Theoretical and experimental studies of hydride addition to iron carbonyl phosphine and phosphite complexes

The hybrid density functional B3LYP method has been used to study the react ions of the organometallic cations [(eta (5)-C5H5)Fe(CO)(2)(PR3)](+) (R = H (1), OMe (8)) with the hydride anion H-. From a comparison of the relative energies of the 14 stationary points located on both potential energy surf aces, it was predicted that the most energetically favorable sites of attac k would be to one of the CO ligands leading to the formyl species (eta (5)- C5H5)Fe(CHO)(CO)(PR3) (R = H (4), OMe (10)) and to the cyclopentadienyl rin g leading to the ring adducts (eta (4)-C5H6)Fe(CO)(2)(PR3) (R = H (7), OMe (12)). Two metallophosphoranes, (eta (5)-C5H5)Fe(CO)(2)(PR3H) (R = H (2), O Me (9)), resulting from attack to the coordinated phosphorus atom, were loc ated and were found to be significantly less stable than the formyl species or the ring adducts. The hydride species (eta (5)-C5H5)Fe(CO)(2)(H) (5) an d (eta (5)-C5H5)Fe(CO)(H)(PR3) (R = H (6), OMe (11)) were located, and sinc e the relative energies of these species were below those of the formyls 4 and 10, it was predicted that once these formyl species are formed they can undergo loss of the carbonyl, phosphine, or phosphite ligands to give the respective hydrides. In addition, two transition states, TS1 and TS2, for d ecomposition of the formyl species 4 to the hydride 5 or 6 were located. Si nce the relative energies of TS1 and TS2 were found to be similar, it was p redicted that both hydrides would be formed from 4. These predictions agree d with the experimental evidence obtained from the reduction of the mononuc lear cations [(eta (5)-C5H5)Fe(CO)(2)(PR3)]BF4 (R = OMe (8a), OEt (13)).