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.