Interception of a Uranium Alkyl-Carbene Complex Utilizing a Bulky Phosphaylide

Area of Science:

• Organometallic Chemistry
• Uranium Chemistry
• Carbene Complexes

Background:

• Uranium carbene complexes are of interest due to their unique bonding and reactivity.
• Synthesizing mono-carbene uranium complexes can be challenging due to competing bis-carbene formation.
• Bulky ligands are often employed to control reactivity and selectivity in organometallic synthesis.

Purpose of the Study:

• To report the synthesis of uranium alkyl-carbene complexes using a bulky phosphaylide reagent.
• To investigate methods for controlling the formation of mono- versus bis-carbene species.
• To explore alternative synthetic routes for accessing specific uranium carbene complexes.

Main Methods:

• Kinetic trapping of alkyl-carbene molecules using H2C=P(Artt)3 (Artt = 3,5-tBu2C6H3).
• Synthesis of an iodide precursor Cp*2U(I)[=CH P(Artt)3] (4-I) for controlled methylation.
• Reaction of the iodide precursor with organometallic reagents (MeLi, MeMgBr) to form carbene complexes.

Main Results:

• Direct reaction with the phosphaylide reagent yielded significant amounts of undesired bis-carbene species.
• An alternative route via an iodide intermediate (4-I) afforded the mono-carbene product Cp*2U(Me)[=CH P(Artt)3] (1-mono) in good yields.
• The choice of methylating agent was critical; MeLi was effective, while MeMgBr led to undesired byproducts like Cp*2UMe2.
• Synthesis of other mixed carbene complexes, such as Cp*2U(OtBu)[=CH P(Artt)3] (6-OtBu), was also demonstrated.

Conclusions:

• A novel synthetic strategy was developed to selectively produce mono-carbene uranium complexes.
• The use of an iodide intermediate and MeLi provides a reliable route to these challenging compounds.
• This work expands the accessibility of diverse uranium carbene complexes for further study.