Extending the chemistry of the uranyl ion: Lewis acid coordination to a U=O oxygen

Treatment of the thf adduct UO2(NCN)thf (NCN = (Me3SiN)CPh(NSiMe3)]) (1) with 2 equiv of B(C6F5)3 provides UO{OB(C6F5)3}(NCN)2 (2) the first example of a neutral uranyl complex exhibiting Lewis basic behavior. The crystal structure of 2 shows a U=O-B interaction with an elongated U=O bond (1.898(3) A). Raman spectroscopy suggests weakening of the O=U=O bonding, giving the lowest reported symmetric stretching frequency for a monomeric uranyl complex, nu1 = 780 cm-1. The borane can be selectively removed using PMe3 to give the coordinatively unsaturated UO2(NCN)2 (3) or using tBuNC to provide UO2(CNBut)(NCN)2 (4), the first example of an isonitrile coordinated to uranium.