Electronic communication in oligometallic complexes with ferrocene-based tris(1-pyrazolyl)borate ligands

Oligomerization of an ansa-ferrocene with pyrazabole bridge

Ansa-ferrocenes with pyrazabole bridges are chemically robust entities and therefore suitable building blocks for the synthesis of rigid-rod polymers that combine redox-active Fe(II) centers and beltene-like  faces. The specific monomers we developed bear OEt groups at both tetracoordinated boron atoms (for solubility reasons) and ethynyl substituents at the 4-positions of the two pyrazole rings. Polymerization was accomplished by a condensation reaction with 1,4-diiodobenzene using a Sonogashira-Hagihara-type protocol. Thereby, oligomers with a number-average molecular weight of Mn = 7.6 kDa and dispersity of Ð = 1.55 were obtained, suggesting an average chain length of about 14 repeating units based on gel permeation chromatography (GPC) analysis in THF relative to narrow polystyrene standards. The molecular-weight determination was complemented by MALDI-TOF mass spectrometry and (heteronuclear) NMR spectroscopy to verify the intact pyrazabole monomer repeat units and the nature of the end-groups. The oligomers were further characterized by UV−vis spectroscopy and cyclic voltammetry, which demonstrated the successful synthesis of a new class of redox-active materials.

Synthesis and characterization of ferrocene-chelating heteroscorpionate complexes of nickel(II) and zinc(II)

The first example of a ferrocene-chelating heteroscorpionate, [Li(THF)2][fc(PPh2)(BH[(3,5-Me)2pz]2)] ((fc(P,B))Li(THF)2, fc = 1,1'-ferrocenediyl) is described. Starting from a previously reported compound, fcBr(PPh2), a series of ferrocene derivatives, fc(PPh2)(B[OMe]2), [Li(OEt2)][fc(PPh2)(BH3)], [Li(THF)2][fc(PPh2)(BH[(3,5-Me)2pz]2)] (pz = pyrazole), was isolated and characterized. Compound (fc(P,B))Li(THF)2 allowed the synthesis of the corresponding nickel and zinc complexes, (fc(P,B))NiCl, (fc(P,B))NiMe, (fc(P,B))ZnCl, and (fc(P,B))ZnMe. All compounds were characterized by NMR spectroscopy, while the zinc and nickel complexes were also characterized by X-ray crystallography. The redox behavior of (fc(P,B))NiCl, (fc(P,B))NiMe, (fc(P,B))ZnCl, and (fc(P,B))ZnMe was studied by cyclic voltammetry and supported by density functional theory calculations.

Ferrocenyl-substituted tris(pyrazolyl)borates--a new ligand type combining redox activity with resistance to hydrogen atom abstraction

The low-temperature syntheses of ferrocenyl-substituted tris(pyrazolyl)borate ligands Tp(Fc*) (hydrobis(3-ferrocenylpyrazolyl)mono(5-ferrocenylpyrazolyl)borate), Tp(Fc,Me*) (hydrobis(3-ferrocenyl-5-methylpyrazolyl)mono(5-ferrocenyl-3-methylpyrazolyl)borate), and Tp(Fc,iPr) (hydrotris(3-ferrocenyl-5-isopropylpyrazolyl)borate) are reported. The Tl salts of Tp(Fc*) and Tp(Fc,Me*) can be thermally isomerized to the symmetric Tp(Fc) (hydrotris(3-ferrocenylpyrazolyl)borate) and Tp(Fc,Me) (hydrotris(3-ferrocenyl-5-methylpyrazolyl)borate) species, respectively. Conversely, upon heating, the thermal isomerization of Tp(Fc,iPr) results in the generation of a mixture of regioisomers. These ligands display a reversible three-electron oxidation. The preparations of Tp(CF3,Fc)Tl (hydrotris(3-trifluoromethyl-5-ferrocenylpyrazolyl)borate) and PhTp(Fc) (phenyltris(3-ferrocenylpyrazolyl)borate) are also reported.

Reactions of acids with naphthyridine-functionalized ferrocenes: protonation and metal extrusion

Reaction of 1,8-naphthyrid-2-yl-ferrocene (FcNP) with a variety of acids affords protonated salts at first, whereas longer reaction time leads to partial demetalation of FcNP resulting in a series of Fe complexes. The corresponding salts [FcNP·H][X] (X = BF(4) or CF(3)SO(3) (1)) are isolated for HBF(4) and CF(3)SO(3)H. Reaction of FcNP with equimolar amount of CF(3)CO(2)H for 12 h affords a neutral complex [Fe(FcNP)(2)(O(2)CCF(3))(2)(OH(2))(2)] (2). Use of excess acid gave a trinuclear Fe(II) complex [Fe(3)(H(2)O)(2)(O(2)CCF(3))(8)(FcNP·H)(2)] (3). Three linear iron atoms are held together by four bridging trifluoroacetates and two aqua ligands in a symmetric fashion. Reaction with ethereal solution of HCl afforded [(FcNP·H)(3)(Cl)][FeCl(4)](2) (4) irrespective of the amount of the acid used. Even the picric acid (HPic) led to metal extrusion giving rise to [Fe(2)(Cl)(2)(FcNP)(2)(Pic)(2)] (5) when crystallized from dichloromethane. Metal extrusion was also observed for CF(3)SO(3)H, but an analytically pure compound could not be isolated. The demetalation reaction proceeds with an initial proton attack to the distal nitrogen of the NP unit. Subsequently, coordination of the conjugate base to the electrophilic Fe facilitates the release of Cp rings from metal. The conjugate base plays an important role in the demetalation process and favors the isolation of the Fe complex as well. The 1,1'-bis(1,8-naphthyrid-2-yl)ferrocene (FcNP(2)) does not undergo demetalation under identical conditions. Two NP units share one positive charge causing the Fe-Cp bonds weakened to an extent that is not sufficient for demetalation. X-ray structure of the monoprotonated FcNP(2) reveals a discrete dimer [(FcNP(2)·H)](2)[OTf](2) (6) supported by two N-H···N hydrogen bonds. Crystal packing and dispersive forces associated with intra- and intermolecular π-π stacking interactions (NP···NP and Cp···NP) allow the formation of the dimer in the solid-state. The protonation and demetalation reactions of FcNP and FcNP(2) with a variety of acids are reported.

Synthesis and oxidation of hexafluoroisopropoxyborylferrocenes

The ferrocenylboranes (BOhfip2)Fc and 1,1'-(BOhfip2)2Fc were prepared (Fc = ferrocenyl, Ohfip = (CF3)2CH-O); 1,1'-(BOhfip2)2Fc was further oxidized giving [1,1'-(BOhfip2)2Fc]+[Al(ORF)4]– by oxidation of 1,1'-(BOhfip2)2Fc with Ag+[Al(ORF)4]– (RF = C(CF3)3). Their X-ray crystal structures were determined and give further information on the Fe–B interaction through the dip angles α*. In [1,1'-(BOhfip2)2Fc]+[Al(ORF)4]–, this Fe–B interaction is enfeebled: the dip angles α* (0.3º and 5.4º) are significantly smaller than in (BOhfip2)Fc (7.8º) and 1,1'-(BOhfip2)2Fc (8.0º), and the hexafluoroisopropoxy moieties are twisted out of the Cp plane by up to 66.1º. NMR and vibrational spectra support the crystal structure assignments.

(Acetonitrile-κN)chloridobis[2-(pyridin-2-yl)phenyl-κC,N]iridium(III)

The Ir(III) atom of the title compound, [Ir(C(11)H(8)N)(2)Cl(CH(3)CN)], displays a distorted octa-hedral coordination. The pyridyl groups are in trans positions [N-Ir-N = 173.07 (10)°], while the phenyl groups are trans with respect to the acetonitrile and chloride groups [C-Ir-N = 178.13 (11) and C-Ir-Cl = 176.22 (9)°]. The pyridyl-phenyl groups only show a small deviation from planarity, with the dihedral angle between the planes of the two six-membered rings in each pyridyl-phenyl group being 5.6 (2) and 5.8 (1)°. The crystal packing shows inter-molecular C-H⋯Cl, C-H⋯π(acetonitrile) and C-H⋯π(pyridyl-phen-yl) contacts.

Metallacycles of Iron, Zinc, and Cadmium Assembled by Polytopic Bis(pyrazolyl)methane Ligands and Fluoride Abstraction from BF4-

Reactions of the arene-linked bis(pyrazolyl)methane ligands m-bis[bis(1-pyrazolyl)methyl]benzene (m-[CH(pz)2]2C6H4, Lm) and 1,3,5-tris[bis(1-pyrazolyl)methyl]benzene (1,3,5-[CH(pz)2]3C6H3, L3) with BF4- salts of divalent iron, zinc, and cadmium result in fluoride abstraction from BF4- and formation of fluoride-bridged metallacyclic complexes. Treatment of Fe(BF4)2.6H2O and Zn(BF4)2.5H2O with Lm leads to the complexes [Fe2(mu-F)(mu-Lm)2](BF4)3 (1) and [Zn2(mu-F)(mu-Lm)2](BF4)3 (2), in which a single fluoride ligand and two Lm molecules bridge the two metal centers. The reaction of [Cd2(thf)5](BF4)4 with Lm results in the complex [Cd2(mu-F)2(mu-Lm)2](BF4)2 (3), which contains dimeric cations in which two fluoride and two Lm ligands bridge the cadmium centers. Equimolar amounts of the tritopic ligand L3 and Zn(BF4)2.5H2O react to give the related monofluoride-bridged complex [Zn2(mu-F)(mu-L3)2](BF4)3 (4), in which one bis(pyrazolyl)methane unit on each ligand remains unbound. NMR spectroscopic studies show that in acetonitrile the zinc metallacycles observed in the solid-state remain intact in solution.

Silver(I) Complexes of Fixed, Polytopic Bis(pyrazolyl)methane Ligands: Influence of Ligand Geometry on the Formation of Discrete Metallacycles and Coordination Polymers

Reactions of the arene-linked bis(pyrazolyl)methane ligands m-bis[bis(1-pyrazolyl)methyl]benzene, (m-[CH(pz)2]2C6H4, Lm), p-bis[bis(1-pyrazolyl)methyl]benzene, (p-[CH(pz)2]2C6H4, Lp), and 1,3,5-tris[bis(1-pyrazolyl)methyl]benzene (1,3,5-[CH(pz)2]3C6H3, L3) with AgX salts (pz = 1-pyrazolyl; X = BF4- or PF6-) yield two types of molecular motifs depending on the arrangement of the ligating sites about the central arene ring. Reactions of the m-phenylene-linked Lm with AgBF4 and AgPF6 afford complexes consisting of discrete, metallacyclic dications: [Ag2(mu-Lm)2](BF4)2 (1) and [Ag2(mu-Lm)2](PF6)2 (2). When the p-phenylene-linked Lp is treated with AgBF4 and AgPF6, acyclic, cationic coordination polymers are obtained: {[Ag(mu-Lp)]BF4}infinity (3) and {[Ag(mu-Lp)]PF6}infinity (4). Reaction of the ligand L3, containing three bis(pyrazolyl)methane units in a meta arrangement, with an equimolar amount of AgBF4 again yields discrete metallacyclic dications in which one bis(pyrazolyl)methane unit on each ligand remains unbound: [Ag2(mu-L3)2](BF4)2 (5). Treatment of L3 with an excess of AgBF4 affords a polymer of metallacycles, {[Ag3(mu-L3)2](BF4)3}infinity (6), with one of the bis(pyrazolyl)methane units on each ligand bound to a silver cation bridging two metallacycles. The supramolecular structures of the silver(I) complexes 1-6 are organized by noncovalent interactions, including weak hydrogen bonding, pi-pi, and anion-pi interactions.

Synthesis, characterization and spectroscopic studies of the dihydrobis(1,2,3-benzotriazolyl)borate anion and its complexes with MCl2·py2

The preparation of sodium dihydrobis(1,2,3-benzotriazolyl)borate was realised by refluxing one mole of sodium borohydride with two moles of 1,2,3-benzotriazole in toluene over a period of 12 h. Its complexes with MCl2?py2 [where M= Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and py = Pyridine] were characterized by elemental analysis as well as magnetic, spectroscopic and conductivity measurements. On the basis of these studies, it is proposed that the geometry of all the complexes is octahedral. The ligand field parameters 10 Dq, B and ? show extensive overlap between the M-L orbital. The molar conductance of 10-3Msolutions of the complexes in DMSO suggest them to be non-ionic in nature.

3,5-Dimethyl and 3,5-Di-tert-butylpyrazolato Complexes with Alkali Metals: Monomeric, Dimeric, Cluster, and 1D Chain Structures

The pyrazolato complexes [(Me(2)pz)(THF)Li] (1), [((t)Bu(2)pz)Li](4) (2), [((t)Bu(2)pzH)((t)()Bu(2)pz)Li](2) (2a), [(Me(2)pz)Na] (3), [((t)Bu(2)pz)Na](4), [((t)Bu(2)pz)(6)(OH)Na(7)] (4a), [((t)Bu(2)pz)(18-crown-6)Na] (4b), and [((t)Bu(2)pz)K] (5) were synthesized by metalation reactions between R(2)pzH (R = Me, (t)()Bu) and alkyllithium, elemental sodium, or potassium. All the complexes were characterized by spectroscopic methods and microanalysis, and in addition, the crystal structures of 2, 2a, 3, 4a, 4b, and 5 were obtained by single-crystal X-ray diffraction. They show monomeric, dimeric, cluster, and 1D chain structures in the solid state. Ab initio calculations on the structure and stabilities of the monomeric pzM complexes were performed at the MP2 level of theory showing good agreement with the coordination preferences of the pyrazolato ligand to a particular alkali ion.