Dipyrrolyldiketone ligands (dpkH) are used with Ti(OiPr)4 to afford monomeric titanium(IV) complexes displaying the general formula C 2-[Ti(dpk)2(OiPr)2]. The dpkH ligands employed consist of two dipyrrolyldiketone compounds (2H and 3H) and three diphenyl-substituted analogues (4H–6H). The behavior of these octahedral [Ti(dpk)2(OiPr)2] species in solution was investigated by 1H NMR at variable temperatures. Dynamic phenomena were evidenced, and the activation parameters associated with these processes (ΔH ⧧, ΔS ⧧, and ΔG ⧧) were retrieved. [Ti(dpk)2(OiPr)2] complexes are precursors for the formation of high-nuclearity aggregates whose structures depend on the substituents on the diketone backbone. The crystal structures of monomeric ([Ti(1)2(OiPr)2]; 1 is the 1,3-diphenyl-1,3-propanedionato ligand) and [Ti(2)2(OEt)2]), dimeric ([Ti2(1)4(μ2-O)2]), and tetrameric ([Ti4(4)8(μ2-O)4]) species have been established, and the origin of this structural diversity is discussed. The solid-state optical properties of several complexes were determined and interpreted with the help of DFT calculations. Finally, the dinuclear complex [Ti(6)2(μ2-O)2] was synthesized, where ligand 6 incorporates six long alkyl chains (C16H33). This complex shows rich mesomorphic properties, with an original room-temperature plastic crystal phase followed by a hexagonal columnar liquid-crystalline phase.
Reacting nickel(ii)perchlorate with a bidentate P,N-ligand in methanol leads to P,C-bond cleavage and gives a five-coordinate nickel complex wherein the nickel(ii) site is coordinated by a tridentate P,N,P-ligand and a bidentate N,C-ligand. The carbanion of the latter is the result of the P,C-bond cleaving process. The diamagnetic nickel(ii) complex was characterized by means of elemental analysis, NMR spectroscopy, cyclic voltammetry and X-ray structure analysis.
Organometallic COz Reservoires from Nickel(0)-1-Azadiene Acetophenone1-Azadiene-type ligands yield with nickel(0) binuclear organometallic compounds of the type [Ni(l-azadiene),], (n = 1, 2). The structures of the complexes 1 (n = 2, ligand A) and 3 (n = 1, ligand C) have been characterized by X-ray crystallography. 1 is unreactive towards COz, 3 and similar compounds are able to react with COz to give metallacyclic carbamato complexes of Ni(I1). In these compounds COz is activated and can carboxylate acetophenone to yield benzoylic The X-ray analysis of the monomeric model compound (bipy)Ni(A) (11) shows that only the olefin part is coordinated. 6 and 11 can also react with CO2. Cu(1) complexes with 1-azadiene-type ligands are not reactive towards COz.I-Azadiene bilden mit Nickel(0)-Zentren metallorganische Komplexe, die aus zwei Grunden interessant sind: -Im Unterschied zur Koordination an anderen Metallen konnen diese flexiblen Ligandsysteme gegenuber Nickel(0) auch als verbruckende Liganden wirken, so daD binucleare Nickel(0)-Komplexe entstehen, deren wesentliches Strukturmerkmal ein bimetallischer Diazadinickelacycloocta-13-dien-Ring ist[1,21.-Einige 1 -Azadien-nickel(0)-Verbindungen fungieren als reversible CO2-Carrier, indem sie unter oxidativer Kopplung der Azaolefinkomponente rnit CO2 zu Metallacyclen reagieren, aus denen CO2 bei hoherer Temperatur wieder eliminiert werden kannC3]. Diese Eigenschaft von 1 -Azadienkomplexen, CO2 zu fixieren, ist offenbar fur das Zentralatom Nickel(0) singular.Anliegen dieser Arbeit war es, neue Nickel(0)-und Kupfer(1)-1 -azadienverbindungen zu synthetisieren und uber Struktur-Reaktivitatsuntersuchungen Informationen daruber zu gewinnen, wodurch die C02-Reaktivitat gesteuert werden kann. Durch Einbau von Nickel(0) in l-hzadienEinheiten enthaltene Ligandsysteme hoher Komplexitat sollten daruber hinaus Funktions-Einheiten evolviert werden, die CO2 nicht nur reversibel fixieren, sondern auch in der Weise aktivieren, dab es unter C-C-Verknupfung auf organische Substrate (z.B. Acetophenon) ubertragen werden kann. Damit wurde in metallorganischen Reaktionen ein wichtiges biologisches Prinzip der Umwandlung von Kohlendioxid in organische Materie realisiert r4].
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