Dimethylalane, [Me₂AlH]_n, in the Vapor Phase and in Hydrocarbon Solution:  Gas-Phase Electron Diffraction, Spectroscopic, Colligative, and ab Initio Studies

Abstract

The nature of dimethylalane, [Me 2 AlH] n , in the vapor phase and in hydrocarbon solutions has been reinvestigated experimentally by gas electron diffraction (GED), IR and mass spectrometric, and vapor pressure depression measurements, and also by quantum chemical calculations. The predominant vapor species at low pressures and temperatures near 470 K is the dimer (n ) 2), but at temperatures near 330 K the vapor consists of a mixture of the dimer and a smaller proportion (ca. 30%) of the trimer (n ) 3). The results of the GED measurements have been analyzed, together with those of ab initio calculations, using the SARACEN method to determine the most reliable structures of the doubly hydrogen-bridged dimer, Me 2 Al(µ-H) 2 AlMe 2 , and singly hydrogen-bridged trimer, Me 2 Al(µ-H)Me 2 Al(µ-H

Catalyst Deactivation Processes during 1-Hexene Polymerization

“…dimer from monomer has ΔG = -20.8 kcal mol -1 at 298 K in toluene while the cyclic trimer is the most stable form. From this paper, and based on the calculated enthalpy change for R = Me, which is nearly identical, (Me 2 AlH is also trimeric in solution 53 ) one can estimate that monomeric [Me 2 AlH] ~ 10 -10 M under the conditions studied here.…”

Organocatalytic C−F Bond Activation with Alanes

“…Aluminum hydrides form strongly bridged dimers or oligomers, which is a testament to the electron deficiency of Al III . Aluminum hydride 1 b can exist in different oligomeric forms [Me 2 AlH] n , but the dimer dominates at low concentration in hydrocarbon solution (<0.2 m ) . Therefore, we included only the dimer in DFT studies, not possible higher order oligomers; this also ensures comparability of results in comparison to 1 a , which only exists in dimeric form.…”

List of the participants***

“…It is probable that the distortion of the coordination from tetrahedral at the central zinc atom arises from interligand interactions, which give an approximate C 2 axis through H5⋅⋅⋅Zn1⋅⋅⋅H6. The six‐membered {Zn(μ‐H)} 3 rings are reminiscent of the {Ga(μ‐H)} 3 rings in [(R 2 GaH) 3 ] (R=Me, Et, i Pr, t Bu)25 or [(R 2 AlH) 3 ] (R=Me,26 t Bu27). The structure of 6 can thus be considered as a fragment of polymeric zinc hydride, the growth of which has been restricted by the bulky ligands R. Alternatively 6 may be viewed as a triple ion comprising a central {ZnH 4 } 2− dianion, as found in M 2 [ZnH 4 ] and M 3 [ZnH 4 (H)],9 and two {RZn(μ‐H)ZnR} + cations.…”