Synthesis, Structure, and Magnetic Properties of Mn(salpn)N_3, a Helical Polymer, and Fe(salpn)N₃, a Ferromagnetically Coupled Dimer (salpnH₂ = <i>N</i>,<i>N</i>‘-bis(Salicylidene)-1,3-diaminopropane)

The preparation, crystal structures, and variable temperature magnetic susceptibility data are presented for two azido-bridged Schiff base complexes of Mn(III) and Fe(III). Mn(salpn)N3 (1), where salpn is the dianion of N,N‘-bis(salicylidene)-1,3-diaminopropane, crystallizes in the orthorhombic system, space group Pna21, with a = 11.947(2) Å, b = 11.818(2) Å, c = 11.227(5) Å, and Z = 4. Fe(salpn)N3 (2) crystallizes in the monoclinic system, space group P21/c, with a = 10.199(7) Å, b = 14.081(6) Å, c = 12.017(3) Å, β = 105.19(3)°, and Z = 4. In 1, salpn coordinates in the equatorial mode, with two azide ions coordinating in axial positions. The azide ions act as “end-to-end” (μ-(1,3)) bridges, leading to an infinite helical chain propagating along the crystallographic c axis. In striking contrast, 2 has a dimeric structure in which the Schiff base adopts a cis-octahedral coordination mode. The dimer is held together by two “head-on” (μ-(1,1)) bridging azide ions. The polymeric compound, 1, is weakly antiferromagnetic (J = −4.03 cm-1, Hex = −2J∑SiSi+1), while 2 is weakly ferromagnetic (J = 0.76 cm-1, Hex = −2JS1S2)

Rhenium(V) Dioxo Complexes with Dihydrobis(pyrazolyl)borates: Synthesis and Reactivity toward Electrophilic Substrates

The compounds trans,trans-[ReO2(py)4][ReO2{H2B(pz*)2}2] (pz* = pz (1), 3,5-Me2pz (2)) have been prepared by reacting trans-[ReO2(py)4]Cl with the corresponding dihydrobis(pyrazolyl)borate. Compounds 1 and 2 react with electrophilic substrates, such as ClXMe3 (X = Si, Sn), leading to the neutral monoxo derivatives [ReO(OSiMe3){H2B(pz*)2}2] (pz* = pz (3), 3,5-Me2pz (4)) and [ReO(OSnMe3){H2B(pz)2}2] (5) and regenerating trans-[ReO2(py)4]Cl. Compounds 1 and 3 crystallize from dichloromethane/n-hexane as yellow crystals, with one molecule of solvated CH2Cl2 in the case of 1. Crystallographic data:  1, triclinic space group P1̄, a = 9.419(1) Å, b = 9.584(1) Å, c = 12.652(1) Å, α = 89.03(1)°, β = 82.41(1)°, γ = 72.75(1)°, V = 1080.9(2) Å3, Z = 2; 3, monoclinic space group P21/n, a = 10.785(2) Å, b = 17.680(2) Å, c = 11.971(2) Å, β = 98.67(1)°, V = 2256.5(6) Å3, Z = 4

Neutral <i>trans</i>-Dioxorhenium(V) Complexes with the Anionic Tetrakis(pyrazolyl)borate Ligand

Reduction of [ReO3{η3-B(pz)4}] (1) with PPh3 in the presence of mono- or bidentate σ-donor ligands (pyridines, imidazoles, or diphosphines) is a very convenient method for the synthesis of the neutral dioxorhenium(V) complexes:  trans-[ReO2{η2-B(pz)4}(L)2] (L = py (3), 4-Mepy (4), 4-NMe2py (5), 1-MeImz (6)) and trans-[ReO2{η2-B(pz)4}(P⌒P)] (P⌒P = dmpe (7), dppe (8)). In the presence of pyridine or dimethylphosphinoethane, the analogous [ReO3{η3-HB(pz)3}] is also reduced by PPh3 to trans-[ReO2{η2-HB(pz)3}(py)2] (9) and trans-[ReO2{η2-HB(pz)3}(dmpe)] (10), respectively. In contrast, the reaction of [ReO2(py)4]Cl with K[B(pz)4] leads to a mixture of species from which were identified the neutral mono-oxo complexes [ReO(η2-N,O)(μ-O)B(pz)3}(pz)(pzH)2] (11) and [ReO{(η2-N,O)(μ-O)B(pz)3}Cl(py)2] (12). Complexes 3−12 were characterized by different techniques, namely, IR, 1H/31P{1H} NMR spectroscopies and X-ray crystallographic analysis (5, 10, and 11). Compound 5 crystallizes from dichloromethane/n-hexane as orange crystals containing 3 molecules of solvated CH2Cl2 (crystal data:  triclinic space group P1̄, with cell parameters a = 10.907(2) Å, b = 11.113(1) Å, c = 16.922(2) Å, α = 97.91(1)°, β = 102.37(1)°, γ = 94.21(1)°, V = 1973(1) Å3, Z = 2). Compound 10 crystallizes from dichloromethane/n-hexane as yellowish crystals containing one molecule of pzH (crystal data:  orthorhombic space group Pnma, with cell parameters a = 18.422(2) Å, b = 11.850(1) Å, c = 11.434(1) Å, α = β = γ = 90°, V = 2496.1(4) Å3, Z = 4). Compound 11 crystallizes from dichloromethane/n-hexane in the monoclinic space group P21/n, with cell parameters a = 10.890(1) Å, b = 15.162(1) Å, c = 14.137(2) Å, β = 102.07(1)°, V = 2282.6(4) Å3, Z = 4

Neutral <i>trans</i>-Dioxorhenium(V) Complexes with the Anionic Tetrakis(pyrazolyl)borate Ligand

Reduction of [ReO3{η3-B(pz)4}] (1) with PPh3 in the presence of mono- or bidentate σ-donor ligands (pyridines, imidazoles, or diphosphines) is a very convenient method for the synthesis of the neutral dioxorhenium(V) complexes:  trans-[ReO2{η2-B(pz)4}(L)2] (L = py (3), 4-Mepy (4), 4-NMe2py (5), 1-MeImz (6)) and trans-[ReO2{η2-B(pz)4}(P⌒P)] (P⌒P = dmpe (7), dppe (8)). In the presence of pyridine or dimethylphosphinoethane, the analogous [ReO3{η3-HB(pz)3}] is also reduced by PPh3 to trans-[ReO2{η2-HB(pz)3}(py)2] (9) and trans-[ReO2{η2-HB(pz)3}(dmpe)] (10), respectively. In contrast, the reaction of [ReO2(py)4]Cl with K[B(pz)4] leads to a mixture of species from which were identified the neutral mono-oxo complexes [ReO(η2-N,O)(μ-O)B(pz)3}(pz)(pzH)2] (11) and [ReO{(η2-N,O)(μ-O)B(pz)3}Cl(py)2] (12). Complexes 3−12 were characterized by different techniques, namely, IR, 1H/31P{1H} NMR spectroscopies and X-ray crystallographic analysis (5, 10, and 11). Compound 5 crystallizes from dichloromethane/n-hexane as orange crystals containing 3 molecules of solvated CH2Cl2 (crystal data:  triclinic space group P1̄, with cell parameters a = 10.907(2) Å, b = 11.113(1) Å, c = 16.922(2) Å, α = 97.91(1)°, β = 102.37(1)°, γ = 94.21(1)°, V = 1973(1) Å3, Z = 2). Compound 10 crystallizes from dichloromethane/n-hexane as yellowish crystals containing one molecule of pzH (crystal data:  orthorhombic space group Pnma, with cell parameters a = 18.422(2) Å, b = 11.850(1) Å, c = 11.434(1) Å, α = β = γ = 90°, V = 2496.1(4) Å3, Z = 4). Compound 11 crystallizes from dichloromethane/n-hexane in the monoclinic space group P21/n, with cell parameters a = 10.890(1) Å, b = 15.162(1) Å, c = 14.137(2) Å, β = 102.07(1)°, V = 2282.6(4) Å3, Z = 4

Synthesis and Structural Investigations of [Mn₃O₄(phen)₄(H₂O)₂](NO₃)₄·2.5H₂O: A Water-Bound Complex Obtained by Cerium(IV) Oxidation

The trinuclear manganese complex [Mn3O4(phen)4(H2O)2](NO3)4·2.5H2O, 1 (where, phen = 1,10-phenanthroline), has been synthesized by the Ce(IV) oxidation of a concentrated solution of manganese(II) acetate and phen in 1.6 N nitric acid. The complex crystallizes in the triclinic space group P1̄ with a = 10.700(2) Å, b = 12.643(3) Å, c = 20.509(4) Å, α = 78.37(3)°, β = 83.12(3)°, γ = 82.50(3)°, and Z = 2. The structure was solved by direct methods and refined by least-squares techniques to the conventional R (Rw) factors of 0.055 (0.076) based on 4609 unique reflections with Fo ⩾ 6.0σ(Fo). The structure of the cation consists of an oxo-bridged Mn3O44+ core, with the geometry of the manganese atoms being octahedral. The coordination polyhedron of one of the manganese atoms (Mn(1)) consists of two μ oxo ligands and two pairs of nitrogen atoms of two phen moieties, whereas that of each of the remaining two manganese atoms consists of three μ-oxo ligands, two nitrogen atoms of a phen moiety, and the oxygen atom of a water molecule. The complex represents the second example for water coordination to manganese(IV) centers in complexes with a Mn3O44+ core. Optical spectra in ligand buffer (pH 4.5) reveal complete conversion of the complex into a MnIIIMnIV species. The observed room-temperature (298 K) magnetic moment of 3.75 μB indicates the presence of strong antiferromagnetic coupling in the complex

Single and Multiple Insertion of Alkynes into Pd−Acyl and Pd−Aryl Bonds in Cationic Palladium Complexes with Phosphine−Imine (P∼N) Ligands

Neutral and cationic Pd(II)−alkyl and Pd(II)−aryl complexes with phosphine−imine (P∼N) ligands show unusual reactivity toward alkynes. No insertion of alkyne has been observed into the neutral palladium complexes or the cationic Pd−alkyl complex. On the other hand, smooth insertion of alkynes into the cationic complexes [(P∼N)Pd(COMe)(MeCN)]+ (4) and [(P∼N)Pd(Ph)(MeCN)]+ (5) was observed, resulting in the formation of single- and double-insertion products, respectively. All the inserted products were isolated and characterized by spectroscopic methods. Single-crystal X-ray analyses for some alkyne insertion complexes indicate that the products are stabilized by intramolecular coordination via either a carbonyl oxygen or a π-phenyl coordination with η2 mode. Higher order insertions of ethyl propiolate in the complexes [(P∼N)Pd(Ph)(MeCN)]+ (5) and [(P∼N)Pd(C(Ph)C(Ph)C(Ph)CPh2)(MeCN)]+ (13) leading to the oligomeric species are found to proceed smoothly, but disubstituted alkynes such as diphenylacetylene do not undergo such insertion

Palladium(II) Complexes with Phosphorus−Nitrogen Mixed Donors. Efficient Catalysts for the Heck Reaction

Pd(II) complexes of phosphine−nitrogen (P−N) bidentate donors act as efficient catalysts for the Heck reaction. In a typical example, reaction of phenyl iodide with methyl acrylate in N-methylpyrrolidinone (NMP) at ca. 130 °C provides the Heck product with a turnover number of up to 106. In addition, the coupling reaction of 4-bromoacetophenone with olefin in a quantitative yield was achieved by using the same catalyst in the presence of sodium iodide

Single and Multiple Insertion of Alkynes into Pd−Acyl and Pd−Aryl Bonds in Cationic Palladium Complexes with Phosphine−Imine (P∼N) Ligands

Neutral and cationic Pd(II)−alkyl and Pd(II)−aryl complexes with phosphine−imine (P∼N) ligands show unusual reactivity toward alkynes. No insertion of alkyne has been observed into the neutral palladium complexes or the cationic Pd−alkyl complex. On the other hand, smooth insertion of alkynes into the cationic complexes [(P∼N)Pd(COMe)(MeCN)]+ (4) and [(P∼N)Pd(Ph)(MeCN)]+ (5) was observed, resulting in the formation of single- and double-insertion products, respectively. All the inserted products were isolated and characterized by spectroscopic methods. Single-crystal X-ray analyses for some alkyne insertion complexes indicate that the products are stabilized by intramolecular coordination via either a carbonyl oxygen or a π-phenyl coordination with η2 mode. Higher order insertions of ethyl propiolate in the complexes [(P∼N)Pd(Ph)(MeCN)]+ (5) and [(P∼N)Pd(C(Ph)C(Ph)C(Ph)CPh2)(MeCN)]+ (13) leading to the oligomeric species are found to proceed smoothly, but disubstituted alkynes such as diphenylacetylene do not undergo such insertion

Copper-Catalyzed Activation of α‑Amino Peroxy and Hydroxy Intermediates to Iminium Ion Precursor: An Access to C4-Substituted 3,4-Dihydroquinazolines via Oxidative Cross Coupling Strategy

A simple and straightforward approach to access C4-substituted-3,4-dihydroquinazolines has been achieved, where copper-catalyzed activation of α-amino peroxide and hydroxide intermediates to iminium ion precursors has been realized as an important step. Reactions of these intermediates with alkynes, indoles, pyrrole, and silylenol ether afforded the structurally diverse C4-substituted-3,4-dihydroquinazoline derivatives in good yields

Study of Insertion of Olefins and/or Carbon Monoxide into Phosphine−Imine Palladium Methyl Complexes

Palladium methyl complexes with a phosphine−imine (P∼N) bidentate ligand, [Pd(P∼N)MeCl] (1), [Pd(P∼N)Me(CH3CN)](BF4) (2), and [Pd(P∼N)Me(PPh3)](BF4) (3), are treated with CO to result in the corresponding Pd−acyl complexes 4−6. NMR studies indicate the formation of a sole isomer with the acyl group cis to the phosphine donor. The neutral complex 4 and the triphenylphosphine-substituted complex 6 cannot serve for the insertion of ethylene. However, the acetonitrile complex 5 appears to be active in the insertion reaction with various alkenes as well as ethylene/CO (E-CO) co-oligomerization, resulting in the products 7−14 and 16, which have been isolated and characterized by spectroscopic methods. X-ray structures of 1, 2, 3, 4, 7, 10, 11, and 13 are revealed