Structures and dynamic solution behavior of cationic, two-coordinate gold(I)-π-allene complexes.

Published

Journal Article

A family of seven cationic gold complexes that contain both an alkyl substituted π-allene ligand and an electron-rich, sterically hindered supporting ligand was isolated in >90% yield and characterized by spectroscopy and, in three cases, by X-ray crystallography. Solution-phase and solid-state analysis of these complexes established preferential binding of gold to the less substituted C=C bond of the allene and to the allene π face trans to the substituent on the uncomplexed allenyl C=C bond. Kinetic analysis of intermolecular allene exchange established two-term rate laws of the form rate=k(1)[complex]+k(2)[complex][allene] consistent with allene-independent and allene-dependent exchange pathways with energy barriers of ΔG(≠)(1)=17.4-18.8 and ΔG(≠)(2)=15.2-17.6 kcal mol(-1), respectively. Variable temperature (VT) NMR analysis revealed fluxional behavior consistent with facile (ΔG(≠)=8.9-11.4 kcal mol(-1)) intramolecular exchange of the allene π faces through η(1)-allene transition states and/or intermediates that retain a staggered arrangement of the allene substituents. VT NMR/spin saturation transfer analysis of [{P(tBu)(2)o-binaphthyl}Au(η(2)-4,5-nonadiene)](+)SbF(6)(-) (5), which contains elements of chirality in both the phosphine and allene ligands, revealed no epimerization of the allene ligand below the threshold for intermolecular allene exchange (ΔG(≠)(298K)=17.4 kcal mol(-1)), which ruled out the participation of a η(1)-allylic cation species in the low-energy π-face exchange process for this complex.

Full Text

Duke Authors

Cited Authors

  • Brown, TJ; Sugie, A; Leed, MGD; Widenhoefer, RA

Published Date

  • May 2012

Published In

Volume / Issue

  • 18 / 22

Start / End Page

  • 6959 - 6971

PubMed ID

  • 22529058

Pubmed Central ID

  • 22529058

Electronic International Standard Serial Number (EISSN)

  • 1521-3765

International Standard Serial Number (ISSN)

  • 0947-6539

Digital Object Identifier (DOI)

  • 10.1002/chem.201103289

Language

  • eng