Structural elucidation of a methylenation reagent of esters: synthesis and reactivity of a dinuclear titanium(iii) methylene complex

Transmetallation of a zinc methylene complex [ZnI(tmeda)]₂(μ-CH₂) with a titanium(iii) chloride [TiCl₃(tmeda)(thf)] produced a titanium methylene complex. The X-ray diffraction study displayed a dinuclear methylene structure [TiCl(tmeda)]₂(μ-CH₂)(μ-Cl)₂. Treatment of an ester with the titanium methylene complex resulted in methylenation of the ester carbonyl to form a vinyl ether. The titanium methylene complex also reacted with a terminal olefin, resulting in olefin-metathesis and olefin-homologation. Cyclopropanation by methylene transfer from the titanium methylene proceeded by use of a 1,3-diene. The mechanistic study of the cyclopropanation reaction by the density functional theory calculations was also reported.

Transmetallation of a zinc methylene complex [ZnI(tmeda)]₂(μ-CH₂) with a titanium(iii) chloride [TiCl₃(tmeda)(thf)] produced a titanium methylene complex.     

Inhibition of [FeFe]-hydrogenase by formaldehyde: proposed mechanism and reactivity of FeFe alkyl complexes

The mechanism for inhibition of [FeFe]-hydrogenases by formaldehyde is examined with model complexes. Key findings: (i) CH₂ donated by formaldehyde covalently link Fe and the amine cofactor, blocking the active site and (ii) the resulting Fe-alkyl is a versatile electrophilic alkylating agent. Solutions of Fe₂[(μ-SCH₂)₂NH](CO)₄(PMe₃)₂ (1) react with a mixture of HBF₄ and CH₂O to give three isomers of [Fe₂[(μ-SCH₂)₂NCH₂](CO)₄(PMe₃)₂]⁺ ([2]⁺). X-ray crystallography verified the NCH₂Fe linkage to an octahedral Fe(ii) site. Although [2]⁺ is stereochemically rigid on the NMR timescale, spin-saturation transfer experiments implicate reversible dissociation of the Fe–CH₂ bond, allowing interchange of all three diastereoisomers. Using ¹³CH₂O, the methylenation begins with formation of [Fe₂[(μ-SCH₂)₂N¹³CH₂OH](CO)₄(PMe₃)₂]⁺. Protonation converts this hydroxymethyl derivative to [2]⁺, concomitant with ¹³C-labelling of all three methylene groups. The Fe–CH₂N bond in [2]⁺ is electrophilic: PPh₃, hydroxide, and hydride give, respectively, the phosphonium [Fe₂[(μ-SCH₂)₂NCH₂PPh₃](CO)₄(PMe₃)₂]⁺, 1, and the methylamine Fe₂[(μ-SCH₂)₂NCH₃](CO)₄(PMe₃)₂. The reaction of [Fe₂[(μ-SCH₂)₂NH](CN)₂(CO)₄]²⁻ with CH₂O/HBF₄ gave [Fe₂[(μ-SCH₂)₂NCH₂CN](CN)(CO)₅]⁻ ([4]⁻), the result of reductive elimination from [Fe₂[(μ-SCH₂)₂NCH₂](CN)₂(CO)₄]⁻. The phosphine derivative [Fe₂[(μ-SCH₂)₂NCH₂CN](CN)(CO)₄(PPh₃)]⁻ ([5]⁻) was characterized crystallographically.

The mechanism for inhibition of [FeFe]-hydrogenases by formaldehyde is examined with model complexes.     

Replacement of the Common Chromium Source CrCl3(thf)3 with Well-Defined [CrCl2(μ-Cl)(thf)2]2

CrCl₃(thf)₃ is a common starting material in the synthesis of organometallic and coordination compounds of Cr. Deposited as an irregular solid with no possibility of recrystallization, it is not a purity guaranteed chemical, causing problems in some cases. In this work, we disclose a well-defined form of the THF adduct of CrCl₃ ([CrCl₂(μ-Cl)(thf)₂]₂), a crystalline solid, that enables structure determination by X-ray crystallography. The EA data and XRD pattern of the bulk agreed with the revealed structure. Moreover, its preparation procedure is facile: evacuation of CrCl₃·6H₂O at 100 °C, treatment with 6 equivalents of Me₃SiCl in a minimal amount of THF, and crystallization from CH₂Cl₂. The ethylene tetramerization catalyst [iPrN{P(C₆H₄-p-Si(nBu)₃)₂}₂CrCl₂]⁺[B(C₆F₅)₄]⁻ prepared using well-defined [CrCl₂(μ-Cl)(thf)₂]₂ as a starting material exhibited a reliably high activity (6600 kg/g-Cr/h; 1-octene selectivity at 40 °C, 75%), while that of the one prepared using the impure CrCl₃(thf)₃ was inconsistent and relatively low (~3000 kg/g-Cr/h). By using well-defined [CrCl₂(μ-Cl)(thf)₂]₂ as a Cr source, single crystals of [(CH₃CN)₄CrCl₂]⁺[B(C₆F₅)₄]⁻ and [{Et(Cl)Al(N(iPr)₂)₂}Cr(μ-Cl)]₂ were obtained, allowing structure determination by X-ray crystallography, which had been unsuccessful when the previously known CrCl₃(thf)₃ was used as the Cr source.     

Migratory insertion of isocyanide into a ketenyl–tungsten bond as key step in cyclization reactions

Treatment of the side-on tungsten alkyne complex of ethinylethyl ether [Tp*W(CO)₂(η²-C,C′-HCCOCH₂CH₃)]⁺ {Tp* = hydridotris(3,4,5-trimethylpyrazolyl)borate} (2a) with n-Bu₄NI afforded the end-on ketenyl complex [Tp*W(CO)₂(κ¹-HCCO)] (4a). This formal 16 ve complex bearing the prototype of a ketenyl ligand is surprisingly stable and converts only under activation by UV light or heat to form a dinuclear complex [Tp*₂W₂(CO)₄(μ-CCH₂)] (6). The ketenyl ligand in complex 4a underwent a metal template controlled cyclization reaction upon addition of isocyanides. The oxametallacycles [Tp*W(CO)₂{κ²-C,O-C(NHXy)C(H)C(Nu)O}] {Nu = OMe (7), OEt (8), N(i-Pr)₂ (9), OH (10), O_1/2 (11)} were formed by coordination of Xy-NC (Xy = 2,6-dimethylphenyl) at 4a and subsequent migratory insertion (MI) into the W-ketenyl bond. The resulting intermediate is susceptible to addition reactions with protic nucleophiles. Compounds 2a-PF₆, 4a/b, and 7–11 were fully characterized including XRD analysis. The cyclization mechanism has been confirmed both experimentally and by DFT calculations. In cyclic voltammetry, complexes 7–9 are characterized by a reversible W(ii)/W(iii) redox process. The dinuclear complex 11 however shows two separated redox events. Based on cyclic voltammetry measurements with different conducting electrolytes and IR spectroelectrochemical (SEC) measurements the W(ii)/W(iii) mixed valent complex 11⁺ is assigned to class II in terms of the Robin-Day classification.

The prototype ketenyl ligand is bound end-on despite a formal 16 valence electron count at the metal. This situation opens a reaction pathway for a multicomponent cyclization centred on the migration of the ketenyl ligand.     

Synthesis,crystal structures and physical properties of two terephthalate-bridged copper(II) and nickel(II) complexes

Two ₂-terephthalate (tp) bridged complexes, [Cu₂(tp)(pren)₄](ClO₄)₂ (pren = 1,3-diaminopropane) (1) and [Ni₂(tp)(pren)₄(Him)₂](ClO₄)₂ (Him = imidazole) (2), have been synthesized and characterized by X-ray single-crystal structural analysis. In the discrete dinuclear [Cu₂(tp)(pren)₄]²⁺ cation of complex (1), each Cu^II atom has a square-pyramidal geometry, being coordinated by four nitrogen atoms (avg. 2.031 Å) from two pren ligands at the basal plane and one oxygen atom [2.259(3) Å] from a bis-monodentate tp group at the axial position. In the discrete dinuclear [Ni₂(tp)(pren)₄(Him)₂]²⁺ cation of complex (2), each Ni^II center is coordinated by five nitrogen atoms [Ni—N 2.069(3)–2.109(2) Å] from one Him group and two pren groups, and completed by one oxygen atom [Ni—O 2.138(3) Å] from a bis-monodentate tp group to furnish a distorted octahedron. Magnetic susceptibility studies show that the pair of metal atoms, although being separated by >11.5 Å, exhibit weak intramolecular antiferromagnetic interactions in complexes (1) (g = 2.07 and J = –3.4 cm^–1) and (2) (g = 2.10 and J = –0.7 cm^–1). The electrochemical behaviors of the complexes have also been studied by cyclic voltammogram processes.     

Synthesis of Co2Pt, Co2Pd and MoPd2 mixed-metal clusters with the P–N–P assembling ligands (Ph2P)2NH (dppa) and (Ph2P)2NMe (dppaMe). Crystal structure of [Co2Pt(μ3-CO)(CO)6(μ-dppa)]

Heterometallic triangular platinum–cobalt, palladium–cobalt and palladium–molybdenum clusters stabilized by one or two bridging diphosphine ligands such as Ph₂PNHPPh₂ (dppa) or (Ph₂P)₂NMe (dppaMe) or by mixed ligand sets Ph₂PCH₂PPh₂ (dppm)/dppa have been prepared with the objectives of comparing the stability and properties of the clusters as a function of the short-bite diphosphine ligand used and of the metal carbonyl fragment they contain. Ligand redistribution reactions were observed during the purification of [Co₂Pd(μ₃-CO)(CO)₄(μ-dppa)(μ-dppm)] (4) by column chromatography with the formation of [Co₂Pd(μ₃-CO)(CO)₄(μ-dppm)₂] and the dinuclear complex [(OC)₂ Cl] (5). The latter was independently prepared by reaction of [Pd(dppa-P,P′)₂](BF₄)₂ with Na[Co(CO)₄]. Attempts to directly incorporate the ligand (Ph₂P)₂N(CH₂)₃Si(OMe)₃ (dppaSi) into a cluster or to generate it by N-functionalization of coordinated dppa were unsuccessful, in contrast to results obtained recently with related clusters. The crystal structure of [Co₂Pt(μ₃-CO)(CO)₆(μ-dppa)] (1) has been determined by X-ray diffraction.     

Copper(II) complexes of tetradentate N2S2 donor sets: Synthesis,crystal structure characterization and reactivity

Two mononuclear and one dinuclear copper(II) complexes, containing neutral tetradentate NSSN type ligands, of formulation [Cu^II(L¹)Cl]ClO₄ (1), [Cu^II(L²)Cl]ClO₄ (2) and [Cu^II₂(L³)₂Cl₂](ClO₄)₂ (3) were synthesized and isolated in pure form [where L¹ = 1,2-bis(2-pyridylmethylthio)ethane, L² = 1,3-bis(2-pyridylmethylthio)propane and L³ = 1,4-bis(2-pyridylmethylthio)butane]. All these green colored copper(II) complexes were characterized by physicochemical and spectroscopic methods. The dinuclear copper(II) complex 3 changed to a colorless dinuclear copper(I) species of formula [Cu^I₂(L³)₂](ClO₄)₂,0.5H₂O (4) in dimethylformamide even in the presence of air at ambient temperature, while complexes 1 and 2 showed no change under similar conditions. The solid-state structures of complexes 1, 2 and 4 were established by X-ray crystallography. The geometry about the copper in complexes 1 and 2 is trigonal bipyramidal whereas the coordination environment about the copper(I) in dinuclear complex 4 is distorted tetrahedral.     

The approach to 4d/4f-polyphosphides

The first 4d/4f polyphosphides were obtained by reaction of the divalent metallocenes [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] or [Cp*Mo(CO)₂(η³-P₃)]. Treatment of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] gave the 16-membered bicyclic compounds [(Cp₂*Ln)₂P₂(CpMo(CO)₂)₄] (Ln = Sm, Yb) as the major products. From the reaction involving samarocene, the cyclic P₄ complex [(Cp*₂Sm)₂P₄(CpMo(CO)₂)₂] and the cyclic P₅ complex [(Cp*₂Sm)₃P₅(CpMo(CO)₂)₃] were also obtained as minor products. In each reaction, the P₂ unit is reduced and a rearrangement occurred. In dedicated cases, a P–P bond formation takes place, which results in a new aggregation of the central phosphorus scaffold. In the reactions of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [Cp*Mo(CO)₂P₃] a new P–P bond is formed by reductive dimerization and the 4d/4f hexaphosphides [(Cp*₂Ln)₂P₆(Cp*Mo(CO)₂)₂] (Ln = Sm, Yb) were obtained.     

Coordination behavior of 3,4-bis(2-pyridylmethylthio)toluene with copper(II) ions: Synthesis,structural characterization and reactivity,and DNA binding study of the dinuclear copper(II) complex

On reaction of different copper(II) salts with 3,4-bis(2-pyridylmethylthio)toluene (L) having neutral tetradentate NSSN donor set in different chemical environments, two mononuclear copper(II), one dinuclear copper(I) and one dinuclear copper(II) complexes, formulated as [Cu^II(L)(H₂O)₂](NO₃)₂ (1), [Cu^II(pic)₂] (2), [Cu^I₂(L)₂](ClO₄)₂ (3) and [Cu^II₂(L)₂Cl₂](ClO₄)₂ (4), respectively, were isolated in pure form [where pic = picolinate]. All the complexes were characterized by physicochemical and spectroscopic methods. The product of the reactions are dependent on the counter anion of copper(II) salts used as reactant and on the reaction medium. Complexes 1 and 4 were obtained with nitrate and perchlorate copper(II) salts, respectively. On the other hand, C–S bond cleavage was observed in the reaction of L with copper(II) chloride to form in situ picolinic acid and complex 2. Dinuclear complexes 3 and 4 were separated out when copper(II) perchlorate was allowed to react with L in methanol and in acetonitrile, respectively, under aerobic condition. The X-ray diffraction analysis of the dinuclear complex 3 shows a highly distorted tetrahedral geometry about each copper ion. Complex 4 is converted to 3 in acetonitrile in presence of catechol. The spectral study of complex 4 with calf thymus DNA is indicative of a groove binding mode interaction.     

Transfer of polyantimony units

Transfer reagents are useful tools in chemistry to access metastable compounds. The reaction of [Cp′′₂ZrCl₂] with KSb(SiMe₃)₂ leads to the formation of the novel polyantimony triple decker complex [(Cp′′Zr)₂(μ,η^1:1:1:1:1:1-Sb₆)] (1, Cp′′ = 1,3-di-tertbutyl-cyclopentadienyl), containing a chair-like Sb₆⁶⁻ ligand. Compound 1 represents a valuable transfer reagent to form novel antimony ligand complexes. Thus, the reaction of 1 with Cp^R-substituted transition metal halides of nickel, cobalt and iron leads to the formation of a variety of novel Sb_n ligand complexes, such as the cubane-like compounds [(Cp′′′Ni)₄(μ₃-Sb)₄] (2) and [(Cp′′′Co)₄(μ₃-Sb₄)] (3a) or the complexes [(Cp^BnCo)₃(μ₃-Sb)₂] (4) and [(Cp′′′Fe)₃(μ₃-Sb)₂] (5), representing a trigonal bipyramidal structure. Moreover, beside the transfer of Sb₁ units, also the complete entity can be transferred as seen in the iron complex [(Cp′′′Fe)₃(μ_3,η^4:4:4-Sb₆)] (6). DFT calculations shed light on the bonding situation of the products.

The synthesis and characterization of the unique polyantimony complex [(Cp′′Zr)₂(μ,η^1:1:1:1:1:1-Sb₆)] (1) is described. Compound 1 was used as antimony source to transfer Sb_n units to late transition metal fragments [Cp^RM] (M = Fe, Co, Ni).     

Synthesis of a heterobimetallic actinide nitride and an analysis of its bonding

Reaction of [K(DME)][Th{N(R)(SiMe₂CH₂)}₂(NR₂)] (R = SiMe₃) with 1 equiv. of [U(NR₂)₃(NH₂)] (1) in THF, in the presence of 18-crown-6, results in formation of a bridged uranium–thorium nitride complex, [K(18-crown-6)(THF)₂][(NR₂)₃U^IV(μ-N)Th^IV(NR₂)₃] (2), which can be isolated in 48% yield after work-up. Complex 2 is the first isolable molecular mixed-actinide nitride complex. Also formed in the reaction is the methylene-bridged mixed-actinide nitride, [K(18-crown-6)][K(18-crown-6)(Et₂O)₂][(NR₂)₂U(μ-N)(μ–κ²-C,N–CH₂SiMe₂NR)Th(NR₂)₂]₂ (3), which can be isolated in 34% yield after work-up. Complex 3 is likely generated by deprotonation of a methyl group in 2 by [NR₂]⁻, yielding the new μ-CH₂ moiety and HNR₂. Reaction of 2 with 0.5 equiv. of I₂ results in formation of a U^V/Th^IV bridged nitride, [(NR₂)₃U^V(μ-N)Th^IV(NR₂)₃] (4), which can be isolated in 42% yield after work-up. The electronic structure of 4 was analyzed with EPR spectroscopy, SQUID magnetometry, and NIR-visible spectroscopy. This analysis demonstrated that the energies of 5f orbitals of 4 are largely determined by the strong ligand field exerted by the nitride ligand.

The heterobimetallic actinide nitride [(NR₂)₃U^V(μ-N)Th^IV(NR₂)₃] (R = SiMe₃) has an m_J = 5/2 ground state and its highest energy 5f excited state is primarily 5f-N_nitride σ-antibonding in character.     

Hydridotetrylene [Ar*EH] (E = Ge,Sn, Pb) coordination at tantalum,tungsten, and zirconium

In a reaction of tantalocene trihydride with the low valent aryl tin cation [Ar*Sn(C₆H₆)][Al(OC{CF₃}₃)₄] (1a) the hydridostannylene complex [Cp₂TaH₂–Sn(H)Ar*][Al(OC{CF₃}₃)₄] (2) was synthesized. Hydride bridged adducts [Cp₂WH₂EAr*][Al(OC{CF₃}₃)₄] (E = Sn 3a, Pb 3b) were isolated as products of the reaction between Cp₂WH₂ and cations [Ar*E(C₆H₆)][Al(OC{CF₃}₃)₄] (E = Sn 1a, Pb 1b). The tin adduct 3a exhibits a proton migration to give the hydridostannylene complex [Cp₂W(H) Sn(H)Ar*][Al(OC{CF₃}₃)₄] 4a. The cationic complex 4a is deprotonated at the tin atom in reaction with base ^MeNHC at 80 °C to give a hydrido-tungstenostannylene [Cp₂W(H)SnAr*] 5a. Reprotonation of metallostannylene 5a with acid [H(Et₂O)₂][BAr^F] provides an alternative route to hydridotetrylene coordination. Complex 4a adds hydride to give the dihydrostannyl complex [Cp₂W(H)–SnH₂Ar*] (7). With styrene 4a shows formation of a hydrostannylation product [Cp₂W(H) Sn(CH₂CH₂Ph)Ar*][Al(OC{CF₃}₃)₄] (8). The lead adduct 3b was deprotonated with ^MeNHC to give plumbylene 5b [Cp₂W(H)PbAr*]. Protonation of 5b with [H(Et₂O)₂][Al(OC{CF₃}₃)₄] at −40 °C followed by low temperature NMR spectroscopy indicates a hydridoplumbylene intermediate [Cp₂W(H) Pb(H)Ar*]⁺ (4b). Hydrido-tungstenotetrylenes of elements Ge (5c), Sn (5a) and Pb (5b) were also synthesized reacting the salt [Cp₂W(H)Li]₄ with organotetrylene halides. The metallogermylene [Cp₂W(H)GeAr*] (5c) shows an isomerization via 1,2-H-migration to give the hydridogermylene [Cp₂W Ge(H)Ar*] (9), which is accelerated by addition of AIBN. 9 is at rt photochemically transferred back to 5c under light of a mercury vapor lamp. Zirconocene dihydride [Cp₂ZrH₂]₂ reacts with tin cation 1a to give the trinuclear hydridostannylene adduct 10 [({Cp₂Zr}₂{μ-H})(μ-H)₂μ-Sn(H)Ar*][Al(OC{CF₃}₃)₄]. Deprotonation of 10 was carried out using benzyl potassium to give neutral [({Cp₂Zr}₂{μ-H})(μ-H)μ-Sn(H)Ar*] (11). 11 was also obtained from the reaction of low valent tin hydride [Ar*SnH]₂ with two equivalents of [Cp₂ZrH₂]₂. The trihydride Ar*SnH₃ reacts with half of an equivalent of [Cp₂ZrH₂]₂ under evolution of hydrogen and formation of a dihydrostannyl complex 13 [Cp₂Zr(μ-H)SnH₂Ar*]₂ and with further equivalents of Ar*SnH₃ to give bis(hydridostannylene) complex [Cp₂Zr{Sn(H)Ar*}₂].

Low valent cations of tin and lead were used to form hydridotetrylene coordination compounds. The mobility of the hydrogen substituent was investigated in deprotonation equilibria as well as in 1,2-H-shift reactions.     

Ruthenafuran Complexes Supported by the Bipyridine-Bis(diphenylphosphino)methane Ligand Set: Synthesis and Cytotoxicity Studies

Mononuclear and dinuclear Ru(II) complexes cis-[Ru(κ²-dppm)(bpy)Cl₂] (1), cis-[Ru(κ²-dppe)(bpy)Cl₂] (2) and [Ru₂(bpy)₂(μ-dpam)₂(μ-Cl)₂](Cl)₂ ([3](Cl)₂) were prepared from the reactions between cis(Cl), cis(S)-[Ru(bpy)(dmso-S)₂Cl₂] and diphosphine/diarsine ligands (bpy = 2,2′-bipyridine; dppm = 1,1-bis(diphenylphosphino)methane; dppe = 1,2-bis(diphenylphosphino)ethane; dpam = 1,1-bis(diphenylarsino)methane). While methoxy-substituted ruthenafuran [Ru(bpy)(κ²-dppe)(C^O)]⁺ ([7]⁺; C^O = anionic bidentate [C(OMe)CHC(Ph)O]⁻ chelate) was obtained as the only product in the reaction between 2 and phenyl ynone HC≡C(C=O)Ph in MeOH, replacing 2 with 1 led to the formation of both methoxy-substituted ruthenafuran [Ru(bpy)(κ²-dppm)(C^O)]⁺ ([4]⁺) and phosphonium-ring-fused bicyclic ruthenafuran [Ru(bpy)(P^C^O)Cl]⁺ ([5]⁺; P^C^O = neutral tridentate [(Ph)₂PCH₂P(Ph)₂CCHC(Ph)O] chelate). All of these aforementioned metallafuran complexes were derived from Ru(II)–vinylidene intermediates. The potential applications of these metallafuran complexes as anticancer agents were evaluated by in vitro cytotoxicity studies against cervical carcinoma (HeLa) cancer cell line. All the ruthenafuran complexes were found to be one order of magnitude more cytotoxic than cisplatin, which is one of the metal-based anticancer agents being widely used currently.     

Optimization of crystal packing in semiconducting spin-crossover materials with fractionally charged TCNQδ− anions (0 < δ < 1)

Co-crystallization of the prominent Fe(ii) spin-crossover (SCO) cation, [Fe(3-bpp)₂]²⁺ (3-bpp = 2,6-bis(pyrazol-3-yl)pyridine), with a fractionally charged TCNQ^δ− radical anion has afforded a hybrid complex [Fe(3-bpp)₂](TCNQ)₃·5MeCN (1·5MeCN, where δ = −0.67). The partially desolvated material shows semiconducting behavior, with the room temperature conductivity σ_RT = 3.1 × 10⁻³ S cm⁻¹, and weak modulation of conducting properties in the region of the spin transition. The complete desolvation, however, results in the loss of hysteretic behavior and a very gradual SCO that spans the temperature range of 200 K. A related complex with integer-charged TCNQ⁻ anions, [Fe(3-bpp)₂](TCNQ)₂·3MeCN (2·3MeCN), readily loses the interstitial solvent to afford desolvated complex 2 that undergoes an abrupt and hysteretic spin transition centered at 106 K, with an 11 K thermal hysteresis. Complex 2 also exhibits a temperature-induced excited spin-state trapping (TIESST) effect, upon which a metastable high-spin state is trapped by flash-cooling from room temperature to 10 K. Heating above 85 K restores the ground-state low-spin configuration. An approach to improve the structural stability of such complexes is demonstrated by using a related ligand 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) to obtain [Fe(bzimpy)₂](TCNQ)₆·2Me₂CO (4) and [Fe(bzimpy)₂](TCNQ)₅·5MeCN (5), both of which exist as LS complexes up to 400 K and exhibit semiconducting behavior, with σ_RT = 9.1 × 10⁻² S cm⁻¹ and 1.8 × 10⁻³ S cm⁻¹, respectively.

Co-crystallization of the cationic complex [Fe(3-bpp)2]²⁺ with fractionally charged TCNQ^δ− anions (0 < δ < 1) affords semiconducting spin-crossover (SCO) materials. The abruptness of SCO is strongly dependent on the interstitial solvent content.     

Synthesis and DNA-binding properties of binuclear platinum complexes with two <Emphasis Type="Italic">trans</Emphasis>-[Pt(NH<Subscript>3</Subscript>)<Subscript>2</Subscript>Cl]<Superscript>+</Superscript> units bridged by 4,4′-dipyridyl sulfide or selenide

Two novel dinuclear platinum complexes, {trans-[Pt(NH₃)₂Cl]₂(dpsu)}(NO₃)₂ (1) and {trans-[Pt(NH₃)₂Cl]₂ (dpse)}(NO₃)₂ (2) (dpsu = 4,4-dipyridyl sulfide and dpsu = 4,4-dipyridyl selenide) have been prepared for use as potential antitumor drugs. Compared to the known monofunctional complex, [cis-Pt(NH₃)₂Cl(4-methylpyridine)]NO₃, (1) exhibits an almost two-fold stronger DNA-binding ability, a result suggesting that (1) may bind bifunctionally to DNA. Kinetic studies show that (1) significantly impedes intercalation of ethidium bromide (EtdBr) into DNA in 0.3 mol dm^–3 KNO₃ but not in 0.3 mol dm^–3 KCl, indicating that the hydrolysis is the first step upon addition of the complex to DNA. Also, the complex may interact with DNA by non-intercalation. Unlike its dinuclear analogs linked by aliphatic diamines, complex (1) does not induce a transition of poly(dG–dC) · poly(dG–dC) from the B form to the Z form. Moreover, complex (1) significantly inhibits the cleavage activity of BamHI endonuclease, but has no effect on that of EcoRI endonuclease. In contrast, its cis analog containing two [cis-Pt(NH₃)₂Cl]⁺ units greatly inhibits those of both BamHI and EcoRI, a result suggesting that the two isomers with the same aromatic ligand probably have different properties of DNA binding, and that (1) possibly shows higher DNA-binding selectivity than its cisanalog.     

Terminal and Internal Alkyne Complexes and Azide-Alkyne Cycloaddition Chemistry of Copper(I) Supported by a Fluorinated Bis(pyrazolyl)borate

Copper plays an important role in alkyne coordination chemistry and transformations. This report describes the isolation and full characterization of a thermally stable, copper(I) acetylene complex using a highly fluorinated bis(pyrazolyl)borate ligand support. Details of the related copper(I) complex of HC≡CSiMe₃ are also reported. They are three-coordinate copper complexes featuring η²-bound alkynes. Raman data show significant red-shifts in C≡C stretch of [H₂B(3,5-(CF₃)₂Pz)₂]Cu(HC≡CH) and [H₂B(3,5-(CF₃)₂Pz)₂]Cu(HC≡CSiMe₃) relative to those of the corresponding alkynes. Computational analysis using DFT indicates that the Cu(I) alkyne interaction in these molecules is primarily of the electrostatic character. The π-backbonding is the larger component of the orbital contribution to the interaction. The dinuclear complexes such as Cu₂(μ-[3,5-(CF₃)₂Pz])₂(HC≡CH)₂ display similar Cu-alkyne bonding features. The mononuclear [H₂B(3,5-(CF₃)₂Pz)₂]Cu(NCMe) complex catalyzes [3 + 2] cycloadditions between tolyl azide and a variety of alkynes including acetylene. It is comparatively less effective than the related trinuclear copper catalyst {μ-[3,5-(CF₃)₂Pz]Cu}₃ involving bridging pyrazolates.     

Self assembly of asymmetric tetranuclear Cu(II) [2 × 2] grid-like complexes and of a dinuclear Ni(II) complex from pyridyl-phenol Schiff base ligands

Self assembly of N-salicylidene 2-aminopyridine (L1H) with Cu(NO₃)₂·3H₂O affords [Cu₄(L1)₄(NO₃)₃(CH₃OH)][Cu(L1)(NO₃)₂](2-aminopyridinium)(NO₃)·5CH₃OH (1) which is composed of an asymmetric [2 × 2] grid-like cationic complex that co-crystallizes with a Cu(II) mononuclear anion. This remarkable tetranuclear unit presents three penta-coordinated and one hexa-coordinated Cu(II) sites. This quadruple helicate structure reveals strong anti-ferromagnetic coupling (J = −340(2) cm⁻¹) between Cu(II) ions through a double alkoxo bridge. Reacting L1H with Cu(NO₃)₂·3H₂O in slightly different conditions affords however a more symmetric tetranuclear grid-like complex: [Cu₄(L1)₄(NO₃)₂(OH)₂](2-aminopyridinium)(OH)·CH₃OH) (2). A dinuclear Ni(II) complex, [Ni₂(L2)₂(L2H)₂(NCS)₂(CH₃OH)₂]·2CH₃OH (3), obtained with another related donor ligand (L2H = N-salicylidene 3-aminomethylpyridine) was also prepared.     

Yttrium complexes derived from 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-dimethoxycalix[4]arene (LH2). Synthesis,properties, and structures of the [LY(thf)(μ-Cl)]2 and [LY(thf)3]+[L2Y]– complexes

5,11,17,23-Tetra-tert-butyl-25,27-dihydroxy-26,28-dimethoxycalix[4]arene (1, LH₂) was deprotonated with two equivalents of potassium naphthalenide in THF at room temperature. The reaction of a dipotassium derivative of 1 prepared in situ with anhydrous YCl₃ in a THF medium afforded the corresponding yttrium alkoxychloride [LY(thf)(-Cl)]₂·4thf (2·4thf) in 71% yield. According to the X-ray diffraction data, complex 2 has a dimeric structure. The reaction of equimolar amounts of [(Me₃Si)₂N]₃Y and compound 1 in a THF—toluene mixture at 60 °C was accompanied by the complete replacement of the bis(trimethylsilyl)amide ligands to form the homoligand ionic complex [LY(thf)₃]⁺[L₂Y]^– (3). The structure of the latter was established by X-ray diffraction analysis.     

Synthesis and molecular structures of dinuclear complexes with 1,2-dihydro-1,2-diphenyl-naphtho[1,8-c,d]1,2-diphosphole as a bridging ligand

A bisphosphine in which a PhP-PPh bond bridges 1,8-positions of naphthalene, 1,2-dihydro-1,2-diphenyl-naphtho[1,8-cd]-1,2-diphosphole (1), was used as a bridging ligand for the preparation of dinuclear group 6 metal complexes. Free trans-1, a more stable isomer having two phenyl groups on phosphorus centers mutually trans with respect to a naphthalene plane, was allowed to react with two equivalents of M(CO)₅(thf) (M = W, Mo, Cr) at room temperature to give dinuclear complexes (OC)₅M(μ-trans-1)M(CO)₅ (M = W (2a), Mo (2b), Cr (2c)). The preparation of the corresponding dinuclear complexes bridged by the cis isomer of 1 was also carried out starting from the free trans-1 in the following way. Mono-nuclear complexes M(trans-1)(CO)₅ (M = W (3a), Mo (3b), Cr (3c)) which had been prepared by a reaction of trans-1 with one equivalent of the corresponding M(CO)₅(thf) (M = W, Mo, Cr) complex, were heated in toluene, wherein a part of the trans-3a-c was converted to their respective cis isomer M(cis-1)(CO)₅. Each cis trans mixture of the mono-nuclear complexes 3a-c was treated with the corresponding M(CO)₅(thf) to give a cis trans mixture of the respective dinuclear complexes 2a-c. The cis isomer of the ditungsten complex 2a was isolated, and its molecular structure was confirmed by X-ray analysis, showing a shorter W?W distance of 5.1661(3) Å than that of 5.8317(2) Å in trans-2a.     

New ferromagnetic dinuclear triply-bridged copper(II) compounds containing carboxylato bridges: Synthesis,X-ray structure and magnetic properties

The new triply-bridged dinuclear copper(II) complexes, [Cu₂(μ-O₂CH)(μ-OH)₂(dpyam)₂](ClO₄) · H₂O (1), [Cu₂(μ-O₂CCH₃)(μ-OH)(μ-OH₂)(dpyam)₂](S₂O₈) (2), [Cu₂(μ-O₂CCH₃)(μ-OH)(μ-OH₂)(bpy)₂](NO₃)₂ (3), [Cu₂(μ-O₂CCH₃)(μ-OH)(μ-OH₂)(phen)₂](BF₄)₂ · 0.5H₂O (4), [Cu₂(μ-O₂CCH₂CH₃)(μ-OH)(μ-OH₂)(phen)₂](NO₃)₂ (5) and [Cu₂(μ-O₂CCH₃)(μ-OH)(μ-Cl)(bpy)₂]Cl · 8.5H₂O (6) (dpyam = di-2-pyridylamine, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline), have been synthesized and characterized crystallographically and also their spectroscopic and magnetic properties have been studied. A structural classification of this type of dimers, based on the data obtained from X-ray diffraction analysis in the present work and those reported in the literature has been performed. In these complexes, the local geometry around the copper centre is generally a distorted square pyramid and distorted trigonal bipyramid with different degrees of distortion. The global geometry of the dinuclear complexes can be described in terms of the relative arrangement of the two five-coordinate environments, giving rise to different classes (A–F) of complexes. The most logical explanations have been provided for each class describing different magnetic interactions. Practically, there is a clear correlation between structural data and J values of the class B complexes. Extended Hückel calculations were performed for the present complexes 1–6, as well as for some other class B complexes, showing the different molecular orbitals involved in their corresponding frontier orbitals, together with their energy. The results are found to be useful for the proper interpretation and correlation of the magnetic data and the dinuclear structure of the present complexes.