Stereoselective formation of a meso-diruthenium(ii,ii) complex and tuning the properties of its monoruthenium analogues

Abstract

A novel bis(bidentate) ligand dgpm (dgpm = diguanidylpyrimidine) was synthesized by a catalyst-free C-N bond forming reaction in high yield (90%) by microwave-assisted heating. The ligand was coordinated to two [Ru(bpy)2](2+) cores to afford a meso-di-Ru(II,II) complex (1-meso) with high diastereoselectivity over its homochiral form. Three mononuclear ether-functionalized Ru(II) complexes (2: ethoxyether; 3: butoxyether; 4: 2-hydroxy-1-ethoxyether) were also isolated. The ligand and complexes were fully characterized by a variety of techniques including X-ray crystallography. In cyclic voltammetric studies, the complexes exhibit a Ru(III/II) couple, which is ~500 mV less positive than the Ru(III/II) couple in Ru(bpy)3(2+). The (1)MLCT absorption maxima of all the complexes (510-550 nm) are considerably red-shifted as compared to that of Ru(bpy)3(2+) (450 nm). The (3)MLCT emission maxima of complexes 1-meso and 3 are also red-shifted by about 120 nm compared to that of Ru(bpy)3(2+) (620 nm), whereas the corresponding maxima for complexes 2 and 4 are shifted by 75 nm and 25 nm, respectively. These relative trends in redox potentials and (1)MLCT maxima are in good agreement with DFT and TD-DFT calculations, performed for all complexes. Complexes 1-meso and 3 display emission from a Ru(II)-to-bpy (3)MLCT state, which is rarely the emitting state at λ > 700 nm in [Ru(bpy)2(N-N)](2+) complexes when the ancillary ligand is neutral.

Blue‐Emissive Cobalt(III) Complexes and Their Use in the Photocatalytic Trifluoromethylation of Polycyclic Aromatic Hydrocarbons

“…The electron-deficient CCF 3 radical is then well-suited to add to the most electron-rich position of pyrene in ar egioselective fashion. Thet wo-photon excitation mechanism is supported by aq uadratic dependencyo ft he product yield on irradiation density as assessed by quantitative 19 FNMR spectroscopy (Supporting Information, Figures S29 and S30). Thet wo photocatalytic cycles are closed via at hird SET wherein 2 is reduced to pyrene and 6 is oxidized to [ML 2 ] 3+ .F inally,facile deprotonation of 7 with K 2 HPO 4 as the base affords the desired CF 3 -pyrene.Reaction kinetics for mono(trifluoromethylation) of pyrene using complex 1 was found to be slower, but results in ac leaner conversion to the product when compared to the similar kinetics using [Ir(dF(CF 3 )ppy) 2 -(bpy)][PF 6 ]a st he photoredox catalyst (Supporting Information, Figures S27, S28).…”

“…[19] 1 and 2 were found to be amongst the strongest photo-oxidants to date,a nd this rare property was exploited in photoredox catalysis for regioselective mono(trifluoromethylation) of conjugated arenes as ap roof of principle.T he photocatalytic mechanism was found to proceed by ar eductive quenching pathway that is distinct from the other earthabundant photocatalysts reported to date. Thet wo novel homoleptic Co III complexes 1 and 2 incorporate six-membered chelate ligands L1 (dgpy) and L2 (dgpz), respectively,that contain the strongly s-donating hpp moiety (hpp = 1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) (Scheme 1).…”

“…[19] Thee lectrochemical behavior of 1, 2,a nd 3 have been examined by cyclic voltammetry (Supporting Information, Figures S10-S12) and differential pulse voltammetry.The first oxidation and first reduction processes are monoelectronic. Thea ppearance of multiple peaks over 0-4 ppm region in 1 HNMR spectra of 1 and 2 suggests that upon coordination the exchange between the equatorial and the axial protons in the saturated backbone of L1 is slow compared to the NMR timescale.…”

Blue‐Emissive Cobalt(III) Complexes and Their Use in the Photocatalytic Trifluoromethylation of Polycyclic Aromatic Hydrocarbons

“…Thet wo novel homoleptic Co III complexes 1 and 2 incorporate six-membered chelate ligands L1 (dgpy) and L2 (dgpz), respectively,that contain the strongly s-donating hpp moiety (hpp = 1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) (Scheme 1). [19] 1 and 2 were found to be amongst the strongest photo-oxidants to date,a nd this rare property was exploited in photoredox catalysis for regioselective mono(trifluoromethylation) of conjugated arenes as ap roof of principle.T he photocatalytic mechanism was found to proceed by ar eductive quenching pathway that is distinct from the other earthabundant photocatalysts reported to date. [2] Ligands L1 and L2 were synthesized following previously reported procedures.…”

“…Thea ppearance of multiple peaks over 0-4 ppm region in 1 HNMR spectra of 1 and 2 suggests that upon coordination the exchange between the equatorial and the axial protons in the saturated backbone of L1 is slow compared to the NMR timescale. [19] Thee lectrochemical behavior of 1, 2,a nd 3 have been examined by cyclic voltammetry (Supporting Information, Figures S10-S12) and differential pulse voltammetry.The first oxidation and first reduction processes are monoelectronic. 1 and 2 show irreversible ligand-based oxidations at 1.75 and 1.98 Vv s. SCE, respectively,a ssigned by DFT calculations (Figure 1; Supporting Information, Tables S3-S5).…”