1,720,984 research outputs found
On the stabilisation of a singlet nitrene by the phosphaniminato and related imine-type substituents, a quantum chemical investigation
No full textSchoeller W, Rozhenko AB. On the stabilisation of a singlet nitrene by the phosphaniminato and related imine-type substituents, a quantum chemical investigation. EUROPEAN JOURNAL OF INORGANIC CHEMISTRY. 2001;(3):845-850.The substituent effects on the singlet-triplet energy separations are explored for phosphanylnitrenes and related congeners from the Group 14 to Group 16 elements. Imine-type substituents (e.g, phosphaniminato, methyleneimine etc.) are more effective than amino groups in lowering the energy of a singlet below that of a triplet state. It is due to an effective stabilisation of the singlet and a destabilisation of the triplet
Stable non-push-pull phosphanylcarbenes: NMR spectroscopic characterization of a methylcarbene
No full textDespagnet E, Gornitzka H, Rozhenko AB, Schoeller W, Bourissou D, Bertrand G. Stable non-push-pull phosphanylcarbenes: NMR spectroscopic characterization of a methylcarbene. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION. 2002;41(15):2835-2837
1,2-diphosphetes with unusual structures - A quantum chemical investigation of bonding properties
No full textSchoeller W, Tubbesing U, Rozhenko AB. 1,2-diphosphetes with unusual structures - A quantum chemical investigation of bonding properties. EUROPEAN JOURNAL OF INORGANIC CHEMISTRY. 1998;(7):951-955.According to quantum chemical calculations at an ab initio level parent 1,2-diphosphete is slightly more stable than its corresponding 1,4-diphosphabutadiene structural isomer. The quantum chemical calculations indicate that substituents at phosphorus and to a much less extent at carbon exert strong influences on the equilibrium geometries of 1,2-diphosphete structures: pi donors at phosphorus strongly elongate the P-P bond while electronegative substituents at phosphorus increase the interflap angle of the four-membered ring systems, bringing an envelope conformation to the fore. The lengthening of the P-P bond gives rise to a Mobius-type delocalization within the ring moiety
Encapsulated guest molecules in the dimer of octahydroxypyridine[4]arene
No full textLetzel M, Decker B, Rozhenko AB, Schoeller W, Mattay J. Encapsulated guest molecules in the dimer of octahydroxypyridine[4]arene. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. 2004;126(31):9669-9674.Recently a new type of calix[4]arenes has been synthesized via condensation of 2,6-dihydroxypyridine and a number of aldehydes. This type of pyridine[4]arenes forms capsules consisting of two single pyridine[4]arenes. These capsules can incorporate different guest molecules, like carboxylic acids and amides in this case. We proved that the guest acids really are incorporated inside the cavity of the capsules by electrospray mass spectrometry, NMR spectroscopy, and theoretical calculations
Conjugation in phosphabutadienes: Ab initio investigation and NMR spectral manifestation: II. Magnetic shielding in iminophosphines and heterobutadienes derived from them
No full textRozhenko AB, Povolotskii MI, Schoeller W. Conjugation in phosphabutadienes: Ab initio investigation and NMR spectral manifestation: II. Magnetic shielding in iminophosphines and heterobutadienes derived from them. RUSSIAN JOURNAL OF GENERAL CHEMISTRY. 2004;74(4):500-514.The conjugation effects in iminophosphines H3C-N=P-R (R = H, Hlg, OH, NH2, PH2, SiH3 SH) and heterobutadienes H3C-N=P-X=CY2 (X = N, P; Y = NH2, H) and their manifestations in NMR spectra are analyzed by RHF and MP2 calculations using the 6-31+G and 6-311+G basis sets with different numbers of polarization functions. The contribution of pi-mesomeric interactions to the electronic structure of these compounds is estimated from the theoretical and experimental structural parameters, calculated natural atomic charges and bond indices, surfaces of rotational coordinates of the potential energy, and energy balances of isodesmic reactions, and also from the experimental and theoretically calculated (GIAO) N-15 and P-31 NMR chemical shifts. The configuration of model heterobutadienes relative to the P=N double bond and the trans conformation of the N=P-X=C fragment, suggested by the calculation results, are consistent with the structural data for the compounds Mes*-N=P-X=C(NR2)(2) (X = N, P; R = Alk). The character of pi-mesomeric interactions in the examined series of iminophosphines and butadienes derived from them is discussed. The conjugation effects influence the stability of phosphabutadienes insignificantly
On the d(6)-transition metal complex formation of electron-rich methylenephosphanes, a quantum chemical investigation
No full textSchoeller W, Rozhenko AB, Grigoleit S. On the d(6)-transition metal complex formation of electron-rich methylenephosphanes, a quantum chemical investigation. EUROPEAN JOURNAL OF INORGANIC CHEMISTRY. 2001;(11):2891-2898.d(6)-Transition metal fragments M(CO)(5) (M = Cr, Me, W) form mono- and binuclear complexes with methylenephosphanes. In the mononuclear complexes the metal fragment adds to the lone pair at the phosphorus atom without considerable geometrical change of the original phosphaalkene moiety. Amino substitution at the phosphorus atom yields a slightly more stable complex than amino substitution at the carbon atom. The latter substitution pattern causes an inverse polarization of the P-C pi -bond. As a further consequence, in the corresponding transition metal complexes, the phosphorus atom is slightly pyramidalized. In the binuclear complexes the transition metal atoms tend to adopt a distorted bipyramidal arrangement at the phosphorus atom with concomitant lengthening of the P-C bond. The stretching of the P-C pi -bond is required to form a second lone pair for coordination at the phosphorus atom. However, the longest P-C bonds are achieved by C-diamino-substituted methylenephosphanes with overall bulky alkyl groups at the phosphorus and nitrogen atoms. It has the effect of not only extending the P-C bond but also widening the angle at the phosphorus atom
On the ligand properties of the P- versus the N-heterocyclic carbene for a Grubbs catalyst in olefin metathesis
No full textSchoeller W, Schroeder D, Rozhenko AB. On the ligand properties of the P- versus the N-heterocyclic carbene for a Grubbs catalyst in olefin metathesis. JOURNAL OF ORGANOMETALLIC CHEMISTRY. 2005;690(24-25):6079-6088.The 1.4-diphospha-2-azol-5-ylidene is a homologue to the Ender's type carbene. It is a possible candidate for a ligand in the metathesis reaction of olefins. Based on density functional calculations the differences between the electronic structures of both systems are evaluated. The NHC (N-heterocyclic carbene) possesses a larger singlet-triplet energy separation than the PHC (P-heterocyclic carbene) analogue. Thus the latter exerts a larger Lewis acidity than the former. In comparison with, the donor-ability (a-basicity) in both systems is similar. As a consequence for the PHC carbene a Ru-fragment as a ligand for catalysis is stronger bound. This causes in the olefin metathesis a lower dissociation energy (compared to the NHC analogue) with respect to the formation of the catalyst active 14el species. As a consequence, the olefin will be weaker bound as well. This can be overcome by attaching sterically demanding substituents such as mesityl or super-mesityl to the phosphorus atoms. They induce mutual steric hindrance with concomitant increase of the S-T separation of the free carbene. Thus the Lewis acidity of the carbene is reduced. On this basis for the PHC's with larger S-T energy separations the dissociation energy of the phosphine fragment is raised and the adding olefin fragment will be stronger bound to the transition metal. While these effects describe the electronic situation in the reactive species, steric effects at the ligand carbene mediate the stabilities of the individual intermediates in the metathesis reaction by exertion of inter- and intra-ligand repulsion. (c) 2005 Elsevier B.V. All rights reserved
On the transition metal complexation (Fischer-type) of phosphanylcarbenes
No full textSchoeller W, Eisner D, Grigoleit S, Rozhenko AB, Alijah A. On the transition metal complexation (Fischer-type) of phosphanylcarbenes. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. 2000;122(41):10115-10120.The formation of a Fischer-type transition metal complex with a W(CO)(5) fragment is evaluated for the phosphanylcarbenes, Arduengo-type carbenes, and Bertrand-type carbenes by means of quantum chemical investigations at a density functional level with effective core potential methods. Accordingly, the stabilities of the complexes depend strongly on the substitution pattern of the carbenic unit. Amino-substituted carbenes as well as the Arduengo-type carbene form stable transition metal complexes. The stabilities of the complexes decrease for the phosphanylcarbenes and are at a minimum for the hitherto unknown transition metal complexes of the push-pull-type carbene of Bertrand. The matter is analyzed in terms of distortion energies required to bring the carbene units into the geometrical standard state for complexation with the transition metal fragment. The arguments evaluated for the phosphanylcarbenes should hold equally well for other carbenes substituted with electropositive ligands. For the mono-phosphanylcarbenes, eta (1) as well as eta (2) structures are investigated. For the diphosphanylcarbenes, a new structural type of metal complexes is predicted in which the transition metal fragment is strongly bound to a cyclic structural valence isomer of the carbene
NMR spectroscopic and computational study of static and dynamic E/Z isomerism in aminoiminophosphines R2N-P = NMes
No full textGudat D, Hoffbauer W, Rozhenko AB, Schoeller W, Povolotskii MI. NMR spectroscopic and computational study of static and dynamic E/Z isomerism in aminoiminophosphines R2N-P = NMes. MAGNETIC RESONANCE IN CHEMISTRY. 2000;38(10):861-866.The P-31 NMR spectra of the iminophosphines R2N-P=NMes* [R = Me (2a), Et (2b), i-Pr (2c); Mes* = 2,4,6-tri-tert-butylphenyl] were studied in the solid state under magic angle spinning conditions and in solution. Evaluation of the solid-state data in connection with CIAO quantum chemical model calculations allows the characterization of the P-31 nuclear magnetic shielding tensors and leads to assignment of Z-configuration for the double bond in 2a and of the E-configuration for the double bonds in 2b and c. Comparison of the shifts delta(iso) with the chemical shift in solution (delta(soln)) indicates that this configuration is retained in solution only for 2c, whereas solutions of 2a and b contain rapidly exchanging equilibrium mixtures of both E- and Z-isomers. The analysis of the temperature dependence of delta(soln) allows for the first rime the evaluation of Delta H and Delta S for this isomerization. The results reveal that in the case of 2b the configuration of the more stable stereoisomer is opposite to the conformation observed in the solid state. Copyright (C) 2000 John Wiley & Sons, Ltd
Donor-acceptor interactions with electrophilic terminal phosphinidene complexes
No full textGrigoleit S, Alijah A, Rozhenko AB, Streubel R, Schoeller W. Donor-acceptor interactions with electrophilic terminal phosphinidene complexes. JOURNAL OF ORGANOMETALLIC CHEMISTRY. 2002;643-644:223-230.Donor-acceptor interactions of Lewis bases, such as amine, phosphine, cyanic acid and phosphaalkine with various phosphinidene complexes carrying a W(CO)(5) fragment are studied by means of density functional calculations. Accordingly, the donor interactions can be divided into two categories. In terms of energy an amine binds stronger than a phosphine to a phosphinidene. the resulting Do-P bond is longer (N-P) or equal (P-P) with respect to a corresponding single bond, This tendency is also revealed in the corresponding transition metal complexes. In all cases the singlet-triplet energy separation values of the resulting donor-adducts are fairly small. A donor with a pi-system, such as HCN yields a shorter N-P bond, but the resulting donor-adduct is even less stable with respect to decomposition into a singlet PH complex and cyanic acid. Similar considerations with HCP reveal only a weak donor addition of this fragment to the parent PH complex but a facile rearrangement of the adduct to the diphosphirene transition metal complex. The diaminophosphino-PH possesses a singlet ground state, its corresponding transition metal complex reveals a fairly small singlet-triplet energy separation. It can be considered as a nucleophilic PH complex in contrast to the other homologues which reveal an electrophilic behaviour. (C) 2002 Published by Elsevier Science B.V
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