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