An alternative approach to Al2O2 ring systems by unexpected cleavage of stable Al-F- and Si-O- bonds

The reaction of dimethyl aluminum fluoride (Me2AlF, DMAF) with 2,6-diisopro pylphenol and triethylcitrate, respectively, leads to the products (RO)(6)A l4F2Me4 (R = 2,6-i-Pr2C6H3) (1) and (ROAlFMe)(2) (R = C(CH2COOEt)(2)(COOEt) ) (2), containing Al2O2 ring systems. Both aluminum-mu-oxo fluorides have b een structurally characterized. Fluorine exchange in the reaction of 2,6-di isopropylphenol with DMAF has been monitored using F-19 NMR spectroscopy. T he proposed processes in solution are confirmed by the solid-state structur e of 1. Compound 1 contains four aluminum centers forming three four-member ed ring systems. The two outer cycles consist of bridging-OR groups, wherea s the aluminum atoms in the central cycle are connected via fluorine atoms. Two of the aluminum atoms are 4-fold coordinated, and two are 5-fold coord inated. Compound 1 contains a rare four-membered Al2F2 ring system. Compoun d 2 exhibits a dimeric structure, with oxygen rather than fluorine atoms br idging the aluminum atoms. A further carboxy oxygen atom binds coordinative ly to one aluminum atom in 2. The aluminum atoms are 5-fold coordinated. In search of an alternative approach to synthesizing Al2O2 ring systems, it h as been found that neither DMAF nor trimethyl aluminum (Me3Al, TMA) reacts with (Me3Si)(2)O, whereas the reaction of diisobutyl aluminum hydride (i-Bu 2AlH, DIBAH) with (Me3Si)(2)O leads to (i-Bu2AlOSiMe3)(2) (3). In compound 3 the aluminum centers in the four-membered Al2O2 ring system are only 4-fo ld coordinated. This is the first example of a structurally characterized a luminum product obtained from (Me3Si)(2)O under cleavage of the Si-O bond.