Complexes of alkenes, alkynes, and dienes - IONiC VIPEr

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  • 1.Complexes of alkenes, alkynes, and dienes Created by Margaret L. Scheuermann, Princeton University; Abby R. O’Connor, The College of New Jersey, oconnora@tcnj.edu. Copyright Scheuermann and O’Connor, 2014. This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this license visit http://creativecommons.org/about/license/
  • 2.2 History & Utility W. C. Zeise, Annalen der Physik, 1831, 21, 497. Review: Hunt. Platin. Met. Rev. 1984, 28, 76. First example Popular starting materials and precatalysts: Catalytic intermediates: Alkene hydrogenation^* Alkene dimerization/ oligomerization/ polymerization^* Olefin metathesis^* Mizoroki-Heck^* Wacker Oxidation^ Hydrofunctionalization- Hydroboration/ hydosilylation^/ hydrocyanation^/ hydroamination^/ hydroformylation^/ etc. ^ significant industrial use; * Nobel Prize
  • 3.Orbital Overlap- Octahedral Example 3 C-C π C-C π* C-C σ C-C σ* M-olefin σ M-olefin π M-olefin σ* M-olefin π* M-olefin π* M-olefin σ* M-olefin π M-olefin σ dz2 dxz (or dyz) dx2-y2 Dxy (or dyz or dxz) Olefin Olefin along x (or y) axis Olefin along z axis x y z
  • 4.Types of π-bound ligands 4 Extremes Less backbonding into π*… electron poor metal center More backbonding into π*… electron rich metal center
  • 5.Properties 5 Rotation around metal-olefin bond Orientation determined by steric and electronic factors Bond lengths and angles Electron rich metal centers tend to form more stable olefin complexes NMR As backbonding increases so do geometry differences C-C bonds get longer sp2 becomes more sp3-like sp becomes more sp2-like can help relieve ring strain Buchwald. JACS 1986, 165, 7441. late metals Low oxidation states high d-electron counts low overall charge When backbonding is minimal (electron poor metal center) 1H and 13C shifts resemble free olefin When backbonding is significant (electron rich metal center) 1H and 13C resonances shift upfield- smaller δ
  • 6.Synthesis & Reactivity 6 Ligand substitution* Reduction β-hydride elimination* Displacement by ligand substitution* Nucleophilic attack* (when metal center is a poor π donor) Insertion* R = H, alkyl, aryl α β * Often present in catalytic cycles