Synthesis, properties, and redox behavior of di(1-azulenyl)(2- and 3-thienyl)methyl cations and dications composed of two di(1-azulenyl)methylium units connected with 2,5-thiophenediyl and 2,5-thienothiophenediyl spacers

The titled stable monocations, di(1-azulenyl)(2- and 3-thienyl)methyl cations 7a,b and 8a,b and dications composed of two di(1-azulenyl)methylium units connected with 2,5-thiophenediyl and 2,5-thieno[3,2-b]thiophenediyl spacers 9a,b and 10a,b were prepared by hydride abstraction of the corresponding methane derivatives. These mono- and dications 7a,b, 8a,b, 9a,b, and 10a,b showed high stability with large pK(R)+ values. The values of monocations 7a,b and 8a,b were 11.2-11.8 +/- 0.1 and 11.4-12.4 +/- 0.1, respectively. Two cation units in dications 9a,b and 10a,b were neutralized via one step at the pH of 11.1-11.7 +/- 0.1, which corresponds to the average of the pK(R)+ values of the dications and half-neutralized monocations. Electrochemical behavior of 7a,b, 8a,b, 9a,b, and 10a,b was examined by cyclic voltammetry (CV). Formation of the thienoquinoid products 18a,b and 19a,b from 9a,b and 10a,b was characterized by UV-vis spectroscopy under electrochemical reduction conditions. Chemical reduction of 9a,b and 10a,b with Zn powder in acetonitrile afforded 18a,b and 19a,b as deep-colored crystals, which exhibited rather high electron-donating ability.     

Synthesis and redox behavior of azulene-substituted benzene derivatives and (eta(5)-cyclopentadienyl)[tetra- and di(6-azulenyl)cyclobutadiene]cobalt complexes

1,2-Di(6-azulenyl)tetraphenylbenzenes and (6-azulenyl)pentaphenylbenzenes were synthesized by Diels-Alder reactions of di(6-azulenyl)acetylenes and 6-(phenylethynyl)azulenes with tetraphenylcyclopentadienone. Cobalt-mediated cyclooligomerization of mono- and di(6-azulenyl)acetylenes afforded 1,3,5- and 1,2,4-tri(6-azulenyl)benzene derivatives together with (eta(5)-cyclopentadienyl)[tetra- and di(6-azulenyl)cyclobutadiene]cobalt complexes. The redox behavior of these novel (6-azulenyl)benzene derivatives and [tetra- and di(6-azulenyl)cyclobutadiene]cobalt complexes was examined by cyclic voltammetry (CV). Mono(6-azulenyl)benzenes exhibited a reduction wave upon CV. In contrast, 1,2-di(6-azulenyl)benzenes showed a two-step reduction wave at the similar potential region upon CV, which revealed the formation of a dianion stabilized by 6-azulenyl substituents under electrochemical reduction conditions. Three 6-azulenyl substituents on benzene in a 1,2,4 relationship also increased electron-accepting properties because of the formation of a closed-shell dianionic structure, whereas 1,3,5-tri(6-azulenyl)benzenes were reduced stepwise.     

Synthesis, stabilities, and redox behavior of mono-, di-, and tetracations composed of di(1-azulenyl)methylium units connected to a benzene ring by phenyl- and 2-thienylacetylene spacers. A concept of a cyanine-cyanine hybrid as a stabilized electrochromic system

This paper describes the preparation of two tetracations 4a(4+) and 4b(4+) composed of di(1-azulenyl)methylium units based on a new structural principle of a cyanine-cyanine hybrid for the design of electrochromic materials with two color changes. Di- and monocations 5a(2+), 5b(2+) and 6a+, 6b+ composed of di(1-azulenyl)methylium units were also prepared for the purpose of comparison. The pKR+ values of the tetracations are rather high despite their tetracationic structure, although the stability of these cations decreases with the increase of the number of the existing cation units. The cyclic voltammetry (CV) of these cations revealed the presumed multielectron redox properties. However, the tetracations did not exhibit the idealized electrochemical behavior, in which subsequent two-electron reduction was presumed as the cyanine-cyanine hybrid, probably due to the less effective electrochemical interaction among the positive charges. The scope of the creation of the novel polyelectrochromic materials taking the new structural principle is demonstrated by these examples.     

Synthesis and intramolecular pericyclization of 1-azulenyl thioketones

Several azulene-substituted thioketones, 1-thiobenzoylazulene (1a) and di(1-azulenyl) thioketone (2a) and their derivatives (1b and 2b-d) with alkyl substituents on each azulene ring, were prepared and their intramolecular pericyclization reaction was examined. The thioketones with a 3-alkyl substituent on each azulene ring exhibited the presumed pericyclization reaction under thermal and acid-catalyzed conditions, although the cases of the 1-azulenyl thioketones without the 3-alkyl substituents afforded a complex mixture under similar conditions. The intramolecular reaction following the intramolecular hydrogen transfer afforded the products 13b, 14b, and 14c. The products 13b and 14b were converted into the corresponding cations 18(+) and 19(+), which have structural similarity with that of the phenalenyl cation. These cations exhibited the expected two-step reduction waves upon CV, although the ESR analysis revealed that the neutral radical state did not have the presumed high stability.     

Azulene-substituted aromatic amines. synthesis and amphoteric redox behavior of N,N-Di(6-azulenyl)-p-toluidine and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine and their derivatives

[reaction: see text] N,N-Di(6-azulenyl)-p-toluidine (1a) and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine (2a) and their derivatives with 1,3-bis(ethoxycarbonyl) substituents on each 6-azulenyl group (1b and 2b) were prepared by Pd-catalyzed amine azulenylation and characterized as a study into new aromatic amines for multistage amphoteric redox materials. The redox behavior of each compound was characterized by cyclic voltammetry. These compounds undergo facile reduction to stable anion radicals and dianion diradicals owing to the resonance stabilization between the 6-azulenyl groups and exhibit electrochemical oxidation depending on the amine subunits. The ESR measurement of anion radicals and a dianion diradical generated by the electrochemical reduction of amine 1b and diamine 2b revealed that the unpaired electron of these radicals delocalizes over the entire azulene ring including the central nitrogen atoms. UV-vis spectral analysis of amines 1a,b and diamines 2a,b, taken during the electrochemical reduction, exhibited a gradual decrease of the absorption bands of the neutral species along with an increase of the new absorption maxima at 625, 605, 640, and 610 nm, respectively, with the development of well-defined isosbestic points at 502, 562, 478, and 545 nm, respectively. As indicated by a combined ESR and UV-vis spectral study, the species giving rise to the new absorption maxima are concluded to be the generation of anion radicals and dianion diradicals of aromatic amines and diamines with high thermodynamic stability.     

Synthesis and properties of hexakis(6-octyl-2-azulenyl)benzene as a multielectron redox system with liquid crystalline behavior

[structure: see text] This paper describes the cyclotrimerization reaction of di(2-azulenyl)acetylenes (2a,b) catalyzed by Co2(CO)8 to produce hexa(2-azulenyl)benzene derivatives (1a,b). The cyclooligomerization of 2a and 2b utilizing CpCo(CO)2 as a catalyst produced (eta5-cyclopentadienyl)[tetra(2-azulenyl)cyclobutadiene]cobalt complexes (3a,b). The redox behavior of hexakis(6-octyl-2-azulenyl)benzene (1b), bis(6-octyl-2-azulenyl)acetylene (2b), and the cobalt complexes 3a and 3b along with 6-octyl-2-phenylazulene (19) was examined by cyclic voltammetry (CV). The reduction of compound 1b exhibited multiple-electron transfers in one step upon CV with a reduction potential similar to that of compound 19. However, the CVs of compounds 2b, 3a, and 3b were characterized by stepwise waves because of the reduction of each azulene ring. The mesomorphic behaviors of 1b, 2b, and 19 were also studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques. A new series of azulene derivatives, 1b, 2b, and 19, substituted by a long alkyl chain at the 6-position shows mesomorphism with crystalline polymorphs. Compound 1b showed a large temperature range of hexagonal columnar mesophases (Col(ho)) from 115.5 to 199.9 degrees C. Compound 2b has rectangular columnar (Col(ro)), smectic E (S(E)), and nematic (N) mesophases. Compound 19 exhibited an S(E) mesophase.     

Synthesis, properties, and redox behavior of mono-, bis-, and tris[1,1,4,4,-tetracyano-2-(1-azulenyl)-3-butadienyl] chromophores binding with benzene and thiophene cores

Mono-, bis-, tris-, and tetrakis(1-azulenylethynyl)benzene and mono- and bis(1-azulenylethynyl)thiophene derivatives 5-10 have been prepared by Pd-catalyzed alkynylation of ethynyl arenes with 1-iodoazulene derivative or the 1-ethynylazulene derivative with tetraiodobenzene and iodothiophenes under Sonogashira-Hagihara conditions. Compounds 5-10 reacted with tetracyanoethylene in a [2+2] cycloaddition reaction to afford the corresponding 1,1,4,4,-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-3-butadienyl chromophores 12-16 in excellent yields, except for the reaction of the tetrakis(1-azulenylethynyl)benzene derivative. 1,1,4,4,-Tetracyano-2,3-bis(1-azulenyl)butadiene (17) was also prepared by the similar reaction of bis(1-azulenyl)acetylene (11) with tetracyanoethylene (TCNE). The redox behavior of novel azulene derivatives 12-17 was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed multistep electrochemical reduction properties. Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions.     

Reaction of azulenes with 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate (TPT) and synthesis of the parent azulene

2-Azulenyl trifluoromethanesulfonate was prepared by the reaction of 2-hydroxyazulene with trifluoromethanesulfonic anhydride in the presence of triethylamine as a base. Under the use of pyridine, 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate further reacted with 2-azulenyl trifluoromethanesulfonate to give 1-(1-trifluoromethanesulfonyl-1,4-dihydropyridin-4-yl)azulenyl trifluoromethanesulfonate. Moreover, we found that azulenes also reacted with 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate to give 4-(1-azulenyl)-1,4-dihydropyridine derivatives and 6-(1-azulenyl)-1-trifluoromethanesulfonyl-1-aza-hexa-1,3,5-triene depending on the reaction conditions. 2-Azulenyl trifluoromethanesulfonate was converted finally into the parent azulene in excellent yield by palladium-catalyzed reduction using formic acid as a reducing reagent.     

Cleavage of dinitrogen to yield a (t-BuPOCOP)molybdenum(IV) nitride

(t-BuPOCOP)MoI(2) (1; t-BuPOCOP = C(6)H(3)-1,3-[OP(t-Bu)(2)](2)) has been synthesized from MoI(3)(THF)(3). Upon reduction of 1 with Na/Hg under dinitrogen molecular nitrogen is cleaved to form [(t-BuPOCOP)Mo(I)(N)](-). The origin of the N atom was confirmed using (15)N(2). Protonation of [(t-BuPOCOP)Mo(I)(N)](-) results in the formation of a neutral species in which it is proposed that the proton has added across the Mo-P bond.     

Synthesis, Characterization, and Crystal Structures of New Dications Bearing the -Se-Se- Bridge

Starting from 1,3-dimethyl-4-imidazoline-2-selone (1), 1,2-bis(2-selenoxo-3-methyl-4-imidazolinyl-2-)ethane (3) and 1,3-dimethylimidazolidine-2-selone (4), the following six compounds, [(C(5)H(8)N(2)Se-)(2)](2+).2Br(-) (I), [(C(5)H(8)N(2)Se-)(2)](2+).2I(-) (II), [(C(5)H(8)N(2)Se-)(2)](2+).Cl(-).I(3)(-) (III) [(C(5)H(10)N(2)Se-)(2)](2+).Br(-).IBr(2)(-) (IV), [(C(5)H(7)N(2)Se-)(2)](2+).I(3)(-).(1)/(2)I(4)(-) (V) and [(C(5)H(7)N(2)Se-)(2)](2+).2I(-).CH(3)CN (VI), in which the selenium compounds are oxidized to dications bearing the uncommon -Se-Se- bridge, have been prepared, and I-V crystallographically characterized. I and III were obtained by reacting 1 with IBr and ICl respectively, while II was obtained by reduction of previously described hypervalent selenium compound of 1 (5) bearing the I-Se-I group with elemental tellurium. These three compounds contain the same [(C(5)H(8)N(2)Se-)(2)](2+) dication balanced by two bromides in I, two iodides in II, and Cl(-) and I(3)(-) in III. However, on the basis of the Se-Cl bond length of 2.778(5) ?, III can also be considered as formed by the [(C(5)H(8)N(2)Se-)(2)Cl](+) cation, with I(3)(-) as counterion. Similarly to III, compound IV, which was obtained by reacting 4 with IBr, can be considered as formed by [(C(5)H(10)N(2)Se-)(2)Br](+) cations and IBr(2)(-) anions. As in II, compound V has been prepared by reduction of the hypervalent selenium compound of 3 (6) bearing two I-Se-I groups with elemental tellurium. In V, the [(C(5)H(7)N(2)Se-)(2)](2+) cation is balanced by I(3)(-) and half I(4)(2-) anions. The structural data show that all the cations are very similar, with Se-Se bond lengths ranging from 2.409(2) to 2.440(2) ?. FT-IR and FT-Raman spectra of I-VI allow one to identify two bands around 230 +/- 10 and 193 +/- 5 cm(-1) that are common to all compounds. These bands are generally strong in the FT-Raman and weak in the FT-IR spectra and should contain a contribution of the nu(Se-Se) stretching vibration. The spectra are also in good agreement with the structural features of the polyhalide anions present in the crystals. Crystallographic data are as follows: I is monoclinic, space group P2(1), with a = 9.849(6) ?, b = 11.298(5) ?, c = 7.862(6) ?, beta = 106.44(2) degrees, Z = 2, and R = 0.0362; II is monoclinic, space group P2(1), with a = 8.063(6) ?, b = 11.535(5) ?, c = 10.280(5) ?, beta = 107.13(2) degrees, Z = 2, and R = 0.0429, III is monoclinic, space group P2(1)/n, with a = 10.431(7) ?, b = 18.073(5) ?, c = 11.223(6) ?, beta = 100.76(2) degrees, Z = 4, and R = 0.0490; IV is monoclinic, space group P2(1)/n, with a = 10.298(5) ?, b = 18.428(7) ?, c = 11.475(6) ?, beta = 104.10(4) degrees, Z = 4, and R = 0.0300; V is triclinic, space group P&onemacr;, with a = 7.456(6) ?, b = 11.988(5) ?, c = 12.508(5) ?, alpha = 79.32(2) degrees, beta = 85.49(2) degrees, gamma = 80.62(2) degrees, Z = 2, and R = 0.0340.     

Divalent germanium compound with a radical-anionic ligand: molecular structures of (dpp-BIAN)*- GeCl and its hydrochloration products [(dpp-BIAN)(H)2]*+ [GeCl3]- and [[(dpp-BIAN)(H)2*+]2(Cl-)]+ [GeCl3]- (dpp-BIAN=1,2-Bis[(2,6-diisopropylphenyl)imino]acenaphthene)

The germanium(II) compound (dpp-BIAN)GeCl (1), which contains the radical anion of dpp-BIAN can be prepared either by reacting free dpp-BIAN ligand with 2 equiv of GeCl2(1,4-dioxane) in Et2O or by metathetical reaction of the sodium salt of dpp-BIAN with germanium dichloride in Et2O or benzene. The reaction of benzene solutions of 1 with 2 or 3 equiv of HCl led to protonation of the dpp-BIAN ligand affording [(dpp-BIAN)(H)2]*+[GeCl3]- (2) and [[(dpp-BIAN)(H)2*+]2(Cl-)]+ [GeCl3]- (3), which incorporate the radical cation of the protonated ligand. Compounds 1-3 have been characterized by elemental analysis, IR, UV-vis, and electron spin resonance (ESR) spectroscopy. Molecular structures of 1-3 were determined by single-crystal X-ray diffraction. In molecule 1, the Ge atom is positioned at the apex of the slightly distorted trigonal pyramid. The Ge-N bond lengths in 1 are 2.0058(19) and 2.004(2) A. The molecular structure of 2 consists of contact ions [(dpp-BIAN)(H)2]+ and [GeCl3]-. In the molecular structure of 3, two radical cations of [(dpp-BIAN)(H)2]+ are "coordinated" by the chlorine anion. The ESR signal of 1 indicates the presence of a dpp-BIAN radical anion and shows a hyperfine structure due to the coupling of an unpaired electron to 14N, 73Ge, 35Cl, 37Cl, and 1H nuclei (AN=0.48 (2 N), AGe=0.96, ACl=0.78 (35Cl), ACl=0.65 (37Cl), AH=0.11 (4 H) mT, g=2.0014). Both 2 and 3 reveal ESR signals of radical cation [(dpp-BIAN)(H)2]*+ (septet, AN=0.53, AH=0.48 mT, g=2.0031).     

Realization of unusual ligand binding motifs in metalated container molecules: synthesis, structures, and magnetic properties of the complexes [(LMe)Ni2(mu-L')]n+ with L'=NO3-, NO2-, N3-, N2H4, pyridazine, phthalazine, pyrazolate, and benzoate

A series of dinickel(II) complexes with the 24-membered macrocyclic hexaazadithiophenol ligand H(2)L(Me) was prepared and examined. The doubly deprotonated form (L(Me))(2-) forms complexes of the type [(L(Me))Ni2II(mu-L')](n+) with a bioctahedral N(3)Ni(II)(mu-SR)(2)(mu-L')Ni(II)N(3) core and an overall calixarene-like structure. The bridging coordination site L' is accessible for a wide range of exogenous coligands. In this study L'=NO(3)(-), NO(2)(-), N(3)(-), N(2)H(4), pyrazolate (pz), pyridazine (pydz), phthalazine (phtz), and benzoate (OBz). Crystallographic studies reveal that each substrate binds in a distinct fashion to the [(L(Me))Ni(2)](2+) portion: NO(2)(-), N(2)H(4), pz, pydz, and phtz form mu(1,2)-bridges, whereas NO(3)(-), N(3)(-), and OBz(-) are mu(1,3)-bridging. These distinctive binding motifs and the fact that some of the coligands adopt unusual conformations is discussed in terms of complementary host-guest interactions and the size and form of the binding pocket of the [(L(Me))Ni(2)](2+) fragment. UV/Vis and electrochemical studies reveal that the solid-state structures are retained in the solution state. The relative stabilities of the complexes indicate that the [(L(Me))Ni(2)](2+) fragment binds anionic coligands preferentially over neutral ones and strong-field ligands over weak-field ligands. Secondary van der Waals interactions also contribute to the stability of the complexes. Intramolecular ferromagnetic exchange interactions are present in the nitrito-, pyridazine-, and the benzoato-bridged complexes where J=+6.7, +3.5, and +5.8 cm(-1) (H=-2 JS(1)S(2), S(1)=S(2)=1) as indicated by magnetic susceptibility data taken from 300 to 2 K. In contrast, the azido bridge in [(L(Me))Ni(2)(mu(1,3)-N(3))](+) results in an antiferromagnetic exchange interaction J=-46.7 cm(-1). An explanation for this difference is qualitatively discussed in terms of bonding differences.     

Bond-formation versus electron transfer: C-C-coupling reactions of hydrocarbon dications with benzene

The bimolecular reactions of several hydrocarbon dications C(m)H(n)(2+) (m = 6-10, n = 4-9) with neutral benzene are investigated by tandem mass spectrometry using a multipole instrument. Not surprisingly, the major reaction of C(m)H(n)(2+) with benzene corresponds to electron transfer from the neutral arene to the dication resulting in the pair of monocationic products C(m)H(n)(+) + C(6)H(6)(+). In addition, also dissociative electron transfer takes place, whereas proton transfer from the C(m)H(n)(2+) dication to neutral benzene is almost negligible. Interestingly, the excess energy liberated upon electron transfer from the neutral arene to the C(m)H(n)(2+) dication is not equally partitioned in the monocationic products in that the cations arising from the dicationic precursor have a higher internal energy content than the monocations formed from the neutral reaction partner. In addition to the reactions leading to monocationic product ions, bond-forming reactions with maintenance of the two-fold charge are observed, which lead to a condensation of the C(m)H(n)(2+) dications with neutral benzene under formation of intermediate C(m+6)H(n+6)(2+) species and then undergo subsequent losses of molecular hydrogen or neutral acetylene. This reaction complements a recently proposed dicationic route for the formation of polycyclic aromatic hydrocarbons under extreme conditions such as they exist in interstellar environments.     

Crystal structures and spectroscopic characterization of radical cations and dications of oligothiophenes stabilized by annelation with bicyclo[2.2.2]octene units: sterically segregated cationic oligothiophenes

The remarkably stable SbF(6)(-) salts of the radical cations of bithiophene 1(2T) and terthiophene 1(3T), completely surrounded by bicyclo[2.2.2]octene (BCO) units, were obtained by one-electron oxidation of the neutral precursors with NO(+)SbF(6)(-), and their solid-state structures were determined by X-ray crystallography. In these radical cations, the presence of quinoidal character was apparent, as shown by the increased planarity and by comparison of the bond lengths with those of the neutral precursors. The shortest intermolecular pi-pi distances in the crystal structure of 1(2T)(*)(+)SbF(6)(-) (distance between two sp(2) carbon atoms, 4.89 A) and 1(3T)(*)(+)SbF(6)(-) (distance between an sp(2) carbon and a sulfur atom, 3.58 A) were found to be longer than the sums of the van der Waals radii of the corresponding atoms. In accord with this, no apparent change was observed in ESR and UV-vis-NIR spectra of solutions of 1(2T)(*)(+) and 1(3T)(*)(+) upon lowering the temperature, indicating that the pi- (or sigma-) dimer formation is inhibited in solution as well as in the solid state. The dications 1(2T)(2+) and 1(3T)(2+) were generated with the stronger oxidant SbF(5) in CH(2)Cl(2) at -40 degrees C and characterized by NMR spectroscopy. In the (1)H NMR spectra, two conformers were observed for each dication of both 1(2T)(2+) (transoid (t) and cisoid (c)) and 1(3T)(2+) (t,t and c,t) at room temperature due to the high rotational barrier around the inter-ring bond(s) between thiophene rings, which was caused by the enhanced double bond character of these bonds following two-electron oxidation. This is supported by DFT calculations (B3LYP/6-31G(d)), which predicted the rotational barriers in the dications of unsubstituted bithiophene and terthiophene to be 27.6 and 22.9 kcal mol(-)(1), respectively. In the case of quaterthiophene and sexithiophene surrounded by BCO frameworks 1(4T) and 1(6T), oxidation with even one molar equivalent of NO(+)SbF(6)(-) afforded the dication salts 1(4T)(2+)2SbF(6)(-) and 1(6T)(2+)2SbF(6)(-), which were isolated as stable single crystals and allowed the X-ray crystallography. In their crystal structures, the cationic pi-systems became planar again due to the great contribution of quinoidal resonance structures, and the pi-systems, which were arrayed in a parallel geometry, were also segregated by the steric effect of BCO units. The degree and tendency of changes in the bond lengths of thiophene rings of 1(4T)(2+) and 1(6T)(2+) as compared with neutral precursors were similar to those of 1(2T)(*)(+)SbF(6)(-) and 1(3T)(*)(+)SbF(6)(-), respectively, implying that the contribution of quinoidal character is modulated by the amount of positive charge per thiophene unit.     

Cyclopentadienyl chromium diimine and pyridine-imine complexes: ligand-based radicals and metal-based redox chemistry

Paramagnetic CpCr(III) complexes with antiferromagnetically-coupled anionic radical diimine and pyridine-imine ligands were prepared and characterized. The diimine chloro CpCr[(ArNCR)(2)]Cl complexes (1: Ar = 2,6-iPr(2)C(6)H(3) (Dpp), R = H; 2: Ar = 2,6-Me(2)C(6)H(3) (Xyl), R = Me; 3: Ar = 2,4,6-Me(3)C(6)H(2) (Mes), R = Me) were synthesized by treatment of previously reported Cr(diimine)(THF)(2)Cl(2) precursors with NaCp. Reduction of 1 with Zn gives CpCr[(DppNCH)(2)], 4, resulting from reduction of Cr(III) to Cr(II) with retention of the ligand-based radical. Alkoxide complexes CpCr[(DppNCH)(2)](OCR(2)R') (5: R = Me, R' = Ph; 6: R = iPr, R' = H) were synthesized by protonolysis of Cp(2)Cr with HOCR(2)R' in the presence of the neutral diimine and catalytic base. The corresponding radical pyridine-imine complexes CpCr(PyCHNMes)Cl (9), CpCr(PyCHNMes) (8), and CpCr(PyCHNMes)(OCMe(2)Ph) (11), were prepared by analogous routes. Oxidation of 8 with iodine gives CpCr(PyCHNMes)I (10) where oxidation of Cr(II) to Cr(III) again occurs with retention of the anionic pyridine-imine radical ligand. The molecular structures of complexes 1, 2, 4-8, 10 and 11 were determined by single-crystal X-ray diffraction. Unusual low energy bands were observed in the UV-vis spectra of the reported complexes, with particularly strong transitions observed for the Cr(II) complexes 4 and 8. The electronic structure of pyridine-imine complexes 8 and 10 were investigated by theoretical calculations.     

Negishi cross-coupling reaction catalyzed by an aliphatic, phosphine based pincer complex of palladium. biaryl formation via cationic pincer-type Pd(IV) intermediates

The aliphatic, phosphine-based pincer complex [(C(10)H(13)-1,3-(CH(2)P(Cy(2))(2))Pd(Cl)] (1) is a highly active Negishi catalyst, enable to quantitatively couple various electronically activated, non-activated, deactivated, sterically hindered and functionalized aryl bromides with various diarylzinc reagents within short reaction times and low catalyst loadings. Experimental observations strongly indicate that a molecular mechanism is operative with initial chloride dissociation of 1 and formation of the cationic T-shaped 14e(-) complex [(C(10)H(13)-1,3-(CH(2)P(C(6)H(11))(2))(2))Pd](+) (B), which undergoes oxidative addition of an aryl bromide (Ar'Br) to yield the cationic, penta-coordinated aryl bromide pincer complexes of type [(C(10)H(13)-1,3-(CH(2)P(Cy(2))(2))Pd(Br)(aryl')](+) (C) with the metal center in the oxidation state of +IV and the aryl unit in cis position relative to the aliphatic pincer core. Subsequent transmetalation with Zn(aryl)(2) result in the cationic diaryl pincer complexes of type [(C(10)H(13)-1,3-(CH(2)P(Cy(2))(2))Pd(aryl)(aryl')](+) (D), which reductively eliminate the coupling products, thereby regenerating the catalyst. The neutral square planar aryl pincer complex--a possible key intermediate in the catalytic cycle--was found to be reversibly formed in the reaction mixture but is not involved in the catalytic mechanism. Similarly, palladium nanoparticles as the catalytically active form of 1 could have been excluded.     

Reduction of benzophenone and 9(10H)-anthracenone with the magnesium complex [(2,6-iPr2C6H3-bian)Mg(thf)3

The reduction of benzophenone with the magnesium complex [(2,6-iPr(2)C(6)H(3)-bian)Mg(thf)(3)] (1), containing the 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene dianion, affords the pinacolato complex [(2,6-iPr(2)C(6)H(3)-bian)Mg(thf)](2)[micro-O(2)C(2)Ph(4)].(C(6)H(6))(4) (2). The reaction of 1 with 9(10H)-anthracenone yields the 9-anthracenolato complex [(2,6-iPr(2)C(6)H(3)-bian)Mg(OC(14)H(9))(thf)(2)] (3). Complexes 2 and 3 were characterized by elemental analyses, UV/Vis, IR, and ESR spectroscopy, as well as by single crystal X-ray diffraction. Complex 2 dissociates in solution with splitting of the bridging pinacolato unit, forming the biradical diimino/ketyl complex [(2,6-iPr(2)C(6)H(3)-bian)Mg(thf)(OCPh(2))].     

Electrochemical behavior of nickeladithiolene S,S'-dialkyl adducts: evidence for the formation of a metalladithiolene radical by electrochemical redox reactions

The electrochemical behavior of nickeladithiolene S,S'-dialkyl adducts (alkyl = benzyl, methyl, tert-butyl) was investigated by using cyclic voltammetry (CV), visible, near-IR, and ESR spectroscopies and bulk electrolyses. The redox potentials of the S,S'-dialkyl adducts were influenced by the electron-donating effect of the functional group on the sulfur atoms. The nickeladithiolene S,S'-dibenzyl adduct [Ni[S(SCH(2)Ph)C(2)Ph(2)](2)] (2) eliminated one benzyl radical by one-electron reduction, and then the monobenzyl adduct anion [Ni(S(2)C(2)Ph(2))[S(2)(CH(2)Ph)C(2)Ph(2)]](-) (3(-)) was formed. Anion 3(-) was also formed by the reaction of nickeladithiolene dianion [Ni(S(2)C(2)Ph(2))(2)](2)(-) (1(2-)) with 1 equiv of benzyl cation. When anion 3(-) was oxidized, the long-lived nickeladithiolene radical [Ni(S(2)C(2)Ph(2))[S(2)(CH(2)Ph)C(2)Ph(2)]] (3) was formed. The visible, near-IR, and ESR spectra of radical 3 could be measured and assigned. When radical 3 was further oxidized, the oxidant 3(+) eliminated one benzyl cation, and then free nickeladithiolene (1) was generated.     

Resorcinol based acyclic dimeric and cyclic di- and tetrameric cyclodiphosphazanes: synthesis, structural studies, and transition metal complexes

The condensation reaction of resorcinol with cis-[ClP(μ-N(t)Bu)(2)PN(H)(t)Bu] produced a difunctional derivative 1,3-C(6)H(4)[OP(μ-N(t)Bu)(2)PN(H)(t)Bu](2) (1), whereas the similar reaction with [ClP(μ-N(t)Bu)](2) resulted in the formation of a 1:1 mixture of dimeric and tetrameric species, [{P(μ-N(t)Bu)}(2){1,3-(O)(2)-C(6)H(4)}](2) (2a) and [{P(μ-N(t)Bu)}(2){1,3-(O)(2)-C(6)H(4)}](4) (2b), which were separated by repeated fractional crystallization and column chromatography. The reaction of dimer 2a with H(2)O(2) and selenium produces tetrachalcogenides [{(O)P(μ-N(t)Bu)}(2){1,3-(O)(2)-C(6)H(4)}](2) (3) and [{(Se)P(μ-N(t)Bu)}(2){1,3-(O)(2)-C(6)H(4)}](2) (4), respectively. The reaction between the dimer (2a) and [Pd(μ-Cl)(η(3)-C(3)H(5))](2) or AuCl(SMe(2)) yielded the corresponding tetranuclear complexes, [{((Cl)(η(3)-C(3)H(5))Pd)P(μ-N(t)Bu)}(2){1,3-(O)(2)-C(6)H(4)}](2) (5) and [{(ClAu)P(μ-N(t)Bu)}(2){1,3-(O)(2)-C(6)H(4)}](2) (6) in good yield. The complexes 5 and 6 are the rare examples of phosphorus macrocycles containing two or more exocyclic transition metal fragments. Treatment of 1 with copper halides in 1:1 molar ratio resulted in the formation of one-dimensional (1D) coordination polymers, [(CuX){1,3-C(6)H(4){OP(μ-N(t)Bu)(2)PN(H)(t)Bu}}(2)](n) (7, X = Cl; 8, X = Br; 9, X = I), which showed the helical structure in solid state because of intramolecular hydrogen bonding, whereas similar reactions of 1 with 4 equiv of copper halides also produced 1D-coordination polymers, [(Cu(2)X(2))(2){1,3-C(6)H(4){OP(μ-N(t)Bu)(2)PN(H)(t)Bu}(2)}](n) (10, X = Cl; 11, X = Br; 12, X = I), but containing Cu(2)X(2) rhomboids instead of CuX linkers. The crystal structures of 1, 2a, 2b, 4, 7-9, and 12 were established by X-ray diffraction studies.     

A neutral, monomeric germanium(I) radical

Stoichiometric reduction of the bulky β-diketiminato germanium(II) chloride complex [((But)Nacnac)GeCl] ((But)Nacnac = [{N(Dip)C(Bu(t))}(2)CH](-), Dip = C(6)H(3)Pr(i)(2)-2,6) with either sodium naphthalenide or the magnesium(I) dimer [{((Mes)Nacnac)Mg}(2)] ((Mes)Nacnac = [(MesNCMe)(2)CH](-), Mes = mesityl) afforded the radical complex [((But)Nacnac)Ge:](?) in moderate yields. X-ray crystallographic, EPR/ENDOR spectroscopic, computational, and reactivity studies revealed this to be the first authenticated monomeric, neutral germanium(I) radical.