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Facile non‐radiative decay of low‐lying metal‐centered (MC) dd excited states has been well documented to pose a significant obstacle to the development of phosphorescent NiII complexes due to substantial structural distortions between the dd excited state and the ground state. Herein, we prepared a series of dinuclear Ni2II,II complexes by using strong σ‐donating carbene‐phenyl‐carbene (CNHC Cphenyl CNHC) pincer ligands, and prepared their dinuclear Pt2II,II and Pd2II,II analogues. Dinuclear Ni2II,II complexes bridged by formamidinate/α‐carbolinato ligand exhibit short Ni−Ni distances of 2.947–3.054 Å and singlet metal‐metal‐to‐ligand charge transfer (1MMLCT) transitions at 500–550 nm. Their 1MMLCT absorption energies are red‐shifted relative to the Pt2II,II and Pd2II,II analogues at ~450 nm and ≤420 nm respectively. One‐electron oxidation of these Ni2II,II complexes produces valence‐trapped dinuclear Ni2II,III species, which are characterized by EPR spectroscopy. Upon photoexcitation, these Ni2II,II complexes display phosphorescence (τ=2.6–8.6 μs) in the NIR (800–1400 nm) spectral region in 2‐MeTHF and in the solid state at 77 K, which is insensitive to π‐conjugation of the coordinated [CNHC Cphenyl CNHC] ligand. Combined with DFT calculations, the NIR emission is assigned to originate from the 3dd excited state. Studies have found that the dinuclear Ni2II,II complex can sensitize the formation of singlet oxygen and catalyze the oxidation of cyclo‐dienes under light irradiation. [ABSTRACT FROM AUTHOR]

A Cu/Co tandem catalysis protocol was developed to conduct the hydroformylation of olefins using CO2/H2 and PMHS (polymethylhydrosiloxane) as a readily available and environmentally friendly hydride source. This methodology was performed via a two‐step approach consisting of the copper‐catalyzed reduction of CO2 by hydrosilane and subsequent cobalt‐promoted hydroformylation with H2 and the in situ formed CO. The optimized triphos oxide ligand, which presumably facilitates the migratory insertion of CO gives moderate to excellent yields for both terminal and internal alkenes. This earth‐abundant metal catalysis provides a reliable and efficient way to afford useful aldehydes in industry using silicon by‐product PMHS as hydrogen source and renewable CO2 as carbonyl source. [ABSTRACT FROM AUTHOR]

Facile non-radiative decay of low-lying metal-centered (MC) dd excited states has been well documented to pose a significant obstacle to the development of phosphorescent Ni II complexes due to substantial structural distortions between the dd excited state and the ground state. Herein, we prepared a series of dinuclear Ni 2 II,II complexes by using strong σ-donating carbene-phenyl-carbene (C NHC  C phenyl  C NHC ) pincer ligands, and prepared their dinuclear Pt 2 II,II and Pd 2 II,II analogues. Dinuclear Ni 2 II,II complexes bridged by formamidinate/α-carbolinato ligand exhibit short Ni-Ni distances of 2.947-3.054 Å and singlet metal-metal-to-ligand charge transfer ( 1 MMLCT) transitions at 500-550 nm. Their 1 MMLCT absorption energies are red-shifted relative to the Pt 2 II,II and Pd 2 II,II analogues at ~450 nm and ≤420 nm respectively. One-electron oxidation of these Ni 2 II,II complexes produces valence-trapped dinuclear Ni 2 II,III species, which are characterized by EPR spectroscopy. Upon photoexcitation, these Ni 2 II,II complexes display phosphorescence (τ=2.6-8.6 μs) in the NIR (800-1400 nm) spectral region in 2-MeTHF and in the solid state at 77 K, which is insensitive to π-conjugation of the coordinated [C NHC  C phenyl  C NHC ] ligand. Combined with DFT calculations, the NIR emission is assigned to originate from the 3 dd excited state. Studies have found that the dinuclear Ni 2 II,II complex can sensitize the formation of singlet oxygen and catalyze the oxidation of cyclo-dienes under light irradiation., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A Cu/Co tandem catalysis protocol was developed to conduct the hydroformylation of olefins using CO 2 /H 2 and PMHS (polymethylhydrosiloxane) as a readily available and environmentally friendly hydride source. This methodology was performed via a two-step approach consisting of the copper-catalyzed reduction of CO 2 by hydrosilane and subsequent cobalt-promoted hydroformylation with H 2 and the in situ formed CO. The optimized triphos oxide ligand, which presumably facilitates the migratory insertion of CO gives moderate to excellent yields for both terminal and internal alkenes. This earth-abundant metal catalysis provides a reliable and efficient way to afford useful aldehydes in industry using silicon by-product PMHS as hydrogen source and renewable CO 2 as carbonyl source., (© 2024 Wiley-VCH GmbH.)

This study seeks to address the need for the development of highly active paraffin activation catalysts that are reusable and based on cheap earth abundant metals. Hence, a series of related halide-free 1,3,4-trisubstituted-1,2,3-triazolium ionic liquids (IL)( 3a–3f ) bearing a variety of substituents were synthesized and fully characterized by spectroscopic and analytical techniques. Crystal structure of the halide derivative, compound 2f is also reported. With the IL as solvents for the dissolution of FeCl 2 , FeCl 3 , CoCl 2 , and NiCl 2 , a series of catalyst systems were developed and used to activate the catalytic oxidation of n -octane in the presence of H 2 O 2 as the oxidant in a biphasic IL/H 2 O system. All systems tested were found to be active under optimum conditions yielding oxygenated products (mainly octanones). The role of the substituents around the triazole ring was to influence catalytic efficiency in terms of conversion of the substrate n -octane and selectivity to oxygenated products (octanols, octanal, octanones, and octanoic acid). In a test for recyclability, recovered IL dissolved catalysts were found to be effective up to three cycles without any significant loss of catalytic activity before leaching to the aqueous phase resulted in loss of activity. [ABSTRACT FROM AUTHOR]

• Novel Mn(P,N) and Mn(P,N,N) complexes were synthesized and characterized. • The complexes were applied in asymmetric hydrogenation of ketones. • The P-N and N-N tether length strongly affect coordination and catalytic properties. • High activities and enantioselectivities (up to 95%) were obtained. • A qualitative stereochemical model explaining enantioselectivity has been proposed. Manganese complexes modified by simple alkane-diyl based P,N (Ph 2 PCH(CH 3)(CH 2) m CH(CH 3)NHC 2 H 5 ; m = 0, 1) and potentially tridentate P,N,N (Ph 2 PCH(CH 3)(CH 2) m CH(CH 3)NH(CH 2) n N(CH 3) 2 ; m = 0, 1; n = 2, 3) type ligands have been synthesized and tested in the asymmetric hydrogenation of ketones. The combined coordination and catalytic studies led to the conclusion that the N-N tether length of the P,N,N type compounds plays a crucial role in determining the chemoselectivity, while the length of the P-N skeleton has been shown to affect the catalytic activity. Mn-catalysts containing P,N,N ligands with the proper tether lengths (m = 0, n = 1) provided high enantioselectivities (up to 95% ee) and activities in the asymmetric hydrogenation of acetophenone derivatives. The influence of substitution of the acetophenone substrate and the reaction conditions is demonstrated. Based on quantum chemistry calculations, a qualitative model explaining the origin of enantioselectivity is proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

• Intersystem crossing (ISC) rate of a metal complex is determined by not only SOC constant of the metal ion. • Various photophysical mechanisms are possible for transition metal complexes. • Emission properties other than single phosphorescence can be achieved by molecular design. • Uncommon emission properties open up novel applications in many areas. • Triplet excited state of earth-abundant metal complexes can be exploited for use by the novel mechanisms. Luminescence properties and excited state reactivities of photoactive transition metal complexes have been harnessed for various applications in the fields of electroluminescent devices, luminescent sensing and bio-imaging, and solar energy conversion as well as photo-redox catalysis in organic transformation. While, beyond the conventional phosphorescence from triplet excited sates that are populated through heavy metal atom induced intersystem crossing (ISC), the past decade has witnessed blooming reports on intriguing luminescence behaviors such as sole fluorescence, dual fluorescence/phosphorescence, thermally activated delayed fluorescence (TADF), and dual phosphorescence. All these findings reveal that the possible photophysical mechanisms of transition metal complexes remain relatively underexplored. On one hand, the intersystem crossing (ISC) rate that is crucial to the depopulation of the singlet excited state and thus the population efficiency of the triplet excited state has proven to be not simply dependent on the spin-orbit coupling constant of the metal atom. On the other hand, the decay paths for triplet excited state(s) through reverse ISC (T 1 → S 1) and direct radiation from higher triplet excited state have been opened by appropriate ligand design. Moreover, these novel emission properties of transition metal complexes have expanded their applications into the fields of ratiometric sensing/imaging, noble-metal-free high efficiency emitters and photocatalysts and beyond. This review is aimed to discuss the unconventional emission properties and applications of transition metal complexes that were reported mainly in the past decade by focusing on the structural factors that are at play in realizing the novel excited state properties. It is conceived to provide a better understanding of the excited state properties tuning and to direct the design of new emissive metal complexes with tailored functions. [ABSTRACT FROM AUTHOR]