Luminescent dinuclear Cu(I) complexes containing rigid tetraphosphine ligands.

The synthesis and the photophysics of three dinuclear copper(I) complexes containing bis(bidentate)phosphine ligands are described. The steric constraint imposed by tetrakis(di(2-methoxyphenyl)phosphanyl)cyclobutane) (o-MeO-dppcb) in combination with 2,9-dimethyl-1,10-phenanthroline in one of the complexes leads to interesting photophysical properties. The compound shows an intense emission at room temperature in deoxygenated acetonitrile solution (Φ = 49%) and a long excited-state lifetime (13.8 µs). Interestingly, at low temperature, 77 K, the emission maximum shifts to lower energy, and the excited-state lifetime increases. This observation leads to the conclusion that a mixing between the excited triplet and singlet states is possible and that the degree of mixing and population of state strongly depends on temperature, as the energy difference is quite small. The electroluminescent properties of this compound were therefore tested in light-emitting electrochemical cells (LEECs), proving that the bright emission can also be obtained by electrically driven population of the singlet state.

Oxidative quenching within photosensitizer-acceptor dyads based on bis(bidentate) phosphine-connected osmium(II) bipyridyl light absorbers and reactive metal sites.

For the first time oxidative quenching of OsP2N4 chromophores by reactive PtII or PdII sites containing cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) is directly observed despite the presence of a saturated cyclobutane backbone "bridge". This dramatic effect is measured as a sudden temperature-dependent onset of a reduction in phosphorescence lifetime in [Os(bpy)2(dppcb)MCl2](SbF6)2 (M = Pt, 1; Pd, 2). The appearance of this additional energy release is not detectable in [Os(bpy)2(dppcbO2)](PF6)2 (3), where dppcbO2 is cis, trans, cis-1,2-bis(diphenylphosphinoyl)-3,4-bis(diphenylphosphino)cyclobutane. Obviously, the square-planar metal centers in 1 and 2 are responsible for this effect. In line with these observations, the emission quantum yields at room temperature for 1 and 2 are drastically reduced compared with 3. Since this luminescence quenching implies strong intramolecular interaction between the OsII excited states and the acceptor sites and depends on the metal⋯metal distances, also the single crystal X-ray structures of 1-3 are given.

First microwave-assisted synthesis of an electron-rich phosphane and its coordination chemistry with platinum(II) and palladium(II)

The P-O ligand 3-(di(2-methoxyphenyl)phosphanyl)propionic acid (HL) was synthesized by a microwave-assisted reaction of a secondary phosphane. The coordination of HL to Pt(II) yielded the neutral mononuclear complex trans-[PtCl(κ(2)-P,O-L)(κ-P-HL)] (1), while the reaction of PdClMe(η(4)-COD) (COD = 1,4-cyclooctadiene) with HL in the presence of NEt(3) gave the anionic Pd(II) compound of the formula (HNEt(3))[PdClMe(κ(2)-P,O-L)] (2). Upon crystallization of the latter compound the neutral chloride-bridged dimetallic compound cis-[Pd(µ-Cl)Me(HL)](2) (3) was obtained. HL, 1 and 3·CH(2)Cl(2) have been characterized by single crystal X-ray structure analyses.

Surprising photochemical reactivity and visible light-driven energy transfer in heterodimetallic complexes.

The bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) has been used for the synthesis of a series of novel heterodimetallic complexes starting from [Ru(bpy)(2)(dppcb)]X(2) (1; X = PF(6), SbF(6)), so-called dyads, showing surprising photochemical reactivity. They consist of [Ru(bpy)(2)](2+)"antenna" sites absorbing light combined with reactive square-planar metal centres. Thus, irradiating [Ru(bpy)(2)(dppcb)MCl(2)]X(2) (M = Pt, 2; Pd, 3; X = PF(6), SbF(6)) dissolved in CH(3)CN with visible light, produces the unique heterodimetallic compounds [Ru(bpy)(CH(3)CN)(2)(dppcb)MCl(2)]X(2) (M = Pt, 7; Pd, 8; X = PF(6), SbF(6)). In an analogous reaction the separable diastereoisomers (ΔΛ/ΛΔ)- and (ΔΔ/ΛΛ)-[Ru(bpy)(2)(dppcb)Os(bpy)(2)](PF(6))(4) (5/6) lead to [Ru(bpy)(CH(3)CN)(2)(dppcb)Os(bpy)(2)](PF(6))(4) (9), where only the RuP(2)N(4) moiety of 5/6 is photochemically reactive. By contrast, in the case of [Ru(bpy)(2)(dppcb)NiCl(2)]X(2) (4; X = PF(6), SbF(6)) no clean photoreaction is observed. Interestingly, this difference in photochemical behaviour is completely in line with the related photophysical parameters, where 2, 3, and 5/6, but not 4, show long-lived excited states at ambient temperature necessary for this type of photoreaction. Furthermore, the photochemical as well as the photophysical properties of 2-4 are also in accordance with their single crystal X-ray structures presented in this work. It seems likely that differences in "steric pressure" play a major role for these properties. The unique complexes 7-9 are also fully characterized by single-crystal X-ray structure analyses, clearly showing that the stretching vibration modes of the ligand CH(3)CN, present only in 7-9, cannot be directly influenced by "steric pressure". This has dramatic consequences for their photophysical parameters. The trans-[Ru(bpy)(CH(3)CN)(2)](2+) chromophore of 9 acts as efficient "antenna" for visible light-driven energy transfer to the Os-centred "trap" site, resulting in k(en) ≥ 2 × 10(9) s(-1) for the energy transfer. Since electron transfer is made possible by the use of this intervening energy transfer, in dyads like 2-4 highly reactive M(0) species (M = Pt, Pd, Ni) could be generated. These species are not stable in water and M(II) hydride intermediates are usually formed, further reacting with H(+) to give H(2). Thus, derivatives of 3, namely [M(bpy)(2)(dppcb)Pd(bpy)](PF(6))(4) (M = Os, Ru) dissolved in 1:1 (v/v) H(2)O-CH(3)CN produce H(2) during photolysis with visible light.

Regio- and chemoselective oxidation of the bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane via cobalt(II) mediated dioxygen activation.

The bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) has been regioselectively oxidized leading to novel, hemilabile ligands. [Co2Cl4(dppcb)] (1a) is transformed via cobalt(II) mediated dioxygen activation into [Co2Cl4(2,3-trans-dppcbO2)] (2a) in excellent yield, where 2,3-trans-dppcbO2 is cis,trans,cis-2,3-bis(diphenylphosphinoyl)-1,4-bis(diphenylphosphino)-cyclobutane. By contrast, the in situ presence of dioxygen during the synthesis of Co2Br4(dppcb)] (1b) produces both [Co2Br4(2,3-trans-dppcbO2)] (2b) and [Co2Br4(1,3-trans-dppcbO2)] (3), where 1,3-trans-dppcbO2 is cis,trans,cis-1,3-bis(diphenylphosphinoyl)-2,4-bis(diphenylphosphino)-cyclobutane. The new compounds 2a, 2b and 3 have been obtained as pure, crystalline solids and all three X-ray structure analyses have been performed showing folded cyclobutane rings. Interestingly, the corresponding reaction using [Co2I4(dppcb)] (1c) proceeds chemoselectively. Thus, [Co2I4(dppcbO3)] (4), where dppcbO3 is cis,trans,cis-1,2,3-tris(diphenylphosphinoyl)-4-diphenylphosphinocyclobutane, is formed in excellent yield and also fully characterized by an X-ray structure analysis showing two different conformations of 4. However, [Co2(NO3)4(dppcb)] (1d) shows no dioxygen activation at all. Therefore, in order to reveal the mechanism of this oxidation [Co2I4(DMF)2(dppcb)] (5) has been prepared and its X-ray structure is presented. The synthesis of [Co2I4(PMe2Ph)2(dppcb)] (6) proves that this is a common reaction pathway. Furthermore, because the product distribution of the oxidation strongly depends on the kind of halides present, the whole series Co2X4(dppcbO4)] (X = Cl, 7a; Br, 7b; I, 7c) has been prepared, where dppcbO4 is cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphinoyl)-cyclobutane, and all three X-ray structures are given, also showing folded cyclobutane rings. It seems likely that coordination of dppcb to cobalt(II) is essential to form the regio- and chemoselectively oxygenated molecules.

A novel linkage-isomeric pair of dinuclear Pd(II) complexes bearing a bis-bidentate tetraphos ligand.

The tetraphosphane all trans tetrakis-(di(2-methoxyphenyl)phosphanyl)cyclobutane) (o-MeO-dppcb) has been employed to coordinate metal dichlorides (metal = Ni(II), Pd(II) and Pt(II)), stereoselectively yielding the dinuclear complexes [Ni(2)Cl(4)(micro-(kappaP(1):kappaP(2):kappaP(3):kappaP(4)-o-MeO-dppcb))] and [Pt(2)Cl(4)(micro-(kappaP(1),kappaP(2):kappaP(3),kappaP(4)-o-MeO-dppcb))], characterized by two six and two five-membered metallacycles, respectively. Conversely, the reaction with PdCl(2) led, under comparable synthetic conditions, to the formation of the linkage-isomeric pair [Pd(2)Cl(4)(micro-(kappaP(1),kappaP(2):kappaP(3),kappaP(4)-o-MeO-dppcb))] and [Pd(2)Cl(4)(micro-(kappaP(1):kappaP(2):kappaP(3):kappaP(4)-o-MeO-dppcb))] in a ca. 4 : 1 ratio. The compounds obtained have been characterized in solution by multinuclear NMR spectroscopy and in the solid state by CP-MAS NMR spectroscopy, XRPD and single crystal X-ray diffraction. Compounds and have been tested as catalyst precursors for the CO-ethene-propene co-and terpolymerization in water-acetic acid mixtures. Their catalytic performance has been compared to that of [PdCl(2)(o-MeO-dppe)] (o-MeO-dppe = 1,2-(bis(di(2-methoxyphenyl)phosphanyl))ethane) and of [PdCl(2)(o-MeO-dppp)] (o-MeO-dppp = 1,3-bis(di(2-methoxyphenyl)phosphanyl)propane). The most striking result that emerged from the CO-ethene copolymerization study was that was three times more productive than , outperforming, under identical catalytic conditions, even 1b and 1c, that are classified amongst the most active catalysts for the CO-ethene copolymerization reaction.