Cationic Tantalum Hydrides Catalyze Hydrogenolysis and Alkane Metathesis Reactions of Paraffins and Polyethylene.

Sulfated aluminum oxide ( SAO ), a high surface area material containing sulfate anions that behave like weakly coordinating anions, reacts with Ta(═CH t Bu)(CH 2 t Bu) 3 to form [Ta(CH 2 t Bu) 2 (O-) 2 ][ SAO ] ( 1 ). Subsequent treatment with H 2 forms Ta-H + sites supported on SAO that are active in hydrogenolysis and alkane metathesis reactions. In both reactions Ta-H + is more active than related neutral Ta-H sites supported on silica. This reaction chemistry extends to melts of high-density polyethylene (HDPE), where Ta-H + converts 30% of a low molecular weight HDPE ( M n = 2.5 kg mol -1 ; Đ = 3.6) to low molecular weight paraffins under hydrogenolysis conditions. Under alkane metathesis conditions Ta-H + converts this HDPE to a high MW fraction ( M n = 6.2 kDa; Đ = 2.3) and low molecular weight alkane products (C 13 -C 32 ). These results show that incorporating charge as a design element in supported d 0 metal hydrides is a viable strategy to increase the reaction rate in challenging reactions involving reorganization of C-C bonds in alkanes.