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

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

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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

M3 - Article

AN - SCOPUS:85056636164

SN - 0022-328X

VL - 880

SP - 187

EP - 195

JO - Journal of Organometallic Chemistry

JF - Journal of Organometallic Chemistry

ER -