共查询到20条相似文献,搜索用时 31 毫秒
1.
To appreciate the chemistry of N-heterocyclic carbenes (NHCs), eight carbenic tautomers of pyridine (azacyclohexadienylidenes) are studied at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G∗ and B3LYP/6-311++G∗∗//B3LYP/6-31+G∗ levels of theory. Various thermodynamic parameters are calculated for these minima, along with a kinetic focus on carbene-pyridine tautomerization. Appropriate isodesmic reactions show stabilization energies of 2-azacyclohexa-3,5-dienylidene (1) and 4-azacyclohexa-2,5-dienylidene (6) as 119.4 and 104.1 kcal/mol, rather close to that of the synthesized 1,3-dimethylimidazol-2-ylidene (129.2 kcal/mol). Three different mechanisms are suggested for the tautomerizations including: [1,2]-H shift, [1,4]-H shift, and three sequential [1,2]-H shifts. The calculated energy barrier for [1,2]-H shift of 1 is 44.6 kcal/mol, while the first [1,2]-H shift for the proposed sequential mechanism of 6 requires 65.1 kcal/mol. Three preliminary minimum templates are introduced, which may possess the potential of synthetic consideration: 2,6-di(X)-3,5-dichloro-4-azacyclohexa-2,5-dienylidene for X=Mes, t-Bu, and Ad. 相似文献
2.
Rushdi I. Yousef Tobias Rüffer Harry Schmidt Dirk Steinborn 《Journal of organometallic chemistry》2005,690(5):1178-1191
MgMe2 (1) was found to react with 1,4-diazabicyclo[2.2.2]octane (dabco) in tetrahydrofuran (thf) yielding a binuclear complex [{MgMe2(thf)}2(μ-dabco)] (2). Furthermore, from reactions of MgMeBr with diglyme (diethylene glycol dimethyl ether), NEt3, and tmeda (N,N,N′,N′-tetramethylethylenediamine) in etheral solvents compounds MgMeBr(L), (L = diglyme (5); NEt3 (6); tmeda (7)) were obtained as highly air- and moisture-sensitive white powders. From a thf solution of 7 crystals of [MgMeBr(thf)(tmeda)] (8) were obtained. Reactions of MgMeBr with pmdta (N,N,N′,N″,N″-pentamethyldiethylenetriamine) in thf resulted in formation of [MgMeBr(pmdta)] (9) in nearly quantitative yield. On the other hand, the same reaction in diethyl ether gave MgMeBr(pmdta) · MgBr2(pmdta) (10) and [{MgMe2(pmdta)}7{MgMeBr(pmdta)}] (11) in 24% and 2% yield, respectively, as well as [MgMe2(pmdta)] (12) as colorless needle-like crystals in about 26% yield. The synthesized methylmagnesium compounds were characterized by microanalysis and 1H and 13C NMR spectroscopy. The coordination-induced shifts of the 1H and 13C nuclei of the ligands are small; the largest ones were found in the tmeda and pmdta complexes. Single-crystal X-ray diffraction analyses revealed in 2 a tetrahedral environment of the Mg atoms with a bridging dabco ligand and in 8 a trigonal-bipyramidal coordination of the Mg atom. The single-crystal X-ray diffraction analyses of [MgMe2(pmdta)] (12) and [MgBr2(pmdta)] (13) showed them to be monomeric with five-coordinate Mg atoms. The square-pyramidal coordination polyhedra are built up of three N and two C atoms in 12 and three N and two Br atoms in 13. The apical positions are occupied by methyl and bromo ligands, respectively. Temperature-dependent 1H NMR spectroscopic measurements (from 27 to −80 °C) of methylmagnesium bromide complexes MgMeBr(L) (L = thf (4); diglyme (5); NEt3 (6); tmeda (7)) in thf-d8 solutions indicated that the deeper the temperature the more the Schlenk equilibria are shifted to the dimethylmagnesium/dibromomagnesium species. Furthermore, at −80 °C the dimethylmagnesium compounds are predominant in the solutions of Grignard compounds 4-6 whereas in the case of the tmeda complex7 the equilibrium constant was roughly estimated to be 0.25. In contrast, [MgMeBr(pmdta)] (9) in thf-d8 revealed no dismutation into [MgMe2(pmdta)] (12) and [MgBr2(pmdta)] (13) even up to −100 °C. In accordance with this unexpected behavior, 1:1 mixtures of 12 and 13 were found to react in thf at room temperature yielding quantitatively the corresponding Grignard compound 9. Moreover, the structures of [MgMeBr(pmdta)] (9c), [MgMe2(pmdta)] (12c), and [MgBr2(pmdta)] (13c) were calculated on the DFT level of theory. The calculated structures 12c and 13c are in a good agreement with the experimentally observed structures 12 and 13. The equilibrium constant of the Schlenk equilibrium (2 9c ? 12c + 13c) was calculated to be Kgas = 2.0 × 10−3 (298 K) in the gas phase. Considering the solvent effects of both thf and diethyl ether using a polarized continuum model (PCM) the corresponding equilibrium constants were calculated to be Kthf = 1.2 × 10−3 and Kether = 3.2 × 10−3 (298 K), respectively. 相似文献
3.
Schiff base N,N′-bis(salicylidene)-p-phenylenediamine (LH2) complexed with Pt(en)Cl2 and Pd(en)Cl2 provided [Pt(en)L]2 · 4PF6 (1) and Pd(Salen) (2) (Salen = N,N′-bis(salicylidene)-ethylenediamine), respectively, which were characterized by their elemental analysis, spectroscopic data and X-ray data. A solid complex obtained by the reaction of hexafluorobenzene (hfb) with the representative complex 1 has been isolated and characterized as 3 (1 · hfb) using UV–Vis, NMR (1H, 13C and 19F) data. A solid complex of hfb with a reported Zn-cyclophane 4 has also been prepared and characterized 5 (4 · hfb) for comparison with complex 3. The association of hfb with 1 and 4 has also been monitored using UV–Vis and luminescence data. 相似文献
4.
Angel García-Raso Juan J. Fiol Andrés Tasada Francisca M. Albertí Ferran Bádenas Xavier Solans Mercè Font-Bardia 《Polyhedron》2007
The reaction of N9,N9′-(tri or tetramethylene)-bisadenines (Ade2Cx; x = 3 or 4) in HCl 2 M at 50 °C with MCl2 · 2H2O [M = Zn(II), Cd(II)] yields outer sphere compounds like the previously described [(H-Ade)2C3][ZnCl4] · H2O (3) and [(H-Ade)2C3]2[Cd2Cl8(H2O)2] · 4H2O (4) for Ade2C3 and the new {[(H-Ade)2C4][Cd2Cl6(H2O)2] · 2H2O}n (5) for Ade2C4. On the other hand, only in case of Zn(II) complexes by changing [HCl] to 0.1 M, the inner sphere compounds [H-(Ade)2C3(ZnCl3)] (6) and [H-(Ade)2C4(ZnCl3)] · 1.5H2O (7) are obtained. X-ray diffraction study of compound 6, which represents the first inner sphere complex with a N9,N9′-bisadenine, shows a zwitterionic form with one adenine ring protonated at N(1) while the other ring is coordinated via N(7) to a ZnCl3 moiety as in other alkyl-adenine derivatives. In addition, with Ade2C4, is also possible to obtain another inner sphere complex: [(H-Ade)2C4(ZnCl3)2] · 3H2O (8). 相似文献
5.
Li-Cheng Song Xiang Luo Yong-Zhen Wang Bin Gai Qing-Mei Hu 《Journal of organometallic chemistry》2009,694(1):103-10917
Treatment of parent compounds [(μ-SCH2)2X]Fe2(CO)6 (A, X = O; B, X = NBu-t; C, X = NC6H4OMe-p) with N-heterocyclic carbene IMes (IMes = 1,3-bis(mesityl)imidazol-2-ylidene) generated in situ through reaction of imidazolium salt IMes ·HCl with n-BuLi or t-BuOK afforded the monocarbene-substituted complexes [(μ-SCH2)2X]Fe2(CO)5(IMes) (1, X = O; 2, X = NBu-t; 3, X = NC6H4OMe-p). Similarly, the monocarbene and dicarbene-substituted complexes [(μ-SCH2)2NBu-t]Fe2(CO)5[I∗Mes(CH2)3I∗Mes]·HBr (4) and [(μ-SCH2)2CH2Fe2(CO)5]2[μ-I∗Mes(CH2)3I∗Mes] (5, I∗Mes = 1-(mesityl)imidazol-2-ylidene) could be prepared by reactions of parent compound B with the mono-NHC ligand-containing imidazolium salt [I∗Mes(CH2)3I∗Mes] · HBr and parent compound [(μ-SCH2)2CH2]Fe2(CO)6 (D) with di-NHC ligand I∗Mes(CH2)3I∗Mes (both NHC ligands were generated in situ from reaction of n-BuLi with imidazolium salt [I∗MesI∗Mes(CH2)3I∗Mes] · 2HBr), respectively. The imidazolium salt [I∗Mes(CH2)3I∗Mes] · 2HBr was prepared by reaction of 1-(mesityl)imidazole with Br(CH2)3Br. All the new model compounds 1-5 and imidazolium salt [I∗Mes(CH2)3I∗Mes] · 2HBr were fully characterized by elemental analysis, spectroscopy, and X-ray crystallography. On the basis of electrochemical studies of 1 and 2, compound 2 was found to be a catalyst for proton reduction to hydrogen. In addition, an EECC mechanism for this electrocatalytic reaction is preliminarily suggested. 相似文献
6.
Ekkehardt F. Hahn Beate Heidrich Alexander Hepp Tania Pape 《Journal of organometallic chemistry》2007,692(21):4630-4638
N-Heterocyclic carbene ligands (NHC) were metalated with Pd(OAc)2 or [Ni(CH3CN)6](BF4)2 by in situ deprotonation of imidazolium salts to give the N-olefin functionalized biscarbene complexes [MX2(NHC)2] 3-7 (3: M = Pd, X = Br, NHC = 1,3-di(3-butenyl)imidazolin-2-ylidene; 4: M = Pd, X = Br, NHC = 1,3-di(4-pentenyl)imidazolin-2-ylidene; 5: M = Pd, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 6: M = Ni, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 7: M = Ni, X = I, NHC = 1-methyl-3-allylimidazolin-2-ylidene). Molecular structure determinations for 4-7 revealed that square-planar complexes with cis (5) or trans (4, 6, 7) coordination geometry at the metal center had been obtained. Reaction of nickelocene with imidazolium bromides afforded the η5-cyclopentadienyl (η5-Cp) monocarbene nickel complexes [NiBr(η5-Cp)(NHC)] 8 and 9 (8: NHC = 1-methyl-3-allylimidazolin-2-ylidene; 9: NHC = 1,3-diallylimidazolin-2-ylidene). The bromine abstraction in complexes 8 and 9 with silver tetrafluoroborate gave complexes [NiBr(η5-Cp)(η3-NHC)] 10 and 11. The X-ray structure analysis of 10 and 11 showed a trigonal-pyramidal coordination geometry at the nickel(II) center and coordination of one N-allyl substituent. 相似文献
7.
Petr Novák Lenka Kolá?ová Jaroslav Hole?ek 《Journal of organometallic chemistry》2007,692(20):4287-4296
The set of starting tri-, di- and monoorganotin(IV) halides containing N,C,N-chelating ligand (LNCN = {1,3-[(CH3)2NCH2]2C6H3}−) has been prepared (1-5) and two compounds structurally characterized ([LNCNPh2Sn]+I3− (1c), LNCNSnBr3 (5)) in the solid state. These compounds were reacted with KF with 18-crown-6, NH4F or LCNnBu2SnF to give derivatives containing fluorine atom(s). Triorganotin(IV) fluorides LNCNMe2SnF (2a) and LNCNnBu2SnF (3a) revealed monomeric structural arrangement with covalent Sn-F bond both in the coordinating and non-coordinating solvents, except the behaviour of 3a that was ionized in the methanol solution at low temperature. The products of fluorination of LNCNSnPhCl2 (4) and 5 were described by NMR in solution as the ionic hypervalent fluorostannates or the oligomeric species reacting with chloroform, methanol or moisture to zwitterionic monomeric stannate LNCN(H)+SnF4− (5c), which was confirmed by XRD analysis in the solid state. 相似文献
8.
The reactions of Mo2(O2CCH3)4 with different equivalents of N,N′-bis(pyrimidine-2-yl)formamidine (HL1) and N-(2-pyrimidinyl)formamide (HL2) afforded dimolybdenum complexes of the types Mo2(O2CCH3)(L1)2(L2) (1) trans-Mo2(L1)2(L2)2 (2) cis-Mo2(L1)2(L2)2 (3) and Mo2(L2)4 (4). Their UV–Vis and NMR spectra have been recorded and their structures determined by X-ray crystallography. Complexes 2 and 3 establish the first pair of trans and cis forms of dimolybdenum complexes containing formamidinate ligands. The L1 ligands in 1–3 are bridged to the metal centers through two central amine nitrogen atoms, while the L2 ligands in 1–4 are bridged to the metal centers via one pyrimidyl nitrogen atom and the amine nitrogen atom. The Mo–Mo distances of complexes 1 [2.0951(17) Å], 2 [2.103(1) Å] and 3 [2.1017(3) Å], which contain both Mo?N and Mo?O axial interactions, are slightly longer than those of complex 4 [2.0826(12)–2.0866(10) Å] which has only Mo?O interactions. 相似文献
9.
The stereodynamic behaviour of 1-(trifluoromethylsulfonyl)piperidine 1, 4-(trifluoromethylsulfonyl)morpholine 2, 1,4-bis(trifluoromethylsulfonyl)piperazine 3 and 4-(trifluoromethylsulfonyl)thiomorpholine 1,1-dioxide 4 was studied by low-temperature 1H, 13C and 19F NMR spectroscopies. In acetone solution, compounds 1, 2 and 4 were found to exist as mixtures of two conformers in the ratio of 4:1, 4:1 and 8:1, respectively, differing by orientation of the CF3 group with respect to the ring. Compound 3 exists as a mixture of three conformers in the ratio of 3:28:69 also differing by the orientation of the two CF3 groups. Unlike the previously studied N-trifyl substituted 1,3,5-triheterocyclohexanes, the preferred conformers of compound 1 and of 1,4-diheterocyclohexanes 2-4 are those with the CF3 group directed outward from the ring, which is caused by intramolecular interactions of the oxygen atoms of the CF3SO2N groups with the equatorial hydrogens in the α-position. B3LYP/6-311+G(d,p) calculations of the energy, geometry and NMR parameters corroborate the experimental data. The calculated Perlin effects for all conformers of compounds 1-4 as well as those measured for the major conformers of compounds 3 and 4 were analyzed by the use of the NBO analysis. 相似文献
10.
The reaction of PhHgOAc with 2-NCH3NCTPPH (2) gave a mercury(II) complex of (phenylato)(2-N-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N″)-mercury(II), [HgPh(2-NCH3NCTPP); 7]; the coordination sphere around Hg(1) in 7 was a four-coordinate derivative with a seesaw geometry and dipole–dipole (DD) interaction governed the longitudinal relaxation rate for Hg(1)–Ph–H2,6 protons of 7 in CDCl3 (0.01 M) at 599.95 MHz. 相似文献
11.
Felix D. Sokolov Damir A. Safin Maria G. Babashkina Nail G. Zabirov Vasiliy V. Brusko Nikolay A. Mironov Dmitry B. Krivolapov Igor A. Litvinov Rafael A. Cherkasov Boris N. Solomonov 《Polyhedron》2007
For N-(thio)phosphorylthioureas of the common formula RC(S)NHP(X)(OiPr)2HLI (R = N-(4′-aminobenzo-15-crown-5), X = S), HLII (R = N-(4′-aminobenzo-15-crown-5), X = O), HLIII (R = PhNH, X = S), HLIV (R = PhNH, X = O), and (N,N′-bis-[C(S)NHP(S)(OiPr)2]2-1,10-diaza-18-crown-6) H2LV, salts LiLI,III,IV, NaLI–IV, KLI–IVM2LV (M = Li+, Na+, K+), Ba(LI,III,IV)2, and BaLV have been synthesized and investigated. Compounds NaLI,II quantitatively drop out as a deposit in ethanol medium, allowing the separation of Na+ and K+ cations. This effect is not displayed for the other compounds. The crystal structures of HLIII and the solvate of the composition [K(Me2CO)LIII] have been investigated by X-ray crystallography. 相似文献
12.
Maria Daoudi Abdelali Kerbal Jean-Pierre Launay Taibi Ben Hadda Pierre H. Dixneuf 《Tetrahedron》2006,62(13):3123-3127
A series of tridentate ligands N,N-bis-[(di-substituted-1-pyrazolyl)methyl]arylamines 2-3a,b and benzylamine 4a,b, tetradentate N,N′-bis-[(di-substituted-1-pyrazolyl)methyl]para-phenylenediamines 7a,b and hexadentate N,N,N′,N′-tetra-[(di-substituted-1-pyrazolyl)methyl]para-phenylenediamines 8a,b has been prepared in good yield by condensation of arylamines, benzylamine or para-phenylenediamine with N-hydroxymethyl disubstituted pyrazoles 1a,b. The synthesis and characterisation of these various polydentate ligands are described. 相似文献
13.
Guo-Lin Xu 《Journal of organometallic chemistry》2003,683(2):388-397
Three diruthenium(III) compounds Ru2(L)4Cl2, where L is mMeODMBA (N,N′-dimethyl-3-methoxybenzamidinate, 1a), DiMeODMBA (N,N′-dimethyl-3,5-dimethoxy benzamidinate, 1b), or DEBA (N,N′-diethylbenzamidinate, 1c), were prepared from the reactions between Ru2(OAc)4Cl and respective HL under reflux conditions. Metathesis reactions between 1 and LiC2Y resulted in bis-alkynyl derivatives Ru2(L)4(C2Y)2 [Y=Ph (2), SiMe3 (3), SiiPr3 (4) and C2SiMe3 (5)]. The parent compounds 1 are paramagnetic (S=1), while bis-alkynyl derivatives 2-5 are diamagnetic and display well-solved 1H- and 13C-NMR spectra. Molecular structures of compounds 1b, 1c, 2c, 3c and 4b were established through single crystal X-ray diffraction studies, which revealed RuRu bond lengths of ca. 2.32 Å for parent compounds 1 and 2.45 Å for bis-alkynyl derivatives. Cyclic voltammograms of all compounds feature three one-electron couples: an oxidation and two reductions, while the reversibility of observed couples depends on the nature of axial ligands. 相似文献
14.
Federica Ianni Andrea Carotti Maura Marinozzi Gloria Marcelli Alessandro Di Michele Roccaldo Sardella Wolfgang Lindner Benedetto Natalini 《Analytica chimica acta》2015
A chiral chromatography method enabling the simultaneous diastereo- and enantioseparation of Nα-Boc-N4-(hydroorotyl)-4-aminophenylalanine [Boc-Aph(Hor)-OH, 1] was optimized with a quinine-based zwitterionic stationary phase. The polar-ionic eluent system consisting of ACN:MeOH:water—49.7:49.7:0.6 (v/v/v) with formic acid (4.0 mM) and diethylamine (2.5 mM), allowed the successful separation of the four acid stereoisomers: αd,d-/d,l-1 = 1.08; αd,l-/l,d-1 = 1.08; αl,d-/l,l-1 = 1.40. 相似文献
15.
Freddy Tjosaas 《Journal of organometallic chemistry》2007,692(24):5429-5439
Palladium complexes of N-phenyl-2-pyridylamine (4) and dipyridylamine substrates (7, 11) have been studied. Due to the coordination ability of the pyridine-nitrogen atoms, the pyridyl substrates, 4, 7, 11 were subjected to Pd(OAc)2 complexations and a number of N-aryl-2-pyridylamine Pd complexes (13-17) were isolated and characterised, in particular by NMR and ESI-MS. A new method for the preparation of the acetato-bridged six-membered ring palladacycle complex (13) of 4 is reported. The dipyridyl amines 7, 11 formed cis/trans bis-dentate acetato-bridged dimeric Pd2Lig2(OAc)2 (14a,b/16a,b) and Pd3Lig2(OAc)4 complexes (15a,b/17a,b). The N-aryl-2-pyridylamine substrates (4, 7, 11) were prepared by oxidative nucleophilic substitution, by 1,3-cycloaddition reaction or by Buchwald amination. 相似文献
16.
The coordinating properties of N-o-chlorobenzamido-meso-tetraphenylporphyrin (N-NHCO(o-Cl)C6H4-Htpp; 11) have been investigated for the Zn2+ ion. Insertion of Zn results in the formation of the zinc complex Zn(N-NCO(o-Cl)C6H4-tpp)(MeOH) · MeOH (12 · MeOH). The diamagnetic 12 · MeOH can be transformed into the diamagnetic Zn(N-NHCO(o-Cl)C6H4-tpp)Cl · CH2Cl2 (13 · CH2Cl2) in a reaction with aqueous hydrogen chloride (2%). X-ray structures for 12 · MeOH and 13 · CH2Cl2 have been determined. The coordination sphere around the Zn2+ ion in 12 · MeOH is a distorted trigonal bipyramid with N(2), N(4) and O(2) lying in the equatorial plane, whereas for the Zn2+ ion in 13 · CH2Cl2, it is a square-based pyramid in which the apical site is occupied by the Cl(1) atom. 相似文献
17.
Yoshikatsu Ito 《Tetrahedron》2007,63(15):3108-3114
Photocarboxylation of 1,1-diphenylethylene with N,N,N′,N′-tetramethylbenzidine (TMB) in MeCN under bubbling of CO2 proceeded with high catalytic efficiency, giving 3,3-diphenylacrylic acid (DPA) and 3-hydroxy-3,3-diphenylpropionic acid (20). The turnover number (TON=(DPA+20)/TMB) reached 17. Similarly, 1-phenyl-1-cyclohexene yielded cis-2-acetamido-2-phenylcyclohexanecarboxylic acid with TON 5.9. As compared with related N,N-dimethylaniline derivatives, TMB is more resistant to photodecomposition, has the much larger absorbance in the S0→S1 transition, and has the lower quenching efficiency by CO2. Probably these factors are partly responsible for the high TON observed for TMB. 相似文献
18.
Elena Mas-Marzá Eduardo Peris Beatriz Royo 《Journal of organometallic chemistry》2006,691(12):2708-2712
Compound MoO2Cl2(THF)2 reacts with two equivalents of 1,3-dialkyl substituted 4,5-dimethylimidazol-2-ylidenes to give the dioxomolybdenum(VI) complexes MoO2Cl2(LR)2 [R = Me (1), i-Pr (2)]. Treatment of MoO2Cl2(THF)2 with one equivalent of the N-heterocyclic carbenes LMe, Li-Pr and C1Ln-Bu (LMe = 1,3,4,5-tetramethylimidazol-2-ylidene, Li-Pr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, and C1Ln-Bu = 1,3-dibutyl-4,5-dichloroimidazol-2-ylidene) affords the monocarbene adducts MoO2Cl2(LR) [R = Me (3), i-Pr (4)] and MoO2Cl2(C1Ln-Bu) (5), respectively. Decomposition of complexes 1-5 affords a molybdenum oxychloride anion [Mo2O5Cl4]2− as an imidazolium salt. 相似文献
19.
A series of N-(2-pyridyl)benzamides (1)-(11) and their nickel complexes, [N-(2-pyridyl)benzamide]dinickel(II) di-μ-bromide dibromide (12)-(16) and (aryl)[N-(2-pyridyl)benzamido](triphenylphosphine)nickel(II) (17)-(24), were synthesized and characterized. The single-crystal X-ray analysis revealed that 12 and 14 are binuclear nickel complexes bridged by bromine atoms and each nickel atom adopts a distorted trigonal bipyramidal geometry. The key feature of the complexes 17, 19 and 23 is each has a six-membered nickel chelate ring including a deprotonated secondary nitrogen atom and an O-donor atom. The nickel complexes show moderate to high catalytic activity for ethylene oligomerization with methylaluminoxane (MAO) as cocatalyst. The activity of 12-16/MAO systems is up to 3.3 × 104 g mol−1 h−1 whereas for 17-24/MAO systems it is up to 4.94 × 105 g mol−1 atm−1 h−1. The influence of Al/Ni molar ratio, reaction temperature, reaction period and PPh3/Ni molar ratio on catalytic activity was investigated. 相似文献
20.
Vadapalli Chandrasekhar Bani Mahanti Kotamarthi Bhanuprakash 《Journal of organometallic chemistry》2011,696(14):2711-2719
The reaction of the cyclometalated chloro-bridged iridium(III) dimer, [(ppy)2 Ir(μ-Cl)]2 (ppy - 2-phenyl pyridine) with N-aryl picolinamides (LH, LH-NO2, LH-CH3, LH-l, LH-F) resulted in the formation of neutral heteroleptic complexes [Ir(ppy)2L] (1), [Ir(ppy)2L-NO2](2), [Ir(ppy)2L-CH3](3), [Ir(ppy)2L-Cl](4) and [Ir(ppy)2L-F] (5). These complexes contain a six-coordinate iridium with a 2C, 4N coordination environment. The N-aryl picolinamide ligands are deprotonated during complexation and the resulting amidates bind to iridium in a chelating manner (N, N). Optical spectroscopic studies revealed that the complexes 1-5 exhibited intense π→π∗ absorptions in the ultraviolet region. In addition low energy transitions due to 1MLCT, 1LLCT and 3MLCT are also seen. The emission spectra of 1-5, upon excitation at 450 nm, show a single emission with a λmax around 513 nm. The lifetimes of this emission are in between 7.4 and 9.6 μs while the quantum yields are quite high and range from 0.2 to 0.5. Based on density functional theory (DFT) calculations on 1 and 3, the three highest occupied orbitals are composed of ligand π orbitals mixed with Ir-d orbitals while the three lowest unoccupied orbitals are mostly π orbitals of the ligands. From the time dependent DFT calculations it is revealed that the lowest energy electronic singlet and triplet excitations are a mixture of MLCT and LLCT. 相似文献