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Functional pincer ligands that engage in metal–ligand cooperativity and/or are capable of redox non-innocence have found a great deal of success in catalysis. These two properties may be found in metal complexes of the 2,6-bis(pyrazol-3-yl)pyridine (bpp) ligands. With this goal in mind, we have attempted the coordination of 2,6-bis(5-trifluoromethylpyrazol-3-yl)pyridine (LCF3) and its tBu analogue 2,6-bis(5-tert-butylpyrazol-3-yl)pyridine (LtBu) to Mo(0) by reactions with mixed phosphine/carbonyl complexes [Mo(CO)2(MeCN)n−1(PMe3−nPhn)5−n] 1–3 (1 ≤ n ≤ 3). These afforded mixtures of several Mo compounds among which low yields of heptacoordinated Mo(II) complexes [Mo(CO)2(bpp)(PMe3−nPhn)2] 4a–c (LCF3-supported) and 5a–c (LtBu -supported) bearing a doubly deprotonated bpp ligand were systematically produced. More selective syntheses of 4a–c and 5a–c were achieved by repeating these experiments in the presence of an oxidant (AgOAc or Ag2O), with moderate to good yields. 4a–c and 5a–c were characterized by means of NMR, IR and UV-Vis spectroscopies, sc-XRD and cyclic and square-wave voltammetries for 4a, 4b and 5b. The deprotonated LtBu ligand in 5a–c is re-protonated with 2 equiv. of HOTf to afford the dicationic [Mo(CO)2(LtBu)(PMe3−nPhn)2][OTf]2 complexes 6a–c. Acidic treatment of 4a–c led to the decomposition of the complexes. [ABSTRACT FROM AUTHOR]

Octahedral Mn(I) complexes bearing tridentate donor ligands [(L∩L′∩L′′)(CO)2MnX] have recently emerged as major players in catalytic (de)hydrogenation processes. While most of these systems are still based on structurally rigid pincer scaffolds imposing a meridional coordination mode, for some more flexible tridentate ligands a facial arrangement of donor moieties becomes possible. Accordingly, the geometry of the corresponding Mn(I) hydrides [(L∩L′∩L′′)(CO)2MnH] directly involved in the catalytic processes, namely the nature of the donor extremity located in the trans-position of the hydride (CO and L for mer- and fac-configurations, respectively) may influence their hydride transfer ability. Herein, low-temperature IR and NMR spectroscopy studies of two model Mn(I) complexes, mer-[(L1)(CO)2MnH] and fac-[(L2)(CO)2MnH], bearing similar triphosphine ligands (L1 = PhP(CH2CH2PPh2)2; L2 = MeC(CH2PPh2)3) in the presence of B(C6F5)3 as the H− abstractor revealed for the first time a higher kinetic hydricity of the tripodal system. Even for the pincer complex, hydride transfer proceeds from the non-covalent adduct fac-[(L1)(CO)2MnH]⋯B(C6F5)3 with the facial geometry arising from the mer-to-fac isomerization of the initial mer-[(L1)(CO)2MnH]. The higher reactivity of the fac-hydride derivatives was found to be consistent with the catalytic performance of the corresponding Mn(I) bromide complexes in the benchmark ester hydrosilylation. [ABSTRACT FROM AUTHOR]

A novel reactivity of 5‐barbiturate imidazo[1,5‐a]pyridinium 1⋅H with [Ru(2‐methylallyl)2(COD)] was explored which led to the formation of an uncommon, zwitterionic complex [Ru(1')(1⋅H)], composed of the NHC ligand 1', cyclometallated at one ortho‐methyl position of the N‐mesityl substituent, and the zwitterionic precursor 1⋅H. Barbiturate moieties coordinate either through a η3 mode or through coordination of the anionic oxygen atom to ensure the coordination saturation and stability to the complex. The addition of pivalic acid results in the protonolysis of the Ru‐Calkyl bond and demetallation of the N‐mesityl, while triphenylphosphine and pyridine are able to displace the rather labile 1⋅H ligand. Attempts to incorporate an alkylidene fragment from these complexes led to the isolation of a rare complex 7 bearing an alkylidene tethered to a η5‐cyclopentadienyl ligand formed by phenylacetylene tetramerization. [ABSTRACT FROM AUTHOR]

Donor–acceptor systems for CO2 activation combining a formally zero-valent group 6 metal as the donor with the Lewis acid Al(C6F5)3 (AlCF) are reported. They were obtained from AlCF adducts of N2-complexes by N2-to-CO2 substitution. One species was capable of C–O cleavage. The boron analogues led to intractable mixtures. [ABSTRACT FROM AUTHOR]

Hofmann coordination polymers (CPs) with cationic ligands provide an innovative strategy for recognizing π‐electron‐rich aromatic molecules – similar to the "little blue box". In this study, we demonstrate that hydroquinone molecules can be incorporated into these coordination polymers when redox‐active bipyridinium derivatives are used as axial ligands. The insertion leads to a significant structural modification, resulting in a shift of the spin transition by 150 K and an approximate 23 % increase in volume, caused by the strong donor‐acceptor π‐π stacking interaction formed between the ligands and the guest molecule. These findings have been confirmed through temperature‐dependent single crystal X‐ray diffraction, magnetic measurements and optical reflectivity measurements. [ABSTRACT FROM AUTHOR]

In this paper, we report the synthesis of six novel triazole-based heteroscorpionate ligands based on heterocycle metathesis reactions and their iron(II) complexes. Single crystal structure analyses were performed, the spectroscopic and magnetic properties of the obtained complexes were studied and their spin crossover–structural relationships were compared to those obtained for their pyrazole-based analogues reported in the literature. In particular, the amino derivative complex bis[hydrobis(pyrazol-1-yl)(3-amino-1,2,4-triazol-1-yl)]iron(II) obtained by post-synthetic catalytic nitro-group reduction under pressure of hydrogen in an autoclave presents a scarce gradual spin crossover behavior at room temperature. The profile of the SCO curve can be explained by the presence of only relatively weak H bonds, spreading only in one dimension. Among the interesting spin transition behaviors observed for the different complexes, such stable, complete and gradual spin crossover at room temperature makes this neutral complex a good candidate for sublimation and future investigation as an active element notably for thermoreflectance-based surface microthermometry applications. [ABSTRACT FROM AUTHOR]

The reaction of a sterically shielded Mg hydride complex, bearing a bulky β‐diketiminato (BDI) ligand, with CO2 leads to the formation of polynuclear complexes. CO2 not only inserts into the metal hydride bond yielding formate ions, but also adds onto the γ‐C of the BDI ligand. This reactivity gives rise to the formation of soluble tri‐ and tetranuclear structures in THF, leading to a hexameric structure associated with a change in the coordination mode of the BDI ligand at 60 °C in THF within four days. The insoluble hexameric complex was isolated in high reproducible yield from the solution and characterized by X‐ray diffraction analysis. The reaction affording the hexameric complex was shown to be completed within 1 h at room temperature in toluene. Similar reactions of CO2 with a BDI calcium hydride complex proceeds less cleanly and a pure product could not be isolated. [ABSTRACT FROM AUTHOR]

A sterically encumbered dinuclear amidinato magnesium hydride 3 with bridging hydrido ligands was synthesized from the metalation of the corresponding amidine 1 with dibutylmagnesium and subsequent treatment with phenylsilane. This complex reacts stoichiometrically with 1 atm of carbon dioxide at room temperature in tetrahydrofuran (THF) to the corresponding bis(thf) adduct of the dinuclear formate complex 4‐2 thf with bridging formate anions. This complex is stable in THF at 60 °C for more than 16 hours but decomposes into the amidine 1 upon removal of ligated thf ligands. Complex 3 efficiently catalyzes the reduction of carbon dioxide with 9‐BBN, yielding bis(boryl)acetal (R2BO)2CH2, and with silanes H4‐nSiPhn (n=1, 2, and 3). The bis(silyl)acetal is quantitatively accessible for Ph3SiH (n=3) whereas during the reduction of CO2 with hydrogen‐richer silanes (n=1, 2) siloxanes form and methane evolves. [ABSTRACT FROM AUTHOR]