Synthesis and CO2 Insertion Reactivity of Allyluranium Metallocene Complexes

The U4+ metallocene allyl chloride complexes (C5Me5)2U­[η3-CH2C­(R)­CH2]Cl (R = H, Me) can be synthesized by reaction of (C5Me5)2UCl2 with 1 equiv of the corresponding allyl Grignard reagents, [CH2C­(R)­CH2]­MgCl, in hydrocarbon solvents. Bis­(allyl)­uranium complexes can also be obtained in this manner using 2 equiv of the corresponding allyl Grignard, and X-ray crystallographic studies reveal the presence of both η3- and η1-allyl ligands: (C5Me5)2U­[η3-CH2C­(R)­CH2]­[η1-CH2C­(R)CH2]. Sodium amalgam reduction of (C5Me5)2U­[η3-CH2C­(R)­CH2]Cl generates the U3+ metallocene allyl complexes (C5Me5)2U­[η3-CH2C­(R)­CH2]. Carbon dioxide reacts with the U4+ allyl complexes to form the U–C insertion products (C5Me5)2U­[κ2O,O′-O2CCH2CHCH2]2–xClx (x = 0, 1). The dicarboxylate (C5Me5)2U­[κ2O,O′-O2CCH2CHCH2]2, which has a 171.98(5)° O–U–O angle, reacts with Me3SiCl to regenerate (C5Me5)2UCl2 and liberate Me3SiOC­(O)­CH2CHCH2.