Four‐Membered Heterometallacyclic d0 and d1 Complexes of Group 4 Metallocenes with Amidato Ligands

A study of the coordination chemistry of different amidato ligands [(R)N?C(Ph)O] (R=Ph, 2,6‐diisopropylphenyl (Dipp)) at Group 4 metallocenes is presented. The heterometallacyclic complexes [Cp₂M(Cl){κ²‐N,O‐(R)N?C(Ph)O}] M=Zr, R=Dipp ( 1 a ), Ph ( 1 b ); M=Hf, R=Ph ( 2 )) were synthesized by reaction of [Cp₂MCl₂] with the corresponding deprotonated amides. Complex 1 a was also prepared by direct deprotonation of the amide with Schwartz reagent [Cp₂Zr(H)Cl]. Salt metathesis reaction of [Cp₂Zr(H)Cl] with deprotonated amide [(Dipp)N?C(Ph)O] gave the zirconocene hydrido complex [Cp₂M(H){κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 3 ). Reaction of 1 a with Mg did not result in the desired Zr(III) complex but in formation of Mg complex [(py)₃Mg(Cl) {κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 4 ; py=pyridine). The paramagnetic complexes [Cp′₂Ti{κ²‐N,O‐(R)N?C(Ph)O}] (Cp′=Cp, R=Ph ( 7 a ); Cp′=Cp, R=Dipp ( 7 b ); Cp′=Cp*, R=Ph ( 8 )) were prepared by the reaction of the known titanocene alkyne complexes [Cp₂′Ti(η²‐Me₃SiC₂SiMe₃)] (Cp′=Cp ( 5 ), Cp′=Cp* ( 6 )) with the corresponding amides. Complexes 1 a , 2 , 3 , 4 , 7 a , 7 b , and 8 were characterized by X‐ray crystallography. The structure and bonding of complexes 7 a and 8 were also characterized by EPR spectroscopy.     

Synthesis and characterization of 2-hydroxy-pyridine modified Group 4 alkoxides

The reaction of Group 4 metal alkoxides ([M(OR)₄]) with the potentially bidentate ligand, 2-hydroxy-pyridine (2-HO-(NC₅H₄) or H-PyO), led to the isolation of a family of compounds. The products isolated from the reaction of [M(OR)₄] [where M = Ti, Zr, or Hf; OR = OPrⁱ (OCH(CH₃)₂), OBu^t (OC(CH₃)₃), or ONep (OCH₂C(CH₃)₃] under a variety of stoichiometries with H-PyO were identified by single crystal X-ray diffraction as [(OPrⁱ)₂(PyO-κ²(O,N))Ti(μ-OPrⁱ)]₂ (1), [(ONep)₂Ti(μ(O)-PyO-κ²(O,N))₂(μ-ONep)Ti(ONep)₃] (2), [(ONep)₂Ti(μ(O)-PyO-κ²(O,N))(η¹(N),μ(O)-PyO)(μ-O)Ti(ONep)₂]₂ (2a), [H][(PyO-κ²(O,N))(η¹(O)-PyO)Ti(ONep)₃] (3), [(OR)₂Zr(μ(O)-PyO-κ²(O,N))₂(μ-OR)Zr(OR)₃] (OR = OBu^t (4), ONep (5)), [(OR)₂Zr(μ(O,N)-PyO-κ²(O,N))₂(μ(O,N)-PyO)Zr(OR)₃] (OR = OBu^t (6), ONep (7)), [[(OBu^t)₂Zr(μ(O)-PyO-(κ²(N,O))(μ(O,N)-PyO)₂Zr(OBu^t)](μ₃-O)]₂ (6a), [[(ONep)(PyO-κ²(N,O))Zr(μ(O,N)-PyO-κ²(N,O))₂(μ(O)-PyO-κ²(N,O))Zr(ONep)](μ₃-O)]₂ (7a), [(OBu^t)(PyO-κ²(O,N))Zr(μ(O)-PyO-κ²(O,N))₂((μ(O,N)-PyO)Zr(OBu^t)₃] (8), [(OBu^t)₂Hf(μ(O)-PyO-κ²(N,O))₂(μ-OBu^t)Hf(OBu^t)₃] (9), [(OR)₂ M(μ(O)-PyO-κ²(N,O))₂(μ(O,N)-PyO)M(OR)₃] (OR = OBu^t (10), ONep (11)), and [(ONep)₃Hf(μ-ONep)(η¹(N),μ(O)-PyO)]₂Hf(ONep)₂ (12)·tol. The structural diversity of the binding modes of the PyO led to a number of novel structure types in comparison to other pyridine alkoxy derivatives. The majority of compounds adopt a dinuclear arrangement (1, 2, 4–11) but oxo-based tetra- (2a and 7a), tri- (12), and monomers (3) were observed as well. Compounds 1–12 were further characterized using a variety of analytical techniques including Fourier Transform Infrared Spectroscopy, elemental analysis, and multinuclear NMR spectroscopy.     

Synthesis and properties of terthiophene and bithiophene derivatives functionalized by BF2 chelation: a new type of electron acceptor based on quadrupolar structures

Terthiophene and bithiophene derivatives functionalized by BF(2) chelation were synthesized as a new type of electron acceptor, and their properties were compared to those of bifuran and biphenyl derivatives. These new compounds are characterized by quadrupolar structures due to resonance contributors generated by BF(2) chelation. The bithiophene derivative has a strong quadrupolar character compared with the bifuran and biphenyl derivatives because their hydrolytic analyses indicated that the bithiophene moiety has a larger on-site Coulomb repulsion than the others. The terthiophene derivative has a smaller on-site Coulomb repulsion than the bithiophene derivative due to the addition of a thiophene spacer. These BF(2) complexes exhibit long-wavelength absorptions and according to measurements of ionization potentials and absorption edges they have energetically low-lying HOMOs and LUMOs. The crystal structure of the bithiophene derivative is of the herringbone type, with short F···S and F···C contacts affording dense crystal packing. n-Type semiconducting behaviour was observed in organic field-effect transistors based on these BF(2) complexes.     

Double cation adduction in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of electron deficient anthraquinone derivatives

Six anthraquinone derivatives were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS). Clear (pseudo) molecular ions were observed for all the compounds. Interestingly, for some derivatives, strong ions with double cation adduction were also recorded in the positive mode. It is remarkable that all these ions are singly charged. In this work, possible mechanisms for the double cation adduction were investigated and discussed. It appears that the double cation adduction was due to the electron deficient nature of the derivatives, and formed by taking up two singly charged cations and one electron. Substituents on the anthraquinone ring were found to have a significant effect on the double cation adduction. In contrast, no considerable influence of the acidity of MALDI matrix/solution was observed, even on the double proton adduction. Furthermore, it was demonstrated that double cation adduction might occur in the MALDI gas-phase plume. In addition to the anthraquinones, three more electron deficient compounds of different types, i.e. a perylene bisimide derivative (PB), 3,7-decanoylamino-4,8-dihydrobenzo[1,2-b:4,5-b']dithiophene-4,8-dione (TQ) and 6,6-phenyl C61-butyric acid methyl ester (PCBM), were also analyzed with MALDI TOF MS. The results indicate that the 'abnormal' double cation adduction might be a 'normal' phenomenon in the MALDI TOF MS analysis of many electron deficient compounds.     

Synthesis and structures of the chelating diamido zirconium and hafnium compounds

The chelating diamide lithium complex [Me₂Si{NLiCH(Me)Ph}₂]₂ (1) was synthesized. The X‐ray structure of complex 1 reveals that in the solid state it is a dimer; every lithium atom is three coordinated. The [{Me₂Si{NCH(CH₃)Ph}₂}ZrCl₂LiCl(OEt₂)₂]₂ (2) and [{Me₂Si{NCH(CH₃)Ph}₂}HfCl₂LiCl(OEt₂)₂]₂ (3) complexes were formed by treatment of complex 1 with ZrCl₄ and HfCl₄ respectively in diethyl ether at ambient temperature. Complexes (2) and (3) were also characterized by X‐ray single‐crystal diffraction. Copyright © 2005 John Wiley & Sons, Ltd.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)amide Ligands

A study regarding coordination chemistry of the bis(diphenylphosphino)amide ligand Ph₂P‐N‐PPh₂ at Group 4 metallocenes is presented herein. Coordination of N,N‐bis(diphenylphosphino)amine ( 1 ) to [(Cp₂TiCl)₂] (Cp=η⁵‐cyclopentadienyl) generated [Cp₂Ti(Cl)P(Ph₂)N(H)PPh₂] ( 2 ). The heterometallacyclic complex [Cp₂Ti(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Ti ) can be prepared by reaction of 2 with n‐butyllithium as well as from the reaction of the known titanocene–alkyne complex [Cp₂Ti(η²‐Me₃SiC₂SiMe₃)] with the amine 1 . Reactions of the lithium amide [(thf)₃Li{N(PPh₂)₂}] with [Cp₂MCl₂] (M=Zr, Hf) yielded the corresponding zirconocene and hafnocene complexes [Cp₂M(Cl){κ²‐N,P‐N(PPh₂)₂}] ( 4 Zr and 4 Hf ). Reduction of 4 Zr with magnesium gave the highly strained heterometallacycle [Cp₂Zr(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Zr ). Complexes 2 , 3 Ti , 4 Hf , and 3 Zr were characterized by X‐ray crystallography. The structures and bondings of all complexes were investigated by DFT calculations.     

A Soluble Ladder‐Conjugated Star‐Shaped Oligomer Composed of Four Perylene Diimide Branches and a Fluorene Core: Synthesis and Properties

A new ladder‐conjugated star‐shaped oligomer electron‐transporting material TetraPDI‐PF , with four perylene diimide (PDI) branches and a fluorene core, was efficiently synthesized. The oligomer is highly soluble in dichlorobenzene with a solubility of 155 mg mL^?1, which is higher than those of PDI (35 mg mL^?1) and PDI‐Phen (70 mg mL^?1). Demonstrated by thermogravimetric analysis (TGA), the oligomer exhibits excellent thermal stability with the decomposition temperature (T_d) of 291.2 °C, which is 65 °C higher than that of PDI. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to investigate the electrochemical properties. Although the CV curves of TetraPDI‐PF are successively scanned for 15 cycles, they still remain invariable reduction potentials. The oligomer also shows outstanding photostability, even better than PDI, which maintains 99 % fluorescence intensity after irradiation for 10 min using maximum laser intensity. In the steady‐state space‐charge‐limited current (SCLC) devices, TetraPDI‐PF exhibits higher intrinsic electron mobility of 2.22×10^?5 cm² V^?1 s^?1, three orders of magnitude over that of PDI (3.52×10^?8 cm² V^?1 s^?1). The bulk heterojunction (BHJ) organic solar cells (OSCs) using TetraPDI‐PF as non‐fullerene acceptors and P3HT as donors give optimum power conversion efficiency (PCE) of 0.64 %, which is 64 times that of the PDI:P3HT BHJ cells.     

Spectroscopic and computational investigations of stable radical anions of triosmium benzoheterocycle clusters

The variable temperature (1)H and (13)C NMR and EPR spectra of the stable radical anions [Os(3)(CO)(9)(micro(3)-eta(2)-L)(micro-H)] (LH=phenanthridine, 1; 5,6-benzoquinoline, 2), and [Os(3)(CO)(10)(micro(3)-eta(2)-L)(micro-H)] (LH=quinoxaline, 3) are reported. The radical anions 1(-), 2(-), and 3(-) can be prepared by both exhaustive electrolysis and partially by chemical reduction with cobaltocene and with sodium dispersion (only with sodium dispersion in the case of 3(-)). DFT calculations on 1-3 reveal that the LUMO for the electron-deficient compounds 1 and 2 involves significant contributions from both the heterocyclic ligand and the two metal atoms bridged by the ligand and the micro-hydride. The character of this orbital rationalizes the previously observed regioselective reactions of these complexes with nucleophiles. In contrast, the LUMO for the electron precise 3 involves only ligand-based orbitals. Partial chemical reduction of 1 and 2 requires an excess of either cobaltocene or sodium, and their (1)H and (13)C NMR spectra reveal selective line broadening of those proton resonances that are predicted by DFT calculations to bear the greatest amount of free spin density. The variable temperature behavior of the partially chemically reduced species of 1 and 2 indicates that electron transfer between the reduced/unreduced cluster pair and between the cobaltocene/cobaltocenium pair occurs on the NMR timescale. The radical anions of 1 and 2 prepared by exhaustive electrolysis show an EPR signal at room temperature, while the NMR signals are uniformly broadened. Compound 3 appears to be partially reduced by sodium at room temperature and shows uniformly broadened (1)H NMR resonances at room temperature that sharpen significantly at -80 degrees C. The temperature dependence of the spectra are discussed in terms of the effects of relative electron nuclear relaxation processes, chemical exchange, and the results of the DFT calculations.     

2]borametallocenophanes of group 4 metals: synthesis and structure

We report a series of [2]borametallocenophanes of Ti, Zr, and Hf with various ligand systems. The ligands have been synthesized in high yields starting from 1,2-dibromo-1,2-bis(dimethylamino)diborane(4) upon reaction with Na[C5H5] and Li[C13H9], respectively. All compounds were fully characterized by multinuclear NMR spectroscopy and, for selected examples, by X-ray analysis.     

Interactions of hafnocene and zirconocene dihydrides with acetylenes. Synthesis of the first acetylene complex of hafnium

The first acetylene complex of hafnium, Cp₂Hf[Me₃SiC=CHf(H)Cp₂], was synthesized by the reaction of hafnocene dihydride Cp₂HfH₂ with bis(trimethylsilyl)acetylene in benzene. The reaction is accompanied by elimination of the Me₃Si group from the molecule of the initial acetylene, as a result of which the acetylenide derivative of hafnium Cp₂Hf(C=CSiMe₃)(H) acts as an acetylene ligand in the complex. Under analogous conditions, the reaction of zirconocene dihydride Cp₂ZrH₂ with bis(trimethylsilyl)acetylene affords an analogous acetylene complex of zirconium Cp₂Zr(M₃SiC=CZr(H)Cp₂]. Reactions of Cp₂HfH₂ with tolane and 3-hexyne proceed differently than the reaction with bis(trimethylsilyl)acetylene. Here the corresponding hafnacyclopentadiene metallacycles are the final products. For preliminary communication, see Ref. 3. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 853–856, April, 1997.     

Novel Thiazolo[5,4‐d]thiazole‐Based Organic Dyes for Quasi‐Solid‐State Dye‐Sensitized Solar Cells

A series of novel metal‐free organic dyes containing the thiazolo[5,4‐d]thiazole moiety were designed and synthesized for quasi‐solid‐state dye‐sensitized solar cells (DSSCs). Different alkoxy chains were introduced into the electron donor part of the dye molecules for comparison. The optical, electrochemical, and photovoltaic properties for all sensitizers were systematically investigated. It was found that the sensitizers with the different alkoxy groups have similar photophysical and electrochemical properties, such as absorbance and energy levels, owing to their close chemical structures. However, the quasi‐solid‐state DSSCs based on the resulting sensitizers exhibit different performance parameters. The quasi‐solid‐state DSSC based on sensitizer FNE74 with two octyloxy chains possessed the highest solar energy conversion efficiency of 5.10 % under standard AM 1.5G sunlight illumination without the use of coadsorbant agents.     

Combining high electron affinity and intramolecular charge transfer in 1,3-dithiole-nitrofluorene push-pull diads

Attaching electron-rich 1,3-dithiol-2-ylidene moieties to polynitrofluorene electron acceptors leads to the formation of highly conjugated compounds 6 to 11, which combine high electron affinity with a pronounced intramolecular charge transfer (ICT) that is manifested as an intense absorption band in their visible spectra. Such a rare combination of optical and electronic properties is beneficial for several applications in optoelectronics. Thus, incorporation of fluorene-dithiole derivative 6a into photoconductive films affords photothermoplastic storage media with dramatically increased photosensitivity in the ICT region. A wide structural variation of the dithiole and fluorene parts of the molecules reveals excellent correlation between the ICT energy and the reduction potential with the Hammett's parameters for the substituents. Although only a small solvatochromism of the ICT band was observed, heating the solution led to a pronounced blueshift, which was probably as a result of increased twisting around the C9=C14 bond that links the fluorene and dithiole moieties. X-ray crystallographic analysis of 7a, 8a, 10a, 11a and 13a confirms an ICT interaction in the ground state of the molecules. The C9=C14 double bond between the donor and acceptor is substantially elongated and its length increases as the donor character of the dithiole moiety is enhanced.     

Homoleptic organometallic anions of Ti, Zr, Hf, and Nb

Reactions of C(6)H(5)Li and 4-CH(3)C(6)H(4)Li with halides of Ti, Ir, Hf, and Nb lead to the formation of homoleptic organometallic anions of these metals. Owing to their thermal instability and their sensitivity towards H(2) O and O(2) , these compounds are characterized by single-crystal structure determinations at low temperature, whereas other physical data could only be obtained occasionally. Three pentacoordinate complex anions [Ti(C(6)H(5))(5)](-), [Ti(4-CH(3)C(6)H(4))(5)](-), and [Zr(C(6)H(5))(5)](-) have square-pyramidal structures that display only slight deviations from the ideal geometry, in contrast to the already known structures of [Ti(CH(5))(5)](-). The hexacoordinate complex anions [Zr(C(6)H(5))(6)](2-), [Zr(4-CH(3)C(6)H(4))(6)](2-), [Nb(C(6)H(5))(6)](2-), and [Nb(4-CH(3)C(6)H(4))(6)](2-) all have trigonal-prismatic structures, in accord with the known hexamethyl complex dianions. In contrast, the hexacoordinate complex anion [Hf(C(6)H(5))(6)](2)(-) has an octahedral or close to octahedral structure, in contrast to the known trigonal-prismatic structures of [Ta(C(6)H(5))(6)](-) and [Ta(4-CH(3)C(6)H(4))(6) (-). A qualitative explanation for this structural variability is given.     

Synthesis, ionisation potentials and electron affinities of hexaazatrinaphthylene derivatives

Several hexaazatrinaphthylene derivatives and a tris(thieno)hexaazatriphenylene derivative have been synthesised by reaction of the appropriate diamines with hexaketocyclohexane. The crystal structure of 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene has been determined by X-ray diffraction; this reveals a molecular structure in good agreement with that predicted by density functional theory (DFT) calculations and pi-stacking with an average spacing between adjacent molecular planes of 3.18 A. Solid-state ionisation potentials have been measured by using UV photoelectron spectroscopy and fall in the range of 5.99 to 7.76 eV, whereas solid-state electron affinities, measured using inverse photoelectron spectroscopy, vary in the range -2.65 to -4.59 eV. The most easily reduced example is a tris(thieno)hexaazatriphenylene substituted with bis(trifluoromethyl)phenyl groups; DFT calculations suggest that the highly exothermic electron affinity is due both to the replacement of the outermost phenylene rings of hexaazatrinaphthylene with thieno groups and to the presence of electron-withdrawing bis(trifluoromethyl)phenyl groups. The rather exothermic electron affinities, the potential for adopting pi-stacked structures and the low intramolecular reorganisation energies obtained by DFT calculations suggest that some of these molecules may be useful electron-transport materials.