Reactions of β-diketiminatoaluminum hydrides with tert-butyl hydrogenperoxide – Facile formation of dialuminoxanes containing Al–O–Al groups

Reversible O-H Bond Activation by Tripodal tris(Nitroxide) Aluminum and Gallium Complexes

Herein, we report the preparation and characterization of the Group 13 metal complexes of a tripodal tris(nitroxide)-based ligand, designated (TriNOx3-)M (M = Al (1), Ga (2), In (3)). Complexes 1 and 2 both activate the O-H bond of a range of alcohols spanning a ∼10 pKa unit range via an element-ligand cooperative pathway to afford the zwitterionic complexes (HTriNOx2-)M-OR. Structures of these alcohol adduct products are discussed. We demonstrate that the thermodynamic and kinetic aspects of the reactions are both influenced by the identity of the metal, with 1 having higher reaction equilibrium constants and proceeding at a faster rate relative to 2 for any given alcohol. These parameters are also influenced by the pKa of the alcohol, with more acidic alcohols reacting both to more completion and faster than their less acidic counterparts. Possible mechanistic pathways for the O-H activation are discussed.

Undirected C-H Bond Activation in Aluminium Hydrido Enaminonates

Two new aluminium hydrido complexes were synthesized by reacting AlH₃ with the enaminone ligand N-(4,4,4-trifluorobut-1-en-3-on)-6,6,6-trifluoroethylamine (HTFB-TFEA) in different molar ratios to obtain mono- and di-hydrido-aluminium enaminonates. Both air and moisture sensitive compounds could be purified via sublimation under reduced pressure. The spectroscopic analysis and structural motif of the monohydrido compound [H-Al(TFB-TBA)₂] (3) showed a monomeric 5-coordinated Al(III) centre bearing two chelating enaminone units and a terminal hydride ligand. However, the dihydrido compound exhibited a rapid C-H bond activation and C-C bond formation in the resulting compound [(Al-TFB-TBA)-HCH2] (4a), which was confirmed by single crystal structural data. The intramolecular hydride shift involving the migration of a hydride ligand from aluminium centre to the alkenyl carbon of the enaminone ligand was probed and verified by multi-nuclear spectral studies (¹H,¹H NOESY, 13C, ¹⁹F, and ²⁷Al NMR).

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

Towards deeper understanding of multifaceted chemistry of magnesium alkylperoxides

Despite considerable progress in the multifaceted chemistry of non-redox-metal alkylperoxides, the knowledge about magnesium alkylperoxides is in its infancy and only started to gain momentum. Harnessing the well-defined dimeric magnesium tert-butylperoxide [(^f5BDI)Mg(μ-η²:η¹-OOtBu)]₂ incorporating a fluorinated β-diketiminate ligand, herein, we demonstrate its transformation at ambient temperature to a spiro-type, tetranuclear magnesium alkylperoxide [(^f5BDI)₂Mg₄(μ-OOtBu)₆]. The latter compound was characterized by single-crystal X-ray diffraction and its molecular structure can formally be considered as a homoleptic magnesium tert-butylperoxide [Mg(µ-OOtBu)₂]₂ terminated by two monomeric magnesium tert-butylperoxides. The formation of the tetranuclear magnesium alkylperoxide not only contradicts the notion of the high instability of magnesium alkylperoxides, but also highlights that there is much to be clarified with respect to the solution behaviour of these species. Finally, we probed the reactivity of the dimeric alkylperoxide in model oxygen transfer reactions like the commonly invoked metathesis reaction with the parent alkylmagnesium and the catalytic epoxidation of trans-chalcone with tert-butylhydroperoxide as an oxidant. The results showed that the investigated system is among the most active known catalysts for the epoxidation of enones.

Aluminum Complexes with Redox-Active Formazanate Ligand: Synthesis, Characterization, and Reduction Chemistry

The synthesis of aluminum complexes with redox-active formazanate ligands is described. Salt metathesis using AlCl₃ was shown to form a five-coordinate complex with two formazanate ligands, whereas organometallic aluminum starting materials yield tetrahedral mono(formazanate) aluminum compounds. The aluminum diphenyl derivative was successfully converted to the iodide complex (formazanate)AlI₂, and a comparison of spectroscopic/structural data for these new complexes is provided. Characterization by cyclic voltammetry is supplemented by chemical reduction to demonstrate that ligand-based redox reactions are accessible in these compounds. The possibility to obtain a formazanate aluminum(I) carbenoid species by two-electron reduction was examined by experimental and computational studies, which highlight the potential impact of the nitrogen-rich formazanate ligand on the electronic structure of compounds with this ligand.

The synthesis of a series of aluminum complexes with redox-active formazanate ligands is described and crystallographic, spectroscopic, and voltammetric characterization data are presented. The reduction chemistry of these newly synthesized complexes has been explored and the results are supported by a computational (DFT) study.

On the non-innocence of “Nacnacs”: ligand-based reactivity in β-diketiminate supported coordination compounds

While β-diketiminate (BDI or ‘nacnac’) ligands have been widely adopted to stabilize a wide range of metal ions in multiple oxidation states and coordination numbers, in several occurrences these ligands do not behave as spectators and participate in reactivity.