By irradiating crystals of a (diphosphine)Pt(0) complex containing 2,2'-dibromotolane as ligand with sunlight, a rare example of selective carbon-carbon bond cleavage in the solid state could be observed.

Keywords: P ligands / S ligands / Rearrangement / Thiosulfines / PlatinumA series of Pt 0 (η 2 -nbe) complexes [nbe = norbornene (bicyclo[2.2.1]hept-2-ene)] bearing bridged bisphosphane ligands with various bite angles (5a-c) was treated with 3,3,5,5-tetraphenyl-1,2,4-trithiolane (1) at 50°C in a toluene solution. These reactions resulted in the formation of the appropriate dithiolato complexes 6a-c as well as the η 2 -thioketone complexes 7a-c with respect to the 31 P{ 1 H} NMR spectroscopic data. All isolated complexes were fully characterized. Kinetic investigations using 31 P{ 1 H} NMR spectroscopy revealed

A series of various (bisphosphane)(η(2)-tolane)Pt(0) complexes, exhibiting a manifold of substitution patterns of the tolane ligand (5a-g) and different rigid bisphosphanes defining various P-Pt-P bite angles at the Pt center (9a-b) have been theoretically investigated using time-dependent density functional theory (TD-DFT). UV/Vis absorption spectra have been calculated in order to rationalize the photochemistry of the complexes. Metal-ligand charge transfer (MLCT) transitions from the Pt atom to the alkyne are assigned as the photochemical "active" states responsible for promoting the C(aryl)-C(ethynyl) bond activation. The steric, the electronic effects, as well as the P-Pt-P bite angle play an important role in determining the presence/absence of photochemical "active" states of d→π*(alk) character. Thus, electron-withdrawing substituted series and ortho-substituted complexes are best candidates to achieve C(aryl)-C(ethynyl) bond activation. C-Br bond cleavage is also theoretically rationalized. The observed photochemical C(aryl)-C(ethynyl) bond cleavage is, oppositely to C-Br bond activation, reversible under thermal conditions regaining the appropriate Pt(0) complexes by reductive elimination (see T. Weisheit, D. Escudero, H. Petzold, H. Görls, L. González and W. Weigand, Photochemical behavior of (bisphosphane)(η(2)-tolane)Pt(0) complexes in solution and in the solid state. Part A: Experimental considerations, Dalton Trans., 2010, 39, DOI: 10.1039/B925562a). In this part, we rationalize and clarify the thermal reductive elimination reactions via mechanistic DFT studies on the ground state.

A series of various (diphosphine)(η(2)-tolane)Pt(0) complexes exhibiting manifold substitution pattern of the tolane ligand (5a-g) and different rigid diphosphines defining various bite angles at the Pt center (9a-b) have been synthesized. All compounds were isolated and characterized by means of spectroscopic methods and additionally by X-ray structure determination (5a-e, 9a-b). In view of potential C(aryl)-C(ethynyl) bond activation, we investigated their photochemical behavior in the solid state as well as in solution by irradiating with sunlight. The reactivity towards C(aryl)-C(ethynyl) bond activation in the crystalline state and in solution is discussed in relation to substituents attached to the tolane ligand and on the extent of the torsion of its phenyl rings. Complexes 5a-c and 9a either bearing electron withdrawing bromides or possessing a large dihedral angle of the phenyl rings, showed selective oxidative addition of the C(aryl)-C(ethynyl) bond to the Pt center in the solid state, yielding complexes 6a-c and 10a, respectively. In contrast, 5d-f and 9b proved to be unreactive under similar conditions because of their electron donating methoxy groups as well as the reduced twisting of their phenyl or pyridyl moieties of the tolane ligands. Irradiation of complexes 5a and 5b with sunlight in solution revealed the formation of the appropriate C-Br activated compounds 7a and 7b along with 6a and 6b in a 1 : 1 mixture. The observed photochemical C(aryl)-C(ethynyl) bond activation is reversible under thermal conditions, regaining the appropriate Pt(0) complexes by reductive elimination.

Keywords: 1,2,4-Trithiolanes / S ligands / Oxidative addition / Metallacycles / Reactive intermediates Reactions of 1,2,4-trithiolanes with Pt 0 complexes often proceed via an oxidative addition of the Pt 0 complex fragment into the S-S bond and subsequent extrusion of a thioketone molecule by ring contraction. The six-membered intermediate 5a, formed in the course of the reaction of the parent 1,2,4-trithiolane (1a) and Pt 0 complex 4, was detected by

Two unsymmetrical 1,2,4-trithiolanes (1d and 1e) were reacted with [Pt(0)(PPh(3))(2)(η(2)-nbe)] (6; nbe=norborn-2-ene) and [Pt(0)(dppn)(η(2)-nbe)] (11; dppn=1,8-bis(diphenylphosphanyl)naphthalene)), respectively. Their treatment with compound 6 resulted in the formation of six-membered platinacycles of type 7, which selectively underwent fragmentation into dithiolato complexes and thiobenzophenone (4b). The isolation of the first stable C-substituted member of this class of compounds (i.e., compound 7e) permitted kinetic studies of this process by using UV/Vis spectroscopy. These results, together with DFT calculations, allowed us to propose a mechanism for the reactions of compound 6 with 1,2,4-trithiolanes. In contrast, similar treatment of compound 11 with compounds 1d and 1e at room temperature did not result in any reaction. Heating the appropriate samples to 110 °C led to the formation of dithiolato complexes and η(2)-thioketone compounds, thus pointing to a thermally induced [3+2]-cycloreversion of the heterocycles as an initial step of the reaction.

Summary Aim: In this contribution we investigated the potential transfer of an established method for the synthesis of 223Ra-labelled calixarene complexes to a hospital radiopharmaceutical environment. For this purpose, commercially available [223Ra]RaCl2 solution in pharmaceutical grade (Xofigo®) was reacted with three calixarene derivatives. Methods: A wellestablished two-phase extraction method using a two-phase solvent system was performed for complexation of the radium ions with calixarenes under slightly basic conditions. Moreover, the complexation reaction was conducted in homogenous medium (water / THF) as well as under elevated temperature. Results: The investigated reaction conditions did not allow the isolation of the desired products. Analytical evidence for the presence of radium-calixarene species by means of activity measurement, TLC as well as HPLC could not been proven unambiguously. Conclusion: We address the non-conversion of the educts to the large excess of sodium ions in the used Xofigo® solution, what may explain the hampered reaction for all conducted experiments. Finally the transfer of the published complexation concept into a radiopharmaceutical routine environment was not successful.

Diferrocenyl thioketone reacts smoothly with (bisphosphane)Pt(0) complexes in toluene solution at room temperature yielding 1:1 adducts identified as ferrocenyl (Fc) functionalized platinathiiranes. Their structures were unambiguously confirmed by means of spectroscopic methods as well as by X-ray diffraction analysis. A unique, ferrocene-rich platinathiirane, bearing three Fc-units, was prepared starting with [bis(diphenylphosphino)ferrocene] Pt(0(η2-norbornene). For comparison, a similar platinathiirane with one Fc-unit was obtained from the reaction of the latter complex with thiobenzophenone. Quantum-chemical calculations were carried out to describe the bonding pattern and frontier molecular orbitals of the ferrocene-rich platinathiirane complexes. These calculations confirmed that the C=S bond loses its formally double-bond character upon complexation (bisphosphane)Pt(0). Cyclic voltammetry measurements were performed to characterize the obtained platinathiiranes in CH2Cl2 solutions. For comparison, the cyclic voltammogram for diferrocenyl thioketoneas a mixed-valent (FeII-FeIII) compound was also recorded and analyzed. The results point out to a diffusion controlled electrode process in case of differocenyl thioketone and mixed diffusion and adsorption controlled electrode process in the case of the studied platinathiiranes.