Valence electronic structure of bridging methylenes: UV photoelectron spectroscopy of .mu.-methylene-bis[dicarbonyl(.eta.5-cyclopentadienyl)manganese

Abstract

The He I photoelectron spectrum of ..mu..-CH/sub 2/-((eta/sup 5/-C/sub 5/H/sub 4/CH/sub 3/)Mn(CO)/sub 2/)/sub 2/ in the ionization energy range below 11 eV is reported and compared with the ionizations of (eta/sup 5/-C/sub 5/H/sub 4/CH/sub 3/)Mn(CO)/sub 3/ and (eta/sup 5/-C/sub 5/H/sub 4/CH/sub 3/)Mn(CO)/sub 2/(C/sub 2/H/sub 4/). Excellent agreement is found between the observed ionizations and the predictions of parameter-free molecular orbital calculations. The valence orbitals of the ..mu..-CH/sub 2/ group appear to have near ideal matching with the frontier orbitals of the (eta/sup 5/-C/sub 5/H/sub 4/CH/sub 3/)Mn(CO)/sub 2/ fragments to produce the bonding and stability of this cyclopropane analogue. An effective charge transfer from the metals to the methylene occurs in this interaction which results in a high negative charge on the methylene carbon and formation of a net metal-metal bond. The bonding of the bridging methylene in this complex is also compared with the bonding of a terminal methylene with the analogous (eta/sup 5/-C/sub 5/H/sub 5/)Mn(CO)/sub 2/ species. It is concluded that the formation of the metal-metal bond is an important factor in the greater stability of the bridging system.