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491.
Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)amide Ligands
M Haehnel S Hansen A Spannenberg P Arndt T Beweries U Rosenthal 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10546-10553
A study regarding coordination chemistry of the bis(diphenylphosphino)amide ligand Ph(2) P-N-PPh(2) at Group?4 metallocenes is presented herein. Coordination of N,N-bis(diphenylphosphino)amine (1) to [(Cp(2) TiCl)(2) ] (Cp=η(5) -cyclopentadienyl) generated [Cp(2) Ti(Cl)P(Ph(2) )N(H)PPh(2) ] (2). The heterometallacyclic complex [Cp(2) Ti(κ(2) -P,P-Ph(2) P-N-PPh(2) )] (3?Ti) can be prepared by reaction of 2 with n-butyllithium as well as from the reaction of the known titanocene-alkyne complex [Cp(2) Ti(η(2) -Me(3) SiC(2) SiMe(3) )] with the amine 1. Reactions of the lithium amide [(thf)(3) Li{N(PPh(2) )(2) }] with [Cp(2) MCl(2) ] (M=Zr, Hf) yielded the corresponding zirconocene and hafnocene complexes [Cp(2) M(Cl){κ(2) -N,P-N(PPh(2) )(2) }] (4?Zr and 4?Hf). Reduction of 4?Zr with magnesium gave the highly strained heterometallacycle [Cp(2) Zr(κ(2) -P,P-Ph(2) P-N-PPh(2) )] (3?Zr). Complexes 2, 3?Ti, 4?Hf, and 3?Zr were characterized by X-ray crystallography. The structures and bondings of all complexes were investigated by DFT calculations. 相似文献
492.
Yucelen GI Choudhury RP Vyalikh A Scheler U Beckham HW Nair S 《Journal of the American Chemical Society》2011,133(14):5397-5412
We report the identification and elucidation of the mechanistic role of molecular precursors and nanoscale (1-3 nm) intermediates with intrinsic curvature in the formation of single-walled aluminosilicate nanotubes. We characterize the structural and compositional evolution of molecular and nanoscale species over a length scale of 0.1-100 nm by electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy ((27)Al liquid-state, (27)Al and (29)Si solid-state MAS), and dynamic light scattering. Together with structural optimization of key experimentally identified species by solvated density functional theory calculations, this study reveals the existence of intermediates with bonding environments, as well as intrinsic curvature, similar to the structure of the final nanotube product. We show that "proto-nanotube-like" intermediates with inherent curvature form in aqueous synthesis solutions immediately after initial hydrolysis of reactants, disappear from the solution upon heating to 95 °C due to condensation accompanied by an abrupt pH decrease, and finally form ordered single-walled aluminosilicate nanotubes. Detailed quantitative analysis of NMR and ESI-MS spectra from the relevant aluminosilicate, aluminate, and silicate solutions reveals the presence of a variety of monomeric and polymeric aluminate and aluminosilicate species (Al(1)Si(x)-Al(13)Si(x)), such as Keggin ions [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+) and polynuclear species with a six-membered Al oxide ring unit. Our study also directly reveals the complexation of aluminate and aluminosilicate species with perchlorate species that most likely inhibit the formation of larger condensates or nontubular structures. Integration of all of our results leads to the construction of the first molecular-level mechanism of single-walled metal oxide nanotube formation, incorporating the role of monomeric and polymeric aluminosilicate species as well as larger nanoparticles. 相似文献
493.
Haskell P. Rosenthal 《Israel Journal of Mathematics》1972,13(3-4):361-378
LetC denote the Banach space of scalar-valued continuous functions defined on the closed unit interval. It is proved that ifX is a Banach space andT:C→X is a bounded linear operator withT
*
X
* non-separable, then there is a subspaceY ofC, isometric toC, such thatT|Y is an isomorphism. An immediate consequence of this and a result of A. Pelczynski, is that every complemented subspace ofC with non-separable dual is isomorphic (linearly homeomorphic) toC.
The research for this paper was partially supported by NSF-GP-30798X.
An erratum to this article is available at . 相似文献
494.
On Commutators of Idempotents 总被引:2,自引:0,他引:2
It is shown that a pair of idempotent operators on a Banach space is triangularizable if their commutator is nilpotent. Moreover, if every operator on Hilbert space has an invariant subspace, then a pair of idempotents on Hilbert space is triangularizable if their commutator is quasinilpotent. These results are generalized from idempotents to quadratic operators. 相似文献
495.
496.
Tom van Dijk Dr. Sebastian Burck Amos J. Rosenthal Dr. Martin Nieger Dr. Andreas W. Ehlers Dr. J. Chris Slootweg Prof. Dr. Koop Lammertsma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9328-9331
Iminophosphanes are a new group of 1,3‐P,N‐ligands, readily obtainable from secondary phosphanes and nitrilium ions, having a tunable N‐donor site by means of varying the imine substituents. These ligands give, in high yields, monodentate gold complexes and bidentate rhodium and iridium complexes. Crystal structures are reported for both the ligands and the complexes. 相似文献
497.
Jinyoung Yang Evgeny Levi Radu V. Craiu Jeffrey S. Rosenthal 《Journal of computational and graphical statistics》2019,28(2):276-289
One of the most widely used samplers in practice is the component-wise Metropolis–Hastings (CMH) sampler that updates in turn the components of a vector-valued Markov chain using accept–reject moves generated from a proposal distribution. When the target distribution of a Markov chain is irregularly shaped, a “good” proposal distribution for one region of the state–space might be a “poor” one for another region. We consider a component-wise multiple-try Metropolis (CMTM) algorithm that chooses from a set of candidate moves sampled from different distributions. The computational efficiency is increased using an adaptation rule for the CMTM algorithm that dynamically builds a better set of proposal distributions as the Markov chain runs. The ergodicity of the adaptive chain is demonstrated theoretically. The performance is studied via simulations and real data examples. Supplementary material for this article is available online. 相似文献
498.
Vladimir V. Burlakov Marc A. Bach Marcus Klahn Perdita Arndt Wolfgang Baumann Anke Spannenberg Uwe Rosenthal 《Macromolecular Symposia》2006,236(1):48-53
The recently described reaction products of zirconacyclopropenes Cp′2Zr(η2-Me3SiC2SiMe3) and five-membered zirconacyclocumulenes (zirconacyclopenta-2,3,4-trienes) Cp*2Zr(η4-1,2,3,4-RC4R), Cp* = η5-pentamethylcyclopentadienyl, R = Me, Me3Si and Ph, with i-Bu2AlH are active catalysts in the polymerization of ethylene and in the ring opening polymerization of ε-caprolactone. Here we describe the different activity of these complexes after thermal activation or if additional i-Bu2AlH together with water are added. These results are compared to those which were obtained with the complexes Cp2Zr(η4-1,2,3,4-H2C4H2), rac-(EBTHI)ZrF2, rac-(EBTHI)ZrCl2, [rac-(EBTHI)Zr(H)(µ-H)]2 and rac (EBTHI)Zr(F)CH2-CH2(2-Py) after activation with i-Bu2AlH together with water. 相似文献
499.
500.
Joseph P. Kennedy Gyorgyi Fenyvesi Richard P. Levy Ken S. Rosenthal 《Macromolecular Symposia》2001,172(1):56-66
A series of amphiphilic networks (membranes), consisting of hydrophilic poly(N,N‐dimethylacrylamide) (PDMAAM) main chains crosslinked by hydrophobic telechelic polyisobutylene di‐ and trimethacrylates (MA‐PIB‐MA or ∅︁(PIB‐MA)3) have been synthesized and used for the preparation of thin‐walled tubules suitable for the immunoisolation of porcine islets. The molecular weight cut‐off (MWCO) ranges, insulin and glucose diffusion coefficients and permeabilities of various membranes have been determined. The molecular weight of the PDMAAM moiety between two hydrophobic crosslinking points (Mc,hydrophilic) controls permeability, which in turn can be controlled by synthesis conditions. The strengths and elongations of water‐swollen membranes crosslinked with ∅︁(PIB‐MA)3 are superior by a factor of about two to those prepared with MA‐PIB‐MA. Based on the values from these experiments, a well‐defined membrane prepared with ∅︁(PIB‐MA)3 was selected and used to encapsulate porcine islet cells. Gratifyingly, the encapsulated islet cells remain functional and viable, and cells within the tubule release insulin upon glucose challenge. These in vitro experiments are sufficiently promising to encourage us to continue our studies to develop a bioartificial pancreas. 相似文献