A series of novel 4,4Ј-disubstituted organic-organometallic stilbenes were synthesized, that is, the 4Ј-substituted stil--in which R = C 2 H 2 C 6 H 4 -RЈ-4Ј with RЈ = NMe 2 , OMe, SiMe 3 , H, I, CN, NO 2 ) (1-7). In these compounds the PtCl grouping can be considered to be present as a donor substituent. Their synthesis involved a Horner-Wadsworth-Emmons reaction of [PtCl(NCN-CHO-4)] (9) with the appropriate phosphonate ester derivatives (8a-g). Under these reaction conditions, the C-Pt bond in aldehyde 9 was not affected, and the platinated stilbene products were obtained in 53-90 % yield. The solidstate structures of complexes 1, 2 and 5-7 were determined by single-crystal X-ray diffraction, which revealed interesting bent conformations for 2, 5 and 7. Linear correlations were found between both the 13 C{ 1 H} (C ipso to Pt) and the
Ausschließlich trans‐Koordination wird mit SPANphos erreicht, einem C2‐symmetrischen Spiro‐Diphosphan‐Liganden, der in nur drei Stufen aus Standardreagentien zugänglich ist. Der große intramolekulare P‐P‐Abstand, der cis‐Koordination ausschließt, wird in den Strukturen des Liganden und des Komplexes [PtCl2(SPANphos)] im Kristall deutlich.
The relatively insensitive surface plasmon resonance (SPR) signal detection of low‐molecular‐mass analytes that bind with weak affinity to a protein—for example, carbohydrate–lectin binding—is hampering the use of biosensors in interaction studies. In this investigation, low‐molecular‐mass carbohydrates have been labeled with an organoplatinum(II) complex of the type [PtCl(NCNR)]. The attachment of this complex increased the SPR response tremendously and allowed the detection of binding events between monosaccharides and lectins at very low analyte concentrations. The platinum atom inside the organoplatinum(II) complex was shown to be essential for the SPR‐signal enhancement. The organoplatinum(II) complex did not influence the specificity of the biological interaction, but both the signal enhancement and the different binding character of labeled compounds when compared with unlabeled ones makes the method unsuitable for the direct calculation of biologically relevant kinetic parameters. However, the labeling procedure is expected to be of high relevance for qualitative binding studies and relative affinity ranking of small molecules (not restricted only to carbohydrates) to receptors, a process of immense interest in pharmaceutical research.
A series of 4,4′-disubstituted organic-organometallic stilbenes, i.e., the 4′-substituted stilbenoid-NCN-pincer platinum(II) complexes [PtCl(NCN-R-4)] (NCN-R-4 ) [C 6 H 2 (CH 2 NMe 2 ) 2 -2,6-R-4] -in which R ) C 2 H 2 C 6 H 4 -R′-4′ with R′ ) NPh 2 , NMe 2 , OMe, SiMe 3 H, I, CN, NO 2 ) (1-8), were studied for their electronic, electrochemical, and NLO properties. Complex 7 was also chemically oxidized using Cu(II)Cl 2 , yielding the [Pt(IV)Cl 3 (NCN(C 2 H 2 C 6 H 4 -CN-4′)-4)] complex 11. In contrast to 1 and 7, 11 did not show luminescent properties in solution at room temperature. In the solid state (X-ray crystallography) 11 has an overall bent structure, with the pincer moiety and the cyano group beneath the plane of the central double bond. Stilbenoid pincer complex 1 (R′ ) NPh 2 ) was also studied with UV/vis spectroscopy in a series of different solvents. The compound shows an intense low-energy transition band, appearing at a lower energy (λ max ) 374-379 nm) than 2 (R′ ) NMe 2 ), which contains a stronger donor group. The UV/vis absorption data of a selected series of stilbenoid pincer platinum complexes were interpreted in terms of a qualitative orbital model based on DFT and TD-DFT calculations. The trends observed in the transition energies correlate well with the donor/acceptor properties of the substituents. It was shown that the HOMO-LUMO gap of the stilbenoid pincer platinum compounds decreases when going from an electron-neutral group (R′ ) H) toward an electron-donating (R′ ) NMe 2 ) or -accepting (R′ ) NO 2 ) group. The fluorescence properties of 1 were also investigated using fluorescence and laser spectroscopy, showing that the metal center favors nonradiative decay from the excited state to the ground state. For 7 (R′ ) CN), solid-state 13 C CP/MAS NMR measurements were performed, and a value of 1 J( 13 C, 195 Pt) ) 1003 ( 15 Hz was obtained for the C ipso carbon, reflecting π-contributions in the carbon-metal bond. The cyclic voltammetry study on the complexes revealed an irreversible oxidation from Pt(II) to Pt(IV). In general the oxidation potential is influenced by the electronic character of the R′ substituent. The influence of the para R′ substituent on the hyperpolarizability of the compound was investigated using the femtosecond (frequencyresolved) HRS technique. For 1-7 good zzz values were measured ( zzz ranging from (164-1324) × 10 -30 esu) with the highest value for 6 (R′ ) I). The higher zzz values were found for the compounds that contain a low-energy UV/vis absorption band and/or a large absorption coefficient. Donor-acceptor complexes 7 and 8 were successfully applied in an organic light-emitting diode (OLED). In the electroluminescence spectrum of 7 (R′ ) CN) a low-energy emission band was observed at 643 nm. This band also appeared in the solid-state luminescence spectra of 7, however, only at low temperatures (298-15 K). The emission band was assigned to result from a triplet excited state. The present study shows that the introduction of a NCN-pincer platinum fragment ...
The synthesis of the two novel diphosphine compounds 1,2-bis(3-(diphenylphosphino)-4-methoxyphenyl)benzene (1; Terphos), and 1,2-bis(2-diphenylphosphino)benzene (2), both derived from a terphenyl backbone structure, are described. Straightforward synthetic routes have been employed to obtain these ligands in good yields from cheap starting materials. The coordination of ligands 1 and 2 with PtCl2(cod) has been studied by NMR spectroscopy, and the X-ray crystal structures of the resulting complexes 4 and 5 were determined. The 31P NMR spectra of the mononuclear products demonstrate solely cis coordination for both bidentate ligands, with corresponding coupling constants J Pt - P of 3810 Hz (cis-[PtCl2(1)], complex 4) and 3712 Hz (cis-[PtCl2(2)], 5). The bite angles P1−Pt−P2 were 98.74 and 105.89°, respectively, in the distorted square-planar complexes. The new diphosphines have been applied in the platinum/tin-catalyzed hydroformylation of 1-octene, and both ligands give active and selective platinum catalysts.
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