Trimethylaluminum

"Trimethylaluminium is the chemical compound with the formula Al₂(CH₃)₆, abbreviated as Al₂Me₆, (AlMe₃)₂ or the abbreviation TMA. Thispyrophoric, colorless liquid is an industrially important organoaluminium compound. It evolves white smoke (aluminium oxides) when the vapor is released into the air."

"Al₂Me₆ exists as a dimer, analogous in structure and bonding to diborane. As with diborane, the molecules are connected by 2 3-center-2-electron bonds: the shared methyl groups bridge between the two aluminium atoms. The Al-C(terminal) and Al-C(bridging) distances are 1.97 and 2.14 Å, respectively.^[1] The carbon atoms of the bridging methyl groups are each surrounded by five neighbors: three hydrogen atoms and two aluminium atoms. The methyl groups interchange readily intramolecularly and intermolecularly."

"3-Centered-2-electron bonds are an utterance of "electron-deficient" molecules and tend to undergo reactions with Lewis bases that would give products consisting of 2-centered-2-electron bonds. For example upon treatment with amines gives adducts R₃N-AlMe₃. Another reaction that gives products that follow the octet rule is the reaction of Al₂Me₆ with aluminium trichloride to give (AlMe₂Cl)₂."