Nonclassical hydrides

The iron subgroup exhibits a plethora of nonclassical M H Si interactions both for mono- and dinuclear complexes. Iron in the high formal oxidation states IV and ruthenium in the high formal oxidation states IV-VI are particularly prone to form such species. Some of them having three or more hydrides will be discussed in Section IV. 

The compound [Fe(H)3(SiR3)(CO)(dppe)] (126) features a 7i-accepting ligand (CO), a metal from the first transition series (Fe) with contracted 3d shell, and a high formal oxidation state (IV) all these factors promote the formation of a-com-plexes. In view of this and the nonclassical nature of [Fe(H)2(ri-H2)(PBuPh2)3], the occurrence of a Si-H o-bonding seems very likely. As in 125, equivalent hydrides were observed in the room temperature NMR spectra of 126, with the /(P-H)... 

The combination of steps 1 and 2 corresponds to a 1,2 hydride shift (R = H) or a Wagner-Meerwein rearrangement (R = alkyl). The intermediate bridged nonclassical structure... 

The C—H—C bond is not linear, the angle being about 170° according to high-level MO calculations. Several bridged cycloalkyl carbocations of the type 2 have been prepared [236]. Complexes between a number of alkyl cations and alkanes have been detected in mass spectrometric experiments [235]. The nonclassical structure of the ethyl cation, 3, may be cited as another example of hydride bridging (for a discussion, see ref. 55). 

Core electron spectroscopy for chemical analysis (ESCA) is perhaps the most definitive technique applied to the differentiation between nonclassical carbocations from equilibrating classical species. The time scale of the measured ionization process is of the order of 10 16 s so that definite species are characterized, regardless of (much slower) intra- and intermolecular exchange reactions—for example, hydride shifts, Wagner-Meerwein rearrangements, proton exchange, and so on. 

---