Electron-withdrawing CF3 Research Articles

Impact of Substituents on Excited-State and Photosensitizing Properties in Cationic Iridium(III) Complexes with Ligands of Coumarin 6.

A series of bis-cyclometalated cationic iridium (Ir) complexes were synthesized employing two coumarin 6 ligands and a 2,2'-bipyridine (bpy) with various substituents as new sensitizers, realizing both features of strong visible-light absorption and long-lived excited state. Complexes 2-4, with electron-donating methyl and methoxy groups, absorbed visible light strongly (ε: 126 000-132 000 M(-1) cm(-1)) and exhibited room-temperature phosphorescence with remarkably long lifetimes (21-23 μs) in dichloromethane. In contrast, the excited state of prototype complex 1 without any substituents was short-lived, particularly in highly polar acetonitrile. Phosphorescence of complex 5 with the strong electron-withdrawing CF3 groups was too weak to be detected at room temperature even in less polar dichloromethane. The triplet energies of their coumarin ligand-centered ((3)LC) phosphorescent states were almost invariable, demonstrating that selective tuning of the excited-state lifetime is possible through this "simple chemical modification of the bpy ligand" (we name it the "SCMB" method). The spectroscopic and computational investigations in this study suggest that a potential source of the nonradiative deactivation is a triplet ligand-to-ligand charge-transfer state ((3)LLCT state, coumarin 6 → bpy) and lead us to conclude that the energy level of this dark (3)LLCT state, as well as its thermal population, is largely dependent on the substituents and solvent polarity. In addition, the significant difference in excited-state lifetime was reflected in the photosensitizing ability of complexes 1-5 in visible-light-driven hydrogen generation using sodium ascorbate and a cobalt(III) diglyoxime complex as an electron donor and a water-reduction catalyst, respectively. This study suggests that the SCMB method should be generally effective in controlling the excited state of other bis-cyclometalated cationic Ir(III) complexes.

Synthesis and characterization of new fluorinated photoactive polyamides based on xanthene pendant: Evaluation of antibacterial and heavy metal ions removal behavior

ABSTRACTA series of novel organosoluble polyamides (PAs) bearing different functional groups such as flexible ether, substituted imidazole, and xanthene rings and electron-withdrawing CF3 groups were synthesized from diamines and various dicarboxylic acids. The structures of diamines and PAs were fully characterized by elemental analysis, Fourier transform infrared spectroscopy, and proton nuclear magnetic resonance spectroscopy. The PAs showed good solubility in aprotic and polar organic solvents, with high thermal stability exhibiting the glass transition temperatures (Tgs) and 10% weight loss temperatures (T10%) in the range of 184–277°C and 410–480°C in N2 atmosphere, respectively. These polymers showed fluorescence emission upon irradiation with UV light. Diamine compounds and two of synthesized polymers were also screened for antibacterial activity against gram-positive and gram-negative bacteria, and the obtained results for all four combinations showed good inhibition. Extraction capability for heavy metal ions such as Cr3+, Pb2+, Hg2+, Cd2+, and Co2+ from aqueous solutions was also tested at 25°C and pH 7–8.

Effect of the Introduction of a CF<sub>3</sub> Group to a Silyl-Anchor Azobenzene Dye on Sensitization Property in Dye-Sensitized Solar Cells

The effect of the introduction of a CF3 group to a silyl-anchor moiety of the sensitizer on the sensitizing property for the dye-sensitized solar cell was examined by using alkoxysilyl-anchor azobenzene dyes. The cell sensitized by the silyl-anchor dye with the electron-withdrawing CF3 group in the silyl-anchor moiety exhibited higher photovoltaic performance than that by the silyl-anchor dye without the CF3 group.

Effects of Ligand Halogenation on the Electron Localization, Geometry and Spin State of Low-Coordinate (β-Diketiminato)iron Complexes.

This contribution explores the influences of incorporating electron-withdrawing CF3 and halide groups into β-diketiminate iron complexes of tetrazene and isocyanide. The synthesis of a new halogenated β-diketimine (LCF3,ClH) was accomplished via two different methods, including a novel microwave-assisted synthesis that improves the yield of the difficult condensation. Treatment of an iron(II) complex of this ligand with reductant and azide gives two diiron complexes with novel tetrazenes as bridging ligands. Structural and Mössbauer data show that the bridging tetrazene is a radical anion. The halogenation of the supporting ligand also influences iron(I) complexes of the type LFe(CNtBu)2, which are low-spin and square-planar with alkyl substituents but high-spin and pseudotetrahedral with halogen substituents. DFT calculations suggest that the changes from halogenation come from a combination of steric and electronic effects, and that the electronic influence of ligand halogenation is minor.

An Insight of the Results Provided by Color‐Tuning Studies Made on Ir(III) Complexes: A pi‐Neutral CF3 Group Viewed by Adjusting Energies of pi‐type Molecular Orbitals

AbstractThe pi‐nature of a CF3 group can be understood through analysis of its bond orbitals (BOs) mixed into the pi‐type molecular orbitals of CF3‐substituted Ir(ppy)2MDPA+ complexes (ppy=2‐phenyl‐pyridine and MDPA=methylated 2,2′‐dipyridyl amine). It has been found that, through this natural bond orbital analysis, the parent’s molecular orbitals (MOs) can be stabilized by χρ*CF BO via negative hyperconjugation and, simultaneously, destabilized by electron lp(F) BO. Since these two competing pi‐effects are virtually counterbalanced as indicated by the vanishing values of crystal orbital overlap populations, the chemical substitution strategy originated from lowering of HOMO by using this electron‐withdrawing CF3 group has been found effective in color‐tuning to blue region. Based on reduced shielding effect due to de‐ creased χρ‐electron density, the reported position dependent CF3‐substitution effects on pi‐type MOs can also be understood through HOMO/LUMO wavefunction analysis.

Ab initio study of charge transfer between lithium and para-disubstituted benzenes

The present work examines how substituents affect the interaction of lithium with the benzene ring and considers whether two configurations, “loose” and “tight,” can be found for the investigated set of complexes as in the lithium complexes with polyaromatic hydrocarbons. The two conformations were actually found for the electron-donating substituents, whereas for the electron-withdrawing substituents, CF3 and NO2, only tight conformation could be optimized. For complexes in the loose conformation [with the N(CH3)2, NH2, OH, H, Cl, and CH3 substituents], the transfer of electron density was directed from the region occupied by a disubstituted benzene to that occupied by Li. The amount of transferred density was very similar for all the complexes (0.21–0.25 a.u.). By contrast, in the tight complexes, the density transfer direction was opposite and the amount of the transferred density depended on the electronegativity of the substituents on benzene ring, being −0.09, −0.09, −0.13, −0.15, −0.15, −0.20, and −0.30 a.u. for N(CH3)2, NH2, OH, H, Cl, CF3, and NO2, respectively. Geometries of the loose and tight conformations differed notably. The six-membered ring was significantly more warped in the tight conformation than in the loose one: In the latter, the ring was nearly planar, whereas in the former, the ring had the boat structure.

Electronic and Steric Effects in Rollover C–H Bond Activation

Steric and electronic factors in rollover C–H bond activation of substituted 2,2′-bipyridines, mediated by platinum(II), have been investigated by comparing the influence of two substituents, CH3 and CF3, on the progress of the reaction. The substituents were chosen to have similar steric hindrance but different electronic effects and were placed in position 6 (i.e., near one of the nitrogen atoms) or in position 5, which allows, in part, electronic and steric influence to be distinguished. The ligands studied, 6-methyl-2,2′-bipyridine, 5-methyl-2,2′-bipyridine, 6-trifluoromethyl-2,2′-bipyridine, and 5-trifluoromethyl-2,2′-bipyridine, were compared to unsubstituted 2,2′-bipyridine in the reaction with the electron-rich complex [Pt(Me)2(DMSO)2]. The electron-withdrawing CF3 group was found to have a significant effect in accelerating the cyclometalation reaction. The substituent in position 6 influences the stability of the intermediate adduct [Pt(N,N)(Me)2] (N,N = chelated bipyridine), as indicated by density functional theory calculations. The steric hindrance of substituted bipyridines was also evaluated by defining and measuring the angle ζ in [Pt(N,N)(Me)2] adducts. The presence of a substituent in position 6 causes destabilization of the adduct, acceleration of the cyclometalation reaction, and regioselectivity of C–H bond activation

Chloro- and Trifluoromethyl-Substituted Flanking-Ring m-Terphenyl Isocyanides: η6-Arene Binding to Zero-Valent Molybdenum Centers and Comparison to Alkyl-Substituted Derivatives

Presented herein are synthetic and structural studies exploring the propensity of m-terphenyl isocyanide ligands to provide flanking-ring η(6)-arene interactions to zerovalent molybdenum centers. The alkyl-substituted m-terphenyl isocyanides CNAr(Mes2) and CNAr(Dipp2) (Ar(Mes2) = 2,6-(2,4,6-Me3C6H2)2C6H3; Ar(Dipp2) = 2,6-(2,6-(i-Pr)2C6H3)2C6H3) react with Mo(η(6)-napthalene)2 in a 3:1 ratio to form tris-isocyanide η(6)-arene Mo complexes, in which a flanking mesityl or 2,6-diisopropylphenyl group, respectively, of one isocyanide ligand is bound to the zerovalent molybdenum center. Thermal stability and reactivity studies show that these flanking ring η(6)-arene interactions are particularly robust. To weaken or prevent formation of a flanking-ring η(6)-arene interaction, and to potentially provide access to the coordinatively unsaturated [Mo(CNAr(R))3] fragment, the new halo-substituted m-terphenyl isocyanides CNAr(Clips2) and CNAr(DArF2) (Ar(Clips) = 2,6-(2,6-Cl2C6H3)2(4-t-Bu)C6H2; Ar(DArF2) = 2,6-(3,5-(CF3)2C6H3)2C6H3) have been prepared. Relative to their alkyl-substituted counterparts, synthetic and structural studies demonstrate that the flanking aryl rings of CNAr(Clips2) and CNAr(DArF2) display a lower tendency toward η(6)-binding. In the case of CNAr(DArF2), it is shown that an η(6)-bound 3,5-bis(trifluoromethyl)phenyl group can be displaced from a zerovalent molybdenum center by three molecules of acetonitrile. This observation suggests that the CNAr(DArF2) ligand effectively masks low-valent metal centers in a fashion that provides access to low-coordinate isocyano targets such as [Mo(CNAr(R))3]. A series of Mo(CO)3(CNAr(R))3 complexes were also prepared to compare the relative π-acidities of CNAr(Mes2), CNAr(Clips2), and CNAr(DArF2). It is found that CNAr(DArF2) shows increased π-acidity relative to CNAr(Mes2) and CNAr(Clips2), despite the fact that its electron-withdrawing CF3 groups are fairly distal to the terminal isocyano unit.

Structures and Phosphorescence Properties of Triphosphine-Supported Au2Ag2 and Au8Ag4 Alkynyl Cluster Complexes

The synthesis, structure, and phosphorescence properties of two families of triphosphine-supported Au(I)–Ag(I) heteronuclear alkynyl cluster complexes with unprecedented Au2Ag2 and Au8Ag4 cluster structures are described. The phosphorescence emission over the whole visible light region was systematically tuned through modification of the electronic effects in aromatic acetylide ligands to attain bright phosphorescence with different luminescent colors. Introduction of electron-withdrawing CF3 to phenylacetylides results in the emission spectral blue-shift, while it shows progressive red-shift upon introducing electron-donating But, OMe, or NMe2. As demonstrated from both experimental and theoretical studies, the phosphorescence arises primarily from 3LLCT/3IL and Au2Ag2/Au8Ag4 cluster-centered 3[d→p] transitions.

Spectroscopic and Theoretical Study on Electronically Modified Chromophores in LOV Domains: 8‐Bromo‐ and 8‐Trifluoromethyl‐Substituted Flavins

Two chemically synthesized flavin derivatives, 8-trifluoromethyl- and 8-bromoriboflavin (8-CF(3)RF and 8-BrRF), were photochemically characterized in H(2)O and studied spectroscopically after incorporation into the LOV domain of the blue light photoreceptor YtvA from Bacillus subtilis. The spectroscopic studies were paralleled by high-level quantum chemical calculations. In solution, 8-BrRF showed a remarkably high triplet quantum yield (0.97, parent compound riboflavin, RF: 0.6) and a small fluorescence quantum yield (0.07, RF: 0.27). For 8-CF(3)RF, the triplet yield was 0.12, and the fluorescence quantum yield was 0.7. The high triplet yield of 8-BrRF is due to the bromine heavy atom effect causing a stronger spin-orbit coupling. Theoretical calculations reveal that the decreased triplet yield of 8-CF(3)RF is due to a smaller charge transfer and a less favorable energetic position of T(2), required for intersystem crossing from S(1) to T(1), as an effect of the electron-withdrawing CF(3) group. The reconstitution of the LOV domain with the new flavins resulted in the typical LOV photochemistry, consisting of triplet state formation and covalent binding of the chromophore, followed by a thermal recovery of the parent state, albeit with different kinetics and photophysical properties.

Impact of Ligand Modification on Hydrogen Photogeneration and Light-Harvesting Applications Using Cyclometalated Iridium Complexes

To explore structure-activity relationships with respect to light-harvesting behavior, a family of bis-cyclometalated iridium complexes [Ir(C^N)(2)(Hbpdc)] 2-5 (where C^N = 2-phenylbenzothiazole and its functionalized derivatives, and H(2)bpdc =2,2'-bipyridine-4,4'-dicarboxylate) was synthesized using a facile method. The photophysical and electrochemical properties of these complexes were investigated and compared to those of analogue 1 (C^N = (4-trifluoromethyl)-2-phenylbenzothiazole); they were also investigated theoretically using density functional theory. The molecular structures of complexes 2-4 were determined by X-ray crystallography, which revealed typical octahedral coordination geometry. The structural modifications involved in the complexes were accomplished through the attributes of electron-withdrawing CF(3) and electron-donating NMe(2) substituents. The UV-vis spectra of these species, except for that of 5, displayed a broad absorption in the low-energy region, which originated from metal-to-ligand charge-transfer transitions. These complexes were found to exhibit visible-light-induced hydrogen production and light-to-electricity conversion in photoelectrochemical cells. The yield of hydrogen production from water using these complexes was compared, which revealed substantial dependences on their structures, particularly on the substituent of the cyclometalated ligand. Among the systems, the highest turnover number of 1501 was achieved with complex 2, in which the electron-withdrawing CF(3) substituent was connected to a phenyl ring of the cyclometalated ligand. The carboxylate anchoring groups made the complexes highly suitable for grafting onto TiO(2) (P25) surfaces for efficient electron transfer and thus resulted in an enhancement of hydrogen evolution compared to the unattached homogeneous systems. In addition, the combined incorporation of the electron-donating NMe(2) group and the electron-withdrawing CF(3) substituent on the cyclometalated ligand caused complex 5 to not work well for hydrogen production. Their incorporation, however, enhanced the performance of 5 in the light-harvesting application in nanocrystalline TiO(2) dye-sensitized solar cells, which was attributed to the intense absorption in the visible region.

Substituent effect on the photophysical properties, electrochemical properties and electroluminescence performance of orange-emitting iridium complexes

A series of bis(2-phenylbenzothiozolato-N,C(2'))iridium(acetylacetonate) [(bt)(2)Ir(acac)] derivatives, 1-4, were synthesized. Different substituents (CF(3), F, CH(3), OCH(3)) were introduced in the benzothiazole ring to study the substituent effect on the photophysical, electrochemical properties and electroluminescent performance of the complexes, and finally to select high-performance phosphors for use in organic light-emitting diodes (OLEDs). All complexes 1-4 and (bt)(2)Ir(acac) are orange-emitting with tiny spectral difference, despite the variation of the substituent. However, the phosphorescent quantum yield increases with the electron-withdrawing ability of the substituent. This is in contrast to the previous observation that the substituent in the phenyl ring bonded to the metal center of (bt)(2)Ir(acac) not only affected the luminescent quantum efficiency but also greatly tuned the emission color of the complexes. Quantum chemical calculations revealed that the substituents in this position do not make a significant contribution to both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which probably accounts for the fact that they do no strongly influence the bandgap and emission color of the complexes. Orange OLEDs were fabricated using 1-4 as doped emitters. The electron-withdrawing CF(3) and F groups favor improving the electroluminescence efficiency in comparison with that of the parent (bt)(2)Ir(acac), while electron-donating CH(3) and OCH(3) are not favorable for light emission. The complex 1 based OLED exhibited a maximum luminance efficiency of 54.1 cd A(-1) (a power efficiency of 24 lm W(-1) and an external quantum efficiency of 20%), which are among the best results ever reported for vacuum deposited orange OLEDs so far.

Influence of Electron-Donating and Electron-Withdrawing Substituents on the Chemiluminescence Behavior of Coelenterazine Analogs

Abstract Coelenterazine analogs 3a–3e possessing various substituents at the para-position of the 6-phenyl group (R = CF3, F, H, OMe, and NMe2) were synthesized, and the chemiluminescent properties of 3a–3e in dimethyl sulfoxide (DMSO) were investigated quantitatively. Chemiluminescence maxima observed in the range of 454–478 nm showed a bathochromic shift as the electron-donating ability of R increased. Chemiluminescence quantum yields (ΦCL) were obtained in the range of 0.0006–0.0018. The analog 3a possessing the electron-withdrawing CF3 group showed a slight decrease in its ΦCL value. The fluorescence quantum yields (ΦF) of the light emitter, 2-acetamidopyrazine anions 4a−–4e−, were observed in the range of 0.005–0.21 and showed substituent dependency in that the increment in the electron-withdrawing ability of R decreases the ΦF value. The efficiency of generation of the singlet-excited 4a−–4e− (ΦS) showed a small change in the range of 0.008–0.015. From these quantitative analyses of the quantum efficiencies, we found that an electron-donating substituent R is not required for the efficient generation of a singlet-excited light emitter, but is required for the high ΦF of the emitter.

Synthesis, photophysical and NMR evaluations of thiourea-based anion receptors possessing an acetamide moiety

The synthesis and photophysical evaluation of three diaryl thiourea-based anion receptors (4–6) for comparison with their urea counterparts (1–3) is outlined. These anion receptors posses an acetamide functionality on one of the aryl groups and an electron-withdrawing CF3 group on the other. By varying the position of the acetamide group, in the o-, m- and p-positions of 4–6, respectively, the anion binding ability was both tuneable and found to be, in some cases, significantly different from that seen for the urea analogues 1–3. The binding affinities of the receptors 4–6, as well as the binding stoichiometries, were evaluated using UV–vis absorption spectroscopy in MeCN. However, these receptors were not sufficiently emissive to quantify the anion recognition using fluorescence. The results confirmed strong binding of these receptors to anions such as fluoride, acetate, phosphate, pyrophosphate and chloride. Nevertheless, the overall results obtained did not conform to the anticipated trends seen for 1–3, which is most likely due to the enhanced binding affinity of the thiourea analogues 4–6. The binding interactions were also investigated by using 1H NMR which confirmed that these receptors interacted with the anions in a stepwise manner, where the primary anion binding interaction occurred at the thiourea side, which led to an activation of the acetamide moiety towards the second anion binding interaction, an example of an allosteric activation mode.

Effect of Heme Modification on Oxygen Affinity of Myoglobin and Equilibrium of the Acid−Alkaline Transition in Metmyoglobin

Functional regulation of myoglobin (Mb) is thought to be achieved through the heme environment furnished by nearby amino acid residues, and subtle tuning of the intrinsic heme Fe reactivity. We have performed substitution of strongly electron-withdrawing perfluoromethyl (CF(3)) group(s) as heme side chain(s) of Mb to obtain large alterations of the heme electronic structure in order to elucidate the relationship between the O(2) affinity of Mb and the electronic properties of heme peripheral side chains. We have utilized the equilibrium constant (pK(a)) of the "acid-alkaline transition" in metmyoglobin in order to quantitatively assess the effects of the CF(3) substitutions for the electron density of heme Fe atom (rho(Fe)) of the protein. The pK(a) value of the protein was found to decrease by approximately 1 pH unit upon the introduction of one CF(3) group, and the decrease in the pK(a) value with decreasing the rho(Fe) value was confirmed by density functional theory calculations on some model compounds. The O(2) affinity of Mb was found to correlate well with the pK(a) value in such a manner that the P(50) value, which is the partial pressure of O(2) required to achieve 50% oxygenation, increases by a factor of 2.7 with a decrease of 1 pK(a) unit. Kinetic studies on the proteins revealed that the decrease in O(2) affinity upon the introduction of an electron-withdrawing CF(3) group is due to an increase in the O(2) dissociation rate. Since the introduction of a CF(3) group substitution is thought to prevent further Fe(2+)-O(2) bond polarization and hence formation of a putative Fe(3+)-O(2)(-)-like species of the oxy form of the protein [Maxwell, J. C.; Volpe, J. A.; Barlow, C. H.; Caughey, W. S. Biochem. Biophys. Res. Commun. 1974, 58, 166-171], the O(2) dissociation is expected to be enhanced by the substitution of electron-withdrawing groups as heme side chains. We also found that, in sharp contrast to the case of the O(2) binding to the protein, the CO association and dissociation rates are essentially independent of the rho(Fe) value. As a result, the introduction of electron-withdrawing group(s) enhances the preferential binding of CO to the protein over that of O(2). These findings not only resolve the long-standing issue of the mechanism underlying the subtle tuning of the intrinsic heme Fe reactivity, but also provide new insights into the structure-function relationship of the protein.

Mechanism of ethylene hydroformylation on platinum complexes with hydrophosphoryl ligands: a DFT study

The mechanism of ethylene hydroformylation on model organoplatinum hydrides [(R2PO)2H]Pt(PR3)(H)] (R = H, Me, CF3) was studied within the framework of the density functional theory with the PBE gradient-corrected functional and the TZ2p basis set. The presence of a free coordination site in these square-planar 16-electron platinum complexes provides the possibility of alkene coordination in the first step without energetically unfavorable dissociation of one of the metal-ligand bonds. High strength of the —PR2O—H....O—R2 hydrogen bond results in the formation of a bidentate ligand in the coordination sphere of the metal atom. This ligand makes the geometry of the catalytic center rigid, thus enhancing the regioselectivity of the process. The proton can reversibly migrate with ease within the —PR2O—H... O—R2 hydrogen bond, thus providing fine adjustment of the electron density in the catalytic center in each reaction step and acting as a molecular switch. The rate-limiting step in the hydroformylation is the CO insertion into the Pt-Et σ-bond. Electron-donating Me groups at the phosphorous atoms hamper, while electron-withdrawing CF3 groups facilitate, the process.

A new nickel(II) coordination polymer derived from [Ni(N,N-ethylenebis(1,1,1-trifluoroacetylacetoneiminato)] and 1,4-diazabicyclo[2.2.2]octane

The presence of two electron-withdrawing CF3 groups in [Ni{N,N-ethylenebis(1,1,1-trifluoroacetylacetoneiminato)}] (NiL) has been demonstrated to promote axial coordination by pyridine (Py) ligands to form the corresponding octahedral base adduct complex in the solid state, while the corresponding solid products do not form in the absence of the CF3 groups. The change to octahedral geometry is accompanied by a spin-state change of the nickel from low- to high-spin. The structure of the octahedral product, [NiL(Py)2], has been confirmed by X-ray diffraction. In an extension of this study, [NiL] was reacted with the difunctional (stronger) base 1,4-diazabicyclo[2.2.2]octane (dabco); the X-ray structure of the product confirmed the formation of a one-dimensional coordination polymer in which dabco axially bridges [NiL] units in a highly linear fashion. This product represents an example of a new class of one-dimensional polymeric structures in which a difunctional base (in this case dabco) links square planar [NiL] units of the present type.

A thermally resistant and air-stable n-type organic semiconductor: Naphthalene diimide of 3,5-bis-trifluoromethyl aniline

We report a thermally resistant and air-stable n-type semiconductor based on our study of naphthalene diimide (NTCDI) derivatives ( N1, N2, and N3) with various numbers of electron-withdrawing CF 3 groups. The device using N3, which contains aromatic NTCDI, was found to exhibit an electron mobility ( μ e) of 0.15 (±0.04) cm 2/V s (the maximum μ e observed was 0.24 cm 2/V s) and an I on/I off (at V d = 80 V) of approximately 2 × 10 5. Moreover, the N3 device exhibits excellent air stability, even when exposed to the open air for 42 days, and significantly better thermal resistance than the previously reported benzylic imide derivative R1.

Bis- and Mono(amidate) Complexes of Yttrium: Synthesis, Characterization, and Use as Precatalysts for the Hydroamination of Aminoalkenes

A high-yielding synthetic route is disclosed for yttrium bis- and mono(amidate) complexes using the reaction of amide proligand and Y(N(SiMe3)2)3 starting materials. The structure, bonding, and solution phase characterization data for this new class of complexes are presented. The modular nature of the amidate ligand allows for easy addition of electron-withdrawing CF3 groups in the ligand backbone to tune electronic properties of the resulting precatalysts. The amidate ligands in the bis(amidate) complexes were found to be highly fluxional on the NMR time scale, while the mono(amidate) yttrium complex required heating to 110 °C before ligand redistribution was observed. Three bis(amidate) complexes with differing electronic properties and one mono(amidate) complex have been used as precatalysts for hydroamination using a wide range of aminoalkene substrates. Bis(amidate) complexes bearing the more electron-withdrawing amidate ligands were found to be the most active precatalysts for intramolecular alkene hydroamination.

How to Stabilize η3-Silapropargyl/Alkynylsilyl Complex of [CpL2M]+(L = CO, PMe3, or PF3 and M = W or Mo): Theoretical Prediction

We theoretically investigated here how to stabilize a new transition metal η3-silapropargyl/alkynylsilyl complex CpL2M(η3-R22SiCCR1) (M = W or Mo; L = CO, PMe3, or PF3; Cp = C5H5; R1 = H, Me, tBu, or CF3; R2 = H, Me, or F) which is an interesting silicon analogue of a transition metal η3-propargyl complex. Though this complex was experimentally proposed as an intermediate in the synthesis of a tungsten acetylide−silylene complex Cp(CO)2W(CCtBu)(SiPh2), it has not been synthesized yet. From theoretical computations with DFT method, we wish to propose that the combination of electron-withdrawing CF3 on C, σ-electron-withdrawing/π-electron-donating F on Si, Mo center, and CO is the best to stabilize the η3-silapropargyl/alkynylsilyl form. However, the combination of bulky tBu on C, either H or Me on Si, W center, and PMe3 is the best to stabilize the acetylide−silylene form, which is also an interesting species. The reasons are discussed herein.