Synthesis and characterization of transition metal malondialdiminates

Schmit, Claire E.

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https://hdl.handle.net/2142/125697 Copy

Description

Title

Synthesis and characterization of transition metal malondialdiminates

Author(s)

Schmit, Claire E.

Issue Date

2024-07-10

Director of Research (if dissertation) or Advisor (if thesis)

Girolami, Gregory

Doctoral Committee Chair(s)

Girolami, Gregory

Committee Member(s)

• Abelson, John
• Olshansky, Lisa
• Mirica, Liviu

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• dialdiminium
• dialdimine
• dialdiminate
• chemical vapor deposition
• precursor
• crystal structures
• transition metal complexes

Abstract

Convenient preparations of N,N′-dialkyl-1,3-propanedialdiminium chlorides, N,N′-dialkyl-1,3-propanedialdimines, and lithium N,N′-dialkyl-1,3-propanedialdiminates in which the alkyl groups are methyl, ethyl, iso-propyl, or tert-butyl are described. For the dialdiminium salts, the N2C3 backbone is always in the trans-s-trans configuration. Three isomers are present in solution except for the tert-butyl compound, for which only two isomers are present; increasing the steric bulk of the N-alkyl substituents shifts the equilibrium away from the Z,Z isomer in favor of the E,Z, and E,E isomers. For the neutral dialdimines, crystal structures show that the methyl and iso-propyl compounds adopt the E,Z form, whereas the tert-butyl compound is in the E,E form. In aprotic solvents all four dialdimines (as well as the lithium dialdiminate salts) adopt cis-s-cis conformations in which there presumably is either an intramolecular hydrogen bond (or a lithium cation) between the two nitrogen atoms. A series of volatile magnesium(II) and zinc(II) bis(β-dialdiminato) complexes (of stoichiometry M[RN(CH)3NR]2 where R = methyl, ethyl, iso-propyl, or tert-butyl) have been prepared and investigated as potential precursors for the chemical vapor deposition of thin films. Several of the compounds have been characterized crystallographically; the metal centers adopt pseudo-tetrahedral geometries with the two ligands forming six-membered rings with the metal. All compounds sublime cleanly both in vacuum and under 1 atm of N2, and the most volatile compounds (those having N-methyl substituents) have vapor pressures of 1 Torr at 88 (Mg) and 90 °C (Zn). In general, metal complexes of N,N′-dialkyl-β-dialdiminate ligands are more volatile than their corresponding N,N′-dialkyl-β-diketiminate and N,N′-dialkylamidinate analogues. Four copper(II) N,N′-dialkyl-β-dialdiminate complexes of stoichiometry Cu[RN(CH)3NR]2 where R = methyl, ethyl, iso-propyl, or tert-butyl have been synthesized and characterized by IR, NMR, EPR, and UV-Vis spectroscopy, and by X-ray crystallography. The compounds are unusual examples of copper(II) in nearly perfectly tetrahedral coordination environments, which is enforced by the steric bulk of the N-alkyl groups near the metal center. The tetrahedral geometry is reflected in the magnetic susceptibility, which is larger than usual for copper(II) as a result of spin-orbit coupling caused by the T ground state. The UV-Vis spectra show a strong correlation between larger interligand dihedral angles (i.e., more tetrahedral geometries) and a shift of the MLCT band maxima to longer wavelengths. The EPR spectra show that the gz value is large and the Az value is small relative to similar β-dialdiminate and β-diketiminate copper(II) complexes, a result that is also consistent with the tetrahedral geometries. Three new copper(I) complexes derived from N,N′-dialkyl-β-dialdiminate anions (alkyl = iso-propyl or tert-butyl) are reported. Treatment of the CuBr with Li(tBuN(CH)3NtBu) affords the tetrameric copper(I) compound [Cu(tBuN(CH)3NtBu)]4. In this tetramer, the β-dialdiminate ligands adopt open-chain conformations that link the copper(I) centers into a boat-shaped 24-membered ring. Interestingly, the tetramer dissociates over several hours in solution into a dimer of stoichiometry [Cu(tBuN(CH)3NtBu)]2. When copper(II) chloride is treated with Li(tBuN(CH)3NtBu) or copper(II) methoxide is treated with H(iPrN(CH)3NiPr), redox reactions can take place in which the metal center is reduced to copper(I) and the β-dialdiminate anion is oxidized. Two copper(I) complexes containing oxidized β-dialdiminate groups have been isolated: in both complexes, the oxidized group has been dehydrogenated and trimerized through C-C bond formation. All three compounds have been characterized by X-ray crystallography; selected NMR, IR, EA, and UV-Vis spectra are also reported. A series of volatile cobalt(II) and nickel(II) N,N′-dialkyl-bis(β-dialdiminato) complexes of stoichiometry M[RN(CH)3NR]2 where R = methyl, ethyl, iso-propyl, or tert-butyl have been prepared and characterized. NMR, IR, and UV-vis spectra are reported, along with their magnetic properties and crystal structures. NMR studies indicate that spin density is delocalized directly into the π-orbitals of the β-dialdiminate ligand similar to other N,N′-diaryl and β-diketiminato compounds of cobalt(II) and nickel(II), and magnetic measurements find magnetic moments larger than the spin-only values suggesting the presence of orbital contributions to the magnetic moment. In the UV-Vis spectra, the higher energy spin-allowed d-d transition is identified in the visible (or near visible) region. Overall, these new cobalt(II) and nickel(II) compounds are similar to their N,N′-diaryl and β-diketiminato analogues, but have lower molecular masses and thus are more volatile, making them potentially useful precursors for the chemical vapor deposition (CVD) of cobalt- or nickel-containing films. Three N,N′-di(tert-butyl)-1,3-propanedialdiminate compounds of titanium, vanadium, and chromium with stoichiometry M[tBuN(CH)3NtBu]2 have been synthesized and investigated by X-ray crystallography, IR, NMR, EPR, UV-vis spectroscopy, and SQIUD magnetometry in order to elucidate the oxidation states and electronic ground states present in these compounds. X-ray crystallography shows that all three compounds are monomers in which the metal centers are nearly perfectly tetrahedral. These compounds are formally divalent, but the spectroscopic and magnetic data show that the titanium and vanadium complexes contain dianionic (i.e., reduced) β-dialdiminate radicals which strongly couple anti-ferromagnetically with unpaired electrons on the oxidized metal center, which is most likely in the +3 oxidation state. This antiferromagnetic coupling leads to a diamagnetic ground state for the titanium complex and a S = ½ ground state for the vanadium compound. In contrast, the chromium compound contains an unoxidized chromium(II) center and two monoanionic β-dialdiminate ligands.

Graduation Semester

2024-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/125697

Copyright and License Information

Copyright 2024 Claire Schmit

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