Carbon, the XCR3Y Fragment

Among the attempts to synthesize five-coordinate carbon species with a linear XCR3X structure only those by Martin and his coworkers will be mentioned here [38-40]. Eight molecules of type 44 with different counter ions and in different 

The examples presented in this chapter also illustrate a development of the structure correlation method itself. Initially, it was applied to whatever representatives of a specific fragment happened to be available (Cd). Later, directed searches in the CSD [6] led to sometimes surprising new types of correlations (Sn). More recently, compounds have been synthesized in a planned way and their structures determined, so that a specific structural feature or reactivity problem could be studied (Si, B). We have also seen that the methods and interpretations of structure correlation can be applied to results of quantum-chemical calculations. Combinations of kinetic, mechanistic, and computational studies together with structure correlations, are just beginning to illuminate as yet poorly understood problems of chemical reactivity and selectivity, e.g. the factors differentiating between substitutions proceeding with retention or inversion at Si. 

The authors thank Drs. A. Bieniok, D. De Bidder and V. Malogajski for help with CSD searches and with the drawings. This work was supported by the Schweizeri-scher Nationalfonds. 

8 Ligand Rearrangement and Substitution Reactions of Transition Metal Complexes 

Throughout this chapter, reference will be made to techniques and approaches described elsewhere in this book, and a certain familiarity with these topics will be assumed Methods of representing molecular conformation, and different coordinate systems (Chapter 1), ways of dealing with symmetry aspects (Chapter 2), data retrieval from the Cambridge Structural Database (CSD Chapter 3) [3], and multivariate statistical techniques such as principal component analysis (PCA) and cluster analysis (CA Chapter 4). 

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