X—H cr-bonds

Silane complexes were the first species formed solely by coordination of a metal to a CT-bond. The bonding in these complexes was recognized to be imusual and was described as a hydride bridged M-Si bond, instead of the later language of an X-H cr-bond coordinated to a transition metal. The first monomeric example of such a complex was the manganese piano stool complex shown in Figure... 

The observation of a bent Cr-H-Cr bond in the tetraethylammonium salt without an accompanying substantial deformation of the linear architecture of the nonhydrogen atoms in the [Cr2(CO)io(M2-H)] monoanion reflects the inherent flexibility of the bond. The deformability of the[M2(CO)io(M2-H)] monoanion species to adopt an appreciably bent, staggered carbonyl structure was first reported by Bau and co-workers (23) from neutron diffraction studies of two crystalline modifications of the electronically equivalent, neutral W2(CO)9(NO)(m2-H) molecule. Subsequent x-ray diffraction studies (15) of the analogous [W2(CO)io(m2-H)] monoanion found that the nonhydrogen backbone can have either an appreciably bent structure for the bis(triphenylphosphine)-iminium salt or a linear structure for the tetraethylammonium salt, with the W-W separation 0.11 A less in the bent form. Crystal packing forces probably were responsible (15) for the different molecular configurations of the monoanion in the two lattices. In solution, however, all known salts of the [W2(CO)io(m2-H)] monoanion exhibit the same three-band carbonyl ir absorption spectrum char-... 

In the solid state, crystal packing forces should be considered since they can appreciably affect the crystal structure. For example, as previously mentioned, the replacement of the tetraethylammonium cation by the bis(triphenylphos-phine)iminium cation for the [ W2(CO)io(m2-H)] species dramatically changes the solid-state structure of the monoanion. For further insight into the possible influence of packing forces on the nature of the Cr-H-Cr bond in the [Cr2-(CO)io(M2-H)]- monoanion, a neutron diffraction study of the corresponding bis(triphenylphosphine)iminium salt, that has been shown by x-ray diffraction... 

Why should you not also include element-H cr bonds in your list of bonds to make and break Because it is much easier to make and break element-H than other kinds of cr bonds, especially in polar reactions, you will usually make and break the necessary element-H a bonds naturally on the way to making and breaking cr bonds between heavy atoms. After you have made and broken the cr bonds between heavy atoms, if you have not yet arrived at the product, then look at the cr bonds involving H atoms. 

Oxidative additions can occur at all sorts of X-Y bonds, but they are most commonly seen at H-H (also H-Si, H-Sn, or other electropositive elements) and carbon-halogen bonds. In the oxidative addition of H2 to a metal, a d orbital containing a lone pair interacts with the cr orbital of Ik, lengthening and breaking the H-H cr bond. The two pairs of electrons from the metal and the II2 cr bond are used to form two new M-H bonds. C-H bonds can oxidatively add to metals in the same way, and this process, called C H bond activation, is of enormous current interest for its potential applications to petrochemical processing and green chemistry. Si-H, Si-Si, B-B, and other bonds between electropositive elements undergo oxidative addition, too. 

Vol pin and coworkers have developed significant new chemistrywith RCOX-2AIX3 complexes (R = alkyl, aryl X = Cl, Br) as efficient aprotic superacids for isomerizations and transformation of alkanes and cycloalkanes. The systems also promote cleavage of C—C and C—H cr-bonds. These aprotic superacid systems were reported to be frequently more convenient and superior to protic and Lewis acid systems in their activity. 

However the gas phase experiments were performed on X-H---cr hydrogen bonds, for example T-shaped structure for FH- H2 complex was found [22]. The ab initio calculations on that complex were performed up to the MP2/aug-cc-pV5Z... 

Hydrated forms of the hydroxide ion have been much less well characterized though the monohydrate [H302] has been discovered in the mixed salt Na2[NEt3Me][Cr PhC(S)=N-(0) 3]. NaH302.18H20 which formed when [NEt3Me]I was added to a solution of tris(thiobenzohydroximato)chromate(III) in aqueous NaOH. ° The compound tended to lose water at room temperature but an X-ray study identified the centro-symmetric [HO-H-OH] anion shown in Fig. 14.15. The central O-H-O bond is very short indeed (229 pm) and is... 

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