Preface
Page: i-ii (2)
Author: Nejib Ben Hussein Mekni and Noureddine Raouafi
DOI: 10.2174/9789815040647122010001
Acknowledgements
Page: iii-iii (1)
Author: Nejib Ben Hussein Mekni and Noureddine Raouafi
DOI: 10.2174/9789815040647122010002
General Introduction
Page: 1-2 (2)
Author: Nejib Ben Hussein Mekni and Noureddine Raouafi
DOI: 10.2174/9789815040647122010003
PDF Price: $15
Abstract
This first chapter is a general introduction to the book in which we give a
background on the Ca-Cσ-bond containing organocalcium compounds, which are less
studied as compared to other organometallic compounds.
We describe the interest in synthesizing the synthesized organometallic intermediates
and products as well as their application fields such as chemistry, biology, medicine,
pharmacology, and industry.
It is indicated that such compounds are not well-known because of the low reactivity of
calcium elements, the low solubility of oraganocalcium intermediates and products in
common organic solvents, their instability resulting from their high reactivity, cause
their degradation and the degradation of their preferred ethereal solvents.
Despite the significant difference in electronegativity value between the two elements,
the Ca-Cσ-bonds have a covalent polar character. In many cases, the coordination
considerably decreases the calcium electropositive character, facilitating the formation
of the Ca-Cσ-covalent bond.
The difficulties in synthesizing such compounds, their degradation property and
catalytic behaviour as well as the spectroscopy technics used to identify their structures
are also described.
Calcium Element
Page: 3-19 (17)
Author: Nejib Ben Hussein Mekni and Noureddine Raouafi
DOI: 10.2174/9789815040647122010004
PDF Price: $15
Abstract
In this second chapter, we have grouped the physical and chemical
properties of elemental calcium and calcium cation species as well as their importance
in the human body, especially in the skeleton and cell, as well as their applications in
the chemical, electrical, and biological life fields.
In a nutshell, we describe the history of the organocalcium Ca-Cσ-bond containing
compounds.
Then, we expose the encountered challenges and difficulties in the synthesis of
organocalcium Ca-C containing compounds: before, during and after the
organocalcium preparation and the solutions to overcome these difficulties.
We have grouped the calcium activation methods, the nature of the solvent, the
substrate structure, temperature and the optimal experimental reaction conditions.
Organocalcium (Ca-C) σ-bond Containing Compounds
Page: 20-55 (36)
Author: Nejib Ben Hussein Mekni and Noureddine Raouafi
DOI: 10.2174/9789815040647122010005
PDF Price: $15
Abstract
Compared to other organometallics, the number of organocalcium
compounds and their related publications are limited. In this chapter, we grouped
different Ca-Cσ-bond containing organocalcium compounds described in the literature,
(Alkyl, silyl, cycloalkyl, benzyl, alkenyl, alkynyl, diene, diyne, phenyl, biphenyl,
anthracene, halo thiophene and picoline derivatives) with the specificity for each kind
of compounds. We discuss the stabilizing factors of structures including: conjugation,
hyperconjugation, complexing heteroatom lone pairs and π-bonding electron pairs.
The different synthetic processes used to avoid synthetic problems of substrate and
calcium source reactivity, intermediate and product stability and solubility, reaction
temperature, yields and decomposition reactions of both intermediates and products, as
well as the orientation of the reaction sides in some reactions, are also grouped
(thiophene and picoline derivatives).
The halo aromatic organocalcium compounds are described to be the most stable
intermediates, giving the best yields.
Some calculations that correlate with experimental results are mentioned. Particular
calcium reagents, such as Ca*, CaI2
and particular reactions as well as exchange
(transmetalation) reactions are also examined.
Some examples of the geometrical structures, which give C-Ca-C bent angles, and
bond lengths obtained from X-ray are gathered.
Coordination, Degrading Agent, Catalyst Property and Spectroscopy of Organocalcium Compounds
Page: 56-82 (27)
Author: Nejib Ben Hussein Mekni and Noureddine Raouafi
DOI: 10.2174/9789815040647122010006
PDF Price: $15
Abstract
In addition to the coordination of the calcium to the n electron pairs, some
examples of coordination to the π electron pairs are observed resulting from calcium
interactions with highly conjugated systems. The complex structures vary from
ordinary to close to the unexpected organocalcium inverse sandwich.
The organocalcium Ca-C bond containing compounds are highly reactive. They
degrade and act as degrading agents on the solvent. The study of the effect of five
factors: temperature, concentration, organic group, counter ion and coordinated donor
solvent, shows an intramolecular degradation mechanism. Organocalcium complexes
are more stable in the THP than in the THF ethereal media.
Calcium and organocalcium Ca-Cσ-bond containing derivatives are described as
efficient pre-catalysts for catalytic conversions of alkenes by polymerization,
hydroamination, hydrosilylation, hydrogenation, and hydrophosphination. The
activation process is suggested as an electrostatic interaction between the alkene and
Lewis acidic calcium metallic species, leading to both vertical and horizontal
polarization of the π bond electron density, resulting in an incentive for nucleophilic
attack. Some researchers illustrate that the organocalcium derivatives may be described
as “Trojan horses”
X-ray constitutes the most efficient technique to characterize the organocalcium
structures for crystalized compounds, affording interesting information about angle
values and bond lengths.
The 43Ca, 13C and 1H NMR spectroscopy constitutes an alternative, secondary and
complementary tool for characterizing both soluble, and even insoluble compounds,
monitoring the reaction progress and making specific experimental manipulations.
The coupling constants 1JCa-C, and 2JCa-C-H are not mentioned and there is no mass
spectrometry nor IR spectroscopy studies
Conclusion
Page: 83-85 (3)
Author: Nejib Ben Hussein Mekni and Noureddine Raouafi
DOI: 10.2174/9789815040647122010007
Abstract
Ca-Cσ-bonds containing organocalcium compounds are prepared from
different synthetic methods. Several difficulties and challenges are encountered before,
during and at the end of the reaction.
Organocalcium derivatives are insoluble in common organic solvents and show
degrading properties. Ethers are the solvents of choice and THF gave the best results.
The products are generally ethereal six-coordinated calcium centers (L4CaRX), with a
Ca-C bond length of around 250 pm, depending on many factors.
Arylcalcium derivatives are the easiest to prepare and are more stable than the other
organocalcium compounds because of the conjugation effect phenomena. Ethereal
solvents have a slight influence on the Schlenk-equilibrium type between RCaX or
CaR2
and CaX2
.
Almost all types of the main classes of σ-bond containing organocalcium derivatives
are synthesized. Calcium carbon double bond was never formed.
X-ray analysis is the best technique for the characterization of crystallizable
organocalcium compounds. The 43Ca NMR does not provide interesting information
about the structures. The 13C and 1H NMR data constitute an interesting tool that
contributes the elucidation of the structure of the organocalcium compounds, especially
for the non-crystalized compounds.
Reactivity, chemical behaviour and 13C NMR chemical shift values of organocalcium
complexes exhibit more similarities to the organolithium rather than the
organomagnesium derivatives and were explained on the basis of their comparable
electronegativity values.
Subject Index
Page: 86-91 (6)
Author: Nejib Ben Hussein Mekni and Noureddine Raouafi
DOI: 10.2174/9789815040647122010008
Introduction
This reference describes the chemistry of organocalcium compounds that contain a Ca-C σ-bond. It collects the information about this niche group of organometallic compounds into 4 easy-to-read chapters. It is intended for scholars in the field of organic chemistry, and researchers in industrial chemistry and chemical engineering departments. Key features: - Presents a comparison to homologous compounds of other alkaline earth metals. - Explains the main problems encountered in the synthesis of organocalcium compounds with reference to the reactivity of calcium, the low solubility in common solvents and the high reactivity of the formed intermediates and products - Highlights many concepts about the Ca-C bond such as the steric hindrance, degrading agent properties, organocalcium spectroscopy, and more