Preparation and characterization of M2(SeAr′)6 and mixed ligand M2(OR)2(SeAr′)4 species (M = Mo, W)

Toluene solutions of M₂(NMe₂)₆ (M = Mo, W) react with mesitylene selenol (Ar′SeH) to give M₂(SeAr′) ₆ complexes. MO₂(OR)₆ (R = ^tBu, CH₂^tBu) react with excess> 6 fold) Ar′SeH to give Mo₂ (SeAr′)₆, whilst W₂(OR)₆(py)₂ (R = ⁱPr, CH₂^tBu) react with excess (> 6 fold) Ar′SeH to give W₂(OR)₂(SeAr′)₄. Reaction of MO₂(OPrⁱ)₆ with Ar′SeH produces Mo₂(OPrⁱ)₂ (SeAr′)₄ which crystallizes in two different space groups. These areneselenato complexes are air-stable and insoluble in common organic solvents. X-ray crystallographic studies revealed that the Mo₂(SeAr′)₆ and W₂(SeAr′)₆ compounds are isostructural in the solid state and adopt ethane-like staggered configurations with the following important structural parameters, M---M (W---W/Mo---Mo) 2.3000(11)/2.2175(13) Å, M---Se 2.430 (av.)/2.440 (av.) Å, M---M---SE 97.0° (av.)°. In the solid state W₂(OⁱPr)₂(SeAr′)₄ adopts the anti-configuration with crystallographically imposed C_i symmetry and W---W 2.3077(7) Å, W---Se 2.435 (av.) Å, W---O 1.858(6) Å; W---W---SE 100.27(3)°, 93.8(3)° and W---W---O 108.41(17)°. Mo₂(OPrⁱ)₂(SeAr′) ₄ crystallizes in both P and A2/a space groups in which the molecules are isostructural with each other and the tungsten analogue. Important bond lengths and angles are Mo---Mo 2.180(24) Å, Mo---Se 2.432(av.) Å, Mo---O 1.872(9) Å, Mo---Mo---Se 99.39(9)°, 94.71(8)°, Mo---Mo---O 107.55(28)°.     

Synthesis and characterization of two cyclic organosiloxanes by multinuclear NMR spectroscopy and X-ray crystallography

1,3-[2′,6′-Pyridinebis(methyleneoxy)]-1,3-bis(diphenyl)cyclodisiloxane (9) and 2,6-pyridinebis(1,1-diphenylethoxy)diphenylsilane (11) were obtained from 2,6-pyridinediol derivatives with dichlorodiphenylsilane. An N→Si interaction is present in 2,6-pyridinebis(1,1-diphenylethoxy)diphenylsilane, which also shows fluxional behavior. The activation energy of 13.2 kcal mol⁻¹ for 11 was obtained for the intramolecular exchange between the phenyl groups from a variable-temperature ¹H-NMR study. The compounds were characterized by ¹H-, ¹³C- and ²⁹Si-NMR and their structures were established by X-ray crystallographic studies.     

β-二亚胺基Ni(Ⅱ)配合物的合成及其催化乙烯聚合研究

合成了一系列带有不同取代基的β-二亚胺配体及其Ni(Ⅱ)的配合物.利用核磁共振谱、元素分析和单晶X射线衍射等手段对配体及配合物进行了表征.元素分析和单晶结构分析表明,在相同的实验条件下苯基取代的β-二亚胺配体锂盐与NiCl2反应只能得到双配体化合物1;而2,6-二甲基苯基及2,6-二异丙基苯基取代的配体锂盐与NiCl2反应得二聚的单氯化物2和3,2个Ni原子通过双氯桥连接在一起.配合物2和3经烷基铝活化后催化乙烯聚合可得到高分子量聚乙烯,活性可达到2.0×105gPE/(molcat·h),分子量最高可达到100万以上.     

o-Hydroxyarylphosphines and diphosphines: metallation-rearrangement versus P---O reduction of o-halogenoaryloxyphosphines by sodium

o-Bromo- and o-chloroaryloxyphosphines 1 may react with sodium in two competing ways: (i) metal halogen exchange followed by rapid intramolecular 1,3-rearrangement to give sodium o-hydroxylato-arylphosphines 2, later converted to their OSiMe₃ derivatives 3, and (ii) reductive cleavage of the P---O bond to give diphosphines 4 or phosphides. The o-metallation is preferred with the more reactive bromides and bulky phosphino substituents or screened P---O bonds by substituents at 6-position. The reduction is favoured in the case of the less reactive aryl chlorides, small alkyl and flat phenyl substituents at phosphorus. Mixtures of meso- and rac-diphosphines are formed from asymmetric derivatives ArOPRR′. The meso-isomer of 1,2-di(tert-butyl)-1,2-diphenyldiphosphine is preferred.     

The effect of substituents on the phenyl portion of the imido ligand on the structure and properties of molybdenum(VI) imido complexes

Anilines with alkyl substituents on the phenyl ring (ArNH2 = 2,4,6-trimethylaniline; 2,3-, 2,4-, 2,6-, and 3,4-dimethylaniline; and 2,6-diisopropylaniline) react with MoO(X)2(dtc)2 (X = Cl or Br; dtc = diethyldithiocarbamate) in methanol in the presence of 2 equiv of triethylamine to form ionic imido complexes of the type [MoNAr(dtc)3]2[Mo6O19] or MoNAr(dtc)3]4[Mo8O26]. The same reaction in THF with butyllithium as base yields imido complexes of the type MoNAr(X)2(dtc)2. The structures of three ionic, five chloro, and two bromo complexes have been determined by X-ray crystallography. In all complexes, the molybenum center is a distorted pentagonal bipyramid. While the structures are similar, the angles of the imido linkages differ. The effect of the substituents on the phenyl ring of the imido ligand on the 95Mo NMR chemical shifts was determined. The Mo nucleus becomes more deshielded with the substituents in the following order: 3,4-Me2 < 2,3-Me2 < 2,4-Me2 < 2,6-Me2 < 2,4,6-Me3 < 2,6 isopropyl. Complexes with more deshielded 95Mo centers tend to have angles of the imido linkage that are closer to 180 degrees.     

Group 4 metallacarboranes of constrained geometries derived from B(cage)- and C(cage)-silylamido-substituted carborane ligands: a synthetic and structural investigation

The reactions of RNHSi(Me)₂Cl (1, R=t-Bu; 2, R=2,6-(Me₂CH)₂C₆H₃) with the carborane ligands, nido-1-Na(C₄H₈O)-2,3-(SiMe₃)₂-2,3-C₂B₄H₅ (3) and Li[closo-1-R′-1,2-C₂B₁₀H₁₀] (4), produced two kinds of neutral ligand precursors, nido-5-[Si(Me)₂N(H)R]-2,3-(SiMe₃)₂-2,3-C₂B₄H₅, (5, R=t-Bu) and closo-1-R′-2-[Si(Me)₂N(H)R]-1,2-C₂B₁₀H₁₀ (6, R=t-Bu, R′=Ph; 7, R=2,6-(Me₂CH)₂C₆H₃, R′=H), in 85, 92, and 95% yields, respectively. Treatment of closo-2-[Si(Me)₂NH(2,6-(Me₂CH)₂C₆H₃)]-1,2-C₂B₁₀H₁₁ (7) with three equivalents of freshly cut sodium metal in the presence of naphthalene produced the corresponding cage-opened sodium salt of the “carbons apart” carborane trianion, [nido-3-{Si(Me)₂N(2,6-(Me₂CH)₂C₆H₃)}-1,3-C₂B₁₀H₁₁]³⁻ (8) in almost quantitative yield. The reaction of the trianion, 8, with anhydrous MCl₄ (M=Ti and Zr) in 1:1 molar ratio in dry tetrahydrofuran (THF) at −78 °C, resulted in the formation of the corresponding half-sandwich neutral d⁰-metallacarborane, closo-1-M[(Cl)(THF)_n]-2-[1′-η¹σ-N(2,6-(Me₂CH)₂C₆H₃)(Me)₂Si]-2,4-η⁶-C₂B₁₀H₁₁ (M=Ti (9), n=0; M=Zr (10), n=1) in 47 and 36% yields, respectively. All compounds were characterized by elemental analysis, ¹H-, ¹¹B-, and ¹³C-NMR spectra and IR spectra. The carborane ligand, 7, was also characterized by single crystal X-ray diffraction. Compound 7 crystallizes in the monoclinic space group P2₁/c with a=8.2357(19) Å, b=28.686(7) Å, c=9.921(2) Å; β=93.482(4)°; V=2339.5(9) ų, and Z=4. The final refinements of 7 converged at R=0.0736; wR=0.1494; GOF=1.372 for observed reflections.     

Theoretical investigations of the substituent effect on the absorption and emission properties for a series of platinum (II) complexes supported by tetradentate N2O2 chelates

The photophysical properties, which vary as R is varied, of a series of [Pt(N₂O₂)] complexes bearing bis(phenoxy)bipyridine auxiliaries with different substituents R=H (Pt-H) (1), 4,4′-2NH₂ (Pt-NH₂) (2), 4,4′-2tBu (Pt-tBu) (3), 4,4′-2CN (Pt-CN) (4), and 4,4′-2NO₂ (Pt-NO₂) (5) are investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The solvent effects are discussed in CH₂Cl₂, CH₃CN and CH₃OH solutions, respectively, by polarizable continuum model (PCM). It is anticipated that compared with σ-donor substituents, π-acceptors have more dramatic effects on the electronic and optical properties in this series of complexes. Introduction of π-electron withdrawing substituents on bipyridine ligand will benefit the LLCT (or MLCT) and prohibit the non-radiative pathways via d–d transitions by increasing the energy gap between the HOMO–LUMO and d–d transitions. The results also reveal that the lowest-energy excitations of all complexes show blue-shifts in the polarized solution and when the polarity of the solvent increases from CH₂Cl₂, CH₃CN and CH₃OH, the low-energy broad absorption band exhibit blue-shifts. The lowest-energy excitations and photoluminescence of all complexes are dominated by π(phenoxy)→π^*(bpy/NO₂) (LLCT) excited state mixed with some energetically dπ (Pt)→π^*(bpy/NO₂) (MLCT) transition.     

Oxidation of 2,6-di-tert-butylphenol with polymer anchored molybdenyl and vanadyl complexes

The oxidation of 2,6-di-tert-butylphenol with tert-butylhydroperoxide (Bu^tO₂H) has been studied using polymer (XAD₄) anchored salicylaldoxime, 1,3-propylene-bis-salicylaldimine and o-phenylene-bis-salicylaldimine complexes of molybdenum and vanadium in acetonitrile. The predominant products formed in the oxidation reactions were 2,6-di-tert-butylbenzoquinone (BQ) and 3,3′-5,5′-tetra-tert-butyldiphenoquinone (dPQ), whereas with some only 2,6-di-tert-butylbenzoquinone was formed. This is the first reported use of polymer anchored molybdenyl and vanadyl complexes in selective oxidation of 2,6-di-tert-butylphenol. Solvent plays an important role in this reaction. The effects of varying the ligand, metal and the support on the catalytic activity in the oxidation of 2,6-di-tert-butylphenol have been studied. With polymer anchored MoO₂(salpen), 81% of 2,6-di-tert-butylbenzoquinone was formed from 2,6-di-tert-butylphenol.     

Dynamic chirality in selected diaryl methane containing drugs. An exploratory ab initio conformational study

Diaryl methane molecules (Ar–CH₂–Ar) represent double rotor conformational problems. The simplest diaryl methane, diphenyl methane (Ph–CH₂–Ph), governs certain symmetric conformational potential energy surface (PES) topology. With the replacement of one of the phenyl groups by a heterocyclic moiety, the PES topology may change dramatically. The induction of point-chirality, in the prochiral CH₂ group, by axis-chirality or plane-chirality is explored within the framework of ‘dynamic chirality’.     

Titanium imido complexes containing 1,3,5-triazacyclohexane ligands

The syntheses of the 1,3,5-trimethyl- and tri-tert-butyl-1,3,5-triazacyclohexane-supported imido complexes [M(NR)(R′₃tach)Cl₂] (M = Ti or Zr (NMR only); R = Bu^t or 2,6-C₆H₃Prⁱ₂; R′ = Me or Bu^t) are reported, along with that of the thermally robust dibenzyl derivative [Ti(NBu^t)(Me₃tach)(CH₂Ph)₂]. The tert-butylimido ligand in [Ti(NBu^t)(Me₃tach)Cl₂] undergoes exchange with ArNH₂ (Ar = 4-C₆H₄Me or 2,6-C₆H₄Me or 2,6-C₆H₃Prⁱ₂) to form the corresponding arylimides [Ti(NAr)(Me₃tach)Cl₂]. The Me₃tach ring in [Ti(NR)(Me₃tach)Cl₂] undergoes slow exchange with Bu^t₃tach or Me₃tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) to give the ring-exchanged products [Ti(NR)(Bu^t₃tach)Cl₂] and [Ti(NR)(Me₃tacn)Cl₂], respectively. The complexes [Ti(NR)(Me₃tach)X₂] (R = Bu^t or 2,6-C₆H₃Prⁱ₂; X = Cl or CH₂Ph) exhibit room-temperature dynamic NMR behaviour via an unusual trigonal twist of the facially coordinated Me₃tach ligand, and the activation parameters for these processes have been measured and are discussed. The X-ray structures of [Ti(NR)(Bu^t₃tach)Cl₂] (R = Bu^t or 2,6-C₆H₃Prⁱ₂) and [Ti(NBu^t)(Me₃tach)(X)₂] [X= Cl or CH₂Ph) are reported. Me₃tach and Bu^t₃tach = 1,3,5-trimethyl- and tri-tert-butyl-1,3,5-triazacyclohexane, respectively.     

New arylchlorogermylenes stabilized by two ortho side-chain donor ligands

Arylchlorogermylenes stabilized by two ortho side-chain donor ligands (aryl=2,6-(CH₂NR₂)₂C₆H₃ with R=Et: 1 and R=i-Pr: 2) were synthesized; 1 was characterized by an X-ray analysis and intramolecular coordinations N→Ge were evidenced from the two side-chains. In this paper, all known stable and isolated halogermylenes are reviewed. Significant bond lengths of their X-ray structures are reported and compared. Surprisingly, attempts to obtain chlorogermylenes bearing a substituent with a strong electron-withdrawing effect such as 2,4,6-tris(trifluoromethyl)phenyl (Ar′) or 2,6-bis(trifluoromethyl)phenyl (Ar″) led us to new compounds, the diarylchlorogermanes Ar′₂GeHCl or Ar″₂GeHCl.     

Mixed alkyl isocyanide-1,4-diaza-1,3-butadiene complexes of molybdenum(II) and tungsten(II)

The reactions of M(CO)₄(R′-DAB) (M = Mo) or W; R′-DAB = R′-N=CHCH=NR′ (R′ = i-propyl, t-butyl, or cyclohexyl) with SnCl₄ in dichloromethane solution result in the formation, in high yield, of the orange, diamagnetic, seven-coordinate oxidative-addition products M(CO)₃(R′-DAB)(SnCl₃)Cl. The reactions of Mo(CO)₃(R′-DAB)(SnCl₃)Cl (R′ = i-Pr or Cy) with an excess of alkyl isocyanide RNC (R = CHMe₂, CMe₃, or C₆H₁₁) in the presence of KPF₆ lead to the formation of [Mo(CNR)₄(R′-DAB)Cl]PF₆ or [Mo(CNR)₅(R′-DAB)](PF₆)₂ depending upon the reaction stoichiometry and reaction conditions. The monocationic chloro species are converted to [Mo(CNR)₅(R′-DAB)](PF₆)₂ upon reflux with the stoichiometric amount of RNC. Under similar reactions conditions M(CO)₃(t-Bu-DAB)(SnCl₃)Cl (M = Mo or W) derivatives react with alkyl isocyanides with the reductive-elimination of the elements of SnCl₄ and the formation of octahedral M(CO)₃(CNR)(t-Bu-DAB). The dark red compounds [Mo(CNCMe₃)₅(R′-DAB)](PF₆)₂ (R′ = i-Pr or Cy) react readily with cyanide ions at ambient temperatures in methanol to yield [Mo(CNCMe₃)₄(R′-DAB)(CN)]PF₆. Attempts to thermally dealkylate the parent complexes [Mo(CNCMe₃)₅(R′-DAB)](PF₆)₂ (R′ = i-Pr or Cy) to these same cyano species were unsuccessful.     

Structural and spectral studies of N-2-(pyridyl)-, N-2-(3-, 4-, 5-, and 6-picolyl)- and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenylthioureas

Structures of the following compounds have been obtained: N-(2-pyridyl)-N′-2-thiomethoxyphenylthiourea, PyTu2SMe, monoclinic, P2₁/c, a=11.905(3), b=4.7660(8), c=23,532(6) Å, β=95.993(8)°, V=1327.9(5) ų and Z=4; N-2-(3-picolyl)-N′-2-thiomethoxyphenyl-thiourea, 3PicTu2SeMe, monoclinic, C2/c, a=22.870(5), b=7.564(1), c=16.941(4) Å, β=98.300(6)°, V=2899.9(9) ų and Z=8; N-2-(4-picolyl)-N′-2-thiomethoxyphenylthiourea, 4PicTu2SMe, monoclinic P2₁/a, a=9.44(5), b=18.18(7), c=8.376(12) Å, β=91.62(5)°, V=1437(1) ų and Z=4; N-2-(5-picolyl)-N′-2-thiomethoxyphenylthiourea, 5PicTu2SMe, monoclinic, C2/c, a=21.807(2), b=7.5940(9), c=17.500(2) Å, β=93.267(6)°, V=2893.3(5) ų and Z=8; N-2-(6-picolyl)-N′-2-thiomethoxyphenylthiourea, 6PicTu2SMe, monoclinic, P2₁/c, a=8.499(4), b=7.819(2), c=22.291(8) Å, β=90.73(3)°, V=1481.2(9) ų and Z=4 and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenyl-thiourea, 4,6LutTu2SMe, monoclinic, P2₁/c, a=11.621(1), b=9.324(1), c=14.604(1) Å, β=96.378(4)°, V=1572.4(2) ų and Z=4. Comparisons with other N-2-pyridyl-N′-arylthioureas having substituents in the 2-position of the aryl ring are included.     

Intramolecular meta photocycloaddition of 6-arylhex-2-enes Part 2

The course of the intramolecular meta photocycloaddition of ring-substituted (E)- and (Z)- 6-phenylhex-2-enes depends on the position and nature of the substituent. In this paper, the effects of methyl and cyano groups and the fluorine atom are described. The results are in agreement with a reaction mechanism in which the excited phenyl ring becomes polarized when it is approached by the alkene. The dipolar character becomes particularly apparent in the case of fluorine which, depending on its position, can stabilize either the negative charge through its inductive effect or the positive charge through its mesomeric effect. The configuration of the terminal methyl group sterically influences the photoreaction. The Z alkenes readily undergo the 1′,3′-addition, but fail to add in the 2′,6′-mode, even if substituents which strongly promote this mode are present. The E alkenes seem to suffer from steric hindrance in the 2′,6′- and the 1′,3′-mode, but the electronic effects of activating substituents provide compensation and substituents may have a pronounced influence on the ratio of the two modes.     

Synthesis, structure and reactions of seven-coordinate, phosphine-supported, halide-activated carbonyl- and alkyne-complexes of niobium(I)

The complexes (Hal)Nb(CO)₃(PR₃)₃ (PR₃ = PEt₃, Hal = I; PR₃ = PMe₂Ph, Hal = Cl, Br, I) and (Hal)Nb(CO)_4/2(dppe)_1/2 (Hal = Br, I) have been prepared by oxidative halogenation of carbonylniobate with pyridinium halides (Hal = Cl, Br) or iodine (Hal = I). In the tricarbonyls, one CO and one PR₃ are labile and can be displaced by a four-electron donating alkyne to give all-trans-[(Hal)Nb(CO)₂(RCCR′)(PR₃)₂] (PR₃ = PMe₂Ph; Hal = Cl, Br, I: R, R′ = H, Et, Ph; R = H, R′ = Ph. PR₃ = PEt₃, Hal = I: R, R′ = Pr; R = H, R′ = Bu, Ph; R = Me, R′ = Et). In the case of acetylene, INb(CO)(HCCH)₂(PEt₃)₂ is also formed. PR₃ can be displaced by P(OMe) ₃. In the tetracarbonyls, two CO ligands are replaced by two isonitriles to form INb(CO)₂(CNR)₂dppe (R = ^tBu, Cy), or by one alkyne to form (Hal)Nb(CO)₂(PhCCPh)dppe (Hal = Br, I). In these complexes, the remaining CO ligands occupy cis positions. The structure of BrNb(CO)₂(dppe)₂·THF, INb(CO)₂(dppe)₂·hexane and INb(CO)₂(PEt₃)₂(MeCCEt) have been determined by a single crystal X-ray diffraction study. The alkyne complexes are best regarded as octahedral with the centre of the alkyne ligand occupying the positions trans to the halide and the CC axis aligned with the OC---Nb---CO axis. The complexes (Hal)Nb(CO)₂(dppe)₂ adopt a trigonal prismatic structure with the halide capping the tetragonal face spanned by the four phosphorus functions. The crystal structure of a by-product, Br₂Nb(CO)(H₂CPhPCH₂CH₂PPh₂)₂·1/2THF has also been determined. The geometry is pentagonal bipyramidal, with one of the bromine atoms and the CO on the axis. Some ⁹³ Nb NMR data for the Nb^I complexes are presented, and preliminary observations on the reactions between the π-alkyne complexes and H₂ or H⁻ are reported.     

High-performance liquid chromatography of the coordination isomers of triphenylphosphine-substituted homo- and hetero-bimetallic carbonyl complexes of manganese and rhenium

The isocratic normal-phase high-performance liquid chromatography of a series of triphenylphosphine (PPh₃)-substituted homo- and hetero-dinuclear metal carbonyl complexes [MM′ (CO)_10−n(PPh₃)_n, where M,M′ = Mn, Re; N = 1,2] is reported. A column packed with silica bonded with phenyl groups was used after preliminary experiments showed that columns packed with conventional silica, and with silica bonded with amion-cyano groups were unsatisfactory for separation. The mobile phases used were hexane-toluene (8:2) and hexane-dichloromethane (90:10). The results suggest that besides the symmetry-imposed polarity of the complexes, the nature of the metal and substituent ligand also determine their retention characteristics.     

(2,6-Diphenyl) phenyl methacrylate—2. Radical copolymerization with methyl methacrylate. The Tgs of its copolymers with an addendum on the polymerization of (2,6-diphenyl) phenyl acrylate

The radical copolymerization of (2,6-diphenyl) phenyl methacrylate (1) with methyl methacrylate in DMF with AIBN at 70°C has the reactivity ratios r₁ = 0.071 and r₂ = 1.42, from which Q₁ = 1.45 and e₁ = 1.20. The copolymers had M_ns in the range of 10,000–40,000 and T_gs ranging from 406 to 480 K from which the hypothetical T_g for poly-1 was deduced as 500 K (227°C). Unlike 1, (2,6-diphenyl) phenyl acrylate could be polymerized to oligomers with M_n of the order of 2500.     

Novel cyclopentadienyl silanes and disilanes: synthesis, structure and gas-phase pyrolysis

The new chloro(cyclopentadienyl)silanes Cp′SiH_yCl_3−y (Cp′=Me₄EtC₅, y=1: 1; Cp′=Me₄C₅H, y=1: 2; y=0: 3; Cp′=Me₃C₅H₂, y=1: 4 and pentachloro(cyclopentadienyl)disilanes Cp′Si₂Cl₅ (Cp′=Me₅C₅ 5, Me₄EtC₅ 6, Me₄C₅H 7, Me₃C₅H₂ 8, Me₃SiC₅H₄ 9) are synthesized in good yields via metathesis reactions. Treatment of 1–9 with LiAlH₄ leads under Cl–H exchange to the hydridosilyl compounds Cp′SiH₃ (Cp′=Me₄EtC₅ 10, Me₄C₅H 11, Me₃C₅H₂ 12) and to the hydridodisilanyl compounds Cp′Si₂H₅ (Cp′=Me₅C₅ 13, Me₄EtC₅ 14, Me₄C₅H 15, Me₃C₅H₂ 16, Me₃SiC₅H₄ 17). Complexes 1–17 are characterized by ¹H, ¹³C, and ²⁹Si-NMR spectroscopy, IR spectroscopy, mass spectrometry and CH-analysis. The structures of 6, 7 and 9 are determined by single-crystal X-ray diffraction analysis. Pyrolysis studies of the cyclopentadienylsilanes 10–12 and disilanes 13–17 show their suitability as precursors in the MOCVD process.     

A comparison of linear optical properties and redox properties in chalcogenopyrylium dyes bearing ortho-substituted aryl substituents and tert-butyl substituents

A series of thiapyrylium pentamethine dyes (4 and 12-15) bearing 2,2'-di-tert-butyl-6,6'-diphenyl, 2,2'-di-tert-butyl-6,6'-bis(2,6-dimethylphenyl), 2,2'-di-tert-butyl-6,6'-bis(2-methylphenyl), 2,2',6,6'-tetrakis(2,6-dimethylphenyl), and 2,2',6,6'-tetrakis(2-methylphenyl) substituents, respectively, were prepared and their linear optical properties and electrochemical redox properties were measured and compared to thiapyrylium pentamethine dyes 3 and 5. The tert-butyl and 2,6-dimethylphenyl substituents give nearly identical chromophores with respect to values of lambda(max), molar extinction coefficients (epsilon), bandwidths at half-height (nu(1/2)), and lack of absorption in the visible spectrum. The 2-methylphenyl substituent imparts linear optical properties that are intermediate between those of the tert-butyl and phenyl substituents. The 2,6-dimethylphenyl and 2-methylphenyl substituents impart greater oxidative stability based on anodic shifts in oxidation potential.     

Polarography of non-benzenoid aromatic and related substances—VI Polarographic and spectrophotometric study of steric hindrance of coplanarity in 3-phenylsydnones

Substitution of alkyl groups on the ortho-position of 3-phenylsydnone causes a steric hindrance in coplanarity of the sydnone and phenyl rings. This was proved from the shift of the polarographic half-wave potentials (in excess of the polar effects), from the ultra-violet spectra, and from scale models. The behaviour of 3-o-tolylsydnone resembles more that of 3-benzylsydnone than that of 3-phenylsydnone. In 3′,4′-dihydroquinolino[1′,2′-c]-sydnone, the —CH₂ CH₂—bridge brings the sydnone and phenyl rings into a nearly coplanar position, shown on scale models, and its polarographic and spectrophotometric behaviour resembles that of 3-phenylsydnone.