Kirill Nikitin

Molecular Dials: Hindered Rotations in Mono- and Diferrocenyl Anthracenes and Triptycenes

The syntheses, X-ray crystal structures, and molecular dynamics of 9-ferrocenylanthracene, 3, 9,10-diferrocenylanthracene, 4, 9-ferrocenyltriptycene, 7, and 9,10-diferrocenyltriptycene, 8, are reported. At 193 K, 3 exhibits C(s) symmetry via oscillation of the ferrocenyl only about the anthracene plane; at higher temperatures, complete rotation about the C(9)-ferrocenyl linkage becomes evident with a barrier of 10.6 kcal mol(-1). At 193 K, the ferrocenyls in 4 give rise to syn (C(2v)) and anti (C(2h)) rotamers that also interconvert at room temperature. In the corresponding triptycyl systems, 7 and 8, these rotational barriers increase to 17 kcal mol(-1); 9,10-diferrocenyltriptycene exists as slowly interconverting meso and racemic rotamers, in which the ferrocenyl moieties are, respectively, eclipsed (C(2v)) or staggered (C2). 2D-EXSY NMR data recorded with different mixing times indicate clearly that these interconversions proceed in a stepwise manner, for example, rac→meso→rac, thus behaving as a set of molecular dials.

Palladium-catalyzed carbonylation of aryl iodides in aqueous media

Abstract Carbonylation of ArI in aqueous media under 1 atm CO in the presence of phosphineless palladium complexes and some base leads to aromatic acids.

Turning Regioselectivity into Stereoselectivity: Efficient Dual Resolution of P‐Stereogenic Phosphine Oxides through Bifurcation of the Reaction Pathway of a Common Intermediate

Synthetic routes that provide facile access to either enantiomeric form of a target compound are particularly valuable. The crystallization-free dual resolution of phosphine oxides that gives highly enantioenriched materials (up to 94 % ee) in excellent yields is reported. Both enantiomeric oxides have been prepared from a single intermediate, (RP )-alkoxyphosphonium chloride, which is formed in the course of a selective dynamic kinetic resolution using a single enantiomer of menthol as the chiral auxiliary. The origin of the dual stereoselectivity lies in bifurcation of the reaction pathway of this intermediate, which works as a stereochemical railroad switch. Under controlled conditions, Arbuzov-type collapse of this intermediate proceeds through CO bond fission with retention of the configuration at the phosphorus center. Conversely, alkaline hydrolysis of the PO bond leads to the opposite SP  enantiomer.

Restricted rotation in 9-phenyl-anthracenes: a prediction fulfilled.

The calculated phenyl rotation barrier in 9-phenylanthracene has been reported as ~21 kcal mol(-1), but experimental verification of this barrier is limited by its intrinsic symmetry. V-T NMR indicated the barrier to interconversion of the syn (C(2v)) and anti (C(2h)) rotamers of 9,10-bis(3-fluorophenyl)anthracene to be ~21 kcal mol(-1). Likewise, the V-T NMR spectra of 9-(1-naphthyl)-10-phenylanthracene reveal that the rotational barrier of the unsubstituted phenyl ring is at least 21 kcal mol(-1).

A NEW ARGUMENT IN FAVOR OF THE ETHER ELIMINATION MECHANISM : FORMATION OF ACETALS ON ACTION OF MOLYBDENUM ALKOXIDES ON CARBONYL COMPOUNDS

Abstract Molybdenum oxomethoxide and ethoxide are found to react very rapidly with aldehydes and ketones in both alcohol and hydrocarbon media transforming the latter into acetals and ketals respectively. The colloid solution of the molybdenum blue usually formulated as “MoO2.88·H2O” appears to be the major inorganic product of this reaction. The reaction mechanism includes presumably formation of a semiacetal molybdate and its subsequent decomposition with elimination of acetal. Different reaction pathways of metal alkoxides interaction with aldehydes and ketones are discussed.

Synthesis of 5-methoxylated 3-pyrrolin-2-ones via the rearrangement of chlorinated pyrrolidin-2-ones

The reaction of N-substituted 4-methyl-2-pyrrolidinones or 4-diethoxyphosphoryl analogues, carrying at least two chlorine atoms between the C(3) and C(6) carbons, with alkaline methoxide in methanol afforded the corresponding 5-methoxylated 3-pyrrolin-2-ones, useful adducts for the preparation of agrochemicals or medicinal compounds.

Direct evidence of a multicentre halogen bond: unexpected contraction of the P–XXX–P fragment in triphenylphosphine dihalides

Triphenylhalophosphonium halides, Ph(3)PX(2), form crystals comprising bridged linear cations [Ph(3)P-X-X-X-PPh(3)](+) where the X(3) bridge is shortened from 6.56 Å in Cl-Cl-Cl to 6.37 Å in the Br-Br-Br system. It is proposed that this structure is stabilised by five-centre/six-electron (5c-6e) hypervalent interactions.

Joining the rings: the preparation of 2- and 3-indenyl-triptycenes, and curious related processes.

The indenyltriptycenes, and , where the 3- or 2-indenyl, respectively, is attached at the 9-position of the triptycene, are attractive prototypes of molecular gearing systems that can also incorporate a brake. These molecules have been prepared from their respective indenylanthracenes, and , by the [4 + 2] cycloaddition of benzyne to the anthracene fragment, and the rotational barriers about the indenyl-triptycenyl single bonds in (12 kcal mol(-1)) and (<9 kcal mol(-1)) have been measured. The precursor anthracenes, and , were prepared by using palladium-catalysed coupling reactions. Unexpectedly, the Heck-type reaction of 9-bromoanthracene, , with indene leads to the formation of 3-indenylanthracene ; moreover, this process is accompanied by a novel palladium-catalysed carbocyclisation reaction leading to the indenophenanthrylene . The addition of benzyne to 9-(3-indenyl)anthracene, , yields the corresponding indenyltriptycene, , and, surprisingly, the anthracenyl methano-bridged phenanthrene . It has been demonstrated that 2-arylindenes can act as 1,3-dienes in the [4 + 2] cycloadditions of benzyne. The products , , and have been characterised by X-ray crystallography.

Nanostructures from nanoparticles

This paper reviews recent experimental approaches to the development of surface nanostructures from nanoparticles. The formation of nanowires by electron beam writing in films of gold nanoparticles passivated with a specially designed class of ligand molecules (dialkyl sulfides) is presented, together with illustrations of practical nanostructures. Potential applications of this methodology are discussed. Another alternative to the controlled fabrication of arrays of nanoparticles, based on nanocrystals which contain molecular recognition elements in the ligand shell, is also surveyed. These particles aggregate in the presence of specifically designed molecular dications which act as a molecular binder. Finally, recent work on the formation of nanoscale surface architectures using x-ray patterning of self-assembled monolayers is introduced. Current and potential future applications of these surface nanostructures are discussed.

Hammond Postulate Mirroring Enables Enantiomeric Enrichment of Phosphorus Compounds via Two Thermodynamically Interconnected Sequential Stereoselective Processes.

The dynamic resolution of tertiary phosphines and phosphine oxides was monitored by NMR spectroscopy. It was found that the stereoselectivity is set during the formation of the diastereomeric alkoxyphosphonium salts (DAPS), such that their initial diastereomeric excess (de) limits the final enantiomeric excess (ee) of any phosphorus products derived from them. However, (31)P NMR monitoring of the spontaneous thermal decomposition of the DAPS shows consistent diastereomeric self-enrichment, indicating a higher rate constant for decomposition of the minor diastereomer. This crucial observation was confirmed by reductive trapping of the unreacted enriched DAPS with lithium tri-sec-butylborohydride (commercially distributed as L-Selectride reagent) at different time intervals after the start of reaction, which gives progressively higher ee of the phosphine product with time. It is proposed that the Hammond postulate operates for both formation and decomposition of DAPS intermediate so that the lower rate of formation and faster subsequent collapse of the minor isomer are thermodynamically linked. This kinetic enhancement of kinetic resolution furnishes up to 97% ee product.