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