Bonding of tris(.eta.5-cyclopentadienyl)-actinide complexes. 3. Interaction of .pi.-neutral, .pi.-acidic, and .pi.-basic ligands with (.eta.5-C5H5)3U

Abstract

A qualitative treatment of the bonding in Cp{sub 3}M (Cp = {eta}{sup 5}-C{sub 5}H{sub 5}) compounds under C{sub 3{upsilon}} symmetry reveals that the Cp{sub 3}{sup 3{minus}} ligand field contains a high-lying a{sub 2} orbital which is restricted by symmetry to interact only with metals that contain f orbitals. Quantitative investigation of the electronic structure of 5f{sup 3} Cp{sub 3}U via X{alpha}-SW molecular orbital calculations with quasi-relativistic corrections reveals that the Cp ligands donate electron density primarily into the U 6d orbitals while the three principally metal-based valence electrons are housed in the 5f orbitals. Electronic structure calculations of Cl{sub 3}U show that although Cl can be considered isolobal with Cp, it is a poorer donor ligand. Calculations of Cp{sub 3}U bonded to a fourth ligand L (L = H, CO, NO, OH) indicate that the {sigma}-bonding framework is essentially the same for {pi}-neutral (H), {pi}-acidic (CO, NO), or {pi}-basic (OH) ligands: Electron density is donated from the {sigma} orbital of the fourth ligand into a uranium orbital that is primarily 6d{sub z{sup 2}} in character with minor contributions from the 5f{sub z{sup 3}} orbital, the 7p{sub z} orbital, and the 7s orbital. In the {pi}-bonding framework, the U 5f orbitalsmore » are responsible for back-donation into the {pi}* orbitals of CO an NO, while acceptance of electron density from the {pi} orbitals of OH involves the U 6d orbitals and, to a lesser extent, the U 5f orbitals. The bonding scheme of Cp{sub 3}UNO suggests that this molecule may prove to be a rather unusual example of a linear NO{sup {minus}} ligand.« less