A novel class of luminescent tricarbonyl rhenium(I) complexes of general formula [Re2(mu-X)2(CO)6(mu-diaz)] (X=halogen and diaz=1,2-diazine) was prepared by reacting [ReX(CO)5] with 0.5 equiv of diazine (seven different ligands were used). The bridging coordination of the diazine in these dinuclear complexes was confirmed by single-crystal X-ray analysis. Cyclic voltammetry in acetonitrile showed for all the complexes (but the phthalazine derivative) a chemically and electrochemically reversible ligand-centered reduction, as well as a reversible metal-centered bielectronic oxidation. With respect to the prototypical luminescent [ReCl(CO)3(bpy)] complex, the oxidation is more difficult and the reduction easier (about +0.3 V), so that a similar highest occupied molecular orbital-lowest unoccupied molecular orbital gap is observed. All of the complexes exhibit photoluminescence at room temperature in solution, with broad unstructured emission from metal-to-ligand charge-transfer states, at lambda in the range 579-620 nm. Lifetimes (tau=20-2200 ns) and quantum yields (Phi up to 0.12) dramatically change upon varying the bridging ligand X and the diazine substituents: in particular, quantum yields decrease in the series Cl, Br, and I and in the presence of substituents at the alpha positions of the pyridazine ring. A combined density functional and time-dependent density functional study of the geometry, relative stability, electronic structure, and photophysical properties of all the pyridazine derivatives was performed. The nature of the excited states involved in the electronic absorption spectra was ascertained, and trends in the energy of the highest occupied and lowest unoccupied molecular orbitals upon changing the pyridazine substituents and the bridging halogen ligands were discussed. The observed emission properties of these complexes were shown to be related to a combination of steric and electronic factors affecting their ground-state geometry and their stability.

No abstract

The synthesis and propene polymerization performance of the novel rac-[CH 2 (3-tert-butyl-1-indenyl) 2 ]ZrCl 2 (2) and rac-[CH 2 (3-tert-butyl-1-indenyl) 2 ]ZrMe 2 (2-Me 2 ) are described. The ligand precursor, bis(1-tert-butyl-3-indenyl)methane (L2), is obtained in ca. 80% conversion from the condensation of 3-tert-butylindene and formaldehyde in DMF at room temperature and is isolated as a yellow powder by washing with pentane. Red 2 is obtained in 50-60% yield and free from its meso stereoisomer by reacting an Et 2 O solution of the ligand dianion, (L2)Li 2 (Et 2 O) x , with a slurry of ZrCl 4 in either pentane or toluene. Yellow 2-Me 2 is prepared in 90% yield by reaction of 2 with excess MeMgCl in toluene. Alternatively, 2-Me 2 (contaminated with about 5% of its meso isomer) can be obtained directly from the ligand L2, by reacting L2 in Et 2 O with 4 equiv of MeLi and then 1 equiv of ZrCl 4 in toluene. Both 2 and 2-Me 2 are remarkably soluble in pentane (2, ca. 1.7 g/L; 2-Me 2 , ca. 13 g/L) and toluene (2, ca. 50 g/L). 2/MAO and 2-Me 2 /MAO polymerize liquid propene with good activities to highly isotactic (mmmm ) 95-98%), fully regioregular polypropene with medium-high molecular weights (M h w ) 70 000-780 000) and high melting points (T m ) 154-163 °C) in the T p range 30-70 °C. The behavior of 2 is compared to that of the prototypical Montell zirconocene rac-[Me 2 C(3-t-Bu-Ind) 2 ]ZrCl 2 (1). 2 is the first example of a highly efficient and at the same time simple and inexpensive zirconocene catalyst for isotactic polypropene. The molecular structures of 2 and its Hf analogue (Hf-2) have been determined and compared to that of 1.

The previously known anion [(C6F5)3B(mu-OH)B(C6F5)3]- (2) has been prepared by a two-step procedure, involving deprotonation of (C6F5)3BOH2 to give [B(C6F5)3OH]- (1), followed by addition of B(C6F5)3. The solution structure and the dynamics of 2 have been investigated by 1H and 19F NMR spectroscopy. The reaction of [NHEt3]2 with NEt3 resulted in the formation of [NHEt3]+ [(C6F5)3BOH]-, [NHEt3]+ [(C6F5)3BH]-, and (C6F5)3B- (CH2CH=N+ Et2). This indicates that in the presence of a nucleophile anion 2 can dissociate to B(C6F5)3 and 1. The reaction of [HDMAN]2 with 1,8-bis(dimethylamino)naphthalene (DMAN) confirmed this trend. In the presence of water, 2 transformed into the adduct [(C6F5)3BO(H)H...O(H)B(C6F5)3]- (3), containing the borate 1 hydrogen-bonded to a water molecule coordinated to B(C6F5)3. The same compound is formed by treating (C6F5)3BOH2 with 0.5 equiv of a base. A competition study established that for 1 the Lewis acid-base interaction with B(C6F5)3 is about 5 times preferred over H-bonding to (C6F5)3BOH2. The X-ray single-crystal analysis of [2-methyl-3H-indolium]3 provided the first experimental observation of an asymmetric H-bond in the [H3O2]- moiety, the measured O-H and H...O bond distances being significantly different [1.14(2) vs 1.26(2) A]. The reaction of NEt3 with an equimolar mixture of B(C6F5)3 and bis(pentafluorophenyl)borinic acid, (C6F5)2BOH, afforded the novel borinatoborate salt [NHEt3]+ [(C6F5)3BOB(C6F5)2]- ([NHEt3]4). X-ray diffraction showed that the B-O bond distances are significantly shorter than in [(C6F5)3B(mu-OH)B(C6F5)3]-. Variable-temperature 19F NMR revealed high mobility of the five aryl rings, at variance with the more crowded anion 2. 2D NMR correlation experiments showed that in CD2Cl2 the two anions [(C6F5)3BOH]- and [(C6F5)3BH]- form tight ion pairs with [NHEt3]+, in which the NH proton establishes a conventional (BO...HN) or an unconventional (BH...HN), respectively, hydrogen bond with the anion. The diborate anions 2-4, on the contrary, gave loose ion pairs with the ammonium cation, due both to the delocalized anionic charge and to the more sterically encumbered position of the oxygen atoms that should act as H-bond acceptors.

The synthesis and full characterization of new platinum complexes bearing a bulky asymmetric dianionic tridentate ligand is reported. The hindrance of the ligand prevents detrimental intermolecular interactions yielding to highly emitting species in both crystalline state and thin-film. Such properties prompted their successful use in solution-processed OLEDs, showing remarkable external quantum efficiency up to 5.6%.