Advanced

Cyclometalation reactions on rhodium(I). Evidence for a chelate effect and competing C-H and C-O oxidative additions

Sjövall, Sven LU ; Andersson, Carlaxel LU and Wendt, Ola F. LU (2001) In Organometallics 20(23). p.4919-4926
Abstract

The ligand Ph2PC6H4(CH2N(Me)CO(Et)) reacts with (bis(diphenylphosphino)butane) (2,5-norbornadiene)rhodium tetrafluoroborate (2a) and (bis(diphenylphosphino)ethane)(2,5-norbornadiene) rhodium tetrafluoroborate (2b) at room temperature in the presence of hydrogen to displace the norbornadiene and give the chelate complexes 3a,b, in which the phosphorus and the oxygen atoms are coordinated to give an eight-membered ring. At elevated temperatures these complexes are converted into cyclometalated Rh(III) benzyl hydride complexes. Rate law, activation parameters, and reactivity trends of this latter transformation indicate that displacement of one of the phosphine functionalities of the... (More)

The ligand Ph2PC6H4(CH2N(Me)CO(Et)) reacts with (bis(diphenylphosphino)butane) (2,5-norbornadiene)rhodium tetrafluoroborate (2a) and (bis(diphenylphosphino)ethane)(2,5-norbornadiene) rhodium tetrafluoroborate (2b) at room temperature in the presence of hydrogen to displace the norbornadiene and give the chelate complexes 3a,b, in which the phosphorus and the oxygen atoms are coordinated to give an eight-membered ring. At elevated temperatures these complexes are converted into cyclometalated Rh(III) benzyl hydride complexes. Rate law, activation parameters, and reactivity trends of this latter transformation indicate that displacement of one of the phosphine functionalities of the bis-chelating phosphine takes place before the C-H activation. Complex 3b was characterized by X-ray crystallography. On the other hand, under ambient conditions the ligand (±)-Ph2PC6H4(CH(Me)O(CO)Et) undergoes activation of either the benzylic C-O or C-H bond, depending on the nature of the Rh precursor used. Thus, 2b gives overall elimination of propionic acid to result in a styrene complex, which was characterized by X-ray crystallography, whereas bis(2,5-norbornadiene)rhodium tetrafluoroborate gives a mixture of Rh(III) benzyl hydride stereoisomers. The difference in reactivity is discussed in terms of different mechanisms for the two processes.

(Less)
Please use this url to cite or link to this publication:
author
; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Organometallics
volume
20
issue
23
pages
8 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • scopus:0035851939
ISSN
0276-7333
DOI
10.1021/om010543x
language
English
LU publication?
yes
id
a14e8f8d-9d21-41d9-9d55-a38dd534d97d
date added to LUP
2019-05-03 15:10:34
date last changed
2020-01-30 03:41:16
@article{a14e8f8d-9d21-41d9-9d55-a38dd534d97d,
  abstract     = {<p>The ligand Ph<sub>2</sub>PC<sub>6</sub>H<sub>4</sub>(CH<sub>2</sub>N(Me)CO(Et)) reacts with (bis(diphenylphosphino)butane) (2,5-norbornadiene)rhodium tetrafluoroborate (2a) and (bis(diphenylphosphino)ethane)(2,5-norbornadiene) rhodium tetrafluoroborate (2b) at room temperature in the presence of hydrogen to displace the norbornadiene and give the chelate complexes 3a,b, in which the phosphorus and the oxygen atoms are coordinated to give an eight-membered ring. At elevated temperatures these complexes are converted into cyclometalated Rh(III) benzyl hydride complexes. Rate law, activation parameters, and reactivity trends of this latter transformation indicate that displacement of one of the phosphine functionalities of the bis-chelating phosphine takes place before the C-H activation. Complex 3b was characterized by X-ray crystallography. On the other hand, under ambient conditions the ligand (±)-Ph<sub>2</sub>PC<sub>6</sub>H<sub>4</sub>(CH(Me)O(CO)Et) undergoes activation of either the benzylic C-O or C-H bond, depending on the nature of the Rh precursor used. Thus, 2b gives overall elimination of propionic acid to result in a styrene complex, which was characterized by X-ray crystallography, whereas bis(2,5-norbornadiene)rhodium tetrafluoroborate gives a mixture of Rh(III) benzyl hydride stereoisomers. The difference in reactivity is discussed in terms of different mechanisms for the two processes.</p>},
  author       = {Sjövall, Sven and Andersson, Carlaxel and Wendt, Ola F.},
  issn         = {0276-7333},
  language     = {eng},
  month        = {11},
  number       = {23},
  pages        = {4919--4926},
  publisher    = {The American Chemical Society (ACS)},
  series       = {Organometallics},
  title        = {Cyclometalation reactions on rhodium(I). Evidence for a chelate effect and competing C-H and C-O oxidative additions},
  url          = {http://dx.doi.org/10.1021/om010543x},
  doi          = {10.1021/om010543x},
  volume       = {20},
  year         = {2001},
}