Unexpected Redox Chemistry of P∩N- and As∩N-Rhenium(I) Tricarbonyl Complexes in the Presence of CO2 Acting as an Acid.

This study reports on Re tricarbonyl complexes bearing 8-(diphenylphosphanyl)quinoline, P∩N, and 8-(diphenylarsanyl)quinoline, As∩N, as bidendate ligands. We studied the reactivity of these complexes in comparison with fac-Re(N∩N)(CO)3Cl (with N∩N = 2,2'-bipyridine or 4,4'-dimethyl-2,2'-bipyridine). We used a combination of electrochemical and spectroelectrochemical methods with time-resolved spectroscopy over 10 orders of magnitude (100 ps-1 s) to investigate the peculiar reactivity of one-electron-reduced Re(CO)3(P∩N)Cl and Re(CO)3(As∩N)Cl complexes also in the presence of protons.

Noncovalent Synergy: Aurophilicity and Aryl Stacking in Bis(gold(I)aryl)-dmpm Complexes.

Bis(dimethylphosphino)methane (dmpm) was used as a ligand to synthesize four semi-supported dinuclear gold(I) complexes, dmpm(AuR)2 (R = Cl, C6H5, C6Cl5, and C6F5), which were studied concerning the synergistic effects of two weak noncovalent interactions: aurophilic and aryl-aryl stacking interactions. The chloro-substituted complex was synthesized by the ligand substitution of (tht)AuCl with dmpm and further functionalized by the reaction with PhMgBr or in situ-generated C6Cl5Li to afford the phenyl- and pentachlorophenyl-substituted compounds, respectively. The pentafluorophenyl-substituted gold complex was generated by the ligand substitution of (tht)Au(C6F5) with dmpm. All complexes were characterized by multinuclear NMR spectroscopy, CHN analyses, and X-ray diffraction experiments. Additionally, the basic photoluminescence properties of dmpm(AuCl)2, dmpm(AuC6Cl5)2, and dmpm(AuC6F5)2 were examined. The aggregation behavior of dmpm(AuC6F5)2 was further investigated by variable-temperature diffusion-ordered NMR spectroscopy experiments.

Relativistic effects in triphenylbismuth and their influence on molecular structure and spectroscopic properties.

Relativistic effects in triphenylbismuth have been investigated using a combined experimental and theoretical approach. The influence of these effects on the molecular structure (determined by gas electron diffraction) has been evaluated by means of quantum chemical calculations which consider scalar-relativistic and relativistic effects causing electronic spin-orbit coupling. Besides the molecular structure, different types of spectroscopic techniques (IR, NMR, UV-vis) have been applied and their results have been set in contrast with the results derived from quantum chemical calculations.

Synthesis, structural and photophysical properties of dimethylphosphino(perfluoro-)phenylene-based gold(I) dimers.

Starting with 1,2-dibromobenzene and 1,2,3,4-tetrafluorobenzene, dimethyl(2-(trimethylstannyl)phenyl)phosphane, Me2P(o-C6H4)SnMe3, and dimethyl-[2,3,4,5-tetrafluoro-6-(trimethylstannyl)phenyl]phosphane, Me2P(o-C6F4)SnMe3, were synthesized and used in tin-gold exchange reactions to prepare two gold(I) dimers, bis[(2-dimethylphosphino)phenyl]di-gold(I), [Au2(µ-2-C6H4PMe2)2], and bis[(2-dimethylphosphino)-3,4,5,6-tetrafluorophenyl]di-gold(I), [Au2(µ-2-C6F4PMe2)2], respectively. Both tin precursor molecules, as well as the gold(I) complexes, were characterized by multinuclear NMR spectroscopy, CHN analysis and X-ray diffraction experiments. Both gold(I) dimers were further investigated by the means of computational as well as photophysical methods.

Antimony-Oxo Porphyrins as Photocatalysts for Redox-Neutral C-H to C-C Bond Conversion.

The use of high-valent antimony-oxo porphyrins as visible-light photocatalysts operating via direct hydrogen atom transfer has been demonstrated. Computational analysis indicates that the triplet excited state of these complexes shows an oxyl radical behavior, while the SbV center remains in a high-valent oxidation state, serving uniquely to carry the oxo moiety and activate the coordinated ligands. This porphyrin-based system has been exploited upon irradiation to catalyze C-H to C-C bond conversion via the addition of hydrogen donors (ethers and aldehydes) onto Michael acceptors in a redox-neutral fashion without the need of any external oxidant. Laser flash photolysis experiments confirmed that the triplet excited state of the photocatalyst triggers the desired C-H cleavage.

Stable Europium(III) Complexes with Short Linkers for Site-Specific Labeling of Biomolecules.

In this study, two new terpyridine-based EuIII complexes were synthesized, the structures of which were optimized for luminescence resonance energy-transfer (LRET) experiments. The complexes showed high quantum yields (32 %); a single long lifetime (1.25 ms), which was not influenced by coupling to protein; very high stability in the presence of chelators such as ethylenediamine-N,N,N',N'-tetraacetate and ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid; and no interaction with cofactors such as adenosine triphosphate and guanosine triphosphate. A special feature is the short length of the linker between the EuIII ion and the maleimide or hydrazide function, which allows for site-specific coupling of cysteine mutants or unnatural keto amino acids. As a consequence, the new complexes appear particularly suited for accurate distance measurements in biomolecules by LRET.

Borate-based ligands with two soft heterocycle/thione groups and their sodium and bismuth complexes.

Two novel sodium complexes [NaBb] (1) (Bb = dihydrobis(2-mercapto-benzimidazolyl)borate) and [NaBt(Me)] (2) (Bt(Me) = dihydrobis(2-mercapto-4-methylthiazolyl)borate) have been prepared and characterized by using two heterocycles, 2-mercapto-benzimidazole and 2-mercapto-4-methylthiazole, as well as NaBH4 as precursors. The dipodal boron centred soft ligands Bb and Bt(Me) were prepared in situ. The reactivity of [NaBb] (1) and [NaBt(Me)] (2) towards Bi(III) ions has been studied. The resulting complex [BiBb2Cl] (3) contains an MS4 core with κ(3)-S,S,H coordination mode, while the complex [BiBt(Me)3] (4) with an MS6 core adopts a coordination mode κ(2)-S,S. A reaction of BiCl3 with the heterocyclic precursors 2-mercapto-benzimidazole (L(1)) and 2-mercapto-4-methylthiazole (L(2)) was also attempted; this afforded the monomeric [BiL(1)4Cl2][BiL(1)2Cl4] (5) and dimeric [BiL(2)2(µ-Cl)Cl]2 (6) bismuth complexes. The bismuth complexes possess distorted octahedral geometries except 3 for which a face-capped octahedron is found. The presence of (B)H···Bi interactions has been identified by X-ray diffraction in 3 with a H···Bi distance of 2.58(1) Å which is uniquely short and unprecedented. Two of the synthesized complexes (4 and 5) have been investigated by luminescence spectroscopy. They feature emission bands in the solid state at room temperature at 674 (4) and 586 nm (5), which are hypsochromically shifted in (frozen) ethanolic solutions at 77 K to 618 and 537 nm, respectively.

The versatile behaviour of a novel Janus scorpionate ligand towards sodium, potassium and bismuth(III) ions.

Alkali metal salts of a novel Janus scorpionate ligand [(Tr(Me))](-) with hard and soft donor sites (N, S) were synthesized by the reaction of 3-mercapto-4-methyl-1,2,4-triazole (L) with NaBH4 and KBH4, respectively, via Trofimenko's protocol. The resulting compounds were the sodium and potassium complexes [Na(Tr(Me))] (1), [K(Tr(Me))] (2) and the mixed ion compound [KNa(Tr(Me))] (3). [K(Tr(Me))] (2) was reacted with bismuth(III) chloride to afford the complexes [Bi(Tr(Me))(Cl)(µ-Cl)2]2 (5) and [Bi(Tr(Me))(Cl)2(µ-Cl)]n (6). Compound 5 was formed when 2 was applied to BiCl3 in a molar ratio 2:1, while 6 was achieved when a ratio of 1:1 was used. The reaction of 3-mercapto-4-methyl-1,2,4-triazole (L) with BiCl3 led to the formation of the complex [Bi(L)4(Cl)2]Cl (7). The products were characterized by NMR and IR spectroscopy, elemental analyses and mass spectrometry. Solid state structures were determined by X-ray diffraction of single crystals of 1, 3, 3a, 5, 6 and 7. The alkali metal scorpionates 1-3 are coordination polymers with alternating orientation of the ligands. They dissociate in solution as observed in NMR measurements. Negative mode ESI-MS data also indicate the presence of monomers. The bismuth complex 5 is dimeric and 6 is polymeric, and both are bridged via chloro ligands. The three bismuth complexes 5, 6 and 7 have highly distorted octahedral coordination geometries. The influence of the stereochemically active lone pair was found to be most pronounced in the dimeric complex 5. The ligand Tr(Me) and all bismuth complexes were also screened for their photo-luminescence activity. Whereas solutions of Tr(Me) exhibit no luminescence, 7 is only emissive at 77 K, and 5 is emissive both at r.t. and 77 K.