Synthesis and reactivity of sterically encumbered diazaferrocenes Ralph John Ugalino CHEM 211
Synthesis and reactivity of sterically encumbered diazaferrocenes
Ralph John UgalinoCHEM 211
Objective
synthesize and characterize novel, sterically demanding diazaferrocenes
METHODS: 1H NMR, VT NMR X-ray crystallography, CV, 57Fe Mossbauer, EPR
Diazaferrocene and ligands
Rationale for synthesis
PROBLEM: η5-κ1 facile haptotropic shifts
SOLUTION: use bulky pyrollyl ligands
Increasing bulkiness
Synthetic schemes
57% yield
60% yield
Structure based on crystallography: 3-Fe
1H-1H NOESY NMR: 3-Fe
23°C, C7D8 solvent
VT NMR: 3-Fe
Only t-Bu region shown
Possible structures
Rotamers…
Cyclic voltammetry: 1-Fe, 5-Fe
100 mV/s, RT, in CH2Cl2 with 0.1 M [Bu4N][PF6]
Cyclic voltammetry: 3-Fe
100 mV/s, RT, in CH2Cl2 with 0.1 M [Bu4N][PF6]
Cyclic voltammetry
degradation of 3-Fe upon oxidation
heterocyclic ferroceniums have anodic shift (~0.5 V) but are less stable than their carbocyclic forms
Mossbauer spectroscopy: 1-Fe, 5-Fe, 3-Fe
Mossbauer spectroscopy: 3-Fe+ , 5-Fe+
Mossbauer spectroscopy
powder sample, 100 or 80 K
quadrupole splitting ΔEQ depends on relative population of unfilled e2g(dx2-y2,dxy), e1g(dxz,dyz)
spin lattice relaxation in diazaferrocenium
p2, p1 : electronic populations of e2g and e1g
EPR spectroscopy: 3-Fe+
g†=1.60g//=4.03*impurity
Electronic transitions
very similar HOMO-LUMO gaps
more orbital mixing in 3-Fe
Stronger Pyr-Fe bond against Cyp-Fe bonds