Synthesis and Coordination Compounds of A Bis(Imino)Acenaphthene (Bian)-Supported N-Heterocyclic Carbene

The bis(imino)acenaphthene-supported N-heterocyclic carbene IPr(BIAN) has been prepared by deprotonation of the precursor imidazolium chloride. Treatment of IPr(BIAN) imidazolium chloride with Ag(2)O afforded the silver complex [IPr(BIAN)]AgCl which can be converted into the corresponding gold complex [IPr(BIAN)]AuCl by reaction with (tht)AuCl (tht = tetrahydrothiophene). The iridium complex [IPr(BIAN)]Ir(COD)Cl was prepared by reaction of the imidazolium chloride with KO(t)Bu and [Ir(COD)Cl](2) and subsequently converted to the carbonyl complex [IPr(BIAN)]Ir(CO)(2)Cl by exposure to an atmosphere of CO. All new compounds were characterized by single-crystal X-ray diffraction, multinuclear NMR, MS and HRMS data.Robert A. Welch Foundation F-0003National Science Foundation 0741973Chemistr

Synthesis, Crystal Structure and Photophysical Properties of Lanthanide Coordination Polymers of 4- 4-(9H-Carbazol-9-Yl)Butoxy Benzoate: The Effect of Bidentate Nitrogen Donors on Luminescence

A new aromatic carboxylate ligand, 4-[4-(9H-carbazol-9-yl)butoxy]benzoic acid (HL), has been synthesized by the replacement of the hydroxyl hydrogen of 4-hydroxy benzoic acid with a 9-butyl-9H-carbazole moiety. The anion derived from HL has been used for the support of a series of lanthanide coordination compounds [Ln = Eu (1), Gd (2) and Tb (3)]. The new lanthanide complexes have been characterized by a variety of spectroscopic techniques. Complex 3 was structurally authenticated by single-crystal X-ray diffraction and found to exist as a solvent-free 1D coordination polymer with the formula [Tb(L)(3)](n). The structural data reveal that the terbium atoms in compound 3 reside in an octahedral ligand environment that is somewhat unusual for a lanthanide. It is interesting to note that each carboxylate group exhibits only a bridging-bidentate mode, with a complete lack of more complex connectivities that are commonly observed for extended lanthanide-containing solid-state structures. Examination of the packing diagram for 3 revealed the existence of two-dimensional molecular arrays held together by means of CH-pi interactions. Aromatic carboxylates of the lanthanides are known to exhibit highly efficient luminescence, thus offering the promise of applicability as optical devices. However, due to difficulties that arise on account of their polymeric nature, their practical application is somewhat limited. Accordingly, synthetic routes to discrete molecular species are highly desirable. For this purpose, a series of ternary lanthanide complexes was designed, synthesized and characterized, namely [Eu(L)(3)(phen)] (4), [Eu(L)(3)(tmphen)] (5), [Tb(L)(3)(phen)] (6) and [Tb(L)(3)(tmphen)] (7) (phen = 1,10-phenanthroline and tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline). The photophysical properties of the foregoing complexes in the solid state at room temperature have been investigated. The quantum yields of the ternary complexes 4 (9.65%), 5 (21.00%), 6 (14.07%) and 7 (32.42%), were found to be significantly enhanced in the presence of bidentate nitrogen donors when compared with those of the corresponding binary compounds 1 (0.11%) and 3 (1.45%). Presumably this is due to effective energy transfer from the ancillary ligands.Council of Scientific and Industrial Research (CSIR-TAPSUN Project) SSL, NWP-55CSIR, New DelhiRobert A. Welch Foundation F-0003Chemistr

A Base Induced Transformation Of A 1,3-Dimethyl-1,3-Di-(1-Adamantyl)Formamidinium Salt Into Beta- Methyl-(1-Adamantyl)Amino Acrylonitriles In Aliphatic Nitriles

A novel 1,3-dimethyl-1,3-di-(1-adamantyl)formamidinium perchlorate has been prepared via the Vilsmeier-Haack reaction of N-methyl-N-(1-adamantyl)formamide and N-methyl-N-(1-adamantyl) amine in a mixture of phosphorus oxychloride and benzene. The new formamidinium salt was found to undergo addition-elimination reactions when treated with sodium hydride in acetonitrile or propionitrile solution, thereby forming the corresponding beta-[methyl(1-adamantyl)amino]acrylonitriles and N-methyl-N-(1-adamantyl) amine. The H-1 and C-13 NMR spectra and the single-crystal X-ray structure of the new formamidinium salt have been determined along with those of the related compound 1,3-di-(1-adamantyl)-1-cyanoamidine and the corresponding beta-(dialkylamino)acrylonitriles.Biochemistr

Synthesis and Crystal Structures of Lanthanide 4-Benzyloxy Benzoates: Influence of Electron-Withdrawing and Electron-Donating Groups On Luminescent Properties

Three new 4-benzyloxy benzoic acid derivatives [4-benzyloxy benzoic acid = HL1; 3-methoxy-4-benzyloxy benzoic acid = HL2; 3-nitro-4-benzyloxy benzoic acid = HL3] have been employed as ligands for the support of six lanthanide coordination compounds [Tb3+ = 1-3; Eu3+ = 4-6] with the aim of testing the influence of electron releasing (-OMe) or electron withdrawing (-NO2) substituents on the photophysical properties. The new complexes have been characterized by a variety of spectroscopic techniques and two of the Tb3+ complexes [1 and 2] have been structurally authenticated by single-crystal X-ray diffraction. Compounds 1 and 2 crystallize in the monoclinic space group P2(1)/n and their molecular structures consist of homodinuclear species that are bridged by two oxygen atoms from two benzoate ligands. In the case of 1, the carboxylate ligands coordinate to the central Tb3+ ion in bidentate chelating and bidentate bridging modes. By contrast, three different coordination modes (bidentate chelating, bidentate bridging and monodentate) are observed in the case of compound 2. Examination of the packing diagrams for 1 and 2 revealed the presence of a one-dimensional molecular array that is held together by intermolecular hydrogen-bonding interactions. The incorporation of an electron-releasing substituent on position 3 of 4-benzyloxy benzoic acid increases the electron density of the ligand and consequently improves the photoluminescence of the Tb3+ complexes. On the other hand, the presence of an electron-withdrawing group at this position dramatically decreases the overall sensitization efficiency of the Tb3+-centered luminescence due to dissipation of the excitation energy by means of a pi*-n transition of the NO2 substituent along with the participation of the ILCT bands. The weaker photoluminescence of the Eu3+ complexes is attributable to the poor match of the triplet energy levels of the 4-benzyloxy benzoic acid derivatives with that of the emitting level of the central metal ion.Department of Science and Technology SR/S1/IC-36/20073Council of Scientific and IndustrialResearch NWP0010CSIR, New DelhiRobert A. Welch Foundation F-0003Chemistr

Facile Syntheses of Thiophene-Substituted 1,4-Diazabutadiene (Alpha-Diimine) Ligands and their Conversion to Phosphenium Triiodide Salts

Four novel N-aryl-2-thienyl substituted 1,4-diazabutadiene (alpha-diimine) ligands 5-8 have been prepared by cyanide ion-catalyzed intermolecular coupling of the appropriate aromatic aldimines. A ligand featuring a phenyl spacer moiety between a thiophene carbon atom and each imino nitrogen atom (12) has been prepared by a similar synthetic route. Ligands 5-8 and 12 were characterized on the basis of (1)H and (13)C NMR, IR and MS-CI spectroscopy. Upon treatment with PI(3) in CH(2)Cl(2) solution, ligands 5-8 undergo redox reactions to furnish the triiodide salts of the corresponding phosphenium cations 13-16 which were characterized by (1)H, (13)C and (31)P NMR, and MS-CI spectroscopy. The phosphenium triiodide salt 15, and ligands 5-7 and 12 were also structurally authenticated.Robert A. Welch Foundation F-0003Chemistr

Boron Di- and Tri-Cations

Previous work on boron di- and tri-cations is reviewed. The structural chemistry of representative examples of these classes of compound has been probed by determination of the single-crystal X-ray structures of [(4-Mepy)(4)B]Br-3 and [py(3)BH]Br-2. The electronic structures of the polycations [(py)(3)BH](2+), [(py)(3)BBr](2+), [(4-Mepy)(3)BH](2+), [(4-Mepy)(4)B](3+), [(Me3P)(3)BH](2+) and [(Me3P)(4)B](3+) have been examined by DFT methods. The atomic charges on these cations were evaluated by Mulliken, natural population analysis (NPA), Hirschfeld and Voronoi deformation density (VDD) methods.Robert A. Welch Foundation F-0003McMaster UniversityNatural Sciences and Engineering Research Council of CanadaChemistr

Tetrakis(imino)pyracene Complexes Exhibiting Multielectron Redox Processes

The differences in redox behavior of the monofunctional bis­(imino)­acenaphthene (BIAN) and bifunctional tetrakis­(imino)­pyracene (TIP) ligands have been explored by treatment of the latter with PI₃, TeI₄, or BI₃. These reactions result in the formation of products involving the transfer of three or four electrons. Accompanying DFT calculations reveal that in each case the extent of electron transfer from each p-block element into the TIP ligand is dependent upon the element–TIP bonding interactions

Tetrakis(imino)pyracene Complexes Exhibiting Multielectron Redox Processes

The differences in redox behavior of the monofunctional bis­(imino)­acenaphthene (BIAN) and bifunctional tetrakis­(imino)­pyracene (TIP) ligands have been explored by treatment of the latter with PI₃, TeI₄, or BI₃. These reactions result in the formation of products involving the transfer of three or four electrons. Accompanying DFT calculations reveal that in each case the extent of electron transfer from each p-block element into the TIP ligand is dependent upon the element–TIP bonding interactions

Tetrakis(imino)pyracene Complexes Exhibiting Multielectron Redox Processes

The differences in redox behavior of the monofunctional bis­(imino)­acenaphthene (BIAN) and bifunctional tetrakis­(imino)­pyracene (TIP) ligands have been explored by treatment of the latter with PI₃, TeI₄, or BI₃. These reactions result in the formation of products involving the transfer of three or four electrons. Accompanying DFT calculations reveal that in each case the extent of electron transfer from each p-block element into the TIP ligand is dependent upon the element–TIP bonding interactions

Understanding the Mechanisms of Cobalt-Catalyzed Hydrogenation and Dehydrogenation Reactions

Cobalt­(II) alkyl complexes of aliphatic PNP pincer ligands have been synthesized and characterized. The cationic cobalt­(II) alkyl complex [(PNHP^Cy)­Co­(CH₂SiMe₃)]­BAr^F₄ (<b>4</b>) (PNHP^Cy = bis­[(2-dicyclohexylphosphino)­ethyl]­amine) is an active precatalyst for the hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols. To elucidate the possible involvement of the N–H group on the pincer ligand in the catalysis via a metal–ligand cooperative interaction, the reactivities of <b>4</b> and [(PNMeP^Cy)­Co­(CH₂SiMe₃)]­BAr^F₄ (<b>7</b>) were compared. Complex <b>7</b> was found to be an active precatalyst for the hydrogenation of olefins. In contrast, no catalytic activity was observed using <b>7</b> as a precatalyst for the hydrogenation of acetophenone under mild conditions. For the acceptorless dehydrogenation of 1-phenylethanol, complex <b>7</b> displayed similar activity to complex <b>4</b>, affording acetophenone in high yield. When the acceptorless dehydrogenation of 1-phenylethanol with precatalyst <b>4</b> was monitored by NMR spectroscopy, the formation of the cobalt­(III) acetylphenyl hydride complex [(PNHP^Cy)­Co^III(κ²-O,C-C₆H₄C­(O)­CH₃)­(H)]­BAr^F₄ (<b>13</b>) was detected. Isolated complex <b>13</b> was found to be an effective catalyst for the acceptorless dehydrogenation of alcohols, implicating <b>13</b> as a catalyst resting state during the alcohol dehydrogenation reaction. Complex <b>13</b> catalyzed the hydrogenation of styrene but showed no catalytic activity for the room temperature hydrogenation of acetophenone. These results support the involvement of metal–ligand cooperativity in the room temperature hydrogenation of ketones but not the hydrogenation of olefins or the acceptorless dehydrogenation of alcohols. Mechanisms consistent with these observations are presented for the cobalt-catalyzed hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols