Conny Vogler

Synthesis, electrochemistry and emission spectroscopy in fluid solution of four isomeric (α-diimine)Re(CO)3Hal complexes

Abstract Complexes (bdz)Re(CO) 3 Hal (Hal = Cl or Br) derived from the four isomeric bidiazine (bdz) chelate ligands 3,3′-bipyridazine, 2,2′-bipyrazine, 2,2′- and 4,4′-bipyrimidine have been synthesized from Re(CO) 5 Hal by thermal substitution. All the complexes were found to show long-wavelength emission at room temperature in chloroform solution after irradiation into the metal-to-ligand charge transfer (MLCT) band. Spectroscopic data and electrochemical reduction potentials confirm the superior polarizing ability of neutral Re(CO) 3 Hal fragments for α-diimine π system, and the electrochemical and photophysical data can be correlated with the established properties of the free ligands, of their anion radicals, and of other d 6 metal (W 0 , Ru II ) complexes.

Spectroelectrochemistry of aromatic ligands and their derivatives: III. Binuclear transition metal complexes of CuI, Mo0, and ReI with 2,2′-bipyrimidine☆

The binuclear complexes [Mo(CO)4]2(bpym) (I), [Re(CO)3Cl]2(bpym) (II), and [[Cu(PPh3)2]2-(bpym)]2+ (III) were subjected to one- and (for I, III) two-electron reduction, and the products studied in situ by UVVisNIR spectroscopy. The spectra were assigned in terms of a simple Huckel molecular orbital scheme, in which the reduction orbital is ligand π(7), related to π(7) of biphenyl, the transition π(6) → π(7) moves to lower energy on successive reduction, and bands observed in the near IR-visible region are due to transitions from π(7) to higher unoccupied orbitals. Detailed assignments are directly related to those of other singly and doubly reduced azabiphenyls; the bpym dianion has been characterized for the first time.

Electrochemistry, electron spin resonance, optical spectroscope, and reactivity of organometallic platinum(II) complexes containing strongly π-accepting aromatic α-diimine ligands

Abstract Low-lying metal-to-ligand charge transfer (MLCT) transitions of the new complexes LPtPh 2 (L = 3,3′-bipyridazine (bpdz), 4,4′-bipyrimidine (bpm), 2,2′-bipyrazine (bpz) and 1,4,7,10-tetraazaphenanthrene (tap)) have been studied by emission and solvent-dependent absorption spectroscope. The complex (bpm) PtPh 2 is strongly solvatochromic, and exhibits five absorption bands in toluene solution, but does not show luminescence. The other complexes emit visible light on excitation in the solid or in acetonitrile solution (bpdz complex). The one- and two-electron-reduced states were generated electrochemically; the ESR spectra of the paramagnetic intermediates, including [(bpy)PtPh 2 ] −· , are consistent with the formulation Pt II /(L −· ). The rate of oxidative addition of iodomethane to Ph 2 Pt(L) correlates with the basicity of L.

Electronic structure of a heterotetranuclear Cu12FeII2 complex bridged by π-accepting 2,2′-bipyrimidine. Close-lying but orthogonal frontier orbitals

Abstract The new complex 1 contains two 1,1′-bis(diphenylphosphino)ferrocene-coordinated copper(I) centers which are connected by the D 2 h -symmetric π acceptor 2,2′-bipyrimidine. Cyclic voltammetry and ESR reveal a ferrocene-based HOMO and a bpym-centered LUMO. There is no detectable HOMO/LUMO absorption band because of orthogonality between the two types of orbitals. The lack of strong solid-state MLCT luminescence is an indirect consequence of the small bite angle of the bis(diphenylphosphino)ferrocene ligand, which cannot induce strong distortion at the copper center.

Zweikernige Bisphosphankupfer(I)-Komplexe mit dem 2,2′-Bipyrimidin-Brückenliganden: Strukturelle Analogie zu „Blauen“ Kupferzentren und Reduktion zu paramagnetischen Spezies / Dinuclear Bis(phosphane)copper(I) Complexes with 2,2′-Bipyrimidine as Bridging Ligand: Structural Analogy to “Blue” Copper Centers and Reduction to Paramagnetic Species

Dinuclear complexes [(PR3)2Cu(μ: η4-bpym)Cu(PR3)2](BF4)2 with the bis-chelating bridging ligand 2,2′-bipyrimidine (bpym) and various monodentate and bidentate phosphanes were synthesized via a four component “self assembly” reaction. The reversible electrochemical reduction to monocationic radical complexes was studied by cyclic voltammetry and electron spin resonance (ESR). Highly resolved ESR spectra revealed the presence of the bpym anion radical ligand via resolved hyperfine coupling with 1H, 14N, 31P, 63Cu and 65Cu nuclei. The variation of phosphane ligands was accompanied by significant changes of electrochemical potentials which were rationalized considering electronic and structural effects. The configurational flexibility of Cu(I) in this environment is evident from the X-ray crystal structure analysis of [(PPh3)2Cu(μ: η4-bpym)Cu(PPh3)2](BF4)2 - H2O• CH3OH for which the coordination at the metal can be described as 3 + 1 (NN′P + P′), qualitatively similar to the (NN′S + S′) arrangement around the type 1 Cu centers of “blue” copper proteins. Intramolecular cooperative π donor/π acceptor/π donor “sandwich” interactions provide parts of the driving force for this highly distorted coordination geometry which illustrates the proclivity of Cu(I) towards such an “entatic state” arrangement.

Einkernige Bis(triphenylphospin)kupfer(I)-Komplexe der Bidiazine / Mononuclear Bis(triphenylphosphine)copper(I) Complexes of the Bidiazines

The cationic d10 metal complexes [(bdz)Cu(PPh3)2+]+ of the π accepting bidiazine (bdz) chelate ligands 3,3′-bipyridazine, 2,2′-bipyrazine, 2,2′- and 4,4′-bipyrimidine were synthesized and compared with the analogous complex of 2,2′-bipyridine. The long wavelength metal-to-ligand charge transfer (MLCT) absorption maxima and the reduction potentials indicate relatively little π* orbital stabilization by +Cu(PPh3)2. The particular d orbital splitting in a tetrahedral ligand field results in an additional contribution from △t to the energy difference between the first and second MLCT band. Only the most easily reduced complexes of 4,4′-bipyrimidine and 2,2′-bipyrazine yield neutral radical complexes (“Cu(0)”) which were characterized by ESR spectroscopy.