An Alternative Approach to Al₂O₂ Ring Systems by Unexpected Cleavage of Stable Al−F− and Si−O− Bonds

Abstract

The reaction of dimethyl aluminum fluoride (Me2AlF, DMAF) with 2,6-diisopropylphenol and triethylcitrate, respectively, leads to the products (RO)6Al4F2Me4 (R = 2,6-i-Pr2C6H3) (1) and (ROAlFMe)2 (R = C(CH2COOEt)2(COOEt)) (2), containing Al2O2 ring systems. Both aluminum-μ-oxo fluorides have been structurally characterized. Fluorine exchange in the reaction of 2,6-diisopropylphenol with DMAF has been monitored using 19F NMR spectroscopy. The proposed processes in solution are confirmed by the solid-state structure of 1. Compound 1 contains four aluminum centers forming three four-membered ring systems. The two outer cycles consist of bridging −OR groups, whereas 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 coordinated. Compound 1 contains a rare four-membered Al2F2 ring system. Compound 2 exhibits a dimeric structure, with oxygen rather than fluorine atoms bridging the aluminum atoms. A further carboxy oxygen atom binds coordinatively 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 has been found that neither DMAF nor trimethyl aluminum (Me3Al, TMA) reacts with (Me3Si)2O, whereas the reaction of diisobutyl aluminum hydride (i-Bu2AlH, DIBAH) with (Me3Si)2O leads to (i-Bu2AlOSiMe3)2 (3). In compound 3 the aluminum centers in the four-membered Al2O2 ring system are only 4-fold coordinated. This is the first example of a structurally characterized aluminum product obtained from (Me3Si)2O under cleavage of the Si−O bond.

Non-aqueous synthesis of high surface area aluminium fluoride-a mechanistic investigation

“…We have succeeded in detecting the introduction of the first fluorine atoms with 1 1)-F 1.727(2) A ˚for CN(Al) 5 6 is significantly longer than the Al-F distances 1.674 A ˚and 1.64 A ˚for five and four-fold coordinated Al atoms, respectively. 10 The structure of 2 confirms the reaction sequence given in Scheme 1, i.e., that fluorination starts at the central Al(1) atom of Al[(m-OiPr) 2 Al(OiPr) 2 ] 3 (Scheme 1a). Fluorine then substitutes one of the m-OiPr groups on aluminium (Scheme 1b).…”

New crystalline aluminum alkoxide oxide fluorides: Evidence of the mechanism of the fluorolytic sol–gel reaction

“…The Al-F distances are very close for both types, 1.671(2) and 1.681(2) A ˚, respectively, and are within a narrow range of 1.67-1.69 A ˚for terminal Al-F bonds with five fold coordinated Al. 12,16, 17 The Al-O distances are 1.828-1.853(3) A ˚for the bridging isopropoxide group and 1.785(3) A ˚for the half protonated group. Similar averaged Al-O bond lengths were reported for the isotypical chloride.…”

Methyl Substitution of Aluminum−Hydride Bonds in a Carbaalane and an Aluminum Imide

“…[3] Bis(trimethylsilyl) ether [(Me 3 Si) 2 O] reacts with neat iBu 2 -AlH under reflux conditions to form (Me 3 SiOAliBu 2 ) 2 , while AlH 3 ·NMe 3 does not react under these conditions. [7] However, we found no reaction or significant solubility of [a] 2 S in hot toluene. [8] Treatment of 1 with an excess (ca.…”