Isolobal theory

The npheld end of the range is marked by white phosphorns P itself that can coordinate to a transition metal either by a vertex atom or with both phosphorns atoms of a common edge bonding to one or two transition metal atoms. It is important to realise that one or more phosphorns atoms in the P tetrahedron can be replaced by an isolobal metal fragment (see Fig. 7.40), with only a moderate downheld shift (for a summary of the isolobal theory see the box story following Chap. 7). 

The isolobal theory, developed by R Hoffman (an excellent account was given by him in the acceptance speech for the Nobel Prize see bibliography), to compare ML cluster fragments from transition metal clusters with CHj and BH cluster fragments from carboranes and boranes has become a very powerful tool to understand the properties and reactivities of main group and transition metal moiehes. 

Other theoretical considerations for synthetic coordination chemistry (isolobal and isoelectronic analogies, chelate, cis and trans effects, factors affecting the acid/ base properties of coordination compounds, bond theories, etc.) are covered in detail in excellent recent monographs [3,34b,104,106] and, for this reason, are not presented in this book. 

It was first demonstrated in exploratory work by the groups of Dahl, Ginsburg, " Sacconi and Huttner that elemental phosphorus can play a role as a ligand for transition metals. These early contributions were followed by extremely successful systematic studies by Scherer and his collaborators, the results of which have been summarized in several review articles. The work was also put into perspective referring to the isolobal principle (CH/P) and to cluster theories. ... 

Non-local density functional theory (DFT) calculations for CpTiCl3 have been performed in order to detail analysis of the metal-Cp bond strength in comparison with the isolobal phosphoraneiminato ligand.4... 

The first two entries are examples of HTMCC with a planar metal framework. In the [AuFe4(CO)i6]" n = 1,2,3) system only the parent monoanion has so far been investigated by X-ray diffraction (Fig. la) whereas the corresponding di- and trianions have only been characterized spectroscopically. The [AuFe4(CO)i6] anion can be considered as a square-planar d Au- + complex stabilized by two bidentate [Fe2(CO)8] ligands, isolobal with diphosphine. Crystal-field theory... 

The set of all these characteristics—the same number of orbitals to be considered, similar symmetry properties, and the same number of electrons—allows us to establish that two fragments are isolobal in the framework of MO theory... 

The H-H and C-H activation reactions at lutetium hydride Cp2LuH and the plausible electronic structure of reaction intermediates have been considered using the theory of isolobal analogy of frontier orbitals [52]. 

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