[Ru(NHC)(P-P)(CO)HF] (NHC = N-heterocyclic carbene; P-P = xantphos, dppf) complexes: Efforts to prepare new hydrodefluorination catalysts

The ruthenium N-heterocyclic carbene (NHC) hydride fluoride complexes Ru(NHC)(P-P)(CO)HF (NHC = ICy (3), IEt₂Me₂ (5), P-P = xantphos; NHC = ICy (7), P-P = dppf) have been prepared by treatment of the corresponding dihydride complexes [Ru(NHC)(P-P)(CO)H₂] (NHC = ICy (2), IEt₂Me₂ (4) P-P = xantphos; NHC = ICy (6), P-P = dppf) with Et₃N·3HF. In all cases, the hydride fluoride complexes exist in solution as two conformers or isomers. Although 3, 5 and 7 could be converted back to 2, 4 and 6, respectively, by heating with Et₃SiH, efforts to generate a catalytic cycle for the hydrodefluorination of aromatic fluorocarbons by subsequent reaction of Ru(NHC)(P-P)(CO)H₂ with C₆F₆ were prevented by the much more favourable cyclometallation of the carbene ligand.     

Metallaheteroborane clusters of group 5 transition metals derived from dichalcogenide ligands

Treatment of group 5 metal polychlorides such as, [Cp_nMCl_4-x] (M = V: n, x = 2; M = Nb: n = 1, x = 0), or [Cp∗TaCl₄] (Cp = η⁵-C₅H₅, Cp∗ = η⁵-C₅Me₅), with [LiBH₄·THF] followed by thermolysis in the presence of diphenyl diselenide yielded metallaheteroborane clusters [{CpV(μ-SePh)}₂(μ-Se)], 1 [(CpNb)₂B₄H₉(μ-SePh)], 2 and [(Cp∗Ta)₂B₄H₁₁(SePh)], 3 in modest yields. Compound 1 is an organovanadium selenolato cluster in which two (CpV) moieties bridged by (μ-Se) and two (μ-SePh) ligands. Compound 2 exhibits a bicapped tetrahedral core with one (μ-SePh) ligand. 3 is a tantalahexaborane cluster in which one of the terminal BH protons is substituted by SePh. Compounds 1-3 have been characterized by mass spectrometry, ¹H, ¹¹B, ¹³C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis of 1-3.     

Cyclometalated platinum(II) complexes containing monodentate phosphines: antiproliferative study

Reaction of cyclometalated platinum(II) precursor [Pt(C^N)Cl(dmso)], 1, C^N = N(1), C(2′)-chelated deprotonated 2-phenylpyridine and dmso = dimethylsulfoxide, with 1 equivalent of triphenyl phosphine, PPh₃, or 1,3,5-triaza-7-phosphaadamantane, PTA, gave the complex [Pt(C^N)Cl(PPh₃)], 2, or [Pt(C^N)Cl(PTA)], 3, respectively. On the basis of careful multinuclear NMR spectroscopy, supported by a number of 2D NMR experiments, structures of the complexes 2 and 3 in solution were determined to be neutral four coordinate. The X-ray crystallography indicated that the solid-state structure of complex 3 comprised a common square-planar geometry around platinum(II). Cytotoxicity of the complexes 2 and 3 was studied in three human cancer cell lines derived from ovarian carcinoma (CH1), lung carcinoma (A549), and colon carcinoma (SW480).     

Synthesis and characterization of aluminum complexes of 2-pyrazol-1-yl-ethenolate ligands

The synthesis and the characterization of some new aluminum complexes with bidentate 2-pyrazol-1-yl-ethenolate ligands are described. 2-(3,5-Disubstituted pyrazol-1-yl)-1-phenylethanones, 1-PhC(O)CH₂-3,5-R₂C₃HN₂ (1a, R = Me; 1b, R = Bu^t), were prepared by solventless reaction of 3,5-dimethyl pyrazole or 3,5-di-tert-butyl pyrazole with PhC(O)CH₂Br. Reaction of 1a or 1b with (R¹ = Me, Et) yielded N,O-chelate alkylaluminum complexes (2a, R = R¹ = Me; 2b, R = Bu^t, R¹ = Me; 2c, R = Me, R¹ = Et). Compound 1a was readily lithiated with LiBuⁿ in thf or toluene to give lithiated species 3. Treatment of 3 with 0.5 equiv of MeAlCl₂ or AlCl₃ yielded five-coordinated aluminum complexes [XAl(OC(Ph)CH{(3,5-Me₂C₃HN₂)-1})₂] (4, X = Me; 5, X = Cl). Reaction of 5 with an equiv of LiHBEt₃ generated [Al(OC(Ph)CH{(3,5-Me₂C₃HN₂)-1})₃] (6). Complex 6 was also obtained by reaction of 3 with 1/3 equiv of AlCl₃. Treatment of 5 with 2 equiv of AlMe₃ yielded complex 2a, whereas with an equiv of AlMe₃ afforded a mixture of 2a and [Me(Cl)AlOC(Ph)CH{(3,5-Me₂C₃HN₂)-1}] (7). Compounds 1a, 1b, 2a-2c and 4-6 were characterized by elemental analyses, NMR and IR (for 1a and 1b) spectroscopy. The structures of complexes 2a and 5 were determined by single crystal X-ray diffraction techniques. Both 2a and 5 are monomeric in the solid state. The coordination geometries of the aluminum atoms are a distorted tetrahedron for 2a or a distorted trigonal bipyramid for 5.     

Comparative reactivity studies of dppf-containing CpRu and (C6Me6)Ru complexes towards different donor ligands (dppf=1,1-bis(diphenylphosphino)ferrocene)

[CpRu(dppf)Cl] (Cp=η⁵-C₅H₅) (1) and [(HMB)Ru(dppf)Cl]PF₆ ((HMB)=η⁶-C₆Me₆) (3) react with different donor ligands to give rise to N-, P- and S-bonded complexes. The stoichiometric reactions of 1 and 3 with NaNCS give the mononuclear complexes [CpRu(dppf)(NCS)] (2) and [(HMB)Ru(dppf)(NCS)]PF₆ (4), respectively, in yields above 80%, while 3 also gives a dppf-bridged diruthenium complex [(HMB)Ru(NCS)₂]₂(μ-dppf) (5) in 67% yield from reaction with four molar equivalents of NaNCS. Compound 5 is also obtained in 70% yield from the reaction of 4 with excess NaNCS. With CH₃CN in the presence of salts, both 1 and 3 give their analogous solvento derivatives [CpRu(dppf)(CH₃CN)]BPh₄ (6) and [(HMB)Ru(dppf)(CH₃CN)] (PF₆)₂ (7). With phosphines, the reaction of 1 gives chloro-displaced complexes [(CpRu(dppf)L]PF₆ (L =PMe₃ (8), PMe₂Ph(9)), whereas the reaction of 3 with PMe₂Ph leads to substitution of dppf, giving [(HMB)Ru(PMe₂Ph)₂Cl] PF₆ (10). The reaction of 1 with NaS₂CNEt₂ gives a dinuclear dppf-bridged complex [{CpRu(S₂CNEt₂)}₂(μ-dppf)] (11), whereas that of 3 results in loss of the HMB ligand giving a mononuclear complex [Ru(dppf)(S₂CNEt₂)₂] (12). With elemental sulfur S₈, 1 is oxidized to give a dinuclear CpRu^III dppf-chelated complex [{CpRu(dppf)}₂(μ-S₂)](BPh₄)Cl (13), whereas 3 undergoes oxidation at the ligand, giving a dppf-displaced complex [(HMB)Ru(CH₃CN)₂Cl]PF₆ (14) and free dppfS₂. The structures of 1, 2, 5-9, 11, 13 and 14 were established by X-ray single crystal diffraction analyses. Of these, 5 and 11 both contain a dppf-bridge between Ru^II centers, while 13 is a dinuclear CpRu^III disulfide-bridged complex; all the others are mononuclear. All complexes obtained were also spectroscopically characterized.     

Coordination polymers and supramolecular structures in Ag(I)triflate-dppf systems (dppf=1,1-bis(diphenylphosphino)ferrocene)

The interaction of silver triflate (OTf⁻=SO₃(CF₃)⁻) and dppf [(C₅H₄PPh₂)₂Fe)] gave different complexes, depending on the stoichiometric proportions and reaction conditions. Under limiting dppf conditions, three different forms (1-3) of [Ag₂(OTf)₂(dppf)]_x were isolated. Single crystal X-ray diffraction analyses showed that the structure of 1 (x=2n) consists of a 2-D polymer comprising a tetra-silver basic unit, while that of 2 (x=2) possesses a discrete tetra-silver framework and that of 3 (x=n) is a linear polymer based on a di-silver repeating unit. The structures are supported by bridging dppf ligands and triflate groups. The crystal lattices of the compounds are stabilized by extensive intermolecular C-H?X hydrogen bonding (H=ring proton of Cp or Ph of dppf; X=O or F of OTf). [Ag(dppf)(OTf)] (4) and the structurally characterized mononuclear [Ag(dppf)₂](OTf) (5) were the sole products obtained from treatment of AgOTf with dppf in molar ratios of 1:1 and 1:2, respectively.     

A novel series of iridium complexes with alkenylquinoline ligands: Theoretical study on electronic structure and spectroscopic property

The ground and the lowest-lying triplet excited state geometries, electronic structures, and spectroscopic properties of a novel series of neutral iridium(III) complexes with cyclometalated alkenylquinoline ligands [(C^N)₂Ir(acac)] (acac = acetoylacetonate; C^N = 2-[(E)-2-phenyl-1-ethenyl]pyridine (pep) 1; 2-[(E)-2-phenyl-1-ethenyl]quinoline (peq) 2; 1-[(E)-2-phenyl-1-ethenyl]isoquinoline (peiq) 3; 2-[(E)-1-propenyl]pyridine (pp) 4; 2-[(E)-1-fluoro-1-ethenyl]pyridine (fpp) 5) were investigated by DFT and CIS methods. The highest occupied molecular orbital is composed of d(Ir) and π(C^N) orbital, while the lowest unoccupied molecular orbital is dominantly localized on C^N ligand. Under the TD-DFT with PCM model level, the absorption and phosphorescence in CH₂Cl₂ media were calculated based on the optimized ground and triplet excited state geometries, respectively. The calculated lowest-lying absorptions at 437 nm (1), 481 nm (2), 487 nm (3), 422 nm (4), and 389 nm (5) are attributed to a {[d_x²-y²(Ir) + d_xz(Ir) + π(C^N)] → [π∗(C^N)]} transition with metal-to-ligand/intra-ligand charge transfer (MLCT/ILCT) characters, and the calculated phosphorescence at 582 nm (1), 607 nm (2), 634 nm (3), 515 nm (4), and 491 nm (5) can be described as originating from the ³{[d_x²-y²(Ir) + d_xz(Ir) + π (C^N)] [π∗(C^N)]} excited state with the ³MLCT/³ILCT characters. The calculated results revealed that the phosphorescent color of these new Ir(III) complexes can be tuned by changing the π-conjugation effect strength of the C^N ligand.     

Synthesis, characterization and antitumor activity study of some cyclometalated organoplatinum(II) complexes containing aromatic N-donor ligands

A general approach has been designed to synthesize some mononuclear and binuclear cyclometalated platinum(II) complexes, containing aromatic N-donor ligands with the presence of one Cl⁻trans to carbon. In this way, cyclometalated platinum(II) complex [Pt(C^N)Cl(dmso)], 1, C^N = N(1),C(2′)-chelated, deprotonated 2-phenylpyridine and dmso = dimethylsulfoxide, was used as a precursor to react with imidazole derivatives (1-methylimidazole, 2a, imidazole, 2b,), monodentate pyridine derivatives (4-methylpyridine, 2c, pyridine, 2d,) and bidentate pyridine derivative (4,4′-bipyridine, 3 and 4,). Synthesized complexes were fully characterized by using multinuclear NMR spectroscopy (¹H, ¹³C{¹H} and ¹⁹⁵Pt), correlation NMR spectroscopy (¹H-¹H COSY, ¹³C{¹H}-¹H Heteronuclear Multiple Quantum Correlation, HMQC, Heteronuclear Multiple Bond Correlation, HMBC, ¹⁵N-¹H HETCOR), elemental analysis, X-ray crystallography and ESI-Mass spectrometry. Antitumor effects of mononuclear cyclometalated platinum(II) complexes 2a, 2c, 2d and 3 were determined on Jurkat, K562, and Raji cell lines and results showed reasonable cytotoxicities.     

Aluminum and zinc complexes supported by functionalized phenolate ligands: Synthesis, characterization and catalysis in the ring-opening polymerization of ε-caprolactone and rac-lactide

A series of aluminum and zinc complexes supported by functionalized phenolate ligands were synthesized and characterized. Reaction of 2-(3,5-R₂C₃N₂)C₆H₄NH₂ (R = Me, Ph) with salicylaldehyde or 3,5-di-tert-butylsalicylaldehyde afforded 2-((2-(1H-pyrazol-1-yl)phenylimino)methyl)phenol derivatives 2a-2d. Treatment of 2a-2d with an equiv. of AlR²₃ (R² = Me, Et) gave corresponding aluminum aryloxides 3a-3e, while reaction with an equiv. of ZnEt₂ afforded zinc aryloxides 4a-4d. Treatment of 2c with 0.5 equiv. of ZnEt₂ formed diphenolato zinc complex 5. All new compounds were characterized by ¹H and ¹³C NMR spectroscopy and elemental analyses. The structures of complexes 3a, 4a and 5 were further characterized by single crystal X-ray diffraction techniques. The catalytic activity of complexes 3-5 toward the ring-opening polymerization of ε-caprolactone was studied. The zinc complexes (4a-4d) exhibited higher catalytic activity than the aluminum complexes (3a-3e). The diphenolato zinc complex 5 showed lower catalytic activity than the ethylzinc complexes 4a-4d. The aluminum complex (3b) is inactive to initiate the ROP of rac-lactide, while the zinc complex (4d) is active initiator for the ROP of rac-lactide, giving atactic polylactide.     

Chiral organotin (IV) carboxylates complexes: Syntheses, characterization, and crystal structures with chiral (S)-(+)-6-methoxy-α-methyl-2-naphthaleneaceto acid ligand

Eight new organotin (IV) carboxylates, (R₃Sn)₄(nap)₄ (R = Me 1, n-Bu 2), [(R₃Sn) (nap)]_n (R = Ph 3, PhCH₂4), (R₂Sn) (nap)₂ (R = n-Bu 5, Ph 6, PhCH₂7) and {[R₂Sn(nap)]₂O}₂ (R = Me 8) (nap = (S)-(+)-6-methoxy-α-methyl-2-naphthaleneaceto anion) have been synthesized. All of the complexes have been characterized by elemental analysis, FT-IR, NMR (¹H, ¹³C and ¹¹⁹Sn) spectra. Among these complexes, complexes 1, 3, 5 and 8 were also characterized by X-ray crystallography diffraction analysis, and the data of X-ray crystallography diffraction indicated that complexes 1, 3 and 5 are new chiral organotin (IV) carboxylates complexes. The structural analyses show that complex 1 has a tetranuclear Sn₄O₈ macrocycle structure, complex 3 has a 1D spring-like chiral helical chain with a columnar channel, complex 5 possesses a dimer structure, and complex 8 has a supramolecular chainlike ladder structure through weak intermolecular non-covalent O^…O interactions.     

Synthesis and characterization of half-sandwich Rh, Ir complexes containing mono-thiolate-ortho-carborane ligand

Two binuclear complexes [Cp^∗M(Cl)Carb^S]₂ (Cp^∗ = η⁵-C₅Me₅, M = Rh (1a), Carb^S = SC₂(H)B₁₀H₁₀, Ir (1b)) were synthesized by the reaction of LiCarb^S with the dimeric metal complexes [Cp^∗MCl(μ-Cl)]₂ (M = Rh, Ir). Four mononuclear complexes Cp^∗M(Cl)(L)Carb^S (L = BuⁿPPh₂, M = Rh (2a), Ir (2b); L = PPh₃, M = Rh (4a), Ir (4b)) were synthesized by reactions of 1a or 1b with L (L = BuⁿPPh₂ (2); PPh₃ (4)) in moderate yields, respectively. Complexes 3a, 3b, 5a, 5b were obtained by treatment of 2a, 2b, 4a, 4b with AgPF₆ in high yields, respectively. All of these compounds were fully characterized by IR, NMR, and elemental analysis, and the crystal structures of 1a, 1b, 2a, 2b, 4a, 4b were also confirmed by X-ray crystallography. Their structures showed 3a, 3b and 5a, 5b could be expected as good candidates for heterolytic dihydrogen activation. Preliminary experiments on the dihydrogen activation driven by these half-sandwich Rh, Ir complexes were done under mild conditions.     

Ruthenium piano-stool complexes containing mono- or bidentate pyrrolidinylalkylphosphines and their reactions with small molecules

Ruthenium piano-stool complexes incorporating the new bidentate aminoalkylphosphine ligand 1,2-bis(dipyrrolidin-1-ylphosphino)ethane (dpyrpe, I) or its monodentate counterpart bis(pyrrolidin-1-yl)methylphosphine (pyr₂PMe, II) have been prepared, [(C₅R₅)RuCl(PP)] (R = Me and PP = dpyrpe, 1; R = Me and PP = (pyr₂PMe)₂, 2; R = H and PP = dpyrpe, 3). Complexes 2 and 3 have been characterized by X-ray crystallography. Complexes 1 and 2 react with NaBAr₄^f in the presence of ligand L to yield [Cp^∗Ru(L)(dpyrpe-κ²P)][BAr^f₄] (L = MeCN, 4a; CO, 4b; N₂, 4c) and [Cp^∗Ru(L)(pyr₂PMe)₂][BAr₄^f] (L = MeCN, 5a; CO, 5b; N₂, 5c). Complex 4a was crystallographically characterized. The CO complexes 4b and 5b were examined using IR spectroscopy in an attempt to establish the electron-donating capabilities of I and II. Complex 1 oxidatively adds H₂ in the presence of NaBAr₄^f to yield the Ru(IV) dihydride [Cp^∗RuH₂(dpyrpe-κ²P)][BAr₄^f], 7.     

Alkynyl Ti-M complexes with M = Cd and Hg: Synthesis, characterization, and reaction chemistry

The synthesis and properties of heterobimetallic Ti-Cd complexes of type {[Ti](μ-η¹:η²-CCR)₂}CdX₂ ([Ti] = Ti(η⁵-C₅H₄SiMe₃)₂; R = SiMe₃: 3a, X = Cl; 3b, X = Br; 3c, X = I; R = Fc: 3d, X = Br; Fc = Fe(η⁵-C₅H₄)(η⁵-C₅H₅) is reported. These compounds were accessible by treatment of [Ti](CCR)₂ (1a, R = SiMe₃; 1b, R = Fc) with the cadmium salts CdX₂ (2a, X = Cl; 2b, X = Br; 2c, X = I) in a 1:1 M ratio in diethyl ether. Dissolving, for example, 3b in tetrahydrofuran afforded coordination polymer [Cd(μ-Br)₂(thf)₂]_n (4) along with the tweezer molecule 1a. Treatment of 3b with two equiv of LiCCFc (5) gave {[Ti](μ-η¹:η²-CCSiMe₃)₂}Cd(CCFc)₂ (6) which eliminated at ambient temperature the all-carbon buta-1,3-diyne FcCC-CCFc (7) producing 1a and elemental Cd. The same reaction behavior was observed, when 2b was reacted with 5. The thus obtained bis(alkynyl) cadmium complex Cd(CCFc)₂ (8) is redox-active at low temperature producing 7 and Cd(0). When mercury halides HgX₂ (9a, X = Cl; 9b, X = Br) are used, then the titanocene dihalides [Ti]X₂ (10a, X = Cl; 10b, X = Br) together with Me₃SiCC-CCSiMe₃ (11) and Hg(0) were formed. Nevertheless, mercury acetylides were available by treatment of Hg(OAc)₂ (12) with HCCFc (13) in a 1:2 M ratio. Thus obtained Hg(CCFc)₂ (14) gave with [CuBr] (15) coordination polymer [{Hg(η²-CCFc)₂}(Cu₂(μ-Br)₂]_n (16), while with [AgPF₆] oxidation of the ferrocenyl moieties took place affording dicationic [Hg(CCFc)₂]²⁺ (18).The structures of 3b and 4 in the solid state are reported. Compound 3b shows the typical characteristics for heterobimetallic organometallic π-tweezer complexes with cadmium in a tetrahedral environment, while 4 corresponds to a one-dimensional coordination polymer in which the Cd(II) ions are linked in a edge-sharing fashion by bromide bridges in the pseudo-equatorial plane. The appropriate tetrahydrofuran molecules are completing the pseudo-octahedral coordination sphere at cadmium.The cyclic voltammogram of 14 is reported showing a single reversible redox event at E⁰ = 0.108 V with ΔE_p = 76 mV indicating that there is no communication between the Fc termini along the mercury acetylide unit.     

Synthesis and structures of dialkyl zirconium complexes with an [OSSO]-type bis(phenolate) ligand bearing a trans-1,2-cyclooctanediylbis(thio) unit

Dimethyl and bis[(trimethylsilyl)methyl] zirconium complexes ([OSSO]ZrR₂) [4, R = Me; 5, R = CH₂SiMe₃] having [OSSO]-type bis(phenolato) ligand 1 based on the trans-1,2-cyclooctanediylbis(thio) core have been synthesized by the reactions of the corresponding dichloro zirconium complex 3 with 2 equiv. of MeMgBr and Me₃SiCH₂MgCl, respectively, in Et₂O/toluene at −78 °C. The molecular structures of these complexes 3-5 were characterized by NMR spectroscopy, elemental analyses, and X-ray crystallography. ¹H and ¹³C NMR data of complexes 3-5 exhibited that they took the C₂-symmetry in solution in the NMR time scale. In the crystal structures of 3-5, each zirconium center lies at the center of a distorted octahedral coordination sphere with cis sulfur atoms and trans oxygen atoms, which adopts a cis-α [(Λ^∗,S^∗,S^∗)] configuration.     

Synthesis and structural characterization of 1′-(diphenylphosphino)ferrocene-1-carboxamide, its corresponding hydrazide, some heterocycles derived from the hydrazide and palladium(II) complexes with these functional phosphinoferrocene ligands

Two polar phosphinoferrocene ligands, 1′-(diphenylphosphino)ferrocene-1-carboxamide (1) and 1′-(diphenylphosphino)ferrocene-1-carbohydrazide (2), were synthesized in good yields from 1′-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) via the reactive benzotriazole derivative, 1-[1′-(diphenylphosphino)ferrocene-1-carbonyl]-1H-1,2,3-benzotriazole (3). Alternatively, the hydrazide was prepared by the conventional reaction of methyl 1′-(diphenylphosphino)ferrocene-1-carboxylate with hydrazine hydrate, and was further converted via standard condensation reactions to three phosphinoferrocene heterocycles, viz 2-[1′-(diphenylphosphino)ferrocen-1-yl]-1,3,4-oxadiazole (4), 1-[1′-(diphenylphosphino)ferrocen-1-carbonyl]-3,5-dimethyl-1,2-pyrazole (5), and 1-[1′-(diphenylphosphino)ferrocene-1-carboxamido]-3,5-dimethylpyrrole (6). Compounds 1 and 2 react with [PdCl₂(cod)] (cod = η²:η²-cycloocta-1,5-diene) to afford the respective bis-phosphine complexes trans-[PdCl₂(L-κP)₂] (7, L = 1; 8, L = 2). The dimeric precursor [(L^NC)PdCl]₂ (L^NC = 2-[(dimethylamino-κN)methyl]phenyl-κC¹) is cleaved with 1 to give the neutral phosphine complex [(L^NC)PdCl(1-κP)] (9), which is readily transformed into a ionic bis-chelate complex [(L^NC)PdCl(1-κ²O,P)][SbF₆] (10) upon removal of the chloride ligand with Ag[SbF₆]. Pyrazole 5 behaves similarly affording the related complexes [(L^NC)PdCl(5-κP)] (12) and [(L^NC)PdCl(5-κ²O,P)][SbF₆] (13), in which the ferrocene ligand coordinates as a simple phosphine and an O,P-chelate respectively, while oxadiazole 4 affords the phosphine complex [(L^NC)PdCl(4-κP)] (11) and a P,N-chelate [(L^NC)PdCl(4-κ²N³,P)][SbF₆] (14) under similar conditions. All compounds were characterized by elemental analysis and spectroscopic methods (multinuclear NMR, IR and MS). The solid-state structures of 1⋅½AcOEt, 2, 7⋅3CH₃CN, 8⋅2CHCl₃, 9⋅½CH₂Cl₂⋅0.375C₆H₁₄, 10, and 14 were determined by single-crystal X-ray crystallography.     

Rhodium(I) carbonyl complexes of quinoline carboxaldehyde ligands and their catalytic carbonylation reaction

The dimeric rhodium precursor [Rh(CO)₂Cl]₂ reacts with quinoline (a) and its three isomeric carboxaldehyde ligands [quinoline-2-carboxaldehyde (b), quinoline-3-carboxaldehyde (c), and quinoline-4-carboxaldehyde (d)] in 1:2 mole ratio to afford complexes of the type cis-[Rh(CO)₂Cl(L)] (1a-1d), where L = a-d. The complexes 1a-1d have been characterised by elemental analyses, mass spectrometry, IR and NMR (¹H, ¹³C) spectroscopy together with a single crystal X-ray structure determination of 1c. The X-ray crystal structure of 1c reveals square planar geometry with a weak intermolecular pseudo dimeric structure (Rh?Rh = 3.573 Å). 1a-1d undergo oxidative addition (OA) with different electrophiles such as CH₃I, C₂H₅I and I₂ to give Rh(III) complexes of the type [Rh(CO)(COR)Cl(L)I] {R = -CH₃ (2a-2d), R = -C₂H₅ (3a-3d)} and [Rh(CO)Cl(L)I₂] (4a-4d) respectively. 1b exhibits facile reactivity with different electrophiles at room temperature (25 °C), while 1a, 1c and 1d show very slow reactivity under similar condition, however, significant reactivity was observed at a temperature ∼40 °C. The complexes 1a-1d show higher catalytic activity for carbonylation of methanol to acetic acid and methyl acetate [Turn Over Frequency (TOF) = 1551-1735 h⁻¹] compared to that of the well known Monsanto’s species [Rh(CO)₂I₂]⁻ (TOF = 1000 h⁻¹) under the reaction conditions: temperature 130 ± 2 °C, pressure 33 ± 2 bar, 450 rpm and time 1 h. The organometallic residue of 1a-1d was also isolated after the catalytic reaction and found to be active for further run without significant loss of activity.     

Synthesis of two-coordinate iron aryloxides and their reactions with organic azide: Intramolecular C-H bond amination

The synthesis and reaction of homoleptic iron(II) complexes with 2,6-di-adamantyl-substituted aryloxides [OC₆H₂-2,6-Ad-4-R]⁻ ([OAr^AdR]⁻, Ad = adamantyl, R = Me, ⁱPr) are described. Monomeric two-coordinate iron aryloxides Fe(OAr^AdR)₂ (R = Me, 1; ⁱPr, 2) were synthesized by the reaction of Fe[N(SiMe₃)₂]₂ with 2 equiv of HOAr^AdR. Treatment of 1 and 2 with 1-azidoadamantane resulted in intramolecular insertion of an adamantyl nitrene into a methylene C-H bond of the aryloxide adamantyl substituent, yielding the corresponding amine-aryloxide complexes Fe(OAr^AdR)(OAr^AdR-NHAd) (R = Me, 3; ⁱPr, 4). Molecular structures of all these complexes are reported.     

Barium bis(5,5-dimethyl-1,1,1-trifluorohexane-2,4-dionate)(crown-ether) complexes: Synthesis,characterization and crystal structure

The preparation of the barium β-diketonate complexes with crown-ethers [Ba(pta)₂(18-crown-6)] (1), [Ba(pta)₂(18-crown-6)] (THF) (2), [Ba(pta)₂(18-dibenzocrown-6)](C₆H₅CH₃) (3), [Ba(pta)₂(18-dibenzocrown-6)] (4) (pta = 1,1,1-trifluoro-5,5-dimethylhexanedionato-2,4; 18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane; 18-dibenzocrown-6 = 6,7,9,10,17,18,20,21-octahydrodibenzo[b,k][1,4,7,10,13,16]-hexaoxacyclooctadecane) is described. The complexes 1 and 2 have been synthesized from reaction of metallic barium with 2 molar equiv. of Hpta and 1 molar equiv. of 18-crown-6 in toluene; the complexes 3 and 4 from reaction of Ba(OH)₂·8H₂O with 1 molar equiv. 18-dibenzocrown-6 and 2 molar equiv. Hpta. The complexes were characterized by elemental analyses, IR-spectroscopy, ¹H NMR spectroscopy. The crystal structures of 2 and 3 were determined by means of single-crystal X-ray diffraction methods. A single-crystal X-ray study of 2 and 3 has shown it be monomeric. The coordination number of Barium cation in 2 and 3 is nine owing to nine oxygen atoms from two pta ligands and crown-ether molecule.     

Targeting nitric oxide synthase with Tc/Re-tricarbonyl complexes containing pendant guanidino or isothiourea moieties

The visualization of inducible nitric oxide synthase (iNOS) in vivo with specific radioactive probes could provide a valuable insight into the diseases associated with upregulation of this enzyme. Aiming at that goal, we have synthesized a novel family of conjugates bearing a pyrazolyl-diamine chelating unit for stabilization of the fac-[M(CO)₃]⁺ core (M = ^99mTc, Re) and pendant guanidino (L¹ = guanidine, L² = N-hydroxyguanidine, L³ = N-methylguanidine, L⁴ = N-nitroguanidine) or S-methylisothiourea (L⁵) moieties for iNOS recognition. L¹-L⁵ reacted with fac-[M(CO)₃(H₂O)]⁺, yielding complexes of the type fac-[M(CO)₃(k³-L)]⁺ (M = Re/^99mTc; 1/1a, L = L¹; 2/2a, L = L²; 3/3a, L = L³; 4/4a, L = L⁴; 5/5a, L = L⁵), which were fully characterized by the usual analytical methods in chemistry and radiochemistry, including X-ray diffraction analysis in the case of 1. The rhenium complexes 1-5 were prepared as “cold” surrogates of the ^99mTc(I) complexes. Enzymatic assays with murine purified iNOS demonstrated that L¹, L², 1 and 2 are poor NO-producing substrates. These assays have also shown that metallation of L⁴ and L⁵ (K_i > 1000 μM) gave complexes with increased inhibitory potency (4, K_i = 257 μM; 5, K_i = 183 μM). The organometallic rhenium complexes permeate through LPS-treated RAW 264.7 macrophage cell membranes, interacting specifically with the target enzyme, as confirmed by the partial suppression of NO biosynthesis (ca. 20% in the case of 4 and 5) in this cell model. The analog ^99mTc(I)-complexes 1a-5a are stable in vitro, being also able to cross cell membranes, as demonstrated by internalization studies in the same cell model with compound 4a (4h, 37 °C; 33.8% internalization). Despite not being as effective as the α-amino-acid-containing metal-complexes previously described by our group, the results reported herein have shown that similar ^99mTc(I)/Re(I) organometallic complexes with pendant amidinic moieties may hold potential for targeting iNOS expression in vivo.     

Influence of multidentate N-donor ligands on highly electrophilic zinc initiator for the ring-opening polymerization of epoxides

A set of multidentate ligands have been synthesized and used to stabilize the putative highly electrophilic zinc species initiating ring-opening polymerization (ROP) of cyclohexene oxide (CHO) and propylene oxide (PO). Reaction of the bidentate C₂-chiral bis(oxazoline) ligand (^R2,R3BOX: R₂ = (4S)-tBu, R₃ = H (a); R₂ = (4S)-Ph, R₃ = H (b); R₂ = (4R)-Ph, R₃ = (5S)-Ph (c)) with Zn(R₁)₂ (R₁ = Et (1), Me (2)) led to the heteroleptic three-coordinate complexes (^R2,R3BOX)ZnR₁, 1a-c and 2a, which were isolated in 92-96% yield. Next, two pyridinyl-functionalized N-heterocyclic carbene (NHC) ligands have been designed and synthesized: the 1,3-bis(2-pyridylmethyl)imidazolinium salt (d) and the protected NHC adduct 2-(2,3,4,5,6-pentafluorophenyl)-1,3-bis(2-pyridylmethyl)imidazolidine (e). The reaction of ligands d and e with ZnEt₂ led directly to the formation of (NHC)ZnEt(Cl) 3d complex with ethane elimination and the adduct (NHC-C₆F₅(H))ZnEt₂4e, respectively, in high yield. In situ combinations of selected complexes 1a-c, 3d and 4e with B(C₆F₅)₃ (1 or 2 equivalents) give active systems for ROP, with high productivity (3.3-5.9 10⁶ g_polym. mol_Zn⁻¹ h⁻¹) and high molecular weight (M_n up to 132 10³ g mol⁻¹) for CHO polymerization. Although the in situ B(C₆F₅)₃-activated zinc species were not isolated, the sterically demanding BOX ligands (1c > 1b > 1a) and functionalized NHC ligands seem to enhance the stability of highly electrophilic zinc complexes over ligand redistribution, allowing a better control of the cationic ROP as reflected particularly for 3d and 4e complexes by their respective efficiency (42-88%).