Hydrides bridging

Hydride-bridged ions of this type are evidently quite stable in favorable cases and can be observed under stable-ion conditions. The Itydride-bridged cyclooctyl and cyclononyl cations can be observed at — 150°C but rearrange, even at that temperature, to methylcy-... 

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]. 

Hydrozirconation of iminoboranes -B=N-R leads to a four-membered ring with a Zr-H-B hydride bridge [209]. 

A number of complexes with carbonyl and hydride bridges have been discussed above and phosphido bridges are discussed below. The most common of the other bridges are sulfur and... 

A DFT study was performed in order to determine the structures of phenylcalcium hydride and its magnesium analog in donor solvents.391 A dimeric phenylcalcium hydride was found to be the most stable species in solution, but monomers or tetramers cannot be excluded at very low or very high concentrations. Hydride bridging is favored over phenyl bridging, and a coordination number of six is predicted to be dominant in solution. 

These authors assumed that the lack of reactivity with the triflate complex is caused by strong binding of the triflate to iridium. Clearly, the tetra-arylborate and the tetra-alkoxyaluminate anions induce the highest rate. When more substrate was added after the reaction had completed and was vented with Ar, the reaction resumed at the same rate with catalysts containing one of the last three anions, whereas the PF6-catalyst had lost all activity. The authors also noted a large difference in the sensitivity to added water. Whereas all catalysts lost some activity upon the addition of 0.05% (v/v) water, the PF6 catalyst completely lost activity. The authors had shown previously that the PF6 catalyst easily forms an inactive trimeric hydride-bridged iridium cluster [88], and it does indeed seem likely that the deactivation proceeds via these clusters. 

Dervisi recently reported similar findings upon treatment of an iridium bis-phosphine catalyst containing a PF6-anion with H2, hydride-bridged dimers and trimers were isolated [90]. 

Alkylaluminum hydrides react with metal hydrides to eliminate RH, and if the metal fragment is bonded to a cyclopentadienyl ring, H2 may also be eliminated to produce a new aluminum-carbon bond, as illustrated in Equations (54)—(57).11,84,83 The hydride-bridged Al-Mo bond in 52 is considerably longer than the direct Al-Mo interaction (294.4(2) vs. 263.6(2) pm).83 A similar reaction with (C5H4R)Co(G2H4)2 yields a mixture of 5382... 

Amongst the hydro-closo-polyborates B H 2- members with n = 6 to 12 are known. All hydro-closo- but also hydro-nido-polyborates act as bases they are, however, not typical Lewis-bases as they miss free electron pairs. However, the negative charge at the hydrogen atoms allows for an interaction with Lewis acids A by formation of hydride bridge bonds (3c2e bonds) ... 

On keeping, this product converted via formal silylene extrusion reaction into the hydride bridged complex 17 ... 

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