A pentanuclear yttrium hydroxo cluster as an oxidation catalyst. Catalytic oxidation of aldehydes in the presence of air

Abstract

The air- and moisture-stable pentanuclear yttrium cluster H(5)[Y(5)(mu(4)-O)(mu(3)-O)(4)(mu-eta](2)-Ph(2)acac)(4)(eta](2)-Ph(2)acac)(6)](Ph(2)acac = dibenzoylmethanide) has been used as a homogeneous catalyst for the oxidation of aldehydes to the corresponding carboxylic acids in the presence of air.

Rare‐Earth Metal Oxo/Hydroxo Clusters – Synthesis, Structures, and Applications

“…We and others have established the synthesis of pentanuclear lanthanide hydroxo clusters by treatment of the trichlorides of the smaller lanthanides [LnCl 3 ·(H 2 O) n ] (n = 6, 7) with dibenzoylmethane (Ph 2 acacH) in organic solvents in the presence of an organic base such as triethylamine or KOtBu. Another route to these compounds is by treatment of [Ln(Ph 2 acac) 3 10 ] (Ln = Y, [10] Nd, [49] Eu, [50][51][52][53] Tb, [52] Dy, [54] Ho, [53] Er, [49,55] Yb; [49] Scheme 3), in which the lanthanide atoms build up a square pyramidal scaffold by occupying its vertices (Figure 6), were obtained. In each of these structures, the square base face of the pyramid is capped by one μ 4 -oxygen atom, whereas its four triangular faces are capped by one μ 3 -oxygen moiety each.…”

“…[37] Beside the usage of alkoxides as ligands, such pentanuclear cluster compounds with other ligands, such as dibenzoylmethane and functionalized versions of it, are also known. [10,[49][50][51][52][53][54][55] According to Evans et al, the reaction between europium metal and 2,6-diisopropylphenol in propan-2-ol leads to the formation of pentanuclear complex H 5 [Eu 5 O 5 (OC 6 H 3 iPr 2 -2,6) 6 -(NCCH 3 ) 8 ] after recrystallization from acetonitrile. [56] This mixedvalence compound features the known square pyramidal cluster core with four Eu II ions at the basal positions and one Eu III ion at the apex.…”

“…[41] The use of tyrosine as an ancillary ligand prevents complete hydrolysis, a process that would otherwise lead to the formation of intractable metal hydroxides and/or oxides. As a result, Zheng et al reported the isolation of a finite-sized pentadecanuclear cluster core surrounded by 10 tyrosine ligands -[Eu 15 (Cl)(μ 3 -L-Tyr) 10 (μ 3 -OH) 20 (LTyrH = L-tyrosine). [41] Zheng et al and others also demonstrated that the use of an ancillary ligand is mandatory, because preventing the cluster core from undergoing further hydrolysis is the most important step in the controlled hydrolysis approach.…”

“…[7][8][9] Furthermore, rare-earth metal clusters have been applied in catalytic processes or as precursors for lanthanide-based oxide materials. [10,11] The term "cluster" was originally used for the description of compounds containing several metals connected by metal-to-metal bonds. [12] Today the term is also used for compounds in which several reasonable scales have been established.…”

“…Recent work has demonstrated that a rational approach towards polynuclear complexes of these kinds is possible. [3,10,[25][26][27][28][29][30][31][32][33][34][35][36] Basically, two different approaches to the preparation of oxo/hydroxo clusters have been investigated.…”