ELECTRON-DISTRIBUTION AND BONDING IN ETA(3)-CYCLOPROPENYL METAL-COMPLEXES

The synthesis of (eta3-C3R3)lr(CO)3 and He I and He II photoelectron s pectra of (eta3-C3R3)-CO(CO)3, (eta3-C3R3)Ir(CO)3, and (eta3-C3R3)Fe(C O)2(NO) (where R = tert-butyl) are reported. The shifts and splittings in ionization energies with the metal and ligand perturbations in thi s series, the changes in ionization peak areas as a function of the ex citation energy, and Fenske-Hall molecular orbital calculations assist in the assignment and interpretation of the spectra. The cobalt compl ex reveals three peaks in the low ionization energy region that are pr imarily metal-based, consistent with the two states of e symmetry and one state of a1 symmetry from the five d orbitals of a formally d10 me tal in C3v Symmetry. The spectrum of the iridium complex has five peak s in this region due to large spin-orbit coupling that splits the e sy mmetry ionizations. The doubly degenerate peaks of the cobalt complex are also expected to be split in the photoelectron spectrum of the iro n-nitrosyl complex due to the lowering to C, symmetry. Only four disti nct peaks are seen for the iron-nitrosyl complex, with two ionization bands at higher energy being merged in a broad envelope. The ionizatio n cross-sections indicate that the eta3-bound C3R3 ligand in these com plexes is best described formally as a cation with a large amount of m ixing and backbonding from the metal d(pi) orbitals to the e(pi) orbi tals of the cyclopropenyl ring. This is compared to the NO+ ligand.