Matrix Isolation Studies of Novel Intermediates in the Reaction of Trimethylaluminum with Ozone

Abstract

The thermal reaction of ozone with trimethyl aluminum was explored using twin jet, concentric jet, and merged jet deposition into cryogenic matrixes. Infrared spectroscopy and density functional theory calculations were employed to identify and characterize the products formed in each case. Together, these deposition techniques provide information over the essentially full course of the gas-phase reaction. At short times with twin jet deposition, the primary product is the O atom insertion product (CH)AlOCH. With merged jet deposition and longer gas-phase mixing times, the methyl peroxy radical HCOO· was seen in good yield along with final stable products HCO, HCOH, and CH. Production of AlO and its deposition onto the walls of the reaction tube as a powdery film was noted as well. All of these outcomes were combined to propose a reaction mechanism for this system. Of particular note, the observation of HCOO· provides clear evidence for a free radical component to the overall mechanism.

Theoretical Study of the Mechanism for the Reaction of Trimethylaluminum with Ozone

“…I 3a1 has been reported as an intermediate in the gas-phase reaction of TMA with O 3 in a previous study. 8 Because I 2a1 was much lower in free energy than the initial state (Al(CH 3 ) 3 + O 3 ) by −70.2 kcal/mol, such a dissociation reaction would be the main path in the gas-phase reaction due to the large internal energy, unless thermal relaxation is very efficient. The reaction of the I 3a1 (Al(CH 3 ) 2 (OCH 3 )) intermediate to form Al(CH 3 ) 2 (CHO) + H 2 , which was suggested in the previous experimental study of the gas-phase reaction, 8 S3.…”

“…8 Because I 2a1 was much lower in free energy than the initial state (Al(CH 3 ) 3 + O 3 ) by −70.2 kcal/mol, such a dissociation reaction would be the main path in the gas-phase reaction due to the large internal energy, unless thermal relaxation is very efficient. The reaction of the I 3a1 (Al(CH 3 ) 2 (OCH 3 )) intermediate to form Al(CH 3 ) 2 (CHO) + H 2 , which was suggested in the previous experimental study of the gas-phase reaction, 8 S3. We also examined H abstraction from the CH 3 group by the O 2 moiety, but the activation energy was much higher (19.7 kcal/mol, TS 3e1 ) than for the other two transition states.…”

“…8−12 For the gas-phase reaction of TMA with O 3 , reaction intermediates have been analyzed at a low temperature (35 K) and room temperature, which showed the formation of Al(CH 3 ) 2 (OCH 3 ), Al(CH 3 ) 2 (CHO), CH 3 OO radical, CH 2 O, CH 3 OH, and C 2 H 6 . 8 For the ALD process using TMA and O 3 , the formation of methoxy (Al(OCH 3 )), formate (Al(OCHO)), bicarbonate (Al(CO 3 H)), and hydroxyl (Al(OH)) species has been reported. 9 The authors proposed a reaction mechanism: two methoxy groups react and generate formate, which decomposes into CO and surface OH group at a high temperature or reacts with O 3 to form bicarbonate, and the bicarbonate decomposes to CO 2 and surface OH groups at high temperature.…”

“…About the gas-phase reactions, possible intermediates for the reaction of TMA with O 3 have been examined. 8 Nguyen et al analyzed the mechanisms for the reactions of TMA with molecular oxygen and H 2 O. 17 Despite the previous works mentioned above, the details of the mechanism for the reaction of TMA with O 3 have not yet been revealed.…”

“…To reveal the reaction mechanism involved in the ALD process using TMA precursor, many experimental studies have been reported. − For the gas-phase reaction of TMA with O 3 , reaction intermediates have been analyzed at a low temperature (35 K) and room temperature, which showed the formation of Al­(CH 3 ) 2 (OCH 3 ), Al­(CH 3 ) 2 (CHO), CH 3 OO radical, CH 2 O, CH 3 OH, and C 2 H 6 . For the ALD process using TMA and O 3 , the formation of methoxy (Al­(OCH 3 )), formate (Al­(OCHO)), bicarbonate (Al­(CO 3 H)), and hydroxyl (Al­(OH)) species has been reported .…”