Facile synthesis of five-membered cyclic RE₂P-H iron(0) complexes

The synthesis of five-membered P-heterocyclic iron(0) complexes possessing a P-H unit and two heteroatoms (E = O, N), directly bound to phosphorus, is described. Initial problems to achieve access via "classical" reduction of P-Cl bonds of P-heterocycle complexes, e.g., leading to P-P coupling, could be solved by a "combined two-step" reduction/complexation. The use of K[Fe(CO)₄H] not only opened access to such heterocyclic phosphane Fe(CO)₄ complexes but also allowed the synthesis of sterically non-shielded 'secondary' heterocyclic phosphane complexes. Spectroscopic and structural parameters are discussed.