Synthesis and structure of the cyclometalated hetero-binuclear Pt-Au complexes with bridging 2-diphenylphosphinopyridine ligand

Stability of metal-metal interactions in transmetallation intermediates based on electronics of bridging arene ligands determined through pyridine titrations

In this contribution, we prepare the dinuclear complex [(CNCF)(PPh3)Pt-Au(PPh3)]+ (2-F) supported by an electron deficient derivative of 2,6-diphenylpyridine (CNC), 2,6-di(4-fluorophenyl)pyridine (CNCF). Solution state spectroscopic data and solid-state structural data reveals formation of the desired dinuclear complex occurs and that it remains intact in solution. The solid state structure of 2-F, compared to [(CNC)(PPh3)Pt-Au(PPh3)]+ (2), reveals a substantial change in the C-Au-P bond angle. We postulated that this change in bond angle arises due to a weaker interaction between [(PPh3)Au]+ and (CNCF)Pt(PPh3) (1-F) vs. (CNC)Pt(PPh3) (1). Through pyridine titration experiments, we demonstrate that the interaction is indeed weaker between [(PPh3)Au]+ and 1-Fvs. 1. Cyclic voltammetry (CV) experiments confirm that 1-F is less electron rich than 1. DFT calculations demonstrate that the HOMO of 1 and 1-F is not dz2, helping explain the differences in electrochemical behavior of 1 and 1-F and bonding between 1 and 1-F with [(PPh3)Au]+.

Redox-Transmetalation Reactions: Easy Access to Homo- and Heterodimetallic d8,d10 Complexes

The ability of the imine PyCH═N-CH2Py (Py = 2-pyridyl, bpi) to behave as a heteroditopic ligand, which is suitable for creating two separate compartments to host metals in different oxidation states, has been developed by studying the reactions of the mixed-valence complexes [(cod)M-Ι(μ-bpi)MΙ(cod)] (M = Rh, Ir) with [M'(Cl)2(PPh3)2] (M' = Pd, Ni). The results depend on the molar ratio of the reagents used (1:1 or 1:2) to give the heterometallic complexes {d10-M',d8-M}-[(PPh3)(Cl)M'0(μ-bpi)MΙ(cod)] (Pd,Rh, 4; Pd,Ir, 5; Ni,Rh, 8; Ni,Ir, 9) and the two-electron mixed-valent compounds [(PPh3)(Cl)M'0(μ-bpi)M'ΙΙ(Cl)] (M' = Ni, 10; Pd, 11), respectively. A redox process occurs in the replacement of the low-valent [(cod)M-I] fragment, whereas the exchange of the [(cod)MI] fragment is redox-neutral. The metal with a d8 configuration in the products exhibits a square-planar geometry coordinated to two (Rh/Ir) or three (Ni/Pd) nitrogen atoms of the bridging bpi ligand. Conversely, the metal with a d10 configuration adopts trigonal-planar geometries, π-bonded to the imine C═N bond. The isolated complexes 4/5 and 10/11, along with the hypothetical heterometallic Pd,Ni compound (12), were studied by DFT methods. Additionally, the T-shaped moiety 'M'ΙΙ(PPh3)(Cl)(η1-CH-N(bpi))', stabilized by a secondary γ-agostic interaction, and the 'M'II(Cl)(κ3N-bpi)' fragment was found to be accessible redoxomers of complexes 10 and 11 by DFT calculations.

Luminescent Heterobimetallic PtII-AuI Complexes Bearing N-Heterocyclic Carbenes (NHCs) as Potent Anticancer Agents

This study aims to probe into new series of heterobimetallic PtII-AuI complexes with a general formula of [Pt(p-MeC6H4)(dfppy)(μ-dppm)Au(NHC)]OTf, NHC = IPr, 2; IMes, 3; dfppy = 2-(2,4-difluorophenyl)pyridinate; dppm = 1,1-bis(diphenylphosphino)methane, which are the resultant of the reaction between [Pt(p-MeC6H4)(dfppy)(κ1-dppm)], 1, with [AuCl(NHC)], NHC = IPr, B; IMes, C, in the presence of [Ag(OTf)]. In the heterobimetallic complexes, the dppm ligand is settled between both metals as an unsymmetrical bridging ligand. Several techniques are employed to characterize the resulting compounds. Moreover, the photophysical properties of the complexes are investigated by means of UV-vis and photoluminescence spectroscopy. Furthermore, the experimental study is enriched by ab initio calculations (density functional theory (DFT) and time-dependent DFT (TD-DFT)) to assess the role of Pt and Au moieties in the observed optical properties. It is revealed that 1-3 is luminescent in the solid state and solution at different temperatures. In addition, the achieved results indicate the emissive properties of 1-3 are originated from a mixed 3IL/3MLCT excited state with major contribution of intraligand charge transfer (dfppy). A comparative study is conducted into the cytotoxic activities of starting materials and 1-3 against different human cancer cell lines such as the pancreas (MIA-PaCa2), breast (MDA-MB-231), cervix (HeLa), and noncancerous breast epithelial cell line (MCF-10A). The achieved results suggest the heterobimetallic PtII-AuI species as optimal compounds that signify the existence of cooperative and synergistic effects in their structures. The complex 3 is considered as the most cytotoxic compound with the maximum selectivity index in our screened complex series. Moreover, it is disclosed that 3 effectively causes cell death by inducing apoptosis in MIA-PaCa2 cells. Furthermore, the finding results by fluorescent cell microscopy manifest cytoplasmic staining of 3 rather than nucleus.

Tetranuclear rollover cyclometalated organoplatinum-rhenium compounds; C-I oxidative addition and C-C reductive elimination using a rollover cycloplatinated dimer

The novel tetranuclear Pt(IV)-Re(VII) complex [Pt₂Me₄(OReO₃)₂(PMePh₂)₂(µ-bpy-2H)], 4, is synthesized through the reaction of silver perrhenate with a new rollover cycloplatinated(IV) complex [Pt₂Me₄I₂(PMePh₂)₂(µ-bpy-2H)], 3. In complex 4, while 2,2'-bipyridine (bpy) acts as a linker between two Pt metal centers, oxygen acts as a mono-bridging atom between Pt and Re centers through an unsupported Pt(IV)-O-Re(VII) bridge. The precursor rollover cycloplatinated(IV) complex 3 is prepared by the MeI oxidative addition reaction of the rollover cycloplatinated(II) complex [Pt₂Me₂(PMePh₂)₂(µ-bpy-2H)], 2. Complex 2 shows a metal-to-ligand charge-transfer band in the visible region, which was used to investigate the kinetics and mechanism of its double MeI oxidative addition reaction. Based on the experimental findings, the classical S_N2 mechanism was suggested for both steps and supported by computational studies. All complexes are fully characterized using multinuclear NMR spectroscopy and elemental analysis. Attempts to grow crystals of the rollover cycloplatinated(IV) dimer 3 yielded a new dimer rollover cyclometalated complex [Pt₂I₂(PMePh₂)₂(µ-bpy-2H)], 5, presumably from the C-C reductive elimination of ethane. The identity of complex 5 was confirmed by single crystal X-ray diffraction analysis.

A heterodinuclear, formal Au+IPt0 complex with weakly bound alkene ligands

[(Ph₃P)AuPt(nbe)₃][BAr₄^F] (nbe = norbornene) constitutes the first olefin-containing, formal Au^+IPt⁰ complex. The unusual coordination mode and the electronic properties have been analyzed spectroscopically and by calculations. The low binding energy of the nbe ligands make this complex a valuable precursor for formal Au^+IPt⁰ complexes and a candidate for heterobimetallic catalysis.

The syntheses and photophysical properties of PNP-based Au(i) complexes with strong intramolecular AuAu interactions

Herein we report the syntheses, X-ray structures and photophysical studies of the dinuclear dimeric gold(i) complexes [ClAu(C6H5N)(PPh2)2]2 (1), [Au(C6H5N)(PPh2)2]2[SbF6]2 (2) and [Au(2,6-Me2C6H3N)(PPh2)2]2[SbF6]2 (4). We have used ligands with different substituents to see the effect of the substituents on the photophysical properties. All these complexes feature strong intramolecular AuAu interactions (2.7987-3.0056 Å) and were found to exhibit excellent luminescence properties with high quantum yields as well as different colors of emission.