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

Abstract

A novel heterobimetallic tantalum/iridium hydrido complex, [{Ta(CH₂^<i>t</i>Bu)₃}{IrH₂(Cp*)}] <b>1</b>, featuring a very short metal-metal bond, has been isolated through an original alkane elimination route from Ta(CH^<i>t</i>Bu)(CH₂^<i>t</i>Bu)₃ and Cp*IrH₄. This molecular precursor has been used to synthesize well-defined silica-supported low-coordinate heterobimetallic hydrido species [≡SiOTa(CH₂^<i>t</i>Bu)₂{IrH₂(Cp*)}], <b>5</b>, and [≡SiOTa(CH₂^<i>t</i>Bu)H{IrH₂(Cp*)}], <b>6</b>, using a surface organometallic chemistry (SOMC) approach. The SOMC methodology prevents undesired dimerization as encountered in solution and leading to a tetranuclear species [{Ta(CH₂^<i>t</i>Bu)₂}(Cp*IrH)]₂, <b>4</b>. 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 <b>6</b> promotes the H/D exchange between fluorobenzene and C₆D₆ or D₂ as deuterium sources with excellent productivity (TON up to 1422; TOF up to 23.3 h^-1) under mild conditions (25 °C, sub-atmospheric D₂ pressure) without any additives.