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’’’₂U(I)Me ( 2 , Cp’’’=η⁵-1,2,4-(Me₃C)₃C₅H₂) with Mes*PHK (Mes*=2,4,6-(Me₃C)₃C₆H₂) in THF yields the base-free terminal uranium phosphinidene metallocene, Cp’’’₂U=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’’’₂U]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’’’₂U(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.