Borate Counteranion Research Articles

Extreme Ultraviolet Photoresponse of Organotin-Based Photoresists with Borate Counteranions.

Organometallic tin-oxo-hydroxo cage compounds offer a promising photoresist platform for extreme ultraviolet photolithography (EUVL). Their reactivity is dominated by the facile breaking of the tin-carbon bonds upon photon or electron irradiation. As the cage is dicationic, it exists as a complex with anions for charge compensation. In the present work, we explore the n-butyltin-oxo cage with two tetrakis(pentafluorophenyl)borate counteranions (TinPFPB). In contrast to the small counterions that are typically used, the bulky PFPB anion absorbs a substantial fraction (∼30%) of the impinging EUV radiation (13.5 nm, 92 eV), and it has its own reactivity upon photoionization. When thin films of the complex are irradiated with EUV radiation at low doses, a positive-tone development is possible, which is rather unique as all other known tin-oxo cage resists show a negative tone (cross-linking) behavior. We propose that the initial positive tone behavior is a result of the chemical modification of the Sn cluster by fragments of the borate anions. For comparison, we include the tetrakis(p-tolyl)borate anion (TB) in the study, which has similar bulkiness, and its complex with the n-butyltin-oxo cage (TinTB) shows the usual negative tone EUV resist behavior. This negative-tone behavior for our control experiment rules out a hypothesis based purely on the steric hindrance of the anion as the cause of the different EUV reactivity.

(η5‐CpR)Ge:]+[BArF4]−/O2 – A Sustainable and Efficient Catalytic System for the Hydrosilylation of Selected Olefins

AbstractThe cationic Ge(II) borates [(η5‐CpR)Ge:]+[BArF4]− (CpR=substituted cyclopentadienyl) efficiently catalyze the anti‐Markovnikov hydrosilylation of alkenes in the presence of oxygen which is investigated using the examples of α‐methylstyrene and 1‐hexene. Full conversion is achieved with a minimal amount of 0.01 mol % of the cationic Ge(II) borate even at rt. The effect of oxygen is investigated and quantified by kinetic measurements which demonstrate that oxygen is an activator which interacts directly with the germanium complex. Solvent‐free hydrosilylation conditions are realized by the introduction of a more lipophilic silylated borate counteranion. Thus, the novel catalytic system is an efficient, sustainable and air‐stable catalyst alternative for the established hydrosilylation catalysts based on noble metal complexes.

Trialkylphosphonium oxoborates as C(sp3)-H oxyanion holes and their application in catalytic chemoselective acetalization.

The use of trialkylphosphonium oxoborates (TOB) as catalysts is reported. The site-isolated borate counter anion in a TOB catalyst increases the availability of C(sp3)-H to interact with electron donor substrates. The catalytic protocol is applicable to a wide range of substrates in the acetalization reaction and provides excellent chemoselectivity in the acetalization over thioacetalization in the presence of alcohols and thiols, which is otherwise hard to achieve using typical acid catalysts. Experimental and computational studies revealed that the TOB catalysts have multiple preorganized C(sp3)-Hs that serve as a mimic of oxyanion holes, which can stabilize the oxyanion intermediates via multiple C(sp3)-H non-classical hydrogen bond interactions.

Hydrosilylation of Carbonyls Catalyzed by Hydridoborenium Borate Salts: Lewis Acid Activation and Anion Mediated Pathways.

The electronically unsaturated three-coordinated hydridoborenium cations [LBH]+[HB(C6F5)3]- (1) and [LBH]+[B(C6F5)4]- (2), supported by a bis(phosphinimino)amide ligand, were found to be excellent catalysts for hydrosilylation of a range of aliphatic and aromatic aldehydes and ketones under mild reaction conditions (L = [{(2,4,6-Me3C6H2N)P(Ph2)}2N]). The key steps of the catalytic cycle for hydrosilylation of PhCHO were monitored via in situ multinuclear NMR measurements for catalysts 1 and 2. The combined effect of carbonyl activation via the Lewis acidic hydridoborenium cation and the hydridic nature of the borate counteranion in 1 makes it a more efficient catalyst in comparison to that of carbonyl activation via the predominant Lewis acid activation pathway operating with catalyst 2. The catalytic cycle of 1 showed hydride transfer from the borate moiety [HB(C6F5)3]- to PhCHO in the first step, forming [PhCH2-O-B(C6F5)3]-, which subsequently underwent σ-bond metathesis with Et3SiH to form the product, PhCH2-O-SiEt3. Quantum chemical calculations also support the borate anion mediated mechanism with 1. In contrast, the reaction catalyzed by 2 proceeds predominantly via the Lewis acid activation of the carbonyl group involving [LB(H)←OC(H)Ph]+[B(C6F5)4]- as the transition state and [LBOCH2Ph]+[B(C6F5)4]- as the intermediate.

Saturated N-Heterocyclic Carbene Based Thiele's Hydrocarbon with a Tetrafluorophenylene Linker.

The synthesis of a SIPr [1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene] derived Kekulé diradicaloid with a tetrafluorophenylene spacer (3) has been described. Two synthetic routes have been reported to access 3. The cleavage of C-F bond of C6 F6 by SIPr in the presence of BF3 led to double C-F activated compound with two tetrafluoro borate counter anions (2), which upon reduction by lithium metal afforded 3. Alternatively, 3 can be directly accessed in one step by reacting SIPr with C6 F6 in presence of Mg metal. Compounds 2 and 3 were well characterized spectroscopically and by single-crystal X-ray diffraction studies. Experimental and computational studies support the cumulenic closed-shell singlet state of 3 with a singlet-triplet energy gap (ΔES-T ) of 23.7 kcal mol-1 .

Synthesis of a Chiral Borate Counteranion, Its Trityl Salt, and Application Thereof in Lewis‐Acid Catalysis

The preparation of a chiral derivative of [B(C6F5)4]– in which the fluorine atom in the para position of each of the C6F5 groups is replaced by a 1,1′‐binaphthalen‐2‐yl group is described. The new counteranion was isolated as its lithium, sodium, and trityl salts. The chiral trityl salt was then used as a catalyst in selected counteranion‐directed Diels–Alder reactions and a Mukaiyama aldol addition, but no asymmetric induction was achieved. Application of the chiral trityl salt to the generation of silicon cations by silicon‐to‐carbon hydride transfer from hydrosilanes failed, presumably as a result of the incompatibility of the relatively electron‐rich naphthyl groups in the borate and the cationic silicon electrophiles.

Electronic effects of ligand substitution on spin crossover in a series of diiminoquinonoid-bridged Fe(II)2 complexes.

A series of four isostructural Fe(II)2 complexes, [(TPyA)2Fe2((X)L)](2+) (TPyA = tris(2-pyridylmethyl)amine; (X)L(2-) = doubly deprotonated form of 3,6-disubstituted-2,5-dianilino-1,4-benzoquinone; X = H, Br, Cl, and F), were synthesized to enable a systematic study of electronic effects on spin crossover behavior. Comparison of X-ray diffraction data for these complexes reveals the sole presence of high-spin Fe(II) at 225 K and mixtures of high-spin and low-spin Fe(II) at 100 K, which is indicative of incomplete spin crossover. In addition, crystal packing diagrams show that these complexes are well-isolated from one another in the solid state, owing primarily to the presence of bulky tetra(aryl)borate counteranions, such that spin crossover is likely not significantly affected by intermolecular interactions. Variable-temperature dc magnetic susceptibility data confirm the structural observations and reveal that 54(1), 56(1), 62(1), and 84(1)% of Fe(II) centers remain high-spin even below 65 K. Moreover, fits to magnetic data provide crossover temperatures of T1/2 = 160(1), 124(1), 121(1), and 110(1) K for X = H, Br, Cl, and F, respectively, along with enthalpies of ΔH = 11.4(3), 8.5(3), 8.3(3), and 7.5(2) kJ/mol, respectively. These parameters decrease with increasing electronegativity of X and thus increasing electron-withdrawing character of (X)L(2-), suggesting that the observed trends originate primarily from inductive effects of X. Moreover, when plotted as a function of the Pauling electronegativity of X, both T1/2 and ΔH undergo a linear decrease. Further analyses of the low-temperature magnetic data and variable-temperature Mössbauer spectroscopy suggest that the incomplete spin crossover behavior in [(TPyA)2Fe2((X)L)](2+) is best described as a transition from purely [FeHS-FeHS] (HS = high-spin) complexes at high temperature to a mixture of [FeHS-FeHS] and [FeHS-FeLS] (LS = low-spin) complexes at low temperature, with the number of [FeHS-FeHS] species increasing with decreasing electron-withdrawing character of (X)L(2-).

Reactivity of Organogold Compounds with B(C6F5)3: Gold–Boron Transmetalation via σ-B/π-Au Species

The reactions of gold-acetylides with B(C6F5)3 afford alkynyl borate species and cationic π-coordinated gold complexes. The analogous reactions with aryl gold species generate gem-diaurated compounds containing a borate counteranion. These new σ-B/π-Au alkynyl borate complexes can be employed as active catalysts in homogeneous catalysis and represent a new silver-free activation pathway. The new alkynyl borate species are fully characterized, and the alkyne fragments are shown to be bound in a σ-B/π-Au fashion. Upon prolonged heating, these compounds undergo a slow C6F5 group transfer to gold affording LAuC6F5 species.

Ion pair symmetrization in metallocenium cations partnered with diborane derived borate counteranions

The thermodynamics of ion pair symmetrization in a series of metallocenium species generated from Cp 2 ″ ZrMe 2 ( Cp ″ = 1 , 2 - Me 2 C 5 H 3 ) were studied using a variety of solution dynamic techniques including line broadening, 2D-EXSY, and 1D-DPFGSE-NOE. Ion pairs were generated by methide abstraction using the corresponding trityl salts [ 1-A] to yield [ Cp 2 ″ ZrMe ] + [ A ] - (A = {C 6F 4-1,2-[B(C 6F 5) 2] 2(μ-O(C 6F 5))} −, 2-O(C 6 F 5 ); {C 6F 4-1,2-[B(C 6F 5) 2] 2(μ-OPh)} −, 2-OPh; {C 6F 4-1,2-[B(C 6F 5) 2] 2(μ-OMe)} −, 2-OMe; and [B(C 6F 5) 4] −, 2-B(C 6 F 5 ) 4 ). The observed activation parameters were interpreted on the basis of a solvent-assisted mechanism of ion pair symmetrization.

Synthesis of the Phenoxonium Cation of an α-Tocopherol Model Compound Crystallized with Non-Nucleophilic [B(C6F5)4]- and (CB11H6Br6)- Anions

The phenoxonium cation of a vitamin E model compound has been crystallized using the non-nucleophilic carborane and tetrakis(pentafluorophenyl)borate counteranions. The crystal structures confirm the assignment of the unusually stable phenoxonium cation and indicate that there is a substantial shortening of the carbon-oxygen bond lengths of the para-carbon atoms in the phenolic ring and a substantial increase of the carbon-oxygen bond length at the quaternary carbon. The crystallographic data are in excellent agreement with structural predictions from molecular orbital calculations.

Synthesis of a Library Chiral α‐Amino Acid‐Based Borate Counteranions and Their Application to Copper Catalyzed Olefin Cyclopropanation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

σ-Delocalization versus π-Resonance in α-Aryl-Substituted Vinyl Cations

The synthesis and isolation of 12 alpha-aryl, beta, beta'-disilyl-substituted vinyl cations 1b-l, 7, and 8 with the tetrakis(pentafluorophenyl)borate counteranion is reported. The vinyl cations are characterized by NMR spectroscopy and are identified by their specific NMR chemical shifts (delta13C(C(+)) = 178.1-194.5; delta13C (Cbeta) = 83.3-89.9; delta13C (Cipso)) = 113.6-115.2; delta (29)Si = 25.0-12.0), supported by density functional calculations at the B3LYP/6-311G(2d,p)//B3LYP/6-31G(d) level. All cations are found to be stable at room temperature in solution and in the solid state. The NMR chemical shifts as well as J-coupling data indicate for vinyl cations, 1b-l, 7, and 8, the occurrence of substantial stabilization through pi-resonance via the aryl substituents and through sigma-delocalization via the beta-silyl groups. For vinyl cation 8, the free enthalpy of stabilization via pi-resonance by the alpha-ferrocenyl substituent is determined by temperature-dependent (29)Si NMR spectroscopy to be DeltaG++ = (48.9 +/- 4.2) kJ mol(-1). A Hammett-type analysis, which relates the (1)J(SiC(beta)) coupling constant and the low-field shift of the (29)Si NMR signal upon ionization, Deltadelta (29)Si, with the electron-donating ability of the aryl group, indicates an inverse relation between the extent of Si-C hyperconjugation and pi-donation. The computed structures (at B3LYP/6-31G(d)) of the vinyl cations 1a-l, 7, and 8 reveal the consequences of Si-C hyperconjugation and of pi-resonance interactions with the aryl groups. The structures, however, fail to express the interplay between sigma-delocalization and pi-conjugation in that the calculated Si-C bond lengths and the C+-C(ipso) bond lengths do not vary as a function of the substituent.

Synthesis of a library of chiral α-amino acid-based borate counteranions and their application to copper catalyzed olefin cyclopropanation

Twenty borate counteranions have been prepared from tartaric acid and α-amino acid derivatives. Ion pairing of these anions to a copper cation can be used to induce enantioselectivity into the copper catalyzed cyclopropanation of styrene. Structural modification of the anion provides insight into the importance of each component of the counteranion in asymmetric induction.

Design, Synthesis, and Characterization of a New Class of Amino Acid-Based Chiral Borate Counteranions

A new class of α-amino acid-tethered borate counteranion has been prepared from α-amino acid, tartaric acid, and HBBr2 building blocks. This anion can be incorporated into transition metal complexes via ion exchange, providing a straightforward nonbonding method to associate metal complexes within a peptide environment.

Coordinating anions: (phosphino)tetraphenylborate ligands as new reagents for synthesis.

Anionic, electron-releasing phosphines that incorporate a borate counteranion within the ligand framework are promising reagents for organometallic catalysis. This report describes the synthesis of a new class of monodentate tertiary phosphines built upon the commonly employed tetraphenylborate anion. These new phosphines are highly stable and strongly electron-releasing and readily coordinate transition metals. Moreover, they are promising reagents for catalysis, as demonstrated by their ability to promote the Suzuki cross-coupling of aryl chloride substrates.

The use of a chiral borate counteranion as a 1H NMR shift reagent for cationic copper(I) complexes

The chiral borate counteranion bis[(R)-1,1′-bi-2-naphtholato]borate (1–) has been found to be a competent chiral 1H NMR shift reagent for cationic copper(I) complexes. This has been demonstrated by the addition of the Cu(NCMe)4+ salt of 1– to two classes of common chiral ligands in asymmetric catalysis: 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl (tol-BINAP) (2) and 2,2′-isopropylidenebis(4-phenyl-2-oxazoline) (3). In the case of ligand 2, the addition of 1 equiv. of either (R,R)-2 or (S,S)-2 to Cu(NCMe)4+1– results in well-resolved 1H NMR resonances for the two enantiomers. Examination of standard solutions of non-enantiopure 2 shows that the copper complex can be an effective NMR shift reagent of a wide range of enantiomeric compositions. Cu(NCMe)4+1– also generates distinct 1H NMR resonances for the two separate enantiomers of 2,2′-isopropylidenebis(4-phenyl-2-oxazoline) (3). However, attempts to employ this copper salt as a chiral NMR shift reagent for rac-3 led to the discovery of a new and unexpected equilibrium: [(R,R)-3]Cu+ + [(S,S)-3]Cu+ [Formula: see text] [(R,R)-3][(S,S)-3]Cu+ + Cu+. Key words: chiral counteranion, copper, chiral NMR shift reagent, ion pairing.

Reactivities of Chromophore-Containing Methyl Tri-n-butylammonium Organoborate Salts as Free Radical Photoinitiators: Dependence on the Chromophore and Borate Counterion

Several UV absorbing chromophores have been incorporated in ammonium triphenylbutyl- and tetraphenylborates as light-harvesting groups, and the reactivity of the resulting salts as unimolecular free radical initiators has been studied. The results are compared with kinetic and thermodynamic data calculated for the primary photochemical step leading to generation of the initiating species. The dependence of the initiation reactivities on the structure of both the chromophore and the borate counteranion is discussed.