Formic acid (FA) is an attractive compound for H2 storage. Currently, the most active catalysts for FA dehydrogenation use precious metals. Here, we report a homogeneous iron catalyst that, when used with a Lewis acid (LA) co-catalyst, gives approximately 1,000,000 turnovers for FA dehydrogenation. To date, this is the highest turnover number reported for a first-row transition metal catalyst. Preliminary studies suggest that the LA assists in the decarboxylation of a key iron formate intermediate and can also be used to enhance the reverse process of CO2 hydrogenation.
No doubt: The high‐quality crystal structure of [Cu(TMG3tren)(O2)]SbF6 (see picture) presents the first unambiguous characterization of a bioinorganic compound in which a dioxygen molecule coordinates end‐on to a CuI ion. This species, which is best described as a superoxo copper(II) complex, serves as a model complex for initially formed Cu–O2 adducts present in a variety of active sites of copper enzymes.
Donor makes the difference: The mononuclear η1‐superoxo copper(II) complex 1 undergoes dioxygen activation with the addition of hydrogen‐atom donors. Net O2‐derived O‐atom insertion into the N‐methyl group of the ligand leads to formation of a copper(II)‐alkoxide product 2. The cupric superoxo species 1 itself is not capable of the observed hydroxylation reaction.
A comprehensive
mechanistic study of N2 activation and
splitting into terminal nitride ligands upon reduction of the rhenium
dichloride complex [ReCl2(PNP)] is presented (PNP– = N(CH2CH2PtBu2)2–). Low-temperature studies using
chemical reductants enabled full characterization of the N2-bridged intermediate [{(PNP)ClRe}2(N2)] and
kinetic analysis of the N–N bond scission process. Controlled
potential electrolysis at room temperature also resulted in formation
of the nitride product [Re(N)Cl(PNP)]. This first example of molecular
electrochemical N2 splitting into nitride complexes enabled
the use of cyclic voltammetry (CV) methods to establish the mechanism
of reductive N2 activation to form the N2-bridged
intermediate. CV data was acquired under Ar and N2, and
with varying chloride concentration, rhenium concentration, and N2 pressure. A series of kinetic models was vetted against the
CV data using digital simulations, leading to the assignment of an
ECCEC mechanism (where “E” is an electrochemical step
and “C” is a chemical step) for N2 activation
that proceeds via initial reduction to ReII, N2 binding, chloride dissociation, and further reduction to ReI before formation of the N2-bridged, dinuclear
intermediate by comproportionation with the ReIII precursor.
Experimental kinetic data for all individual steps could be obtained.
The mechanism is supported by density functional theory computations,
which provide further insight into the electronic structure requirements
for N2 splitting in the tetragonal frameworks enforced
by rigid pincer ligands.
[ReCl3(PPh3)2(NCMe)] reacts with pincer ligand HN(CH2CH2PtBu2)2 (HPNP) to five coordinate rhenium(III) complex [ReCl2(PNP)]. This compound cleaves N2 upon reduction to give rhenium(V) nitride [Re(N)Cl(PNP)], as the first example in the coordination sphere of Re. Functionalization of the nitride ligand derived from N2 is demonstrated by selective C-N bond formation with MeOTf.
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