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

Abstract

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.

Dinuclear Complexes of Flexidentate Pyridine‐Substituted Formazanate Ligands

“…[1][2][3] Formazanates have garnered considerable attention in coordination chemistry due to their ligand-based redox processes, which may facilitate multielectron redox transformations, [4] bond activations [5] and excited-state charge separation. [6] Av ariety of formazanate complexes of many main-group metals [7][8][9][10][11][12][13][14][15][16] andf irst-and second-row transition metals [17][18][19][20][21][22][23] have been described.T hese studies demonstrate the versatile coordination chemistry of formazanate ligandsa nd provides ignificant insight into the opticala nd redox properties of these compounds.S ome coppercomplexesc an also mediate oxygen activation, [24,25] certain cobalt and iron complexes exhibit unique magnetic characteristics, [17,26] and boronc omplexes in many cases feature not only the tunable redoxp roperties but also visible to nearinfrared photoluminescence, [9][10][11][12][13] finding applicationsa sc ellimaging agents [27,28] and electrochemiluminescence emitters. [10] Our group has expanded the coordination chemistry of formazanatest ot hird-row transition metals with as eries of hetero-leptic cyclometalated platinumc omplexes and bis-cyclometalated iridium complexes, [29][30][31] and accessed homoleptic azo-iminate platinum complexes and azo-1,2,3-triazolide iridium complexesv ia hydrogenative cleavage or [3+ +2]...…”

Formazanate coordination compounds: synthesis, reactivity, and applications

“…More recently, Mondol and Otten conducted a study that led to the dramatic expansion of the structural diversity of aluminum formazanate complexes, including the first isolated examples of ligand-supported radical anions and dianions derived from aluminum formazanates. 96 Their work began with the synthesis of tetrahedral AlR 2 complexes (R = Me, Et) that were similar to those reported by Sundermeyer and co-workers. 94 Treatment with one equivalent or excess I 2 resulted in the asymmetrically substituted AlMeI and AlEtI complexes, respectively.…”

“…(b) Synthesis of diphenyl aluminum complex 84 and its conversion to radical anion 84 À , dianion 84 2À , and aluminum diodide complex 85. The attempted conversion of compound 85 to Al(I) carbenoid 86 and the structure of b-diketiminate complex 87 are also included to supplement the discussion above 96.…”

Structure and bonding in reduced boron and aluminium complexes with formazanate ligands

“…The two-electron reduced formazanate aluminium diphenyl compound [PhNNC( p-tol)NNPh]AlPh 2 2− (2 2− ) was synthesized as its disodium salt according to a previously published procedure. 31 The product 2 2− , which has an electron-rich, formally trianionic formazanate ligand, is highly air-sensitive, but stable at room temperature under inert conditions. The 1 H NMR spectrum of 2 2− in THF-d 8 was shown to be temperaturedependent: at 233 K, the spectrum shows 5 inequivalent resonances due to the N-Ph groups.…”

“…Previously, we showed that the ligands in boron and aluminum compounds with formazanate ligands could be sequentially reduced by 1-and 2-electrons at moderate reduction potentials (Scheme 1). 30,31 The 2-electron reduced formazanate boron compound (1 2− ) subsequently reacted with electrophiles (E + ) such as benzyl bromide (BnBr) and water (H 2 O) to form ligand-benzylated and -protonated products ( Bn 1 − and H 1 − in Scheme 1). 32 In these compounds, the formazanate ligands are modified by the 'storage' of [2e − /E + ], which could be converted to Bn • and H • radicals by the homolytic cleavage of the N-C (Bn) and N-H bonds, respectively (Scheme 1).…”