HF Complex Research Articles

Synthesis, Characterization, and Polymerization Behavior of Zirconium and Hafnium Complexes that Contain Asymmetric Diamido-N-Donor Ligands

Two new “NNN” (diamido-N-donor) ligands have been synthesized that contain ethylene/o-phenylene “arms” and a phenyl-substituted amine donor in the central position, [MesitylNH-o-C6H4N(Ph)CH2CH2NHMesityl] (H21) and [t-Bud6-NH-o-C6H4N(Ph)CH2CH2NHMesityl] (H22). The Zr and Hf complexes that have been isolated include [1]MX2 (M = Zr or Hf, X = NMe2, Cl, or Me) and [2]MX2 (M = Zr or Hf, X = NMe2, Cl, Me). The structures of [1]ZrMe2, [2]ZrMe2, and a dimeric species with the formula [MesitylN-o-C6H4NCH2CH2NMesityl]Zr2(NMe2)5 have been determined in X-ray crystallographic studies. Abstraction of a methyl group in [1]MMe2 (M = Zr or Hf) with [Ph3C][B(C6F5)4] gives rise to cationic complexes that are active initiators for the polymerization of 1-hexene. Similar activation of [2]MMe2 (M = Zr or Hf) gives rise to dimeric monocations that eventually break up and react further to yield cationic monomethyl species. In all cases the poly[1-hexene] produced in the presence of the monometallic cations was found to be atactic.

Ethylene polymerization and ethylene/styrene copolymerization with secondary phosphine-pendant and phosphide-pendant complexes of Zr and Hf

Ethylene and styrene polymerizations and ethylene/styrene copolymerization have been examined with a catalytic system obtained by a combination of zirconium or hafnium complexes bearing a secondary phosphine-pendant cyclopentadienyl ligand { η 5 -C 5 H 4 (CH 2 ) 2 P(H)R} (R = 2,4,6-trimethylphenyl (Mes), 2,4,6-tri(i-propyl)phenyl (Tip)) or a phosphide-pendant cyclopentadienyl ligand { η 5 -C 5 H 4 (CH 2 ) 2 PR- κP } with modified methylaluminoxane (MMAO) or a mixture of methylaluminoxane (MAO) and tri-i-butylaluminium (TIBA) as a cocatalyst. These systems show moderate activity in ethylene polymerization (8–316 g mmol −1 h −1 ) but show inactivity in styrene polymerization. In ethylene/styrene copolymerization, these systems afford ethylene/styrene copolymers with a relatively high styrene content (35–87%). The catalytic systems obtained by a combination of zirconium or hafnium complexes bearing a secondary phosphine-pendant cyclopentadienyl ligand or a phosphide-pendant cyclopentadienyl ligand with a cocatalyst show moderate activity in ethylene polymerization but show inactivity in styrene polymerization. In ethylene/styrene copolymerization, these systems afford ethylene/styrene copolymers with a high styrene content.

Carbocationic rearrangement of pivaloyl cation and protonated pivalaldehyde in superacid medium: a novel solution equivalent of the McLafferty rearrangement

Both pivaloyl cation in the presence of hydride donors and protonated pivalaldehyde in superacid media (both aprotic and protic) rearrange to protonated methyl isopropyl ketone involving gitionic dicationic intermediates. In our earlier studies we have found that the rearrangement of pivaladehyde to methyl isopropyl ketone occurs quantitatively in the presence of various superacidic media such as anhydrous HF, triflic acid, boron trifluoride-2,2,2-trifluoroethanol complex (BF 3·2CF 3CH 2OH) etc. Our present study with environmentally more benign and stable amine:HF complexes, namely pyridinium poly(hydrogen fluoride) ( PPHF) ( 5), poly(4-vinylpyridinium) poly(hydrogen fluoride) ( 6), and poly(ethyleniminium) poly(hydrogen fluoride) ( PEIHF) ( 7) shows that these modified HF equivalents can carry sufficient amount of immobilized HF and provide ample acidity for complete isomerization of pivalaldehyde to methyl isopropyl ketone. Calculations on protioformyl, acetyl and pivaloyl dications at the B3LYP/6-311 ++ G(d,p) and CCSD(T)/6-311 ++ G(d,p)//B3LYP/6-311 ++ G(d,p) levels have been performed to compare the nature of protosolvation of formyl, acetyl, pivaloyl cations and protonated pivaladehyde in superacid media. These studies further suggest protosolvation of protonated pivalaldehyde leading to gitionic dications at high acidities resulting in the carbocatioinic rearrangement. The reported carbocationic rearrangement under superacidic activation represents a novel solution chemistry equivalent of the well known gas-phase McLafferty rearrangement.

Construction of a New Asymmetric Reaction Site: Asymmetric 1,4‐Addition of Thiol Using Pentagonal Bipyramidal Hf(salen) Complex as Catalyst.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Computational Study of Ligand Interactions with Hafnium and Zirconium Metal Complexes in the Liquid−Liquid Extraction Process

In this paper we present a computational study of ligand interactions with hafnium and zirconium metal complexes which occur in the liquid-liquid extraction of these metals from their aqueous solutions. Separation of Hf and Zr has been a challenge in liquid-liquid extraction technologies and the existing methodologies, namely the MIBK (methyl isobutyl ketone) process, are used to extract hafnium into the organic phase while on the contrary the TBP (tributyl phosphate) process is used to extract Zr into the organic phase. Understanding the actual interactions taking place, including an estimate of the binding energies and conformations of the guest-host system of the metal complexes and the solvents, would help us to design better and safer extractants. Recent studies in the literature have shown that the quantum chemical based DFT methods have proven to be good tools for such types of studies. Thus in this work we have carried out high-level DFT studies using the hybrid B3LYP/Lanl2dz and BLYP/TZP (with the relativistic corrections) on tetravalent Hf and Zr metal complexes interacting with neutral ligands and compared the results to the experimental observations. These studies show that at the molecular level it is the Hf complex that has larger interaction energy with the ligands, thus indicating that in the mixture of Hf and Zr complexes in solutions which are not complicated by aggregation and polymerization, Hf would be extracted preferably into the organic solvent, in agreement with the experimental observation. We conclude from this study that primary interaction energies (gas-phase stabilization) are sufficient to significantly discriminate Hf and Zr complexes and thus can be used to explain Hf and Zr separation.

Spectroscopy of the OC-HF hydrogen-bonded complex at vHF=3.

The v(HF)=3 levels of the linear OC-HF complex are observed in the range of 10,800-11,500 cm(-1) using intracavity Ti-sapphire laser-induced fluorescence. The vibrational predissociation linewidths of both (30000) and (3001(1)0) states exceed 5 GHz; thus, the measured spectra are not rotationally resolvable. Under the assumption that these levels are not strongly perturbed, the rotational constants of the two levels are determined to be 0.1100(1) cm(-1) for (30000), 0.1081(1), and 0.1065(1) cm(-1) for f and e sublevels of (3001(1)0), respectively, through band contour fitting. The (30000)<--(00000) band origin is at 10,894.46(1) cm(-1), showing a HF wave number redshift of 478.3 cm(-1). The 4.07 redshift ratio of v(HF)=3 to that of v(HF)=1 indicates a significantly nonlinear increase of the intermolecular interaction energy through HF valence excitation. An ab initio interaction potential surface for HF valence coordinates varying from 0.8 to 1.25 A is used to examine vibrational dynamics. The HF valence vibration v(1) is treated perturbatively, showing that the vibrational redshifts are determined essentially in first order with only a very small second-order contribution. The (3001(1)0)<--(00000) combination transition is observed with the band origin at 11,432.66(1) cm(-1), giving the HF intermolecular bending mode to be 538.2 cm(-1). The high frequency of this vibration, compared to that in similar HF complexes, shows the strong angular anisotropy of the intermolecular interaction potential of OC-HF with respect to the HF subunit. The lifetime of the (3001(1)0) level increases to 28 ps from 14 ps for (30000).

Infrared matrix isolation studies of the acetohydroxamic acid complexes with HF and HCl

Argon matrix infrared spectra of the complexes formed between acetohydroxamic acid (CH 3CONHOH) and hydrogen halides (HF, HCl) have been recorded. The experimental results indicate formation of a strong binary complex in which the hydrogen halide molecule acts as a proton donor towards the carbonyl group of acetohydroxamic acid. The H–X stretches and several perturbed CH 3CONHOH vibrations were identified for the two HX complexes; for the HF complex the two librational HF modes were also observed.

Construction of a new asymmetric reaction site: asymmetric 1,4-addition of thiol using pentagonal bipyramidal Hf(salen) complex as catalyst

Pentagonal bipyramidal Hf(salen) complex 1 was found to serve as a catalyst for 1,4-addition reaction of thiol to N-(2-alkenoyl)-2-oxazolidinones.

Highly Isospecific Polymerization of Propylene with Bis(phenoxy-imine) Zr and Hf Complexes Using iBu3Al/Ph3CB(C6F5)4 as a Cocatalyst

Abstract Highly isospecific propylene polymerization was achieved by bis(phenoxy-imine) Zr and Hf complexes combined with iBu3Al/Ph3CB(C6F5)4. Microstructural analyses of the isotactic polymers suggested that the polymerization probably proceeds via a site-control mechanism with a 1,2-insertion of propylene. Among the complexes examined, Hf complex 2 produced the highest tacticity polypropylene ([mmmm] 96.8%, Tm 165.1 °C) that is comparable to that made by the best heterogeneous Ziegler–Natta catalysts.

An MP2 and DFT study of heterocyclic hydrogen complexes C nH mYHX with n=2, m=4 or 5, Y=O, S or N and X=F or Cl

We present a theoretical study through MP2 ab initio molecular orbital calculations and B3LYP density functional theory with the 6-311++G(d,p) basis set of the heterocyclic hydrogen complexes, C n H m YHX, where C n H m Y=C 2H 4O, C 2H 5N and C 2H 4S, and X=F or Cl. This study aided in the elucidation the main changes in the structural, electronic and the vibrational properties in isolated species, due the hydrogen complexes formation, C n H m YHX, revealing systematic tendencies in these chemical systems studied. The complexes has C S symmetry, with the HX subunit lying in the plane perpendicular to that of CYC nuclei of heterocyclic and acting as proton donor in forming a hydrogen bond to the heteroatom, Y. A weak secondary interaction between the CH 2 groups of heterocyclics and the X atoms in HX causes a significant nonlinearity of the primary hydrogen bond. The hydrogen bond linearity deviations in these complexes due to secondary interactions are represented by θ angle. The MP2 intermolecular distances of complexes C 2H 5NHF, C 2H 4OHF and C 2H 4SHF correspond the 1.652, 1.671 and 2.164 Å, respectively, these results are in excellent agreement with experimental results of 1.700 and 2.193 Å found for the last two complexes. In the same way, the MP2 values to θ angle, 14.7, 19.1 and 16.8°, has a better reproduction in the experimental results of 16.5, 21.0 and 16.8°, get to the C 2H 4OHCl, C 2H 4SHCl and C 2H 4SHF complexes, respectively.

Strong hydrogen bonding between neutral noble-gas molecules (HNgF, Ng=Ar, Kr, and Xe) and hydrogen fluoride: a theoretical study

High-level electronic structure calculation has been performed on the hydrogen-bond complexes of the neutral noble-gas molecules, HArF, HKrF, and HXeF with hydrogen fluoride. Hydrogen bonding from either the hydrogen or the fluorine sides was considered. Very strongly bonding strengths (13–18 kcal/mol) were predicted for the fluorine-side complexes while those of the hydrogen-side complexes were found to be normal for polar neutral molecules. Large increases (409 and 364 cm −1) of the H–Ar and H–Kr stretching frequencies were predicted for HArF⋯HF and HKrF⋯HF complexes. The complexation was found to decrease the dissociation barriers of HNgF along the bending coordinates by approximately 20 kcal/mol.

Isotope effects in ethylene–HX complexes (X=F, Cl or Br)

Ab initio calculations were performed at the MP2/6-311++G(2d,2p) level of theory to obtain optimized geometries, dipole moments, binding energies and harmonic vibrational frequencies for the symmetrical T-shaped structures of XH⋯π bonded complexes involving ethylene (as the proton-acceptor) and the hydrogen halide molecules HF, HCl and HBr (as the proton donors). The relative stabilities of the D-containing isotopomers C 2H 4⋯DX and C 2H 2HD⋯HX were also determined from their zero-point energies. It was found that the D-bonded isotopomer (C 2H 4⋯DX) was more thermodynamically stable than the H-bonded isotopomer (C 2H 2HD⋯HX) for HF, HCl and HBr-containing complexes, previous studies on the weakly bound T-shaped complexes C 2H 2⋯HX also found that the D-bonded species was more stable than the H-bonded species.

Regio‐ and Stereochemistry in Propylene Polymerization Catalyzed with Bis(phenoxy‐imine) Zr and Hf Complexes/MAO Systems

AbstractEnd‐group analyses of the oligo‐ and polypropylenes produced with bis(phenoxy‐imine) Zr and Hf complexes with methylaluminoxane (MAO) indicate that the polymerization is initiated by two consecutive 1,2‐insertions and is terminated by a β‐H transfer following a 2,1‐insertion. Our data indicate that chain propagation occurs with prevailing 1,2‐regiochemistry but with considerable regioerrors, and with virtually no stereoselectivity.The polymerization of propylene mediated by bis(phenoxy‐imine) Zr and Hf complexes with MAO.magnified imageThe polymerization of propylene mediated by bis(phenoxy‐imine) Zr and Hf complexes with MAO.

Relaxation phenomena of polar non-polar liquid mixtures under low and high frequency electric field

Simultaneous calculation of the dipole moment μj and the relaxation time τj of a certain number of non-spherical rigid aliphatic polar liquid molecules (j) in non-polar solvents (i) under 9.8 GHz electric field is possible from real e′ij and imaginary e″ij parts of the complex relative permittivity e*ij. The low frequency and infinite frequency permittivities e0ij and e∞ij measured by Purohitet al [1,2] and Srivastava and Srivastava [3] at 25, 35 and 30°C respectively are used to obtain static μs. The ratio of the individual slopes of imaginary σ″ij and real σ′ij parts of high frequency (hf) complex conductivity σ*ij with weight fractionsw jatw j → 0 and the slopes of σ″ij— σ′ij curves for differentw js [4] are employed to obtain τjs. The former method is better in comparison to the existing one as it eliminates polar-polar interaction. The hf μjs in Coulomb metre (C m) when compared with static and reported μs indicate that μs s favour the monomer formations which combine to form dimers in the hf electric field. The comparison among μs shows that a part of the molecule is rotating under X-band electric field [5]. The theoretical μtheos from available bond angles and bond moments of the substituent polar groups attached to the parent molecules differ from the measured μjs and μs to establish the possible existence of mesomeric, inductive and electromeric effects in polar liquid molecules.

Low-temperature NMR studies of the structure and dynamics of a novel series of acid-base complexes of HF with collidine exhibiting scalar couplings across hydrogen bonds.

The low-temperature (1)H, (19)F, and (15)N NMR spectra of mixtures of collidine-(15)N (2,4,6-trimethylpyridine-(15)N, Col) with HF have been measured using CDF(3)/CDF(2)Cl as a solvent in the temperature range 94-170 K. Below 140 K, the slow proton and hydrogen bond exchange regime is reached where four hydrogen-bonded complexes between collidine and HF with the compositions 1:1, 2:3, 1:2, and 1:3 could be observed and assigned. For these complexes, chemical shifts and scalar coupling constants across the (19)F(1)H(19)F and (19)F(1)H(15)N hydrogen bridges have been measured which allowed us to determine the chemical composition of the complexes. The simplest complex, collidine hydrofluoride ColHF, is characterized at low temperatures by a structure intermediate between a molecular and a zwitterionic complex. Its NMR parameters depend strongly on temperature and the polarity of the solvent. The 2:3 complex [ColHFHCol](+)[FHF](-) is a contact ion pair. Collidinium hydrogen difluoride [ColH](+)[FHF](-) is an ionic salt exhibiting a strong hydrogen bond between collidinium and the [FHF](-) anion. In this complex, the anion [FHF](-) is subject to a fast reorientation rendering both fluorine atoms equivalent in the NMR time scale with an activation energy of about 5 kcal mol(-)(1) for the reorientation. Finally, collidinium dihydrogen trifluoride [ColH](+)[F(HF)(2)](-) is an ionic pair exhibiting one FHN and two FHF hydrogen bonds. Together with the [F(HF)(n)()](-) clusters studied previously (Shenderovich et al., Phys. Chem. Chem. Phys. 2002, 4, 5488), the new complexes represent an interesting model system where the evolution of scalar couplings between the heavy atoms and between the proton and the heavy atoms of hydrogen bonds can be studied. As in the related FHF case, we observe also for the FHN case a sign change of the coupling constant (1)J(FH) when the F.H distance is increased and the proton shifted to nitrogen. When the sign change occurs, that is, (1)J(FH) = 0, the heavy atom coupling constant (2)J(FN) remains very large, of the order of 95 Hz. Using the valence bond order model and hydrogen bond correlations, we describe the dependence of the hydrogen bond coupling constants, of hydrogen bond chemical shifts, and of some H/D isotope effects on the latter as a function of the hydrogen bond geometries.

Evolution of the νHF absorption bands of B⋯HF complexes on transition from the gas to liquid phase

Abstract FTIR spectra of the νHF bands in B/HF mixtures (B=Xe, CO2, CO, HCN, CH3CN) have been recorded with densities varying from the dilute gas to liquid at room temperature. The vibration–rotational bands of free HF molecules in all systems were calculated for the density ranging from 1 to 400 amagat, and, by separating the bands, the νHF band shape of bound molecules were determined. It was shown that on transition from the gas to liquid phase the νHF band of B ⋯ HF complexes shifts toward low frequencies and symmetrizes. The vibration–rotational νHF band of these complexes in the gas phase was calculated using a model with the anharmonic coupling between νHF and low-frequency vibrational modes. It was established that the model taking into account the spectral exchange applied to a system consisting of rotational and low-frequency vibrational subsystems provides a correct description of evolution of the νHF complex band with increasing density.

The infrared spectrum of acetylene–HF in helium nanodroplets

Rotationally resolved infrared spectra are reported for the T-shaped acetylene–HF complex in helium nanodroplets, corresponding to excitation of both the H–F and asymmetric C–H stretches. In comparison to the isolated complex, rotation about the A-axis is relatively unhindered by the helium, while overall rotation is slower by a factor of approximately two. An ab initio potential surface is also reported for this system. Although the bent complex, with acetylene acting as a hydrogen donor, is determined to be a local minimum, only the T-shaped isomer is experimentally observed, indicating that the barrier is too small to prevent the metastable bent structure from rearranging to the global minimum.

Intermolecular complexes of HArF and HF

Two neutral nonlinear complexes of HF and HArF with unusual bonding and vibrational characteristics were found to be stable relative to the constituent monomers by ab initio computations at various levels of theory. In the more stable complex, the proton of the HF molecule is bonded to the F atom of HArF, while in the less stable complex the F atom of HF is bonded to the proton of HArF. The intermolecular bonding in the less stable dimer is consistent with a hydrogen bonded complex, but calculations on the more strongly bound dimer suggest that the intermolecular bond in this case is predominantly ionic.

Dynamics of hydrogen–HF complexes in helium nanodroplets

High-resolution infrared spectra are reported for ortho- and para-H2, ortho- and para-D2, and HD binary complexes with HF, solvated in helium nanodroplets. These rotationally resolved spectra provide detailed information on the rotational and vibrational dynamics of these systems. The para-H2–HF complex is observed, indicative of the unusual growth conditions present in the droplets. In the case of the HD–HF complex, extensive line broadening is observed, which we tentatively explain in terms of the near resonance between the HF and HD vibrational frequencies, which presumably facilitates vibrational relaxation.

Ethylene and Ethylene/Propylene Polymerization Behavior of Bis(phenoxy‐imine) Zr and Hf Complexes with Perfluorophenyl Substituents

AbstractThe catalytic properties of bis(phenoxy‐imine) Zr and Hf complexes incorporating perfluorophenyl groups with methylaluminoxane were investigated. The fluorinated complexes produced far higher‐molecular‐weight polyethylenes and ethylene/propylene copolymers with increased activities compared with the non‐fluorinated congeners. Moreover, the fluorinated complexes displayed a higher incorporation ability for propylene.Structures of complexes 1–4.magnified imageStructures of complexes 1–4.