Daniel L. Reger

Syntheses of tris(pyrazolyl)methane ligands and {[tris(pyrazolyl)methane]Mn(CO)3}SO3CF3 complexes: comparison of ligand donor properties

Abstract The known ligands HC(pz)3, HC(3,5-Me2pz)3, HC(3-Phpz)3, and HC(3-tBupz)3 and the new ligand HC(3-iPrpz)3 (pz=pyrazolyl ring) are prepared in CHCl3–H2O using the appropriate pyrazole, an excess of Na2CO3, and tetra-n-butylammonium bromide as the phase transfer catalyst. Using these conditions, good yields of the ligands are consistently obtained. The new ligand PhC(pz)2py (py=pyridyl ring) is prepared in the CoCl2 catalyzed condensation reaction of (pz)2SO and Ph(py)CO. The reaction of HC(pz)3, KOtBu and para-formaldehyde followed by quenching with water yields HOCH2C(pz)3. All of these ligands, except HC(3-tBupz)3, react with [Mn(CO)5]SO3CF3, prepared in situ from Mn(CO)5Br and Ag(SO3CF3), to yield the respective [(ligand)Mn(CO)3]SO3CF3 complex. The carbonyl stretching frequencies and 13C-NMR trends of these complexes indicate that the donor abilities of all of the ligands are fairly similar. The solid state structure of {[HC(3-iPrpz)3]Mn(CO)3}+ shows the HC(3-iPrpz)3 ligand is tridentate with the iso-propyl groups rotated away from the Mn(CO)3 core of the cation relieving any possible steric congestion.

Tris(Pyrazolyl)Methane Ligands: The Neutral Analogs of Tris(Pyrazolyl)Borate Ligands

Abstract Despite the widespread use of tris(pyrazolyl)borate ligands, their isoelectronic, neutral analogs, tris(pyrazolyl)methane ligands, have not been extensively studied. By use of appropriate starting materials, such as [Cu(NCMe)4]PF6 or [Cd2(thf)5](BF4)4, stable cationic complexes of the ligands HC(3,5-Me2pz)3, HC(3-Phpz)3 and HC(3-Bu1pz)3 can be prepared with the metals copper(I), silver(I), cadmium(II), lead(II) and thallium(I). In many cases isoelectronic groups of complexes, such as [HB(3,5-Me2pz)3]2Cd. {[HC(3,5-Me2pz)3]Cd[HB(3,5-Me2pz)3]}+, and {[HC(3,5-Me2pz)3]2Cd}2+, have been prepared and shown to have very similar structures. The 113Cd NMR chemical shifts of the three complexes are also very similar. The isoelectronic complexes {[HC(pz)3]2Pb}2+ and [HB(pz)3]2Pb have similar distorted six-coordinate structures. The isoelectronic pair {[HC(3,5-Me2pz)3]2Pb}2+ and [HB(3,5-Me2pz)3]2Pb have very similar octahedral structures in which the lone pair on the lead(ll) is stereochemically inactive. Thu...

Preparation and reactions of the (dicarbonyl)(η5-cyclopentadienyl)(tetrahydrofuran)iron cation: A convenient route to (dicarbonyl)(η5-cyclopentadiemyl)(η2-olefin)iron cations and related complexes

Abstract The versatile reagent [η5-C5H5)Fe(CO)2(THF)]BF4 has been isolated from the reaction of (η5-C5H5)Fe(CO)2I and AgBF4 in THF and shown to react in CH2Cl2 with olefins to yield [(η5-C5H5)Fe(CO)2(η2-olefin)]BF4 complexes. For most olefins the yields are high. The yield in these reactions can be increased by treating the CH2Cl2 solution of [(η5-C5H5)Fe(Co)2(THF)]BF4 and olefin with gaseous BF3 in order to complex the THF as the BF3-THF adduct. Most striking is the increase in yield for the cyclohexene complex from 17% to 92%.

Poly (pyrazolyl)borate complexes of gallium and indium

Abstract The poly (pyrazolyl)borate family of ligands has been used to prepare a variety of stable complexes of gallium and indium of the general formula [poly(pyrazolyl)borate] m MCI n (CH 3 ) p ( m + n + p =3), and the cationic complexes [poly (pyrazolyl)borate]{ 2 M} + . The results of these studies show that in complexes of potentially multidentate poly (pyrazolyl)borate ligands these two metals prefer four- or six-coordination. The only five-coordinate complexes, [H 2 B(pz) 2 ] 2 MX, that have been prepared contain the dihydrobis(pyrazolyl)borate ligands. These complexes, even the organometallics, are unusually stable. The complex [HB(3,5Me 2 pz) 3 ]InCl 2 (THF) is an excellent starting material for the formation of complexes containing one poly(pyrazolyl)borate ligand and other types of ligands and also intermetallic complexes. A bulky poly (pyrazolyl)borate ligand stabilizes indium(I) in the complex [HB(3-Phpz) 3 ]In.

Production of hydrogen gas from novel chemical hydrides

Abstract Six ligand-stabilized complexes have been synthesized and tested for use as hydrogen storage media for portable fuel cell applications. The new hydrides are: [HC (3,5-Me2pz) 3] LiBH4 (1) , { [H2C (3,5-Me2pz) 2] Li (BH4) } 2 (2) (pz = pyrazolyl ) , [ (TMEDA) Li (BH4) ] 2 (3) (TMEDA = (CH3) 2NCH2CH2N (CH3) 2) , [HC (pz) 3] LiBH4 (4) , { [H2C (pz) 2] Li (BH4) } 2 (5) and Mg(BH4)·23THF (6) (THF = tetrahydrofuran) . Hydrolysis reactions of the compounds liberate hydrogen in quantities which range from 56 to 104 (±5%) percent of the theoretical yield. Gas chromatographic analysis of the product gases from these reactions indicate that hydrogen is the only gas produced. Thermally initiated reactions of the novel compounds with NH4Cl were unsuccessful. Although the amount of hydrogen energy which can be theoretically obtained per unit weight is lower than that of the classical hydrides such as LiBH4 and NaBH4, the reactions are less violent and hydrolysis of compounds 1, 2, 4, 5 and 6 releases less heat per mole of hydrogen generated.

Dinuclear Complexes Containing Linear M–F–M [M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)] Bridges: Trends in Structures, Antiferromagnetic Superexchange Interactions, and Spectroscopic Properties

The reaction of M(BF(4))(2)·xH(2)O, where M is Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II), with the new ditopic ligand m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (L(m)*) leads to the formation of monofluoride-bridged dinuclear metallacycles of the formula [M(2)(μ-F)(μ-L(m)*)(2)](BF(4))(3). The analogous manganese(II) species, [Mn(2)(μ-F)(μ-L(m)*)(2)](ClO(4))(3), was isolated starting with Mn(ClO(4))(2)·6H(2)O using NaBF(4) as the source of the bridging fluoride. In all of these complexes, the geometry around the metal centers is trigonal bipyramidal, and the fluoride bridges are linear. The (1)H, (13)C, and (19)F NMR spectra of the zinc(II) and cadmium(II) compounds and the (113)Cd NMR of the cadmium(II) compound indicate that the metallacycles retain their structure in acetonitrile and acetone solution. The compounds with M = Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) are antiferromagnetically coupled, although the magnitude of the coupling increases dramatically with the metal as one moves to the right across the periodic table: Mn(II) (-6.7 cm(-1)) < Fe(II) (-16.3 cm(-1)) < Co(II) (-24.1 cm(-1)) < Ni(II) (-39.0 cm(-1)) ≪ Cu(II) (-322 cm(-1)). High-field EPR spectra of the copper(II) complexes were interpreted using the coupled-spin Hamiltonian with g(x) = 2.150, g(y) = 2.329, g(z) = 2.010, D = 0.173 cm(-1), and E = 0.089 cm(-1). Interpretation of the EPR spectra of the iron(II) and manganese(II) complexes required the spin Hamiltonian using the noncoupled spin operators of two metal ions. The values g(x) = 2.26, g(y) = 2.29, g(z) = 1.99, J = -16.0 cm(-1), D(1) = -9.89 cm(-1), and D(12) = -0.065 cm(-1) were obtained for the iron(II) complex and g(x) = g(y) = g(z) = 2.00, D(1) = -0.3254 cm(-1), E(1) = -0.0153, J = -6.7 cm(-1), and D(12) = 0.0302 cm(-1) were found for the manganese(II) complex. Density functional theory (DFT) calculations of the exchange integrals and the zero-field splitting on manganese(II) and iron(II) ions were performed using the hybrid B3LYP functional in association with the TZVPP basis set, resulting in reasonable agreement with experiment.

A new synthetic method for the preparation of [(η5-C5H5)Fe(CO)(L)(un)]BF4 (L = CO, PPh3; un = unsaturated hydrocarbon) complexes and reduction of the η2-acetylene complexes

Abstract The reaction of (η5-C5H5)Fe(CO)2I with AgBF4 in CH2Cl2 generates the reactive intermediate [(η5-C5H5)Fe(CO)2]+ in solution which, when mixed with 2 or 3 equivalents of an olefinic or acetylene ligand produces η2-olefin and η2-acetylene complexes in ca. 70% yield. The analogous reaction of (η5-C5H5)Fe(CO)(PPh3)I with AgBF4 in CH2Cl2 produces [(η5-C5H5)Fe(CO)(PPh3)]+ in solution which also reacts readily with olefins and acetylenes to yield new π-complexes. The dicarbonyl complexes are generally more stable than the phosphine-substituted complexes. The η2-acetylene complexes in both systems can be reduced with hydride reagents to yield the corresponding neutral σ-vinyl compounds. Although unstable in the dicarbonyl system, these vinyl compounds in the phosphine system are quite stable and show no tendency to isomerize or thermally decompose to a metal hydride as previously established for the analogous alkyl derivatives. Attempts to prepare cyano-substituted olefin complexes lead instead to new complexes in which the iron bonds to these ligands through the nitrogen lone-pair.

Structurally adaptive multitopic ligands containing tris(pyrazolyl)methane units as supramolecular synthons: manganese carbonyl complexes

Abstract The compounds {p-C6H4[CH2OCH2C(pz)3]2[Mn(CO)3]2}(BF4)2 (1, pz=pyrazolyl ring), {p-C6H4[CH2OCH2C(pz)3]2[Mn(CO)3]2}(OTf)2 (2, OTf−=CF3SO3−), {m-C6H4[CH2OCH2C(pz)3]2[Mn(CO)3]2}(BF4)2 (3) and {1,2,4,5-C6H2[CH2OCH2C(pz)3]4[Mn(CO)3]4}(BF4)4 (4) have been prepared by reaction of the respective ligands with ‘Mn(CO)5+’, prepared ‘in situ’ from the reaction of Mn(CO)5Br and AgBF4 or AgOTf in refluxing acetone. In the structures of all four complexes, the environment around the manganese atom is a slightly distorted octahedron, with the distortion caused by the restricted bite angle of the κ3-bonded tris(pyrazolyl)methane ligand. The structurally adaptive ligands in all four complexes support extended three-dimensional (3D) supramolecular structures. An important organizational feature for the three BF4− complexes is a double π–π and CH⋯π interaction involving the pyrazolyl rings. The double π–π/CH⋯π interaction is intermolecular in 1 and 3 leading to the formation of chains and sheets. In the case of the tetratopic ligand in complex 4, the π–π/CH⋯π interaction is intramolecular between adjacent (ortho) side arms. These supramolecular structures are also supported by weak CH⋯F hydrogen bonds. For 3, classic π–π interactions of the central arene rings are also involved in organizing the 3D network. For 2, the structure is organized solely by CH⋯O hydrogen bonding.

Molybdenum perfluorocarbene complexes

Treatment of (η5-C5H5)Mo(CO)3CF3, (η5-C5H5)Mo(CO)2(PPh3)CF3 and (η5-C5H5)Mo(CO)3C3F7 with SbF5 in liquid SO2 yielded the first known fluorocarbene complexes [(η5-C5H5)Mo(CO)3CF2]SbF6, [(η5-C5H5)Mo(CO)2(PPh3)CF2]SbF6, and [(η5-C5H5)Mo(CO)3CFC2F5]SbF6. These have been shown to exist in solution using NMR spectroscopy, but could not be isolated as the pure solids. Also, BF3 can apparently abstract fluoride ion from perfluoroalkyl compounds although in this case no carbene complexes could be observed directly by spectroscopic techniques. These results support earlier spectroscopic studies which indicated a weakening of the carbon—fluorine bonds at the α carbon in perfluoroalkylmetal complexes.

Halide and hydroxide linearly bridged bimetallic copper(II) complexes: trends in strong antiferromagnetic superexchange interactions.

Centrosymmetric [Cu(2)(μ-X)(μ-L(m)*)(2)](ClO(4))(3) (X = F(-), Cl(-), Br(-), OH(-), L(m)* = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene)], the first example of a series of bimetallic copper(II) complexes linked by a linearly bridging mononuclear anion, have been prepared and structurally characterized. Very strong antiferromagnetic exchange coupling between the copper(II) ions increases along the series F(-) < Cl(-) < OH(-) < Br(-), where -J = 340, 720, 808, and 945 cm(-1). DFT calculations explain this trend by an increase in the energy along this series of the antibonding antisymmetric combination of the p orbital of the bridging anion interacting with the copper(II) d(z(2)) orbital.