Discotic liquid crystals of transition metal complexes X. Phthalocyanine derivatives substituted with n-alkyloxyphenyl side chains

Octakis(alkyloxyphenyl)-phthalocyanine derivatives ((C_nOph)₈PcH₂ n = 8, 10 12 and 18), their corresponding copper (II) complexes ((C_nOph)₈PcCu, n = 10, 12 and 18) and octakis(2-ethylhexyl)-PcH₂ have been synthesized and their mesomorphic properties characterized. (C_nOph)₈PcH₂, (n = 12 and 18) exhibit hexagona disordered columnar mesophases whereas (C_nOph)₈PcCu (n = 12 and 18) yields a rectangular disordered columnar liquid crystal. An alkylphenyl-oxymethyl derivative, (C₁₂phOCH₂)₈PcH₂, was synthesized to determine the influence of the connecting link between the side chains and the phthalocyanine macrocycle on the mesomorphic properties.     

N.M.R. study of collective molecular motions in smectogen liquid crystals

Abstract

The proton spin relaxation dispersion, T ₁(v), was studied by field-cycling techniques over a broad Larmor frequency range in the nematic and smectic phases of several liquid crystals (4,4′-bis-heptyloxyazoxybenzene, 4-cyano-4′-8-alkylbiphenyl, 4-cyano-4′-9-alkylbiphenyl, 4-cyano-4′-11-alkylbiphenyl and 4-cyano-4′-9-alkoxybiphenyl) with different sites of the nitrogen atom. The results can be explained quantitatively in terms of nematic and smectic order fluctuations (T ₁ ∝ v ^1/2, T ₁ ∝ v ¹), molecular self-diffusion, molecular rotations and up to six cross-relaxation resonances due to a nitrogen-proton coupling The order fluctuations contribution and the transition from the v ^1/2 to the v ¹ dispersion profile occurs always at Larmor frequencies in the kilohertz range. Some additional measurements of the frequency dependence of the dipolar relaxation time T _1D(v), are not in accord with existing theories.     

Discotic liquid crystals of transition metal complexes: 22. synthesis and mesomorphism of octa-alkoxy-substituted tetraphenylporphyrin derivatives and their copper(II) complexes

Ten novel long-chain-substituted porphyrin derivatives, tetrakis (3,4-dialkoxyphenyl)porphyrins [abbreviated as (CnO8)TPPM: M=H2, n=4, 6, 8, 10, 12, 16, 18; M=Cu, n=8, 12 and (2EtC6O)8TPPH2], were synthesized and their mesomorphism was investigated. Among them four derivatives, (CnO)8TPPH2(n=12, 16, 18) and (C12O)8TPPCu, exhibited a monotropic discotic lamellar (DL) mesophase.     

Bending crystals. Solid state photomechanical properties of transition metal complexes containing semiquinonate ligands

The properties of transition metal complexes containing catecholate and radical semiquinonate ligands have often been found to be unusual and unexpected. Crystals of Rh(CO)₂(3,6-DBSQ), containing the 3,6-di-tert-butyl-1,2-semiquinonate ligand, form as long thin needles that are observed to bend reversibly upon irradiation with NIR light. Crystallographic characterization reveals a stacked solid state lattice with planar molecules aligned with metal atoms atop one another. Electronic spectra recorded in the solid state and in solution show an intense band at 1600 nm that maps the energy dependence of crystal bend angle. The transition is a property of the stacked assembly, rather than of an individual complex molecule, and appears associated with an MLCT process that transfers charge from an antibonding band formed by interacting Rhd _z ² orbitals to the vacant quinone π* orbital. Related observations have been made on the [Co(μ-pyz)(3,6-DBSQ)(3,6-DBCat)]_npolymer. Photomechanical properties appear associated with electronic transitions that lead to a physical change in axial length of a linear polymer, coupled with a soft solid state lattice that permits axial contraction/expansion without crystal fracture.     

Supramolecular ferroelectric liquid crystals. Hydrogen-bonded complexes between benzoic acids and chiral stilbazoles

Supramolecular ferroelectric liquid crystalline complexes have been obtained from 4-alkoxybenzoic acids and optically active trans-4-substituted-4'-stilbazoles. Chiral smectic C phases are induced by the formation of supramolecular mesogenic structure through the selective intermolecular hydrogen bond between the achiral benzoic acids and the chiral non-mesogenic stilbazoles.     

Formation of racemic crystals of transition metal complexes by grinding 1 : 1 mixtures of enantiomeric crystals

Grinding a 1 : 1 enantiomeric mixture of chiral transition metal complex crystals and subsequent annealing afforded crystals of a racemic compound by diffusion and rearrangement of component molecules, without melting and without racemization of each enantiomeric species.     

Cooperative reactivity of early-late heterodinuclear transition metal complexes with polar organic substrates

A comprehensive investigation into the cooperative reactivity of two chemically complementary metal-complex fragments in early-late heterodinuclear complexes has been carried out. Reaction of the partially fluorinated tripodal amidozirconium complexes [HC-(SiMe2NR)3Zr(mu-Cl)2Li(OEt2)2] (R = 2-FC6H4: 2a, 2,3,4-F3C6H4: 2b) with K[CpM(CO)2] (M=Fe, Ru) afforded the stable metal-metal bonded heterodinuclear complexes [HC[SiMe2NR]3-Zr-MCp(CO)2] (3-6). Reaction of the dinuclear complexes with methyl isonitrile as well as the heteroallenes CO2, CS2, RNCO and RNCS led to insertion into the polar metal-metal bond. Two of these complexes, [HC[SiMe2N(2-FC6-H4)]3Zr(S2C)Fe(CO)2Cp] (9a) and [HC-[SiMe2N(2-FC2H4)]3Zr-(SCNPh)Fe(CO)2-Cp] (12), have been structurally characterized by a single crystal X-ray structure analysis, proving the structural situation of the inserted substrate as a bridging ligand between the early and late transition metal centre. The reactivity towards organic carbonyl derivatives proved to be varied. Reaction of the heterobimetallic complexes with benzyl and ethylbenzoate led to the cleavage of the ester generating the respective alkoxozirconium complexes [HC[SiMe2N(2-FC6H4)]3ZrOR] (R = Ph-CH2: 13a, Et: 13b) along with [CpFe-[C(O)Ph](CO)2], whereas the analogous reaction with ethyl formate gave 13b along with [CpFeH(CO)2]; this latter complex results from the instability of the formyliron species initially formed. Aryl aldehydes were found to react with the Zr-M complexes according to a Cannizzaro disproportionation pattern yielding the aroyliron and ruthenium complexes along with the respective benzoxyzirconium species. The transfer of the aldehyde hydrogen atom in the course of the reaction was established in a deuteriation experiment. [HC[SiMe2-N(2-FC6H4)]3Zr-M(CO)2Cp] reacted with lactones to give the ring-opened species containing an alkoxozirconium and an acyliron or acylruthenium fragment; the latter binds to the early transition metal centre through the acyl oxygen atom, as evidenced from the unusuallly low-field shifted 13C NMR resonances of the RC(O)M units. Ketones containing a-CH units react with the Zr-Fe complexes cooperatively to yield the aldol coupling products coordinated to the zirconium complex fragment along with the hydridoiron compound [CpFeH(CO)2], whereas 1,2-diphenylcyclopropenone underwent an oxygen transfer from the keto group to a CO ligand to give a linking CO2 unit and a cyclopropenylidene ligand coordinated to the iron fragment in [HC-[Si(CH3)2N(2,3,4-F3C6H2)]3Zr(mu-O2C)-Fe(CO)[C3Ph2)Cp] (19). The atom transfer was established by 17O and 13C labelling studies. Similar oxygen-transfer processes were observed in the reactions with pyridine N-oxide, dimethylsulfoxide and methylphenylsulfoxide.     

Vibrational spectra of transition metal hexafluoride crystals. I. Orthorhombic MoF6, WF6, and UF6 neat crystals

Neat crystal Raman spectra of orthorhombic MoF₆, WF₆, and UF₆ are presented and discussed. This work lays the foundation for presentation of two-particle and total band structures in the two following papers. The neat crystal spectra are interpreted in terms of an internal-external mode separation and a conventional factor group analysis. In general, these data lead to four essential conclusions concerning hexafluoride crystals: (a) Fermi resonance plays an important role in producing the observed energy and intensity differences in this series; (b) k = 0 exciton structures are remarkably similar in the three crystals; (c) similarities and differences between these solids can be directly correlated with molecular parameters such as dipole derivatives, polarizabilities, etc.; and (d) phonons (external modes) can be neatly separated into rotational and translational normal modes.     

Semi-empirical LCAO-Xα theory for transition metal complexes. I. An outline of the theory

A semi-empirical theory for transition metal complexes is presented. Unusual aspects of the theory are (1) employment of Xα theory, (2) adoption of theoretical exchange parameter, (3) exclusion of (n + 1)s and (n + 1)p atomic orbitals of a nd-transition metal, and (4) variation of atomic orbitals in LCAO method. Also, an improved Mulliken approximation is proposed and used to simplify the LCAO-Xα equations.     

Spin exchange between transition metal complexes and nitroxyl radicals in nonaqueous media

New complexes of diaza- and tetraaza-containing crown ethers, viz., 1,10-diaza-18-crown-6 (1), 1,4,8,12-tetraazacyclopentadecane (2), 1,4,8,11-tetraazacyclotetradecane (3), and 1,4,8,11-tetraazacyclotetradecane 1,4,8,11-tetrachloride tetraacetic acid tetrahydrate (4), with the divalent copper and nickel ions and the Cl^–, Br^–, ClO₄ ^–, NO₃ ^–, and AcO^– counterions were synthesized. The exchange interactions of these compounds and paramagnetic copper and nickel salts with the TEMPO radical in MeOH—CHCl₃ binary mixtures of different compositions were studied. The plots of the linewidths of the hyperfine coupling components of TEMPO vs. concentration of the ions and temperature show that the frequency of diffusion collisions is the rate-limiting step for spin exchange (strong exchange regime). A strong dependence of the exchange rate constant (k _ex) on the crown ether and counterion structure was found. The isotropic hyperfine coupling constants (a _Cu) and g factors (g _i ) were measured for the Cu^II complexes with the crown ethers. In the case of the crown ether complexes 1—3 with CuCl₂, the a _Cu constant decreases linearly with an increase in g _i = g _i – 2.0023 in the series 3 < 2 < 1, whereas k _ex increases linearly in the same series with a decrease in the contact HFC on the Cu^II nucleus (K) and a decrease in covalence of bonding. For the complexes of 2 with Cu^II and different axial ligands (counterions), k _ex increases in the series Cl^– < ClO₄ ^– AcO^– Br^–; < NO₃ ^–. In the case of the complexes of 2 with NiCl₂, k _ex increases in the series 1 < 4 < 3 2. For the Cu^II and Ni^II salts with the Cl^–, ClO₄ ^–, and NO₃ ^– anions, the k _ex values are almost independent of the anion nature. The correlation of the k _ex values with the electron-spin parameters of the complexes is discussed.     

Further studies on reactions of organic halides with disilanes catalysed by transition metal complexes

The interaction of a range of organic halides with (Cl₃Si)₂ or (Me₃Si)₂ in the presence of a variety of transition metal catalysts (very predominantly Pd⁰ or Pd^II complexes) have been examined. PhSiMe₃ was formed from PhCl[m.y., 15%] (m.y. - maximum yield), PhBr (m.y., 92%, with [PdL₂Br₂] as catalyst (L - PPh₃)), and (contrary to earlier reports) PhI (m.y. 51%, with [PdL₂I₂]). MeSiCl₃ was formed from MeBr (m.y., 78% with [PdL₄]) and MeI (m.y., 91% with [PdL₄]), and EtSiCl₃ from EtBr (m.y., 49%, with [PdL₂“Br₂]; L” - P(C₆H₄OMe-p)₃) and EtI (m.y. 45%, with [PdL₄]). Me₄Si was satisfactorily formed from MeBr (m.y. 42%, with [PdL₄]). Evidence was obtained for the formation of Me₃SiCF₃ from CF₃I. Very poor yields of XC₆H₄CH₂SiMe₃ were obtained from XC₆H₄CH2Br (X - H orp-Me) (with X - H some PhSiMe₃ was formed), butp-O₂NC₆H₄CH₂SiMe₃ was formed in 48% yield fromp-O₂NC₆H₄CH₂Cl with [PdL“₄] as catalyst. PhCOSiMe₃ was formed from PhCOCl (m.y. 52% with [PdL₂I₂]. The nickel complex [NiL₄] was moderately effective as a catalyst for reactions between (Cl₃Si)₂ and MeBr, EtBr, or PhCH₂Br. The new complex [PdL₂(SiCl₃)₂] was prepared by treatment of [PdL₄] with (Cl₃Si)₂ or Cl₃SiH, and shown to catalyse the reaction between MeBr and (Cl₃Si)₂.     

Reversible and irreversible thermochromism of some Schiff base metal complexes

Summary Nickel(II) and copper(II) complexes of Schiff bases derived from salicylaldehyde, 2-hydroxy-1-naphthaldehyde, 2,4-dihydroxybenzaldehyde, 2,3-dihydroxybenzaldehyde or 5-chlorosalicylaldehyde and 8-aminoquinoline have been prepared and characterized. Several of the complexes are thermochromic in the solid state. The origin of the thermochrornism is discussed in terms of changes in ligand field strength and coordination geometry. These changes were studied by means of thermal and spectral methods.     

Physical organic chemistry of transition metal carbene complexes. 23. Kinetic and thermodynamic acidities of cationic benzothienyl- and selenylcarbene complexes of rhenium in aqueous acetonitrile.

The pK(a) values of a cationic selenyl- (5H(+)) and a benzothienylcarbene complex (6H(+)) and rate constants for the reversible deprotonation of these complexes by water, carboxylate ions, primary aliphatic amines, secondary alicyclic amines (5H(+) only), and OH(-) (5H(+) only) were determined in 50% MeCN-50% water (v/v) at 25 degrees C. In comparison with neutral Fischer-type carbene complexes such as 1H, the cationic complexes 5H(+) and 6H(+) are much more acidic, and the intrinsic barriers to proton transfer are substantially higher. This paper discusses a variety of factors that contribute to these differences, with the most important ones being that 5H(+) and 6H(+) are cationic, which makes the C(5)H(5)(NO)(PPh(3))Re moiety a stronger pi-acceptor than the (CO)(5)M moieties, coupled with the fact that the deprotonated forms of 5H(+) and 6H(+ )are aromatic molecules.     

Cycloadditions and annulations of transition metal carbene complexes

The synthetic aspects of several reactions from the multifaceted chemistry of Fischer carbene complexes are examined. Their benzannulation reactions with acetylenes are utilized in the synthesis of anthracyclinones via two approaches which differ by beginning at opposite ends of the molecule with either an aryl or an alkenyl substituted chromium carbene complex. The latter has been employed in a formal synthesis of daunomycinone. The Diels-Alder reactions of ,β-acetylenic chromium carbene complexes provide for a facile entry into substituted cyclohexenyl chromium carbene complexes that are subsequently employed in benzannulation reactions. These tandem cycloaddition/annulation reactions are incorporated into model studies for the synthesis of anthracyclinones and wentilactone A. Their potential is also demonstrated for coupling to yet a third reaction of organochromium compounds ; aromatic nucleophilic substitutions on arene chromium tricarbonyl complexes. The annulations of β,β-disubstituted alkenyl complexes provides for a regio- and stereoselective synthesis of 2,4-cyclohexadienones under neutral conditions at near ambient temperatures.     

Thermal degradation of transition metal carbonyl complexes. Part II

The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)₅py (where M=Cr, Mo, and W; py=pyridine) has been studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) and their results reported. It was found that for each of the three complexes studied, the starting material M(CO)₆ was formed which immediately sublimed unchanged with or without concomitant loss of carbonyl (CO) ligands to give the first large weight loss step. This was closely followed by the volatilisation of the pyridine ligands and at higher temperatures the loss of further CO ligands. The enthalpy changes associated with the above-mentioned steps are reported. The conversion of M(CO)₅py to M(CO)₆ and other products was confirmed by the analysis of residue after pyrolysis in a tube furnace under conditions similar to those observed in TG experiments.

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Zusammenfassung Der thermische Abbau von drei monosubstituierten Hexacarbonylkomplexen der allgemeinen Formel M(CO)₅py (mit M=Cr, Mo und W; py=Pyridin) wurden mittels TG und DSC untersucht. Von jeder der drei Komplexe wird die Ausgangssubstanz M(CO)₆ erhalten, die sofort unverändert mit oder ohne gleichzeitigem Verlust an Carbonyl (CO)-Liganden sublimiert und die erste große Gewichtsverluststufe ergibt. Diesem Schritt folgt gleich die Verflüchtigung des Pyridinliganden und bei höheren Temperaturen die Abgabe weiterer CO-Liganden. Die mit den genannten Schritten einhergehenden Enthalpieveränderungen werden mitgeteilt. Die Umwandlung von M(CO)₅py zu M(CO)₆ und anderen Produkten wurden durch Analyse des Rückstandes nach der Pyrolyse in einem Röhrenofen unter ähnlichen Bedingungen wie in den TG-Versuchen bestätigt.

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()₅, M=, , =. , , , . , . . , .

     

On the electronic structure of transition metal complexes. I. An INDO-MO investigation of some octahedral complex ions

Molecular-orbital calculations within the INDO framework are reported for the hexafluoro, hexachloro, and hexaaquo metallate (II) ions of the first transition series. The parameterization scheme and choice of orbital exponents have been detailed. The results indicate that the method in its present form gives fairly satisfactory predictions of molecular properties.