Methyl Effects on the Stereochemistry and Reactivity of PPP-Ligated Iron Hydride Complexes.

Iron dihydride complexes are key intermediates in many iron-catalyzed reactions. Previous efforts to study molecules of this type have led to the discovery of a remarkably stable -FeH complex, which is supported by bis[2-(diisopropylphosphino)phenyl]phosphine (PPP) along with CO. In this work, the hydrogen on the central phosphorus has been replaced with a methyl group, and the corresponding iron carbonyl dichloride, hydrido chloride, and dihydride complexes have been synthesized. The addition of the methyl group favors the configuration for the Me-P-Fe-H moiety and the geometry for the H-Fe-CO motif, which is distinctively different from the PPP system. Furthermore, it increases the thermal stability of the dihydride complex, -(PPP)Fe(CO)H (PPP = bis[2-(diisopropylphosphino)phenyl]methylphosphine). The variations in stereochemistry and compound stability contribute greatly to the differences between the two PPP systems in reactions with PhCHO, CS, and HCOH.