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

A novel heterobimetallic tantalum/iridium hydrido complex, [{Ta(CH ₂ ^t Bu) ₃ }{IrH ₂ (Cp*)}] 1 , featuring a very short metal-metal bond, has been isolated through an original alkane elimination route from Ta(CH ^t Bu)(CH ₂ ^t Bu) ₃ and Cp*IrH ₄ . This molecular precursor has been used to synthesize well-defined silica-supported low-coordinate heterobimetallic hydrido species [≡SiOTa(CH ₂ ^t Bu) ₂ {IrH ₂ (Cp*)}], 5 , and [≡SiOTa(CH ₂ ^t Bu)H{IrH ₂ (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(CH ₂ ^t Bu) 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 C ₆ D ₆ or D ₂ as deuterium sources with excellent productivity (TON up to 1422; TOF up to 23.3 h ^-1 ) under mild conditions (25 °C, sub-atmospheric D ₂ pressure) without any additives.