Experimental and Computational Studies on a Base-Free Terminal Uranium Phosphinidene Metallocene

The first stable base-free terminal uranium phosphinidene metallocene is presented; and its structure and reactivity have been studied in detail and compared to that of the corresponding thorium derivative. Salt metathesis reaction of the methyl iodide uranium metallocene Cp'''U-2(I)Me (2, Cp'''=eta(5)-1,2,4-(Me3C)(3)C5H2) with Mes*PHK (Mes*=2,4,6-(Me3C)(3)C6H2) in THF yields the base-free terminal uranium phosphinidene metallocene, Cp'''U-2=PMes* (3). In addition, density functional theory (DFT) studies suggest substantial 5f orbital contributions to the bonding within the uranium phosphinidene [U]=PAr moiety, which results in a more covalent bonding between the [Cp'''U-2](2+) and [Mes*P](2-) fragments than that for the related thorium derivative. This difference in bonding besides steric reasons causes different reactivity patterns for both molecules. Therefore, the uranium derivative 3 may act as a Cp'''U-2(II) synthon releasing the phosphinidene moiety (Mes*P:) when treated with alkynes or a variety of hetero-unsaturated molecules such as imines, thiazoles, ketazines, bipy, organic azides, diazene derivatives, ketones, and carbodiimides.