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

A novel heterobimetallic tantalum/iridium hydrido complex,
[{Ta­(CH2tBu)3}­{IrH2(Cp*)}] 1, featuring a very short metal–metal
bond, has been isolated through an original alkane elimination route
from Ta­(CHtBu)­(CH2tBu)3 and Cp*IrH4. This molecular
precursor has been used to synthesize well-defined silica-supported
low-coordinate heterobimetallic hydrido species [SiOTa­(CH2tBu)2{IrH2(Cp*)}], 5, and [SiOTa­(CH2tBu)­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(CH2tBu)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 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.