Thermal fragmentation of the guanidinato aluminum amide precursor [Me2NC(NiPr)2]Al(NMe2)2: An investigation of reactive species by matrix-isolation FTIR spectroscopy and time-of-flight mass spectrometry

The gas-phase thermolysis of the guanidinato aluminum amide precursor [Me2NC(NiPr)2]Al(NMe2)2 (1) in the oven temperature range of ambient temperatures to 600 °C has been investigated with matrix-isolation FTIR spectroscopy and time-of-flight mass spectrometry (argon as carrier gas). Precursor 1 fragments above 300 °C to form iPrCNCiPr (2) and monomeric Al(NMe2)3 (3m). Independent thermolysis series with 2 and the aluminum amide dimer 3d, [Al(NMe2)3]2, were conducted and been used to interpret the results of the fragmentation of precursor 1. Compound 3m was present in the thermolysis range of 350–450 °C and has been identified for the first time. Through a comparison of measured FTIR spectra with the calculated spectrum of 3m (D3 point group symmetry; B3LYP/6-31G(d) level of theory) all expected IR bands were found and could be assigned to normal modes. At thermolysis temperatures of ⩾500 °C signals indicative for H2CNCH3 (4) were found, showing that 3m fragments further at higher temperature. The thermolysis product 2 (iPrCNCiPr) withstands the higher thermolysis temperatures. From our study one can conclude that precursor 1 cleanly delivers the monomeric aluminum alane 3m, which then acts as the reactive material forming species.

Graphical abstractThe guanidinato aluminum amide precursor 1 cleanly produces the reactive intermediate Al(NMe2)3 in gas-phase thermolyses. This monomeric aluminum amide was characterized in argon matrices by matrix-isolation FTIR spectroscopy supported by DFT calculations.Figure optionsDownload full-size imageDownload as PowerPoint slide