| Summary: | Herein is reported the structural characterization and scalable preparation of the elusive iron–phosphido
complex FpP(t
Bu)(F) (2-F, Fp = (Fe(h5
-C5H5)(CO)2)) and its precursor FpP(t
Bu)(Cl) (2-Cl) in 51% and 71%
yields, respectively. These phosphide complexes are proposed to be relevant to an organoiron catalytic
cycle for phosphinidene transfer to electron-deficient alkenes. Examination of their properties led to the
discovery of a more efficient catalytic system involving the simple, commercially available organoiron
catalyst Fp2. This improved catalysis also enabled the preparation of new phosphiranes with high yields
(
t
BuPCH2CHR; R = CO2Me, 41%; R = CN, 83%; R = 4-biphenyl, 73%; R = SO2Ph, 71%; R = POPh2, 70%;
R = 4-pyridyl, 82%; R = 2-pyridyl, 67%; R = PPh3
+, 64%) and good diastereoselectivity, demonstrating
the feasibility of the phosphinidene group-transfer strategy in synthetic chemistry. Experimental and
theoretical studies suggest that the original catalysis involves 2-X as the nucleophile, while for the new
Fp2-catalyzed reaction they implicate a diiron–phosphido complex Fp2(Pt
Bu), 4, as the nucleophile
which attacks the electron-deficient olefin in the key first P–C bond-forming step. In both systems, the
initial nucleophilic attack may be accompanied by favorable five-membered ring formation involving
a carbonyl ligand, a (reversible) pathway competitive with formation of the three-membered ring found
in the phosphirane product. A novel radical mechanism is suggested for the new Fp2-catalyzed system.
|
|---|