Synthesis of Pd complexes combined with photosensitizing of a ruthenium(II) polypyridyl moiety through a series of substituted bipyrimidine bridges. Substituent effect of the bridging ligand on the photocatalytic dimerization of alpha-methylstyrene

Cationic β-Scission of C-H and C-C Bonds for Selective Dimerization and Subsequent Sulfur-Free RAFT Polymerization of α-Methylstyrene and Isobutylene

A series of exo-olefin compounds ((CH3 )2 C(PhY)-CH2 C(=CH2 )PhY) were prepared by selective cationic dimerization of α-methylstyrene (αMS) derivatives (CH2 =C(CH3 )PhY) with p-toluenesulfonic acid (TsOH) via β-C-H scission. They were subsequently used as reversible chain transfer agents for sulfur-free cationic RAFT polymerization of αMS via β-C-C scission in the presence of Lewis acid catalysts such as SnCl4 . In particular, exo-olefin compounds with electron-donating substituents, such as a 4-MeO group (Y) on the aromatic ring, worked as efficient cationic RAFT agents for αMS to produce poly(αMS) with controlled molecular weights and exo-olefin terminals. Other exo-olefin compounds (R-CH2 C(=CH2 )(4-MeOPh)) with various R groups were prepared by different methods to examine the effects of R groups on the cationic RAFT polymerization. A sulfur-free cationic RAFT polymerization also proceeded for isobutylene (IB) with the exo-olefin αMS dimer ((CH3 )2 C(Ph)-CH2 C(=CH2 )Ph). Furthermore, telechelic poly(IB) with exo-olefins at both terminals was obtained with a bifunctional RAFT agent containing two exo-olefins. Finally, block copolymers of αMS and methyl methacrylate (MMA) were prepared via mechanistic transformation from cationic to radical RAFT polymerization using exo-olefin terminals containing 4-MeOPh groups as common sulfur-free RAFT groups for both cationic and radical polymerizations.

Terpyridine Diphosphine Ruthenium Complexes as Efficient Photocatalysts for the Transfer Hydrogenation of Carbonyl Compounds

The cationic achiral and chiral terpyridine diphosphine ruthenium complexes [RuCl(PP)(tpy)]Cl (PP=dppp (1), (R,R)-Skewphos (2) and (S,S)-Skewphos (3)) are easily obtained in 85-88 % yield through a one-pot synthesis from [RuCl₂ (PPh₃ )₃ ], the diphosphine and 2,2':6',2''-terpyridine (tpy) in 1-butanol. Treatment of 1-3 with NaPF₆ in methanol at RT affords quantitatively the corresponding derivatives [RuCl(PP)(tpy)]PF₆ (PP=dppp (1 a), (R,R)-Skewphos (2 a) and (S,S)-Skewphos (3 a)). Reaction of [RuCl₂ (PPh₃ )₃ ] with (S,R)-Josiphos or (R)-BINAP in toluene, followed by treatment with tpy in 1-butanol and finally with NaPF₆ in MeOH gives [RuCl(PP)(tpy)]PF₆ (PP=(S,R)-Josiphos (4 a), (R)-BINAP (5 a)) isolated in 78 % and 86 % yield, respectively. The chiral derivatives have been isolated as single stereoisomers and 3 a, 4 a have been characterized by single crystal X-ray diffraction studies. The tpy complexes with NaOiPr display high photocatalytic activity in the transfer hydrogenation (TH) of carbonyl compounds using 2-propanol as the only hydrogen donor and visible light at 30 °C, at remarkably high S/C (up to 5000) and TOF values up to 264 h^-1 . The chiral enantiomers 2, 2 a and 3, 3 a induce the asymmetric photocatalytic TH of acetophenone, affording (S)- and (R)-1-phenylethanol with 51 and 52 % ee, respectively, in a MeOH/2-propanol mixture.

Unimolecular cooperative metallaphotocatalysis with conjugately bridged Ir-Ni complexes and its applications in organic coupling reactions

Recent advances successfully upgraded the unique cooperative partnership between the two distinct metals in photocatalysis. Herein we are reporting design, synthesis and comprehensive study of series of heteroleptic Ir(III) complexes...

Tetranuclear rollover cyclometalated organoplatinum-rhenium compounds; C-I oxidative addition and C-C reductive elimination using a rollover cycloplatinated dimer

The novel tetranuclear Pt(IV)-Re(VII) complex [Pt₂Me₄(OReO₃)₂(PMePh₂)₂(µ-bpy-2H)], 4, is synthesized through the reaction of silver perrhenate with a new rollover cycloplatinated(IV) complex [Pt₂Me₄I₂(PMePh₂)₂(µ-bpy-2H)], 3. In complex 4, while 2,2'-bipyridine (bpy) acts as a linker between two Pt metal centers, oxygen acts as a mono-bridging atom between Pt and Re centers through an unsupported Pt(IV)-O-Re(VII) bridge. The precursor rollover cycloplatinated(IV) complex 3 is prepared by the MeI oxidative addition reaction of the rollover cycloplatinated(II) complex [Pt₂Me₂(PMePh₂)₂(µ-bpy-2H)], 2. Complex 2 shows a metal-to-ligand charge-transfer band in the visible region, which was used to investigate the kinetics and mechanism of its double MeI oxidative addition reaction. Based on the experimental findings, the classical S_N2 mechanism was suggested for both steps and supported by computational studies. All complexes are fully characterized using multinuclear NMR spectroscopy and elemental analysis. Attempts to grow crystals of the rollover cycloplatinated(IV) dimer 3 yielded a new dimer rollover cyclometalated complex [Pt₂I₂(PMePh₂)₂(µ-bpy-2H)], 5, presumably from the C-C reductive elimination of ethane. The identity of complex 5 was confirmed by single crystal X-ray diffraction analysis.

Syntheses and structure of dinuclear metal complexes containing naphthyl-Ir bichromophore

A series of novel metal complexes were synthesized containing an Ir-cyclometalated bichromophore as a visible-light sensitizer. A new bichromophoric unit containing a naphthyl substituent and methyl substituents on the 2-phenylpyridine chelating ligand was synthesized and characterized for the first time. According to the increased crystallinity of the bichromophoric unit, novel Ir-M metal complexes (M = Pd, Mn, and Ir) were synthesized and fully characterized. The novel Ir-Pd complex maintained photocatalytic activity toward styrenes under visible-light irradiation, and polymerization with p-chlorostyrene, copolymerization with styrene and p-chlorostyrene furnished corresponding polymers.

Photoaccelerated energy transfer catalysis of the Suzuki-Miyaura coupling through ligand regulation on Ir(iii)-Pd(ii) bimetallic complexes

Three bimetallic Ir(iii)–Pd(ii) complexes [Ir(ppy)₂(bpm)PdCl₂](PF₆) (ppy = 2-phenylpyridine, 1), [Ir(dfppy)₂(bpm)PdCl₂](PF₆) (dfppy = (4,6-difluorophenyl)pyridine, 2), and [Ir(pq)₂(bpm)PdCl₂](PF₆) (pq = 2-phenylquinoline, 3) were synthesized by using 2,2′-bipyrimidine (bpm) as a bridging ligand. The influences of the cyclometalated ligand at the Ir(iii) center on the photophysical and electrochemical properties as well as photocatalytic activity for the Suzuki–Miyaura coupling reaction under mild conditions were evaluated. The results revealed that complex 3 enables dramatically accelerating the Suzuki–Miyaura coupling reaction under visible light irradiation at room temperature, due to the effective absorption of visible light and appropriate locus of the excited chromophore. Mechanism studies showed that the chromophore [Ir(pq)₂(bpm)] fragment absorbs visible light to produce the triplet excited state centering on the bridging ligand which boosts the formation of electron rich Pd(ii) units and facilitates the oxidative addition step of the catalytic cycle. Simultaneously, the excited chromophore undergoes energy transfer efficiently to the Pd(ii) reaction site to form the excited Pd(ii) species, resulting in enhancement of Pd(ii) reduction steps of the Suzuki–Miyaura coupling reaction and increasing the reactivity of the catalyst. This provides a new strategy for designing photocatalysts for coupling reaction through altering the cyclometalated ligand to modulate the photophysical properties and the cooperation between two metal units.

A series bimetallic catalysts were synthesized. Relationship between the structure of catalysts and catalytic reactivities were studied and improvement of the catalytic efficiency for Suzuki–Miyaura coupling was accomplished by regulating their chromophores.

Synthesis of Os(ii)-Re(i)-Ru(ii) hetero-trinuclear complexes and their photophysical properties and photocatalytic abilities

Novel Os(ii)–Re(i)–Ru(ii) hetero-trinuclear complexes, which can absorb a wide range of visible light and induce durable CO₂ reduction, were synthesised.

Photofunctional trinuclear complexes containing three different central metals, i.e. Os(ii), Re(i) and Ru(ii), were synthesised for the first time using stepwise Mizoroki–Heck reactions. The vinylene groups in the bridging ligands of the Os(ii)–Re(i)–Ru(ii) trinuclear complexes were selectively reduced by photochemical hydrogenation in moderate yield, affording novel supramolecular photocatalysts which can absorb a wide range of visible light up to 730 nm and induce CO₂ reduction with high selectivity and durability. The turnover numbers of CO formation were over 4300. Details of the photophysical properties of these new trinuclear complexes, especially their intramolecular excitation-energy transfer phenomena, are also reported.

Photochemical and Photobiological Activity of Ru(II) Homoleptic and Heteroleptic Complexes Containing Methylated Bipyridyl-type Ligands

Light-activated compounds are powerful tools and potential agents for medical applications, as biological effects can be controlled in space and time. Ruthenium polypyridyl complexes can induce cytotoxic effects through multiple mechanisms, including acting as photosensitizers for singlet oxygen (¹O₂) production, generating other reactive oxygen species (ROS), releasing biologically active ligands, and creating reactive intermediates that form covalent bonds to biological molecules. A structure-activity relationship (SAR) study was performed on a series of Ru(II) complexes containing isomeric tetramethyl-substituted bipyridyl-type ligands. Three of the ligand systems studied contained strain-inducing methyl groups and created photolabile metal complexes, which can form covalent bonds to biomolecules upon light activation, while the fourth was unstrained and resulted in photostable complexes, which can generate ¹O₂. The compounds studied included both bis-heteroleptic complexes containing two bipyridine ligands and a third, substituted ligand and tris-homoleptic complexes containing only the substituted ligand. The photophysics, electrochemistry, photochemistry, and photobiology were assessed. Strained heteroleptic complexes were found to be more photoactive and cytotoxic then tris-homoleptic complexes, and bipyridine ligands were superior to bipyrimidine. However, the homoleptic complexes exhibited an enhanced ability to inhibit protein production in live cells. Specific methylation patterns were associated with improved activation with red light, and photolabile complexes were generally more potent cytotoxic agents than the photostable ¹O₂-generating compounds.

Switching of the π-electronic conjugations in the reduction of a dithienylethene-fused p-benzoquinone

Visible light unlocks the π-electronic conjugation of a dithienylethene-fused p-benzoquinone derivative to cause a light-driven oxidation reaction.

Synthesis and photocatalytic activity of a naphthyl-substituted photosensitizing BINAP–palladium complex

A novel light-active Pd complex having a BINAP ligand with 2-naphthyl substituents on the phosphines was synthesized and characterized, which is active in the catalytic light-controlled polymerization of 4-methoxystyrene.

Visible-light-controlled homo- and copolymerization of styrenes by a bichromophoric Ir–Pd catalyst

Visible-light-controlled polymerization was achieved by a bichromophoric organopalladium catalyst which possesses a naphthyl-substituted cyclometallated Ir(iii) light-absorbing moiety.

Infrared vibrational spectroscopy of [Ru(bpy)2(bpm)]2+ and [Ru(bpy)3]2+ in the excited triplet state

This work involved a detailed investigation into the infrared vibrational spectra of ruthenium polypyridyl complexes, specifically heteroleptic [Ru(bpy)2(bpm)](2+) (bpy = 2,2'-bipyridine and bpm = 2,2'-bipyrimidine) and homoleptic [Ru(bpy)3](2+), in the excited triplet state. Transient spectra were acquired 500 ps after photoexcitation, corresponding to the vibrational ground state of the excited triplet state, using time-resolved infrared spectroscopy. We assigned the observed bands to specific ligands in [Ru(bpy)2(bpm)](2+) based on the results of deuterium substitution and identified the corresponding normal vibrational modes using quantum-chemical calculations. Through this process, the more complex vibrational bands of [Ru(bpy)3](2+) were assigned to normal vibrational modes. The results are in good agreement with the model in which excited electrons are localized on a single ligand. We also found that the vibrational bands of both complexes associated with the ligands on which electrons are little localized appear at approximately 1317 and 1608 cm(-1). These assignments should allow the study of the reaction dynamics of various photofunctional systems including ruthenium polypyridyl complexes.

Visible-light-enhanced Suzuki–Miyaura coupling reaction by cooperative photocatalysis with an Ru–Pd bimetallic complex

A photo-assisted Suzuki–Miyaura coupling reaction has been realized by a molecule Pd(ii) complex containing a Ru(ii)-polypyridyl derivative as a visible light photosensitizing unit.

Synthesis, structure and magnetism of homodinuclear complexes of Co, Ni and Cu supported by a novel bitriazine scaffold

Btzn (1), an amine-functionalized bi(1,3,5-triazine) 4,4'-(NH(2))(2)-6,6'-(NHC(6)H(5))(2)-2,2'-(1,3,5-C(3)N(3))(2), is reported, and its coordination with Co, Ni and Cu is explored. Reactions of metal salts (2 equiv) with Btzn (1 equiv) result in dimeric species [(Btzn)Co(2)(NCS)(4)(EtOH)(2)(DMF)(2)], (2), [(Btzn)Ni(2)(η(1)-ONO(2))(2)(MeOH)(4)(DMF)(2)]·2[NO(3)], (3), [(Btzn)Cu(2)Cl(4)(DMF)(2)], (4), and [(Btzn)Cu(2)(η(2)-O(2)NO)(2)(OH(2))(2)(DMF)(2)]·2[NO(3)], (5). These complexes are the first examples of the coordination of transition metals with bi(1,3,5-triazine) ligands. Their structures display a bridging bis-bidentate coordination mode for Btzn. Variable-temperature magnetic susceptibility of the complexes reveals antiferromagnetic exchange between the spin carriers, with calculated exchange coupling values (J) of -4.7 cm(-1) for 3, -18.2 cm(-1) for 4, and -5.5 cm(-1) for 5. An in-depth evaluation of the metal geometry highlights the inefficient overlap of the magnetic d-orbitals through the bridging ligand, most likely leading to reduced delocalization and coupling.

cis-2,2'-Bipyrimidine-bridged polynuclear complex: a stairway-like mixed-valent {Fe(4)} cluster

We report the first example of a polynuclear discrete coordination compound exhibiting only bpym bridges and containing a first-row d transition metal. A smooth self-assembly one-pot synthetic route, starting from simply FeCl(2) and FeCl(3) hydrates, allowed us to prepare a tetranuclear Fe(4) cluster with a stairway-like structure and the formula cis-{[(H(2)O)Cl(3)Fe(III)-μ(bpym)Fe(II)Cl(2)]}(2)-μ(bpym) (1) . All spectroscopic data suggest that complex 1 is a valence-localized mixed-valent Fe(II)-Fe(III) cluster with typical Mössbauer lines for both sites, which do not change with temperature. Reflectance spectroscopy did not allow one to distinguish an intervalence charge-transfer band. However, time-dependent density functional theory (DFT) calculations predict a weak high-energy Fe(II) → Fe(III) transition. Regarding the magnetic properties, the high-spin Fe(II) and Fe(III) ions interact in a weakly antiferromagnetic way with isotropic J constants of only a few wavenumbers as derived from direct-current susceptibility and magnetization data. Broken-symmetry DFT calculations support these observations.

Synthesis of Pd complexes directly linked to the light-absorbing [(bpy)(3)Ru](2+) unit and their photochemical reactions toward styrenes

A series of bipyridyl-Pd and Rh complexes containing a [(bpy)(3)Ru](2+) or [(bpy)(2)Ru(phen)](2+) (bpy = 2,2'-bipyridyl, phen = 1,10-phenanthroline) moiety as visible-light absorbing unit was synthesized. The complexes were synthesized via a Suzuki-Miyaura coupling reaction between the Ru complexes having a 4-bromo-2,2'-bipyridyl ligand and a 2,2'-bipyridyl-4-boronic acid and a subsequent reaction with various mononuclear Pd and Rh precursors. There was a noticeable structural difference between the QP (2,2':4',4'':2'',2'''-quaterpyridyne) and PB (5-(2,2'-bipyridyl)-yl-1,10-phenanthroline) complexes, which involved the dihedral angles within the bridging ligand; the PB complexes possessed large dihedral angles but the QP complexes showed small values. This structural difference clearly indicated a strong pi-conjugation through the QP ligand. The electrochemical and photophysical properties of the QP and PB complexes were compared with the parent mononuclear Ru complexes, such as [(bpy)(3)Ru](2+), [(bpy)(2)Ru(phen)](2+), and [(bpy)(2)Ru(bpm)](2+) (bpm = 2,2'-bipyrimidine). The QP and PB complexes showed a (3)MLCT life time that was similar to [(bpy)(3)Ru](2+) and [(bpy)(2)Ru(phen)](2+), which was about 10 times longer (ca. 1 mus) than the corresponding bpm complexes. Reactivity studies with Pd complexes toward styrene dimerizations were examined. The reaction proceeded under visible-light irradiated conditions and the reactivity of the QP complexes was much higher than the corresponding PB complexes. Substantial acceleration of the reaction was observed with the introduction of an Me substituent on the bipyridyl ligand.