Supramolecular Assemblies of Trinuclear Triangular Copper(II) Secondary Building Units through Hydrogen Bonds. Generation of Different Metal−Organic Frameworks, Valuable Catalysts for Peroxidative Oxidation of Alkanes

Abstract

Formation of the trinuclear triangular copper derivative [Cu3(mu3-OH)(mu-pz)3(EtCOO)2(H2O)] x H2O, 1b (Hpz = pyrazole), has been simply achieved by addition of Hpz to a water solution of Cu(EtCOO)2 x H2O and leaving the resulting solution to crystallize at ca. 12 degrees C. When the reaction and crystallization were carried out at a slightly higher temperature (18-22 degrees C), the compound [Cu3(mu3-OH)(mu-pz)3(EtCOO)2(H2O)], 1c, formed. Single-crystal X-ray molecular structure determinations show that both compounds have analogous trinuclear triangular structures, but very different supramolecular assemblies, due mainly, but not only, to the crystallization molecule of H2O in 1b. In particular, contrarily to the previously reported, strictly related, [Cu3(mu3-OH)(mu-pz)3(EtCOO)2(EtOH)], 1a, the propionate ions in 1b and 1c do not bridge different triangular units, whereas they are involved in intra- and intermolecular H-bonds, generating complex supramolecular 2-D MOFs. Compounds 1a and 1c act as remarkably active and selective catalysts or catalyst precursors for liquid biphasic (MeCN/H2O) peroxidative oxidation of cyclohexane and cyclopentane to the corresponding alcohols and ketones.

Metal–Organic Frameworks: Opportunities for Catalysis

“…Recently, Cu 2+ trinuclear networks showed high activity and selectivity for the peroxidative oxidation of cyclohexane to the corresponding alcohols and ketones (MeCN/H 2 O/HNO 3 media). [79] The structure is based on a stable {Cu 3 (m 3 -OH)(m-pyrazole)} SBU for which the tetracoordinate metal has readily accessible axial sites. Its activity is comparable to that of the best molecular systems, such as copper and iron complexes (32 % yield and turnover number (TON) of 44 h À1 ).…”

Coordination Polymers and Metal Organic Frameworks Derived from 1,2,4-Triazole Amino Acid Linkers

“…Combinations with N-heterocyclic compounds (imidazole, pyrazole, triazole, tetrazole, etc.) were also conducted because of their various binding and bridging modes [26][27][28][29][30][31][32][33]. Not surprisingly, in a short course, biomolecules and natural products like amino acids [34][35][36][37][38][39][40][41][42][43][44][45][46], peptides [47], proteins [46], nucleobases [48], magnesium formates [49], carbohydrates [47], metal glutarates [50,51], γ-cyclodextrin [36] leaped into this mainstream as attractive precursors and soon tributaries like metal-peptide frameworks (MPFs) [47], metal-biomolecule frameworks (MBioFs) [46][47][48] surfaced out and established their niche.…”

CS2 elimination and C–S bond cleavage in [Zn(dmpzdtc)2] – Leading to formation of a cyclic octanuclear complex [Zn4(μ-dmpz)5(μ-OH)(μ3-S)(py)]2·py(dmpzdtc=3,5-dimethylpyrazole-1-dithiocarboxylate, dmpz=3,5-dimethylpyrazolate)

“…The mean Zn-N bond length (2.018(5) Å ) is longer than those in [(mppz) 2 Zn 2 (OCH 2 CH 2 S)] 6 (1.984(2) Å ) and [Zn(l-pz)-(pzH)(O 2 CCH 2 CH 3 )] 2 (1.984(3) Å ) [13]. The average Znl 3 -S bond distance (2.295(2) Å ) is slightly shorter than those observed in [Zn 10 S 4 (SEt) 12 (C 5 H 3 (Me) 3 N) 4 ] (2.306(4) Å ) [14] and (Me 4 N) 4 [S 4 Zn 10 (SPh) 16 ] (2.303(3) Å ) [15]. In the six-membered ZnN 2 ZnN 2 ring, the ZnÁ Á ÁZn contacts of 3.562 Å , is significantly longer than ones in the ZnN 2 ZnO and ZnN 2 ZnS rings (3.198-3.234 Å ), but shorter than that found in binuclear complex [{Zn-(Hdmpz)(dmpz)} 2 (l-dmpz) 2 ] (3.747 Å ) [16].…”

“…Several synthetic approaches to metal pyrazolates, including metathesis reactions of metal ions with pyrazole under the presence of bases [1c,2], oxidation reactions of low-valence metal pyrazolates [3], protonolysis reactions of metal carboxylate complexes with pyrazole [4], and self-assembly reactions from cyclic or polymeric metal pyrazolate complexes [1d,3a,5] have been developed. However, the additional approach, CS 2 elimination of the preformed metal 1-pyrazoledithiocarboxylate complexes, has been less explored [6].…”

“…In this approach, the S 2À ion derived from the C-S bond scission works as a bridging ligand to link metal ions or metal cluster fragments into larger clusters. For example, reactions of [Co(PPh 3 ) 3 Cl] and K 2 S 2 C@C(CN) 2 led to the formation of a pentanuclear cobalt cluster compound [Co 5 (l 3 -S) 4 {l-SC@C(CN) 2 } 2 (PPh 3 ) 4 ] in which the l 3 -S 2À and l-SC@CðCNÞ À 2 were assumed to be derived from the C-S bond scission of ½S 2 ðC@CðCNÞ 2 Þ 2À [9]. Therefore, is it possible to have the CS 2 elimination and C-S bond cleavage take place in a same complex so as to make new sulfide clusters?…”