Academic literature on the topic 'Borabenzène'

Quantum-chemical calculations employing different theoretical methods and basis sets have been performed on borabenzene (C5H5B) as well as on its adducts to dinitrogen (N2) and the rare gases Ne, Ar, and Kr. In agreement with previous calculations, the ground state of borabenzene was found to be a planar singlet with six electrons in molecular orbitals of π symmetry and a wide C-B-C bond angle (142.2°). Depending on the method (PUMP2, SAC-CI, CASPT2(8,8)), the lowest triplet state was found to be 28 to 46 kcal mol–1 (1 kcal mol–1 = 4.186 kJ mol–1) higher in energy. The energies associated with the formation of the adducts with N2, Ne, Ar, and Kr were calculated as –14.9, –0.5, –1.4, and –3.5 kcal mol–1 respectively. Our calculated spectrum of the normal modes as well as the electronic excitation spectrum of the N2 adduct reproduce qualitatively the characteristic features of the IR and the UV-vis spectra described by experimentalists. The corresponding calculated spectra (normal modes, UV-vis) of the rare gas adducts were found to be very similar to those of free borabenzene.

The adduct of borabenzene (C5H5B) and pyridine (C5H5N) was studied by means of quantum-chemical ab initio and time-dependent density functional theory calculations at different levels of theory. In the fully optimized structure (MP2/6-311++G**) of the free donor–acceptor complex (C2), the C–B–C angle amounts to 120.6°. The planes of the two aromatic rings enclose a torsion angle of ~40° with a barrier to rotation about the B–N bond of less than 3 kcal mol–1 (1 kcal mol–1 = 4.186 kJ mol–1). The highest computational level applied in this study (complete basis set limit, coupled cluster with single and double excitations (CCSD)) results in an energy associated with the reaction of borabenzene with pyridine of –52.2 kcal mol–1. Natural bond orbital analyses were performed to study the bond between the borabenzene and the pyridine unit of the adduct. The UV-vis spectrum of the adduct was calculated employing time-dependent density functional theory methods and the symmetry-adapted cluster-configuration interaction method. Our calculated electronic excitation spectrum of the pyridine adduct as well as its spectrum of the normal modes qualitatively reproduce the characteristic features of the IR and the UV-vis spectra described by experimentalists and thus allows assignment of the observed absorption bands, which in part agree with those by other authors.

The adduct of borabenzene (C5H5B) and pyridine (C5H5N) was studied by means of quantum-chemical ab initio and time-dependent density functional theory calculations at different levels of theory. In the fully optimized structure (MP2/6-311++G**) of the free donor–acceptor complex (C2), the C–B–C angle amounts to 120.6°. The planes of the two aromatic rings enclose a torsion angle of ~40° with a barrier to rotation about the B–N bond of less than 3kcalmol–1 (1kcalmol–1=4.186kJmol–1). The highest computational level applied in this study (complete basis set limit, coupled cluster with single and double excitations (CCSD)) results in an energy associated with the reaction of borabenzene with pyridine of –52.2kcalmol–1. Natural bond orbital analyses were performed to study the bond between the borabenzene and the pyridine unit of the adduct. The UV-vis spectrum of the adduct was calculated employing time-dependent density functional theory methods and the symmetry-adapted cluster-configuration interaction method. Our calculated electronic excitation spectrum of the pyridine adduct as well as its spectrum of the normal modes qualitatively reproduce the characteristic features of the IR and the UV-vis spectra described by experimentalists and thus allows assignment of the observed absorption bands, which in part agree with those by other authors.

Pyridine-borabenzene (1) and pyridine-2-boranaphthalene (2) can be coordinated to group 6A metals M to form compounds of the type (OC)3M·1 and (OC)3M·2, respectively. X-ray structure determinations prove the ligands to be η6-bonded to the metal via the boron-containing six-membered ring.

Ce mémoire porte sur l'étude de la réactivité du l-chloro-2-( triméthylsilyle )-4- (isopropyle)boracyclohexa-2,5-diène avec des complexes de platine(O) riches en électrons. L'objectif de cette étude est de démontrer la possibilité de former un adduit êta₁-borabenzène impliquant une liaison dative M vers B. Ce complexe serait un des rares exemples d'un métal de transition se liant à un acide de Lewis, du groupe XIII par liaison dative et serait le premier exemple d'une liaison métal borane non supportée par chélation. Lors de nos études avec [(PCy₃)₂Pt(O)], nous avons constaté la formation du borabenzène-PCy₃, formé par la décoordination du ligand PCy₃, et un adduit inorganique [(PCy₃)₂Pt(H)(CI)]. On observe aussi un autre produit de coordination sur le platine qui peut être un composé borane mais qu'il nous fût impossible de caractériser. Par la suite, nous avons coordonné le boracycle à [(IMes)₂Pt(O)]. De multiples expériences RMN ont été effectuées pour caractériser le êta₁-borabenzène[( IMes)₂Pt(H)(CI)]. Notamment, les expériences ROESY ont confirmé la proximité entre certains atomes nous permettant de proposer une structure et un mécanisme de formation.

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2010-2011
Deux des intérêts principaux dans notre groupe de recherche sont les interactions des acides de Lewis du groupe 13 avec des métaux de transition et la chimie du borabenzène. Les complexes des métaux de transition avec les borabenzènes neutres ne sont pas communs et consistent en une interaction n⁶ avec le cycle aromatique. Dans le but de stabiliser un nouveau mode de coordination n¹, l'interaction des boracyclohexadiènes avec des composés de Pt(0)IMes₂ (IMes = l, 3-di(2,4,6-triméthylphényl) imidazolin-2-ylidène) a été étudiée. Les complexes de Pt(II) obtenus contiennent une interaction Pt-Cl-B, qui est un nouveau mode de coordination pour le borabenzène. Ces complexes, et leur réactivité avec une série de bases de Lewis, substrats électrophiles et métaux de transition, ont été examinés par des études RMN et DFT.

Les ligands à base de borabenzène/boratabenzène, uniques en leur genre, demeurent l’un des intérêts centraux du groupe Fontaine en raison de leur aromaticité et de leur stabilité en tant que ligands acides de Lewis. La synthèse d’une phosphine de type L possédant un groupe boratabenzène (di-tert-butylphosphidoboratabenzène) a été faite en deux étapes. D’abord, l’espèce neutre borabenzène-di-tert-butylchlorophosphine est préparée à partir de la di-tert-butylchlorophosphine et de la 1-chloro-2-(triméthylsilyl)boracyclohexa-2,5-diène. La réduction de l’intermédiaire neutre avec du potassium génère le sel de potassium équivalent (di-tert-butylphosphidoboratabenzène de potassium). Des complexes de coordination de métaux du groupe 10 présentant des interactions bis-di-tert-butylphosphidoboratabenzène ont été préparés. Les données cristallographiques des complexes de nickel et de platine correspondants montrent qu’une pléiade de modes de liaisons peuvent être atteints avec le ligand obtenu. La voie réactionelle, ainsi que les calculs de théorie de la functionelle de la densité, permettront de démontrer les qualités de ce ligand en tant qu’excellent donneur d’électrons. Le but ultime demeure non seulement l’étude des interactions se déroulant dans la sphère de coordination d’un complexe montrant un groupement borabenzène/boratabenzène, mais aussi l’étude de leur capacités à activer des petites molécules à base d’éléments du groupe principal.
Borabenzene/boratabenzene transition metal systems remain of active interest within the Fontaine group due to a unique combination of aromaticity and stability within a Lewis acidic ligand framework while in a complexed state. Augmentation to a classic L-type phosphine possessing a boratabenzene element has been achieved (di-tert-butylphosphidoboratabenzene). This ligand was successfully synthesized by reaction of di-tert-butylchlorophosphine with 1-chloro-2-(trimethylsilyl)boracyclohexa-2,5-diene which yielded the neutral borabenzene-di-tert-butylchlorophosphine species. Reduction of this borabenzene-di-tert-butylchlorophosphine species with potassium then yielded the target ligand coordinated to potassium (potassium di-tert-butylphosphidoboratabenzene). Utilizing this new phosphine, reactions were carried out where the species was successfully coordinated within three group 10 metal complexes. Crystallographic data from these nickel and platinum bis-phosphine complexes have shown that a variety of binding modes for this ligand with metal centers can be achieved. The synthetic process along with density functional theory calculations will be discussed. The end goal is synthesis of new transition metal complexes displaying prominent borabenzene/boratabenzene moieties and investigating their interactions within the coordination sphere of metal centers as well as their ability to activate small molecules composed of main group elements.

Environ 90% des composés produits industriellement sont fabriqués à l'aide de catalyseurs. C'est pourquoi la conception de catalyseurs toujours plus performants pour améliorer les procédés industriels actuels est toujours d’intérêt. De la grande variété de complexes avec des métaux de transition rapportés jusqu'à présent, les complexes zwitterioniques attirent notre attention par leurs activités catalytiques souvent supérieures aux complexes cationiques normaux. Un complexe métallique zwitterionique est un fragment métal-ligand neutre où la charge positive est située sur le centre métallique et où la charge négative est délocalisée sur un des ligands liés au métal. Nous proposons la synthèse de ligands anioniques phosphine comportant des groupements borates et boratabenzènes. Cette dernière espèce est un cycle à 6 membres où l’un des atomes de carbone est remplacé par un atome de bore et qui est négativement chargé. La capacité de ces phosphines anioniques à se lier à un centre métallique à l’aide de la paire libre du phosphore est due à la nature du lien P-B qui défavorise l’interaction entre la paire libre du phosphore et l’orbitale p vide du bore. Les propriétés de di-tert-butylphosphido-boratabenzène (DTBB) comme ligand phosphine anionique hautement donneur et encombré ainsi que la découverte de ses modes de coordination inhabituels pour stabiliser les métaux de transition insaturés ont été étudiés au cours de ce travail. De nouvelles perspectives sur les modes de coordination de phosphido-boratabenzène et la force de l’interaction du lien P-B seront discutées ainsi que les applications catalytiques. Nous avons d’abord étudié la coordination η1 avec des complexes de fer, ce qui nous a fourni des données quantitatives précieuses sur la capacité du DTBB d’agir comme ligand très donneur par rapport aux autres ligands donneurs bien connus. La capacité du DTBB à changer de mode de coordination pour soutenir les besoins électroniques du métal a été démontrée par la découverte d’une nouvelle espèce ferrocenyl phosphido-boratabenzène et sa nucléophilie a été étudiée. Au meilleur de notre connaissance, aucun exemple d’un ligand boratabenzène coordonné aux métaux du groupe 11 n’existe dans la littérature. Voilà pourquoi nous avons décidé d’explorer les modes de coordination du ligand DTBB avec Cu(I), Ag(I) et Au(I). A notre grande surprise, le ligand DTBB est capable de stabiliser les métaux du groupe 11 aux états d’oxydation faibles par une liaison MP qui est une coordination du type η1, un mode de coordination guère observé pour les ligands boratabenzène. Pendant nos travaux, notre attention s’est tournée vers la synthèse d’un complexe de rhodium(I) afin de tester son utilité en catalyse. A notre grande satisfaction, le complexe Rh-DTBB agit comme un précatalyseur pour l’hydrogénation des alcènes et alcynes à la température ambiante et à pression atmosphérique et son activité est comparable à celle du catalyseur de Wilkinson. Dans un désir d’élargir les applications de notre recherche, notre attention se tourna vers l’utilisation des composés du bore autres que le boratabenzène. Nous avons décidé de synthétiser une nouvelle espèce phosphido-borate encombrée. Lorsqu’elle réagit avec des métaux, l’espèce phosphido-borate subit un clivage de la liaison P-B. Toutefois, cette observation met en évidence la singularité et les avantages de la stabilité de la liaison P-B lors de l’utilisation du fragment boratabenzène. Ces observations enrichissent notre compréhension des conditions dans lesquelles la liaison P-B du ligand DTBB peut être clivée. Ces travaux ont mené à la découverte d’un nouveau ligand ansa-boratabenzène avec une chimie de coordination prometteuse.
About 90% of industrially produced compounds are made using catalysts. This is why the design of ever more efficient catalysts to improve the current industrial processes remains a subject of interest. A wide variety of complexes with transition metals have been reported so far. Amongst the plethora of metal complexes used as catalysts, zwitterionic complexes are of particular interest due to their increased catalytic activity that often surpasses that of their cationic parent complexes. A zwitterionic complex is a neutral metal-ligand fragment where the positive charge is localized over the metal center and the negative charge is delocalized over the ligands. In order to generate new zwitterionic complexes, we are looking at the coordination chemistry of anionic phosphine ligands bearing boratabenzene functionalities. Boratabenzene is a six-membered heterocycle where one of the C-H fragments has been replaced by a negatively charged B-X fragment. The ability of these anionic phosphines to bind to a metal center by the phosphorous lone pair is due to the nature of the P-B interaction, which disfavours orbital overlap between the lone pair of electrons on phosphorous and the empty p orbital on boron. The properties of di-tert-butylphosphido-boratabenzene (DTBB) as a highly donating and bulky anionic phosphine ligand and the discovery of its unusual coordination modes to stabilize unsaturated transition metals has been explored in the course of this work. New insights into the coordination modes of phosphidoboratabenzene and on the strength of the P-B interaction will be discussed. Catalytic applications of the synthesized complexes will also be presented. First we studied the η1 coordination of DTBB to iron, which had provided valuable quantitative data about the donating capability of the aforementioned ligand against other well-known good donors. The DTBB’s capability to change coordination modes in order to support the electronic needs of the metal has been demonstrated by the discovery of a new pendant ferrocenyl-like phosphidoboratabenzene species and its nucleophilicity has been proved. To the best of our knowledge, no example of a boratabenzene ligand coordinated to group 11 metals has been reported in the literature. This is why we decided to explore the coordination modes of DTBB ligand with Cu(I), Ag(I) and Au(I). To our surprise, the DTBB ligand is capable to stabilize group 11 metals in a low oxidation state featuring a M-P bond by means of a η1 coordination, a scarcely observed coordination mode for boratabenzene ligands. Looking for applications of boratabenzene complexes in catalysis, our attention turned to the synthesis of a rhodium(I) complex. To our delight, the DTBB–Rh complex acts as a precatalyst for the hydrogenation of alkenes and alkynes at room temperature and atmospheric pressure and its activity is comparable to that of Wilkinson’s catalyst. Finally in a desire to expand the concepts of our research, our attention turned to explore the use of alternatives to the boratabenzene moiety. We decided to synthesize a new bulky phosphido-borate species. When reacted with metals, the phosphido-borate undergoes a cleavage of the P-B bond. However, this finding sets forward the singularity and advantage of the P-B bond in boratabenzene moieties. This observations also enrich our understanding of the conditions under which the P-B bond on DTBB ligand can be cleaved; evidence that lead to the discovery of a new ansa-boratabenzene ligand with promising coordination chemistry.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1998.
Vita.
Includes bibliographical references.
Although complexes derived from anionic borabenzenes (boratabenzenes) had been used for a long time, little was known about their neutral counterparts, mostly because an easy synthetic entry to them was not available. A facile three-step synthesis that allows the preparation of large quantities of neutral borabenzenes in three days, from commercially available starting materials is described in Chapter 2. In Chapter 3 it is shown that neutral borabenzenes can be converted into anionic boratabenzenes, thereby providing a versatile new synthesis of this family of compounds. The solid state structures of these complexes are described. The developments in Chapters 2 and 3 allowed us to continue on to studies of both borabenzene and boratabenzene complexes. Chapter 4 deals with the complexation of borabenzenes and boratabenzenes to some common transition metal fragments, mostly Cr(CO)3 and [Rh(olefin) 2 ]+ , as well as structural studies thereof. We also discuss the interconversion between borabenzene- and boratabenzene-metal complexes. Chapter 5 deals with the chemistry of the parent 1-H-boratabenzene. We discuss its synthesis, structure (in the solid state and in solution), and reactivity. In this chapter it is shown that the B-H is hydridic, and that the ring can form R-complexes with transition metals. The electron-donating ability of 1-H-boratabenzene is shown to lie somewhere between that of benzene and of Cp. Chapter 6 is concerned with the chemistry of diphenylphosphidoboratabenzene. This molecule is unique among boratabenzenes in that it prefers to bind main group electrophiles and transition metals through its boron substituent. Solid state structural studies establish that it has the same steric bulk as triphenylphosphine. Comparative studies of its transition metal complexes show that it is considerably more electron-donating than triphenylphosphine.
by Diego Andrés Hoic.
Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2010.
Vita. Cataloged from PDF version of thesis.
Includes bibliographical references.
Part I describes the expansion in scope of a nickel-catalyzed coupling reaction of unactivated alkyl bromides and alkyl boranes to include unactivated alkyl chlorides. The new method is adapted for use outside of a glove box and is also found to be applicable not only to the coupling of primary chlorides, but also to the coupling of bromides and iodides, both primary and secondary. ... This coupling reaction of chlorides is further adapted to the of p-chloro aryl alkyl amines. This work constitutes an extension directing groups for the asymmetric Suzuki-Miyaura reactions halides. ... Part II details work towards an asymmetric Diels-Alder reaction between cyclopentadiene and methacrolein catalyzed by a planar-chiral boron Lewis acid. This system exhibits a level of turnover that is unprecedented in reactions mediated by planar chiral boron heterocycles. Computational studies shed light on the nature of the 7tsymmetry interaction between borabenzenes and complexed carbonyl groups. The selectivity of the borabenzene-catalyzed Diels-Alder reaction is also examined.
by Zhe Lu.
Ph.D.