Migratory insertion of monoborane into the uranium-carbon ?-bond of tricyclopentadienyl(alkyl)uranium(IV) complexes

U(cp) 3R (cp = ? 5-cyclopentadienyl, R = Me or Et) reacts in toluene solution at room temperature with a number of appropriately labile adducts L·BH 3 (L = BH 3, tetrahydrofuran or Me 2S) to give U(cp) 3BH 4 via the non-isolable, but spectroscopically well identified, primary insertion product U(cp) 3(H 3BR); evidence of a corresponding, rather effective, insertion of the resulting BH 2R unit into U-C bonds is also apparent.