A water soluble nanostructured platinum (0) metal catalyst from platinum carbonyl molecular clusters: Synthesis, characterization and application in the selective hydrogenations of olefins, ketones and aldehydes

Water-soluble NHC-stabilized platinum nanoparticles as recoverable catalysts for hydrogenation in water

Aromatic compounds have been hydrogenated in water using recoverable catalysts based on water-soluble platinum nanoparticles capped with NHC ligands.

Synthesis of [Pt12(CO)20(dppm)2]2- and [Pt18(CO)30(dppm)3]2- Heteroleptic Chini-type Platinum Clusters by the Oxidative Oligomerization of [Pt6(CO)12(dppm)]2

The reactions of [Pt₆(CO)₁₂]^2- with CH(PPh₂)₂ (dppm), CH₂═C(PPh₂)₂ (P^P), and Fe(C₅H₄PPh₂)₂ (dppf) proceed via nonredox substitution and result in the heteroleptic Chini-type clusters [Pt₆(CO)₁₀(dppm)]^2-, [Pt₆(CO)₁₀(P^P)]^2-, and [Pt₆(CO)₁₀(dppf)]^2-, respectively. Conversely, the reactions of [Pt₆(CO)₁₂]^2- with Ph₂P(CH₂)₄PPh₂ (dppb) and Ph₂PC≡CPPh₂ (dppa) can be described as redox fragmentation that afford the neutral complexes Pt(dppb)₂, Pt₂(CO)₂(dppa)₃, and Pt₈(CO)₆(PPh₂)₂(C≡CPPh₂)₂(dppa)₂. The oxidation of [Pt₆(CO)₁₀(dppm)]^2- results in its oligomerization to yield the larger heteroleptic Chini-type clusters [Pt₁₂(CO)₂₀(dppm)₂]^2-, [Pt₁₈(CO)₃₀(dppm)₃]^2-, and [Pt₂₄(CO)₄₀(dppm)₄]^2- (for the latter there is only IR spectroscopic evidence). All the clusters were characterized by means of IR and ³¹P NMR spectroscopies and electrospray ionization mass spectrometry. Moreover, the crystal structures of [NEt₄]₂[Pt₆(CO)₁₀(dppm)]·CH₃CN, [NEt₄]₂[Pt₁₂(CO)₂₀(dppm)₂]·2CH₃CN·2dmf, [NEt₄]₂[Pt₁₂(CO)₂₀(dppm)₂]·4dmf, [NEt₄]₂[Pt₆(CO)₁₀(dppf)]·2CH₃CN, Pt₂(CO)₂(dppa)₃·0.5CH₃CN, Pt₈(CO)₆(PPh₂)₂(C≡CPPh₂)₂(dppa)₂·2thf, and Pt(dppb)₂ were determined by single-crystal diffraction (dmf = dimethylformamide; thf = tetrahydrofuran).

Reactions of Platinum Carbonyl Chini Clusters with Ag(NHC)Cl Complexes: Formation of Acid-Base Lewis Adducts and Heteroleptic Clusters

The reactions of anionic platinum carbonyl Chini clusters [Pt_3n(CO)_6n]^2- [n = 2 (1), 3 (2), 4 (3)] with Ag(IPr)Cl [IPr = C₃N₂H₂(C₆H₃ⁱPr₂)₂] afford the neutral acid-base Lewis adducts [Pt₉(CO)₁₈(AgIPr)₂] (4) and [Pt₆(CO)₁₂(AgIPr)₂] (5). These are thermally transformed into the homometallic heteroleptic neutral cluster [Pt₃(CO)₄(IPr)₂] (6). Alternatively, 6 can be obtained from the reactions of 1-3 with an excess of the free IPr carbene ligand. The formation of 6 is sometimes accompanied by trace amounts of [Pt₄(CO)₄(IPr)₃] (7). The reaction of 6 with free IPr affords the closely related [Pt₃(CO)₃(IPr)₃] (8) heteroleptic cluster by substitution of the unique terminal CO ligand with a third IPr ligand. The reactions of 1-3 with Ag(IMes)Cl [IMes = C₃N₂H₂(C₆H₂Me₃)₂] proceed differently from those involving Ag(IPr)Cl. Indeed, the only product isolated after workup is the bimetallic tetranuclear cluster [Pt₃(CO)₃(IMes)₃(AgCl)] (9). 9 slowly reacts under a CO atmosphere, resulting in the pentanuclear [Pt₅(CO)₇(IMes)₃] (10) complex. All of the new clusters 4-10 have been spectroscopically characterized and their molecular structures determined by X-ray crystallography. 4 and 5 retain the original trigonal-prismatic structures of the parent anionic Chini clusters, which are capped by two [Ag(IPr)]⁺ moieties. Conversely, 6-9 are based on a Pt₃ triangular core decorated by CO and N-heterocyclic carbene ligands as well as Pt(CO) (in the case of 7) and AgCl (9) moieties. 10 displays an edge-bridged tetrahedral geometry.

Heteroleptic Chini-Type Platinum Clusters: Synthesis and Characterization of Bis-Phospine Derivatives of [Pt3n(CO)6n]2- (n = 2-4)

The reactions of [Pt_3n(CO)_6n]^2- (n = 2-4) homoleptic Chini-type clusters with stoichiometric amounts of Ph₂PCH₂CH₂PPh₂ (dppe) result in the heteroleptic Chini-type clusters [Pt₆(CO)₁₀(dppe)]^2-, [Pt₉(CO)₁₆(dppe)]^2-, and [Pt₁₂(CO)₂₀(dppe)₂]^2-. Their formation is accompanied by slight amounts of neutral species such as Pt₄(CO)₄(dppe)₂, Pt₆(CO)₆(dppe)₃, and Pt(dppe)₂. A similar behavior was observed with the chiral ligand R-Ph₂PCH(Me)CH₂PPh₂ (R-dppp), and two isomers of [Pt₉(CO)₁₆(R-dppp)]^2- were identified. All the new species were spectroscopically characterized by means of IR and ³¹P NMR, and their structures were determined by single-crystal X-ray diffraction. The results obtained are compared to those previously reported for monodentate phosphines, that is, PPh₃, as well as more rigid bidentate ligands, that is, CH₂═C(PPh₂)₂ (P^P), CH₂(PPh₂)₂ (dppm), and o-C₆H₄(PPh₂)₂ (dppb). From a structural point of view, functionalization of anionic platinum Chini clusters preserves their triangular Pt₃ units, whereas the overall trigonal prismatic structures present in the homoleptic clusters are readily deformed and transformed upon functionalization. Such transformations may be just local deformations, as found in [Pt₉(CO)₁₆(dppe)]^2-, [Pt₉(CO)₁₆(R-dppp)]^2-, [Pt₁₂(CO)₂₂(PPh₃)₂]^2-, and [Pt₉(CO)₁₆(PPh₃)₂]^2-; an inversion of the cage from trigonal prismatic to octahedral, as observed in [Pt₆(CO)₁₀(dppe)]^2- and [Pt₆(CO)₁₀(PPh₃)₂]^2-; the reciprocal rotation of two trigonal prismatic units with the loss of a Pt-Pt contact as found in [Pt₁₂(CO)₂₀(dppe)₂]^2-.

PPh3-derivatives of [Pt3n(CO)6n]2- (n = 2-6) Chini's clusters: syntheses, structures, and 31P NMR studies

The reaction of the [Pt3n(CO)6n](2-) (n = 2-6) Chini's clusters with increasing amounts of PPh3 has been investigated in detail by combined FT-IR, (31)P{(1)H} NMR, and electrospray ionization-mass spectrometry (ESI-MS) studies, showing that up to three CO ligands are gradually substituted by PPh3, resulting in isonuclear phosphine-substituted anionic clusters of general formula [Pt3n(CO)(6n-x)(PPh3)(x)](2-) (n = 2-6; x = 1-3). Further addition of PPh3 results in the elimination of the neutral Pt3(CO)3(PPh3)3 species and formation of lower nuclearity anionic clusters. [Pt12(CO)22(PPh3)2](2-) and [Pt9(CO)16(PPh3)2](2-) have been structurally characterized, and they maintain the trigonal prismatic structures of the parent homoleptic clusters, with the two PPh3 ligands bonded to different external Pt3-triangles in relative cis-position. Conversely, the crystal structure of [Pt6(CO)10(PPh3)2](2-) shows that its metal cage is transformed from trigonal prismatic to trigonal antiprismatic after CO/PPh3 exchange.

Water-Soluble Derivatives of Octanuclear Iron-Oxo-Pyrazolato Complexes; An Experimental and Computational Study

Two water-soluble iron-pyrazolato complexes, [Fe8], have been prepared by the introduction of twelve hydroxyalkyl groups to the periphery of the approximately spherical octanuclear molecule and they are contrasted with their two organosoluble chloroalkyl analogues. All four new complexes, 1 - 4, have been characterized in solution by 1H-NMR and electrospray ionization mass spectroscopy. The one-electron reduction product of the water-soluble 3, [Fe8]-, has been structurally characterized by single crystal diffraction methods. In aqueous media, the four terminal Fe-Cl bonds of [Fe8] are partially hydrolysed and the resulting chloro/aqua/hydroxo species form supramolecular nanoscale aggregates, as determined by dynamic light scattering and electron microscopy. Preliminary computational studies by density functional theory methods have been employed in order to model the H-bonding interactions controlling the competing solvation and aggregation processes.