The 18-Electron, Metal−Metal-Bonded Dimers [η5-C5Ph5Fe(CO)2]2 and [η5-C5Ph4(p-tolyl)Fe(CO)2]2: Their Proclivity To Undergo Spontaneous, Thermal Homolysis to the Corresponding 17-Electron Monomers

The known compound [Cp ‡ Fe(CO) 2 ] 2 and the new, more soluble [Cp † Fe(CO) 2 ] 2 (Cp ‡ = η 5 -C 5 Ph 5; Cp † = η 5 -C 5 Ph 4 ( p -tolyl)) are prepared via a new, very effective route involving hydridic hydrogen atom abstraction from the hydrides, Cp ‡ Fe(CO) 2 H and Cp † Fe(CO) 2 H, by the trityl radical. The dimers dissociate thermally to the corresponding 17-electron monomers, Cp ‡ Fe(CO) 2 and Cp † Fe(CO) 2, which probably assume “planar” ( C 2 v ) structures with OC−Fe−CO bond angles of ∼90°.