Organoaluminum Compounds Containing Multiple Bonds

While efforts purporting the isolation of organoaluminum compounds containing an Al-Al bond may be traced back to the 1960s,1-4 these reports presented 

Copyright 2001 by Academic Press. All rights of reproduction in any form reserved. 

In an attempt to approach a measure of tt-bonding in the Al-Al bond Uhl et al. examined the alkali metal reduction of tetrakis[bis(trimethylsilyl)methyl]dialane. Sodium or potassium reduction of [(Me3Si)2HC]2Al—Al[CH(SiMe3)2]2 in di-methoxyethane (DME) produced dark blue radical monoanions of [(Me3Si)2 HC]2A1—Al[CH(SiMe3)2]2 (Eq. 2).6 

This TT-radical, characterized spectroscopically (ESR, UV-Vis, and IR), displayed remarkable stability. In an interesting side note, similar compounds were isolated by these workers by reaction of tetrakis[bis(trimethylsilyl)methyl]dialane with neopentyllithium or trimethylsilylmethyllithium in the presence of tetra-methylethylenediamine (TMEDA). Structural data were not reported for this interesting compound. 

Coincidentally, another research group was working on the same problem. This team, lead by Porschke, used lithium in combination with TMEDA to reduce the Al-Al bond in [(Me3Si)2HC]2Al—Al[CH(SiMe3)2]2 and afforded an Al-Al one-electron ir-bond in the radical anion [(Me3Si)2HC]2Al—Al[CH(SiMe3)2]2 (Eq. 3).7 

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