Nucleophilic substitution reactions in chromium arene phosphite dicarbonyl chelate complexes

Conclusions An F atom and PhO group on a coordinated P atom in chromium arene phosphite dicarbonyl chelate complexes undergo nucleophilic substitution when treated with PhLi without ring opening to give the corresponding arene diphenylphosphinite chelates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1900–1902, August, 1981.     

Synthesis and structure of triply bridged purinophanes

The title compounds were synthesized as a model for studying the relationship between the hypochromism and the stacking mode of two purine rings. By comparing 1 with other purinophanes it was concluded that the fully overlapped orientation of two purine rings gives the largest hypochromicity.     

Synthesis of an unsymmetrically doubly bridged calix[4]arene in the 1,3-alternate conformation

We report the synthesis of the first calix[4]arene constrained to a 1,3-alternate conformation by one crown ether and one di-aza-benzo crown ether bridgings. Preliminary binding properties are also given.     

Extreme conformational constraints in pi-extended tetrathiafulvalenes: unusual topologies and redox behavior of doubly and triply bridged cyclophanes

Doubly and triply bridged 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (ex-TTF) derivatives have been synthesized. Key steps are the generation and macrocyclization reactions of ex-TTF-dithiolate reagents. The X-ray crystal structures of the doubly bridged cyclophanes 15 and 16 and the triply bridged system 23 show that the saddle-like conformation of the ex-TTF framework is enhanced by the short bridges between the dithiole rings. Unlike all previous ex-TTF derivatives (which display a single quasi-reversible two-electron oxidation wave, D0 --> D2+), cyclic voltammetry of the cyclophanes reveals two reversible, one-electron oxidation steps (D0 --> D*+ --> D2+), with differences between the half-wave potentials (E2(1/2) - E1(1/2)) of 0.22-0.26 V. The conformational changes and gain in aromaticity which drive the second oxidation process in unrestricted ex-TTF systems (including singly bridged cyclophanes) have been prevented by multiple bridging. The radical cation species gives rise to a very broad, low-energy band (lambdamax = 2175 and 2040 nm for 15 and 21, respectively), assigned to an intramolecular interaction. The steric constraints imposed by multiple bridging have become so extreme that the pi-framework of 15, 16, 21, and 23 exhibits remarkable optical and redox behavior which is not characteristic of ex-TTF systems.     

Synthesis and conformational study of the first triply bridged calix[6]azatubes

[reaction: see text] The first C(3)(v)- and D(3)(h)-symmetrical triply bridged calix[6]azatubes were prepared in good yields from the known 1,3,5-tris-methylated calix[6]arene through an efficient [1 + 1] macrocyclization reaction. A remarkably regioselective hexa ipso-nitration reaction led to a calix[6]azatube substituted at the wide rim in alternate position by tBu and nitro groups. A (1)H NMR study showed that, whereas the parent bis-calix[6]arenes self-include their methoxy groups, thereby closing their inner tube, the nitro-substituted calix[6]azatube undergoes a conformational change with the expulsion of the methoxy groups, hence presenting a three-dimensional structure open for host-guest applications.     

Regioselective lithiation of II-(arene)chromium tricarbonyl complexes

Chromium tricarbonyl complexes of 3-methoxybenzyl alcohol and related compounds were selectively lithiated at the 4-position in contrast to the corresponding metal free arene compounds. The resulting 4-lithio complexes were converted to the 4-substituted arene compounds in moderate to excellent yields through the reactions with proper electrophiles and subsequent demetalation.     

Selective functionalization of crown ethers via arene chromium tricarbonyl complexes

The crown ethers dibenzo-16-crown-4 and dibenzo-18-crown-5 and a diaryl polyether were complexed by the chromium tricarbonyl group for the purpose of selective functionalization. This complexation did indeed permit exclusive functionalization of the complexed ring. CHO and CH₂OH functionalities were introduced ortho to the ether group. It was noted that the nature of the two ether chains had a strong influence on the regioselectivity of the functionalization, which occurred preferentially on the side with the polyether chain. Photochemical decomplexation produced functionalized organic crown ethers.     

Stereoselective bis-functionalizations of arene chromium tricarbonyl complexes via brook rearrangements

[reaction: see text] An efficient method has been developed for the stereoselective bis-functionalization of arene chromium tricarbonyl complexes. Initial nucleophilic addition of organolithium reagents to a carbonyl moiety is followed by a 1,4-carbon to oxygen silyl migration (Brook rearrangement) and alkylation of the resultant aryl anion.     

Synthesis and structures of bridged biscyclopentadienyl diiron complexes

Three diiron carbonyl complexes, namely [(η ⁵-C₅H₄)(η ³-C(CH₂)₂)]Fe₂(CO)₅ (1), [(C₂H₅)₂C(η ⁵-C₅H₄)₂]Fe₂(μ-CO)₂(CO)₂ (2), and [(CH₂)₄C(η ⁵-C₅H₄)(η ⁵-C₅H₃)(C₅H₉)]Fe₂(μ-CO)₂(CO)₂ (3), have been synthesized by the reactions of C₅H₄C(Me)₂, C₅H₄C(Et)₂, and C₅H₄C(CH₂)₄, respectively, with Fe(CO)₅ in refluxing xylene. The complexes have been characterized by elemental analysis, IR, and ¹H NMR spectra. The molecular structures of the complexes have been determined by single-crystal X-ray diffraction. The structures of the complexes indicate that fulvenes can be bound to transition metal centers by diverse modes.     

Synthesis and cell phototoxicity of a triply bridged fused diporphyrin appended with six thioglucose units

A triply bridged fused diporphyrin appended with six thioglucose units is reported. This new, chemically, and photochemically stable amphiphilic compound is taken up by breast cancer cells and causes cell death upon light exposure. Photophysical studies reveal absorption bands in the near IR region, and photosensitized formation of singlet oxygen in high quantum yields.     

Synthesis of bis(arene)chromium compounds from 1,4-diphenylbutane and chromium vapour

Bridged dibenzenechromium 1,1′-tetramethylenedibenzenechromium (I) together with bis(1,4-diphenylbutane)chromium (II) and bis-1,4[1′-(δ-phenylbutano)dibenzenechromo]butane (III) were synthesized from the reaction of 1,4-diphenylbutane with chromium vapour.     

Synthesis,characterization and reactivity of some rhenium phosphite complexes

The preparation and characterization of some Re(III), Re(IV) and Re(V) chloro phosphite complexes are reported. Both Re(III) and Re(IV) complexes react with sodium borohydride, yielding the corresponding polyhydrides, ReH₅[P(OEt)₃]₃ and ReH₇[P(OEt)₃]₂. The thermal and photochemical reactivity of these complexes is described.     

1H NMR conformational analysis of disubstituted arene tricarbonyl chromium complexes

The positions of conformational equilibrium in disubstituted arene chromium tricarbonyl complexes, i.e. alkylanisole chromium tricarbonyl complexes and alkylbenzoate chromium tricarbonyl complexes, have been determined by ¹H NMR spectroscopy. It has been found that the donor effect is the dominant factor in determining the preferred conformation.     

Asymmetric synthesis of secondary benzylic alcohols via arene chromium tricarbonyl complexes

(Aryl aldehyde)- and (aryl ketone)-chromium tricarbonyl complexes ortho-substituted with the chiral auxiliary O-methyl-N-(α-methylbenzyl)hydroxylamine undergo diastereoselective addition of Grignard reagents and Super-Hydride^®, respectively, to give the corresponding secondary alcohols in high diastereoisomeric purity. These compounds may be easily decomplexed and deprotected to give the corresponding enantiopure amino alcohols.     

Synthesis and electrochemical properties of bipyrimidine bridged triruthenium complexes

A new μ(4)-bpym-bridged dimer of an oxoacetao-triruthenium complex with carbonyl, [{Ru(3)O(CH(3)COO)(5)(CO)(py)}(2)(μ(4)-bpym)], was synthesized. The complex possesses two stable mixed-valence states associated with Ru(3)(III,III,II)/Ru(3)(III,II,II) and Ru(3)(III,III,III)/Ru(3)(III,III,II). The IR-spectroelectrochemistry reveals ν(CO) spectra in five oxidation states, Ru(3)(III,III,III)-Ru(3)(III,III,III) to Ru(3)(III,II,II)-Ru(3)(III,II,II) and both the mixed-valence states show a spectrum indicating medium interaction between the Ru(3) units.     

Synthesis and conformation studies of multiple bridged p-tert-butylcalix[7]arene diphosphates

p-tert-Butylcalix[7]arene reacting with phosphorus pentachloride and then with water afforded two stereoisomers p-tert-butylcalix[7]arene diphosphates 2a and 2b, representing the first phosphorus multiple bridged calix[7]arene. The more accurate structure of 2a was investigated with the aid of Gaussian03 calculations.     

Ethylene polymerization by chromium complexes with phosphorous‐bridged bisphenoxy ligand

Chromium catalysts combined with phosphorous‐bridged bisphenoxy ligands were found to be highly active for ethylene polymerization. The most efficient catalyst precursor among them, generated by combining bis[3‐tert‐butyl‐5‐methyl‐2‐hydroxyphenyl](phenyl)phosphine hydrochloride ( 1a ) and CrCl₃(THF)₃, was characterized. X‐ray analysis of (3‐tert‐butyl‐5‐methyl‐2‐phenoxy)(3‐tert‐butyl‐5‐methyl‐ 2‐hydroxyphenyl)(phenyl)phosphine bis(tetrahydrofuran)chromium dichloride ( 6 ), obtained by the reaction of 1a and CrCl₃(THF)₃ in the presence of NaH, revealed a unique structure in which one phenol moiety of the bisphenol did not coordinate to the chromium center. Complex 6 showed higher activities than those observed in the in situ catalyst system. Polyethylene of various molecular weights was obtained with differing activators. The highest activity (113.5 kg mmol (cat)^?1 h^?1) was observed when TIBA/TB was used as a cocatalyst. A medium molecular weight polymer with narrow molecular weight distribution (M_w = 128,700, M_w/M_n = 1.8) was obtained using a 6 ‐TIBA/B(C₆F₅)₃ system. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3668–3676, 2007     

Dinuclear trivalent chromium,manganese, iron and cobalt complexes bridged by aromatic diamines

Summary Trivalent chromium, manganese, iron and cobalt salts react withm-phenylenediamine and acetylacetone to give complexes of the type [M(C₁₆H₁₈N₂O₂)X]: X = Cl, Br, NO₃ or NCS for M = chromium(III) and iron(III); X = Cl, Br, OAc or NCS for manganese(III); and X = OH for cobalt(III). Conductance measurements show the complexes to be nonelectrolytes. Molecular weights determined cryoscopically, show the iron complexes to be dinuclear. Magnetic measurements above 85 K reveal the presence of slight antiferromagnetic interactions. The complexes are dimeric five-coordinate square-pyramidal withm-phenylenediamine residues acting as bridges. The electronic spectra are interpreted in terms of the Normalised Spherical Harmonic Hamiltonian Theory and the DT/DQ values which indicate that chromium complexes are slightly distorted, whereas those of manganese are severely distorted.     

Magnetic property of a triply bridged linear trinuclear nickel complex

A new linear trinuclear nickel(II) complex, [Ni₃L₂(OCn)₄] (HL = 2-[(3-dimethylamino-propylimino)-methyl]-phenol, OCn = cinnamate), with phenoxo bridge and a novel tridentate bridging mode (in a 2.21 fashion according to Harris notation), of the cinnamate ligand has been synthesized and characterized by IR spectroscopy, UV-Vis spectroscopy, X-ray crystallography and static magnetic measurements. The molecular structure shows that each nickel ion occupies octahedral coordinating geometry. Apart from the phenoxo bridges, the carboxylic group of cinnamic anion shows two types of bridging modes viz. 2.11 and 2.21. The magnetic data indicate that a moderate intramolecular ferromagnetic and a weak intermolecular antiferromagnetic interaction are present in the complex under study. Broken symmetry density functional theory has been used to estimate the sign and magnitude of the coupling constants to understand the magnetic exchange mechanisms of the present system. The relative abilities of different bridging groups to mediate magnetic exchange interactions between paramagnetic nickel centers have been investigated by DFT calculation with variable angles. The results show that a small change in phenoxo-bridging angle has a very strong impact on the magnetic properties.