Chloro Complexes Research Articles

Synthesis of Differently Substituted tacn‐Based Ligands: Towards the Control of Solubility and Electronic and Steric Properties of Uranium Coordination Complexes

AbstractStarting from phenols R1,R2ArOH (5) and the anisole derivative 3,5‐di‐tert‐butyl‐2‐methoxybenzyl bromide (13), a series of new tacn‐based ligands (R1,R2ArOR3)3tacn (2) have been synthesized with substituents of varying bulkiness and electronic nature at the ortho and para positions with respect to the oxygen coordination site. It was observed that these groups not only determine the steric shielding and solubility properties of 2, but also deactivate the reactivity of the phenols in the modified Mannich reaction when electron‐withdrawing groups are introduced at the para position in 5. Treatment of the ligands with UCl4 in thf led to the isolation of four uranium(IV) chloro complexes [{(R1,R2ArO)3tacn}UIVCl] (14), which were characterized by different spectroscopic and physical methods (e.g., 1H NMR, UV/Vis, SQUID), corroborating the +4 oxidation state in 14. Single‐crystal X‐ray structure analyses revealed that 14a·CH2Cl2·CH3CN and 14b·1.25CH2Cl2 crystallize in the chiral, orthorhombic space group P212121 [a = 24.934(3), b = 27.941(3), c = 9.045(1) Å, V = 6302(2) Å3, Z = 4] and the chiral, hexagonal space group P63 [a = 22.097(3), c = 17.941(2) Å, V = 7587(2) Å3, Z = 4], respectively. Interestingly, complexes 14a,b self‐organize in the solid state into homochiral 1D polymeric superstructures as a result of weak intermolecular C–H···Cl contacts.

Picolyl–NHC Hydrotris(pyrazolyl)borate Ruthenium(II) Complexes: Synthesis, Characterization, and Reactivity with Small Molecules

Ruthenium(II) hydrotris(pyrazolyl)borate chloro complexes bearing picolyl-functionalized N-heterocyclic carbenes [TpRu(κ(2)-C,N-picolyl-(R)I)Cl] (picolyl-(Me)I = 3-methyl-1-(2-picolyl)imidazol-2-ylidene) (1a), picolyl-(iPr)I = 3-isopropyl-1-(2-picolyl)imidazol-2-ylidene (1b), picolyl-(Me)45DClI = 3-methyl-1-(2-picolyl)-4,5-dichloroimidazol-2-ylidene (1c), picolyl-(Ph)I = 3-phenyl-1-(2-picolyl)imidazol-2-ylidene (1d), picolyl-(Me)BI = 3-methyl-1-(2-picolyl)benzoimidazol-2-ylidene (1e)) have been synthesized and characterized. Furthermore, cationic carbonyl derivatives 2a-e have been prepared, characterized, and used to study the donor properties of the picolylcarbene ligands (picolyl-(R)I) via infrared spectroscopy. Also, the reactivity of the 16-electron species [TpRu(κ(2)-C,N-picolyl-(R)I)](+), in situ generated using NaBAr(F)4 (Ar(F) = 3,5-bis(trifluoromethyl)phenyl) as a halide scavenger, toward N2, CH3CN, H2, CH2CH2, S8, and O2 was studied indicating a strong influence of the NHC wingtip and backbone substituents in the product distribution. The crystal structures of [TpRu(κ(2)-C,N-picolyl-(iPr)I)Cl] (1b), [TpRu(κ(2)-C,N-picolyl-(Me)I)CO][BAr(F)4] (2a), [TpRu(κ(2)-C,N-picolyl-(Ph)I)CO][BAr(F)4] (2d), [{TpRu(κ(2)-C,N-picolyl-(Me)I}2(μ-N2)][BAr(F)4]2 (3'a), [{TpRu(κ(2)-C,N-picolyl-(Ph)I)}2(μ-N2)][BAr(F)4]2 (3'd), [TpRu(κ(2)-C,N-picolyl-(iPr)I)(η(2)-CH2CH2)][BAr(F)4] (5b), and [{TpRu(κ(2)-C,N-picolyl-(Me)I)}2(μ-S2)][BAr(F)4]2 (6) are reported.

Unexpected C–H Bond Activation Promoted by Bimetallic Lanthanide Amido Complexes Bearing a META-Phenylene-Bridged Bis(β-diketiminate) Ligand

Treatment of META-[Na(THF)2]2 (1; META = {[2,6-iPr2C6H3NC(Me)C(H)C(Me)N]−}2-(m-phenylene)] with 1 equiv of {Ln[N(SiMe3)2]2(μ-Cl)(THF)}2 (Ln = Y, Yb) in toluene at 110 °C afforded bimetallic lanthanide amido complexes bridged by a chloride and a phenyl group, {Ln[N(SiMe3)2]}2(META′)(μ-Cl) (Ln = Y (2), Yb (3)), which formed via unexpected C–H bond activation of the arene ring. However, the same reactions carried out in both THF and toluene at room temperature gave the bimetallic lanthanide amido–chloro complexes {Ln[N(SiMe3)2]2}META{Ln[N(SiMe3)2]Cl(THF)} (Ln = Y (4), Yb (5)). When they were heated to 110 °C in toluene, complexes 4 and 5 were converted to complexes 2 and 3 via amine elimination. All of these complexes were confirmed by elemental analysis, FT-IR, and X-ray structure analysis and by NMR analysis in the cases of complexes 1, 2, and 4.

Synthesis and characterization of valonea tannin resin and its interaction with palladium (II), rhodium (III) chloro complexes

Valonea tannin (TA) and formaldehyde condensation reaction was carried out under alkaline condition to prepare the valonea tannin–formaldehyde resol resin (TAR). Obtained resin was used as adsorbent for recovery of palladium (II) and rhodium (III) ions from chloride-containing solutions. This kind of recovery was very simple and useful for generating little secondary wastes. Interaction of adsorption also was investigated: Chloropalladium (II) species were reduced to Pd(0), while hydroxyl groups of TAR were oxidized during the adsorption. Proposed adsorption of the aquachlororhodium (III) species mostly takes place via ligand exchange mechanism. TAR, Rh-adsorbed TAR, and Pd-adsorbed TAR were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction spectroscopy, and Fourier transform infrared–attenuated total reflection spectroscopy.

Different coordination modes of dipyridyl ketimine ligands in cationic arene ruthenium complexes

Abstract 2,2′-Dipyridyl- N -arylimines L (L 1 = 2,4,6-trimethyl(di-2-pyridylmethylene)aniline, L 2 = 2,6-diisopropyl(di-2-pyridylmethylene)aniline) react with arene ruthenium dichloride dimer in methanol to give cationic arene ruthenium complexes of the general type [(arene)Ru(η 2 - N , N -L)Cl] + (arene = C 6 H 6 , p -MeC 6 H 4 Pr i ). Two coordination modes of the chelating ligands N , N -L are observed. In the major isomer, the ketimine nitrogen atom and one of the two pyridine nitrogen atoms are coordinated to ruthenium, while in the minor isomer the two pyridine nitrogen atoms coordinate to the metal center. In the case of L 1 , the minor isomer of the p -cymene ruthenium chloro complex could be isolated as the tetrafluoroborate salt and characterized by single crystal X-ray analysis. The molecular structure of the major isomer was determined by X-ray crystallography in the case of the tetraphenylborate salt of the benzene ruthenium chloro derivative. In both structures, the ruthenium atom shows the expected pseudo-tetrahedral coordination geometry.

Abnormal N-Heterocyclic Carbene Gold(I) Complexes: Synthesis, Structure, and Catalysis in Hydration of Alkynes

Two abnormal N-heterocyclic carbene (aNHC) gold(I) complexes, [(aNHC)AuCl], were prepared from C2-protected imidazolium salts. The air-stable complexes chloro(1-isopropyl-3-methyl-2,4-diphenylimidazol-5-ylidene)gold(I) (5) and chloro(1,4-diisopropyl-3-methyl-2-phenylimidazol-5-ylidene)gold(I) (6) were synthesized via transmetalation using (SMe2)AuCl and the corresponding silver salt such as [(aNHC)AgI] or [(aNHC)2Ag][I] and were fully characterized by NMR and mass spectroscopy and by X-ray crystallography. To investigate the structure, bonding, and catalytic activity of the aNHC-based Au complexes in comparison with their traditional NHC analogues, the sterically similar NHC-based Au complexes chloro(1,3-diisopropylimidazol-2-ylidene)gold(I) (7) and chloro(3-isopropyl-1-phenylimidazol-2-ylidene)gold(I) (8) were prepared from 1,3-diisopropylimidazolium iodide (3) and 3-isopropyl-1-phenylimidazolium iodide (4), respectively. X-ray crystallography and density functional theory (DFT) calculations showed that ...

NHC Complexes of Cobalt(II) Relevant to Catalytic C–C Coupling Reactions

Alkyl compounds of cobalt(II) containing aryl-substituted N-heterocyclic carbene ligands have been prepared by reaction of the precursor chloro complexes [CoCl2(IMes)2] and [Co2Cl2(μ-Cl)2(IPr)2] (IMes = 1,3-dimesityl-imidazol-2-ylidene; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with Grignard reagents. Examples of alkyl complexes possessing both four-coordinate and three-coordinate geometries are reported. The chloro complex [CoCl2(IMes)2] adopts a pseudotetrahedral geometry displaying an S = 3/2 ground state, whereas the alkyl complex [Co(CH3)2(IMes)2] adopts a square-planar geometry consistent with an S = 1/2 ground state. In contrast to [Co(CH3)2(IMes)2], [Co(CH2SiMe3)2(IPr)] exhibits a three-coordinate trigonal-planar geometry displaying an S = 3/2 ground state. The catalytic efficacy of [CoCl2(IMes)2] in Kumada couplings is examined, as is the chemistry of the alkyl complexes toward CO. The structure and reactivity of these compounds is discussed in the context of C–C coupling reactions catalyzed by cobalt NHCs.

Electronic structure and catalytic aspects of [Ru(tpm)(bqdi)(Cl/H2O)]n, tpm = tris(1-pyrazolyl)methane and bqdi = o-benzoquinonediimine

The diamagnetic complexes [Ru(tpm)(bqdi)(Cl)]ClO(4) ([1]ClO(4)) (tpm = tris(1-pyrazolyl)methane, bqdi = o-benzoquinonediimine) and [Ru(tpm)(bqdi)(H(2)O)](ClO(4))(2) ([2](ClO(4))(2)) have been synthesized. The valence state-sensitive bond distances of coordinated bqdi [C-N: 1.311(5)/1.322(5) Å in [1]ClO(4); 1.316(7)/1.314(7) Å in molecule A and 1.315(6)/1.299(7) Å in molecule B of [2](ClO(4))(2)] imply its fully oxidised quinonediimine (bqdi(0)) character. DFT calculations of 1(+) confirm the {Ru(II)-bqdi(0)} versus the antiferromagnetically coupled {Ru(III)-bqdi˙(-)} alternative. The (1)H NMR spectra of [1]ClO(4) in different solvents show variations in chemical shift positions of the NH (bqdi) and CH (tpm) proton resonances due to their different degrees of acidity in different solvents. In CH(3)CN/0.1 mol dm(-3) Et(4)NClO(4), [1]ClO(4) undergoes one reversible Ru(II)⇌ Ru(III) oxidation and two reductions, the reversible first electron uptake being bqdi based (bqdi(0)/bqdi˙(-)). The electrogenerated paramagnetic species {Ru(III)-bqdi(0)}(1(2+)) and {Ru(II)-Q˙(-)}(1) exhibit Ru(III)-type (1(2+): <g> = 2.211/Δg = 0.580) and radical-type (1: g = 1.988) EPR signals, respectively, as is confirmed by calculated spin densities (Ru: 0.767 in 1(2+), bqdi: 0.857 in 1). The aqua complex [2](ClO(4))(2) exhibits two one-electron oxidations at pH = 7, suggesting the formation of {Ru(IV)[double bond, length as m-dash]O} species. The electronic spectral features of 1(n) (n = charge associated with the different redox states of the chloro complex: 2+, 1+, 0) in CH(3)CN and of 2(2+) in H(2)O have been interpreted based on the TD-DFT calculations. The application potential of the aqua complex 2(2+) as a pre-catalyst towards the epoxidation of olefins has been explored in the presence of the sacrificial oxidant PhI(OAc)(2) in CH(2)Cl(2) at 298 K, showing the desired selectivity with a wide variety of alkenes. DFT calculations based on styrene as the model substrate predict that the epoxidation reaction proceeds through a concerted transition state pathway.

Nickel(II) Complexes Containing a Pyrrole–Diphosphine Pincer Ligand

A new pincer ligand, (P(2)(Ph)Pyr)(-), based on the anion of 2,5-bis[(diphenylphosphino)methyl]pyrrole has been prepared in four steps from pyrrole. The ligand undergoes oxidation to diphosphine oxide under ambient conditions and was therefore isolated as its borane adduct, H(P(2)(Ph)Pyr)·2BH(3) (2). Delivery of the ligand to nickel(II) was accomplished by the direct reaction of NiCl(2) with 2 in the presence of Et(2)NH to afford [NiCl(P(2)(Ph)Pyr)]. Salt metathesis reactions of the chloro complex afford new compounds including [Ni(CH(3))(P(2)(Ph)Pyr)] and [Ni(NCCH(3))(P(2)(Ph)Pyr)](OTf). In all cases, the ligand gives rise to diamagnetic square-planar complexes, which have been fully characterized in solution and the solid state. All complexes examined display an irreversible oxidation to nickel(III) according to cyclic voltammetry. Reduction of the chloro complex in dichloromethane results in an electrocatalytic process, whereas reduction in tetrahydrofuran leads to the irreversible formation of a nickel(I) species.

Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

A series of aluminum methyl and chloride complexes bearing 2(N-piperazinyl-N′-methyl)-2-methylene-4-R′-6-R-phenolate or 2(N-morpholinyl)-2-methylene-4-R′-6-R-phenolate ([ONER1,R2]-) {[R1 = tBu, R2 = Me, E = NMe (L1); R1= R2 = tBu, E = NMe (L2); R1 = R2 = tBu, E = O (L3)} ligands were synthesized and characterized through elemental analysis, 1H, 13C{1H}, and 27Al NMR spectroscopy, and X-ray crystallography. Reactions of AlMe3 with two equivalents of L1H-L3H gave {[ONER1,R2]2AlMe} (1–3), while reaction of Et2AlCl with two equivalents of L1H and L3H afforded {[ONER1,R2]2AlCl} (4 and 5) as monometallic complexes. The catalytic activity of complexes 1–3 toward ring-opening polymerization (ROP) of ε-caprolactone was assessed. These complexes are more active than analogous Zn complexes for this reaction but less active than the Zn analogues for ROP of rac-lactide. Characteristics of the polymer as well as polymerization kinetics and mechanism were studied. Polymer end-group analyses were achieved using 1H NMR spectroscopy and MALDI-TOF MS. Eyring analyses were performed, and the activation energies for the reactions were determined, which were significantly lower for 1 and 2 compared with 3. This could be for several reasons: (1) the methylamine (NMe) group of 1 and 2, which is a stronger base than the ether (O) group of 3, might activate the incoming monomer via noncovalent interactions, and/or (2) the ether group is able to temporarily coordinate to the metal center and blocks the vacant coordination site toward incoming monomer, while the amine cannot do this. Preliminary studies using 4 and 5 toward copolymerization of cyclohexene oxide with carbon dioxide have been performed. 4 was inactive and 5 afforded polyether carbonate (66.7% epoxide conversion, polymer contains 54.0% carbonate linkages).

Extraction of hexachloroplatinate from hydrochloric acid solutions with phosphorylated hexane-1,6-diyl polymers

A series of diols (diethylene glycol, triethylene glycol, butane-1,4-diol and hexane-1,6-diol) were immobilized onto Merrifield resin and subsequently phosphorylated with dialkyl chlorophosphate (alkyl=Me, Et, Bu). The resins bearing hexane-1,6-diyl groups exhibited very good extraction abilities in regard to precious metal chloro complexes like platinum(IV), palladium(II) and rhodium(III). In batch experiments, more than 98% of Pt(IV) is extracted even when the metal and the hydrochloric acid concentration is enhanced significantly. Elution can be achieved with a solution of 0.5molL−1 thiourea in 0.1molL−1 hydrochloric acid. In the presence of other noble metals, platinum(IV) is preferentially bound. The extraction yield decreases in slightly acidic solution in the following order: Pt(IV)≈Pd(II)>Rh(III) and changes with increasing hydrochloric acid concentration to Pt(IV)>Pd(II)≫Rh(III). At different ratios of metal and acid, the temperature has nearly no influence on the platinum extraction. On slightly acidic media, the extraction of rhodium decreases by 30% when the temperature is increased from 10°C to 40°C. When the acid and metal concentration is enhanced, the palladium extraction decreases by 7–9%, depending on the resin.

Chloro and Alkyl Rare-Earth Complexes Supported byansa-Bis(amidinate) Ligands with a Rigido-Phenylene Linker. Ligand Steric Bulk: A Means of Stabilization or Destabilization?

ansa-Bis(amidinate) ligands with a rigid o-phenylene linker, C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)H}2 (R = Me (1), iPr (2)), were successfully employed for the synthesis of rare-earth chloro and alkyl species. The reaction of dilithium derivatives of 1 and 2 with LnCl3 (Ln = Y, Lu) afforded the monomeric bis(amidinate) chloro lanthanide complexes [C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)}2]Y(THF)(μ-Cl)2Li(THF)2 (R = Me (3), iPr (5)) and [C6H4-1,2-{NC(tBu)N(2,6-Me2C6H3)}2]LuCl(THF)2 (4). Bis(amidinate) ligands in complexes 3 and 4 are coordinated to the metal atoms in a tetradentate fashion, while the bulkier ligand in 5 is tridentate. The alkane elimination reactions of 1 and 2 with equimolar amounts of (Me3SiCH2)3Ln(THF)2 (Ln = Y, Lu) allowed us to obtain the monoalkyl complexes [C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)}2]Ln(CH2SiMe3)(THF)n (Ln = Y, R = Me, n = 1 (6); Ln = Lu, R = Me, n = 1 (7); Ln = Y, R = iPr, n = 2 (8)). The kinetics of thermal decomposition of complexes 6–8 were measured, and for 6 the activation energy was obtained from the temperature dependence of the rate constants (Ea = 67.0 ± 1.3 kJ/mol). Complexes 6 and 7 turned out to be inert toward H2 and PhSiH3. Surprisingly, complex 8 was inert toward H2 and PhSiH3 but rapidly cleaved C–O bonds of DME. The reaction resulted in the formation of the methoxy complex {[C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}2]Y(μ2-OMe)]}2(μ2-DME) (9) and methyl vinyl ether.

Mn(III) based binapthyl Schiff base complex hetrogenized over organo-modified SBA-15: Synthesis, characterization and catalytic application

A heterogenized organocatalyst was synthesized by the covalent anchoring of the complex chloro (S,S)(−)[N-3-tert-butyl-5-chloromethyl salicylidene]-N′-[3′,5′-di-tert-butyl salicylidene] 1,1′-binapthyl-2,2′-diamine manganese(III) over modified mesoporous surface of SBA-15 through the reactive 3-aminopropyl trimethoxysilane (3-APTMS) group. The surface properties of the functionalized catalyst were analyzed by a series of characterization techniques such as elemental analysis, XRD, N2 sorption measurement isotherm, FT-IR, TGA–DTA, XPS, and solid state 13C NMR. The XRD and N2 sorption measurement, UV reflectance and CP MAS NMR spectroscopy (13C and 29Si) of the catalyst confirmed the structural integrity of the mesoporous hosts and the spectroscopic characterization technique proved the successful anchoring of the metal complex over the modified mesoporous support. The screening of the catalyst Mn(III)-L-SBA-15 and neat Mn(III)-L complexes was done in the oxidation reaction of thioanisole (methyl phenyl sulfide) by using TBHP as an oxidant. Mn(III)-L-SBA-15 catalyst shows higher activities and turnover number (TON) and exhibit enhanced enantiomeric excess comparable to homogeneous catalyst [Mn(III)-L]. [Mn(III)-L-SBA-15] catalyst was found more active than homogeneous catalyst [Mn(III)-L]; Moreover bulkier alkene like 1,2-dihydronapthalene was also efficiently epoxidised with the synthesized supported catalyst.

Fluorescence enhancement of N2O2-type dipyrrin ligand in two step responding to zinc(II) ion

Fluorescence imaging is well-suited for the live imaging of biological Zn(II), which has no facile spectroscopic or magnetic signature. The successful application of this methodology requires the development of robust Zn(II) imaging agents that display high sensitivity, selectivity and temporal fidelity. In this study, a N2O2-type dipyrrin based bimolecular zinc(II) complex was produced and shown to have sharper, blue-shifted and more enhanced fluorescence emission. An approximate three-fold fluorescence enhancement was achieved within the micromolar concentration range, which is an important parameter for Zn(II) detection in vivo. The increase in emission intensity was due to the dominant role of aryl-ring rotation in governing the excited state dynamics and fluorescence properties of the dipyrrin dye. Fluorescence titration showed that the ligand complex exhibited very strong zinc(II) binding affinity when compared to that in the binuclear chloro complex. The fluorescence emission changes in the dipyrrin dye to zinc(II) ion could be observed not only using instruments but also by the naked-eye (violet→sky blue).

Binapthyl Schiff base diamine complex covalently bonded to modified SBA-15: Synthesis, characterization and catalytic application

Protected mesoporous SBA-15 phase was synthesized by grafting the complex Chloro (S,S)(−)[N-3-tert-butyl-5-chloromethyl salicylidene]-N′-[3′,5′-di tert-butyl salicylidene] 1,1′-binapthyl-2,2′-diamine manganese(III) through the reactive 3-aminopropyl trimethoxysilane(3-APTMS) group. The surface properties of the functionalized catalyst were analyzed by a series of characterization techniques like elemental analysis, XRD, N2 sorption measurement isotherm, FT-IR, XPS, and solid state 13C NMR. The screening of the catalyst Mn(III)-L-SBA-15 and neat Mn(III)-L complexes was done for the oxidation reaction of thioanisole (methyl phenyl sulfide) using TBHP as an oxidant. Mn(III)-L-SBA-15 catalyst shows higher activities and exhibit enantiomeric excess comparable to homogeneous catalyst.

Analysis of the Activation and Heterolytic Dissociation of H2by Frustrated Lewis Pairs: NH3/BX3(X = H, F, and Cl)

We performed a computational study of H(2) activation and heterolytic dissociation promoted by prototype Lewis acid/base pairs NH(3)/BX(3) (X = H, F, and Cl) to understand the mechanism in frustrated Lewis pairs (FLPs). Although the NH(3)/BX(3) pairs form strong dative bonds, electronic structure theories make it possible to explore the potential energy surface away from the dative complex, in regions relevant to H(2) activation in FLPs. A weakly bound precursor complex, H(3)N·H(2)·BX(3), was found in which the H(2) molecule interacts side-on with B and end-on with N. The BX(3) group is pyramidal in the case of X = H, similar to the geometry of BH(5), but planar in the complexes with X = F and Cl. The latter complexes convert to ion pairs, [NH(4)(+)][BHX(3)(-)] with enthalpy changes of 7.3 and -9.4 kcal/mol, respectively. The minimum energy paths between the FLP and the product ion pair of the chloro and fluoro complexes were calculated and analyzed in great detail. At the transition state (TS), the H(2) bond is weakened and the BX(3) moiety has undergone significant pyramidal distortion. As such, the FLP is prepared to accept the incipient proton and hydride ion on the product-side. The interaction energy of the H(2) with the acid/base pair and the different contributions for the precursor and TS complex from an energy decomposition analysis expose the dominant factors affecting the reactivity. We find that structural reorganization of the precursor complex plays a significant role in the activation and that charge-transfer interactions are the dominant stabilizing force in the activated complex. The electric field clearly has a role in polarizing H(2), but its contribution to the overall interaction energy is small compared to that from the overlap of the p(N), σ(H-H), σ*(H-H), and p(B) orbitals at the TS. Our detailed analysis of the interaction of H(2) with the FLP provides insight into the important components that should be taken into account when designing related systems to activate H(2).

Molecular mechanical perspective on halogen bonding

The nature and strength of halogen bonding in halo molecule-Lewis base complexes were studied in terms of molecular mechanics using our recently developed positive extra-point (PEP) approach, in which the σ-hole on the halogen atom is represented by an extra point of positive charge. The contributions of the σ-hole (i.e., positively charged extra point) and the halogen atom to the strength of this noncovalent interaction were clarified using the atomic parameter contribution to the molecular interaction (APCtMI) approach. The molecular mechanical results revealed that the halogen bond is electrostatic and van der Waals in nature, and its strength depends on three types of interaction: (1) the attractive electrostatic interaction between the σ-hole and the Lewis base, (2) the repulsive electrostatic interaction between the negative halogen atom and the Lewis base, and (3) the repulsive/attractive van der Waals interactions between the halogen atom and the Lewis base. The strength of the halogen bond increases with increasing σ-hole size (i.e., magnitude of the extra-point charge) and increasing halogen atom size. The van der Waals interaction's contribution to the halogen bond strength is most favorable in chloro complexes, whereas the electrostatic interaction is dominant in iodo complexes. The idea that the chloromethane molecule can form a halogen bond with a Lewis base was revisited in terms of quantum mechanics and molecular mechanics. Although chloromethane does produce a positive region along the C-Cl axis, basis set superposition error corrected second-order Møller-Plesset calculations showed that chloromethane-Lewis base complexes are unstable, producing halogen-Lewis base contacts longer than the sum of the van der Waals radii of the halogen and O/N atoms. Molecular mechanics using the APCtMI approach showed that electrostatic interactions between chloromethane and a Lewis base are unfavorable owing to the high negative charge on the chlorine atom, which overcomes the corresponding favorable van der Waals interactions.

Molecular structures of Cu(II), Rh(III) complexes of 2-N substituted N-confused porphyrin inner C-oxide

The crystal structures of a paramagnetic copper(II) complex 2-aza-2-(3′-phenoxypropyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N″-O) copper(II) [Cu(2-NCH2CH2CH2-O-C6H5NCTPPO; 7)] and a diamagnetic rhodium(III) complex chloro (2-aza-2-benzyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N″-O) rhodium(III) [Rh(2-N-CH2C6H5NCTPPO)Cl; 8] have been established. The coordination sphere around the Cu2+ ion in 7 is distorted square planar, whereas for Rh3+ in 8, it is a distorted octahedron. A copper(II) complex 7 has been isolated and characterized by electron spin resonance spectroscopy with a structure incorporating an Cu–O–C unit. The Rh–O 2.043(2)Å and Rh–C(17) 2.170(3)Å distances in 8 suggests a direct interaction between the rhodium center and the π electron density on the carbonyl group in a η2 fashion.

Synthesis and Characterization of Gallic Acid Resin and Its Interaction with Palladium(II), Rhodium(III) Chloro Complexes

Gallic acid (GA) and formaldehyde condensation reaction was carried out under alkaline condition to prepare the gallic acid–formaldehyde resol resin (GAR). Obtained resin was used as adsorbent for recovery of palladium(II) and rhodium(III) ions from chloride-containing solutions. This kind of recovery was very simple and useful for generating little secondary wastes. Interaction of adsorption also was investigated: Chloropalladium(II) species were reduced to Pd(0), while hydroxyl groups of GAR were oxidized during the adsorption. Proposed adsorption of the aquachlororhodium(III) species mostly takes place via ligand exchange mechanism. GAR, Rh-adsorbed GAR, and Pd-adsorbed GAR were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction spectroscopy, and Fourier transform infrared–attenuated total reflection spectroscopy.

Synthesis and Structural Diversity of Group 4 Metal Complexes with Multidentate Tethered Phenoxy-Amidine and Phenoxy-Amidinate Ligands

The coordination chemistry of the multidentate tethered amidine-phenol {4,6-tBu2C6H2O(2-C(NR)═NR}H2 ({LONR}H2, R = iPr, 2,6-iPr2C6H3 (Ar)) and new guanidine-phenol {4,6-tBu2C6H2ON(C6H5)(2-C(NR)═NR}H2 ({LON(Ph)NiPr}H2) pro-ligands with group 4 metals has been studied. σ-Bond and salt metathesis reactions were explored to coordinate these (pro)ligands onto zirconium and hafnium. Alkane elimination reactions between {LONR}H2 and Zr(CH2Ph)4 afforded mixed-ligand monobenzyl {LOHNR}{LONR}Zr(CH2Ph) (R = iPr; 1) and monoligand tribenzyl {LOHNAr}Zr(CH2Ph)3 (R = Ar; 2) complexes, respectively. Alkane and amine elimination reactions between {LON(Ph)NiPr}H2 and Zr(CH2Ph)4 or Hf(NMe2)4 unexpectedly resulted in cleavage of the ligand backbone and eventual isolation of {(Ph)NC6H2(tBu)2O}Zr{(iPrN)2CCH2Ph}2 (3) and {(Ph)NC6H2(tBu)2O}Hf{(iPrN)2CNMe2}2 (4), respectively. Salt metathesis reactions between {LONR}Li2 and ZrCl4(THF)n (n = 0, 2), conducted in 1:1 ratios, led upon crystallization to diverse chloro complexes: [{LONiPr}ZrCl]3(μ3-O)(μ3-Cl) (5), [{LONAr}2ZrCl(μ2-Cl)]2[{LHONAr}ZrCl(μ2-Cl)](μ3–OH) (6), and {LOHNAr}ZrCl3(THF) (7). Similar salt metathesis reactions between the monolithium salts {LHONR}Li and ZrCl4, conducted in 2:1 ratios, allowed the selective preparation of bis(phenoxy-amidine) complexes with pendant amino groups {LOHNR}2ZrCl2 (R = iPr, 8; R = Ar, 9). All complexes were authenticated by elemental analysis, X-ray crystallography, and NMR spectroscopy. Complexes 5, 6, 8, and 9, upon activation with MAO, showed poor to moderate productivities (4–172 (kg of PE) mol–1 h–1) in the polymerization of ethylene, giving linear polymers with large polydispersities.