Cyclopentadienyldicarbonyliron Halides as Electrophiles: Reactions of (.eta.5-C5H5)Fe(CO)2X with RLi in the Presence of PPh3 To Produce (.eta.4-exo-RC5H5)Fe(CO)2(PPh3) and Preparation of [(.eta.5-C5H5)Fe(CO)C(O)Me](.mu.,.eta.1,.eta.1-dppf)[(.eta.4-exo-MeC5H5)Fe(CO)2]