Dimethylaluminum hydride

Nickel(O) reacts with the olefin to form a nickel(0)-olefin complex, which can also coordinate the alkyl aluminum compound via a multicenter bond between the nickel, the aluminum and the a carbon atom of the trialkylaluminum. In a concerted reaction the aluminum and the hydride are transferred to the olefin. In this mechanistic hypothesis the nickel thus mostly serves as a template to bring the olefin and the aluminum compound into close proximity. No free Al-H or Ni-H species is ever formed in the course of the reaction. The adduct of an amine-stabihzed dimethylaluminum hydride and (cyclododecatriene)nickel, whose structure was determined by X-ray crystallography, was considered to serve as a model for this type of mechanism since it shows the hydride bridging the aluminum and alkene-coordinated nickel center [31]. 

The carbaalanes [8, 9] possess clusters formed by aluminum and carbon atoms. They represent a new class of compounds which, in some respects, may be compared to the important class of carbaboranes. Usually, they were obtained by the reaction of aluminum alkynides with aluminum hydrides (hydroalumination) and the release of trialkylaluminum derivatives (condensation). The first carbaalane, (AlMe)g(CCH2Ph)5H 3 [10], was synthesized by the treatment of dimethylalumi-num phenylethynide with neat dimethylaluminum hydride. The idealized stoichiometric ratio of the components is given in Eq. (2), which also shows a schematic drawing of the molecular structure. Compound 3 was isolated in the form of colorless crystals in 60% yield. While 3 is only slightly air-sensitive, the less sterically shielded propynide derivative 4, also shown in Eq. (2), is highly pyrophoric [11],... 

The remaining precipitate of zinc dihydride is washed with three 25-mL portions of freshly distilled tetrahydrofuran. This is accomplished by setting stopcock / at position B with valve L open. The 25-mL portions of tetrahydrofuran are added through stopcock / the mixture is stirred for 5 min, with stopcock / in position C the zinc dihydride is allowed to settle and the supernatant liquid is removed via syringe by returning stopcock / to position B. The wash solution is destroyed in the same way as that described earlier for the more concentrated solution of dimethylaluminum hydride. 

Be—C bridge overlap population = 0.35. We shall see below that similar conditions prevail in dimeric trimethylaluminum, in diborane, and in dimeric dimethylaluminum hydride. 

Fig. 4. The molecular structures of dimeric ) (A) and monomeric ) (fl) trimethylaluminum and dimeric dimethylaluminum hydride ) (C) in the gas phase...

Dimethylaluminum hydride is trimeric in hydrocarbon solution at room temperature The gas is dimeric (by molecular wei t) at 167 °C and 55 mm at 83 °C and 56 mm the average degree of association is 2.5 The molecular stmcture of the dimer (Fig. 4) has been determined by gas-phase electron diffraction at a nozzle temperature of about 170 °C Attempts to determine the molecular stmcture of the trimer by recording... 

The structure of dimeric dimethylaluminum hydride is remarkably similar to that of trimethylaluminum dimer. No significant differences ate found between either the Al—A1 and Al—C( bond distances or the < Q—Al—Q angles in the two compounds. The constancy of the Al-Al-distance is most easily rationaUzed if direct bonding is assumed. The Al—H, distance is considerably longer than the (terminal) Al—H bond in H3A1N(CH3)3 =... 

The molecular structure of trimeric dimethylaluminum hydride can only be a matter for speculation. If metal-metal bonding is important, the AI3H3 ring must be planar. This is in reement with the infrared absorption spectmm of dimethylaluminum hydride in cyclohexane ° If the Al—Hb and Al-Al bond distances are equal to those in the dimer, tire < Hb—Al-Hb angle must be 137°. 

Gas-phase reaction pathways of aluminum organometallic compounds with dimethylaluminum hydride and alane as model systems ... 

Figure 7.2. Molecular structure of the dimeric dimethylaluminum hydride by gas phase electron diffraction [21].

C4HnAl2f Dimethylaluminum hydride dimer (gas-ed), 38B, 1061 C4H1gClNaOaS Tl, Thiourea - thallous chlorate, 35B, 791 C4H1gClNsOnS Tl, Tetrakis(thiourea)thallium(I) perchlorate, 32B, 54 C4H16N903SflTl, Tetrakis(thiourea)thalliumd) nitrate, 32B, 54 C4H2 4AI2B11N2, Di-M-ethyleneimino-bis(bis (tetrahydroborato)aluminum), 42B, 580... 

---