Fluorenyl dendrimer porphyrins: synthesis and photophysical properties

New symmetrical dendrimeric type super-porphyrin bearing sixteen fluorenyl donor groups sixteen fluorenylporphyrin SOFP (1) have been synthesized and characterized. Preliminary photophysical properties are reported; in comparison to the references first generation dendrimer tetrafluorenylporphyrin TOFP (2) bearing four peripheral fluorenyl and second generation dendrimer octafluorenylporphyrin OOFP (3) bearing eight peripheral fluorenyl, the luminescence properties are slightly improved. It is found that the excitation energy transfer occurs from the sixteen fluorenyl units to the porphyrin core, following what the porphyrin emits intense red light.     

Regiospecific nucleophilic substitution in 2,3,4,5,6-pentafluorobiphenyl as model compound for supramolecular systems. Theoretical study of transition states and energy profiles, evidence for tetrahedral SN2 mechanism

2,3,4,5,6-Pentafluorobiphenyl (PFBi) was modified by the nucleophilic substitution of one fluorine using a series of O-, S- and N-nucleophiles, viz. alkaline salts of 2,2,2-trifluoro-ethanol, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctanol, 1,2;3,4-di-O-isopropylidenexylitol, allylsulfane, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctane-1-thiol, 3-aminopropan-1-ol (7), and tert-butyl N-(3-aminopropyl)carbamate (8). All the substitutions took place exclusively at the position para to the phenyl group. (3-Amino-propyl)amino derivative of PFBi (15) was further modified at the terminal amino group by acylation or fluoroalkylation. The reaction of 8 was applied to meso-5,10,15,20-tetrakis-(pentafluorophenyl)porphyrin (20) to afford tris- (21) and tetrakis-substituted (22) products with complete para-regioselectivity. Theoretical studies of the reaction pathways of PFBi with ammonia, microsolvated lithium fluoride or lithium hydroxide revealed that no Meisenheimer-type intermediates are formed in the course of the simulated reactions: instead, tetrahedral S_N2 mechanism was found. Significant regioselectivity of the nucleophilic aromatic substitution, leading to 4-substituted products, was predicted based on relative transition state energies in agreement with the observed experimental results.     

Synthesis,characterisation and X-ray structure of a novel porphyrin array employing Zn–O and O–H…O bonding motifs

The preparation and characterisation of the free-base and zinc metallated derivatives of 5,10,15,20-tetrakis(4-(2-(2-hydroxyethoxy)ethoxy)phenyl)porphyrin 1 is described. The X-ray crystal structure of the Zn(II) adduct 2 dimerises in the solid state via an intermolecular polyether oxygen–Zn(II) interaction (O…Zn = 2.124(4) Å). The porphyrin dimers form discrete layers defined by a distance of 5.10 Å between the porphyrin planes in adjacent layers. A bilayer sheeting arrangement of the porphyrin macrocyclic units is achieved through cooperative hydrogen bonding of the ethoxyethanol arms to form 11-membered macrocycles containing four hydrogen bonds.     

Star-like fluorene based polyamines: non-conjugated building blocks for light-harvesting materials

We report herein a series of novel tetramines (2-6) built using the fluorene core. The design features a diamine conjugated by a fluorene core and two non-conjugated triarylamines dangling through the bridge methine moiety. These polyamines are amorphous in nature and display moderate emission properties that are either dependent on the nature of the arylamine segments or reminescent of the fluorene backbone. The phenyl, naphthyl, fluorenyl and carbazolyl amine based materials are blue emissive while the pyrenylamine based compound emits yellow-green color. We demonstrate a possibility of using blue-emitting fluorene derivatives (2 and 4) blended with poly(N-vinylcarbazole) (PVK) to fabricate organic light emitting diodes (OLEDs). Emissions in the EL devices purely originated from the fluorene derivatives alone (blue) are contaminated with those of complex species (electromer/electroplex) formed by intermolecular interactions.     

A convenient preparation of 2,3,5,6-tetrafluoro-4-iodo-benzaldehyde and its application in porphyrin synthesis

An efficient synthesis of 2,3,5,6-tetrafluoro-4-iodo-benzaldehyde (1) is presented. This new compound was readily obtained via iodination at low temperature of the lithio derivative of 2-(2,3,5,6-tetrafluoro-phenyl)-[1,3]dioxolane (4). The crystal structure of 1 consists of linear polymeric chains, with non-covalent O?I bonding as the directing interaction, responsible for the observed assembly. Aldehyde 1 is further employed in the synthesis of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (6), a potential precursor of supramolecular assemblies.     

Synthesis,X-ray crystal structure,and electrochemistry of trans-bis(ferrocenecarboxylato)(tetraphenylporphyrinato)tin(IV)

trans-Bis(ferrocenecarboxylato)(5,10,15,20-tetraphenylporphyrinato)tin(IV) complex Sn(TPP)(FcCOO)₂ has been synthesized and fully characterized. The X-ray structural analysis of Sn(TPP)(FcCOO)₂ reveals that the tin(IV) center is octahedrally coordinated by the porphyrin occupying the square base and axial coordination of two ferrocenecarboxylato ligands in an anti orientation with respect to each other. The Fe(II) center of the ferrocenecarboxylato ligand lies 5.7 Å from the tin(IV) center of the porphyrin ring. The cyclic voltammogram of Sn(TPP)(FcCOO)₂ exhibits three distinctive redox couples consisting of one oxidative wave and two reductive waves due to the ferrocenecarboxylato ligands and the porphyrin ring, respectively.     

Synthesis and characterization of β-fused porphyrin-BODIPY dyads

Novel dyads in which a porphyrin ring is directly fused through two β-pyrrolic carbons to a BODIPY^® moiety have been prepared using a stepwise approach starting from the copper(II) complex of pyrrolo[2,3-c]-5,10,15,20-tetraphenylporphyrin. Formylation and reaction with 3,5-dimethylpyrrole afforded 8; subsequent BF₂ complexation gave the TPP-BODIPY^® dyad in reasonable yields. Demetalation in TFA/H₂SO₄ led to the corresponding free base 12, opening the way to the subsequent preparation of the Zn complex 13. Both 12 and 13 exhibited complex optical spectra with an intensely red-shifted Q-band. Luminescence spectra displayed a very intense band around 700 nm making these species suitable as near-IR dyes and sensors in biological media. Optical analyses of 12, using the INDO/SCI technique, were performed to obtain information to establish the origin of the novel optical properties. These studies showed that the optical properties of 12 cannot be attributed to deformation of the molecular skeleton, but derive from the increased extension of the conjugation between the TPP and BODIPY^® π-systems.     

Nitrate-selective electrodes based on meso-tetrakis[(2-arylphenylurea)-phenyl]porphyrins as neutral lipophilic ionophores

Polymeric-membrane electrodes for NO₃⁻ anion based on (α,α,α,α)-5,10,15,20-tetrakis [2-(4-methylphenylurea)phenyl]porphyrin I and similar urea-functionalized porphyrins II-IV as neutral ionophores were prepared. The effects of polymeric-membrane composition and test solution pH were tested. The electrodes revealed good selectivity coefficients for NO₃⁻ over a wide variety of other anions, and the values of eight anions were measured. Of the various electrodes prepared, the electrode based on urea-functionalized porphyrin I exhibits a linear stable response over a wide concentration range (1.0×10⁻⁵ to 1.0×10⁻¹) with a slope of −57.4 mV per decade, a detection limit of log[NO₃⁻]=−5.72, and a selectivity coefficient for nitrate against perchlorate anion ().     

Reaction of guaiazulene with o-formylbenzoic acid in diethyl ether (or methanol) in the presence of hexafluorophosphoric acid: comparative studies on H and C NMR spectral properties of 3-guaiazulenylmethylium- and 3-guaiazulenium-ion structures

Reaction of guaiazulene (1) with o-formylbenzoic acid (2) in diethyl ether in the presence of hexafluorophosphoric acid at 25 °C for 90 min gives the corresponding monocarbenium-ion compound, [2-(carboxy)phenyl](3-guaiazulenyl)methylium hexafluorophosphate (3), quantitatively, which upon treatment with aq NaHCO₃ leads to 3-(3-guaiazulenyl)-2-benzofuran-1(3H)-one (5) in 96% isolated yield. Similarly, reaction of 1 with 2 in methanol under the same conditions as the above reaction affords two kinds of inseparable monocarbenium-ion compounds, 3 and (3-guaiazulenyl)[2-(methoxycarbonyl)phenyl]methylium hexafluorophosphate (4) with an equilibrium between them, which upon reaction with a solution of NaBH₄ in ethanol at 25 °C for 30 min leads to 5 in 46% isolated yield and (3-guaiazulenyl)[2-(methoxycarbonyl)phenyl]methane (6) in 37% isolated yield. Along with the ¹H and ¹³C NMR spectral properties of a solution of 5 in trifluoroacetic acid-d₁ at 25 °C, whose molecular structure is converted to a ca. 1:1 equilibrium mixture of 7 possessing a partial structure of the 3-guaiazulenylmethylium-ion and 8 possessing a partial structure of the 3-guaiazulenium-ion, comparative studies on the ¹H and ¹³C NMR spectral properties of 7 and 8 with those of the monocarbenium-ion compound, (3-guaiazulenyl)[4-(methoxycarbonyl)phenyl]methylium hexafluorophosphate (A), 5, and 6 are reported. From these NMR studies, it can be inferred that the positive charge of the 3-guaiazulenylmethylium-ion part of 7 apparently is transferred to the seven-membered ring, generating a resonance form of the 3-guaiazulenylium-ion structure η′, and the same result can be inferred for the previously documented monocarbenium-ion compounds A-I. Moreover, referring to a comparative study on the C-C bond lengths of A observed by the X-ray crystallographic analysis with those of the optimized (3-guaiazulenyl)[4-(methoxycarbonyl)phenyl]methylium-ion structure for A calculated by a WinMOPAC (Ver. 3.0) program using PM3, AM1, or MNDOD as a semiempirical Hamiltonian, the optimized [2-(carboxy)phenyl](3-guaiazulenyl)methylium-ion structure for 3 calculated using PM3 is described.     

Reactions of guaiazulene with methyl terephthalaldehydate and 2-hydroxy- and 4-hydroxybenzaldehydes in methanol in the presence of hexafluorophosphoric acid: comparative studies on molecular structures and spectroscopic, chemical and electrochemical properties of monocarbocations stabilized by 3-guaiazulenyl and phenyl groups

Reaction of guaiazulene (1) with methyl terephthalaldehydate (2) in methanol in the presence of hexafluorophosphoric acid at 25 °C for 2 h under aerobic conditions gives (3-guaiazulenyl)[4-(methoxycarbonyl)phenyl]methylium hexafluorophosphate (5) in 94% yield. Similarly, reactions of 1 with 2-hydroxybenzaldehyde (3) and 4-hydroxybenzaldehyde (4) under the same reaction conditions as 2 give (3-guaiazulenyl)(2-hydroxyphenyl)methylium hexafluorophosphate (6) and (3-guaiazulenyl)(4-hydroxyphenyl)methylium hexafluorophosphate (7) in 89 and 97% yields, respectively. Comparative studies on the molecular structures as well as the spectroscopic, chemical and electrochemical properties of the monocarbocation compounds 5-7 stabilized by 3-guaiazulenyl and 4-(methoxycarbonyl)phenyl (or 2-hydroxy- or 4-hydroxyphenyl) groups are reported.     

Design and synthesis of boron containing 2,4-disubstituted-phthalazin-1(2H)-one and 3,7-disubstituted-2H-benzo[b][1,4] oxazine derivatives as potential HGF-mimetic agents

We synthesized boron containing 2-(4-methoxybenzyl)-4-(4-(4,4,5,5-tetramethyl-1,3,2-dioaborolan-2-yl)phenyl) phthalazin-1(2H)-one 3 and 7-methyl-3-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-2H-benzo[b][1,4] oxazine 8. The reaction of compound 2 with B₂pin₂ using potassium acetate as the base and Pd(PPh₃)₂Cl₂ as the catalyst, produced the corresponding boron-containing derivative 3 as a white solid in 65% yield. Alternatively, we have synthesized compound 8 as a yellow solid in 59% yield using the Miyaura borylation reaction. The potassium trifluoro(4-(-methyl-2H-benzo[b][1,4]oxazine-3-yl)phenylborate 9 was then obtained after treatment of 8 with aqueous solution of KF₂H in methanol as white solid product in 60% yield. The biological activities of the synthetic compounds are currently being evaluated.     

Synthesis and structural characterization of new phosphinooxazoline complexes of iron

The first phosphinooxazoline chelate complexes of iron were synthesized, and their structural and electronic properties were studied.The known phosphinooxazolines 2-(2-(diphenylphosphino)phenyl)-4,5-dihydrooxazole (7a), 2-(2-(diphenylphosphino)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (7b), (S)-4-benzyl-2-(2-(diphenylphosphino)phenyl)-4,5-dihydrooxazole (7e) and (R)-2-(2-(diphenylphosphino)phenyl)-4-phenyl-4,5-dihydrooxazole (7f) were synthesized by a modified three step literature procedure with improved 67-60% overall yields. The new electronically tuned phosphinooxazolines 2-(5-bromo-2-(diphenylphosphino)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (7c), 3-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-4-(diphenylphosphino)-N,N-dimethylaniline (7d) and 2-(2-(diphenylphosphino)-3-(trifluoromethyl)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (7g) were synthesized in three to six steps with 59-29% overall yields. Reaction of 7a-f with CpFe(CO)₂I (110 °C, 2 h, toluene) gave the iodide salts of the new iron phosphinooxazoline complexes [CpFe(CO)(7a-f)]⁺ in 87-21% yield. The new complexes were characterized by X-ray and the molecular structures confirm the octahedral coordination geometry and the half-sandwich structure about the iron center. The impact of different oxazoline ligands on the steric and electronic properties of their iron complexes was determined by analysis of selected bond lengths, ν_CO stretching frequency and the oxidation potentials of the ligands and the iron complexes.     

Supramolecular nanostructured assemblies of different types of porphyrins with fullerene using TiO2 nanoparticles for light energy conversion

TiO₂ nanoparticles were modified with porphyrin derivatives, 5-[4-benzoic acid]-10,15,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (Ar-H₂P-COOH), 5-[4-benzoic acid]-10,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (H-H₂P-COOH), and 5,10,15,20-tetra[4-benzoic acid]-21H,23H-porphyrin (H₂P-4COOH). The porphyrin-modified TiO₂ nanoparticles were deposited on nanostructured OTE/SnO₂ electrode together with nanoclusters of fullerene (C₆₀) in acetonitrile-toluene (3/1, v/v) using an electrophoretic deposition technique to afford the porphyrin-modified TiO₂ composite electrode denoted as OTE/SnO₂/(porphyrin-modified TiO₂ nanoparticle+C₆₀)_n. The porphyrin-modified TiO₂ composite electrodes have efficient light absorbing properties in the visible region, exhibiting the photoactive response under visible light excitation using redox couple. The incident photon-to-photocurrent efficiency (IPCE) values of supramolecular nanostructured electrodes of porphyrin-modified TiO₂ nanoparticles with fullerene [OTE/SnO₂/(Ar-H₂P-COO-TiO₂+C₆₀)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂+C₆₀)_n] are much larger than those of the reference systems of porphyrin-modified TiO₂ nanoparticles without C₆₀ [OTE/SnO₂/(Ar-H₂P-COO-TiO₂)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂)_n]. In particular, the maximum IPCE value (41%) is obtained for OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n under the bias potential of 0.2 V versus SCE. This indicates that the formation of supramolecular complexes between porphyrins and fullerene on TiO₂ nanoparticles plays an important role in improvement of the light energy conversion properties.     

Synthesis of three-dimensionally arranged porphyrin arrays via intramolecular meso-meso coupling

The synthesis and photophysical properties of three-dimensionally arranged porphyrin arrays with through-space electronic communication are reported. 1,3,5-Trioxamethylphenylene bridged Zn(II) porphyrin trimer 3 was coupled by Ag(I)-promoted oxidative coupling reaction to give porphyrin cage 5 comprising three meso-meso linked diporphyrins, which was then transformed by oxidation with DDQ and Sc(OTf)₃ into porphyrin cage 7 comprising three fused diporphyrins. Intramolecular meso-meso coupling reaction was applied to porphyrin pentamer 11 to provide porphyrin array 12 consisting of a porphyrin core flanked by two meso-meso linked diporphyrins. Further oxidation of 12 with DDQ and Sc(OTf)₃ afforded triply stacked porphyrin array 13 that is comprised of a porphyrin core flanked by two porphyrin tapes. UV-vis-NIR absorption and fluorescence spectra of 5, 7, 12, and 13 showed their distorted conformations and electronic interaction within the stacked porphyrin arrays.     

Selenoether ligand assisted Heck catalysis

Selenoether ligands, 2,2′-methylenebis(selanediyl)bis(2,1-phenylene)dimethanol (5), (2,2′-(ethane-1,2-diylbis(selanediyl))bis(2,1-phenylene))dimethanol (6) and (2-(benzylselanyl)phenyl)methanol (7) have been synthesized by reducing di-o-formylphenyl diselenide and reacting the in situ generated selenolate with dibromomethane, 1,2-dibromoethane and benzyl chloride, respectively. The ligands, bis(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenylselanyl)methane (8) and 1,2-bis(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenylselanyl)ethane (9) have been synthesized similarly from bis[2-(4,4-dimethyl-2-oxazolinyl)phenyl] diselenide using electrophiles dibromomethane and 1,2-dibromoethane, respectively. Activity of ligands 5-9 along with 2-(2-(benzylselanyl)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (10) and 1-(2-(benzylselanyl)phenyl)-N,N-dimethylmethanamine (11) were examined for the Heck reaction of aryl halides with olefins. Bidentate Se,N ligand 11 was found to be the best one in the series and constitutes an efficient phosphine-free catalytic system with PdCl₂. The catalytic system showed moderate activity for the coupling of activated aryl chlorides in the presence of tetra-n-butyl ammonium bromide (TBAB). Complexes [10-PdCl₂] (12) and [11-PdCl₂] (13) have shown marginally better activity in comparison to the in situ generated catalysts from PdCl₂ and 10 and 11, respectively in the coupling of 4-bromoacetophenone with n-butylacrylate. Ligand 9 and complex 13 have been characterized by single crystal X-ray diffraction analysis.     

Light-harvesting composites of directly connected porphyrin-phthalocyanine dyads and their coordination dimers

Directly linked porphyrin (Por)-phthalocyanine (Pc) heterodyads (H₂Por-H₂Pc and H₂Por-ZnPc) with an imidazolyl group at porphyrin’s meso-position were synthesized. Introduction of a zinc ion into the porphyrin afforded stable complementary dimers of the heterodyads. The heterodyads and their dimers gave extensive and strong absorption bands owing to the porphyrin and phthalocyanine components and induced an efficient energy transfer from porphyrin to phthalocyanine. Strong fluorescence from phthalocyanine was observed in the case of H₂Por-H₂Pc.     

Synthesis and structural characterization of η-allyl(α-diimine)nickel(II) complexes bearing trimethylsilyl groups

A set of isomeric para- and meta-trimethylsilylphenyl ortho-substituted N,N-phenyl α-diimine ligands [(Ar-NC(Me)-(Me)CN-Ar) Ar=2,6-di(4-trimethylsilylphenyl)phenyl (16); Ar=2,6-di(3-trimethylsilylphenyl)phenyl (17)] have been synthesized through a two-step procedure. The palladium-catalysed cross-coupling reaction between 2,6-dibromophenylamine (7) and 4-trimethylsilylphenylboronic acid (8), 3-trimethylsilylphenylboronic acid (9) was used to prepare 4,4^′-bis(trimethylsilyl)-[1,1^′;3^′,1″]terphenyl-2^′-ylamine (10) and 3,3^′-bis(trimethylsilyl)-[1,1^′;3^′,1″]terphenyl-2^′-ylamine (11). The di-1-adamantylphosphine oxide Ad₂P(O)H (13) and di-tert-butyl-trimethylsilylanylmethylphosphine tert-Bu₂P-CH₂-SiMe₃ (14) were used for the first time as ligands for the Suzuki coupling. The condensation of 2,2,3,3-tetramethoxybutane (15) with anilines 10 and 11 afforded α-diimines 16 and 17. The reaction of π-allylnickel chloride dimer (18), α-diimines (16), (17) and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BAF) (19) or silver hexafluoroantimonate (20) led to two sets of isomeric complexes [η³-allyl(Ar-NC(Me)-(Me)CN-Ar)Ni]⁺ X⁻, [Ar=2,6-di(4-trimethylsilylphenyl)phenyl, X=BAF (3), X=SbF₆ (4); Ar=2,6-di(3-trimethylsilylphenyl)phenyl, X=BAF (5), X=SbF₆ (6)]. The steric repulsion of closely positioned trimethylsilyl groups in 4 caused the distortion of the nickel square planar coordination by 17.6° according to X-ray analysis.     

Reactions of azulenes with 1,2-diaryl-1,2-ethanediols in methanol in the presence of hydrochloric acid: comparative studies on products, crystal structures, and spectroscopic and electrochemical properties

Although reaction of guaiazulene (1a) with 1,2-diphenyl-1,2-ethanediol (2a) in methanol in the presence of hydrochloric acid at 60 °C for 3 h under aerobic conditions gives no product, reaction of 1a with 1,2-bis(4-methoxyphenyl)-1,2-ethanediol (2b) under the same reaction conditions as 2a gives a new ethylene derivative, 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene (3), in 97% yield. Similarly, reaction of methyl azulene-1-carboxylate (1b) with 2b under the same reaction conditions as 1a gives no product; however, reactions of 1-chloroazulene (1c) and the parent azulene (1d) with 2b under the same reaction conditions as 1a give 2-[3-(1-chloroazulenyl)]-1,1-bis(4-methoxyphenyl)ethylene (4) (81% yield) and 2-azulenyl-1,1-bis(4-methoxyphenyl)ethylene (5) (15% yield), respectively. Along with the above reactions, reactions of 1a with 1,2-bis(4-hydroxyphenyl)-1,2-ethanediol (2c) and 1-[4-(dimethylamino)phenyl]-2-phenyl-1,2-ethanediol (2d) under the same reaction conditions as 2b give 2-(3-guaiazulenyl)-1,1-bis(4-hydroxyphenyl)ethylene (6) (73% yield) and (Z)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1-phenylethylene (7) (17% yield), respectively. Comparative studies of the above reaction products and their yields, crystal structures, spectroscopic and electrochemical properties are reported and, further, a plausible reaction pathway for the formation of the products 3-7 is described.     

Silylene-spaced diphenylanthracene derivatives as blue-emitting materials

A novel series of blue emitting silylene-spaced diphenylanthracene derivatives have been synthesized and characterized. The rhodium-catalyzed hydrosilylation of bis[4-(dimethylsilyl)phenyl]anthracene 3-4 yielded stable 9,10-disubstituted (E)-divinylsilylene-diphenylanthracene products 7-10 and salt elimination reaction of bis[4-(chlorodimethylsilyl)phenyl]anthracene 5-6 gave 9,10-disubstituted disilyldiphenylanthracene compounds 11-14. They are fluorescent in the blue region with good quantum efficiencies. The rhodium-catalyzed polyaddition including 2-tert-butyl-9,10-bis[4-(dimethylsilyl)phenyl]anthracene (4) afforded the nonconjugated copolymer 15.     

Heterolytic CH-bond activation in the synthesis of Ni{(2-aryl-κC)pyridine-κN}2 and derivatives

Thermolysis of Ni(OTf)₂ in 2-phenyl-pyridine or 2-tolyl-pyridine afforded the cationic chelate derivatives, [bis(2-aryl-pyridine)Ni{(2-aryl-κC²)pyridine-κN}]OTf (aryl = phenyl, 1a; tolyl, 1b). Addition of KBr to 1a and LiBr to 1b provided the bromides, (2-aryl-pyridine)BrNi{(2-aryl-κC²)pyridine-κN} (aryl = phenyl, 2a; tolyl, 2b). When subjected to KO^tBu in Et₂O, the bromides generated the entitled bis-cyclometalated compounds, Ni{(2-aryl-κC²)pyridine-κN}₂ (aryl = phenyl, 3a; tolyl, 3b). These compounds insert diphenylacetylene into one cyclometalate arm to produce [(2-aryl-κC²)pyridine-κN]Ni[2-(2-(1,2-diphenylethenyl-κC²)aryl)pyridine-κN] (aryl = phenyl, 4a; p-tolyl, 4b). X-ray crystallographic studies were conducted on 1a, 2a, 3a and 4a, and a brief DFT study of 3a confirmed its low spin configuration and rippled geometry.