V. I. Sokolov

Asymmetric cyclopalladation of dimethylaminomethylferrocene

Abstract Palladation of dimethylaminomethylferrocene (I) catalyzed by salts of optically active acids affords optically active planar chiral 2-dimethylaminomethylferrocenylpalladium chloride dimer (II) in high yield. Absolute rotation and optical purity of II were determined by conversion to 2-methylferrocenecarboxylic acid and 2-methylferrocenealdehyde. Factors affecting enantiomeric excess are examined and conditions for maximal asymmetric induction are found.

Reaction of the low-valent transition metal complexes with non-transition organometallic compounds☆

Abstract The zero-valent triphenylphosphine complexes of palladium and platinum were found to react readily under mild conditions with organomercurials RHgX and R2Hg. Final products appear to be σ-bonded organic derivatives of Pd and Pt. In several cazses, the relatively stable intermediates with platinum to mercury bond were isolated. Dibenzylideneacetone-palladium (0) and -platinum(0) complexes exhibits similar reactivity towards organomercurials.

Asymmetric cyclopalladation in the ferrocene series as a tool for enantioselective synthesis. Preparation of some analogues of natural products

Abstract The previously described asymmetric cyclopalladation has been applied to the esters of 7-dimethylamino-7-ferrocenylenanthic acid, I, to afford the optically active palladium derivative, II. The absolute configuration of the chiral plane is determined by the configuration of the inductor: the acylamino acid salt. The palladium atom in II was then substituted by a σ-ketovinyl group using the reaction with pentyl vinyl ketone, to yield III. The latter substance undergoes full reduction when treated with Et 3 SiH + CF 3 COOH (the ionic hydrogenation reaction) resulting in the optically active prostanoic acid analogue, IV. On the other hand, III in the form of the methiodide is reduced by NaBH 4 with the elimination of the amine group and the and the formation of allyl alcohol V. This kind of side chain is characteristic of many prostaglandins. Bromination of II followed by the repeated cyclopalladation opens the way to trisubstitute derivatives. The pathway outlined provides a rapid synthesis of optically active compounds which are the ferrocene analogues of natural prostaglandins.

Enantioselectivity in Enzyme-Catalyzed Electron Transfer to and from Planar Chiral Organometallic Compounds

Asymmetric cyclopalladation of dimethylaminomethylferrocene in the presence of N-acetyl-(R)- or (S)- leucine afforded enantiomerically en- riched palladacycles (S)- and (R)- (Pd{C5H3(CH2NMe2)FeC5H5}(m-Cl))2, respectively. Carbonylation of each enantiomer followed by iodomethyla- tion and reduction by sodium amalgam gave (S)- and (R)-2-methylferrocene carboxylic acid (1) with an optical purity of 80 and 93 %, respectively. (S)- and (R)-1 readily undergo one-electron (1e) oxidation to form the corresponding ferricenium cations by hydrogen perox- ide, catalyzed by horseradish peroxidase (HRP) and chloroperoxidase (CLP) from Caldariomyces fumago (258C, pH 5 - 8 and 2.75, respectively). In the case of HRP, the reaction is strictly first- order with respect to (S)- and (R)-1 (ratea k(HRP)(1)), whereas Michae- lis - Menten kinetics are observed for CLP. The strongly pH-dependent kinetic enantioselectivity is, however, only ob- served in the case of HRP. HRP-gener- ated cations (S)-1 a and (R)-1 a have been used to demonstrate that their enzymat- ic reduction by reduced glucose oxidase (GO) is also enantioselective; the (S)-1 a enantiomer is more reactive than (R)-1 a by a factor of 1.54. The existence of the planar chiral enantioselectivity in the GO catalysis was also confirmed by the cyclic voltammetry study of (S)-1 and (R)-1 in the presence of GO and b-d- glucose with glassy carbon and pyrolytic graphite electrodes. The corresponding enantioselectivity factors k(S)-1 a /k(R)- 1 a are 1.7 and 1.6, respectively. Based on the known X-ray structural data for the active site of GO, it has been tentatively suggested that the enantioselectivity originates from the hydrophobic contact between the enzyme tyr-68 residue and the h 5 -C5H5 ring of 1 a , and a hydrogen bond network formed by his-516 and/or his-559 residues and the carboxylic group of the ferrocene derivative. The findings reported confirm the existence of enantioselective electron transfer be- tween oxidoreductases and organome- tallic compounds with a planar chirality. The lack of kinetic enantioselectivity may be a result of i) the incorrect rate- limiting step, ii) unfavorable pH region, and iii) the deficit of charged groups attached to ferrocenes.

Alternative synthesis of enantiomeric 1-diphenylphosphino-2-dimethylaminomethylferrocene (Kumada's ligand)

Abstract A novel facile synthesis of enantiomeric 1-diphenylphosphino-2-dimethylaminomethylferrocene (III), an important ligand for asymmetric catalysis using metal complexes, has been developed. This substance is prepared in a two-step procedure starting with dimethylaminomethylferrocene (I), in 40% overall yield. The absolute configuration and maximum optical rotation of III are determined through the correlation with the previously described cyclopalladated amine derived from I.

Asymmetric induction in the course of internal palladation of enantiomeric 1-dimethylaminoethylferrocene

Abstract The internal palladation of optically active 1-dimethylaminoethylferrocene proceeds with stereoselectivity 85/15, that is less stereoselective than the asymmetrically induced lithiation of this amine, the sense of diastereomeric preference being the same.

The 13C NMR spectra and structure of ferrocenylcarbenium ions

Abstract The 13 C NMR spectra ofthe series of α,α’ -dideuterated ferrocenylcarbenium ions and their precursors, ferrocenylcarbinols as well as other ferrocene derivatives have been measured. The structures of ferrocenylcarbenium ions is discussed.

Stereochemistry of redox-demercuration of an optically active 8-(α-bromomercuriethyl)quinoline with zerovalent palladium complexes

Abstract A novel organomercurial bearing the metal atom at a chiral centre, 8-(α-bromomercuriethyl)quinoline (I) has been synthesized from the respective bromide and metallic mercury, and resolved via diastereomeric D-camphor sulphonates. Enantiomeric I has been treated with (Ph 3 P) 4 Pd 0 and (dba) 3 Pd 2 0 to give optically active chelate metallocycles II and III which had been previously known in racemic form. In both reactions, (-)I leads to (+)organopalladiums. The optical activity proves the heterolytic reaction mechanism.

New Method to Prepare Nanopalladium Clusters Immobilized on Carbon Nanotubes: A Very Efficient Catalyst for Forming Carbon-Carbon Bonds and Hydrogenation

Preparation of the catalyst has been performed using the direct reaction between the multi-walled carbon nanotubes and zerovalent palladium complex with the easily removed ligand, dibenzylideneacetone, dba. TEM microphotos have been obtained and metal particles dimension measured. Coupling reactions of Suzuki-Miyaura, Heck and Sonogashira are efficiently catalyzed by this catalyst as well as hydrogenation of the triple carbon-carbon bond. The catalyst is re-usable and can work in aqueous media.

A new heterobimetallic palladium–[60]fullerene complex with bidentate bis-1,1′-[P]2-ferrocene ligand

Abstract A new heterobimetallic palladium–[60]fullerene complex with ferrocene bis-phosphine ligand was prepared using alternative paths: either via addition reaction of Pd 2 (dba) 3 ·C 6 H 6 (dba=dibenzylidenacetone) in the presence of 1,1′-bis(diphenylphosphino)ferrocene ( dppf ) to C 60 , or via electrochemical activation of C 60 to generate C 60 2− anions, which then react with PdCl 2 and dppf to yield the target complex. The obtained (η 2 -C 60 )Pd( dppf ) complex was characterized by 1 H- and 31 P-{ 1 H}-NMR and electronic spectroscopy as well as electrochemically.