Exploration of the Laser-Assisted Clustering and Reactivity of Trimethylaluminum with and without NH₃

Abstract

This paper provides results concerning the clustering and laser-assisted reactivity in constrained pulsed gas expansions of trimethylaluminum (TMAl) with and without ammonia. In these experiments, TMAl is introduced with just an Ar buffer gas or co-expanded with ammonia into a high vacuum chamber through a dual-source pulsed nozzle assembly. Independent control of individual gas backing pressures is maintained, and the nozzle assembly can be cooled as well. The output of an ArF excimer laser (193 nm) is focused into the mixing and reaction region of the nozzle source, and a quadrupole mass spectrometer (QMS) is used to characterize the expansion products. Both pressure and laser power dependence studies are used to reveal the origins of individual mass spectral features. Under certain conditions, laser irradiation or expanding, neat TMAl results in the formation of (CH3)4 - x H2 - y Al2, where x = 0, 1 and y = 0, 1. During TMAl expansion with NH3, the parent ion signal for the Lewis acid−base adduct (CH3)3Al:NH3 is observed in the gas phase by the QMS. Laser photolysis of the TMAl/NH3 gas mixture produces reactions involving both precursor and adduct molecules. Also, the formation of a new (CH3)3AlNH2 product as a result of NH2 radical reactivity with the (CH3)3Al:NH3 adduct, i.e., (CH3)3Al:NH3 + NH2 → (CH3)3AlNH2 + NH3, is revealed. Diverse higher mass clusters with Al−N bonded nuclei, e.g., (CH3) k Al l (NH2) m (NH) n , have also been observed. Finally, a comparison of aluminum and gallium metal organic species reveals similar propensities for intermolecular association for the two metals.

Scaffold Hopping with Virtual Screening from IP3 to a Drug‐Like Partial Agonist of the Inositol Trisphosphate Receptor

“…The standard Gibbs energies of the highest points of the reaction pathways are 181, 191, 195, and 156 kJ mol −1 for the mono‐ and bimolecular pathways to [MeAlNH] 6 , bimolecular pathway to [Me 9 Al 6 N 6 H 9 ], and AlN bond breaking pathway, respectively. These values are of the same order of magnitude, which suggest that these processes are competitive at 298 K. This conclusion agrees well with the variety of high‐mass species observed upon laser initiated reactivity of Al(CH 3 ) 3 and NH 3 at low temperatures 11. Compared with the monomolecular mechanism, the formation of TS5 a from two molecules of 1 a proceeds with entropy decrease.…”

“…2 In several cases, gas‐phase nanoparticle formation was observed in the CVD of group 13 nitrides 3–10. Mass spectrometry (MS) monitoring of the laser‐assisted gas‐phase reaction between AlMe 3 and ammonia at low (below room) temperatures allowed a diverse range of high‐mass clusters to be detected, including [Me 2 AlNH 2 ] 3 , [Me 9 Al 6 N 6 H 9 ], and [MeAlNH] 6 , which are presumably intermediates in AlN nanoparticle formation 11. However, the gas‐phase chemistry involved in nanoparticle formation is complex and not yet well‐understood.…”

Reaction Temperature and Partial Pressure Induced Etching of Methylammonium Lead Iodide Perovskite by Trimethylaluminum

“…First, our QMS measurements show that although CH 3 NH 3 + is removed from CH 3 NH 3 PbI 3 by TMA at 75 °C, the reaction product is not CH 3 NH 2 (Figure ). As QMS can detect CH 3 I as desorbed byproducts, QMS should be able to detect CH 3 NH 2 if it is a main byproduct as CH 3 NH 2 has a higher vapor pressure (boiling point is −6 °C compared with 45 °C of CH 3 I) and probably higher ionization cross section than CH 3 I. , Although TMA could take a proton from CH 3 NH 3 + as TMA is a strong Lewis acid, the as-formed CH 3 NH 2 will react with other TMA molecules because TMA could coordinate with R–NHx (R: alkyl) to form stable complexes, − including (CH 3 ) 2 AlNHCH 3 ( m / z = 87), (CH 3 ) 2 AlNH 2 CH 3 + ( m / z = 88), (CH 3 ) 3 AlNH 3 ( m / z = 89), (CH 3 ) 2 AlCH 2 I ( m / z = 198), and (CH 3 ) 2 Al­(NH 2 CH 3 ) 2 + ( m / z = 104). Some of these complexes could present in the product layer as QMS did not detect these species (Figure S4).…”

Initial Gas Phase Reactions between Al(CH3)3/AlH3 and Ammonia: Theoretical Study

“…Structures of reactants, products, and transition states for the unimolecular hydrogen/ methane eliminations have been optimized, and thermodynamic characteristics of corresponding reactions have been obtained. It is shown that the first methane elimination from the AlR 3 NH 3 complex is the highest point on the reaction pathway, and the only one lying above the isolated AlR 3 and NH 3 . Subsequent sequential substitution of methyl groups in AlMe 3 by amido groups is exothermic, and despite the larger activation energies of the intermediate steps, the overall reaction profile is rather downhill.…”

“…10,11 Dissociation enthalpy of the donor− acceptor bond breaking in the AlMe 3 NH 3 adduct was measured by solution calorimetry in hexane (115 ± 1 kJ mol −1 ) 12 and in benzene (95 ± 5 kJ mol −1 ). 11 According to Fourier transform infrared (FTIR) spectroscopic studies on the kinetics of the gas phase reaction between AlMe 3 and NH 3 , the activation energy of methane elimination is 107.5 kJ mol −1 . 13 Structural studies revealed trimeric [Me 2 AlNH 2 ] 3 in the solid state with a skewboat conformation of the Al 3 N 3 ring.…”