Synthesis of new titanatranes containing organic substituents in the atrane fragment

Titanatrane CpTi(OCH(CH₃)CH₂)₃N (3) was prepared by the reaction of CpTiCl₃ with N(CH₂CH(CH₃)OH)₃ in the presence of triethylamine. The reaction of CpTi(OMe)₃ (8) with N(CH₂CH₂OH)₂(CH₂CHPhOH), erythro-N(CH₂CH₂OH)₂(CHPhCHPhOH), and N(CH₂CH₂OH)₂(CH₂CPh₂OH) gave cyclopentadienyltitanatranes 12–14. Compound 8 reacts with threo-N(CH₂CH₂OH)₂(CHPhCHPhOH) to give a mixture of threo-CpTi(OCH₂CH₂)₂(OCHPhCHPh)N and threo-MeOTi(OCH₂CH₂)₂(OCHPhCHPh)N. Slow hydrolysis of the latter product gave threo-[Ti₃O(OMe){(OCH₂CH₂)₂₋ (OCHPhCHPh)N} ₃]₂, which was studied by X-ray diffraction analysis. The crystal structures of 3 and 12 were also determined by X-ray diffraction analysis. The titanium coordination polyhedron in these complexes is a distorted trigonal bipyramid in which the equatorial positions are occupied by three oxygen atoms and the axial positions contain the N atom and the Cp group. The titanium—nitrogen distances (2.313(2), 2.291(2) Å in two independent molecules of 3 and 2.271(2) Å in compound 12) confirm the presence of Ti←N transannular interaction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2736–2744, December, 2005.     

Search for tetrylene structures that can exhibit catalytic activity: a quantum chemical approach

We present the results of a quantum chemical study of a series of tetrylenes (silylenes, germylenes, and stannylenes), aimed at identifying structural and electronic factors affecting the width of the HOMO—LUMO energy gap. Compounds considered in this work contain atoms of Group 14 elements in both di- and tricoordinate states due to additional transannular interaction. They bear substituents bonded to the atom of the Group 14 element through atoms with and without lone electron pairs. It was found that tetrylenes stabilized by both additional transannular interaction and direct bonds between the atom of the Group 14 element and the heteroatom containing a lone electron pair (in this situation the ligand acts as n-donor) are characterized by wide HOMO—LUMO energy gaps, the gap in stannylenes always being narrower than in the related silylenes and germylenes. Localization of the HOMO and LUMO in certain tetrylenes is analyzed.

     

Reactivity of the Lithium Salt of 4H-Cyclopenta[2,1-b:3,4-b']dithiophene

The regioselectivity in reactions of the lithium salt of 4H-cyclopenta[2,1-b:3,4-b']dithiophene with various electrophilic agents [SiMe₃Cl, SnMe₃Cl, D₂O, Re(CO)₅Br] is discussed in terms of the charge and orbital control concepts.     

Green chemistry of polyurethanes: The catalytic <Emphasis Type="Italic">n</Emphasis>-butylaminolysis of ethylene carbonate as a model chain-growth reaction in the formation of nonisocyanate polyurethanes

The kinetic regularities and the mechanism of the catalytic action of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, which is the most active of the known catalysts for the formation of hydroxyurethanes from cyclocarbonates and amines, were studied using the example of the n-butylaminolysis of ethylene carbonate. In contrast with the noncatalytic reaction, which proceeds via two parallel pathways that involve one and two molecules of amine, the catalytic reaction follows a single pathway: the second molecule of amine is replaced by a molecule of the catalyst that accelerates the process in accordance with the mechanism of bifunctional catalysis. Different reaction pathways were studied by quantum chemical calculations based on the density functional method. It was shown that the high activity of 1,5,7-triazabicyclo[4.4.0]dec-5-ene results from the formation of a planar cation-like form of the catalyst. Moreover, the low-energy transition between the cation and the initial 1,5,7-triazabicyclo[4.4.0]dec-5-ene enables the catalyst to simultaneously be a good donor and acceptor of protons. This study presents a new way for finding among bifunctional organic compounds the catalysts that are even more active in the reaction of cyclocarbonates with amines.     

Synthesis and structures of new 1,3,6,2-dioxazaborocanes containing substituents in the ocane fragment

New 1,3,6,2-dioxazaborocanes R¹N(CHR³CR⁴R²O)(CHR⁶CHR⁵O)BX (1–11, X = Ph, 4-MeC₆H₄, Me; R¹ = Me, PhCH₂; R², R³, R⁴, R⁵, R⁶ = H, Ph) were synthesized by the reactions of aryl- or methylboronic acids with dialkanolamines. The treatment of (Me₂NCH₂CH₂O)₃B (15) with MeN(CH₂CH₂OH)(CH₂CPh₂OH) afforded 2-[2-(dime-thylamino)ethoxy]-1,3,6,2-dioxazaborocane (12). 2-Fluoro-1,3,6,2-dioxazaborocanes R¹N(CHR³CHR²O)(CH₂CH₂O)BF (13: R¹ = PhCH₂, R² = R³ = H; 14: R¹ = Me, R² = R³ = Ph, threo) were synthesized by the reaction of bis(trimethylsilyl) ethers of the corresponding dialkanolamines with BF₃·Et₂O. The new borocanes can be used for the synthesis of the corre-sponding germanium derivatives PhCH₂N(CH₂CH₂O)₂GeX₂ (16, X = OEt; 17, X = Cl), as exemplified by the reaction of compound 6. The structures of erythro-MeN(CH₂CH₂O)(CHPhCHPhO)BPh (3), threo-MeN(CH₂CH₂O)(CHPhCHPhO)BPh (4), erythro-MeN(CH₂CH₂O)(CHPhCHPhO)B(4-MeC₆H₄) (8), and PhCH₂N(CH₂CH₂O)₂BF (13) were established by X-ray diffraction. The coordination polyhedra of the boron atoms in these complexes can be described as distorted tetrahedra. The boron-nitrogen distances (1.705(7)–1.723(3) Å) provide unambiguous evidence for the presence of the B←N transannular interaction in these compounds. The structures of the resulting borocanes containing phenyl substituents at the carbon atoms of the ocane skeleton were studied by NMR spectroscopy and quantum chemical density functional theory calculations.     

Density functional study on the bromination of heteroelement-substituted acetylenes

The reactions of heteroelement-containing alkynes H₃SiC≡CH and R₃MC≡CPh [R₃M = H₃Si, Et₃Si, Et₃Ge, (MeO)₃Si, (EtO)₃Ge, N(CH₂CH₂O)₃Si, N(CH₂CH₂O)₃Ge, Bu₃Sn] with one and two bromine molecules were studied in terms of the density functional theory. Transition states along reaction channels leading to products of both addition at the triple bond (cis- and trans-dibromoalkenes and 1,1-dibromoalkenes) and cleavage of the M-C≡ bond were localized.     

A monopole mass filter with a hyperbolic V-shaped electrode

In this article we compare the classical monopole mass filter of von Zahn and the monopole mass filter with a hyperbolic V-shaped electrode. The experimental results and those of computer simulation for both mass spectrometers are presented. We show that the replacement of a conventional 90 degrees V-shaped electrode by an electrode with a hyperbolic profile substantially improves the peak shape of any given mass, and increases the mass resolution by a factor of 3-4 and the abundance sensitivity by a factor of 100. The potential of high analytical performance combined with electroforming techniques for electrode manufacture indicate future practical uses of such instruments. Copyright 1999 John Wiley & Sons, Ltd.     

Comparative Reactivity of Cyclocarbonate Groups of Oligomeric Triglycerides Based on Soybean Oil and Model Compounds in the Reactions of Nonisocyanate Urethane Formation

A comparative study of kinetic patterns has been carried out for the reaction of cyclocarbonate groups of oligomers and model compounds with n-butylamine in dimethylsulfoxide. The objects of study were ethylene carbonate, monofunctional 4-(2-ethylhexyloxymethyl) cyclocarbonate, trifunctional tricyclocarbonate of polyoxypropylene triol, and an oligomer based on soybean oil triglycerides with an average functionality of ~4.5. The most active compound is ethylene carbonate, whereas cyclocarbonate groups of the oligomer based on soybean oil triglycerides exhibit the lowest reactivity. All the reactions studied proceed via two parallel reaction pathways involving one and two amine molecules, respectively, and the second pathway contributes more to the observed rate of urethane formation. The dependence of the activation energy of aminolysis on the inductive effect of substituents in the model 4,5-substituted 1,3-dioxolane-2-ones has been established by DFT quantum chemical calculations.