High-Valent Transition-Metal Alkylidene Complexes: Effect of Ligand and Substituent Modification

Cundari, Thomas R., 1964-; Gordon, Mark S.

doi:10.1021/ja00028a022

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Title

Main Title High-Valent Transition-Metal Alkylidene Complexes: Effect of Ligand and Substituent Modification

Creator

Author: Cundari, Thomas R., 1964-

Creator Type: Personal

Creator Info: University of North Texas; North Dakota State University
Author: Gordon, Mark S.

Creator Type: Personal

Creator Info: North Dakota State University

Publisher

Name: American Chemical Society

Place of Publication: [Washington, DC]

Date

Creation: 1992

Language

English

Description

Content Description: Article on high-valent transition-metal alkylidene complexes and the effect of ligand and substituent modification.
Physical Description: 10 p.

Subject

Keyword: transition metals
Keyword: alkylidene complexes
Keyword: ligands
Keyword: substituents

Source

Journal: Journal of the American Chemical Society, 114(2), American Chemical Society, January 1992, pp. 1-10

Citation

Publication Title: Journal of the American Chemical Society
Volume: 114
Issue: 2
Page Start: 539
Page End: 548
Peer Reviewed: True

Collection

Name: UNT Scholarly Works

Code: UNTSW

Institution

Name: UNT College of Arts and Sciences

Code: UNTCAS

Rights

Rights Access: public

Resource Type

Article

Format

Text

Identifier

DOI: 10.1021/ja00028a022
Archival Resource Key: ark:/67531/metadc107774

Degree

Academic Department: Chemistry

Note

Display Note: Reprinted with permission from the Journal of the American Chemical Society. Copyright 1992 American Chemical Society.
Display Note: Abstract: An ab initio investigation into the effects of ligand and substituent modification on the metal-carbon double bond is reported. Prototypical group IVB (Ti, Zr, Hf) and Group VB (Nb, Ta) alkylidenes are chosen for this study. The MC/LMO/CI (multiconfiguration/localized molecular orbital/configuration interaction) procedure is used to examine the electronic structures of these complexes in terms of the prime resonance contributors to the ground-state wave function. The main conclusion drawn from this work is that the intrinsic nature of the metal-carbon double bond can typically be changed only within certain limits by modification of the electronegativity of the ligands (L) and substituents (Z). In other words, the Ta=C bond in H₃TaCCl₂ and Cl₃TaCH₂ and presumably in experimentally characterized analogues with larger ligands and substituents, e.g., Cp and neopentyl. Significant changes in the electronic structure are effected in three ways: The first way is through the introduction of a highly electropositive substituent, e.g., Li. This makes the metal-carbon bond closer to a triple bond for the Ta-alkylidenes. The second way to change the electronic structure of the alkylidenes significantly is to change the central metal atom. The heaviest members of groups IVB (Hf) and VB (Ta) are the most nucleophilic at the α-carbon. The third way in which the metal-carbon bond could be significantly altered is through the use of π-donor substituents. The introduction of π-donor substituents on Cα increases the electrophilicity of the α-carbon.