A Caltech Library Service

The chemistry of tris(phosphino)borate manganese and iron platforms


Lu, Connie Chih (2006) The chemistry of tris(phosphino)borate manganese and iron platforms. Dissertation (Ph.D.), California Institute of Technology.


The coordination chemistry of monovalent and divalent manganese complexes supported by the anionic tris(phosphino)borate ligand [PhBPiPr3] is presented. The halide complexes, [PhBPiPr3]MnCl and [PhBPiPr3]MnI, have been characterized by XRD, SQUID magnetometry, and EPR spectroscopy. The halide [PhBPiPr3]MnI serves as a precursor to manganese azide, alkyl, and amide species: [PhBPiPr3]Mn(N3), [PhBPiPr3]Mn(CH2Ph), [PhBPiPr3]Mn(Me), [PhBPiPr3]Mn(NH(2,6-iPr2Ph)), [PhBPiPr3]Mn(dbabh), and [PhBPiPr3]Mn(1-Ph(isoindolate)). Collectively, they represent an uncommon motif of low-coordinate polyphosphine-supported manganese species. Some of our synthetic efforts to generate [PhBPiPr3]Mn?Nx species are described, as are theoretical DFT studies that probe the electronic viability of these multiply bonded target structures.

Two tris(phosphino)borate ligands, [PhBPter3] and [PhBPCH2Cy3] are introduced that feature terphenyl and methylcyclohexyl groups on the phosphine arms, respectively. The iron chlorides, [PhBPter3]FeCl and [PhBPCH2Cy3]FeCl, have been prepared as precursors to iron nitrides. Addition of the nitride transfer reagent Li(dbabh) to [PhBPCH2Cy3]FeCl produced the terminal nitride, [PhBPCH2Cy3]Fe(N). The 15N NMR spectrum of the labeled species, [PhBPCH2Cy3]Fe(15N), contains a peak at 929 ppm, consistent with a terminal nitride functionality. Mossbauer spectroscopy of the nitride shows a low isomer shift value of 0.34(1) mm/s and an exceptionally large quadrupole splitting of 6.01(1) mm/s.

Reduction of [PhBPCH2Cy3]FeCl generates a masked iron(I) species that is highly reactive. Combustion analysis of this species is consistent with "[PhBPCH2Cy3]Fe." Other physical methods including VT NMR, EPR, and IR spectroscopies suggest the presence of a paramagnetic species in equilibrium with a diamagnetic species. The paramagnetic component is postulated to be an Fe(III) hydride, wherein a ligand C-H bond has been cyclometalated at the metal center. The reactivity of "[PhBPCH2Cy3]Fe" is consistent with iron(I). For example, its reaction with PMe3 and 1-adamantylazide affords the phosphine adduct, [PhBPCH2Cy3]Fe(PMe3), and the iron imide, [PhBPCH2Cy3]Fe(NAd), respectively. Interestingly, "[PhBPCH2Cy3]Fe" undergoes redox reactions with benzene to give initially a benzene adduct, {[PhBPCH2Cy3]Fe}2(mu-eta3:eta3-C6H6), which decomposes to {[PhBPCH2Cy3]Fe}2(mu-eta5:eta5-6,6'-bicyclohexadienyl) via radical C-C bond coupling. Finally, "[PhBPCH2Cy3]Fe" readily reduces CO2 at rt to give as the major product {[PhBPCH2Cy3]Fe}2(mu-CO)(mu-O), wherein a C=O bond has been cleaved. The minor product has not been definitively established, but one possibility is the oxalate-bridged dimer {[PhBPCH2Cy3]Fe}2(mu-eta2:eta2-O2CCO2) that results from reductive coupling of two CO2 molecules.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:coordination chemistry; small molecule activation
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Peters, Jonas C.
Thesis Committee:
  • Bercaw, John E. (chair)
  • Stoltz, Brian M.
  • Peters, Jonas C.
  • Goddard, William A., III
Defense Date:26 May 2006
Record Number:CaltechETD:etd-06012006-151944
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2364
Deposited By: Imported from ETD-db
Deposited On:02 Jun 2006
Last Modified:26 Dec 2012 02:50

Thesis Files

PDF (CCL_Thesis_Corrected.pdf) - Final Version
See Usage Policy.


Repository Staff Only: item control page