Thermal Dehydrogenation of Base‐Stabilized B2H5+ Complexes and Its Role in CH Borylation

Thermally induced dehydrogenation of the H‐bridged cation L2B2H5+ (L=Lewis base) is proposed to be the key step in the intramolecular CH borylation of tertiary amine boranes activated with catalytic amounts of strong “hydridophiles”. Loss of H2 from L2B2H5+ generates the highly reactive cation L2B2H3+, which in its sp2‐sp3 diborane(4) form then undergoes either an intramolecular CH insertion with BB bond cleavage, or captures BH3 to produce L2B3H6+. The effect of the counterion stability on the outcome of the reaction is illustrated by formation of LBH2C6F5 complexes through disproportionation of L2B2H5+ HB(C6F5)3−.Catlike: In situ formation of a cationic sp2–sp3 diborane(4) is proposed to be the key step in the high‐temperature intramolecular CH borylation of amine boranes activated with catalytic amounts of strong electrophiles. Reaction mechanisms are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/115925/1/anie_201507647_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/115925/2/13401_ftp.pd

Generation of Highly Electrophilic Cationic Boron Complexes and their Application toward Formation of C-B Bonds.

The focus of our research was to achieve better understanding of the processes underlining the chemistry of highly electrophilic boron cations, and to develop the applications of such cations to C-B bond formation. The reactions of Lewis base borane complexes with potent electrophiles such as the trityl cation, bistriflimide and tris(pentafluorophenyl)borane were explored, and the product structures were assigned based on the X ray crystallographic and spectroscopic data. Hydride abstraction from Lewis base borane complexes by trityl cation was shown to be a viable method for generation of unstabilized primary borenium species, and several such L-BH2+ cations were shown to exist in the condensed phase in the form of diborane(6)-type dicationic dimers. We also explored the aliphatic and aromatic borylation chemistry involving B-H borocations, and developed a procedure for the intramolecular C-H borylation of amine boranes that uses only a catalytic amount of a strong electrophile, and produces H2 gas as the sole byproduct. Additionally, the methodology for generation of more substituted unstabilized borocations derived from 9-BBN was developed, and subsequently applied to the borylation of electron rich heteroaromatic compounds. An unusually hindered boronium cation possessing a 9-BBN cage chelated by 1,8-bis(dimethylamino)naphthalene was structurally characterized and shown to be a potent borylating reagent.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/97944/1/aprokofj_1.pd

RECENT CASES

Hydride abstraction from monocationic hydride bridged salts [H­(H₂B–L)₂]⁺ [B­(C₆F₅)₄]¯ (L = Lewis base) generates an observable primary borenium cation for L = <i>i</i>Pr_<i>2</i>NEt, but with L = Me₃N, Me₂NPr, or several <i>N</i>-heterocyclic carbenes, highly reactive dicationic dimers are formed

Relative contractile motion of the rings in a switchable palindromic [3]rotaxane in aqueous solution driven by radical-pairing interactions

Artificial muscles are an essential component for the development of next-generation prosthetic devices, minimally invasive surgical tools, and robotics. This communication describes the design, synthesis, and characterisation of a mechanically interlocked molecule (MIM), capable of switchable and reversible linear molecular motion in aqueous solution that mimics muscular contraction and extension. Compatibility with aqueous solution was achieved in the doubly bistable palindromic [3]rotaxane design by using radical-based molecular recognition as the driving force to induce switching.National Institute of General Medical Sciences (U.S.) (Award F32GM105403)American Society for Engineering Education. National Defense Science and Engineering Graduate Fellowshi

Sudesna mjerenja γγ-raspada stanja 166Ho nastalih reakcijom (n,γ)

Levels of 166Ho were studied using thermal and average resonance neutron capture and with the (d,p) and (d,3He) reactions. We have devoted a large effort to the measurements of the γγ-coincidence spectra in the broad energy region 50 - 6243 keV. Based on these data and those of earlier studies, the levels are grouped into 23 rotational bands. Among them are 6 new ones. The results are in good agreement with the semiempirical and quasiparticle-phonon model, where Coriolis and residual interactions are taken into account. Details of model interpretation have been presented in a previously published paper.Proučavali smo stanja 166Ho nastala termičkim i prosječnim rezonantnim uhvatom neutrona, te (d,p) i (d,3He) reakcijama. Uložili smo velik trud u mjerenjima sudesnih γγ-spektara u širokom energijskom području od 50 do 6243 keV. Na osnovi tih i ranijih podataka, stanja su grupirana u 23 rotacijske vrpce. Među njima je i 6 novih. Ishodi su u suglasju s poluempiričkim i kvazičestično-fononskim modelom, uzimajući u obzir Coriolisovo međudjelovanje i rezidualne interakcije. Podrobnosti modelskog tumačenja objavljene u u ranijem članku

Karboksilesteraza djelomice hidrolizira estere gama-butirobetaina u serumu štakora

Although described some time ago, gamma-butyrobetaine esters and related compounds have not gained much attention from researchers, and their physiological function remains obscure. Formerly we detected GBB-esterase enzymatic activity in rat blood serum using phenylated gamma-butyrobetaine as an artificial substrate of the enzyme and HPLC. The aim of the present work was to develop an assay that would enable spectrophotometric or colorimetric determination of the reaction products of GBB-esterase activity and to reveal individual proteins performing GBB-esterase activity in rat blood serum. For this purpose gammabutyrobetaine 1-naphthyl ester was synthesised. Hydrolysis of this ester releases 1-naphthol, which increases the optical absorbance at 322 nm. We have shown that the enzymatic hydrolysis of GBB 1-naphthyl ester to 1-naphthol in rat blood serum is due to GBB-esterase activity. An attempt was done to purify the enzyme from rat blood serum. By combining DEAE Sepharose at pH 4.2 and affinity chromatography with procainamide we achieved a 68-fold enrichment of GBB-esterase activity in our preparations. Separation of fraction proteins in 2D protein electrophoresis with following mass-spectrometry indicated that GBB esterase activity in rat blood serum is performed in part by carboxylesterase.Premda su poznati već neko vrijeme, esteri gama-butirobetaina (GBB) i srodni spojevi nisu dobili mnogo pozornosti u znanstvenoistraživačkoj zajednici, a njihova fiziološka funkcija i dalje je nerazjašnjena. U ranijem smo istraživanju HPLC-metodom otkrili enzimsku aktivnost GBB-esteraze u serumu štakora rabeći umjetni supstrat ovoga enzima, tj. fenilirani gama-butirobetain. Cilj ovoga istraživanja bio je razviti pretragu koja će omogućiti spektrofotometrijsko ili kolorimetrijsko određivanje reakcijskih produkata nastalih aktivnošću GBB-esteraze te utvrditi koji pojedinačni proteini u serumu štakora posjeduju aktivnost GBB-esteraze. U tu je svrhu sintetiziran gama-butirobetain 1-naftil ester. Njegovom hidrolizom otpušta se 1-naftol koji povećava optičku apsorbanciju na 322 nm. Pokazali smo da u hidrolizi GBB 1-naftil estera u 1-naftol u serumu štakora sudjeluje GBB-esteraza. Pokušali smo pročistiti enzim iz štakorskoga seruma. Kombinacijom DEAE sefaroze pri pH 4,2 i afinitetne kromatografije s prokainamidom dobili smo 68-erostruko povećanje aktivnosti ovoga enzima. Razdvajanjem bjelančevina iz frakcije s pomoću 2D elektroforeze te naknadnom spektrometrijom masa utvrđeno je da u serumu štakora esteraznu aktivnost prema gama-butirobetainu kao supstratu djelomice provodi karboksilesteraza

Study of ^194 Ir via thermal neutron capture and (d,p) reactions

Levels of ^194 Ir were studied using thermal neutron capture reaction. A pair spectrometer was used to measure the high-energy gamma-ray spectrum from thermal-neutron capture in enriched ^193 Ir target over the energy range 4640 - 6100 keV. The low-energy gamma-radiation from the reaction was studied with crystal diffraction spectrometers, and conversion electrons were observed with magnetic spectrometers. The high-sensitivity measurements at the Grenoble reactor, evaluated for transition energies up to 500 keV, are compared with lower-sensitivity measurements at the Wuerenlingen and Salaspils reactors. The comparison helped to obtain reliable isotopic identification for a number of ^194 Ir lines. The multipolarity admixtures for 29 gamma-transitions were determined on the basis of conversion lines from different electron subshells. Prompt and delayed gamma-gamma coincidences were measured using semiconductor and scintillation detectors. The ^193 Ir(d,p) high-resolution spectra, observed with a magnetic spectrometer, are given. All these data contributed to establishing a detailed level scheme of ^194 Ir. Additional data and the interpretation of the results in terms of current models will be presented in a forthcoming paper