Versatility in the synthesis of triazole derivatives was exploited to obtain convenient mesoionic carbenes working as chelating or cyclometalating ligands for the preparation of cationic or neutral iridium(III) complexes. We present the synthesis and characterization of three new cationic cyclometalating iridium(III) complexes (1-3-BF) and a neutral one (4), equipped with functionalized triazolylidene ligands. All the complexes are obtained in good yields, present irreversible or quasi-reversible oxidation and reduction processes, and display good photophysical stability. The complexes emit from MLCT orLC states, depending on the nature of the ancillary ligand. Compounds 1-3-BF display very low photoluminescence quantum yields (PLQY ≈ 1% in acetonitrile solution). Density functional theory calculations show that the luminescence of these three complexes is quenched by the presence of low-lying MC states, leading to a reversible detachment of the neutral ancillary ligands from the metal coordination sphere. On the contrary, this nonradiative deactivation pathway is not present in the case of the neutral complex 4, which in fact shows PLQYs above 10% and is the best emitter of the series. Moreover, complex 4 represents the first reported example of a photochemically and thermally stable neutral triazolide iridium(III) complex.
Triangular clusters [{MFe(CO)4}3]3– (M = Cu, 4; Ag, 5; Au, 6) were selectively obtained
by heating Fe(CO)4(MIMes)2 (M = Cu, 1; Ag, 2; Au, 3; IMes = C3N2H2(C6H2Me3)2). 1–3 were synthesized by
reacting Na2[Fe(CO)4]·2thf
with 2 equiv of M(IMes)Cl. As previously described, the direct reactions
of Na2[Fe(CO)4]·2thf with
one equivalent of M(I) salts resulted in the triangular cluster [{CuFe(CO)4}3]3– for Cu, whereas the square
clusters [{MFe(CO)4}4]4– were
formed for Ag and Au. Thus, depending on the synthetic protocol adopted,
both the triangular [{MFe(CO)4}3]3– and square [{MFe(CO)4}4]4– polymerization isomers can be selectively obtained, at least for
Ag and Au. Polymerization isomerism, that is two compounds having
the same elemental compositions but different molecular weights, was
investigated in [{MFe(CO)4}
n
]
n− (n = 3, 4;
M = Cu, Ag, Au) by means of structural and theoretical methods and
the role of metallophilic interactions was computationally studied
by means of the atoms-in-molecules (AIM) approach.
The bio-based substrate and target product 2,5-bishydroxymethylfuran (BHMF) demonstrated to influence the reaction kinetics in the homogeneous reduction of 5-hydroxymethylfurfural (HMF) catalyzed by the Ru-based Shvo's catalyst. A combined experimental and computational study supports an important role of the -CH2OH moiety which may be involved in the catalytic cycle toward the formation of different intermediates from HMF and BHMF. The reaction is selective and leads to quantitative formation of BHMF working under mild conditions. Furthermore, an optimized recycling procedure which avoids the use of water, allows recover and reuse of the catalyst without loss of activity. The mechanistic insights from this work may be extended to provide a general description of the chemistry of the Shvo's catalyst feeding further bio-based molecules.
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