Vasudevan Subramaniyan

On‐site hydrogen gas production from hydrogen‐rich liquids offers a clean alternative to fossil fuels for combustion that is readily implemented in existing energy infrastructure. A heterogenized (POCOP)‐Ir pincer catalyst can be operated at higher temperatures for higher turnover frequency, but the reaction pathway of the reported complex has not been well understood. Here, we report intermediary states and propose a reaction mechanism for the catalyzed dehydrogenation of isopropanol by in situ X‐ray absorption spectroscopy at elevated temperatures. We identify that the catalytic resting states have the same oxidation state (+1), an insignificance of catalyst poisoning by CO contaminants, and the heat‐induced deactivation pathway resulting in Ir nanoparticles leached from the complex.

Formoxy- and methoxyboranes are selectively produced in excellent yields from CO ₂ (1 atm) reduction with 9-BBN catalyzed by DMSO at room temperature. The X-ray structure of a CO ₂ inserted adduct and C–C bond formation reactions are presented.

Incorporation of cationic ligands within pincer frameworks allowed to develop them from obscure peculiarities into a diverse class of ancillary ligands.

Finding alternative and sustainable ways to produce, store and convert energy is key for reducing fossil fuel-based CO₂ emissions.

Back to the scene: while isolobal to the ubiquitous tertiary phosphines, sulfonium cations as ligands were neglected for decades. This work revives the coordination chemistry of these species showing their potential as ligands for π-acid catalysis.

The reaction between 2,5-bis(diphenylphosphinomethyl)pyrrole and Me₃SiN₃ gave the new pyrrole-based bis(phosphinimine) L1H in an excellent yield. L1H reacts with [CuCl(COD)]₂, AgBF₄, or AgOTf to give the corresponding two-coordinate mononuclear ionic complex formulated as [M(L1H)-κ²N,N}][X] where M = Cu, and Ag; X = [CuCl₂], BF₄ or OTf. Their single crystal X-ray diffraction studies confirmed the two-coordinate geometry formed by the chelate bonding mode of L1H. These 10-membered metallacycles display planar chirality and were also characterized by spectroscopic methods. In addition, in all three structures, there exists a hitherto unknown π-interaction between the pyrrole ring atoms and metal, represented as η2-(Cα-N) in the copper(I) complex, and η3-(Cα-N-Cα’) in the silver(I) complexes. These weak interactions were supported by DFT calculations in terms of their electron densities, non-covalent interaction plots and the decrease in the aromaticity of the pyrrole ring.

The reaction of N,N-di(2,6-bis(isopropyl)phenylimino-pyrrolyl-α-methyl)-N-methylamine H₂L1 with copper(I) sources such as CuX (X = Cl (1), Br (2), and I (3)) afforded bis(chelated) ionic copper(II) complexes of the type [CuL1H]X. A similar type of mononuclear structure was obtained with Cu(NO₃)₂·(H₂O)₃. Conversely, binuclear copper(II) complexes [Cu₂(μ-L1)(μ-OOCCH₃)(μ-OH)](4) and [Cu₂(μ-L1H)(μ-OOCPh)(μ-O)] (5) were obtained from the reaction of Cu(O₂CR)₂·H₂O with H₂L1. Notably, these reactions in the presence of a base yielded the neutral copper(II) complex [CuL1] (6). This product was also obtained from the reaction of complex 2 or 4 with NaOH in methanol. All structures feature a dianionic imino-pyrrole motif and a protonated central amine function except 4. The reaction of H₂L1 with NiCl₂·DME gave the mononuclear complex [NiCl₂(L1H₂)], 7. In contrast to this, the reaction of the newly synthesized sterically less encumbered ligand N,N-di(phenylimino-pyrrolyl-α-methyl)-N-methylamine H₂L2 with NiCl₂·DME gave the binuclear complex [NiCl(L2H₂)(HOMe)]₂[Cl]₂ (8). Both 7 and 8 show the amine-azafulvene ligand form and coordination of the central amine. The reaction of complex 7 with NaHBEt₃ yielded a neutral complex [NiL1] (8) containing the imino-pyrrole form. In the molecular structures, interesting secondary coordination spheres incorporating guest molecules such as CHCl₃ and MeOH in the crystal lattices and the presence of helical enantiomers were observed and analysed. In one case, CHCl₃ was found inside an unusual cage-like structure supported by halogen bonds. Preliminary DFT calculations on the geometry of the nickel complex with H₂L1 showed that the pentacoordinated tbp geometry is more stable than the square planar geometry.

The 1 : 1 reaction between 2‐(3,5‐dimethylpyrazolylmethyl)‐5‐(diphenylphosphinomethyl)pyrrole L and CuX (X=Cl, and Br) in THF afforded the symmetrical binuclear copper(I) complexes [Cu( μ ‐X){ μ ‐C ₄ H ₂ NH‐2‐(CH ₂ PPh ₂ )‐5‐(CH ₂ Me ₂ pz)‐ κ ² P , N }] ₂ , having one type of copper environment. When X=I, the asymmetrical complex having two copper environments was isolated, in addition to the symmetrical complex as crystals. Interestingly, the 1 : 2 ratio reaction between L and CuCl gave a distorted cubane type complex [Cu ₄ Cl ₄ { μ ‐C ₄ H ₂ NH‐2‐(CH ₂ PPh ₂ )‐5‐(CH ₂ Me ₂ pz)‐ κ ² P , N } ₂ ], while the CuBr and CuI reactions did not give similar cubane complexes. Conversely, the 2 : 1 ( L : Cu) ratio reactions using CuX (X=Cl, Br and I) in THF suggest the formation of four coordinate bis‐chelated copper(I) complex of the type [Cu L ₂ ] ⁺ in solution, in addition to the binuclear complexes. The X‐ray solid state structures of [Cu L ₂ X ₂ ] (X=Br and I) are retained in solution, in contrast to its chloride derivative giving two signals in ³¹ P{ ¹ H} NMR spectrum. The formation of the binuclear complexes from [Cu L ₂ ] ⁺ and their equilibria were shown by variable temperature NMR, ³¹ P{ ¹ H} 2D NOESY and HRMS studies. In addition, the reaction of L with [Cu(CH ₃ CN) ₄ ]BF ₄ gave yet another binuclear complex [Cu ₂ L ₂ ][BF ₄ ] ₂ which was characterized by spectroscopic methods. This study lends support for the hemilability of L .