Cundari, Thomas R., 1964-
University of North Texas; North Dakota State University
Gordon, Mark S.
North Dakota State University
Publisher Name: American Chemical Society
Place of Publication: [Washington, DC]
Article on high-valent transition-metal alkylidene complexes and the effect of ligand and substituent modification.
Reprinted with permission from the Journal of the American Chemical Society. Copyright 1992 American Chemical Society.
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.
|Keyword(s):||transition metals | alkylidene complexes | ligands | substituents|
|Source:||Journal of the American Chemical Society, 1992, Washington DC: American Chemical Society, pp. 539-548|
UNT College of Arts and Sciences
UNT Scholarly Works
Publication Title: Journal of the American Chemical Society
Page Start: 539
Page End: 548
Peer Reviewed: Yes