Unsaturated σ-hydrocarbyl transition-metal complexes. Part 3. Crystal and molecular structure of trans-chlorobis(diethylphenylphosphine)(vinyl)platinum(II)

The molecular structure of trans-[PtCl(CHCH2)(PEt2Ph)2] has been determined by X-ray diffraction methods. The crystals are orthorhombic, space group Pbcn, with a= 10.686(2), b= 13.832(4), c= 16.129(4)Å, and Z= 4. The structure has been solved by the heavy-atom method and refined by full-matrix least squares to R 0.044 for 1 420 diffractometric intensity data. The crystals contain discrete molecules in which the platinum co-ordination is square planar. The Pt–Cl bond vector coincides with a crystallographic diad axis about which the atoms of the vinyl group are disordered. Selected bond lengths (Å) are Pt–Cl 2.398(4), Pt–P 2.295(3), and Pt–C 2.03(2). The Pt–CC angle is 127(2)°. From a survey of the available structural data it is concluded that there is little, if any, back donation from platinum to carbon in platinum–alkenyl linkages.

Synthesis of 4-aminoquinoline analogues and their platinum(II) complexes as new antileishmanial and antitubercular agents

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Unusual behaviour of triphenylstibine complexes of zerovalent platinum

The novel triphenylstibine complexes PtL2, PtL3, and (PtL3)nN2 (L = SbPh3) have been synthesised; the binary compounds are unusually unreactive even towards cold mineral acids.

Preparation, characterization and electrochemical studies of dinuclear copper(II) complexes with pseudohalides and bidentate amines on platinum electrode in acetonitrile

The complexes: [Cu(N 3) 2(N,N-diEten)] 2, [Cu(N 3) 2(tmeen)] 2, [Cu(N 3)(NCO)(N,N-diEten)] 2, [Cu(N 3) 2(N,N′-diMeen)] 2 and [Cu(N 3)(NCO)(tmeen)] 2 were prepared, characterized and their electrochemical behavior was investigated by cyclic voltammetry and controlled potential electrolysis. Cyclic voltammograms for all complexes studied are similar and exhibit one pair of current peaks in the range of -0.65 to +0.0 V. The number of electrons obtained from controlled potential electrolysis at ca. -0.55 V for all compounds was 1.8 ≤ n ≤ 2.1, indicating that both copper(II) metallic centres in the molecule were reduced to copper (I). Comparing the peak potential values for these complexes one can observe that the redox process corresponding to copper(II)/copper(I) couple is slightly influenced by the σ-basicity of the ligands. © 1997 Soc. Bras. Química.

Dinuclear Ru-Cu complexes : electronic characterisation and application to dye-sensitised solar cells

Dye-sensitised solar cells have emerged as an important developing technology for low-cost solar energy conversion and a crucial element of these is the dye, responsible for light harvesting and control of interfacial electron-transfer processes.[1] A number of examples of dye exist in the literature which link a ruthenium polypyridyl complex to another platinum group metal complex such as Ru (II), Os (II), Re (I) or Rh (III) via a bridging ligand.[2-6] These systems are often referred to as heterosupramolecular triads when adsorbed on the surface of TiO2 as the semiconductor becomes an active component in the system. A number of problems can arise with these types of sensitisers, for example if a flexible linker, e.g. bis-pyridylethane, is used to couple the two complexes it can be hard to control the orientation of the whole dye. This may lead to the resultant dye cation hole being closer to the surface than desired, and hence the long-lived charge-separated state is not achieved. In addition the size of these dyes may be much larger than that of a mononuclear complex and can lead to poor pore filling on the TiO2 and lower dye coverage, leading to a lower efficiency cell.[7] Despite these issues, efficient charge-separation has been achieved with polynuclear complexes and a long-lived state on the millisecond timescale has been observed for a trinuclear ruthenium complex.[8]

(+/-)-cis-Dichloro[P-(isopropylamino)-dinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine](triethylphosphine)platinum(II) dichloromethane solvate

In the racemic title compound, [PtCl2(C23H20NO2P)-(C6H15P)].CH2Cl2, the platinum(II) ion, which has approximately square-planar coordination geometry, is coordinated to two different monophosphorus ligands in a cis arrangement along with two chloride ions. A significant shortening of the P-N bond [1.604(7) Angstrom] relative to that in phosphinoamines and their complexes was observed.

Cyclometalated complexes derived from calix[4] arene bisphosphites and their catalytic applications in cross-coupling reactions

Palladium and platinum dichloride complexes of a series of symmetrically and unsymmetrically substituted 25,26;27,28-dibridged p-tert-butyl-calix[4]arene bisphosphites in which two proximal phenolic oxygen atoms of p-tert-butyl-or p-H-calix[4]arene are connected to a P(OR) ( R = substituted phenyl) moiety have been synthesized. The palladium dichloride complexes of calix[4]arene bisphosphites bearing sterically bulky aryl substituents undergo cyclometalation by C-C or C-H bond scission. An example of cycloplatinated complex is also reported. The complexes have been characterized by NMR spectroscopic and single crystal X-ray diffraction studies. During crystallization of the palladium dichloride complex of a symmetrically substituted calix[4]arene bisphosphite in dichloromethane, insertion of oxygen occurs into the Pd-P bond to give a P,O-coordinated palladium dichloride complex. The calix[4]arene framework in these bisphosphites and their metal complexes adopt distorted cone conformation; the cone conformation is more flattened in the metal complexes than in the free calix[4]arene bisphosphites. Some of these cyclometalated complexes proved to be active catalysts for Heck and Suzuki C-C cross-coupling reactions but, on an average, the yields are only modest. (C) 2011 Elsevier B.V. All rights reserved.

Chemistry of low-valent platinum dimers

Physical and chemical properties of low-valent platinum dimers, namely [Pt_2(P_2O_5H_2)4]^(4-) and Pt_2(µ-dppm)_2Cl_2, have been investigated using a variety of structural and spectroscopic techniques.

Platinum(II) d^8-d^8 dimers have been shown to exhibit much thermal and photochemical reactivity. Chapter 2 describes studies aimed at elucidating the excited state reduction potenetial of [Pt_2(P_2O_5H_2)4]^(4-), Pt_2, in organic media. By conducting excited state electron transfer studies using derivatized pyridiniums and benzophenones, the excited state reduction potential has been estimated to be ~2 V. The Pt_2 complex undergoes partial oxidation to form Pt(II,III) linear chains. Chapter 3 describes the structural and spectroscopic techniques used to determine the translational symmetries of these [Pt_2(P_2O_5H_2)4]^(4-) (X = Cl, Br), Pt_2X, chains. Pt_2Br has been found to be intermediate between (AAB)_n and (AABCCB)_n, while, Pt_2Cl is of (AABCCB)_n translational symmetry. Investigations into the electronic transitions of Pt_2Cl and Pt_2Br were conducted using high pressure techniques and are presented in Chapter 4. The Pt_2X electronic spectrum exhibits bands attributable to the reduced Pt2 complex and the oxidized Pt_2X_2 complex [Pt_2(P_2O_5H_2)4]^(4-) along with an intervalence charge-tranfer band characteristic of a mixed-valence solid.

Photophysical investigations of a new luminescent chromophore, Pt_2(µ-dppm)_2Cl_2, a d^9-d^9 dimer, and its analogs are described in Chapter 5. The absorption band directly responsible for the observed emission is believed to be very weak and, as of yet, unobserved. Attempts to determine the spin multiplicty and approximate energy of this unobserved transition are described in Chapter 6. Excited-state energy transfer studies indicate that this absorption band is a triplet transition at -13,000 cm^(-1). Although, the Pt_2(µ-dppm)_2Cl_2 excited state is non-luminescent in fluid solution, it has been shown to undergo thermal electron transfer to tetracyanoethylene and photoinduced electron transfer to methylviologen. These experiments are presented in Chapter 7. Preliminary studies, described in Chapter 8, of non-bridged d^9-d^9 platinum(I) dimers have shown that [Pt_2(CNCH_3)_6]^(2+) serves as a versatile precursor in the synthesis of new d^8-d^8 A-frame complexes.

Ancillary ligand effects : from zirconium(IV)-catalyzed homogeneous propylene polymerization to platinum(II)-mediated C-H bond activation

A series of C_s- and C₁-symmetric doubly-linked ansa-metallocenes of the general formula {1,1'-SiMe₂-2,2'-E-('ƞ⁵-C₅H₂-4-R¹)-(ƞ⁵-C₅H-3',5'-(CHMe₂)₂)}ZrC₂ (E = SiMe₂ (1), SiPh₂ (2), SiMe₂ -SiMe₂ (3); R¹ = H, CHMe₂, C₅H₉, C₆H₁₁, C₆H₅) has been prepared. When activated by methylaluminoxane, these are active propylene polymerization catalysts. 1 and 2 produce syndiotactic polypropylenes, and 3 produces isotactic polypropylenes. Site epimerization is the major pathway for stereoerror formation for 1 and 2. In addition, the polymer chain has slightly stronger steric interaction with the diphenylsilylene linker than with the dimethylsilylene linker. This results in more frequent site epimerization and reduced syndiospecificity for 2 compared to 1.

C₁-Symmetric ansa-zirconocenes [1,1 '-SiMe₂-(C₅H₄)-(3-R-C₅H₃)]ZrCl₂ (4), [1,1 '-SiMe₂-(C₅H₄)-(2,4-R₂-C₅H₂)]ZrCl₂ (5) and [1,1 '-SiMe₂-2,2 '-(SiMe₂-SiMe₂)-(C₅H₃)-( 4-R-C₅H₂)]ZrCl₂ (6) have been prepared to probe the origin of isospecificity in 3. While 4 and 3 produce polymers with similar isospecificity, 5 and 6 give mostly hemi-isotactic-like polymers. It is proposed that the facile site epimerization via an associative pathway allows rapid equilibration of the polymer chain between the isospecific and aspecific insertion sites. This results in more frequent insertion from the isospecific site, which has a lower kinetic barrier for chain propagation. On the other hand, site epimerization for 5 and 6 is slow. This leads to mostly alternating insertion from the isospecific and aspecific sites, and consequently, a hemi-isotactic-like polymers. In comparison, site epimerization is even slower for 3, but enchainment from the aspecific site has an extremely high kinetic barrier for monomer coordination. Therefore, enchainment occurs preferentially from the isospecific site to produce isotactic polymers.

A series of cationic complexes [(ArN=CR-CR=NAr)PtMe(L)]⁺[BF₄]⁺ (Ar = aryl; R = H, CH₃; L = water, trifluoroethanol) has been prepared. They react smoothly with benzene at approximately room temperature in trifluoroethanol solvent to yield methane and the corresponding phenyl Pt(II) cations, via Pt(IV)-methyl-phenyl-hydride intermediates. The reaction products of methyl-substituted benzenes suggest an inherent reactivity preference for aromatic over benzylic C-H bond activation, which can however be overridden by steric effects. For the reaction of benzene with cationic Pt(II) complexes, in which the diimine ligands bear 3,5-disubstituted aryl groups at the nitrogen atoms, the rate-determining step is C-H bond activation. For the more sterically crowded analogs with 2,6-dimethyl-substituted aryl groups, benzene coordination becomes rate-determining. The more electron-rich the ligand, as reflected by the CO stretching frequency in the IR spectrum of the corresponding cationic carbonyl complex, the faster the rate of C-H bond activation. This finding, however, does not reflect the actual C-H bond activation process, but rather reflects only the relative ease of solvent molecules displacing water molecules to initiate the reaction. That is, the change in rates is mostly due to a ground state effect. Several lines of evidence suggest that associative substitution pathways operate to get the hydrocarbon substrate into, and out of, the coordination sphere; i.e., that benzene substitution proceeds by a solvent- (TFE-) assisted associative pathway.