Dihydride state

Besides the dihydrides stated above there was another type of hydrocarbons disappearing as fast as component / of the dihydrides. These hydrocarbons have a common chemical formula of C2 +iH , with m = 1, which are plausibly associated with cumulenes of a form of C=C=(C=C=) iC , the four electrons to be attacked one by one by incoming hydrogen atoms. 

A qualitative approach will possibly be more fruitful. Fig. 12 illustrates how the dihydrogen addition step (late with respect to heavy atom locations, early with respect to dihydrogen) might appear for the two diastereomeric pathways of the 16-electron route, with CHIRAPHOS as the ligand. In the alternative 14-electron route, dissociation of the alkene is assumed to occur, followed by irreversible H2 addition. The process in then consummated by reformation of the alkene-rhodium bond, or by a sigma bond metathesis which bypasses the dihydride state. 

At least five types of hydrogen adsorption states on platinum electrodes have been postulated. These are the so-called strongly bound hydrogen, the weakly bound hydrogen, the on-top hydrogen, the dihydride state, and the sub-surface state. Most of these can be detected by cyclic voltammetry and characterized at single crystal electrodes [37-42]. 

MHD2 would, in its turn produce HD. The only way in which HD formation from MHD2 could be avoided would be if the trihydride were in a sense asymmetric, with one M-H bond chemically distinct from the other two and hence unable to reductively-eliminate H2 with either of the other M-H bonds. It is not difficult to envisage such a situation brought about by stereochemical restrictions. However, such a species is without precedent in simple chemical systems. It seems more likely that the observations with the various dihydrogen isotopomers dictate that only a dihydridic state is produced. Point (ii) demonstrates that any metal hydride is not involved in a protolytic equilibrium as shown in Equation (15), or at least that this exchange process is slow. 

In the previous Sections, bulk specimens were alloyed with hydrogen from the gas phase. It was interesting to see whether hydrogen affects the mechanical properties of titanium in a similar way if metal is in a powder state and hydrogen is introduced by mechanical mixing of the metal powder with titanium dihydride, or the interparticle boundaries axe an insurmountable obstacle for hydrogen an eliminate the effects observed in bulk specimens. 

Certain dihydrides of main-group and transition metals are good precursors for metal polysulfides. The reactions of the dihydrides with Ss proceed without a change in the oxidation state of the metals. 

The detailed decomposition (P-H ehminahon) mechanism of the hydrido(alkoxo) complexes, mer-crs-[lr(H)(OR)Cl(PR 3)3] (R = Me, Et, Pr R = Me, Et H trans to Cl) (56, 58, 60), forming the dihydrides mer-cis-[lr H)2Cl PR )2] (57, 59) along with the corresponding aldehyde or ketone was examined (Scheme 6-8). The hydrido(ethoxo) as well as the hydrido(isopropoxo) complexes 60 could also be prepared by oxidative addition of ethanol and isopropanol to the phosphine complexes 39 [44]. In the initial stage of the P-H elimination, a pre-equiUbrium is assumed in which an unsaturated pentacoordinated product is generated by an alcohol-assisted dissociation of the chloride. From this intermediate the transition state is reached, and the rate-determining step is an irreversible scission of the P-C-H bond. This process has a low... 

Similarly to the Ti atom, the singlet state of HfH2 undergoes barrierless coordination of ethylene to make a metallacyclopropane dihydride. Both structural and NBO metrics strongly suggest that we should describe this complex as a simple metallacycle. The characteristics of this class seem to be well represented by the TiC2H4 prototype. 

Lekishvili N., Samakashvili Sh. Reactions of polyaddition of dihydride siloxanes to diallyl- silazanes new approaches. Proceedings of Tbilisi State University, 360, 19-23 (2005) (Geo.). 

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