Dihydride chemistry

REACTION OF OsHCI(CO)(P Pr3)2 WITH n-BuLi THE CHEMISTRY OF THE DIHYDRIDE OsH2(CO)(T)2-CH2=CHEt)(P Pr3)2... 

Hydride transfer reactions from [Cp2MoH2] were discussed above in studies by Ito et al. [38], where this molybdenum dihydride was used in conjunction with acids for stoichiometric ionic hydrogenations of ketones. Tyler and coworkers have extensively developed the chemistry of related molybdenocene complexes in aqueous solution [52-54]. The dimeric bis-hydroxide bridged dication dissolves in water to produce the monomeric complex shown in Eq. (32) [53]. In D20 solution at 80 °C, this bimetallic complex catalyzes the H/D exchange of the a-protons of alcohols such as benzyl alcohol and ethanol [52, 54]. 

The absence of any derivatives of selenophene or tellurophene from the chemical catalogues makes their laboratory synthesis an unavoidable point of departure for any study of their chemistry or other properties. As the range of potential organic selenium or tellurium precursors is also extremely restricted, there has been particular emphasis on routes starting from simple inorganic species such as the elements themselves, the dioxides, the halides, the dihydrides and, in the case of selenium, the selenocyanate anion. 

Unlike the Rh-based hydrogenation of a-(acylamino)acrylates, the corresponding Ru chemistry has not been studied extensively. Ru complexes of (S)-BINAP and (S,S)-CHIRAPHOS catalyze the hydrogenation of (Z)-a-(acylamino)cinnamates to give the protected ( -phenylalanine with 92% ee [74] and 97% ee [75], respectively. It is interesting that the Rh and Ru complexes with the same chiral diphosphines exhibit an opposite sense of asymmetric induction (Scheme 1.6) [13,15,56,74,75]. This condition is due primarily to the difference in the mechanisms the Rh-catalyzed hydrogenation proceeds via Rh dihydride species [76], whereas the Ru-catalyzed reaction takes place via Ru monohydride intermediate [77]. The Rh-catalyzed reaction has been studied in more detail by kinetic measurement [78], isotope tracer experiments [79], NMR studies [80], and MO calculations [81]. The stereochemical outcome is understandable by considering the thermodynamic stability and reactivity of the catalyst-enamide complexes. 

Molybdenocene dihalides, associated chemistry, 5, 573 Molybdenocene dihydrides monomeric complexes, 5, 568 multimetallic complexes, 5, 570 protonation studies, 5, 570 Molybdenocenes... 

However, as also observed in germanium chemistry, a mixture of dihydride with an excess of lithiated reagent behaves as a stannyldianion in reactions with organic halides, polyformaldehyde or epoxides (Scheme 7)29, and it thus appears as an interesting synthetic reagent. 

Oxidative addition of H2, alkanes, and silanes to electron-deficient metal species has attracted considerable attention. A continuum exists between nonclassical, or a, complexes such as r] -U2 or the solvated alkane complexes described above and the classical, or fully oxidatively added, species such as dihydrides. Photochemistry represents a major, and in many cases only, source of the reactive intermediates central to this chemistry. As such, detailed studies have been conducted of the reactions of photointermediates with these reagents in a variety of media and phases. The chemistry of dihydrogen and a bonded complexes has been extensively reviewed by Heinekey and Oldham, " Sweany, and Kubas. ... 

The discovery by Kubas of the coordination of dihydrogen without dissociation gave a new impetus to ruthenium hydride chemistry see Dihydrogen Complexes Related Sigma Complexes).As mentioned already in Section 7, considerable progress in NMR and X-ray techniques have allowed better characterization of many compounds and, in particular, better discrimination between a dihydride or... 

Counting the isomers arising by addition to, or substitution in, a basic framework is a mathematical problem with many practical applications in chemistry. In classical organic chemistry, for example, the number of derivatives of a compound was often cited as proof or disproof of structure. Point group theory that uses concepts familiar to most chemists and is easy to apply when the number of addends/substituents is small provides a unified method for deciding, for example, the number of dihydrides C70H2 of fullerene C70, or the number of trihalo-derivatives C2oHi7FClBr of dodecahedrane. All that is needed to determine such matters is the availability of the permutation character. Ter, of the atoms in the parent molecule. 

The corresponding iridium enamide complexes and their alkyl hydride counterparts are much more stable, and a full NMR characterization of the alkyl hydride proved possible in the DIPAMP series. Here, as in the corresponding rhodium chemistry, the presumed dihydride precursor proved to be elusive [31]. By employing a different approach to enamide complexes in which an iridium bis-enamide complex was allowed to react with the diphosphine (Fig. 6) both major and minor enamide complexes could be prepared separately the path to one of them is shown in Fig. 6. The trick was to employ menthyl esters so that stereo-chemically homogeneous Ir complexes were formed. Some additional structural features of the intermediates were derived from detailed NMR analysis, and especially the role of the OMe group in coordinating to iridium trans to the hydride [32]. 

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