La-mediated dehydrogenation and C–C bond cleavage of 1,4-pentadiene and 1-pentyne: Spectroscopy and formation of La(C5H6) and La(C3H4) radicals

Wenjin Cao; Yuchen Zhang; Dong Sheng Yang

doi:10.1016/j.jorganchem.2018.11.015

La-mediated dehydrogenation and C–C bond cleavage of 1,4-pentadiene and 1-pentyne: Spectroscopy and formation of La(C₅H₆) and La(C₃H₄) radicals

Wenjin Cao, Yuchen Zhang, Dong Sheng Yang

Research output: Contribution to journal › Article › peer-review

4 Scopus citations

Abstract

La atom reactions with 1,4-pentadiene and 1-pentyne are carried out in a laser-vaporization molecular beam source. Both reactions yield a predominant La(C₅H₆) radical from ligand dehydrogenation and a minor La(C₃H₄) species from C–C bond cleavage. The metal-hydrocarbon radicals are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species formed by the two reactions are essentially identical and consist of a single vibronic band system for La(C₅H₆) and two band systems for La(C₃H₄). Each band system exhibits a strong origin band and several weak vibronic ones. Adiabatic ionization energies, metal-ligand vibrational frequencies, and low-frequency ligand-based modes are measured for the two species. La(C₅H₆) is identified as a six-membered lanthanacycle [La(CHCHCHCHCH₂)] (Iso A, C₁), whereas two isomers of La(C₃H₄) are a four-membered metallacycle La(CHCHCH₂) (Iso 1, C₁) and a three-membered ring La(CHCCH₃) (Iso 2, C_s). The ground electronic state of each radical is a doublet and that of the singly charged cation is a singlet. The remaining two electrons that are associated with the isolated La atom or ion are spin paired in a molecular orbital that is bonding combination between a La 5d orbital and a π* antibonding orbital of the C₅H₆ or C₃H₄ fragment. For the 1,4-pentadiene reaction, the formation of the six-membered metallacycle La(C₅H₆) involves La addition to a C=C double bond, La insertion into two C(sp³)–H bonds, and concerted H₂ elimination, whereas the formation of the three- and four-membered La(C₃H₄) rings involves two hydrogen migrations followed by C–C bond breakage to eliminate an ethylene molecule. For the 1-pentyne reaction, the formation of each species requires isomerization of a La(1-pentyne) adduct to a La insertion species and then proceeds with the same elemental steps as those for the diene reaction.

Original language	English
Pages (from-to)	187-195
Number of pages	9
Journal	Journal of Organometallic Chemistry
Volume	880
DOIs	https://doi.org/10.1016/j.jorganchem.2018.11.015
State	Published - Feb 1 2019

Bibliographical note

Publisher Copyright:
© 2018

Funding

We are grateful for the financial support from the National Science Foundation Division of Chemistry (Chemical Structure, Dynamics, and Mechanisms, Grant No. 1800316 ).

Funders	Funder number
National Science Foundation Division of Chemistry
National Science Foundation (NSF)	1800316

Keywords

C-H and C–C bond activation
Density functional and coupled cluster theory calculations
Lanthanide
Laser vaporization molecular beam
Mass-analyzed threshold ionization spectroscopy
Reaction mechanism

ASJC Scopus subject areas

Biochemistry
Physical and Theoretical Chemistry
Organic Chemistry
Inorganic Chemistry
Materials Chemistry

Access to Document

10.1016/j.jorganchem.2018.11.015

Cite this

@article{166bf164dc16492f99c091cfaab16dea,

title = "La-mediated dehydrogenation and C–C bond cleavage of 1,4-pentadiene and 1-pentyne: Spectroscopy and formation of La(C5H6) and La(C3H4) radicals",

abstract = "La atom reactions with 1,4-pentadiene and 1-pentyne are carried out in a laser-vaporization molecular beam source. Both reactions yield a predominant La(C5H6) radical from ligand dehydrogenation and a minor La(C3H4) species from C–C bond cleavage. The metal-hydrocarbon radicals are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species formed by the two reactions are essentially identical and consist of a single vibronic band system for La(C5H6) and two band systems for La(C3H4). Each band system exhibits a strong origin band and several weak vibronic ones. Adiabatic ionization energies, metal-ligand vibrational frequencies, and low-frequency ligand-based modes are measured for the two species. La(C5H6) is identified as a six-membered lanthanacycle [La(CHCHCHCHCH2)] (Iso A, C1), whereas two isomers of La(C3H4) are a four-membered metallacycle La(CHCHCH2) (Iso 1, C1) and a three-membered ring La(CHCCH3) (Iso 2, Cs). The ground electronic state of each radical is a doublet and that of the singly charged cation is a singlet. The remaining two electrons that are associated with the isolated La atom or ion are spin paired in a molecular orbital that is bonding combination between a La 5d orbital and a π* antibonding orbital of the C5H6 or C3H4 fragment. For the 1,4-pentadiene reaction, the formation of the six-membered metallacycle La(C5H6) involves La addition to a C=C double bond, La insertion into two C(sp3)–H bonds, and concerted H2 elimination, whereas the formation of the three- and four-membered La(C3H4) rings involves two hydrogen migrations followed by C–C bond breakage to eliminate an ethylene molecule. For the 1-pentyne reaction, the formation of each species requires isomerization of a La(1-pentyne) adduct to a La insertion species and then proceeds with the same elemental steps as those for the diene reaction.",

keywords = "C-H and C–C bond activation, Density functional and coupled cluster theory calculations, Lanthanide, Laser vaporization molecular beam, Mass-analyzed threshold ionization spectroscopy, Reaction mechanism",

author = "Wenjin Cao and Yuchen Zhang and Yang, {Dong Sheng}",

note = "Publisher Copyright: {\textcopyright} 2018",

year = "2019",

month = feb,

day = "1",

doi = "10.1016/j.jorganchem.2018.11.015",

language = "English",

volume = "880",

pages = "187--195",

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TY - JOUR

T1 - La-mediated dehydrogenation and C–C bond cleavage of 1,4-pentadiene and 1-pentyne

T2 - Spectroscopy and formation of La(C5H6) and La(C3H4) radicals

AU - Cao, Wenjin

AU - Zhang, Yuchen

AU - Yang, Dong Sheng

PY - 2019/2/1

Y1 - 2019/2/1

N2 - La atom reactions with 1,4-pentadiene and 1-pentyne are carried out in a laser-vaporization molecular beam source. Both reactions yield a predominant La(C5H6) radical from ligand dehydrogenation and a minor La(C3H4) species from C–C bond cleavage. The metal-hydrocarbon radicals are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species formed by the two reactions are essentially identical and consist of a single vibronic band system for La(C5H6) and two band systems for La(C3H4). Each band system exhibits a strong origin band and several weak vibronic ones. Adiabatic ionization energies, metal-ligand vibrational frequencies, and low-frequency ligand-based modes are measured for the two species. La(C5H6) is identified as a six-membered lanthanacycle [La(CHCHCHCHCH2)] (Iso A, C1), whereas two isomers of La(C3H4) are a four-membered metallacycle La(CHCHCH2) (Iso 1, C1) and a three-membered ring La(CHCCH3) (Iso 2, Cs). The ground electronic state of each radical is a doublet and that of the singly charged cation is a singlet. The remaining two electrons that are associated with the isolated La atom or ion are spin paired in a molecular orbital that is bonding combination between a La 5d orbital and a π* antibonding orbital of the C5H6 or C3H4 fragment. For the 1,4-pentadiene reaction, the formation of the six-membered metallacycle La(C5H6) involves La addition to a C=C double bond, La insertion into two C(sp3)–H bonds, and concerted H2 elimination, whereas the formation of the three- and four-membered La(C3H4) rings involves two hydrogen migrations followed by C–C bond breakage to eliminate an ethylene molecule. For the 1-pentyne reaction, the formation of each species requires isomerization of a La(1-pentyne) adduct to a La insertion species and then proceeds with the same elemental steps as those for the diene reaction.

AB - La atom reactions with 1,4-pentadiene and 1-pentyne are carried out in a laser-vaporization molecular beam source. Both reactions yield a predominant La(C5H6) radical from ligand dehydrogenation and a minor La(C3H4) species from C–C bond cleavage. The metal-hydrocarbon radicals are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species formed by the two reactions are essentially identical and consist of a single vibronic band system for La(C5H6) and two band systems for La(C3H4). Each band system exhibits a strong origin band and several weak vibronic ones. Adiabatic ionization energies, metal-ligand vibrational frequencies, and low-frequency ligand-based modes are measured for the two species. La(C5H6) is identified as a six-membered lanthanacycle [La(CHCHCHCHCH2)] (Iso A, C1), whereas two isomers of La(C3H4) are a four-membered metallacycle La(CHCHCH2) (Iso 1, C1) and a three-membered ring La(CHCCH3) (Iso 2, Cs). The ground electronic state of each radical is a doublet and that of the singly charged cation is a singlet. The remaining two electrons that are associated with the isolated La atom or ion are spin paired in a molecular orbital that is bonding combination between a La 5d orbital and a π* antibonding orbital of the C5H6 or C3H4 fragment. For the 1,4-pentadiene reaction, the formation of the six-membered metallacycle La(C5H6) involves La addition to a C=C double bond, La insertion into two C(sp3)–H bonds, and concerted H2 elimination, whereas the formation of the three- and four-membered La(C3H4) rings involves two hydrogen migrations followed by C–C bond breakage to eliminate an ethylene molecule. For the 1-pentyne reaction, the formation of each species requires isomerization of a La(1-pentyne) adduct to a La insertion species and then proceeds with the same elemental steps as those for the diene reaction.

KW - C-H and C–C bond activation

KW - Density functional and coupled cluster theory calculations

KW - Lanthanide

KW - Laser vaporization molecular beam

KW - Mass-analyzed threshold ionization spectroscopy

KW - Reaction mechanism

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U2 - 10.1016/j.jorganchem.2018.11.015

DO - 10.1016/j.jorganchem.2018.11.015

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JO - Journal of Organometallic Chemistry

JF - Journal of Organometallic Chemistry

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