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1. Classical Gold Carbonyl Complexes in Tetrahedral and Trigonal‐Planar Settings

   https://doi.org/10.1002/chem.202303339  

   Vanga, Mukundam; Muñoz‐Castro, Alvaro; Dias, H_V_Rasika (December 2023, Chemistry – A European Journal)

   Abstract A unique four‐coordinate, classical gold(I)‐carbonyl complex with substantial backdonation from gold has been isolated by using a B‐methylated and fluorinated tris(pyridyl)borate chelator. Its lighter silver(I) and copper(I) analogs enabled a study of trends in the coinage‐metal family. The B‐arylated ligand version also afforded a gold–carbon monoxide complex that displays a notably low C−O stretch value, but with trigonal planar geometry at the gold. A computational analysis shows that the Au^I−CO bonds of these tris(pyridyl)borate ligand‐supported molecules consist of electrostatic attraction, OC→Au σ‐donation, and very significant Au→CO π‐back‐bonding components. The latter is responsible for the observed C−O stretching frequencies, which are lower than in free CO. 

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2. Investigation of the Effect of the Trifluoropropynyl Ligand on Pt(N^C^N)X (X = Cl, C2CF3) Complexes

   https://doi.org/10.3390/cryst14080678  

   Zimmerman, John H; Cahill, Benjamin J; Thomas, Wilson M; McCarthy, Jackson S; McMillen, Colin D; Wagenknecht, Paul S (August 2024, Crystals)

   Fedin, V P (Ed.)

   The tuning of the luminescent properties of PtII complexes for possible use in organic light-emitting diodes (OLEDs) and sensing applications is commonly achieved by altering the electronic properties of the ligands. Our group recently demonstrated that the trifluoropropynyl ligand is strongly electron-withdrawing and possibly useful for blueshifting emission. Herein, we report the synthesis of two complexes of this trifluoropropynyl ligand, namely PtLC2CF3 and PtLFC2CF3 (L = 1,3-di(2-pyridyl)benzene; LF = 4,6-difluoro-1,3-di(2-pyridyl)benzene). The PtLC2CF3 complex crystallized in the monoclinic space group P21/n with Z = 4. The PtLFC2CF3 complex crystalized in the triclinic space group P-1 with Z = 2. Changing the tridentate ligand from L to LF resulted in a change in the packing structure, with the latter showing a metallophilic interaction (Pt-Pt distance = 3.3341(3) Å). The solution photophysics of the trifluoropropynyl complexes is compared with that of the corresponding Cl complexes, PtLCl and PtLFCl. Replacement of the chloro ligand with the trifluoropropynyl ligand blueshifted the monomer emission by less than 5 nm but blueshifted the excimer emission peaks by 15–20 nm. The complexes of the trifluoropropynyl ligand also favor the excimer emission more than the complexes of the chloro ligand. The excimer emission is quenched by dissolved oxygen significantly more than the corresponding monomer emission. The excimer emission and monomer emission are well separated, and the ratio of monomer to excimer emission is strongly dependent on oxygen concentration. 

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3. Cooperative C–H activation of pyridine by PBP complexes of Rh and Ir can lead to bridging 2-pyridyls with different connectivity to the B–M unit

   https://doi.org/10.1039/D1SC01850G  

   Cao, Yihan; Shih, Wei-Chun; Bhuvanesh, Nattamai; Zhou, Jia; Ozerov, Oleg V. (November 2021, Chemical Science)

   Pyridine and quinoline undergo selective C–H activation in the 2-position with Rh and Ir complexes of a boryl/bis(phosphine) PBP pincer ligand, resulting in a 2-pyridyl bridging the transition metal and the boron center. Examination of this reactivity with Rh and Ir complexes carrying different non-pincer ligands on the transition metal led to the realization of the possible isomerism derived from the 2-pyridyl fragment connecting either via B–N/C–M bonds or via B–C/N–M bonds. This M–C/M–N isomerism was systematically examined for four structural types. Each of these types has a defined set of ligands on Rh/Ir besides 2-pyridyl and PBP. A pair of M–C/M–N isomers for each type was computationally examined for Rh and for Ir, totaling 16 compounds. Several of these compounds were isolated or observed in solution by experimental methods, in addition to a few 2-quinolyl variants. The DFT predictions concerning the thermodynamic preference within each M–C/M–N isomeric match the experimental findings very well. In two cases where DFT predicts <2 kcal mol −1 difference in free energy, both isomers were experimentally observed in solution. Analysis of the structural data, of the relevant Wiberg bond indices, and of the ETS-NOCV partitioning of the interaction of the 2-pyridyl fragment with the rest of the molecule points to the strength of the M–C(pyridyl) bond as the dominant parameter determining the relative M–C/M–N isomer favorability. This M–C bond is always stronger for the analogous Ir vs. Rh compounds, but the nature of the ligand trans to it has a significant influence, as well. DFT calculations were used to evaluate the mechanism of isomerization for one of the molecule types. 

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4. Tris(pyridyl)borates: an emergent class of versatile and robust polydentate ligands for catalysis and materials applications

   https://doi.org/10.1039/D3DT01665J  

   McQuade, James; Jäkle, Frieder (October 2023, Dalton Transactions)

   Tridentate ligands that incorporate pyridyl rather than pyrazolyl groups are emerging as an attractive class of “scorpionate”-type ligands with enhanced electron donation, increased stability, and divergent geometry at the metal centre relative to tris(pyrazolyl)borates originally introduced by Trofimenko. Following our initial reports, the tris(pyridyl)borate (Tpyb) ligand architecture has been adopted by several research groups in pursuit of functional metal complexes that offer new opportunities in catalysis and materials science. While earlier work had been focused on symmetric octahedral complexes, ML2, which are advantageous as highly robust building blocks in materials sciences, recently introduced new ligand designs provide access to heteroleptic metal complexes with vacant sites that lend themselves to applications in catalysis. Signficant progress has also been made in the post-complexation functionalization of these ligands via electrophilic and nucleophilic substitution reactions at the boron centres, opening up new routes for integration of Tpyb complexes with diverse functional materials while also raising interesting mechanistic questions. 

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5. Homoleptic octahedral Co ^II complexes as precatalysts for regioselective hydroboration of alkenes with high turnover frequencies

   https://doi.org/10.1039/d3ra06113b  

   Zhang, Guoqi; Zeng, Haisu; Zadori, Nora; Marino, Camila; Zheng, Shengping; Neary, Michelle C. (September 2023, RSC Advances)

   Monoprotonated homoleptic complex of cobalt(ii) with 4′-pyridyl-2,2′;6′,2′′-terpyridine ligand is an efficient precatalyst for hydroboration of styrene derivatives with Markovnikov selectivity, displaying turnover frequencies up to 47 000 h⁻¹. 

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