Luminescent complexes with ligands containing C=N bond

Data on luminescent complexes with azomethine ligands are generalized and systematized. The synthesis and luminescent properties of complexes with acyclic and cyclic azomethines are considered.     

Synthesis, reactivity, and DFT studies of tantalum complexes incorporating diamido-N-heterocyclic carbene ligands. Facile endocyclic C-H bond activation

The syntheses of tantalum derivatives with the potentially tridentate diamido-N-heterocyclic carbene (NHC) ligand are described. Aminolysis and alkane elimination reactions with the diamine-NHC ligands, (Ar)[NCN]H(2) (where (Ar)[NCN]H(2) = (ArNHCH(2)CH(2))(2)(C(3)N(2)); Ar = Mes, p-Tol), provided complexes with a bidentate amide-amine donor configuration. Attempts to promote coordination of the remaining pendent amine donor were unsuccessful. Metathesis reactions with the dilithiated diamido-NHC ligand ((Ar)[NCN]Li(2)) and various Cl(x)Ta(NR'(2))(5-)(x) precursors were successful and generated the desired octahedral (Ar)[NCN]TaCl(x)(NR'(2))(3-)(x) complexes. Attempts to prepare trialkyl tantalum complexes by this methodology resulted in the formation of an unusual metallaaziridine derivative. DFT calculations on model complexes show that the strained metallaaziridine ring forms because it allows the remaining substituents to adopt preferable bonding positions. The calculations predict that the lowest energy pathway involves a tantalum alkylidene intermediate, which undergoes C-H bond activation alpha to the amido to form the metallaaziridine moiety. This mechanism was confirmed by examining the distribution of deuterium atoms in an experiment between (Mes)[NCN]Li(2) and Cl(2)Ta(CD(2)Ph)(3). The single-crystal X-ray structures of (p)(-Tol)[NCNH]Ta(NMe(2))(4) (3), (Mes)[NCNH]Ta=CHPh(CH(2)Ph)(2) (4), (p)(-Tol)[NCN]Ta(NMe(2))(3) (7), (Mes)[NCCN]Ta(CH(2)(t)Bu)(2) (11), and (Mes)[NCCN]TaCl(CH(2)(t)Bu) (14) are included.     

含磷硫杂配位原子的Pt(Ⅱ)金属有机配合物的合成及其对苯的C-H键活化

本文合成了含磷硫杂配位原子配体的Pt金属有机配合物,并对PtCl~2[Ph~2P(CH~2)~2SCH~3]配合物进行了晶体和分子结构测定,研究了这些Pt 金属配合物对苯的C-H键的活化作用,考察了对苯的光羰化反应性能     

Kinetico-mechanistic studies of cyclometalating C-H bond activation reactions on Pd(ii) and Rh(ii) centres: The importance of non-innocent acidic solvents in the process

The activation of C-H bonds in homogeneous systems has been the subject of study for many years due to its involvement in important industrial catalytic processes. A large number of reviews on the different areas involved have appeared, but those dealing with kinetic studies, including activation parameters, are rather scarce due to the severe difficulties in interpreting experimental data. In this perspective, the information available from kinetico-mechanistic studies of cyclometalation reactions on Pd(ii) and Rh(ii) centres via C-H bond activation is considered. Experimental results from studies performed on complexes of these metal centres indicate that the historically accepted electrophilic substitution classification is not a satisfactory mechanistic term for the process occurring during the reaction. A definite acid-assisted phenomenon is evident for all the processes studied, which contradicts the expected need for a proton abstractor in the reaction. This is even more surprising when considering the expected hydrolysis of M-C bonds in such acidic media, indicating that metalation prevails under these conditions. Only the presence of coordinated acid molecules in solvolytic carboxylic acid media can explain the observations. The fine tuning between the proton abstraction capacity of a coordinated RCO(2)H molecule and its Lewis basicity results in a unique reactivity trend. DFT calculations carried out for these acid-assisted processes fully agree with the experimental trends observed.     

The insertion reaction of acetonitrile on aryl nickel complexes stabilized by bidentate N,N'-chelating ligands

Organometallic complexes to be used as single component precursors in the catalytic dimerization/polymerization of olefins usually must contain a labile ligand that can easily be displaced by the olefin. This is the first step in the activation of the precursor. One commonly used labile ligand is a nitrile. Here we report an example of incompatibility between the nickel or palladium aryl bond and acetonitrile. Neutral [MBr(Mes)NN] complexes in which Mes=2,4,6-Me3C6H2, NN=diazabutadiene (DAD), pyridinylimine (PIM), 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen) gave the expected [M(Mes)(3,5-lut)(NN)][BF4] compounds and the unexpected [Ni(Mes){NH=C(Me)(2,4,6-Me3C6H2)}(NN)][BF4] complexes in the presence of TlBF4 and 3,5-lutidine or acetonitrile. The sequence of reactions that leads to the imine ligand must include an initial insertion of the nitrile on the sigma(Ni-Mes) bond. These ionic complexes remain stable under 20 bar of ethylene.     

Organolutetium vinyl and tuck-over complexes via C-H bond activation

The vinyl C-H bond of tetramethylfulvene is activated in the presence of [(C5Me5)2LuH]x, 1, to form a vinyl organolutetium complex, (C5Me5)2Lu(CH=C5Me4), 2. Also formed in the reaction is the "tuck-over" complex, (C5Me5)2Lu(mu-H)(mu-eta1:eta5-CH2C5Me4)Lu(C5Me5), 3, containing a (CH2C5Me4)2- moiety long postulated to exist in organolutetium chemistry but never crystallographically characterized. Evidence for these C-H bond activations by a "(C5Me5)3Lu" intermediate, 4, is presented. Complex 3 can also be made in high yield by thermolysis of 1. Under H2, 1 catalytically hydrogenates TMF to C5Me5H.     

Syntheses of ketonated disulfide-bridged diruthenium complexes via C-H bond activation and C-S bond formation

The alpha-C-H bonds of 3-methyl-2-butanone, 3-pentanone, and 2-methyl-3-pentanone were activated on the sulfur center of the disulfide-bridged ruthenium dinuclear complex [(RuCl(P(OCH3)3)2)2(mu-S2)(mu-Cl)2] (1) in the presence of AgX (X = PF6, SbF6) with concomitant formation of C-S bonds to give the corresponding ketonated complexes [(Ru(CH3CN)2(P(OCH3)3)2)(mu-SSCHR1COR2)(Ru(CH3CN)3(P(OCH3)3)2)]X3 ([5](PF6)3, R1 = H, R2 = CH(CH3)2, X = PF6; [6](PF6)3, R1 = CH3, R2 = CH2CH3, X = PF6; [7](SbF6)3, R1 = CH3, R2 = CH(CH3)2, X = SbF6). For unsymmetric ketones, the primary or the secondary carbon of the alpha-C-H bond, rather than the tertiary carbon, is preferentially bound to one of the two bridging sulfur atoms. The alpha-C-H bond of the cyclic ketone cyclohexanone was cleaved to give the complex [(Ru(CH3CN)2(P(OCH3)3)2)(mu-SS-1- cyclohexanon-2-yl)(Ru(CH3CN)3(P(OCH3)3)2)](SbF6)3 ([8](SbF6)3). And the reactions of acetophenone and p-methoxyacetophenone, respectively, with the chloride-free complex [(Ru(CH3CN)3(P(OCH3)3)2)2(mu-S2)]4+ (3) gave [(Ru(CH3CN)2(P(OCH3)3)2)(mu-SSCH2COAr)(Ru(CH3CN)3(P(OCH3)3)2)](CF3SO3)3 ([9](CF3SO3)3, Ar = Ph; [10](CF3SO3)3, Ar = p-CH3OC6H4). The relative reactivities of a primary and a secondary C-H bond were clearly observed in the reaction of butanone with complex 3, which gave a mixture of two complexes, i.e., [(Ru(CH3CN)2(P(OCH3)3)20(mu-SSCH2COCH2CH3)(Ru(CH3CN)3(P(OCH3)3)2)](CF3SO3)3 ([11](CF3SO3)3) and [(Ru(CH3CN)2(P(OCH3)3)2)(mu-SSCHCH3COCH3)(Ru(CH3CN)3(P(OCH3)2)](CF3SO3)3 ([12](CF3SO3)3), in a molar ratio of 1:1.8. Complex 12 was converted to 11 at room temperature if the reaction time was prolonged. The relative reactivities of the alpha-C-H bonds of the ketones were deduced to be in the order 2 degrees > 1 degree > 3 degrees, on the basis of the consideration of contributions from both electronic and steric effects. Additionally, the C-S bonds in the ketonated complexes were found to be cleaved easily by protonation at room temperature. The mechanism for the formation of the ketonated disulfide-bridged ruthenium dinuclear complexes is as follows: initial coordination of the oxygen atom of the carbonyl group to the ruthenium center, followed by addition of an alpha-C-H bond to the disulfide bridging ligand, having S=S double-bond character, to form a C-S-S-H moiety, and finally completion of the reaction by deprotonation of the S-H bond.     

Electropolymerization of Pd(II) complexes containing phosphinoterthiophene ligands

A series of Pd complexes of 3'-diphenylphosphino-2,2':5'2' '-terthiophene (1a, dppterth) in which the metal is coordinated in three different modes have been prepared and electropolymerized, resulting in the formation of conductive thin films. In [Pd2(mu-Cl2)(dppterth-P,C3)2] (3a) the metal is P,C-coordinated, in [PdCl2(dppterth-P)2] (4a) the coordination is monodentate via the phosphine, and in [Pd(dppterth-P,C3)(dppterth-P,S1)][PF6] (5a) both P,C- and P,S-coordination modes are found. In 5a, the coordinated thiophene is hemilabile and may be displaced by reaction with more strongly coordinating ligands such as isocyanides. To probe the effect of blocking the alpha-position of the terthienyl moiety with methyl groups, 3'-diphenylphosphino-5-methyl-2,2':5'2' '-terthiophene (1b, Me-dppterth) and 3'-diphenylphosphino-5,5' '-dimethyl-2,2':5'2' '-terthiophene (1c, Me2-dppterth) were prepared, and the corresponding series of Pd complexes was synthesized. One of these complexes, [Pd(Me2-dppterth-P,C3)(Me2-dppterth-P,S1)][PF6] (5c), has been crystallographically characterized. The electropolymerized films prepared from 5a react with isonitriles, and shifts in the absorption spectra of the electropolymerized materials are observed upon reaction. A Pd complex has also been prepared from 5-diphenylphosphino-2,2':5'2' '-terthiophene (2, 5dppterth), and this complex has been electropolymerized. All the electropolymerized thin films have been characterized using EDX analysis, which demonstrates good correspondence with the elemental analysis of the respective monomers, and the maximum conductivities of the films are near 10(-4) S x cm(-1). Comparing the electropolymerization behavior of the complexes, along with their electrochemical and spectroscopic data, allows conclusions to be drawn regarding the involvement of pi-delocalization and the metal group in the conductivity of the materials.     

C-C and C-H bond activation reactions in N-heterocyclic carbene complexes of ruthenium

Thermolysis of Ru(PPh3)3(CO)H2 with the N-heterocyclic carbene bis(1,3-(2,4,6-trimethylphenyl)imidazol-2-ylidene) (IMes) results in C-C activation of an Ar-CH3 bond in one of the mesityl rings of the carbene ligand. Upon addition of IMes to Ru(PPh3)3(CO)H2 at room temperature in the presence of an alkene, C-H bond activation is observed instead. The thermodynamics of these C-C and C-H cleavage reactions have been probed using density functional theory.     

Structural studies of metal complexes containing amide ligands

Complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Pd(II) with di-N-phenyl pyromellitic diimide (PhPMDI) and di-N-pyridyl pyromellitic diimide (PyPMDI) were prepared and characterized based on analytical, molar conductance, magnetic, IR, PMR, electronic and ESR data. Based on analytical and molar conductance, the complexes have been formulated as [M(PhPMDA)(H₂O)₂]_n (M = Mn, Fe, Co, Ni), [Cu(PhPMDA)]_n [Pd₂(PhPMDA)Cl₂(H₂O)₂], [M(PyPMDA)]_n (M = Mn, Fe, Co, Ni and Cu) and [Pd₂(PyPMDA)Cl₂] In all these complexes PhPMDA acts as a mononegative bidentate ligand whereas PyPMDA acts as a mononegative tridentate one in the form of amide rather than imide. The geometries of the complexes have been proposed based on the electronic spectra. The various bonding parameters have been calculated from the ESR spectra of Cu(II) complexes.     

A new dirhodium catalyst with hemilabile tropolonato ligands for C-H bond functionalization

Don't hold on too tightly! In a new dirhodium catalyst for C-H functionalization reactions, two tropolonato ligands are introduced as hemilabile chelating ligands (see scheme). Only two bridges hold the Rh-Rh core together. The tropolonato ligands can liberate a binding site in the equatorial coordination sphere of the catalyst. This opens a doorway to new mechanistic channels in C-H functionalization.     

Thermodynamic and kinetic studies on novel dinuclear platinum(II) complexes containing bidentate N,N-donor ligands

A series of novel dinuclear platinum(II) complexes were synthesized with bidentate nitrogen donor ligands. The two platinum centers are connected by an aliphatic chain of variable length. The selected chelating ligand system should stabilize the complex toward decomposition. The pK(a) values and reactivity of four synthesized complexes, viz. [Pt(2)(N(1),N(4)-bis(2-pyridylmethyl)-1,4-butanediamine)(OH(2))(4)](4+) (4NNpy), [Pt(2)(N(1),N(6)-bis(2-pyridylmethyl)-1,6-hexanediamine)(OH(2))(4)](4+) (6NNpy), [Pt(2)(N(1),N(8)-bis(2-pyridylmethyl)-1,8-octanediamine)(OH(2))(4)](4+) (8NNpy), and [Pt(2)(N(1),N(10)-bis(2-pyridylmethyl)-1,10-decanediamine)(OH(2))(4)](4+) (10NNpy), were investigated. This system is of special interest because only little is known about the substitution behavior of dinuclear platinum complexes that contain a bidentate chelate that forms part of the aliphatic bridging ligand. Spectrophotometric acid-base titrations were performed to determine the pK(a) values of the coordinated water ligands. The substitution of coordinated water by thiourea was studied under pseudofirst-order conditions as a function of nucleophile concentration, temperature, and pressure, using stopped-flow techniques and UV-vis spectroscopy. The results for the dinuclear complexes were compared to those for the corresponding mononuclear reference complex [Pt(aminomethylpyridine)(OH(2))(2)](2+) (monoNNpy), by which the effect of increasing the aliphatic chain length on the bridged complexes could be investigated. The results indicated that there is a clear interaction between the two platinum centers, which becomes weaker as the chain length between the metal centers increases. In addition, quantum chemical calculations were performed to support the interpretation and discussion of the experimental data.     

N-C bond formation of NO ligands on ruthenium complexes with concurrent vinylic C-H activation and subsequent proton-induced reactivities of the resulting nitrosovinyl species

The N-C coupling of ligating NO with 2-vinylpyridines, affording nitrosovinyl complexes, was found. This is of significance since the reaction process involves a C-H activation of the vinyl moiety and subsequent C-N bond formation. Furthermore, we show that the resulting nitrosovinyl complexes are chemically versatile and potentially valuable species. Protonation of the resulting nitrosovinyl complexes in refluxing alcohol afforded the alcohol-incorporated complexes, as well as the ketoimine species. It is interesting to note that a proton-induced reaction with PPh3 trapped their intermediates, leading to the explication of these reaction mechanisms.     

Agostic Si-H bond coordination assists C-H bond activation at ruthenium in bis(phosphinobenzylsilane) complexes

Reaction of a phosphinobenzylsilane compound with ruthenium complexes leads to C-H and/or Si-H activation. The new complex Ru{eta(2)-H-SiMe2CH(o-C(6)H(4))PPh2}2 (5) was isolated and X-ray, NMR and DFT studies reveal that 5 displays two agostic Si-H interactions and two carbon-metallated bonds.     

Solution studies of some technetium complexes containing sulfur ligands

Interactions between technetium and the following series of sulfur ligands are described: 2,5-dimercapto-1,3,4-thiadiazole, 1-methylimidazol-2-thiol, 6,6-dithiodinicotinic acid, 2-amino-6-mercaptopurine and DL--amino-2-thiopheneacetic acid. The complexation reactions have been investigated (species formed,e, stoichiometry, etc.) and the results obtained have been comparatively evaluated with the aim to find relations between structure of the ligands and its complexing activity.     

Structural studies on organotin(IV) complexes formed with ligands containing {S,N,O} donor atoms

A number of complexes of ligands containing {O,N,S} donor atoms (2,3,4,6-tetra-O-acetyl-b-D-thioglucopyranoside, 1-thio-b-D-glucose, 2-aminomercaptopurine, 4-amino-2-mercaptopyrimidine and 2-amino-6-mercaptopurine-9-D-riboside) with di-n-butyltin(IV) oxide, diphenyltin(IV) oxide, tribenzyltin(IV) chloride, and trimethyltin(IV) chloride were prepared in the solid state. It was found that the complexes contain the organotin(IV) moiety and the ligand in a ratio of 1:1 or 2:1. The FTIR and Raman spectra clearly demonstrated that the organotin(IV) moieties react with the {S} atom of the ligands, while di-n-butyltin(IV) oxide is coordinated to the deprotonated hydroxy group. In several cases, the basic part of the ligands also participates in complex formation. Comparison of the experimental Mössbauer D values with those calculated on the basis of the pqs concept revealed that the organotin(IV) moiety has trigonal-bipyramidal geometry, and in certain cases tetrahedral geometry too. Some of the complexes contain the organotin(IV) cation in two different surroundings.