Reactions with main group elements

Kulkami. S.A. Intramolecular dihydrogen bonding in main group elements. Connection with dehydrogenation reactions. J. Phys. Chem.. A 1999. 103. 9330. 

This type of transhalogenation reaction, which is common amongst the halides of main group elements, always proceeds in the direction which pairs the most electropositive element with the most electronegative, since the greatest amount of energy is evolved with this combination. 

Reactions of metal halides with polysulfide dianions are useful methods for the synthesis of polysulfido complexes of main group elements and transition metals. In most of these reactions, similarly to other methods, the chain lengths and coordination types of the polysulfide ligands depend on the other ligands coordinated to the metal, on the ratio between the metal and sulfur, on the reaction temperature, and other parameters. 

Two principle strategies have been employed for the synthesis of siloxide-containing molecular precursors. The first involves a silanolysis, or condensation, reaction of the Si - OH groups with a metal amido, alkyl, hahde, or alkoxide complex. The second method involves salt metathesis reactions of an alkali metal siloxide with a metal hahde. Much of our work has been focused on formation of tris(tert-butoxy)siloxide derivatives of the early transition metals and main group elements. The largely imexplored regions of the periodic table include the lanthanides and later transition metals. 

The reactions of 44a,c with benzonitrile and rm-butylphosphaacetylene show that the Si=As bond easily forms [2+2]-cycloaddition products with main-group-element triple bonds.14 However, as in the case of Si=P bonds, the Si=As bond does not react with the C=C triple bond in al-kynes. 

Two approaches have been used in the synthesis of these types of compounds. Small boron-phosphorus ring compounds can serve as building blocks, and addition and elimination reactions with other main group elements can then extend the cage structure (see Schemes 23 and 24, Section 12.12.6.4.5). Alternatively, an unsaturated carbenoid fragment can be added to the bicyclic fragment as illustrated in Scheme 31 <1998IC490>. 

Double-bond compounds containing heavier main group elements are highly reactive to undergo ready addition reactions with various reagents. 

Tin belongs to the long period elements from Rb to Xe and is a main group element because the 4d shell is filled with electrons. Since the valence electrons are 5s2p2, tin occurs in two valences. Whereas valence 2 is formally always positive, valence 4 has amphoteric properties possessing the formal oxidation states +4 or —4, according to the covalently bound substituents and to the reaction partner. 

CAChe 5.0, available in 2002, includes a new, more powerful, semiempirical method that uses the PM5 Hamiltonian, a MOPAC 2002 offering, modeling of molecules with up to 20,000 atoms, the inclusion of all main group elements in one semiempirical method, and using MOPAC AMl-d, supports the transition metals Pt, Fe, Cu, Ag, Mo, V, and Pd. Researchers can now import and display, in 3D, proteins from the Protein Data Bank (PDB), optimize proteins, dock ligands, and model reactions on protein molecules. 

Reactions of stable nucleophilic carbenes with main group element compounds have recently been reviewed Garmalt, C. J. Cowley, A. H. 

In the reaction of group 13 element halides with metal carbonyl dianions, the analysis is more complex than observed for the reactions with metal monoanions. Upon addition of metal dianions to EX3 or REX3, either one or two halide ions may be eliminated. When only one halide ion is eliminated per added metal dianion, the complexes may still be viewed as E3+ derivatives (Equations (33)-(36)).19 This may be controlled to some extent by the stoichiometry of the reaction. Comparison of Equations (33)19 and (34)19 shows that the electron demand at the main group element can be satisfied by coordination either to an electron-rich metal center 26 or formation of a halide bridge 27. Ligand-stabilized forms may also be prepared in this fashion (Equation (36)).19... 

Reactions of Transition Metal-Group 13 Element Complexes with Main Group Element SiMe3 Complexes... 

Pseudorotation is well established in 5-coordinated species involving the main group elements and is best described by the Berry mechanism which interconverts two trigonal bipyramids via a square pyramid. Its operation here is difficult to reconcile with the highly stereospecific nature of substitution in Pt(II). Nevertheless, the mechanism has had substantial support. It may very well be that (a) is favored by polar solvents and that (b) is prevalent in nonpolar media. The associated reaction profiles are shown in Fig. 7.11. 

Structural units of binary polycompounds with main group elements consist of one-, two- and three-dimensional polymers, as well as cage-like polycyclic anions. These polyanions can be converted into molecular compounds by appropriate chemical reactions. 

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