Divalent Ytterbium and Iron Metallocenes of a Dimethyldihydropyrene-Fused Cyclopentadienyl

The photoisomerizable, dimethyldihydropyrene-fused cyclopentadienide salt LiCpDHP reacts with FeCl2 to form Fe(CpDHP)2 (1). Reaction of the parent cyclopentadiene HCpDHP with Yb[N(SiMe3)2]2[THF]2 similarly affords the bent ytterbium metallocene Yb(CpDHP)2(THF)2 (3). Both metallocenes are formed as a mixture of rac and meso isomers in 3:2 and 1:1 ratios for Fe and Yb, respectively. NMR data are consistent with η5-coordination of the CpDHP ligand in 1, and this is also confirmed to be the case in 3 by X-ray crystallography. Attempts to oxidize the Yb(II) center in 3 with p-tolyldisulfide led to loss of the CpDHP ligand as the dimer (CpDHP)2. Photolysis of either 1 or 3 at wavelengths longer than 490 nm did not result in isomerization to the ring-opened cyclophanediene form of the ligand, in contrast to the lithium salt LiCpDHP

Effective Aromaticity of Tricarbonylchromiumbenzene, about 25 Enhanced over that of Benzene: Structural Evidence from a Complexed Benzannulene

The tricarbonylchromium complex of 2,7-di-tert-butyl-trans-12c,12d-dimethylbenzo[e]dihydropyrene is prepared in 65% yield from the parent annulene. Analysis of the 1H NMR spectrum leads to coupling constant data and Günther's “Q” value data which unequivocally indicate that the tricarbonylchromiumbenzene moiety behaves like an aromatic system of greater bond fixing ability, aromaticity, than benzene itself; this analysis is supported by X-ray structural data and by the rotational position of the tricarbonyl podal. Analysis of chemical shift data indicates that the tricarbonylchromium benzene moiety has about 25% enhanced “aromaticity” over that of benzene

Verdazyl Radicals as Oligopyridine Mimics: Structures and Magnetic Properties of M(II) Complexes of 1,5-Dimethyl-3-(2,2‘-bipyridin-6-yl)-6-oxoverdazyl (M = Mn, Ni, Cu, Zn)

The verdazyl radical 1,5-dimethyl-3-(2,2‘-bipyridin-6-yl)-6-oxoverdazyl (3) was prepared, and its homoleptic metal complexes M(3)22+·2X- (5, M = Mn(II); 6, M = Ni(II); 7, M = Cu(II); 8, M = Zn(II); X = ClO4, PF6) were characterized by single-crystal X-ray diffraction and variable-temperature magnetic susceptibility measurements. Relevant crystallographic parameters are as follows:  5, monoclinic space group Pna21, a = 18.755(4) Å, b = 11.154(3) Å, c = 16.594(4) Å, α = 90.00°, β = 90.00°, γ = 90.00°, V = 3471.4(13) Å3, and Z = 4; 7, triclinic space group P1̋, a = 9.4638(18) Å, b = 9.8442(19) Å, c = 18.769(4) Å, α = 103.746(3)°, β = 92.925(3)°, γ = 94.869(3)°, V = 1687.8(6) Å3, and Z = 2; 8, triclinic space group P1̋, a = 9.4858(14) Å, b = 9.7919(14) Å, c = 18.889(3) Å, α = 104.196(3)°, β = 92.855(3)°, γ = 94.216(3)°, V = 1692.1(4) Å3, and Z = 2. In all cases, the two verdazyl-based ligands bind almost perpendicular to each other in meridional positions, yielding pseudooctahedral metal complexes whose general structural features are strongly reminiscent of metal bis(terpyridine) complexes. The intramolecular metal−verdazyl magnetic exchange coupling is strongly ferromagnetic in 6 (JNi-vd= +240 cm-1), and strongly antiferromagnetic in 5 (JMn-vd= −93 cm-1). Complex 7 exhibits weak ferromagnetic coupling (JCu-vd = −4.5 cm-1). Intramolecular radical−radical coupling in the zinc complex 8 was found to be weakly antiferromagnetic (Jvd-vd = −8 cm-1). Intramolecular radical−radical exchange was generally weak in the four metal complexes, ranging from −10 cm-1 (for 5) to +2 cm-1 (for 7). The low-temperature magnetic behavior of 7 and 8 is complex, possibly arising from a combination of intra- and intermolecular interactions

Effective Aromaticity of Tricarbonylchromiumbenzene, about 25 Enhanced over that of Benzene: Structural Evidence from a Complexed Benzannulene

The tricarbonylchromium complex of 2,7-di-tert-butyl-trans-12c,12d-dimethylbenzo[e]dihydropyrene is prepared in 65% yield from the parent annulene. Analysis of the 1H NMR spectrum leads to coupling constant data and Günther's “Q” value data which unequivocally indicate that the tricarbonylchromiumbenzene moiety behaves like an aromatic system of greater bond fixing ability, aromaticity, than benzene itself; this analysis is supported by X-ray structural data and by the rotational position of the tricarbonyl podal. Analysis of chemical shift data indicates that the tricarbonylchromium benzene moiety has about 25% enhanced “aromaticity” over that of benzene

Synthesis, Structure, and Magnetism of Bimetallic Manganese or Nickel Complexes of a Bridging Verdazyl Radical

Two binuclear metal−radical complexes, formed by the reaction of M(hfac)2·2H2O (M = Mn or Ni; hfac = hexafluoroacetylacetonate) with the 1,5-dimethyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical (3), were synthesized. The binuclear Mn complex 5 (i.e., 3[Mn(hfac)2]2) crystallizes in the monoclinic space group C2/c:  C30H17N6O9F24Mn2, a = 29.947(3), b = 17.143(3), c = 16.276(3) Å, β = 123.748(3)°, Z = 4. The compound consists of two pseudo-octahedral Mn(II) ions, both bearing two hfac ancillary ligands, bridged by the bis(bidentate) radical 3. The temperature dependence of the magnetic susceptibility of 5 reveals moderate antiferromagnetic exchange between each of the Mn(II) ions and the verdazyl radical (J = −48 cm-1). The S = 9/2 ground spin state of the complex was corroborated by low-temperature magnetization versus field measurements. In contrast, the magnetic susceptibility versus temperature behavior of 6 (whose molecular structure is presumed to be analogous to that of 5) indicates that the two Ni(II) ions are strongly ferromagnetically coupled to the verdazyl radical (J = +220 cm-1). The magnetization versus field behavior of 5 is consistent with an S = 5/2 ground-state species

Weak Magnetic Coupling of Coordinated Verdazyl Radicals through Diamagnetic Metal Ions. Synthesis, Structure, and Magnetism of a Homoleptic Copper(I) Complex

Weak Magnetic Coupling of Coordinated Verdazyl Radicals through Diamagnetic Metal Ions. Synthesis, Structure, and Magnetism of a Homoleptic Copper(I) Comple

Synthesis, Structure, and Magnetism of Bimetallic Manganese or Nickel Complexes of a Bridging Verdazyl Radical

Two binuclear metal−radical complexes, formed by the reaction of M(hfac)2·2H2O (M = Mn or Ni; hfac = hexafluoroacetylacetonate) with the 1,5-dimethyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical (3), were synthesized. The binuclear Mn complex 5 (i.e., 3[Mn(hfac)2]2) crystallizes in the monoclinic space group C2/c:  C30H17N6O9F24Mn2, a = 29.947(3), b = 17.143(3), c = 16.276(3) Å, β = 123.748(3)°, Z = 4. The compound consists of two pseudo-octahedral Mn(II) ions, both bearing two hfac ancillary ligands, bridged by the bis(bidentate) radical 3. The temperature dependence of the magnetic susceptibility of 5 reveals moderate antiferromagnetic exchange between each of the Mn(II) ions and the verdazyl radical (J = −48 cm-1). The S = 9/2 ground spin state of the complex was corroborated by low-temperature magnetization versus field measurements. In contrast, the magnetic susceptibility versus temperature behavior of 6 (whose molecular structure is presumed to be analogous to that of 5) indicates that the two Ni(II) ions are strongly ferromagnetically coupled to the verdazyl radical (J = +220 cm-1). The magnetization versus field behavior of 5 is consistent with an S = 5/2 ground-state species

Charge Transfer Chemistry of Benzo[2,1-<i>c</i>:3,4-<i>c</i><i>‘</i>]bis(1,2,3-dithiazole) (BT). Preparation and Structural Characterization of [BT][ClO₄] and [BT]₃[X]₂ (X = ClO₄^- and FSO₃^-)

The heterocyclic π-donor benzo[2,1-c:3,4-c‘]bis(1,2,3-dithiazole) (BT) can be prepared in 60% yield by the condensation of 1,4-diaminobenzene-2,3-dithiol with sulfur monochloride. BT is also formed, in low yield, along with its 5-chloro and 5,6-dichloro derivatives, in the reaction of p-phenylenediamine with sulfur monochloride. Cyclic voltammetry on BT reveals two reversible oxidation waves at 0.61 and 1.10 V (in CH3CN, ref SCE). The ESR signal (g = 2.0175) of the radical cation BT+ [in SO2(l)] exhibits a 1:2:3:2:1 hyperfine structure with aN = 0.161 mT. BT forms radical ion salts by electro-oxidation in the presence of inorganic counterions. In addition to a 1:1 salt [BT][ClO4], the structure of which consists of a simple ionic arrangement of BT+ radical cations and ClO4- anions, BT also forms 3:2 salts, i.e., [BT]3[X]2, with X = ClO4- and FSO3-. The crystal structures of these 3:2 salts consist of triple-decker units of radical cation dimers, i.e., [BT2]2+, and neutral BT molecules. These units are packed into ribbonlike arrays interspersed (to either side) by counterions. The ClO4- and FSO3- salts differ in the way these ribbons are layered on top of one another. Both can be considered as forming slipped π-stacks, but the degree of offset between consecutive layers is considerably larger in the ClO4- salt. The room-temperature conductivity of [BT][ClO4] is ca. 10-5 S cm-1, while that of the two 3:2 salts is ca. 10-2 S cm-1

5,5‘-Bridged Bis(1,2,3-dithiazoles): Spin States and Charge-Transfer Chemistry

Bifunctional 1,2,3-dithiazoles bridged with azine and phenylenediamine spacers have been prepared, with a view to determining the extent of communication between the two dithiazole rings as a function of the electronic and steric demands of the bridge. The crystal structure of the closed-shell diazine derivative [S2NClC2NNC2ClNS2] is rigorously planar. Cyclic voltammetry on this compound indicates two reversible one-electron oxidations. The radical cation state has been characterized by EPR spectroscopy and by crystal structure determination of its 1:1 PF6- salt. The latter reveals little interaction between neighboring radical cations; consistently, the material exhibits a conductivity of σ -5 S cm-1. Insertion of a phenylene group into the diazine bridge to afford [S2NClC2NC6H4NC2ClNS2] leads to significant torsional motion between the phenylene ring and the two end groups, as a result of which the two DTA rings are electronically independent; no radical cation state has been observed for this species. Crystal data for Cl2S4N4C4: a = 5.1469(15), b = 13.343(2), c = 14.2031(17), orthorhombic, Pbca, Z = 4. Crystal data for Cl2S4N4C4PF6: a = 11.699(4), b = 12.753(5), c = 10.461(4), β = 112.17(1)°, monoclinic, C2/c, Z = 4. Crystal data for Cl2S4N4C10H4: a = 3.9477(6), b = 23.790(3), c = 7.3769(9), β =90.793(12)°, monoclinic, P21/c, Z = 2

5,5‘-Bridged Bis(1,2,3-dithiazoles): Spin States and Charge-Transfer Chemistry

Bifunctional 1,2,3-dithiazoles bridged with azine and phenylenediamine spacers have been prepared, with a view to determining the extent of communication between the two dithiazole rings as a function of the electronic and steric demands of the bridge. The crystal structure of the closed-shell diazine derivative [S2NClC2NNC2ClNS2] is rigorously planar. Cyclic voltammetry on this compound indicates two reversible one-electron oxidations. The radical cation state has been characterized by EPR spectroscopy and by crystal structure determination of its 1:1 PF6- salt. The latter reveals little interaction between neighboring radical cations; consistently, the material exhibits a conductivity of σ -5 S cm-1. Insertion of a phenylene group into the diazine bridge to afford [S2NClC2NC6H4NC2ClNS2] leads to significant torsional motion between the phenylene ring and the two end groups, as a result of which the two DTA rings are electronically independent; no radical cation state has been observed for this species. Crystal data for Cl2S4N4C4: a = 5.1469(15), b = 13.343(2), c = 14.2031(17), orthorhombic, Pbca, Z = 4. Crystal data for Cl2S4N4C4PF6: a = 11.699(4), b = 12.753(5), c = 10.461(4), β = 112.17(1)°, monoclinic, C2/c, Z = 4. Crystal data for Cl2S4N4C10H4: a = 3.9477(6), b = 23.790(3), c = 7.3769(9), β =90.793(12)°, monoclinic, P21/c, Z = 2