Aluminum Alkyl Complexes Supported by Bidentate N,N Ligands: Synthesis, Structure, and Catalytic Activity for Guanylation of Amines

Abstract

The reactions of AlMe3 or AlEt3 with 2-pyridyl- or indolyl-substituted imines were studied, leading to the formation of different organoaluminum complexes. While the reactions of the iminopyridine Cy­[NCMe-2-(C5H4N)]2 (L 1 ) derived from 1-(pyridin-2-yl)­ethanone and trans-1,2-cyclohexanediamine with AlEt3 gave the aluminum complex Cy­[NC­(Me)­(Et)-2-(C5H4N)­AlEt2]2 (1), in which the two ketimine groups of the ligand were transformed into the amido functionality through the addition of two ethyl groups, the reaction of L 1 with AlMe3 afforded the aluminum complex Cy­[NC­(CH2)-2-(C5H4N)­AlMe2]2 (2) via a sp3 C–H activation with elimination of two methane molecules. The reactions of indolyl-2-aldimines (2-(RNCH)­C8H5NH (R = t Bu (L 2 H), C6H5 (L 3 H), 2,6-Me2C6H3 (L 4 H)) with AlMe3 or AlEt3 afforded only the deprotonated indolyl aluminum complexes [2-(RNCH)­C8H5N]­AlMe2 (R = t Bu (3), C6H5 (4), 2,6-Me2C6H3 (5)) and [2-(2,6-Me2C6H3NCH)­C8H5N]­AlEt2 (6), respectively. The structures of complexes 2–6 were characterized by spectral methods and X-ray crystallographic analyses. These aluminum complexes showed a high catalytic activity in the addition of amines to carbodiimides to form guanidines. The mechanism of the catalytic process was studied by control experiments and 1H NMR monitoring. Together with the isolation of the complex [2-(2,6-Me2C6H3NCH)­C8H5N]­[CyNC­(4-MeC6H3N)­(NHCy)]­AlMe (7), a probable mechanism for the guanylation reaction was proposed.

Novel aluminium compounds derived from Schiff bases: Synthesis, characterization and catalytic performance in hydroboration

“…The Al←N coordinate bond (1.996(3) Å) is slightly shorter than that in compound 1 . The Al─N single bond (1.874(3) Å) is significantly shorter than the Al←N coordinate bond, and both are slightly longer than those in [Cy[NC(CH 2 )‐2‐(C 5 H 4 N)AlMe 2 ] 2 ] (1.861(1) Å for Al─N and 1.973(1) Å for Al←N), respectively. The N(2)═C(3) (1.296(4) Å) double bond is much shorter than and distinct from the N(1)─C(4) single bond (1.460(4) Å).…”

Ligands with Two Monoanionic N,N‐Binding Sites: Synthesis and Coordination Chemistry

“…The protio ligands are readily accessible by reducing the related bis(iminopyridine)s with NaBH 4 . Although aluminum complexes, which were accessed by reacting the related bis(iminopyridine)s with trialkyl aluminum, were characterized as type E complexes by X‐ray diffraction, for platinum this coordination mode was proposed based on computational calculations . Notably, most of the complexes incorporating bis(aminopyridine)s belong to mononuclear coordination complexes of type F in which the ligand remains in its neutral protonated form, thus being beyond the scope of this review…”

Recent Developments on the Use of Group 13 Metal Complexes in Catalysis

“…For instance, the high affinity of aluminum and silicon for fluorine was recently exploited through the use of Al(C 6 F 5 ) 3 as catalyst for cross‐coupling of silylalkynes with aliphatic fluorides RF . A dinuclear aluminum iminopyridine complex ( 31 , Scheme ) was found to effectively catalyze the addition of amines to carbodiimides to afford guanidines . A related aluminum iminopyridine pincer complex and its next generation improvement, a bispyrazolypyridine compound ( 32 and 33 , Scheme ), can be employed as active catalysts for the electrocatalytic evolution of dihydrogen.…”