Polyoxometalate-Assisted, One-Pot Synthesis of a Pentakis[(triphenylphosphane)gold]ammonium(2+) Cation Containing Regular Trigonal-Bipyramidal Geometries of Five Bonds to Nitrogen

Abstract

Novel intercluster compounds consisting of pentakis[(triphenylphosphane)gold]ammonium(2+) cation (1) and Keggin polyoxometalate (POM) anions, i.e., {[Au(PPh)](μ-N)}[α-PMO] (1-PW for M = W; 1-PMo for M = Mo), were synthesized in 30-36% yield by one-pot reaction of the protonic acid form of the Keggin POMs, H[α-PMO]·nHO (n = 13 for M = W; n = 15 for M = Mo) with monomeric (triphenylphosphane)gold(I) carboxylate [Au(RS-pyrrld)(PPh)] [RS-Hpyrrld = (RS)-2-pyrrolidone-5-carboxylic acid] in the presence of aqueous NH at a molar ratio of 2:15:x (x = 3 for 1-PW; x = 7.5 for 1-PMo). These compounds resulted from the nitrogen-centered phosphanegold(I) clusterization of in situ generated monomeric phosphanegold(I) units, [Au(PPh)] or [Au(L)(PPh)] (L = NH or solvent), during the carboxylate elimination of [Au(RS-pyrrld)(PPh)] in the presence of the Keggin POMs and aqueous NH. The products 1-PW and 1-PMo were characterized by elemental analysis, Fourier transform infrared, thermogravimetric and differential thermal analyses (TGA/DTA), X-ray crystallography, and solid-state cross-polarization magic-angle-spinning (CPMAS) (P and N) and solution (P{H} and H) NMR spectroscopy. The lattice contained three independent {[Au(PPh)](μ-N)} cations, of which two took regular trigonal-bipyramidal (TBP) geometries and the third took a distorted, square-pyramidal (SP) geometry. These geometries are in contrast to those reported by Schmidbaur's group for {[Au(PPh)](μ-N)} cations as BF salts. Density functional theory and ONIOM calculations for {[(LP)Au]N} (L = H or Ph; n = 4-6) showed that the pentacoordinate cluster is energetically most stable and its TBP structure is only 1.6 kcal mol more stable than its SP structure, in accordance with the experimental facts.

Innovative Molecular Design Strategies in Materials Science Following the Aurophilicity Concept

“…Extreme cases exhibiting the enormous influence of aurophilic attractions and its directional flexibility are found in the structural characteristics of main-group element-centered cations {[(L)­Au] n E} m + , with E = O, S, N, P, As and C and L = R 3 P and RNC. Significant variations in the structures of the E-centered multigold cations have been achieved by modifying the anions and the substituents R on the tertiary phosphine ligands. − However, recent studies have shown that rigid and voluminous anions such as polyoxometallates as counterions have an even more drastic effect on the conformation of the cations. , Tetrahedral tetragoldoxonium dications found with innocent anions like tetrafluoroborate are transformed into trigonal pyramidal structures which have an entirely different pattern of aurophilic contacts. In a similar way, trigonal bipyramidal pentagoldammonium dications are distorted to square-pyramidal forms with more intimate intracationic Au···Au contacts.…”

When Gold Cations Meet Polyoxometalates

“…extended the chemistry of gold‐POM SICCs with two electronic deficient species based on gold ammonium clusters. The reactions of 7.5 equiv of [Au(PPh 3 )( R , S )‐pyrrld)] solubilized in a mixture of DCM‐methanol, with 1.5 equiv of aqueous ammonia, and 1 equiv of [H] + 3 [α‐PMo 12 O 40 ] 3− or [H] + 3 [α‐PW 12 O 40 ] 3− contained in a layer of methanol afford the SICCs [{Au(PPh 3 )} 5 ( μ 5 ‐N)] 2+ 3 [α‐PW 12 O 40 ] 3− 2 ( 39 ) or [{Au(PPh 3 )} 5 ( μ 5 ‐N)] 2+ 3 [α‐PMo 12 O 40 ] 3− 2 ( 40 ) with 32.3 or 30.2 % yields, as crystals with the P space group symmetry (Figure ) . Both compounds are isomorphic and best described by ( 39 – 40 ) ⋅ 2 DCM.…”

“…Both geometries relate to the compound [{Au(PPh 3 )} 5 ( μ 5 ‐N)] 2+ [BF 4 ] − ⋅ x DCM (with x ≥0) reported by Schmidbaur et al. which has ammonium gold clusters with D 3 h or C 4 v symmetry, depending on the presence of co‐crystallized molecules of DCM . The 31 P NMR spectra of 39 – 40 are virtually identical to those of SICCs with gold‐oxonium clusters.…”

“…[25] Recently, Nomiya Figure 7). [27] Both compounds are isomorphic and best described by (39)(40)·2DCM. Their unit cells contain two crystallographically-independent [{Au(PPh 3 )} 5 (m 5 -N)] 2 + clusters.…”

Discovery of a New Family of Polyoxometalate-Based Hybrids with Improved Catalytic Performances for Selective Sulfoxidation: The Synergy between Classic Heptamolybdate Anions and Complex Cations

“…One is to combine POMs with organic bases, such as metal–organic frameworks (MOFs), graphene, cyclodextrin, etc. − POM units were located in the cavities of these materials, and these kinds of POM materials are normally harsh in synthesis and complicated in process. , Another way is to combine organic parts with anion clusters of POMs by covalent bonds, but only a few reaction types of modification of the POMs have been developed so far. − The last approach is to develop an organic–inorganic hybrid by introducing functionalized cations. This approach not only ensures the stability and reliability of the material but also introduces the functional type and diversity of organic parts. − Toward the design of a POM hybrid with improved catalytic performance, the synergy has been extensively studied in the field of POM catalysts, while the most reported studies were focused on the synergy between POMs and substrates, such as MOFs, , and the synergy between the same metals in different valence states. − However, when the complex cations were utilized in POM synthesis, most of the previous studies focused on structural decentralization of the POM units, and some attention has been paid to the synergistic effect between POM anions and cations. − Although the intrinsic interaction between the POM anions and complex cations is very similar to that in the POM–MOF system, the latter could also contribute to the catalytic performance improvements and provide a simpler model in catalytic mechanism studies.…”