Synthesis of L2AlH (5), LAlEt2 (6), and LAl(NMe2)2 (7).
Reaction of iminophosphonamide 1 with AlH3 3 NMe3 in
2:1 stoichiometric ratio in n-hexane/THF at -78 C
afforded the iminophosphonamide aluminum complex
[Ph2P(NSiMe3)2]2AlH (5) in moderate yield. The 1
H
NMR spectrum of 5 exhibits a broad singlet at 5.1 ppm
assigned to the AlH and two singlets at -0.22 and
-0.13 ppm, which can be assigned to the 36 protons of
the SiMe3 units. The presence of two non equivalent
SiMe3 groups indicates a restricted fluctionality of these
groups at room temperature. In the IR spectrum one
weak absorption for the AlH stretching frequency is
observed at 1853 cm-1
. Compound 6 was prepared as a
white crystalline solid from the reaction of iminophosphonamide
1 with AlEt3 in n-hexane at -78 C. Reaction
of 1 with Al(NMe2)3 in n-hexane at reflux temperature for
6 h afforded the aluminum amide complex 7. Both
compounds are soluble in common organic solvents such
as n-hexane, toluene, and THF. 5 and 7 are stable in the
solid state under an inert atmosphere and are slowly
oxidized and hydrolyzed on exposure to air whereas 6 is
not stable and very sensitive to air. Therefore we were not
able to determine the elemental analysis. 31P NMR
spectra of 6 and 7 exhibit single resonances at 30.3 and
28.6 ppm, respectively. In both compounds the 1
H
NMR and 29Si NMR spectra exhibit only one singlet
for the SiMe3 groups. In compound 7 the 12 protons
correspond to two NMe2 and resonate at 3.06 ppm while
the aromatic protons appear between 7.03 and 7.83 ppm.