Syntheses of [Pt6 (CO)8 (SnCl2 )(SnCl3 )4 ]4- and [Pt6 (CO)8 (SnCl2 )(SnCl3 )2 (PPh3 )2 ]2- Platinum-Carbonyl Clusters Decorated by SnII Fragments

Metal carbonyl clusters of groups 8-10: synthesis and catalysis

In this review article, we discuss advances in the chemistry of metal carbonyl clusters (MCCs) spanning the last three decades, with an emphasis on the more recent reports and those involving groups 8-10 elements. Synthetic methods have advanced and been refined, leading to higher-nuclearity clusters and a wider array of structures and nuclearities. Our understanding of the electronic structure in MCCs has advanced to a point where molecular chemistry tools and other advanced tools can probe their properties at a level of detail that surpasses that possible with other nanomaterials and solid-state materials. MCCs therefore advance our understanding of structure-property-reactivity correlations in other higher-nuclearity materials. With respect to catalysis, this article focuses only on homogeneous applications, but it includes both thermally and electrochemically driven catalysis. Applications in thermally driven catalysis have found success where the reaction conditions stabilise the compounds toward loss of CO. In more recent years, MCCs, which exhibit delocalised bonding and possess many electron-withdrawing CO ligands, have emerged as very stable and effective for reductive electrocatalysis reactions since reduction often strengthens M-C(O) bonds and since room-temperature reaction conditions are sufficient for driving the electrocatalysis.

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).

Water soluble derivatives of platinum carbonyl Chini clusters: synthesis, molecular structures and cytotoxicity of [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2-

The reactions of [Pt3n(CO)6n]2- (n = 2-5) homoleptic Chini-type clusters with increasing amounts of 1,3,5-triaza-7-phosphaadamantane (PTA) result in the stepwise substitution of one terminal CO ligand per Pt3 triangular unit up to the formation of [Pt3n(CO)5n(PTA)n]2- (n = 2-5). Competition between the nonredox substitution with retention of the nuclearity and the redox fragmentation to afford lower nuclearity heteroleptic Chini-type clusters is observed as a function of the amount of PTA and the nuclearity of the starting cluster. Because of this, [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- are more conveniently obtained via the oxidation of [Pt9(CO)15(PTA)3]2-. All the new species were spectroscopically characterized, and the structures of [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- were determined by single-crystal X-ray diffraction. These clusters may be viewed as heteroleptic Chini-type clusters composed of stacks of four and five Pt3(μ-CO)3(CO)2(PTA) units, respectively. The solubility in water of [Pt12(CO)20(PTA)4]2- and [Pt15(CO)25(PTA)5]2- has been determined and their cytotoxicity towards human ovarian (A2780) cancer cells and their cisplatin-resistant strain (A2780cisR) has been evaluated.

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-.