4-bis-diphosphine ligands from optically active (Z)-olefines

VCD spectroscopy as an excellent probe of chiral metal complexes containing a carbon monoxide vibrational chromophore

Synthesis and stereochemical studies of η3-allyl palladium(II) complexes containing a chiral chelating ligand