David O. Miller

Synthesis, structure, and magnetism of a novel alkoxide bridged nonacopper(II) (Cu9O12) [3 3] square grid generated by a strict self-assembly process

The nonanuclear copper complex [Cu9(2paop-H)6](NO3)12�9H2O (2paop = I) was prepd. and its crystal structure detd. The complex forms a [3 � 3] square grid of copper atoms with the ligand bonding in a heptadentate manner by five nitrogen atoms and two bridging oxygen atoms. Variable temp. magnetic susceptibility and magnetization data show that the complex displays predominantly ferromagnetic behavior at low temp., but a small intramol. antiferromagnetic exchange component may be present. [on SciFinder(R)]

Self-assembled polymetallic square grids ([2 × 2] M4, [3 × 3] M9) and trigonal bipyramidal clusters (M5)—structural and magnetic properties

New self-assembled grids and clusters are reported, with square [2 × 2] M4 (M = Mn(II)4, Cu(II)4), trigonal-bipyramidal Mn(II)5, and square [3 × 3] M9 (M = Mn(II), Cu(II)) examples. These are based on a series of ditopic and tritopic hydrazone ligands involving pyridine, pyrimidine and imidazole end groups. In all cases the metal centres are bridged by hydrazone oxygen atoms with large (>125°) bridge angles, leading to antiferromagnetic exchange for all the Mn systems (J = −2 to −5 cm−1), which results in S = 0 (Mn4), and S = 5/2 (Mn5, Mn9) ground states. The copper systems have a 90° alternation of the Jahn–Teller axes within the Cu4 and Cu8 grid rings (Cu9), which leads to magnetic orbital orthogonality, and dominant ferromagnetic coupling. For the Cu9 grid antiferromagnetic exchange between the ring and the central copper leads to a S = 7/2 ground state, while for the Cu4 grids S = 4/2 ground states are observed. The magnetic data have been treated using isotropic exchange models in the cases of the Cu4 and Cu9 grids, and the Mn5 clusters. However due to the enormity of a fully isotropic calculation a simplified model is used for the Mn9 grid, in which the outer Mn8 ring is treated as the equivalent of an isolated magnetic chain, with no coupling to the central metal ion.

Povarov reactions involving 3-aminocoumarins: synthesis of 1,2,3,4-tetrahydropyrido[2,3-c]coumarins and pyrido[2,3-c]coumarins.

Condensation of 3-aminocoumarin (5) with 4-nitrobenzaldehyde (8) afforded a 2-azadiene (9), which reacted with various electron-rich alkenes (10 examples) in the presence of Yb(OTf)3 to afford 1,2,3,4-tetrahydropyrido[2,3-c]coumarins. Yields were generally good, but the diastereomeric ratios were highly variable. The products arose through a formal [4 + 2] cycloaddition (inverse electron demand Diels-Alder reaction) followed by tautomerization. As such, these are examples of the Povarov reaction. A range of 1,2,3,4-tetrahydropyrido[2,3-c]coumarins was then synthesized using a three-component version of this reaction, which involves in situ formation of the 2-azadiene component. Some of these products were converted into the corresponding pyrido[2,3-c]coumarins upon treatment with various oxidants, the most effective of which proved to be nitrous gases.

Self assembled polynuclear [3×3] grids — structural and magnetic properties of Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes with M9(μ2-O)12 cores

Abstract A series of polynuclear [3×3] square grid complexes of Mn(II), Fe(III), Co(II), Ni(II), and Cu(II) is reported from the high yield self assembly reactions of the linear tritopic ligands H 2 L3 and H 2 L4 and appropriate metal salts. Structural data reveal a complementary matching of the ligand coordination pockets and the coordination requirements of the metal ions in the [3×3] square M 9 (μ 2 -O) 12 , alkoxide bridged grids found in [Mn 9 (L3) 6 ](ClO 4 ) 6 ·18H 2 O, [Mn 9 (L4) 6 ](NO 3 ) 6 ·12H 2 O and [Cu 9 (HL3) 6 ](NO 3 ) 12 ·9H 2 O. Similar structural types are implicated for analogous Ni(II), Co(II), and Fe(III) complexes. The structural and magnetic properties are discussed. The Cu 9 grid system exhibits both intramolecular ferromagnetic and antiferromagnetic coupling, and has an S =7/2 ground state. A similar situation appears to exist for the analogous Fe(III) 9 complex, with a spin ground state approaching S =29/2. The Mn(II) 9 , Ni(II) 9 and Co(II) 9 complexes exhibit intramolecular antiferromagnetic coupling.

Synthesis of 6H-dibenzo[b,d]pyran-6-ones using the inverse electron demand Diels-Alder reaction.

A set of coumarin-fused electron-deficient 1,3-dienes was synthesized, which differ in the nature of the electron-withdrawing group (EWG) at the terminus of the diene unit and (when EWG = CO(2)Me) the nature and position of substituents. These dienes reacted with the enamine derived from cyclopentanone and pyrrolidine to afford the corresponding cyclopenteno-fused 6H-dibenzo[b,d]pyran-6-ones, most likely via a domino inverse electron demand Diels-Alder (IEDDA)/elimination/transfer hydrogenation sequence. The parent diene (EWG = CO(2)Me, no substituents) was reacted with a range of electron-rich dienophiles (mostly enamines) to afford the corresponding 6H-dibenzo[b,d]pyran-6-ones or their nondehydrogenated precursors, which were aromatized upon treatment with a suitable oxidant. The enamines could either be synthesized prior to the reaction or generated in situ. The syntheses of 30 dibenzopyranones are reported.

Non-planar aromatic compounds. Part 4: Fine tuning the degree of bend in the pyrene moiety of [7](2,7)pyrenophanes by modifying the nature of the bridge

Abstract Structures for several mono-, di-, tri- and tetraoxa[7](2,7)pyrenophanes were calculated at the AM1 level of theory and the bend angle ( θ ) of the pyrene system was found to be affected by both the number and the position(s) of the oxygen atom(s). In varying the type of atom X at the 4 position, θ was predicted to decrease with the C–X bond length. Attempted synthesis of 1,4,7-trioxa[7](2,7)pyrenophane gave traces of the target compound as the minor component of a mixture with its recovered precursor. 1 H NMR evidence supports the prediction that it possesses a more bent pyrene unit than that of the current record holder. 4-Oxa[7](2,7)pyrenophane was prepared readily in 11% overall yield over ten steps and its crystallographically measured bend angle is 102.9°.

A non-homoleptic Cu9 [3 × 3] mixed ligand grid: structural and magnetic properties

Abstract The tritopic hydrazide ligand m2poap (from the reaction of 4-methoxy-2,6-dicarboxylic hydrazide and methyl imino-2-picolinate) reacted with Cu(NO3)2 to produce a linear trinuclear diazine (N–N) bridged m2poap complex, and a nona-nuclear Cu(II)9 mixed ligand [3×3] grid complex, containing two 4-chloro-2,6-pyridine dicarboxylate (Clpic2−) ligands, and four deprotonated m2poap ligands. The presence of Clpic2− arises from an impurity in the ligand, which results from hydrolysis of a starting material. Clpic2− connects three Cu(II) centers in an unusual oxygen bridged coordination mode. The smaller bite of this ligand leads to a contraction of the grid, compared with homoleptic [3×3] grid examples, and results in enhanced ferromagnetic exchange within the grid. The trinuclear complex of m2poap exhibits fairly strong antiferromagentic exchange, typical of N–N bridged systems.

Polynuclear copper(II) complexes with μ2-1,1-azide bridges. Structural and magnetic properties

Abstract Two novel, weakly antiferromagnetically coupled, tetranuclear copper(II) complexes [Cu4(PAP)2(μ2-1,1-N3)2(μ2-1,3-N3)2(μ2-CH3OH)2(N3)4 (1) (PAP = 1,4-bis-(2′-pyridylamino)phthalazine) and [Cu4(PAP3Me)2 (μ2-1,1-N3)2(μ2-1,3-N3)2(H2O)2(NO2)2]- (NO3)2 (2) (PAP3Me = 1,4-bis-(3′-methyl-2′-pyridyl)aminophthalazine) contain a unique structural with two μ2-1,1-azide intramolecular bridges, and two μ2-1,3-azide intermolecular bridges linking pairs of copper(II) centers. Four terminal azide groups complete the five-coordinate structures in 1, while two terminal waters and two nitrates complete the coordination spheres in 2. The dinuclear complexes [Cu2(PPD)(μ2-1,1-N3)(N3)2(CF3SO3)]CH3OH) (3) and [Cu2(PPD)(μ2-1,1-N3)(N3)2(H2O)(ClO4)] (4) (PPD = 3,6-bis-(1′-pyrazolyl)pyridazine) contain pairs of copper centers with intramolecular μ2-1,1-azid and pyridazine bridges, and exhibit strong antiferromagnetic coupling. A one-dimensional chain structure in 3 occurs through intermolecular μ2-1,1-azide bridging interactions. Intramolecular Cu-N3-Cu bridge angles in 1 and 2 are small (107.9 and 109.4°, respectively), but very large in 3 and 4 (122.5 and 123.2°, respectively), in keeping with the magnetic properties. 2 crystallizes in the monoclinic system, space group C2/c with a = 26.71(1), b = 13.51(3), c = 16.84(1) A , β = 117.35(3)° and R = 0.070, Rw = 0.050. 3 crystallizes in the monoclinic system, space group P21/c with a = 8.42(1), b = 20.808(9), c = 12.615(4) A , β = 102.95(5)° and R = 0.045, Rw = 0.039. 4 crystallizes in the triclinic system, space group P1, with a = 10.253(3), b = 12.338(5), c = 8.072(4) A , α = 100.65(4), β = 101.93(3), γ = 87.82(3)° and R = 0.038, Rw = 0.036 . The magnetic properties of 1 and 2 indicate the presence of weak net antiferromagnetic exchange, as indicated by the presence of a low temperature maximum in χm (80 K (1), 65 K (2)), but the data do not fit the Bleaney-Bowers equation unless the exchange integral is treated as a temperature dependent term. A similar situation has been observed for other related compounds, and various approaches to the problem will be discussed. Magnetically 3 and 4 are well described by the Bleaney-Bowers equation, exhibiting very strong antiferromagnetic exchange (− 2J = 768(24) cm−1 (3); − 2J = 829(11) cm−1 (4)).

Synthesis, structure and AM1 conformational study of [3]paracyclo[3](1,3)indolophane, a novel chiral cyclophane

Abstract The title compound 5 was synthesized in seven steps with an overall yield of 22%. The two bridges were formed by a conjugate addition of indole to a Michael acceptor and by an intramolecular N-alkylation, respectively. A dynamic NMR study revealed the presence of a conformational process with an activation barrier of 10.9±0.2 kcal/mol, which was assigned to a ring flipping process that interconverts two enantiomeric sets of equilibrating bridge conformers. In the crystal structure of 5, both bridges adopt the pseudo-chair conformation, in accord with the lowest energy conformation identified by an AM1 conformational search.

Thiophene-substituted nickel dithiolene complexes. Precursors for low band gap conjugated metallopolymers

A series of electrochemically polymerizable Ni dithiolene complexes have been prepared and their electrochemical and spectroscopic properties have been characterized. Three thiophene-substituted complexes were anodically polymerized to give polymer films whose electrochemical properties correlated well with their predicted structures. Thus, a complex with two thiophene substituents in one dithiolene ligand [cis-1,2-di(2′-thienyl)-1,2-ethenedithiolene] gave a polymer with electrochemistry characteristic of a poly(dithienylenevinylene), while a complex with one thiophene substituent on each dithiolene ligand [cis-1-(2′-thienyl)-2-phenyl-1,2-ethenedithiolene] gave a polymer with electrochemistry characteristic of a coordination polymer. A polymer prepared from a complex with four thiophene substituents {bis[cis-1,2-di(2′-thienyl)-1,2-ethenedithiolene]nickel} also gave electrochemistry characteristic of a poly(dithienylenevinylene), indicating that it contained extended poly(dithienylenevinylene)-like chains. A cathodically polymerizable complex, bis[cis-1,2-di(4-bromophenyl)-1,2-ethenedithiolene]nickel, is also reported.