Introduction, Scope and Bonding

Three years after the introduction of this series, the editors are pleased to see that the principal aim of providing a forum for the discussion of structure and bonding in complexes, ranging from aspects of chemical physics to biological chemistry, has been achieved. At this point it seems useful to reemphasize the scope of the series. 

The ISO standard clearly differentiates between bonded and unbonded test pieces and in an appendix gives the stress strain relationships, taking account of shape factor. In the scope it is pointed out that comparable results will only be obtained for bonded test pieces if they are of the same shape, and that lubricated and bonded test pieces do not give the same results. There is, however, a very curious little introduction that gives a very narrow view of when compression data is needed and makes a dubious claim about use on thin samples when hardness measurement would be difficult - so is an accurate compression test on thicknesses below 2 mm. 

All animating reagents dealt with in this chapter are listed here references to their preparation are found in the section on Experimental Conditions. Stereochemistry is discussed in the relevant sections of Scope and Limitations. The term animation refers to the formation of a carbon-nitrogen bond, not just to the introduction of an amine group. For a quantum Monte Carlo study of electrophilic animation reagents see ref. 51. 

A more recent example from the Yu group uses alkylboronic acids as aUcyl precursors, which enables a broader product scope and even the introduction of strained cyclopropyl groups [82]. Pyridine directing groups enable the complete ort/io-selectivity in the presence of Ag salts, benzoquinone, and air as oxidants (Scheme 23.19). Interestingly, the protocol can be employed for C-H alkylations of both sp and sp C-H bonds. 

Activation of a C-H bond requires a metallocarbenoid of suitable reactivity and electrophilicity.105-115 Most of the early literature on metal-catalyzed carbenoid reactions used copper complexes as the catalysts.46,116 Several chiral complexes with Ce-symmetric ligands have been explored for selective C-H insertion in the last decade.117-127 However, only a few isolated cases have been reported of impressive asymmetric induction in copper-catalyzed C-H insertion reactions.118,124 The scope of carbenoid-induced C-H insertion expanded greatly with the introduction of dirhodium complexes as catalysts. Building on initial findings from achiral catalysts, four types of chiral rhodium(n) complexes have been developed for enantioselective catalysis in C-H activation reactions. They are rhodium(n) carboxylates, rhodium(n) carboxamidates, rhodium(n) phosphates, and < // < -metallated arylphosphine rhodium(n) complexes. 

The enthalpies of phase transition, such as fusion (Aa,s/f), vaporization (AvapH), sublimation (Asut,//), and solution (As n//), are usually regarded as thermophysical properties, because they referto processes where no intramolecular bonds are cleaved or formed. As such, a detailed discussion of the experimental methods (or the estimation procedures) to determine them is outside the scope of the present book. Nevertheless, some of the techniques addressed in part II can be used for that purpose. For instance, differential scanning calorimetry is often applied to measure A us// and, less frequently, AmpH and AsubH. Many of the reported Asu, // data have been determined with Calvet microcalorimeters (see chapter 9) and from vapor pressure against temperature data obtained with Knudsen cells [35-38]. Reaction-solution calorimetry is the main source of AsinH values. All these auxiliary values are very important because they are frequently required to calculate gas-phase reaction enthalpies and to derive information on the strengths of chemical bonds (see chapter 5)—one of the main goals of molecular energetics. It is thus appropriate to make a brief review of the subject in this introduction. 

This review is written to cover the needs of synthetic chemists with interests in oxidizing alkenes by addition of nitrogenous substituents. Whilst some aspects have been covered in previous reviews (noted in the text), most notably in the Tetrahedron Report No. 144, Amination of Alkenes and prior reviews on aziridines and nitrenes, the present review is the fust conq>ilation of references to the whole range of these particular bond-forming processes. A review by Whitham provides a useful general introduction to reaction mechanisms of additions to alkenes in greater detail than can be covered here. The oxidation requirement excludes from the scope the additions of N H and most additions of N + Metal or N + C. Hence, unmodified Michael and Ritter reactions are excluded. These topics are mostly covered in Volume 4 of the present series. 

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