ChemInform Abstract: Ab initio Investigations of Structure and Stability of (R3SiAl)4, R: H, Me, tBu

Schneider, Uwe; Ahlrichs, Reinhart; Horn, Hans W.; Schaefer, Andreas

doi:10.1002/chin.199225027

Cited by 61 publications

(64 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[41] Geometry optimisations for non-transition-metal systems used the 6-31G(d), [42] 6-31+G(d) [43] and 6-311+G(d) [44] basis sets at both the hybrid density functional (B3LYP [45,46] ) and QCISD [47] levels of theory. Cobalt complexes were optimised with B3LYP using the Schaefer-HornAhlrichs split-valence basis set [48] augmented with standard polarisation functions. [49] Optimised geometries were confirmed to be minima or transition states by calculating their normal vibrations within the harmonic approximation at the level of the geometry optimisation.…”

Section: Methodsmentioning

confidence: 99%

The Cyclooligomerisation of Acetylene at Metal Centres

Winget

Clark

2008

Eur J Inorg Chem

View full text Add to dashboard Cite

Density‐functional theory (DFT) and QCISD(T) calculations have been used to investigate the mechanism of cyclodimerisation and cyclotrimerisation of acetylene at a cyclopentadienyl‐CoI centre. In contrast to earlier investigations, we find that the most favourable mechanism for the formation of benzene involves the insertion of an acetylene molecule into a Co–C bond of the well known cobaltacyclopentadienyl intermediate. The product of this reaction then undergoes very facile ring‐closure to benzene. This mechanism is found to be more favourable than the concerted Diels–Alder path, which is the highest in energy of the three mechanisms considered. The remaining reaction path involves initial addition of an acetylene molecule to the cyclopentadienyl ligand followed by rearrangement to give a 1,3,5‐hexatrien‐1‐ylcyclopentane ligand system, which cleaves to give benzene and cyclopentadienyl ligands. Spin crossovers between the singlet and triplet states are found for the ring‐closure of the cobaltacyclopentadienyl intermediate to give a cyclobutadiene complex and for the concerted Diels–Alder process. These spin crossovers and the reaction mechanisms in general are rationalised in terms of the concept of electron‐transfer catalysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

show abstract

Section: Methodsmentioning

confidence: 99%

The Cyclooligomerisation of Acetylene at Metal Centres

Winget

Clark

2008

Eur J Inorg Chem

View full text Add to dashboard Cite

show abstract

“…[27] Triple-z and double-z all-electron basis sets proposed by Ahlrichs et al were used for the metal and for the rest of the atoms, respectively. [28,29] The broken symmetry approach was employed to describe the unrestricted solutions of the antiferromagnetic spin states, [30] which were obtained from the guess functions generated with the fragment tool implemented in the Gaussian code. The full geometry was used for [Cu 3 A C H T U N G T R E N N U N G (pyr)A C H T U N G T R E N N U N G (m 3 -CO 3 )]·A C H T U N G T R E N N U N G (ClO 4 ) 4 ·H 2 O. DF calculations were also performed on a dinuclear model in which the copper(II) ions were perfectly placed in the carbonate plane and, to allow close positions for the metal atoms, the peripheral ligands were placed in a plane perpendicular to that built from the carbonate group.…”

Section: Esi-msmentioning

confidence: 99%

A Trinuclear Copper(II) Cryptate and Its μ₃‐CO₃ Cascade Complex: Thermodynamics, Structural and Magnetic Properties

Mateus

Delgado

Lloret

et al. 2011

Chemistry A European J

View full text Add to dashboard Cite

The 2,4,6-triethylbenzene-capped hexaamine macrobicycle with pyridyl spacers (pyr) was able to coordinate three copper(II) ions within its cavity. Potentiometric studies performed at 298.2 K in MeOH/H(2)O (50:50 v/v) and at ionic strength 0.10 mol dm(-3) in KNO(3) revealed that trinuclear species predominate in solution from pH 5.0, the hydroxo complexes being the main species, which start forming at unusual very low pH values. The single-crystal X-ray determination of the trinuclear complex showed that the three copper centres have square-planar geometry, arranged in an almost equilateral triangle, and have carbonate bridging the three metal centres. The presence of carbonate resulted from fixation of atmospheric CO(2). The present study represents the first μ(3)-CO(3)-bridged trinuclear copper(II) complex located in the interior of a macrobicyclic cavity. The magnetic data of [Cu(3)(pyr)(μ(3)-CO(3))]·(ClO(4))(4) showed ferromagnetic intramolecular interactions [J=3.80 cm(-1), based on the Hamiltonian H=-J(S(1)S(2)+S(2)S(3)+S(1)S(3))] yielding a spin quartet, S=3/2, ground state. Density functional calculations on the experimental geometry of the trinuclear complex showed that the ferromagnetic nature of the magnetic coupling can be attributed to the syn-anti conformation of the carbonato bridge, and a magneto-structural correlation, based on the different conformations (syn-anti, syn-syn and anti-anti), is presented. The interesting properties observed, namely the lowering of the pK(a) of coordinated water molecules to unusual values and the good fit of the carbonate anion between the copper centres, derive from the special architecture of pyr.

show abstract

“…[57] The BP86 GGA functional of Becke and Perdew was used. [58] The TZVP triple-z basis set with one polarization function was used for main group atoms, [59] while the relativistic SDD effective core potential in combination with a triple-z basis set was used for the Au atom.…”

Section: Preparation Of Enantioenriched Dienyne Acetate (2)mentioning

confidence: 99%

Gold‐ and Platinum‐Catalyzed Cycloisomerization of Enynyl Esters versus Allenenyl Esters: An Experimental and Theoretical Study

Marion

Lemière

Correa

et al. 2009

Chemistry A European J

128

View full text Add to dashboard Cite

Ester-way to heaven: Unexpected formation of bicyclo[3.1.0]hexene 4 was the main focus of combined experimental and theoretical studies on the Au-catalyzed cycloisomerization of branched dienyne 1 (see scheme), which provided better understanding of the mechanistic details governing the cyclization of enynes bearing a propargylic ester group.Experimental and theoretical studies on Au- and Pt-catalyzed cycloisomerization of a branched dienyne with an acetate group at the propargylic position are presented. The peculiar architecture of the dienyne precursor, which has both a 1,6- and a 1,5-enyne skeleton, leads, in the presence of alkynophilic gold catalysts, to mixtures of bicyclic compounds 3, 4, and 5. Formation of unprecedented bicyclo[3.1.0]hexene 5 is the main focus of this study. The effect of the ancillary ligand on the gold center was examined and found to be crucial for formation of 5. Further mechanistic studies, involving cyclization of an enantioenriched dienyne precursor, (18)O-labeling experiments, and DFT calculations, allowed an unprecedented reaction pathway to be proposed. We show that bicyclo[3.1.0]hexene 5 is likely formed by a 1,3-OAc shift/allene-ene cyclization/1,2-OAc shift sequence, as calculated by DFT and supported by Au-catalyzed cyclization of isolated allenenyl acetate 7, which leads to improved selectivity in the formation of 5. Additionally, the possibility of OAc migration from allenyl acetates was supported by a trapping experiment with styrene that afforded the corresponding cyclopropane derivative. This unprecedented generation of a vinyl metal carbene from an allenyl ester supports a facile enynyl ester/allenenyl ester equilibrium. Further examination of the difference in reactivity between enynyl acetates and their corresponding [3,3]-rearranged allenenyl acetates toward Au- and Pt-catalyzed cycloisomerization is also presented.

show abstract

ChemInform Abstract: Ab initio Investigations of Structure and Stability of (R3SiAl)4, R: H, Me, tBu

Cited by 61 publications

References 1 publication

The Cyclooligomerisation of Acetylene at Metal Centres

The Cyclooligomerisation of Acetylene at Metal Centres

A Trinuclear Copper(II) Cryptate and Its μ₃‐CO₃ Cascade Complex: Thermodynamics, Structural and Magnetic Properties

Gold‐ and Platinum‐Catalyzed Cycloisomerization of Enynyl Esters versus Allenenyl Esters: An Experimental and Theoretical Study

Contact Info

Product

Resources

About

ChemInform Abstract: Ab initio Investigations of Structure and Stability of (R3SiAl)4, R: H, Me, tBu

Cited by 61 publications

References 1 publication

The Cyclooligomerisation of Acetylene at Metal Centres

The Cyclooligomerisation of Acetylene at Metal Centres

A Trinuclear Copper(II) Cryptate and Its μ3‐CO3 Cascade Complex: Thermodynamics, Structural and Magnetic Properties

Gold‐ and Platinum‐Catalyzed Cycloisomerization of Enynyl Esters versus Allenenyl Esters: An Experimental and Theoretical Study

Contact Info

Product

Resources

About

A Trinuclear Copper(II) Cryptate and Its μ₃‐CO₃ Cascade Complex: Thermodynamics, Structural and Magnetic Properties