A Caltech Library Service

Investigations on low-valent group 8 and 9 metalloradicals


Takaoka, Ayumi (2012) Investigations on low-valent group 8 and 9 metalloradicals. Dissertation (Ph.D.), California Institute of Technology.


Tetradentate, monoanionic, tris(phosphino)silyl ligands were chelated to group 8 and 9 transition metals to stabilize complexes with unusual oxidation states and/or geometries. Initial studies with the [SiPPh3]− ligand on ruthenium established the flexibility of this ancillary ligand in stabilizing complexes with strongly trans influencing ligands in trans dispositions. A related ligand scaffold, [SiPiPr3]−, was subsequently used to stabilize mononuclear complexes of Ru(I) and Os(I), the first examples to be isolated and thoroughly chracterized. EPR spectroscopy and DFT calculations supported their metalloradical character, and further studies highlighted their reactivity in both one- and two-electron redox processes. The ability of the [SiPiPr3]− scaffold to stabilize d7 metalloradicals of group 8 metals was extended to group 9 metals, and a series of d7 complexes of cobalt, rhodium, and iridium were synthesized in which their ancillary ligands, oxidation states, spin states, and geometry are conserved. Similar to the previously reported [SiPiPr3]Fe(N2) complex, the related [SiPiPr3]Ru(N2) complex was shown to exhibit N−N coupling of organic azides to yield azoarenes catalytically. Detailed mechanistic studies conclusively showed that the Ru(III) imide species, whose iron analog is the key intermediate in the [SiPiPr3]Fe system, is not involved in the mechanism for the [SiPiPr3]Ru system. Instead, a mechanism in which free nitrene is released during the catalytic cyle is favored. Finally, hybrid ligands with multiple thioether donors in place of phosphine donors on the [SiPR3]− scaffold were synthesized to stabilize a number of dinitrogen complex of iron. These complexes featured rare examples of S−Fe−N2 linkages.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry;Inorganic Chemistry;Coordination Chemistry;Metalloradicals;Ruthenium(I)
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Awards:The Herbert Newby McCoy Award, 2012
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Peters, Jonas C.
Thesis Committee:
  • Agapie, Theodor (chair)
  • Okumura, Mitchio
  • Gray, Harry B.
  • Peters, Jonas C.
Defense Date:17 January 2012
Author Email:ayumitakaoka (AT)
Record Number:CaltechTHESIS:01202012-105759966
Persistent URL:
Related URLs:
URLURL TypeDescription
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6770
Deposited By: Ayumi Takaoka
Deposited On:26 Jan 2012 23:39
Last Modified:25 Sep 2014 19:05

Thesis Files

PDF - Final Version
See Usage Policy.


Repository Staff Only: item control page