Incorporation of Boron into Uranium Metallacycles: Synthesis, Structure, and Reactivity of Boron-Containing Uranacycles Derived from Bis(alkynyl)boranes.

The reaction of uranacyclopropene complex (C5 Me5 )2 U[η2 -1,2-C2 (SiMe3 )2 ] with B-aryl bis(alkynyl)borane PhB(C≡CPh)2 led to the first six-membered uranium metallaboracycle, while the reaction with B-amino bis(alkynyl)borane (Me3 Si)2 NB(C≡CPh)2 afforded an unexpected uranaborabicyclo[2.2.0] complex via [2+2] cycloaddition. The reaction with CuCl revealed the non-innocent property of the rearranged bis(alkynyl)boron species towards oxidant. The reactions with isocyanide DippNC: (Dipp=2,6-iPr2 -C6 H3 ) and isocyanate tBuNCO afforded the novel uranaborabicyclo[3.2.0] complexes. All new complexes have been structurally characterized. DFT calculations were performed to provide more insights into the electronic structures and the reaction mechanism.