Halide Transfer Research Articles

Dichlorido(crown ether)lanthanoid(III) tetrachloroaluminate complexes

Reactions between LnCl3, AlCl3 and a crown ether (18-crown-6 and dibenzo18-crown-6) in MeCN have led to the isolation of four new lanthanoid halide crown ether complexes, [PrCl(μ-Cl)(18-crown-6)]2[AlCl4]2·2MeCN (1), [YbCl2(18-crown-6)][AlCl4]·MeCN (2), and [LnCl(μ-Cl)(dibenzo18-crown-6)}2][AlCl4]2·6.5MeCN (Ln = La, 3, Pr, 4). 1 was also obtained by unexpected halide transfer on addition of 18-crown-6 (18C6) to MeCN solutions of [Pr(MeCN)9][AlCl4]3. Complexes 1, 3 and 4 have dinuclear chloride-bridged nine-coordinate cations, and 2 has an eight coordinate mononuclear cation.

Halide-Coupled Double Electron Transfer with Electron-Rich Diboranes.

The ditriflato-diborane B2 (μ-hpp)2 (OTf)2 (hpp=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate) acts as a stable surrogate of the elusive dication [B2 (hpp)2 ]2+ , being both electrophilic (vacant boron p orbitals) and nucleophilic (filled B-B bond orbital). This combination of seemingly contrasting behaviors could be used to develop a metallomimetic diborane chemistry, with Lewis σ-basic and π-acidic substrates being bound and reduced at the diborane. Here, we report on a novel reaction type within this general theme, in which double electron transfer from the diboron unit to the boron-bound organic substrate is coupled with halide transfer in the other direction. Novel diborylated dienamines are synthesized in this way. The scope of this unprecedented reaction motif and the reaction pathways are elucidated.

Cu-Catalyzed C(sp3)–N Coupling and Alkene Carboamination Enabled by Ligand-Promoted Selective Hydrazine Transfer to Alkyl Radicals

Selective delivery of an N-nucleophile onto an alkyl radical is a challenging step in redox catalysis. In this work, di-tert-butyl hydrazodiformate was found to be a unique effective amination reagent in Cu-catalyzed C(sp3)–N bond formation reactions that involve alkyl radical intermediates. This method is applicable to both electron-deficient and electron-rich radicals, and we were thus able to achieve the direct C–N coupling of activated bromides, as well as the carboamination of general alkenes based on this chemistry. Mechanistic studies suggest that the hydrazodiformate forms a reducing dinuclear complex with Cu and the ligand which, upon 1e-oxidation, turns into an open-shell species with the major spin density on N atoms. With the assistance of a ligand, this species can selectively deliver the hydrazine moiety onto an alkyl radical (prior to halide transfer), leading to the formation of a C(sp3)–N bond. The products obtained with this amination method could be easily deprotected to afford alkyl hydrazines and further derived to primary amines or N-heterocycles.

Pillared Metal-Organic Framework Initiating Intermolecular Atom-Transfer Radical Addition via Visible-Light-Induced Electron Transfer Activation of Haloalkanes.

Herein, a novel metal-organic framework (MOF) with a pillared-layer structure was rationally synthesized to initiate intermolecular atom-transfer radical addition (ATRA) via photoinduced electron transfer activation of haloalkanes. The MOF synthesized via the controllable pillared-layer method is of excellent visible-light absorption and high chemical stability. Photocatalytic experiments show the atom transfer of various alkyl halides (R-X, X = Cl/Br/I) onto diverse olefins was successfully achieved to produce functional ATRA products. The mechanism and experimental investigations reveal the prepared MOF serves as an efficient photocatalyst with strong reduction potential to activate haloalkane substrates via photoinduced electron transfer, generating a highly reactive alkyl radical to trigger the ATRA reaction. Key events in the ATRA reaction, including alkyl radical photogeneration as well as halide transfer, have been further regulated to achieve preferable photocatalytic performance with higher yields, shorter reaction time, and desirable cycling capability. It is notable that the work is the first report on photoinduced electron transfer activation of halides by a MOF photocatalyst for the ATRA reaction, providing a new blueprint for MOFs to develop photoinduced radical reactions.

EPC-SAFT advanced - Part I: Physical meaning of including a concentration-dependent dielectric constant in the born term and in the Debye-Hückel theory

The transition from aqueous electrolyte systems to non-aqueous electrolyte systems is highly demanded in industrial applications and especially challenging for physics-based thermodynamic models. Electrolyte thermodynamics is a complex matter, and still not all physico-chemical effects are accounted for in state-of-the-art equations of state. The dielectric constant of non-aqueous electrolyte systems changes drastically compared to aqueous systems. One main consequence is that ions are very differently solvated in non-aqueous medium compared to aqueous medium. The Born term represents a methodology to account for the influence of solvation energies of ions, which is based on influences of solvent and salt on the dielectric constant. Utilizing the Born term in electrolyte models is extensively debated, and it is often reasonably neglected in predominantly aqueous systems. Yet, it has a significant influence on transferability from aqueous to non-aqueous media i.e., systems with a large difference in polarity or permittivity compared to aqueous systems. In this work, a modified Born term was combined with electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT) by introducing additionally a salt concentration-dependent dielectric constant, henceforth called altered Born contribution. The new methodology was validated against infinite dilution properties for ion-solvent interactions: Gibbs energy of hydration and Gibbs energy of transfer of alkali halides from water to alcoholic solvents. Further, mean ionic activity coefficients (MIACs) of alkali halides in alcoholic solvents were quantitatively correct predicted with the advanced ePC-SAFT approach. Original ePC-SAFT parameters were applied for all predictions, and no further binary parameters were adjusted. Based on the success of the model predictions, the transferability of pure-ion ePC-SAFT parameters to organic solvents was verified and the incorporation of concentration-dependent dielectric constant into the altered Born contribution and Debye-Hückel theory was proven to be meaningful methods for the transfer of electrolyte thermodynamic models from aqueous to non-aqueous systems.

Computational Study on the Catalytic Reaction Mechanism of Heme Haloperoxidase Enzymes

AbstractHeme haloperoxidases are unique enzymes in biology that react H2O2 and halides on a heme center to generate hypohalide, which reacts with a substrate by halide transfer. We studied model complexes of the active site of heme haloperoxidase and investigated the reaction mechanism starting from an iron(III)‐hydrogen peroxide‐heme complex. We find two stepwise proton transfers by active site Glu and His residues to form Compound I and water, whereby the second proton transfer step is rate‐determining. In a subsequent reaction with chloride the oxygen atom transfer is studied to form hypohalide. Overall, the free energy of activation of the second proton transfer and oxygen atom transfer to halide are similar in energy with free energies of activation of around 20 kcal mol−1. The calculations show that during oxygen atom transfer from Compound I to halide, significant charge‐transfer happens prior to the transition state. This implies that the reaction may be enhanced in polar environments and through second‐coordination sphere effects. The studies show that the conversion of H2O2 and halide on a heme center is fast and few intermediates along the reaction mechanism will have a lifetime that is long enough to enable trapping and characterization with experimental methods. A range of active site models and density functional theory methods were tested, but little effect is seen on the mechanism and optimized geometries.

DFT studies of isomerization in palladium(IV) chemistry and alkyl halide transfer from palladium(IV) to palladium(II)

A DFT study of alkyl halide exchange from Pd(IV) to Pd(II) centers supports proposals for an SN2 process in which nucleophilic Pd(II) square-planar complexes attack the axial alkyl group in electrophilic square-pyramidal Pd(IV) centers, leading to transfer of R+ from Pd(IV) to Pd(II) involving a transition structure of the form [R2(bpy)··R··PdR2 (bpy)]+ (bpy = 2,2′-bipyridine). Computation accounts for the selectivity in benzyl (Bn) over methyl transfer from PhMeBnPdIV(bpy)Br to Me2PdII(bpy), giving PhMePdII(bpy) and BnMe2PdIV(bpy). Transition structures are formed by the interaction of a dz2-like HOMO at the Pd(II) nucleophile and the Pd-C σ* LUMO at the cationic Pd(IV) electrophile. Isomerization of octahedral palladium(IV) complexes via halide loss followed by involvement of trigonal-bipyramidal transition structures to facilitate isomerization is also examined. A lower barrier for Bn+ than Me+ transfer is attributed to stabilisation of the transition structure by delocalisation of positive charge within the benzyl group, reflected in a higher total charge density for the benzyl group than found for the methyl group.

A Comparative Review on the Catalytic Mechanism of Nonheme Iron Hydroxylases and Halogenases

Enzymatic halogenation and haloperoxidation are unusual processes in biology; however, a range of halogenases and haloperoxidases exist that are able to transfer an aliphatic or aromatic C–H bond into C–Cl/C–Br. Haloperoxidases utilize hydrogen peroxide, and in a reaction with halides (Cl−/Br−), they react to form hypohalides (OCl−/OBr−) that subsequently react with substrate by halide transfer. There are three types of haloperoxidases, namely the iron-heme, nonheme vanadium, and flavin-dependent haloperoxidases that are reviewed here. In addition, there are the nonheme iron halogenases that show structural and functional similarity to the nonheme iron hydroxylases and form an iron(IV)-oxo active species from a reaction of molecular oxygen with α-ketoglutarate on an iron(II) center. They subsequently transfer a halide (Cl−/Br−) to an aliphatic C–H bond. We review the mechanism and function of nonheme iron halogenases and hydroxylases and show recent computational modelling studies of our group on the hectochlorin biosynthesis enzyme and prolyl-4-hydroxylase as examples of nonheme iron halogenases and hydroxylases. These studies have established the catalytic mechanism of these enzymes and show the importance of substrate and oxidant positioning on the stereo-, chemo- and regioselectivity of the reaction that takes place.

Gradient Optical Elements: Methods of Obtaining and Measuring Refractive Index Distribution Profiles

The basic methods of obtaining gradient optical elements are presented, the primary one being ion-exchange diffusion. Anew method developed by the authors for obtaining gradient optical media, which is based on the discovery of halide ion transfer in solid glasses, is noted. Methods of measuring the distribution profiles of the refractive index which have been realized in practice are examined as a question that holds a special place in the technology of gradient optical elements and is an independent scientific problem in its own right. It is shown that in a number of cases, because of the size effect, it is desirable to use an empirical method to adjust the ion-exchange processing regimes.

Zhenfeng Xi

Angewandte Chemie International EditionVolume 55, Issue 13 p. 4124-4124 Author ProfileFree Access Zhenfeng Xi First published: 11 November 2015 https://doi.org/10.1002/anie.201510083AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract “My favorite food is noodles. My favorite piece of music is Going Home (Kenny G) ...” This and more about Zhenfeng Xi can be found on page 4124. 1 Table 1. Zhenfeng Xi Date of birth: April 2, 1963 Position: Professor of Organometallic Chemistry, Peking University (PKU) E-mail: zfxi@pku.edu.cn Homepage: http://www.chem.pku.edu.cn/xizf/revised/ Education: 1983 BSc, Xiamen University 1989 MSc with Douman Jin, Nanjing University, Zhengzhou University, and the Henan Institute of Chemistry 1996 PhD with Tamotsu Takahashi, Hokkaido University 1996–1997 Postdoctoral position with Tamotsu Takahashi, Hokkaido University Awards: 2000 Outstanding Young Investigator Award, Hong Kong Qiu Shi Science & Technologies Foundation; 2001 Chang Jiang Professorship; 2004 Yaozeng Huang Organometallic Chemistry Award, Chinese Chemical Society (CCS); CCS–BASF Award; 2005 Eli Lilly Research Excellence Award; 2014 CCS–AkzoNobel Chemical Sciences Award Current research interests: Organo-di-metallic reagents; reactive organometallic and organic intermediates; metallacycles; catalytic cleavage of C−Si bonds and C−N bonds; ligand design Hobbies: Walking, music, reading My favorite food is noodles. My favorite piece of music is Going Home (Kenny G). The principal aspect of my personality is perseverance. The biggest problem that scientists face is moving away from fundamental research. My favorite piece of research is the chemistry of organodilithium reagents. When I'm frustrated, I sit by myself and calm down. The most important thing I learned from my parents is every cloud has a silver lining. I chose chemistry as a career because I am fascinated by the nature of change in chemical reactions and by the range of properties that result from the endless options for the combination of elements. If I were not a scientist, I would be a gardener. My most exciting discovery to date has been synergistic effects of organo-di-metallic reagents. Guaranteed to make me smile is watching babies playing with their toys. My 5 top papers: References 1“2,6-Diazasemibullvalenes: Synthesis, Structural Characterization, Reaction Chemistry, and Theoretical Analysis”: S. Zhang, J. Wei, M. Zhan, Q. Luo, C. Wang, W.-X. Zhang, Z. Xi, J. Am. Chem. Soc. 2012, 134, 11964. (Sheds light on a previously unexplored class of highly strained ring systems.) 2“Cyclopentadiene-Phosphine/Palladium-Catalyzed Cleavage of C−N Bonds in Secondary Amines: Synthesis of Pyrrole and Indole Derivatives from Secondary Amines and Alkenyl or Aryl Dibromides”: W. Geng, W.-X. Zhang, W. Hao, Z. Xi, J. Am. Chem. Soc. 2012, 134, 20230. (Application of a new cyclopentadiene–linker–phosphine ligand.) 3“Intramolecular C−F and C−H bond cleavage promoted by butadienyl heavy Grignard reagents”: H. Li, X.-Y. Wang, B. Wei, L. Xu, W.-X. Zhang, J. Pei, Z. Xi, Nat. Commun. 2014, 5, 4508. (Heavy Grignard reagents were synthesized and applied to the synthesis of perfluoro-π-extended pentalene derivatives.) 4“Transfer of Aryl Halide to Alkyl Halide: Reductive Elimination of Alkylhalide from Alkylpalladium Halides Containing syn-β-Hydrogen Atoms”: W. Hao, J. Wei, W. Geng, W.-X. Zhang, Z. Xi, Angew. Chem. Int. Ed. 2014, 53, 14533; Angew. Chem. 2014, 126, 14761. (A system that forms alkyl–I bonds by reductive elimination, despite the presence of syn-β-hydrogen atoms that might be expected to undergo β-hydride elimination to form olefins.) 5“Dianions as Formal Oxidants: Synthesis and Characterization of Aromatic Dilithionickeloles from 1,4-Dilithio-1,3-butadienes and Ni(cod)2”: J. Wei, W.-X. Zhang, Z Xi, Angew. Chem. Int. Ed. 2015, 54, 5999; Angew. Chem. 2015, 127, 6097. (Dianions with suitable π conjugation can behave as non-innocent ligands or redox-active ligands to make aromatic metalloles.) Volume55, Issue13March 18, 2016Pages 4124-4124 ReferencesRelatedInformation

Reaction of a polyphosphino ruthenium(II) acetate complex with Grignard reagents: Halogenation, alkylation and β-elimination

(PMe3)4Ru(H)OAc has been prepared from (PPh3)3Ru(H)OAc via phosphine exchange followed by solvent partitioning between acetonitrile and pentane. Complexes of the type (PMe3)4Ru(H)R (R = Et, nPr, nBu, iBu, H) have been synthesized through reaction with the corresponding Grignard reagents, RMgCl, and were found to be moderately stable provided the alkyl group is primary. Treatment with bulkier alkylmagnesium chlorides led instead to the dihydrido complex (PMe3)4RuH2. In some cases, the reaction was complicated by transfer of halide from the Grignard reagent to form, for example, (PMe3)4Ru(H)Cl.

ChemInform Abstract: Transfer of Aryl Halide to Alkyl Halide: Reductive Elimination of Alkylhalide from Alkylpalladium Halides Containing syn‐β‐Hydrogen Atoms.

AbstractUnsymmetrical alkynes (VIII) react regioselectively to yield compounds (IX).

Transfer of Aryl Halide to Alkyl Halide: Reductive Elimination of Alkylhalide from Alkylpalladium Halides Containing syn‐β‐Hydrogen Atoms

Abstractβ‐Hydride abstraction is a well‐accepted elementary step for catalytic cycles in organometallic chemistry. It is usually anticipated that alkylpalladium halides containing syn‐β‐hydrogen atoms will undergo β‐hydride abstraction to afford the Heck‐type products. However, this study discloses that the above general knowledge is only conditionally correct. Our experimental results demonstrate that the reductive elimination of alkylhalides from alkylpalladium halides containing syn‐β‐hydrogen atoms may surpass the β‐hydride abstraction or even become exclusive in certain cases.

Transfer of aryl halide to alkyl halide: reductive elimination of alkylhalide from alkylpalladium halides containing syn-β-hydrogen atoms.

β-Hydride abstraction is a well-accepted elementary step for catalytic cycles in organometallic chemistry. It is usually anticipated that alkylpalladium halides containing syn-β-hydrogen atoms will undergo β-hydride abstraction to afford the Heck-type products. However, this study discloses that the above general knowledge is only conditionally correct. Our experimental results demonstrate that the reductive elimination of alkylhalides from alkylpalladium halides containing syn-β-hydrogen atoms may surpass the β-hydride abstraction or even become exclusive in certain cases.

Ionic Liquids, Superionic Glasses, Quasi-Ionic Liquids, Quasi-Liquid Ionics, All with High Conductivities but Some with Little Fluidity. Where does the Paradigm End?

Ionic liquids (ILs) are interesting in electrochemistry mainly because of their ability to carry high ionic currents in two distinct cases: (i) for the aprotic class of ILs it is for current flow within a large window of electrochemical stability and hence the support a range of battery electrochemistries[1], and (ii) for the protic class of ILs (PILs) it is for their tunability within a very wide "acidity window"[2]. For case (i), the stability window can extend to almost 6 volts (liquids), and much more at the oxidative end if the liquid has vitrified[3]. The protic ionic liquids are prepared by proton transfer from a Bronsted acid to a Bronsted base, and have been widely studied. Much less well- studied are the "halide-transfer" ionic liquids in which a halide ion is transferred from a halogenated molecular liquid to a strong Lewis acid[4, 5]. Where the proton transfer can be 100% complete in most cases, it is difficult to obtain 100 % halide transfer. In some cases the conductivity is apparently much more complex in nature involving transient oxygen links to the Lewis acid[6]. This means that members of this class of ionic liquid tend to be of low ionicity relative others examined on a Walden plot, although they can still be highly conducting due to their high fluidities. Finally we will discuss some new cases where the conductivity is liquid-like (10 mScm-1), while the system formally has solidified. These are obtained from ionic liquids that have frozen only in the first stage where the centers of mass have become ordered but the rotational and positional order of alkali cations, remains liquid-like[7].[1] J.S. Wilkes, Green industrial applications of ionic liquids. (Editors, R. D. Rogers, K. R. Seddon, and S. Volkov.) (2003) 295-320.[2] C.A. Angell, Y. Ansari, Z.-F. Zhao, Faraday Discussion, 154 (2012) 9-27.[3] A. Hayashi, S. Hama, F. Mizuno, K. Tadanaga, T. Minami, M. Tatsumisago, Solid State Ionics, 175 (2004) 683-686.[4] K. Xu, N.D. Day, C.A. Angell, J. Electrochem. Soc. , 143 (1996) L209-L211.[5] T.G. Tucker, C.A. Angell, (to be published).[6] K. Xu, S.S. Zhang, C.A. Angell, J. Electrochem. Soc. , 143 (1996) 3548-3554[7] T.G. Tucker, C.A. Angell, (to be published), (2014).

Imaging ion-molecule reactions: Charge transfer and halide transfer reactions of O+ with CH3Cl, CH3Br, and CH3I

Velocity map images have been recorded for the charge transfer reactions of O+(4S) with CH3Cl, CH3Br, and CH3I at collision energies near 4eV. The production of methyl halide cations occurs for all systems, with relative abundances ranging from 10 to 15% of the total reaction yield. In addition, small yields of the dissociative charge transfer products Br+ and I+ are observed. The velocity space images show that charge transfer is energy resonant, and occurs by long range electron transfer. The predominant product in all three systems is CH3+, which may form by dissociation of the nascent CH3X+ product on a quartet potential energy surface, or by halide ion abstraction from CH3X by O+ following a spin-changing transition from the initial quartet surface to a doublet surface. The kinetic energy distributions for CH3+ formation show both a sharp low energy feature that appears to describe the formation of CH3++O(3P)+X(2P), in addition to a higher energy component that describes the more exoergic channel forming CH3++XO(2Π). The relative intensity of this high energy feature increases as the halogen atom X changes from Cl to Br to I, a progression that correlates with the strength of the halogen atom spin–orbit splitting. This observation supports the conclusion that the formation of the CH3+ products via the most exoergic channels, i.e., CH3++XO(2Π), does occur through spin-changing collisions from quartet to doublet state surfaces that are mediated by spin–orbit coupling.

On divorcing isomers, dissecting reactivity, and resolving mechanisms of propane C[sbnd]H and aryl C[sbnd]X (X = halogen) bond activations mediated by a ligated copper(III) oxo complex

The long suspected presence of two isomeric copper complexes (A and B), proportionally dependent on ESI cone voltage, was confirmed by their isolation, separation and characterization in a travelling wave ion mobility spectrometry–mass spectrometer (TWIMS–MS) with modifications to allow for ion/molecule reactions to be performed. Despite their small difference in cross-sectional area (∼1%) the isomers were well resolved, in part due to a strong interaction of isomer B with the N2 buffer gas. The reactivity of each TWIMS-separated isomer was probed: propane reacted with isomer A via CH bond activation and O-atom transfer, while no such reactions were observed for isomer B; the aryl halides PhX (X=F, Cl, Br, I) also reacted solely with A, via either concerted oxidation and halide transfer, or O-atom transfer. DFT calculations reveal that the aryl CX bond activation of PhX by isomer A involves several mechanistic pathways.

Enhanced transparent-conducting fluorine-doped tin oxide films formed by Aerosol-Assisted Chemical Vapour Deposition

We report a systematic study into the importance of carrier solvent on the Aerosol-Assisted Chemical Vapour Deposition (AACVD) of fluorine-doped tin oxide (FTO) films. In particular, the resultant effects on both the optical transparency and electrical conductivity properties are reported with optimised films showing figures-of merit significantly beyond commercial products. Depositions were carried out at substrate temperatures of 500, 550 and 600 °C using either N2 or air as the carrier gas. The carrier solvent was found to have a marked effect on film quality and performance characteristics. Hall Effect results indicate that use of propan-2-ol as carrier solvent and air as carrier gas gave the best performing n-type FTO thin films overall that exhibited high optical transparency (>80% at 550 nm) and resistivity values of 4 × 10−4 Ω cm, with charge carrier density and carrier mobility values of 4 × 1020 cm−3 and 39 cm2 V−1 s−1 respectively, in addition to haze values of 10–15%. Such parameters are ideal for thin film solar cell applications and have significantly higher figures of merit compared to current commercial materials. Success of this method of deposition is attributed, in part, to a halide transfer reaction in which part fluorine substitution of the tin precursor occurs in the solvent resulting in a direct tin–fluorine bond. The work shows the key role carrier solvents play in AACVD in directing the system chemistry.

Synthesis of dihalogenidoindium(III) ions by halide transfer involving tellurium compounds in the presence of hard and soft ligands

In this article we present the synthesis and structural characterization of the coordination compounds trans-[InCl2(OPPh3)4][PhTeCl4], trans-[InBr2(OPPh3)4][PhTeBr4], cis-[InBr2(dmso)4][PhTeBr4] and cis-[InBr2(1,10-phen)2][PhTeBr4]. These complexes contain indium(III) and tellurium(IV) stabilized by hard and soft ligands. We have also discussed the facile tendency of the tellurium atoms to exchange their oxidation levels as well as the influence of the size of the ligands on the stereochemistry of the indium complexes.

Reactivity of Lewis Acid Activated Diaza- and Dithiaboroles in Electrophilic Arene Borylation

Hydride abstraction from N,N′-bis(adamantyl)-1-hydrido-1,3,2-benzodiazaborole with catalytic [Ph3C][closo-CB11H6Br6] resulted in a low yield of arene borylation and a major product derived from migration of both adamantyl groups to the arene backbone. In contrast, the related aryl-substituted diazaborole N,N′-(2,6-diisopropylphenyl)-1-bromo-1,3,2-diazaborole did not borylate benzene or toluene, being resistant to halide abstraction even with strong halide acceptors: e.g., [Et3Si][closo-CB11H6Br6]. The reactivity disparity arises from greater steric shielding of the boron pz orbital in the 2,6-diisopropylphenyl-substituted diazaboroles. Boron electrophiles derived from 1-chloro-1,3,2-benzodithiaborole ((CatS2)BCl) are active for arene borylation, displaying reactivity between that of catecholato- and dichloro-boron electrophiles. [(CatS2)B(NEt3)][AlCl4] is significantly less prone to nucleophile-induced transfer of halide from [AlCl4]¯ to boron compared to catecholato and dichloro borocations, enabling it to borylate arenes containing nucleophilic −NMe2 moieties in high conversion (e.g., N,N,4-trimethylaniline and 1,8-bis(dimethylamino)naphthalene). Calculations indicate that the magnitude of positive charge at boron is a key factor in determining the propensity of chloride transfer from [AlCl4]¯ to boron on addition of a nucleophile.