The
demand for harmless and efficient energy sources is remarkably
expanding, particularly after the increased awareness of global warming,
greenhouse gas emissions, immense fossil fuel consumption, and so
forth. Formic acid is considered a potential candidate as an energy
carrier for reversible hydrogen storage owing to its decomposition
to hydrogen (H2) and carbon dioxide (CO2) in
the presence of suitable catalysts. However, selective and efficient
decomposition of formic acid using classical heterogeneous catalysis
is still challenging because most heterogeneous catalysts which are
known are ill defined. Herein, we report a promising heterogeneous
approach toward formic acid dehydrogenation using a ruthenium PN3P pincer complex, [Ru–H(CO) (
tBuPN3P)] (I), immobilized on a fibrous
silica nanosphere, KCC-1, with a strong Lewis acid character [(Si–O–Si)
(Si–O−)2Al–H]. The resulting
heterogeneous catalyst, [Ru(H) (CO) (tBuPN3P)]@[(Si–O–Si)
(Si–O−)2Al–H] (III), has been fully characterized by advanced solid-state characterization
techniques. In this compound, Al is tetrahedrally coordinated. It
is a single-site catalyst which exhibits good stability toward water,
high pressures, and high temperatures as well as good activity in
formic acid dehydrogenation. An excellent turnover number of 600,000
and a recyclability of up to 45 cycles are observed.
The single-site silica-supported group IV metal amido complex [Ti(NMe 2 ) 4 ] gives the tris(amido)-supported fragment [(Si−O−)Ti(−NMe 2 ) 3 ], which transforms into a three-membered metallacycle (called a metallaaziridine) by an α-H transfer between two amido ligands. When the three-membered metallacycle reacts with 1-octene, it gives a five-membered metallacycle by insertion of the double bond into the M−C bond of the metallaziridine. These two metallacycles, key intermediates in the catalytic cycle of the hydroaminoalkylation of terminal olefins, were isolated and fully characterized following the surface organometallic chemistry (SOMC) concept and procedures. This paper shows that surface organometallic chemistry can be used to identify and fully characterize three-and five-membered metallacycles of Ti in the hydroaminoalkylation of olefins. Article pubs.acs.org/Organometallics
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