Iminoacyl Alkyl Complexes of Zirconium Supported by a Ferrocene-Linked Diphosphinoamide Ligand Scaffold

2016 ◽  
Vol 69 (5) ◽  
pp. 555 ◽  
Author(s):  
Nathan R. Halcovitch ◽  
Michael D. Fryzuk
Keyword(s):  
General Formula ◽  
Mechanistic Studies ◽  
Hydrogen Shift ◽  
Alkyl Complexes ◽  
Rate Determining Step ◽  
Zirconium Complexes ◽  
Alkyl Derivatives ◽  
Benzyl Substituent

Zirconium dialkyl complexes of the general formula fc(NPiPr2)2ZrR2 (where fc = 1,1′-ferrocenyl, R = CH3, CH2Ph, CH2tBu, tBu) have been synthesized and characterized via the addition of alkyl lithium or potassium benzyl derivatives to the dichloride complex fc(NPiPr2)2ZrCl2(THF). Addition of 2,6-dimethylphenylisocyanide to these alkyl derivatives generates the corresponding mono iminoacyl alkyl zirconium complexes. On thermolysis, the iminoacyl moiety containing a benzyl substituent undergoes rearrangement to yield a new complex that contains an alkene-amido fragment. Mechanistic studies point to a 1,2 hydrogen shift as the rate-determining step.

DENSITY FUNCTIONAL THEORY STUDY ON THE MECHANISM OF TRIMETHYLAMINE-CATALYZED BAYLIS–HILLMAN REACTION

2010 ◽  
Vol 09 (supp01) ◽  
pp. 65-75 ◽  
Author(s):  
JING LI ◽  
WAN-YI JIANG
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Dft Method ◽  
Polarizable Continuum Model ◽  
Functional Theory ◽  
Reaction Barrier ◽  
Hydrogen Shift ◽  
Rate Determining Step ◽  
The Density Functional Theory ◽  
Polarizable Continuum

The trimethylamine-catalyzed Baylis–Hillman reaction of formaldehyde and vinylaldehyde has been studied with the density functional theory (DFT) method of B3LYP/6-31+G(d,p). In the gas phase, the reaction involves an amine–formaldehyde–vinylaldehyde trimolecular addition transition structure followed by rate-determining intramolecular 1,3-hydrogen shift. When a bulk solvent effect of water was considered with conductor-like polarizable continuum model (CPCM), the reaction was found to follow the sequence of Michael-addition of amine to vinylaldehyde (step 1), addition of formaldehyde (step 2), and 1,3-hydrogen shift (step 3), with the 1,3-hydrogen shift as rate-determining. The overall reaction barrier is significantly reduced. When a molecule of water is involved in the reaction, the 1,3-hydrogen shift is significantly promoted so that the rate-determining step becomes the C–C bond formation. The calculated overall reaction barrier is in agreement with experimental observations.

Proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives. FMO analysis of the effect of methyl and benzo substitution

1986 ◽  
Vol 64 (6) ◽  
pp. 1240-1245 ◽  
Author(s):  
Erwin Buncel ◽  
Helen A. Joly ◽  
John R. Jones
Keyword(s):  
Proton Transfer ◽  
Reaction Scheme ◽  
Frontier Molecular Orbital ◽  
Neutral Species ◽  
Ph Profile ◽  
Hydroxide Ion ◽  
Methyl Substitution ◽  
Rate Determining Step ◽  
Alkyl Derivatives ◽  
Conjugate Acid

The rate–pH profile for detritiation from the C-2 position of 1-methylimidazole has been determined in aqueous solution at 85 °C. The profile is consistent with a mechanism involving attack by hydroxide ion on the conjugate acid of the substrate to give an ylid intermediate in the rate-determining step. At higher pH, hydroxide-catalyzed exchange of the neutral species becomes increasingly important. Comparison of the second-order rate constants derived from the rate–pH profiles of imidazole, 1-methylimidazole, benzimidazole, and 1-methylbenzimidazole showed that methyl substitution caused the rate to increase by 2-to 3-fold while benzo annelation increased the rate by 10- to 20-fold. Frontier molecular orbital (FMO) analysis of the reaction scheme for proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives has been used to explain the rate-accelerating effect of methyl substitution and benzo annelation in these processes.

Metal complex catalyzed reactions of anils. III. Kinetic and mechanistic studies

1977 ◽  
Vol 55 (12) ◽  
pp. 2432-2441 ◽  
Author(s):  
A. R. Boate ◽  
D. R. Eaton
Keyword(s):  
Aqueous Solution ◽  
Metal Complex ◽  
Metal Atom ◽  
Nucleophilic Attack ◽  
Mechanistic Studies ◽  
Acetone Molecule ◽  
Rate Determining Step ◽  
Catalyzed Reactions ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of the homogeneously catalyzed formation and hydrolysis of anils in non-aqueous solution have been studied. The catalysts used are zinc complexes of thiourea. It is shown that all the evidence obtained, kinetic and otherwise, is consistent with a model in which the rate determining step for anil formation is nucleophilic attack by an aniline held in the second coordination sphere of the metal complex on an acetone molecule directly bound to the metal atom. Analogous mechanisms are suggested for anil hydrolysis and for transimination.

scholarly journals Mechanism of Iodine(III)-Promoted Oxidative Dearomatizing Hydroxylation of Phenols: Evidence for Radical-Chain Pathway

2020 ◽  
Author(s):  
Karol Kraszewski ◽  
Ireneusz Tomczyk ◽  
Aneta Drabinska ◽  
Krzysztof Bienkowski ◽  
Renata Solarska ◽  
...  
Keyword(s):  
High Resolution Mass Spectrometry ◽  
Hypervalent Iodine ◽  
Synthetic Approach ◽  
Chain Mechanism ◽  
Mechanistic Studies ◽  
Radical Chain ◽  
Oxidative Dearomatization ◽  
Radical Chain Mechanism ◽  
Rate Determining Step ◽  
Mechanism Of The Reaction

In the recent years, the dearomatization of phenols with the addition of nucleophiles to the aromatic ring, induced by hypervalent iodine(III) reagents and catalysts, has emerged as a highly useful synthetic approach. However, experimental mechanistic studies of this important process have been extremely scarce. As a result, the mechanism of the reaction remained elusive and as of today there exist as many as three distinct mechanistic proposals. In this report, we describe systematic investigations of the dearomatizing hydroxylation of phenols using an array of experimental techniques. Kinetics, EPR spectroscopy, and reactions with radical probes demonstrate that all the previously suggested mechanisms are incorrect, and that the transformation in fact proceeds via a radical-chain mechanism, with the aryloxyl radical being the key chain-carrying intermediate. Moreover, UV and NMR spectroscopy, high-resolution mass spectrometry, and cyclic voltammetry show that before reacting with the aryloxyl radical, water molecule becomes activated by the interaction with the iodine(III) center, causing this formally nucleophilic substrate to act as an electrophile. The C–O bond formation is identified as the rate-determining step of the reaction. This step generates the dearomatized product and an iodanyl(II) species, which is the second chain-carrying radical. The radical-chain mechanism emerging from our investigations allows to rationalize all other existing observations regarding the iodine(III)-promoted oxidative dearomatization of phenols.<br>

scholarly journals Mechanism of Iodine(III)-Promoted Oxidative Dearomatizing Hydroxylation of Phenols: Evidence for Radical-Chain Pathway

2020 ◽  
Author(s):  
Karol Kraszewski ◽  
Ireneusz Tomczyk ◽  
Aneta Drabinska ◽  
Krzysztof Bienkowski ◽  
Renata Solarska ◽  
...  
Keyword(s):  
High Resolution Mass Spectrometry ◽  
Hypervalent Iodine ◽  
Synthetic Approach ◽  
Chain Mechanism ◽  
Mechanistic Studies ◽  
Radical Chain ◽  
Oxidative Dearomatization ◽  
Radical Chain Mechanism ◽  
Rate Determining Step ◽  
Mechanism Of The Reaction

In the recent years, the dearomatization of phenols with the addition of nucleophiles to the aromatic ring, induced by hypervalent iodine(III) reagents and catalysts, has emerged as a highly useful synthetic approach. However, experimental mechanistic studies of this important process have been extremely scarce. As a result, the mechanism of the reaction remained elusive and as of today there exist as many as three distinct mechanistic proposals. In this report, we describe systematic investigations of the dearomatizing hydroxylation of phenols using an array of experimental techniques. Kinetics, EPR spectroscopy, and reactions with radical probes demonstrate that all the previously suggested mechanisms are incorrect, and that the transformation in fact proceeds via a radical-chain mechanism, with the aryloxyl radical being the key chain-carrying intermediate. Moreover, UV and NMR spectroscopy, high-resolution mass spectrometry, and cyclic voltammetry show that before reacting with the aryloxyl radical, water molecule becomes activated by the interaction with the iodine(III) center, causing this formally nucleophilic substrate to act as an electrophile. The C–O bond formation is identified as the rate-determining step of the reaction. This step generates the dearomatized product and an iodanyl(II) species, which is the second chain-carrying radical. The radical-chain mechanism emerging from our investigations allows to rationalize all other existing observations regarding the iodine(III)-promoted oxidative dearomatization of phenols.<br>

scholarly journals Titanium and zirconium complexes of the N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-butadiene ligand: syntheses, structures and uses in catalytic hydrosilylation reactions

2014 ◽  
Vol 43 (39) ◽  
pp. 14876-14888 ◽  
Author(s):  
Srinivas Anga ◽  
Kishor Naktode ◽  
Harinath Adimulam ◽  
Tarun K. Panda
Keyword(s):  
Metathesis Reaction ◽  
Zirconium Complexes ◽  
Alkyl Derivatives ◽  
Catalytic Hydrosilylation

Various Ti and Zr complexes with Dipp2DAD ligand and their alkyl derivatives are obtained via salt metathesis reaction and catalytic hydrosilylation reactions by Zr alkyl complex are reported.

Mechanistic studies of amination of ketenimines: change of rate-determining step by N-substituents through electronic effects

Tetrahedron ◽  
2006 ◽  
Vol 62 (1) ◽  
pp. 171-181 ◽  
Author(s):  
Kuangsen Sung ◽  
Fu-Lin Chen ◽  
Pin-Mei Huang ◽  
Shu-Min Chiang
Keyword(s):  
Mechanistic Studies ◽  
Electronic Effects ◽  
Rate Determining Step
Sign in / Sign up

Export Citation Format

Share Document