Carbon monoxide reduction. [Fe(η⁵-C₅H₅)(Ph₂PCH₂CH₂PPh₂)(CO)H]: reactions and formation by reduction of the complex [Fe(η⁵-C₅H₅)(Ph₂PCH₂CH₂PPh₂)(CO)]PF₆

Abstract

The preparation of the cations of [Fe(η5-C5H5)(dppe)(CO)]PF6(1)(dppe = Ph2PCH2CH2PPh2) and [Fe(η5-C5H5)(PPh3)2(CO)]PF6(5) and their reduction with LiAlH4 to form the complexes [Fe(η5-C5H5)(dppe)(CO)H](2) and [Fe(η5-C5H5)(PPh3)(CO)H](6), respectively, is described. Evidence is presented for the intermediacy of [Fe(η5-C5H5)(dppe)(CHO)](4) in the low-temperature reduction of (1). High-temperature reduction of (1) occurs with loss of regioselectivity yielding both [Fe(η5-C5H5)(dppe)(CH3)](9) and [Fe(η4-C5H6)(dppe)(CO)](8). The latter product is formed exclusively by exo attack on the cyclopentadienyl ligand as evidenced by carrying out the reduction with LiAlD4. The disproportionation of (2) in toluene to give [{Fe(η5-C5H5)(CO)H}2(µ-dppe)](12) and its subsequent thermal and photochemical elimination of dihydrogen has been studied. In contrast, in tetrahydrofuran solutions, (2) disproportionates to (9)via(4). The thermal migration of hydrogen from (2) to produce (8) has been studied. The use of [Fe(η5-C5H5)(dppe)(CO)D](3) has shown this migration to be endo first-order and intramolecular with a kinetic isotope effect close to unity.