Organometallic Platinum(II) and Palladium(II) Complexes as Donor Ligands for Lewis-Acidic d10 and s2 Centers. In: Canty AJ, editor. Higher Oxidation State Organopalladium and Platinum Chemistry. Berlin: Springer Berlin Heidelberg; 2011. pp. 157-84. [DOI: 10.1007/978-3-642-17429-2_7]

Influence of the Steric/Electronic Properties of N-Aryl Substituents in Cycloplatinated Guanidinate(1-) Complexes on the Formation of Discrete Pt → Ag Complexes and One-Dimensional Coordination Polymer

The reactions of cycloplatinated guanidinate(1-) complexes 1-6 with AgTFA (TFA = OC(O)CF₃) in 1:1 and 1:2 Pt^II/Ag^I molar ratios afforded complexes containing three types of Pt₂Ag₂ skeletons (7-10, 11, and 13), one 1D CP containing Pt₂Ag₃ skeleton (16), and a Pt₂Ag₄ complex (17) in 91-95% (method 1), 73-82% (method 2) (7-10), and 54-79% (11, 13, 16, and 17) yields. The reactions of 11 with 2,6-XylNC (2,6-Xyl = 2,6-Me₂C₆H₃) and 4-DMAP (4-dimethylaminopyridine) gave a neutral complex 18 and an ionic complex 19, respectively. Molecular structures of 12 complexes were unambiguously determined by single-crystal X-ray diffraction. Ten complexes contain unprecedented PtAg skeletons and are shown to contain multiple number of dative Pt → Ag bonds supported by the TFA ligand, platinated carbon of the TAG ligand, or both these ligands in conjunction with the Ag-Ag contacts stabilized by argentophilic interaction. Further, the new complexes were characterized by analytical, IR, and multinuclear NMR (¹⁹F, ¹H, ¹³C{¹H}, and ¹⁹⁵Pt) spectroscopies, powder X-ray diffraction, and TGA/DTA. In solution, 9 and 19 exist in more than one form as identified by multinuclear NMR, and this behavior is ascribed to the restricted (N₂)C-N(H)Ar single-bond rotation of the TAG ligand. The photophysical properties of 9 and 11 are reported.

Model Compounds for Intermediates and Transition States in Sonogashira and Negishi Coupling: d8-d10 Bonds in Large Heterobimetallic Complexes Are Weaker than Computational Chemistry Predicts

We report an experimental study, with accompanying DFT calculations, on a series of heterobimetallic complexes with Pd(II) and Cu(I), Ag(I), or Au(I). The isolable pincer complexes are models for the intermediates and transition state for the transmetalation step in Sonogashira and Negishi coupling reactions, among which, according to the DFT calculations, only the transition state has the two metal centers within bonding distance. Furthermore, we report a substituted version of an analogous heterobimetallic complex in which a competing dissociation sets an upper-bound on the strength of the d⁸-d¹⁰ metal-metal bond. Analysis of the structures in the solid state and in solution, and the competitive dissociation experiment in the gas phase, indicate that the dispersion-corrected DFT method used in the study appears to overestimate the strength of the metal-metal interaction, thus distorting the shape of the computed potential energy surface systematically for transmetalation.

Reactions of Cycloplatinated Guanidine Complexes with Hg(OC(O)CF3)2: Formation of a One-Dimensional Coordination Polymer Containing a Pt2Hg(μ2-S(O)Me2-S,O) Repeating Unit versus a Discrete Pt2Hg2 Complex

Separate reactions of cycloplatinated 2-tolyl- and 2-anisylguanidine complexes, [Pt{κ²(C,N)}(OC(O)CF₃)(S(O)Me₂)] (1 and 2), with Hg(OC(O)CF₃)₂ in 1:0.5 and 1:1 molar ratios afforded the one-dimensional coordination polymer (1D CP) {[Pt^III{κ²(C,N)}(OC(O)CF₃)₂]₂Hg⁰}(μ₂-S(O)Me₂-S,O)·C₇H₈ (3·C₇H₈) as bright red crystals and the discrete tetrametallic complex [Pt^II{κ²(C,N)}(μ₂-OC(O)CF₃)₂Hg^I-]₂ (4) as yellow crystals in good yields. The two different products obtained in the aforementioned reactions are ascribed to the subtle differences in the N substituent of the guanidinate(1-) ligands in 1 and 2. The plausible mechanisms of formation of 3 and 4 are outlined. Complexes 3 and 4 were characterized by elemental analyses and IR and multinuclear NMR (¹H, ¹³C{¹H}, ¹⁹F, and ¹⁹⁵Pt) spectroscopy. Complex 4 was also characterized by ¹⁹⁹Hg NMR spectroscopy. The molecular structures of 3·C₇H₈ and 4 were determined by single-crystal X-ray diffraction studies. 1D CP 3·C₇H₈ contains a Pt(III)-Hg(0)-Pt(III)(μ₂-S(O)Me₂-S,O) repeating unit with a pair of unsupported Pt-Hg covalent bonds, while 4 contains a Pt(II)-Hg(I)-Hg(I)-Pt(II) chain with a pair of trifluoroacetate ligand supported Pt→Hg coordinate bonds. 1D CP 3·C₇H₈ falls apart into a mixture of three species, namely 6-8 and 9-11 in C₆D₆ and CDCl₃, respectively, as revealed by multinuclear NMR spectroscopy. In CDCl₃, 4 partially isomerizes to [Pt^II(OC(O)CF₃)(μ₂-OC(O)CF₃){κ³μ₂(C,N,O)}Hg^I-]₂ (12), wherein each Pt→Hg coordinate bond is supported by one μ₂-bridging trifluoroacetate ligand and one chelating bridging guanidinate(1-) ligand, as inferred from variable-temperature ¹H and ¹⁹F NMR spectroscopy. Complex 12 is the major species and 4 is the minor species in CDCl₃, while opposite situation prevails in C₆D₆. The observance of a mixture of two solution species for 4 is ascribed to a rapid "carboxylate shift" process induced by the oxygen atom of the ═N(C₆H₄(OMe)-2) unit of the guanidinate(1-) ligand through neighboring-group participation. UV-visible absorption and emission spectra of 4 were measured in CHCl₃, and from the outcome of the investigation, the possible existence of [Cl₂(H)C-Cl···Pt^II(OC(O)CF₃)(μ₂-OC(O)CF₃){κ³μ₂(C,N,O)}Hg^I-]₂ (12″) was suggested, which is likely to have a pair of Pt-Hg covalent bonds made possible by CHCl₃ coordination on the sixth site of the Pt(II) atom.

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.

New Pt→M (M = Ag or Tl) complexes based on anionic cyclometalated Pt(ii) complexes

Anionic cyclometalated complexes (NBu₄)[Pt(CNC)X] (X = Cl (1), CN (2), or S-2py (pyridine-2-thiolate) (3); -CNC- = 2,6-di(phen-2-ide)-pyridine) have been used as precursors in the synthesis of heteropolynuclear Pt-Ag or Pt-Tl complexes containing donor-acceptor metal-metal bonds. Their reaction with AgClO₄ or [Ag(OClO₃)(PPh₃)] produces complexes in which the nuclearity and structure seem to be determined by the ability of the ligand X to form bridges between the metals. Thus, the characteristic linear bridging of the cyano ligand leads to the formation of an octanuclear [{Pt(CNC)(μ-CN)}₄Ag₄] (4) or tetranuclear [{Pt(CNC)(μ-CN)}₂{Ag(PPh₃)}₂] (6) complex, with CN bridges between different "Pt-Ag" units. However, the S-2py ligand can act as a bridge between Pt and Ag of the same "Pt-Ag" unit, giving rise to the complex [{Pt(CNC)(S-2py)}₂Ag₂]·CH₂Cl₂ (5). On the other hand, the reaction of 1-3 with TlPF₆ yields the complexes [PtTl(CNC)Cl] (7), [PtTl(CNC)(CN)] (8), and (NBu₄)[{Pt(CNC)(S-2py)}₂Tl] (9), while with [Tl(S-2py)], [PtTl(CNC)(S-2py)] (10) is obtained. The structures of all these Pt-Tl complexes show great variation, with several geometric arrangements which sometime co-exist in the same crystal structure: discrete Pt-Tl, Pt-Tl-Pt and Pt-Tl-Pt-Tl units, as well as infinite Pt-Tl-Pt-Tl chains. This variability could be due to the lability of the Pt-Tl bonds and the ability of the thallium center to establish secondary interactions with donor atoms or aromatic π electron density from neighboring moieties.

Electrophilic activation of alkynes for enyne cycloisomerization reactions with in situ generated early/late heterobimetallic Pt-Ti catalysts

In situ formation of heterobimetallic Pt-Ti catalysts enables rapid room temperature catalysis in enyne cycloisomerization reactions. The Lewis acidic titanium atom in the ligand framework is shown to be essential for fast catalysis. A range of enyne substrates are efficiently cyclized to carbocycles and heterocycles in high yield.

Preparation and characterization of a novel macroporous silica-bipyridine asymmetric multidentate functional adsorbent and its application for heavy metal palladium removal

The effective removal of heavy metal ¹⁰⁷Pd(II) from highly active liquid waste (HLW) is very valuable for reducing its hazardous and risk to public health and environment. For this purpose, a novel silica-bipyridine multidentate functional adsorbent was synthesized by vacuum infusing a new asymmetric N-donor ligand CA-MTBP (bipyridine derivative) into the macroporous SiO₂-P support. SEM, N₂ adsorption-desorption isotherms, TGA, XRD, FT-IR, ²⁹Si solid-state NMR and XPS spectroscopy were utilized to systematically characterize the physicochemical properties of the adsorbent. The characterization results indicated that CA-MTBP was successfully immobilized onto the pores of SiO₂-P by intermolecular interaction. Strong hydrogen-bonding interactions identified by single crystal structure of the ligand and ²⁹Si NMR may play a key role in achieving this immobilization. TGA and TOC studies showed that CA-MTBP/SiO₂-P had excellent thermal stability and highly HNO₃ resistance. EDS and XPS investigations provided directly evidences for Pd(II) being selectively adsorbed onto the adsorbent. The adsorbent had excellent adsorption capability, fast adsorption kinetics and high selectivity for Pd(II) over other typical tested metals in HNO₃ media.

A route to small clusters: a twisted half-hexagram-shaped M4(OH)4 cluster and its capacity for hosting closed-shell metals

The secret to making a new M₄(OH)₄ core structure lies in combining different oxidation states, coordination geometries and bridging systems. The spatial distribution of Pt(ii) atoms in Pt₄(OH)₄ is capable of cradling incoming Ag(i) centers.

Unusual Metal-Metal Bonding in a Dinuclear Pt-Au Complex: Snapshot of a Transmetalation Process

The dinuclear Pt-Au complex [(CNC)(PPh3 )Pt Au(PPh3 )](ClO4 ) (2) (CNC=2,6-diphenylpyridinate) was prepared. Its crystal structure shows a rare metal-metal bonding situation, with very short Pt-Au and Au-Cipso (CNC) distances and dissimilar Pt-Cipso (CNC) bonds. Multinuclear NMR spectra of 2 show the persistence of the Pt-Au bond in solution and the occurrence of unusual fluxional behavior involving the [Pt(II) ] and [Au(I) ] metal fragments. The [Pt(II) ]⋅⋅⋅ [Au(I) ] interaction has been thoroughly studied by means of DFT calculations. The observed bonding situation in 2 can be regarded as a model for an intermediate in a transmetalation process.

C–H reductive elimination during the reaction of cycloplatinated(ii) complexes with pyridine-2-thione: kinetic follow up

Reactions of the cycloplatinated(ii) complexes [PtR(ppy)(SMe₂)], 1, where ppy = deprotonated 2-phenylpyridine and R = Me or p-MeC₆H₄, with pyridine-2-thione, C₅H₅SN, were studied by UV-vis and ¹H NMR spectroscopies and on the basis of the data a mechanism is proposed.

Silver ion enhanced C–H activation in Pt(ii) hydroxo complexes

Addition of stoichiometric Ag(i) salt to monomeric Pt(ii) hydroxo complexes supported by a bulky diimine ligand results in significantly enhanced rates of C–H activation relative to the silver free systems.