DOCSLIB.ORG

Reactions of Titanium Imides and Hydrazides with Boranes Simona Mellino,† Laura C

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Reactions of Titanium Imides and Hydrazides with Boranes Simona Mellino,† Laura C This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. Article pubs.acs.org/Organometallics Reactions of Titanium Imides and Hydrazides with Boranes Simona Mellino,† Laura C. Stevenson,† Eric Clot,*,‡ and Philip Mountford*,† † Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K. ‡ Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM-ENSCM, Universitéde Montpellier, cc 1501, Place Eugené Bataillon, F-34095 Montpellier Cedex 5, France *S Supporting Information ABSTRACT: We report the first reactions of titanium imido, alkylidene hydrazido, and dimethylhydrazido compounds with the F F * i boranes H2BTex, 9-BBN, HBAr 2, and HBPin (Tex = tert-hexyl; Ar =C6F5). Reactions of Cp Ti{MeC(N Pr)2}(NTol) with F * i ′ − H2BTex, 9-BBN, or HBAr 2 resulted in the hydride-bridged adducts Cp Ti{MeC(N Pr2)2}{N(Tol)HBRR } without B H bond * i F β cleavage. Cp Ti{MeC(N Pr)2}(NNCPh2)(4) reacted with HBAr 2 via a sequence of steps involving adducts at the - and then α − -nitrogen of the NNCPh2 ligand, before slow 1,2-addition of B H across the N CPh2 double bond of 4, forming * i F Cp Ti{MeC(N Pr)2}{NN(BAr 2)CHPh2}(17). The other boranes reacted immediately with 4 to form homologues of 17. fi * i These products are the rst examples of borylhydrazido(2-) complexes. Reaction of Cp Ti{MeC(N Pr2)2}(NNMe2)(2) with F * i F − HBAr 2 gave the hydride-bridged adduct Cp Ti{MeC(N Pr2)2}{N(NMe2)HBAr 2}, whereas with HBPin B H bond cleavage * i occurred to form the borylhydrazide(1-)-hydride Cp Ti{MeC(N Pr)2}(H){N(BPin)NMe2}. Finally, reaction of 2 with 9-BBN * i dimer resulted in H2 elimination and formation of Me2NBC8H14 and Cp Ti{MeC(N Pr)2}(NBC8H14), a rare example of a borylimido compound. − * ■ INTRODUCTION addition to the Ti S bond of Cp 2Ti(S)(py) and to a strained 9c,d A series of reviews and recent papers have charted the tantalum imide was reported some time ago. Very recently a 1 scandium imide was shown to activate Si−H bonds by 1,2- remarkable developments in Group 4 imido (L)M(NR), 9e 2 addition to Sc−Nα, albeit in a reversible equilibrium. hydrazido (L)M(NNR2), and alkylidene hydrazido/diazoal- 3 The situation with hydrazides and alkylidene hydrazides is kane (L)M(NNCR2) compounds over the last ca. 25 years (L = supporting ligand set; R = H or hydrocarbyl). Other classes better established, at least for titanium. Andersen and Bergman * η2 of Group 4 imido-type compounds featuring heteroatom found that Cp 2Ti( -NNCHTol) reacted with PhSiH3 or − substituents have also been recently reported, namely the Ph2SiH2 by 1,2-addition to Ti Nα forming alkylidene titanium tert-butoxyimides (L)Ti(NOtBu)4 and borylimides hydrazide(1-)-hydride products, 1, as illustrated in Figure 1.3c 5 * (L)Ti(NBR2). In general, the dominant feature of these We subsequently reported that the dimethylhydrazide Cp Ti- compounds is their addition or insertion reactions with {MeC(NiPr) }(NNMe )(2) forms analogous 1,2-addition − 2 2 unsaturated compounds at the M Nα multiple bond itself products, 3 (Figure 1), with primary aryl silanes ArSiH3 or 2 4 6 (best described as a σ π triple bond). For certain hydrazido, BuSiH in a reversible equilibrium.10 No reaction occurred with 3c 4a,c 3 alkylidene hydrazido, and tert-butoxyimido compounds, the diphenylhydrazido or imido counterparts of 2. DFT − − reductive cleavage of the Nα Nβ or Nα Oβ bond can occur calculations found that, without additional coordination of with reducing substrates such as CO, isonitriles, and alkynes. the β-NMe group in 3,1,2-additiontoTi−Nα was Less commonly, dating from Bergman and Wolczanski’s first 2 7 thermodynamically unfavorable. The alkylidene hydrazide reports on these compounds, Group 4 imides can also activate * i − − analogue of 2,CpTi{MeC(N Pr)2}(NNCPh2)(4), also the C H bonds of organic substrates, and also the H H bond ′ 1a−c,e,g fi reacted with ArSiH3 or Ph2SiH2, forming N,N -disubstituted of H2. As documented in the reviews, many signi cant 3d,8 hydrazide(2-) products 5, featuring net 1,3 Si−H bond addition advances regarding these aspects have been achieved. − 3e − − across the N N CPh2 moiety of 4. Mechanistically, this In contrast, Si H and, especially, B H bond activation − − reactions of Group 4 imido and hydrazido-type compounds proceeds via 1,2-addition of Si HtoTiNα to give a with silanes and boranes are still poorly developed, although hydrazide(1-)-hydride intermediate, analogous to 1 and 3, they are better known for transition metal−heteroatom multiple bonds in general.9 There are no reported Si−H Received: June 23, 2017 additions to Group 4 imides. In related chemistry, Si−H 1,2- © XXXX American Chemical Society A DOI: 10.1021/acs.organomet.7b00477 Organometallics XXXX, XXX, XXX−XXX Organometallics Article − − ′ i 3c,e,5b,9f,10 Figure 1. Examples of products of Si HorB H bond activation with imido and hydrazido compounds (Ar = 2,6-C6H3 Pr2). followed by hydride migration to the electrophilic NβCPh2 carbon. Very recently we also reported the reductive Nα−Nβ bond Me cleavage reactions of Ti(N2N )(NNPh2)(py) with PhSiH3 5b and Ph2SiH2. DFT and kinetic studies found that this reaction proceeds via concerted Si−H bond addition across the Ti−Nα bond to again form a hydrazide(1-)-hydride intermediate (cf. 1 ff and 3). Subsequent hydride migration to the Nα atom of the so- with di erent types of primary and secondary boranes. A part of η2 − 5b formed -N(SiH2R)NPh2 ligand is coupled with Nα Nβ bond this work has been reported in a preliminary communication. cleavage, forming 6 (Figure 1). Furthermore, reaction of Me μ ■ RESULTS AND DISCUSSION Ti(N2N )(NNPh2)(py) with 9-BBN ([( -H)BC8H14]2) formed the borylamide counterpart 7, and DFT and kinetic As described in the Introduction, we found previously that studies established an analogous mechanism to that for 6.5b,11 A titanium half-sandwich amidinate compounds of the type * i ′ homologous compound to 6 was formed using HBMes2 (Mes Cp Ti{MeC(N Pr)2}(NR) (R = hydrocarbyl, NCPh2 or NR 2) ’ − = 2,4,6-C6H2Me3), but with pinacol borane (HBPin) or Piers provided good starting points for developing Si H bond 12 F F 3e,10 borane (HAr 2,Ar =C6F5) mixtures or undesired products activation chemistry of imido and hydrazido compounds. of ligand transmetalation were obtained.11 We therefore used this class of compound for our current study The Nα−Nβ bond cleavage processes leading to 6 and 7 were with boranes. Preliminary screening with several borane types the first of their type with silanes or boranes. More generally, (vide infra) established that the tolylimide Cp*Ti{MeC- Me i * the reactions of Ti(N2N )(NNPh2)(py) with HBR2 were the (N Pr)2}(NTol) (10), alkylidene hydrazide Cp Ti{MeC- i * first B−H activation reactions reported for any metal hydrazide. (N Pr)2}(NNCPh2)(4), and dimethylhydrazide Cp Ti{MeC- i Furthermore, the first B−H activation reaction of an imide was (N Pr)2}(NNMe2)(2)(Figure 2) gave the best outcomes in described only recently by Chen for a scandium compound terms of reactivity and product isolation. For example, the tert- 9f * i t reacting with 9-BBN, forming 8 (Figure 1). Subsequently butylimide Cp Ti{MeC(N Pr)2}(N Bu) did not react with * i Walter et al. reported the first B−H 1,2-addition reaction of an boranes, and the diphenylhydrazide Cp Ti{MeC(N Pr)2}- η t actinide imide for ( -C5H2 Bu3)2Th(NTol) (Tol = 4-C6H4Me) (NNPh2) reacted only with 9-BBN, under forcing conditions with 9-BBN.13 No well-defined reactions of Group 4 imides as discussed later on. In a similar way, we screened a number of with the B−H bonds of boranes have so far been reported. However, Lancaster recently showed that reaction of Cp2HfCl2 F with 2 equiv of the lithiated borylamide LiNH2BHAr 2 formed F Cp2Hf{N(H)HBAr 2}(9) as one component of a mixture, with F 14 the overall elimination of H3NBHAr 2 and LiCl. Although 9 appears formally to be the product of the 1,2-addition of F − HBAr 2 to the Hf Nα bond of Cp2Hf(NH) (not known as an isolated species), the mechanism of its formation is unclear and probably proceeds via an amidohydroborate intermediate that is subsequently dehydrohalogenated by additional F LiNH2BHAr 2. Overall, the B−H bond activation reactions of Group 4 imides and hydrazides/alkylidene hydrazides have not been developed in any detail, although there are encouraging and interesting precedents as outlined above. In this contribution Figure 2. Principal titanium compounds and hydroboranes (shown in we report the reactions of titanium compounds of this type their monomeric form) used in this study. B DOI: 10.1021/acs.organomet.7b00477 Organometallics XXXX, XXX, XXX−XXX Organometallics Article hydroboranes possessing different substitution patterns at associated angles for the supporting ligand sets are comparable boron. The successful candidate boranes carried forward from and within the expected ranges.21 The Ti(1)−N(1) bond these trials are listed in Figure 2 and represent primary distances are very similar, and their average value of 1.877(1) Å 15 fi (H2BTex, Tex = tert-hexyl) and secondary boranes.
Load more

Recommended publications
  • Thermodynamic Hydricity of Small Borane Clusters and Polyhedral Closo-Boranes
    molecules Article Thermodynamic Hydricity of Small Borane Clusters y and Polyhedral closo-Boranes Igor E. Golub 1,* , Oleg A. Filippov 1 , Vasilisa A. Kulikova 1,2, Natalia V. Belkova 1 , Lina M. Epstein 1 and Elena S. Shubina 1,* 1 A. N. Nesmeyanov Institute of Organoelement Compounds and Russian Academy of Sciences (INEOS RAS), 28 Vavilova St, 119991 Moscow, Russia; [email protected] (O.A.F.); [email protected] (V.A.K.); [email protected] (N.V.B.); [email protected] (L.M.E.) 2 Faculty of Chemistry, M.V. Lomonosov Moscow State University, 1/3 Leninskiye Gory, 119991 Moscow, Russia * Correspondence: [email protected] (I.E.G.); [email protected] (E.S.S.) Dedicated to Professor Bohumil Štibr (1940-2020), who unfortunately passed away before he could reach the y age of 80, in the recognition of his outstanding contributions to boron chemistry. Academic Editors: Igor B. Sivaev, Narayan S. Hosmane and Bohumír Gr˝uner Received: 6 June 2020; Accepted: 23 June 2020; Published: 25 June 2020 MeCN Abstract: Thermodynamic hydricity (HDA ) determined as Gibbs free energy (DG◦[H]−) of the H− detachment reaction in acetonitrile (MeCN) was assessed for 144 small borane clusters (up 2 to 5 boron atoms), polyhedral closo-boranes dianions [BnHn] −, and their lithium salts Li2[BnHn] (n = 5–17) by DFT method [M06/6-311++G(d,p)] taking into account non-specific solvent effect (SMD MeCN model). Thermodynamic hydricity values of diborane B2H6 (HDA = 82.1 kcal/mol) and its 2 MeCN dianion [B2H6] − (HDA = 40.9 kcal/mol for Li2[B2H6]) can be selected as border points for the range of borane clusters’ reactivity.
    [Show full text]
  • Boranes: Physical & Chemical Properties, Encyclopaedia of Occupational Health and Safety, Jeanne Mager Stellman, Editor-In
    Boranes: Physical & chemical properties, Encyclopaedia of Occupational Health and Safety, Jeanne Mager Stellman, Editor-in-Chief. International Labor Organization, Geneva. 2011. Chemical Name Colour/Form Boiling Point Melting Molecular Solubility in Relative Density Relative Vapour Inflam. Flash Auto CAS-Number (°C) Point (°C) Weight Water (water=1) Vapour Pressure/ Limits Point (°C) Ignition Density (Kpa) Point (°C) (air=1) BORON polymorphic: alpha- 2550 2300 10.81 insol Amorphous, 1.56x 580 3 -5 7440-42-8 rhombohedral form, clear 2.3 g/cm ; 10 red crystals; beta- alpha-- @ 2140 °C rhombohedral form, black; rhombohedral, - alpha-tetragonal form, 2.46 g/cm3; - black, opaque crystals with alpha-- metallic luster; amorphous tetragonal, - form, black or dark brown 2.31 g/cm3; - powder; other crystal beta-rhom- forms known bohedral, - 2.35 g/cm3 BORIC ACID, DISODIUM powder or glass-like 1575 741 201.3 2.56 g/100 g 2.367 SALT plates; white, free-flowing 1330-43-4 crystals; light grey solid BORON OXIDE rhombic crystals; 1860 450 69.6 2.77 g/100 g 1.8 1303-86-2 colourless, (amorphous); semitransparent lumps or 2.46 hard, white crystals (crystalline) BORON TRIBROMIDE colourless liquid 90 -46.0 250.57 reacts 2.6431 8.6 5.3 10294-33-4 @ 18.4 °C/4 °C @ 14 °C BORON TRICHLORIDE 12.5 -107 117.16 1.35 4.03 2.99 Pa 10294-34-5 @ 12 °C/4 @ 12.4 °C BORON TRIFLUORIDE colourless gas -99.9 -126.8 67.82 reacts 3.08g/1.57 l 2.4 10 mm Hg 7637-07-2 @ 4 °C @ -141 °C.
    [Show full text]
  • Boranes: Structure & Bonding
    18-Aug-20 Boranes: Structure & Bonding PROF. K.K. UPADHYAY DEPARTMENT OF CHEMISTRY INSTITUTE OF SCIENCE, BHU VARANASI - 221005 An Introduction to Boranes . For undergraduate students, boranes means only diborane which is not true. Boranes means electron deficient molecules but probably that is not true. Boranes are a class of compounds comprising of several hundreds of compounds ranging from simple to polyhedral to macro polyhedral types having intriguing structures. 1 18-Aug-20 10 11 . Boron is an element with atomic no. 5 having two isotopes 5B (20%) and 5B (80%). It occupies group XIII and is a p-block element. .Boranes are binary compounds of boron and hydrogen and are the fourth most extensive group of hydrides after the Carbon, Phosphorous and Silicon hydrides. BH 3 is the simplest of all the boranes but non-existent. B2H6 is the dimer of BH 3 and is the most primitive among the existing boranes. Boranes are not found in the nature. These are always synthesised in the laboratory. Very first synthesis was carried out in 19 th century by protolysis of metal borides. 2Mg 3B2 + 12HCl 6MgCl 2 + mixture of boranes . But neither correctly analysed nor identified. 2 18-Aug-20 . The first systematic study of boranes was performed by Alfred stock during the year 1912-1936. He used Schlenk line technique for the synthesis of boranes in a systematic way. Alfred Stock . He studied nature, stoichiometry and reactivity of boranes in a systematic way. 3 NaBH 4 + 4 BF 3→ 3 NaBF 4 + mixture of boranes BCl 3 + 3 H 2 → mixture of boranes + 3 HCl - 3- BH 4 + BX 3 → mixture of boranes + HBX (X = Cl, Br) Schlenk line 2x4 + 1x6 = 14 electrons 2x3 + 1x6 = 12 electrons .
    [Show full text]
  • Innovation Infosheet Preparation of Amine Boranes, Ammonia Borane, and Phosphine Boranes
    Innovation Infosheet Downloaded September 29, 2021 Preparation of Amine Boranes, Ammonia Borane, and Phosphine Boranes Track Code: 2014-RAMA-66892 Categories: - Chemistry and Chemical Analysis Keywords: - Amine-Boranes - Chemistry and Chemical Analysis - Hydrogen Storage Amine and phosphine-boranes, the classic Lewis base-Lewis acid (LB-LA) pairs have been known and valued for over a century, with uses that include hydrogen storage applications. There are major drawbacks associated with current procedures for making amine-boranes, including low efficiency and other issues such as formation of highly unpleasant odors from the necessary reactions. In addition, removal of dimethyl sulfide for reuse of the solvent THF adds additional steps in the synthetic process. Therefore, as the demand for large quantities of amine- boranes increases, there is a need for more effective methods for making ammonia borane and amine-boranes. Researchers at Purdue University have developed several new procedures to efficiently make ammonia borane and amine boranes in large quantities. In addition, due to the stability of sodium borohydride (SBH) and ammonia borane in water, water can be used in the production process, allowing for an efficient, cost-effective synthesis of ammonia borane from SBH. Advantages: -Simplest possible synthesis of ammonia borane from sodium borohydride -Prepare ammonia-borane in large quantities Potential Applications: -Method for making a more pure ammonia borane and amine borane People: - Ramachandran, Padinjaremadhom V (Project
    [Show full text]
  • Prep Aration and Pro Perties of Trifluoromethyl• Boranes Everett Duane Baker a Thesis Oregon State College Master of Science
    PREP ARATION AND PRO PERTIES OF TRIFLUOROMETHYL• BORANES by EVERETT DUANE BAKER A THESIS submitted to OREGON STATE COLLEGE in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE June 1961 APTBOVEDT Redacted for Privacy Arroolat. Profilts sf Chrrl. tlt In 0hrr.gr of, l{rt or Redacted for Privacy Ghrlrarn of Drpuhcat of Chralttry Redacted for Privacy Chr lrun Sobool Orrdurtr Comtttrr Redacted for Privacy Dorn of &rrductr Scbool Drtr thrrlr 1r prrcntod )g Au2a2t l%O Iypod by LrAnna Ermlr ACKNOWLEDGMENT Tbe author wishes to express his sincere appre­ ciation to Dr- Theran D. Parsons tor h1s guidance and encouragement throughout tha course of this inves­ tigation. The material aid ot the Office ot Naval Research fellowship is acknowledged w1th appreciation. TABLE OF CONTENTS Page I. INTRODUCTION ' • 1 • • ... • • • • • • • • • • • • II. EXPERIMENTAL • •• ,, ... • ••• • • • .... • • • 1) A~ Appara tue and Eqatpme.nt. .. • • • • • • • • • • 1) B. Reagen t8 • • • • • • • • • • • • • • • • • • .1) c. P~epal!lt1ona and ·lteactiona • • • • • , , • • .15 Figure I , • • • • ·• ... ·• • • • • • • • • • .16 Table I • •· • • • • • • , • • • • • • • • ~ Figure 2 • • • • • • • • • • • • • • • • • •. :~~ lli. DISCUSSION AND CONCLUSIONS ·• .. • • . ·• . .29 IV, BIB.LIOGRAl?iY • • • • .• • • • • • • • • • • • • • •34 PREPARATION AND PROPERTIES OF TRIFLUROMETHYL-BOR ANES I. INTRODUCTION The elucidatio.n or the struct\ll'es of the boron hydrides and their ~erivatives, and of certain compounds of aluminum, has caused great interest in electron deficient bonding. Lipscomb (14) reviewed the s t ructures ot the boron hydrides. Evidence was cited which s how s that diborane has a structure in which. two of the hydrogen atoms form a bridge between the two boron atoms: H H H \. 1\ I B B / \. / \ H H H The grouping of the atoms bonde d to a boron a tom is ap prox imately tetrahedral in configuration.
    [Show full text]
  • Green Hypergolic Fuels with Consistently Low Ignition Delays P
    DOI: 10.1002/chem.201405224 Communication & Propellants Amine–Boranes: Green Hypergolic Fuels with Consistently Low Ignition Delays P. Veeraraghavan Ramachandran,*[a] Ameya S. Kulkarni,[a] Mark A. Pfeil,[b] Jacob D. Dennis,[b] Jared D. Willits,[b] Stephen D. Heister,[b] Steven F. Son,[c] and Timothe L. Pourpoint[b] ergetic influence of several reactions.[5] Interestingly, recent re- Abstract: Complexation of amines with borane converts ports have identified 38 amines such as N,N,N’,N’-tetramethyl- them to hypergols or decreases their ignition delays (IDs) ethylenediamine or 1,4-dimethylpiperazine (DMPZ, 1o), alone multifold (with white fuming nitric acid as the oxidant). or mixed with azido compounds, as potential hypergolic With consistently low IDs, amine–boranes represent fuels.[6] A modern trend in propellant research considers ionic a class of compounds that can be promising alternatives liquids (ILs) as future fuels for space applications.[7] The incor- to toxic hydrazine and its derivatives as propellants. A poration of boron in the IL structure[8] or as nanoparticle addi- structure–hypergolicity relationship study reveals the nec- tives[9] has provided new openings. IL solubilized boranes as essary features for the low ID. hypergolic fluids have been recently reported by Shreeve and Gao.[10] Their study identified triethylamine–borane as the most efficient “additive” for decreasing IDs of ILs.[10b] Chemical rockets used in space and missile applications For nearly a decade, we have been investigating amine–bor- depend on propellants
    [Show full text]
  • Group 13 (3A) - the Elements - Boron
    Group 13 (3A) - The Elements - Boron ! Boron is a hard, crystalline, black, semimetal found in borate ores such as borax, Na 2B4O5(OH) 4@8H 2O, found in vast deposits in Death Valley, Nevada & California. ! The element boron has powerful abilities to strengthen, toughen and make fire-resistant glasses, metals, wood, and fibers. It is used in approximately three hundred high-tech products. A few of its uses are as soldering flux, in welding rods, as preservatives for wood and fabric, as fire retardant, in insecticides, in pottery glaze, as antiseptics, in hybrid fuels, and in experimental fuel cells. 1 ! Impure boron is obtained by reduction of the oxide with Mg, followed by washing with alkali, HCl( aq ), and HF( aq ). B2O3 + 3Mg∆ 3MgO + 2B (~95% pure) ! High purity boron is obtained with difficulty by pyrolysis or reduction of a halide over a hot Ta, W, or BN surface. Ta 2BI 3(g) + 3H 2(g) 800-1000oC 2B( s) + 6HI( g) 1Death Valley National Park website: http://www.nps.gov/deva/faqs.htm Boron Physical and Chemical Properties ! Boron is very non-reactive and high melting (m.p. = 2300 oC), making it useful for fire resistant and high-temperature applications. ! Naturally occurring boron consists of two stable isotopes, 10 B (19.6%) and 11 B (80.4%). ! Boron has several crystal forms, all containing B 12 icosahedra ( Ih). • Individual icosahedra are linked by 3 c-2 e bonds. ! Boron, boron nitride (BN), and carborundum (BC), have hardness approaching diamond. Mohs scale: diamond = 10, BC = 9.3 ! BN has forms isomorphous with diamond and graphite, but it resists oxidation up to 800 oC.
    [Show full text]
  • NHI- and NHC-Supported Al(III) Hydrides for Amine–Borane Dehydrocoupling Catalysis
    inorganics Communication NHI- and NHC-Supported Al(III) Hydrides for Amine–Borane Dehydrocoupling Catalysis Catherine Weetman 1 , Nozomi Ito 2, Masafumi Unno 2 , Franziska Hanusch 1 and Shigeyoshi Inoue 1,* 1 WACKER-Institute of Silicon Chemistry and Catalysis Research Center, Technische Universität München, Lichtenbergstraße 4, 85748 Garching bei München, Germany 2 Department of Chemistry and Chemical Biology, Gunma University, Kiryu 376-8515, Japan * Correspondence: [email protected]; Tel.: +49-89-289-13596 Received: 26 June 2019; Accepted: 12 July 2019; Published: 24 July 2019 Abstract: The catalytic dehydrocoupling of amine–boranes has recently received a great deal of attention due to its potential in hydrogen storage applications. The use of aluminum catalysts for this transformation would provide an additional cost-effective and sustainable approach towards the hydrogen economy. Herein, we report the use of both N-heterocyclic imine (NHI)- and carbene (NHC)-supported Al(III) hydrides and their role in the catalytic dehydrocoupling of Me2NHBH3. Differences in the σ-donating ability of the ligand class resulted in a more stable catalyst for NHI-Al(III) hydrides, whereas a deactivation pathway was found in the case of NHC-Al(III) hydrides. Keywords: aluminum; amine–borane; dehydrocoupling; homogeneous catalysis; N-heterocyclic carbenes; N-heterocyclic imines 1. Introduction Main group chemistry has seen a resurgence of interest in recent years, driven by the need for more economically viable and eco-friendly processes. Whilst catalytic transformations using transition metals are well established, the long-term sustainability of these naturally low-abundance metals is limited. In contrast, use of p-block elements such as aluminum allows for the use of earth-abundant and environmentally benign elements, with aluminum being the third most abundant element in the Earth’s crust.
    [Show full text]
  • Boron-Based Hydrogen Storage: Ternary Borides and Beyond
    IV.C.8 Boron-Based Hydrogen Storage: Ternary Borides and Beyond Technical Barriers John J. Vajo (Primary Contact), Jason Graetz, This project addresses the following technical barriers Vitalie Stavila, Lennie Klebanoff, Eric Majzoub from the Hydrogen Storage section of the Fuel Cell HRL Laboratories, LLC Technologies Office Multi-Year Research, Development, and 3011 Malibu Canyon Road Demonstration Plan: Malibu, CA 90265 Phone: (310) 317-5745 (A) System Weight and Volume Email: [email protected] (C) Efficiency DOE Manager (E) Charging and Discharging Rates Katie Randolph Phone: (720) 356-1759 Technical Targets Email: [email protected] This project is conducting initial studies of hydrogen Contract Number: DE-EE0006630 storage in ternary borides/mixed-metal borohydrides and Subcontractors lithiated boranes. Results of these studies will be applied • Sandia National Laboratories, Livermore, CA toward developing hydrogen storage materials that meet the • University of Missouri, St. Louis, MO following DOE hydrogen storage system targets. • Specific energy: 5.5 wt% H Project Start Date: August 1, 2014 2 Project End Date: January 31, 2016 • Energy density: 40 g-H2 /L FY 2015 Accomplishments Overall Objectives • Calculation of stable Mg-based ternary borides with Mn, Fe, and Co Improve the hydrogen cycling kinetics of high capacity boron-based hydrogen storage materials • Synthesis of single-phase Mg/Mn (1:1, 3:1, and 9:1) ternary borides • Eliminating multiple-phase reaction barriers using ternary borides and mixed-metal borohydrides that
    [Show full text]
  • Bonding with Boron Long Ago, a Global Search for Borane Superfuels Led Fortuitously to the Discovery of Carboranes
    in your element Bonding with boron Long ago, a global search for borane superfuels led fortuitously to the discovery of carboranes. Ken Wade recalls his own undistinguished part in the space race, and notes how carboranes revitalized boron hydride chemistry and modified our ideas of chemical bonding. n the 1950s, during the space race, the carboranes (C2Bn–2Hn), mixed hydrides of communist east and capitalist west built boron and carbon with novel triangular- Iever bigger and more powerful rockets faced (deltahedral) structures that packed to threaten to lob nuclear payloads at each Closo their n boron and carbon atoms closely on other. Progress was marked by how far down spherical surfaces, held together by only test ranges nose cones were recovered, until (n+1) electron pairs, too few to allocate bleeps emitted by the first Sputnik showed a pair to each of their (3n–6) atom–atom who had won the race into orbit. Down below, links. Dubbed ‘electron-deficient’, they engineers continued designing and building were really ‘electron-sufficient’, as adding better rocket motors, while chemists sought electrons caused their structures to open higher-energy fuels. Boron attracted attention Nido up into fragments of bigger deltahedra. for a while because burning its hydrides Plotting their shapes against formula types (boranes) generated more heat per kilogram or electron numbers creates a pattern of than burning hydrocarbons. Although the complete deltahedra or fragments thereof, thermally unstable boranes seemed far from first reported by carborane pioneer ideal as fuels or fuel additives, the USA and Robert E. Williams in 1971, now routinely USSR invested millions of dollars and roubles, featured in textbooks.
    [Show full text]
  • Titanium( IV ) Tttetallocycles
    6529 Synthesisand Reactions of Bis(cyclopentadienyl)titanium( IV ) tttetallocycles JosephX. McDermott,r Michael E. Wilson,and GeorgeM. Whitesides* Contributionfromthe Deportment oJ'Chenti.strr', Massachusetts Institute oJ Techrutlogt', Cantbridge,Ma.ssachusett.s 02139. ReceiredJanuarr 16, 1976 Abstract: 1,4-Tctramethylenebis(cyclopentadienyl)titanium(lV)(l) was preparedbv rcactionbetween dichlorobis(cyclopen- tadicnyl)titanium(lV) and 1.4-dilithiobutane:it could be isolatedat low tcmperature.but its thermal lability was such that it could be characterizedonly through its reactions.Compound I and the analogoussix-membered metallocycle I .5-penta- methylcncbis(cvclopentadienyl)titanium(lV)(5) were much more stablethan an acyclictitanium alkyl. di-n-butylbis(cyclo- pentadienyl)titanium(lV)(3). Thermal decompositionsof 3 and 5 appearto take place by unexceptionalp-climination and reductionreactions involving titanium hydrides.These reactions yield, respectively'.u mixture of butenesand n-butaneand a mixture of pentenesand cyclopentane.By contrast,thermal decompositionof I (4 h,0'C) takesplace in part by a path that clcavesa carbon-carbon bond of the titanocyclopentanering and generatesethylene: I -butcnc is the secondmajor product of this decomposition.Carbonylation of I yieldscyclopcntanone; carbonylation of 3. 5. and dimethylbis(cyclopentadienyl)titanr- um(lV) takesplace less readily, if at all. Theseresults indicate that the high stabilit;-of the titanocyclopcntanering, presum- ably reflecting suppressionof the p-elimination of metal hydride, is accompaniedbl abnormally high reactivity in carbonyla- tion and in thermal decompositionby carbon-carbon fragmentation. Several functional equivalentsof titanocene (CpzTi- N:TiCp:, [CplTiH].-, [Cp:Ti]:. Cp:TiCl: reducedwith lithium naphthalenide)react directll'with olefinsand form titanocy- cloDentanerings. The best vields in thesereactions are obtained usine benzonorbornadiene.norbornene. and ethylene. A dominant decompositionreaction of transition metal SchemeI.
    [Show full text]
  • Diborane Final AEGL Document
    Acute Exposure Guideline Levels for Selected Airborne Chemicals Volume 3 Subcommittee on Acute Exposure Guideline Levels Committee on Toxicology Board on Environmental Studies and Toxicology Division on Earth and Life Studies THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, D.C. 20001 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This project was supported by Contract Nos. DAMD17-89-C-9086 and DAMD17-99-C- 9049 between the National Academy of Sciences and the U.S. Army. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the organizations or agencies that provided support for this project. International Standard Book Number 0-309-08883-6 (Book) International Standard Book Number 0-309-51590-4 (PDF) Additional copies of this report are available from: The National Academies Press 500 Fifth Street, N.W. Box 285 Washington, DC 20055 800-624-6242 202-334-3313 (in the Washington metropolitan area) http://www.nap.edu Copyright 2003 by the National Academy of Sciences. All rights reserved. Printed in the United States of America The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare.
    [Show full text]