Reduction of cationic P-coordinated (diphenylphosphino)alkyne iron complexes with sodium borohydride

The reaction of cationic complexes [(η5-C5H5)Fe(CO)2(PPh 2CCR)]+ (R=H, Me, tBu, Ph, Tol) with NaBH4 at -78°C in THF yielded the neutral complexes [(η4-C5H6)Fe(CO)2(PPh 2CCR)], which were characterized by elemental analysis, and NMR and IR spectroscopy. This result is consistent with the idea that the electrophilic character of the cation [(η5-C5H5)Fe(CO)2(PPh 2CCR)]+ is mainly located on the [(η5-C5H5)Fe(CO)2] fragment and the polarization of the alkyne does not change the direction of the nucleophilic attack with respect to the cation [(η5-C5H5)Fe(CO)2(PPh 3)]+. The comparison between spectroscopic data of cationic and neutral complexes supplies new information about the influence of metal on the alkyne function in P-coordinated (diphenylphosphino)alkynes. © 1999 Elsevier Science S.A.