Reactions of AlR₃ (R = Me, Et) with H₂NCH₂CH₂NMe₂:  Synthesis and Characterization of Amido- and Imidoalanes

Abstract

The reactions of R3Al (R = Me, Et) with N,N-dimethylethylenediamine (DMEDA) in a 1:1 molar ratio produce adducts, R3Al·NH2C2H4NMe2 (1a, R = Me; 1b, R = Et), which upon heating in refluxing toluene result in alkane elimination to afford the chelated monomers (2a, R = Me; 2b, R = Et), respectively. Compounds 2a,b form adducts with 1 equiv of R3Al through the 3-coordinate nitrogen atom to produce (3a, R = Me; 3b, R = Et), which can be alternatively prepared by the reaction of R3Al with DMEDA in a 2:1 molar ratio by alkane elimination at room temperature. Thermolysis of 3a,b at 140 °C in sealed ampules produces a mixture of cis and trans isomers of tetrametallic imidoalanes, (4a, R = Me; 4b, R = Et). Slow recrystallization of the isomeric mixture affords crystals of only the cis isomer for both 4a and 4b, but in solution cis-4a and cis-4b equilibrate with the respective trans isomers. The cis → trans isomerization of 4a has been studied by 1H NMR spectroscopy. The equilibrium has been observed to follow reversible first-order kinetics with ΔH° = 1.67 ± 0.60 kJ mol-1 and ΔS° = 9.07 ± 2.80 J mol-1 K-1. The activation parameters for the cis → trans conversion are ΔH 1 = 125.8 ± 9.3 kJ mol-1 and ΔS 1 = 89.7 ± 1.2 J mol-1 K-1, and those for the reverse process are ΔH - 1 = 124.2 ± 9.3 kJ mol-1 and ΔS - 1 = 80.7 ± 1.2 J mol-1 K-1. Pyrolysis of 4a,b in the presence of 2 equiv of DMEDA at 190 °C in sealed ampules gives hexameric imidoalanes, (RAlNC2H4NMe2)6 (5a, R = Me; 5b, R = Et), by alkane elimination. Compounds 5a,b can be also prepared by pyrolysis of 2a,b under similar conditions, but in lower yields. The molecular structures of cis-4b and 5b have been determined by single-crystal X-ray diffraction. The molecular geometry of cis-4b involves one four-membered Al2N2 ring and two five-membered AlN2C2 rings of cis conformation, and it has approximate C 2 symmetry with the C 2 axis going through the center of the Al2N2 ring. The hexameric imidoalane 5b consists of a hexagonal prism of the (AlN)6 cage formed by two flat six-membered (AlN)3 rings linked together by six transverse Al−N bonds.

Synthesis of a Hexadentate Hexameric Aluminum Imide and Its Metathesis Reactions

“…A thorough literature search for this type of compounds was done and we found that a hexameric aluminum imide with six NMe 2 groups has been reported. [2] Treatment of 2 with SiMe 3 Br or SiMe 3 Cl in toluene under refluxing conditions resulted in the formation of compounds [BrAlNCH 2 (C 4 H 3 S)] 6 (3) and [ClAlNCH 2 (C 4 H 3 S)] 6 (4), respectively. In a similar way, PhCϵCH reacts with 2 to give [PhCϵCAlNCH 2 (C 4 H 3 S)] 6 (5) and evolution of H 2 (Scheme 1).…”

“…In our continuing efforts to synthesize functionalized aluminum imides, which can act as potential complexation agents, we have treated 2-cyanothiophene with AlH 3 ·NMe 3 . Herein we report the synthesis and metathesis reactions of an aluminum imide containing six thiophene groups, [HAlNCH 2 (C 4 H 3 S)] 6 (2).…”

“…[1a, 2,8] Compound 3 crystallizes in the cubic space group Pa3 with one sixth of the molecule in the asymmetric unit. An ORTEP plot depicting the spatial arrangement of the atoms in compound 3 is shown in Figure 2.…”

Synthesis and structure of tetrakis(isopropylimino)bis-[tris(dimethylamino)silylamino]alane

“…Since AlH groups are capable of hydrogen elimination reactions with NH groups, a hybrid pre-ceramic precursor for Al-Si-C-N nanocomposites has been prepared by the reaction of (HAlN i Pr) 6 with a ring-type [MeSi(H)NH] n , but no structure of the precursor molecule was reported. [3] Although many cage-type compounds containing the (AlN) 6 skeleton such as (HAl-NCH 2 R) 6 (RAlNR 0 ) 6 (R 0 = C 2 H 4 NMe 2 ) have been prepared [8,9] no cage-type molecule containing (AlN) 6 skeleton coordinated with silylamino groups has been reported to date.…”

Fluorine functionalized compounds of group 13 elements

“…Compounds containing Al-N bonds are important due primarily to their various applications as reducing agents [40], important synthetic intermediates [41,42] and as precursor for chemical vapour deposition of aluminum nitride [43]. This class of compounds containing Al-N bonds also incorporate aluminum imide clusters which are oligomeric in nature and are of the composition (RNAlH)n (n = 4, 6, or 8) [44][45][46].…”