Synthesis of Aluminum N,N‐Dialkylcarbamates by Insertion of CO₂ into Al−N Bonds

Abstract

Despite decades of research on various carbamates and their important applications, only one aluminum N,N-dialkylcarbamate (ADC) with an aluminum:carbamate ratio of 1 : 3 has been structurally described and comprehensively studied so far, namely tris(diisopropyl)carbamate. The reasons for this situation include problems with the used synthetic routes. The process of CO 2 insertion into AlÀ N bonds of tris(dialkylamido)alanes resolved these difficulties. Using this advantageous synthetic route, the dimethyl and diethyl, as well as the pyrrolidino, piperidino, and N-methylpiperazino derivatives were now successfully prepared. These ADCs were investigated by solid-state NMR spectroscopy, where line-shape analyses of the 27 Al NMR spectra allowed conclusions with respect to the determination of the quadrupole coupling parameters. Furthermore, data of an intermediate during the CO 2 insertion into tris(diisopropylamido)alane were obtained by in-situ IR spectroscopy, which were complemented by NMR measurements of samples periodically taken during the reaction. Partial hydrolysis of tris(pyrrolidino)carbamate revealed a complex Al 3 (μ 3 -O) cluster structure, which was elucidated by single crystal X-ray diffraction.

Syntheses and ligand exchange experiments of N,N-dialkylcarbamate bridged {Al3(μ3-O)}7+ complexes

“…On the one hand, aluminum tris(pyrrolidino)carbamate and aluminum tris(piperidino)carbamate can be prepared and purified according to our previous paper. 29 In this case, the ADC is added to the reaction mixture as a white powder. On the other hand, we found that this purification is not necessary, so that the ADC can be prepared in situ .…”

“…The syntheses and detailed investigations of the two corresponding tris(dialkylamido)alanes (TDAs) and aluminum N , N -dialkylcarbamates (ADCs) were published by us elswhere. 29,56…”

“…Aluminum( iii ) ions with the strong tendency to be in an octahedral coordination sphere often form multinuclear {Al 3 (μ 3 -O)} 7+ complexes, as we have published elsewhere. 29 Comparable crystal structures were shown by Abram et al 30 , Rola-Noworyta et al 31 and Liu et al 32 If this process occurs in a highly ordered fashion, even the formation of metal–organic frameworks (MOFs) becomes possible. 33 There are several MOFs containing oxo-bridged trinuclear aluminum complexes: MIL-96, 34 MIL-100, 35 NH2-MIL-101(Al), 36 Al-soc-MOF-1/Al-soc-MOF-2/Al-soc-MOF-3, 37 PCN-333(Al), 38 Al-soc-MOF-1d, 39 BUT-8(Al), 40 515-MOF, 41 SNNU-5-Al 42 and NU-1501-Al.…”

“…The syntheses and detailed investigations of the two corresponding tris(dialkylamido)alanes (TDAs) and aluminum N,N-dialkylcarbamates (ADCs) were published by us elswhere. 29,56 Preparation of compound (1a) [Al 3 (m 3 -O)(OOC-pyrr) 6 -(pyrrH) 3 ] + [Cl] À . CO 2 was bubbled through a solution of 1.382 g (2.91 mmol) of tris(pyrrolidino)alane in 29.1 mL of benzene under stirring for 20 min (gas flow 40 mL min À1 ), which caused an exothermic reaction.…”

“…Instead of them, carbamate ligands are the bridging ligands in the compounds of this work. The structures are formed by the insertion of CO 2 into the Al-N bonds of tris(dialkylamido)alanes (TDAs), 29,56 which is why the corresponding aluminum N,N-dialkylcarbamates (ADCs) are the reactants for the carbamate bridged {Al 3 (m 3 -O)} 7+ complexes.…”