Favored C?H Activation in Comparison to Cyclopropyl C?C Activation using a Vaska-Analogous Complex

2005 ◽  
Vol 347 (2-3) ◽  
pp. 398-404 ◽  
Author(s):  
Klaus Ruhland ◽  
Eberhardt Herdtweck
Keyword(s):  
Analogous Complex

The Little Sycamore Site and the Early Milling Stone Cultures of Southern California

1954 ◽  
Vol 20 (2) ◽  
pp. 112-123 ◽  
Author(s):  
William James Wallace
Keyword(s):  
San Diego ◽  
Southern California ◽  
Coastal Region ◽  
San Diego County ◽  
University Of Southern California ◽  
Santa Barbara ◽  
Field Methods ◽  
Analogous Complex ◽  
La Jolla ◽  
The University

The Presence in the southern California coastal region of prehistoric cultures showing considerable use of milling stones has been recognized for some years. Attention was called to this fact by the publication in 1929 of David Banks Rogers’ Prehistoric Man of the Santa Barbara Coast. Rogers distinguished a sequence of three aboriginal cultures in the Santa Barbara area, the earliest of which (Oak Grove) was characterized by the employment of this form of grinding implement almost to the exclusion of other artifacts. In the same year Malcolm J. Rogers noted a somewhat analogous complex (now La Jolla) in western San Diego County (M. J. Rogers 1929: 456-7). Occurrences of similar assemblages have been reported upon since (Treganza and Malamud 1950; Walker 1952).An investigation conducted at the Little Sycamore site (Ven 1) in Ventura County by a class in archaeological field methods from the University of Southern California uncovered evidence of yet another milling stone complex.

High- and low-spin complexes with similar, ligands. II. Iron(II) complexes with sterically hindered analogues of 2,2'-bipyridyl

1972 ◽  
Vol 25 (8) ◽  
pp. 1631 ◽  
Author(s):  
CM Harris ◽  
S Kokot ◽  
HRH Patil ◽  
E Sinn ◽  
H Wong
Keyword(s):  
Spectral Data ◽  
High Spin ◽  
Steric Hindrance ◽  
Field Potential ◽  
Ligand Field ◽  
Apparent Difference ◽  
Field Splitting ◽  
Analogous Complex ◽  
Sterically Hindered ◽  
Direct Change

Benzo substitution cis to the nitrogen of 2,2'-bipyridyl (bipy), to form 2-(2'-pyridyl)quinoline (pq), transforms the tris-complex with iron(11) from low spin in Fe(bipy)32+ to essentially high spin but near the crossover in Fe(pq)32+. For this complex, the ligand field splitting near the crossover, Δc is estimated from magnetic and spectral data as c. 12000 cm-l. A similar value but 150 cm-l lower is estimated for the analogous complex with the sterically related ligand 2-methyl-1,10-phenanthroline. This apparent difference in Δ values could arise from a direct change in ligand field potential, or from other factors, such as a change in distortion effects. Due to steric hindrance, pq prefers to form bis-complexes Fe(pq)2X2, pseudooctahedral and high spin, with suitable monodentates, X = Cl2 Br, NCS, ClO4. Double benzo substitution of bipy to form 2,2'-biquinolyl (biq) so increases steric hindrance that the tris-complex could not be formed. Instead biq forms pseudotetrahedral complexes Fe(biq)22+ and Fe(biq)X2 (X = Cl, Br).

Charge - Transfer Complexes of Metal Dithiolenes XXIV: Ion Pairs of the Tetrakis(dimethylamino)ethene Dication with Dithiolene Metalate Dianions

1997 ◽  
Vol 52 (1) ◽  
pp. 65-68 ◽  
Author(s):  
Matthias Lemke ◽  
Falk Knoch ◽  
Horst Kisch
Keyword(s):  
Ion Pairs ◽  
Reorganization Energy ◽  
Ion Pair ◽  
Charge Transfer Complexes ◽  
Central Metal ◽  
Similar Reduction ◽  
Analogous Complex ◽  
Marcus Model ◽  
A Chain ◽  
The One

The dication of tetrakis(dimethylamino)ethene (TDAE2+) forms ion pair complexes with [M(mnt)2]2-, mnt2-= maleonitrile-2,3-dithiolate, M(II) = Ni, Pd, Pt, and Zn. According to X-ray analysis the structure of {TDAE2+[Pt(mnt)2]2- } consists of a chain-like arrangement of planar dianions and twisted (71°) dications. Shortest interionic contacts are 11 pm longer than the corresponding van der Waals radii. In the UV-VIS diffuse reflectance spectra of the complexes with a d8 central metal there is no unambiguous evidence for the presence of an ion pair CT band. This band is observed, however, at 450 nm when the d10 metal Zn(II) is present. Application of the Hush-Marcus model affords a reorganization energy of 110 kJ / mol for electron transfer from [Zn(mnt)2]2- to TDAE2+. This value is 40 kJ / mol higher than the one reported for the analogous complex wherein TDAE2+ is replaced by a 2,2′-bipyridinium acceptor of similar reduction potential

Einkernige Bis(triphenylphospin)kupfer(I)-Komplexe der Bidiazine / Mononuclear Bis(triphenylphosphine)copper(I) Complexes of the Bidiazines

1992 ◽  
Vol 47 (8) ◽  
pp. 1057-1062 ◽  
Author(s):  
Conny Vogler ◽  
Wolfgang Kaim
Keyword(s):  
Esr Spectroscopy ◽  
Energy Difference ◽  
Ligand Field ◽  
Additional Contribution ◽  
Neutral Radical ◽  
Long Wavelength ◽  
Reduction Potentials ◽  
Ligand Charge Transfer ◽  
Analogous Complex ◽  
Orbital Stabilization

The cationic d10 metal complexes [(bdz)Cu(PPh3)2+]+ of the π accepting bidiazine (bdz) chelate ligands 3,3′-bipyridazine, 2,2′-bipyrazine, 2,2′- and 4,4′-bipyrimidine were synthesized and compared with the analogous complex of 2,2′-bipyridine. The long wavelength metal-to-ligand charge transfer (MLCT) absorption maxima and the reduction potentials indicate relatively little π* orbital stabilization by +Cu(PPh3)2. The particular d orbital splitting in a tetrahedral ligand field results in an additional contribution from △t to the energy difference between the first and second MLCT band. Only the most easily reduced complexes of 4,4′-bipyrimidine and 2,2′-bipyrazine yield neutral radical complexes (“Cu(0)”) which were characterized by ESR spectroscopy.

scholarly journals Rotational Spectroscopy Meets Quantum Chemistry for Analyzing Substituent Effects on Non-Covalent Interactions: The Case of the Trifluoroacetophenone-Water Complex

Molecules ◽  
2020 ◽  
Vol 25 (21) ◽  
pp. 4899
Author(s):  
Juncheng Lei ◽  
Silvia Alessandrini ◽  
Junhua Chen ◽  
Yang Zheng ◽  
Lorenzo Spada ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Substituent Effects ◽  
Equilibrium Structure ◽  
Proton Donor ◽  
Rotational Spectroscopy ◽  
Donor And Acceptor ◽  
Analogous Complex ◽  
Non Covalent Interactions ◽  
Covalent Interactions

The most stable isomer of the 1:1 complex formed by 2,2,2-trifluoroacetophenone and water has been characterized by combining rotational spectroscopy in supersonic expansion and state-of-the-art quantum-chemical computations. In the observed isomer, water plays the double role of proton donor and acceptor, thus forming a seven-membered ring with 2,2,2-trifluoroacetophenone. Accurate intermolecular parameters featuring one classical O-H···O hydrogen bond and one weak C-H···O hydrogen bond have been determined by means of a semi-experimental approach for equilibrium structure. Furthermore, insights on the nature of the established non-covalent interactions have been unveiled by means of different bond analyses. The comparison with the analogous complex formed by acetophenone with water points out the remarkable role played by fluorine atoms in tuning non-covalent interactions.

Six-coordinate mononuclear dysprosium(iii) single-molecule magnets with the triphenylphosphine oxide ligand

2020 ◽  
Vol 49 (15) ◽  
pp. 4694-4698
Author(s):  
Kuduva R. Vignesh ◽  
Dimitris I. Alexandropoulos ◽  
Haomiao Xie ◽  
Kim R. Dunbar
Keyword(s):  
Ab Initio ◽  
Single Molecule ◽  
Energy Barrier ◽  
Triphenylphosphine Oxide ◽  
Single Molecule Magnets ◽  
Analogous Complex ◽  
Halide Ligands

Three rare octahedral mononuclear DyIII complexes bearing triphenylphosphine oxide and halide ligands are reported. The Cl− and Br− analogues exhibit SMM behavior under a small dc field. Ab initio CASSCF calculations reveal a higher energy barrier for an analogous complex with iodides.

scholarly journals Responsibility for Another’s Debt: Suretyship, Solidarity, and Imperfect Delegation

2010 ◽  
Vol 55 (2) ◽  
pp. 211-255
Author(s):  
Michelle Cumyn
Keyword(s):  
Basic Structure ◽  
Civil Code ◽  
Legal Evolution ◽  
Civil Code Of Quebec ◽  
Analogous Complex ◽  
The Law

Legal evolution is often achieved by taking a fresh look at venerable institutions whose interpretation has become thwarted, constricted, or stale. Presumptions established to protect debtors and sureties at articles 1525 and 2335 of the Civil Code of Québec have prevented jurists from borrowing freely from the rules of solidarity and suretyship. Where one person is undoubtedly responsible for the debt of another, even in the absence of a suretyship agreement, the author argues it should be possible to apply the law of suretyship by analogy. Where two persons are each liable to perform the same obligation in full, it is likewise appropriate to apply the rules of solidarity. The author’s analysis proceeds in three parts: an introduction of the basic structure of suretyship and solidarity (Part I), a discussion of important differences in the law of suretyship and solidarity (Part II), and an argument that the solidarity and suretyship models should be used to illuminate analogous complex relations where multiple persons are responsible for the same debt (Part III). More specifically, in the situation of imperfect delegation, where a person assumes liability to a creditor for payment of a debt owed by another, but the original debtor is not discharged and remains liable in case of non-payment by the new debtor, it is appropriate to apply by analogy the law of suretyship.

scholarly journals CheZ-Mediated Dephosphorylation of the Escherichia coli Chemotaxis Response Regulator CheY: Role for CheY Glutamate 89

2003 ◽  
Vol 185 (5) ◽  
pp. 1495-1502 ◽  
Author(s):  
Ruth E. Silversmith ◽  
Gerald P. Guanga ◽  
Laurie Betts ◽  
Carolyn Chu ◽  
Rui Zhao ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Active Site ◽  
Response Regulator ◽  
Salt Bridge ◽  
Flagellar Motor ◽  
Loop Modeling ◽  
Wild Type ◽  
X Ray ◽  
Phosphorylated Form ◽  
Analogous Complex

ABSTRACT The swimming behavior of Escherichia coli at any moment is dictated by the intracellular concentration of the phosphorylated form of the chemotaxis response regulator CheY, which binds to the base of the flagellar motor. CheY is phosphorylated on Asp57 by the sensor kinase CheA and dephosphorylated by CheZ. Previous work (Silversmith et al., J. Biol. Chem. 276:18478, 2001) demonstrated that replacement of CheY Asn59 with arginine resulted in extreme resistance to dephosphorylation by CheZ despite proficient binding to CheZ. Here we present the X-ray crystal structure of CheYN59R in a complex with Mn2+ and the stable phosphoryl analogue BeF3 −. The overall folding and active site architecture are nearly identical to those of the analogous complex containing wild-type CheY. The notable exception is the introduction of a salt bridge between Arg59 (on the β3α3 loop) and Glu89 (on the β4α4 loop). Modeling this structure into the (CheY-BeF3 −-Mg2+)2CheZ2 structure demonstrated that the conformation of Arg59 should not obstruct entry of the CheZ catalytic residue Gln147 into the active site of CheY, eliminating steric interference as a mechanism for CheZ resistance. However, both CheYE89A and CheYE89Q, like CheYN59R, conferred clockwise flagellar rotation phenotypes in strains which lacked wild-type CheY and displayed considerable (≈40-fold) resistance to dephosphorylation by CheZ. CheYE89A and CheYE89Q had autophosphorylation and autodephosphorylation properties similar to those of wild-type CheY and could bind to CheZ with wild-type affinity. Therefore, removal of Glu89 resulted specifically in CheZ resistance, suggesting that CheY Glu89 plays a role in CheZ-mediated dephosphorylation. The CheZ resistance of CheYN59R can thus be largely explained by the formation of the salt bridge between Arg59 and Glu89, which prevents Glu89 from executing its role in catalysis.

Substrate activation by the Wilkinson analogous complex containing η2-chelated and η1 P-bonded (methoxyethyl)dicyclohexylphosphine as a hemilabile ligand

1996 ◽  
Vol 526 (1) ◽  
pp. 175-183 ◽  
Author(s):  
Ekkehard Lindner ◽  
Berthold Keppeler ◽  
Hermann A. Mayer ◽  
Karlheinz Gierling ◽  
Riad Fawzi ◽  
...  
Keyword(s):  
Substrate Activation ◽  
Analogous Complex

Variable Structure of the Cu2S2 Core in Doubly Thiolate-Bridged Dicopper(I) Complexes. An X-Ray Crystallographic, Electrochemical and EPR Study of (dmp)2(o-CH3C6H4S)2Cu2, dmp = 2,9-Dimethyl-1,10-phenanthroline, and a Comment on the Nature of Phenanthroline-Containing “Cu(0)” Complexes

1995 ◽  
Vol 50 (1) ◽  
pp. 115-122 ◽  
Author(s):  
Andreas F. Stange ◽  
Eberhard Waldhör ◽  
Michael Moscherosch ◽  
Wolfgang Kaim
Keyword(s):  
Variable Structure ◽  
Structural Flexibility ◽  
Nitrous Oxide Reductase ◽  
Epr Spectrum ◽  
Tetrahedral Configuration ◽  
Methyl Substitution ◽  
Bond Angles ◽  
Spin Pairing ◽  
Analogous Complex ◽  
Epr Signal

The molecular and crystal structure of the dicopper(I) complex (dmp)2(μ-o-CH3C6H4S)2Cu2 (1), dmp = 2,9-dimethyl-1,10-phenanthroline, has been determined. With Cu/S/Cu and S/Cu/S bond angles between 80 and 100°, the planar structure of the central CuSCuS four-membered ring is much more symmetric for 1 as compared to the analogous complex 2 of unsubstituted 1,10-phenanthroline which has a folded Cu2S2 core with bond angles between 67 and 108°. This result illustrates a considerable structural flexibility of the LCu(μ-SR)2CuL entity which is being discussed as a possible model for CuA centers of cytochrome c oxidase or nitrous oxide reductase. Oxidation of both complexes 1 and 2 remains irreversible even at cyclovoltammetric scan rates of 1 V/s. However, the methyl substitution in complex 1 causes increased reversibility of the electronically coupled dmpbased reduction processes. Accordingly, the EPR spectrum of 1- · is characterized by hyperfine splitting from dmp- · and a relatively small 63,65Cu coupling of 0.53 mT. The stabilization of 2,9-disubstituted 1,10-phenanthroline radical anions by coordination to Cu(I) is also demonstrated by detection of a single broad EPR line at g 2.0028 for the formal “Cu(0)” complex Cu(dpp)2 = CuI(dpp-·)(dpp), dpp = 2,9-diphenyl-1,10-phenanthroline. While the EPR signal of Cu(dpp)2 loses intensity on cooling, possibly due to dimerization and spin-pairing, the distorted tetrahedral configuration with essential orthogonal arrangement of dpp π systems seems to disfavour an intramolecular electron hopping.

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