Metal-Metal Synergy in Well-Defined Surface Tantalum-Iridium Heterobimetallic Catalysts for H/D Exchange Reactions

A novel heterobimetallic tantalum/iridium hydrido complex, [{Ta((CH2Bu)-Bu-t)(3)}{IrH2(Cp*)}] 1, featuring a very short metal-metal bond, has been isolated through an original alkane elimination route from Ta((CHBu)-Bu-t)-((CH2Bu)-Bu-t)(3) and Cp*IrH4. This molecular precursor has been used to synthesize well-defined silica-supported low-coordinate heterobimetallic hydrido species [ SiOTa((CH2Bu)-Bu-t)(2){IrH2(Cp*)}], 5, and [ SiOTa((CH2Bu)-Bu-t)H{IrH2(Cp*)}], 6, using a surface organometallic chemistry (SOMC) approach. The SOMC methodology prevents undesired dimerization as encountered in solution and leading to a tetranuclear species [{Ta((CH2Bu)-Bu-t)(2)}(Cp*IrH)](2), 4. This approach therefore allows access to unique low-coordinate species not attainable in solution. These original supported Ta/Ir species exhibit drastically enhanced catalytic performances in H/D exchange reactions with respect to (i) monometallic analogues as well as (ii) homogeneous systems. In particular, material 6 promotes the H/D exchange between fluorobenzene and C6D6 or D-2 as deuterium sources with excellent productivity (TON up to 1422; TOF up to 23.3 h(-1)) under mild conditions (25 degrees C, sub-atmospheric D-2 pressure) without any additives.