Synthesis and electrochemistry of phenyl-functionalized diiron propanedithiolate complexes with bidentate phosphine ligands

Carbonyl substitution reactions of [μ-(SCH₂)₂CHC₆H₅]Fe₂(CO)₆ with bidentate phosphine ligands, cis-1,2-bis(diphenylphosphine)ethylene (cis-dppv) and N,N-bis(diphenylphosphine)propylamine [(Ph₂P)₂N-Pr-n], yielded an asymmetrically substituted chelated complex [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(k ²-dppv) and a symmetrically substituted bridging complex [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄[μ-(PPh₂)₂N-Pr-n] under different reaction conditions. Both complexes were fully characterized by spectroscopic methods and by X-ray crystallography. Their electrochemical behaviors were observed by cyclic voltammetry, and the catalytic electrochemical reduction of protons from acetic or trifluoroacetic acid to give dihydrogen mediated by complex [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(k ²-dppv) was investigated.     

Nickel complexes of carboxylate-containing polydentate ligands as models for the active site of urease

Two new carboxylate-containing polydentate ligands have been synthesized, the symmetric ligand 2,6-bis[N-(N-(carboxylmethyl)-N-((1-methylimidazol)methyl)amine)methyl]-4-methylphenolate (BCIMP) and the corresponding asymmetric ligand 2-(N-isopropyl-N-((1-aminomethyl)-4-methylphenol (ICIMP). The ligands have been used to prepare model complexes for the active site of the dinuclear nickel enzyme urease, viz. [Ni(2)(BCIMP)Ac(2)](-) (6), [Ni(2)(BCIMP)(Ph(2)Ac)(2)](-) (7), [Ni(2)(ICIMP)(Ph(2)Ac)(2)] (14), [Ni(4)(ICIMP)(2)(Ph(2)Ac)(2)][ClO(4)](2) (15), [Ni(4)(ICIMP)(2)(Ph(2)Ac)(2)(DMF)(2)][ClO(4)](2) (16), and [Ni(4)(ICIMP)(2)(Ph(2)Ac)(2)(urea)(H(2)O)][ClO(4)](2) (17), where the latter complex contains urea coordinated in a unidentate fashion through the carbonyl oxygen. The N(2)O-N(2)O(2) donor set of ICIMP provides a good framework for the preparation of urease models, but in some cases tetranuclear nickel complexes are formed due to coordination of the carboxylate moiety of one dinickel-ICIMP unit to one or both of the nickels of a second Ni(2) unit. Reactivity and kinetics studies of 7 and 15 show that these model complexes catalyze hydrolysis of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) at basic pH. In this assay, complexes based on the asymmetric ligand ICIMP exhibit a significantly faster rate of hydrolysis than the corresponding BCIMP complexes. Magnetic measurements indicate that there are weak antiferromagnetic interactions between the nickel ions in complex 16.     

Reduction of the pertechnetate anion with bidentate phosphine ligands

The reduction of ammonium pertechnetate with bis(diphenylphosphino)methane (dppm), and with diphenyl-2-pyridyl phosphine (Ph(2)Ppy), has been investigated. The neutral Tc(II) complex, trans-TcCl(2)(dppm)(2) (1), has been isolated from the reaction of (NH(4))[TcO(4)] with excess dppm in refluxing EtOH/HCl. Chemical oxidation with ferricinium hexafluorophosphate results in formation of the cationic Tc(III) analogue, trans-[TcCl(2)(dppm)(2)](PF(6)) (2). The dppm ligands adopt the chelating bonding mode in both complexes, resulting in strained four member metallocycles. With excess PhPpy, the reduction of (NH(4))[TcO(4)] in refluxing EtOH/HCl yields a complex with one chelating Ph(2)Ppy ligand and one unidentate Ph(2)Ppy ligand, mer-TcCl(3)(Ph(2)Ppy-P,N)(Ph(2)Ppy-P) (3). The cationic Tc(III) complexes, trans-[TcCl(2)(Ph(2)P(O)py-N,O)(2)](PF(6)) (4) and trans-[TcCl(2)(dppmO-P,O)(2)](PF(6)) (5) (Ph(2)P(O)py = diphenyl-2-pyridyl phosphine monoxide and dppmO = bis(diphenylphosphino)methane monoxide), have been isolated as byproducts from the reactions of (NH(4))[TcO(4)] with the corresponding phosphine. The products have been characterized in the solid state and in solution via a combination of single-crystal X-ray crystallography and spectroscopic techniques. The solution state spectroscopic results are consistent with the retention of the bonding modes revealed in the crystal structures.     

Ruthenium bidentate phosphine complexes for the coordination and catalytic dehydrogenation of amine- and phosphine-boranes

Addition of the amine–boranes H₃B ? NH₂tBu, H₃B ? NHMe₂ and H₃B ? NH₃ to the cationic ruthenium fragment [Ru(xantphos)(PPh₃)(OH₂)H][BAr^F₄] ( 2 ; xantphos=4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene; BAr^F₄=[B{3,5‐(CF₃)₂C₆H₃}₄]^?) affords the η¹‐B? H bound amine–borane complexes [Ru(xantphos)(PPh₃)(H₃B ? NH₂tBu)H][BAr^F₄] ( 5 ), [Ru(xantphos)(PPh₃)(H₃B ? NHMe₂)H][BAr^F₄] ( 6 ) and [Ru(xantphos)(PPh₃)(H₃B ? NH₃)H][BAr^F₄] ( 7 ). The X‐ray crystal structures of 5 and 7 have been determined with [BAr^F₄] and [BPh₄] anions, respectively. Treatment of 2 with H₃B ? PHPh₂ resulted in quite different behaviour, with cleavage of the B? P interaction taking place to generate the structurally characterised bis‐secondary phosphine complex [Ru(xantphos)(PHPh₂)₂H][BPh₄] ( 9 ). The xantphos complexes 2 , 5 and 9 proved to be poor precursors for the catalytic dehydrogenation of H₃B ? NHMe₂. While the dppf species (dppf=1,1′‐bis(diphenylphosphino)ferrocene) [Ru(dppf)(PPh₃)HCl] ( 3 ) and [Ru(dppf)(η⁶‐C₆H₅PPh₂)H][BAr^F₄] ( 4 ) showed better, but still moderate activity, the agostic‐stabilised N‐heterocyclic carbene derivative [Ru(dppf)(ICy)HCl] ( 12 ; ICy=1,3‐dicyclohexylimidazol‐2‐ylidene) proved to be the most efficient catalyst with a turnover number of 76 h^?1 at room temperature.     

Synthesis and characterisation of nonclassical ruthenium hydride complexes containing chelating bidentate and tridentate phosphine ligands

The synthesis and characterisation of nonclassical ruthenium hydride complexes containing bidentate PP and tridentate PCP and PNP pincer-type ligands are described. The mononuclear and dinuclear ruthenium complexes presented have been synthesised in moderate to high yields by the direct hydrogenation route (one-pot synthesis) or in a two-step procedure. In both cases [Ru(cod)(metallyl)(2)] served as a readily available precursor. The influences of the coordination geometry and the ligand framework on the structure, binding, and chemical properties of the M--H(2) fragments were studied by X-ray crystal structure analysis, spectroscopic methods, and reactivity towards N(2), D(2), and deuterated solvents.     

Binuclear Copper(II) Complexes in which other copper(II) complexes are coordinated as bidentate ligands

Twelve new copper(II) complexes in which N,N′-bis-(2-pyridylmethyl)-oxamidatocopper(II) or N,N′-bis(2-pyridylethyl)-oxamidatocopper(II) coordinates as a bidentate ligand have been isolated and characterized. These complexes have a structure bridged by the oxamide group (including two tetranuclear complexes formed by olation of two binuclear complexes, of. Fig. 1), and possess Cu? Cu interaction resulting in a sub-normal magnetic moment at room temperature. In one of them, [Cu₂(PMoxd) (bipy)₂] (NO₃)₂ (cf. Fig. 2), each copper(II) ion has a five-coordinated environment.     

Reactivity of allylphosphines with iridium complexes: Diallylphosphines as new bidentate ligands

Addition of four equivalents of t-butyldiallylphosphine 1a to a solution of one equivalent of [(COE)₂IrCl]₂ in CHCl₃ at low temperature produced two isomers of thecomplex [t-Bu(C₃H₅)PCH₂CH=CH)]IrHCl(COE)-[PtBu(C₃H₅)₂] ( 2a ), which evolve at 40°C to [t-Bu(C₃H₅)PCH₂CH=CH)]IrCl(C₈H₁₅)[PtBu(C₃H₅)₂] ( 3a ), by a hydride transfer from iridium to the cyclooctene (COE) ligand. It is reasonable that the unsaturation at the iridium center is fulfilled by interactions with the allyl moieties of the phosphine that are not metalated. This has been demonstrated by bubbling CO into a solution of 3a in CHCl₃ at room temperature to obtain the carbonyl complex [t-Bu(C₃H₅)-PCH₂CH=CH)]Ir(CO)Cl(C₈H₁₅)[PtBu(C₃H₅)₂] ( 4a ). Under the same conditions, the reaction of diisopropylamindiallylphosphine 1b and anisyldiallylphosphine 1c afforded a mixture of isomers 3b and 3c , respectively. These results show that diallylphosphines can be considered to be a new family of bidentate ligands. Finally, the reaction of these phosphines with [(COD)IrCl]₂ (COD = 1,5 cyclooctadiene) shows the formation of tetracoordinated iridium (I) complexes IrCl(COD)(PR3), which are thermally stable. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:253–259, 1998     

Bio-inspired hydrogenase models: mixed-valence triion complexes as proton reduction catalysts

Mixed-valence triiron complexes Fe(3)(CO)(7-x)(PPh(3))(x)(μ-edt)(2) (x = 0-2) have been prepared and are shown to act as proton reduction catalysts. Catalysis takes place via an ECEC mechanism with a reduced overpotential of ca. 0.45 V for Fe(3)(CO)(7)(μ-edt)(2) as compared to the corresponding diiron complex.     

Effect of dentate number of anchored phosphine ligands on the composition and catalytic properties of their palladium complexes

Mono-, di- and triphosphine ligands anchored by a Si–C bond to the surface of silica have been synthesized. Complexes of Pd(II) and Pd(O) with these ligands have been obtained. On the basis of elemental analysis and UV spectroscopy, structures of the complexes formed are suggested. The catalytic properties of the above complexes in the selective hydrogenation of cyclopentadiene are compared.

---

-, - , Si–C . Pd(II) Pd(O) . - . .

     

Titanium complexes bearing bidentate benzimidazole-containing ligands and their behavior in ethylene polymerization

A series of potentially bidentate benzimidazolyl ligands of the type (Bim)CH₂D (where Bim = benzimidazolyl and D = NMe₂L1, NEt₂L2, NPrⁱ₂L3, OMe L4 and SMe L5) has been reacted with Ti(NMe₂)₄ to give five- and six-coordinate Ti(IV) complexes of the type [(Bim)CH₂D]Ti(NMe₂)₃ and [(Bim)CH₂D]₂Ti(NMe₂)₂, respectively. The X-ray structures of [(Bim)CH₂OMe]Ti(NMe₂)₃, [(Bim)CH₂NMe₂]₂Ti(NMe₂)₂ and [(Bim)CH₂OMe)]₂Ti(NMe₂)₂ are reported along with an evaluation of their behavior in ethylene polymerization.     

Template controlled self-assembly of bidentate phosphine complexes with hemilabile coordination behaviour

Template-assisted self-assembly of ditopic catechol phosphines creates complexes containing a chelating diphosphine ligand, which display hemilabile coordination properties with prospects for applications in catalysis.     

Pd(II) complexes with mixed benzothiazolin-2-ylidene and phosphine ligands and their catalytic activities toward C-C coupling reactions

Novel Pd(II) mixed N,S-heterocyclic carbene (NSHC)-phosphine complexes of the general formula [PdBr(2)(NSHC)(PR(3))] were obtained from bridge cleavage of dinuclear NSHC complexes of type [PdBr(2)(NSHC)](2) [NSHC = 3-benzylbenzothiazolin-2-ylidene and 3-propylbenzothiazolin-2-ylidene] with triphenylphosphine, tricyclohexylphosphine and 2-diphenylphosphanyl-pyridine. All complexes have been fully characterized by (1)H and (13)C NMR spectroscopy, ESI mass spectrometry and elemental analysis. The X-ray crystal structures of complexes 3-8 are reported. The complexes exhibit moderate to good catalytic activity in the Suzuki-Miyaura coupling reaction of aryl bromides and chlorides.     

Heterobimetallic complexes as oxygen donor bidentate ligands: synthesis of early-late trinuclear complexes

The early-late heterometallic complexes [TiCp^∗((OCH₂)₂Py)(μ-O)M(COD)] (M = Rh, Ir) behave as four-electron donor ligands yielding the polynuclear cationic complexes [TiCp^∗(OCH₂)₂ Py(μ-O){M(COD)}₂]OTf (M = Rh (1), Ir (2)). The molecular structure of complex 1 has been established through an X-ray diffraction study.     

Synthesis,characterization, thermal,electrochemical, and DFT studies of mononuclear cyclopalladated complexes containing bidentate phosphine ligands and their biological evaluation as antioxidant and antibacterial agents

The non-symmetric phosphorus ylides and their Pd(II) complexes have been synthesized as potential antioxidant and antibacterial compounds and their structures were elucidated using a variety of physicochemical techniques. The reaction of 1 equiv non-symmetric phosphorus ylides, Ph₂PCH₂PPh₂C(H)C(O)PhX (X = Br (Y¹), Cl (Y²), NO₂ (Y³), OCH₃ (Y⁴)) with [Pd(dppe)Cl₂] (M¹), followed by treatment with 2 equiv AgOTf led to monomeric chelate complexes, [(dppe)Pd(Ph₂PCH₂PPh₂C(H)C(O)PhX)] (OSO₂CF₃)₂ (X = Br (C¹), Cl (C²), NO₂ (C³), OCH₃ (C⁴)), which contain a five-membered P,P chelate ring in one side and a five-membered P,C chelate ring in the other side. Palladium ion complexes were synthesized and investigated by cyclic voltammetry, FT-IR, UV–visible, multinuclear (¹H, ³¹P and ¹⁹F) NMR, thermal analysis and ESI-mass spectroscopic studies. Some complexes and ligands have been studied by powder XRD and single crystal X-ray diffraction techniques. FT-IR and ³¹P NMR studies revealed that the ylides Y are coordinated to the metal ions via the terminal phosphorus (P_c) of the ylides and methene group (CH). The proposed coordination geometry around the Pd atom in these complexes is defined as slightly distorted square planar by UV-Visible and DFT studies. Thermal stability of all complexes was also shown by TG/DTG methods. Furthermore, the electrochemical behavior of the complexes was investigated by cyclic voltammetry. The results indicate that all complexes are successfully synthesized from the initial ligands. All complexes were analyzed for their antioxidant properties by DPPH free radical scavenging assay. In addition, the antibacterial effects of the hexane-solved complexes were investigated by disc diffusion method against four Gram positive and negative bacteria. All complexes represented antibacterial activity against bacteria tested especially on Gram positive ones. A theoretical study on the structure, ¹H and ³¹P NMR chemical shifts and the interaction energy between the Pd²⁺ ion and ligands dppe and ylide Y is also reported.     

Synthesis of nickel complexes with bidentate N,O-type ligands and application in the catalytic oligomerization of ethylene

The dinuclear complexes [Ni(micro-Cl){(4,5-dihydro-4,4-dimethyloxazol-2-yl)methanol}](2)Cl(2) and [Ni(micro-Cl){(pyridin-2-yl)methanol}](2)Cl(2) 16 have been synthesized in high yields by reaction of NiCl(2) with 2 mol. equiv. of the ligands 4,5-dihydro-4,4-dimethyloxazol-2-yl)methanol 13 or (pyridin-2-yl)methanol 15, respectively. The reaction of NiCl(2) with 3 mol. equiv. of 15 afforded in high yield the mononuclear, octahedral mer-[Ni{(pyridin-2-yl)methanol}(3)Cl(2)] complex 18. The reaction of 16 with NaH led to the deprotonation of one of the pyridine alcohol ligands to form [Ni{(pyridin-2-yl)methanol}{(pyridin-2-yl)methanolate}Cl] 21 in which the metal is coordinated by one pyridine alcohol and one pyridine alcoholate ligand. The crystal structures of the dinuclear, chloride-bridged octahedral complexes in 14.C(6)H(12) and in 16.3CH(2)Cl(2) and of the mononuclear, octahedral complex 18 in 18.CH(2)Cl(2) have been determined by X-ray diffraction. In the latter case, intermolecular OH...Cl bonding interactions generate a centrosymmetric pseudo-dimer. Complexes 14, 16, and 21 have been tested in ethylene oligomerization with AlEtCl(2) (Al/Ni ratios of 2, 4 or 6) or MAO (50, 100 or 200 equiv.) as co-catalysts under 10 bar of ethylene and yielded mostly dimers and trimers. Complex 16 in the presence of 6 equiv. of AlEtCl(2) proved to be the most active system with a turnover frequency (TOF) up to 187 500 C(2)H(4) (mol Ni h)(-1). Complex 16 with 200 equiv. of MAO was also the most active, with TOF up to 104 300 C(2)H(4) (mol Ni h)(-1) under 30 bar of ethylene.     

Preparation of hydride complexes of ruthenium with bidentate phosphite ligands

Hydride complex RuH₂(PFFP)₂ (1) [PFFP = (CF₃CH₂O)₂PN(CH₃)N(CH₃)P(OCH₂CF₃)₂] was prepared by allowing the compound RuCl₄(bpy) · H₂O (bpy = 1,2-bipyridine) to react first with the phosphite PFFP and then with NaBH₄. Chloro-complex RuCl₂(PFFP)₂ (2) was also prepared, either by reacting RuCl₄(bpy) · H₂O with PFFP and zinc dust or by substituting triphenylphosphine with PFFP in the precursor complex RuCl₂(PPh₃)₃. Hydride derivative RuH₂(POOP)₂ (3) (POOP = Ph₂POCH₂CH₂OPPh₂) was prepared by reacting compound RuCl₃(AsPh₃)₂(CH₃OH) first with the phosphite POOP and then with NaBH₄. Depending on experimental conditions, treatment of carbonylated solutions of RuCl₃ · 3H₂O with POOP yields either the cis- or trans-RuCl₂(CO)(PHPh₂)(POOP) (4) derivative. Reaction of both cis- and trans-4 with LiAlH₄ in thf affords dihydride complex RuH₂(CO)(PHPh₂)(POOP) (5). Chloro-complex all-trans-RuCl₂(CO)₂(PPh₂OMe)₂ (6) was obtained by reacting carbonylated solutions of RuCl₃ · 3H₂O in methanol with POOP. Treatment of chloro-complex 6 with NaBH₄ in ethanol yielded hydride derivative all-trans-RuH₂(CO)₂(PPh₂OMe)₂ (7). The complexes were characterised spectroscopically and the X-ray crystal structures of complexes 1, 3, cis-4 and 6 were determined.     

The synthesis of some bidentate ligands containing both phosphine and nitrile groups

Both (C₆H₅)₂P(CH₂)₃CN and (C₆H₅)₂P(CH₂)₄CN have been obtained from the reaction of Br(CH₂)_nCN (n = 3, 4) with (C₆H₅)₂POCH₃ followed by reduction with (C₆H₅)₂SiH₂. These phosphine-nitrile ligands form L₂PdCl₂ complexes which are shown by IR measurements to have trans geometries with the phosphine portions of the ligands coordinated. Reactions of o-BrC₆H₄CN with CH₃(CH₂)₃Li followed by R₂PCl (R = C₆H₅ or (CH₃)₂N) have been used to provide good yields of the corresponding R₂P-o-C₆H₄CN products.     

Photoinduced intramolecular proton transfer of phenol-containing ligands and their zinc complexes

N,N'-Bis(salicylidene)hydrazine (L(I)), a bis-2-hydroxybenzene-type ligand H2L, its tert-butyl derivative (L(II)), and the corresponding Zn2+ complexes of the type Zn2(LH)2L (Zn-I and Zn-II) were synthesized. The molecular structure of Zn-II was determined by X-ray crystallography at -170 degrees C. The photoreactions of the four compounds in solution were studied by time-resolved UV-vis spectroscopy using nanosecond laser pulses. A weak but strongly Stokes shifted fluorescence signal of the ligands L(I) or L(II) is suggested to be due to excited-state intramolecular proton transfer (ESIPT) from the phenolic hydroxy group to the nitrogen of the methine bond in analogy to the fast enol --> keto tautomerization of other 2-hydroxybenzenes. A transient with the maximum at 480 nm, bleaching at 370 nm, and a lifetime of 0.01-0.3 ms is attributed to the trans-keto tautomer, formed via internal conversion. The decay occurs via trans --> cis isomerization and proton back-transfer to the enol form. Quenching by water indicates a proton-catalyzed reaction. To account for similar fluorescence and transient properties in the cases of the Zn2+ complexes, a photoinduced tautomerism at one of the two free phenolic hydroxy groups is proposed. The rapid ESIPT followed by a relatively slow relaxation process is reversible.     

Enhanced lasing properties of dissymmetric Eu(III) complex with bidentate phosphine ligands

The luminescent and lasing properties of Eu(III) complexes were enhanced by using an dissymmetric Eu(III) complex. The photophysical properties (the emission spectral shapes, the emission lifetimes, the emission quantum yields, and the stimulated emission cross section (SEC)) were found to be dependent on the geometrical structures of Eu(III) complexes. The geometrical structures of Eu(III) complexes were determined by X-ray single crystal analyses. The symmetrical group of Eu(hfa)3(BIPHEPO) (tris(hexafluoroacetylacetonato)europium(III) 1,1'-biphenyl-2,2'-diylbis(diphenylphosphine oxide)) was found to be C1, which was more dissymmetric than Eu(hfa)3(TPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry) and Eu(hfa)3(OPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry). The analytical data were supported by Judd-Ofelt analysis. The most dissymmetrical Eu(III) complex, Eu(hfa)3(BIPHEPO), showed large electron transition probability and large SEC (4.64 x 10(-20) cm2). The SEC of Eu(hfa)3(BIPHEPO) was superior to even the values of Nd-glass laser for practical use (1.6-4.5 x 10(-20) cm2). The lasing properties of Eu(III) complexes in polymer thin film were measured by photopumping of a Nd:YAG laser (355 nm). The threshold energy of lasing oscillation was found to be 0.05 mJ. The increasing rate of the lasing intensity of Eu(hfa)3(BIPHEPO) as a function of the excitation energy was much larger than that of Eu(hfa)3(TPPO)2 and Eu(hfa)3(OPPO)2. The dissymmetrical structure of Eu(hfa)3(BIPHEPO) promoted the enhancement of the lasing property.