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Title: Hydride oxidation from a titanium–aluminum bimetallic complex: insertion, thermal and electrochemical reactivity

Abstract

We report the synthesis and reactivity of paramagnetic heterometallic complexes containing a Ti(III)-μ-H-Al(III) moiety. Combining different stoichiometries amounts of Cp 2TiCl and KH 3AlC(TMS) 3 (Cp = cyclopentadienyl, TMS = trimethylsilyl) resulted in the formation of either bimetallic Cp 2Ti(μ-H) 2(H)AlC(TMS) 3 (2) or trimetallic (Cp 2Ti) 2(μ-H) 3(H)AlC(TMS) 3 (3) via salt metathesis pathways. While these complexes were indefinitely stable at room temperature, the bridging hydrides were readily activated upon exposure to heteroallenes, heating, or electrochemical oxidation. In each case, formal hydride oxidation occurred, but the isolated product maintained the +3 oxidation state at both metal centers. The nature of this reactivity was explored using deuterium labelling experiments and Density Functional Theory (DFT) calculations. It was found that while C–H activation from the Ti(III) bimetallic may occur through a σ-bond metathesis pathway, chemical oxidation to Ti(IV) promotes bimolecular reductive elimination of dihydrogen to form a Ti(III) product.

Authors:
 [1];  [2]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [2]
  1. Univ. of California, Berkeley, CA (United States)
  2. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1399463
Grant/Contract Number:
AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 8; Journal Issue: 7; Journal ID: ISSN 2041-6520
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Brown, Alexandra C., Altman, Alison B., Lohrey, Trevor D., Hohloch, Stephan, and Arnold, John. Hydride oxidation from a titanium–aluminum bimetallic complex: insertion, thermal and electrochemical reactivity. United States: N. p., 2017. Web. doi:10.1039/c7sc01835e.
Brown, Alexandra C., Altman, Alison B., Lohrey, Trevor D., Hohloch, Stephan, & Arnold, John. Hydride oxidation from a titanium–aluminum bimetallic complex: insertion, thermal and electrochemical reactivity. United States. doi:10.1039/c7sc01835e.
Brown, Alexandra C., Altman, Alison B., Lohrey, Trevor D., Hohloch, Stephan, and Arnold, John. Wed . "Hydride oxidation from a titanium–aluminum bimetallic complex: insertion, thermal and electrochemical reactivity". United States. doi:10.1039/c7sc01835e. https://www.osti.gov/servlets/purl/1399463.
@article{osti_1399463,
title = {Hydride oxidation from a titanium–aluminum bimetallic complex: insertion, thermal and electrochemical reactivity},
author = {Brown, Alexandra C. and Altman, Alison B. and Lohrey, Trevor D. and Hohloch, Stephan and Arnold, John},
abstractNote = {We report the synthesis and reactivity of paramagnetic heterometallic complexes containing a Ti(III)-μ-H-Al(III) moiety. Combining different stoichiometries amounts of Cp2TiCl and KH3AlC(TMS)3 (Cp = cyclopentadienyl, TMS = trimethylsilyl) resulted in the formation of either bimetallic Cp2Ti(μ-H)2(H)AlC(TMS)3 (2) or trimetallic (Cp2Ti)2(μ-H)3(H)AlC(TMS)3 (3) via salt metathesis pathways. While these complexes were indefinitely stable at room temperature, the bridging hydrides were readily activated upon exposure to heteroallenes, heating, or electrochemical oxidation. In each case, formal hydride oxidation occurred, but the isolated product maintained the +3 oxidation state at both metal centers. The nature of this reactivity was explored using deuterium labelling experiments and Density Functional Theory (DFT) calculations. It was found that while C–H activation from the Ti(III) bimetallic may occur through a σ-bond metathesis pathway, chemical oxidation to Ti(IV) promotes bimolecular reductive elimination of dihydrogen to form a Ti(III) product.},
doi = {10.1039/c7sc01835e},
journal = {Chemical Science},
number = 7,
volume = 8,
place = {United States},
year = {Wed May 31 00:00:00 EDT 2017},
month = {Wed May 31 00:00:00 EDT 2017}
}

Journal Article:
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  • Titanium alkyls Cp*{sub 2}TiR (1, R = Me; 2, R = Et) were compared in their behavior toward a range of reactive molecules. Cp{sup *}{sub 2}TiR-L could be formed by the reaction of 1 and ME{sub 3}CC{triple_bond}N. Active-hydrogen-containing substrates HX (X = O{sub 2}C(H)Me{sub 2}, OEt, C{triple_bond}CMe), produced Cp*{sub 2}TiX and RH. Polar, unsaturated molecules like Me{sub 3}CN{triple_bond}C, CO, and paraformaldehyde inserted to give Cp*{sub 2}Ti({eta}{sup 2}-C(R){double_bond}NCMe{sub 3}), Cp*{sub 2}Ti({eta}{sup 2}-C(O)R), and Cp*{sub 2}TiOCH{sub 2}R for both 1 and 2. 35 refs., 3 tabs.
  • Four kinds of hydrogen bridges have been found in a single complex: Ti-H2-A1, Ti-H-A1, Ti-H-Ti, and A1-H-A1. The aluminum hydride complexes of titanium that form in the Cp/sub 2/TiC1/sub 2/-LiA1H/sub 4/ catalytic system are distinguished by the variety and complexity of their stereochemistry, because of the formation of Ti-(n/sup 5/:n/sup 1/-C/sub 5/H/sub 4/)-A1 hydrogen bridges, and because the coordination number of aluminum can be four and five.
  • Large-scale CO2 hydrogenation could offer a renewable stream of industrially important C1 chemicals while reducing CO2 emissions. Critical to this opportunity is the requirement for inexpensive catalysts based on earth-abundant metals instead of precious metals. We report a nickel-gallium complex featuring a Ni(0)→Ga(III) bond that shows remarkable catalytic activity for hydrogenating CO2 to formate at ambient temperature (3150 turnovers, turnover frequency = 9700 h-1), compared with prior homogeneous Ni-centred catalysts. The Lewis acidic Ga(III) ion plays a pivotal role by stabilizing reactive catalytic intermediates, including a rare anionic d10 Ni hydride. The structure of this reactive intermediate shows a terminalmore » Ni-H, for which the hydride donor strength rivals those of precious metal-hydrides. Collectively, our experimental and computational results demonstrate that modulating a transition metal center via a direct interaction with a Lewis acidic support can be a powerful strategy for promoting new reactivity paradigms in base-metal catalysis. The work was supported as part of the Inorganometallic Catalysis Design Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences under Award DE-SC0012702. R.C.C. and M.V.V. were supported by DOE Office of Science Graduate Student Research and National Science Foundation Graduate Research Fellowship programs, respectively. J.C.L., S.A.B., and A.M.A. were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.« less
  • The reaction of (C/sub 5/Me/sub 5/)/sub 2/Sm(THF)/sub 2/ with internal alkynes to form a new class of organolanthanide complexes, the enediyls, is reported. These can be converted into the first organosamarium hydride complex, a molecule that represents a new crystallographically characterized class of organolanthanide hydrides.
  • The iridium allyl hydride complex (/eta//sup 5/-C/sub 5/Me/sub 5/)(/eta//sup 3/-C/sub 3/H/sub 5/)(H)Ir (2) has been prepared from ((/eta//sup 5/-C/sub 5/Me/sub 5/)IrCl/sub 2/)/sub 2/, and its reaction with arenes and alkanes has been investigated. The hydride reacts with C-H bonds in benzene and cyclopropane in the presence of phosphines L, leading to the phenyl and cyclopropyl complexes (/eta//sup 5/-C/sub 5/Me/sub 5/)(L)Ir(n-propyl)(R) (3,4, and 5). Irradiation of 2 in the presence of PMe/sub 3/ takes a different course, giving the previously uncharacterized (/eta//sup 5/-C/sub 5/Me/sub 5/)Ir(PMe/sub 3/)/sub 2/ (6). Thermal reaction of 2 in alkane solvents such as n-butane and isobutane, whichmore » are capable of ..beta..-elimination, leads to products 8a, 8b, and 9 formed by replacement of the allyl group in 2 by a substituted allyl ligand formed by overall dehydrogenation of the alkane. Thermolysis of 2 in the presence of arenes such as n-propylbenzene and cumene leads to more complicated products resulting from intermolecular C-H activation followed by cyclometalation (e.g., 13, 15) and/or dimerization (20). The structure of cyclometalated dimer 20 has been determined by X-ray diffraction. Mechanistic studies, including kinetics, isotope tracer experiments, and intra-versus intermolecular isotope effect determinations, implicate the coordinatively unsaturated species (/eta//sup 5/-C/sub 5/Me/sub 5/)(/eta//sup 2/-propene)Ir (complex A in Scheme XX) as the initially formed intermediate in the thermal reactions of 1 with alkanes and arenes. Significant differences exist between the behavior of this intermediate (cf. Schemes XIX and XXIII) and that of the closely related phosphine-substituted complex (/eta//sup 5/-C/sub 5/Me/sub 5/)(PMe/sub 3/Ir) studied earlier; possible reasons for these differences are discussed.« less