NN Ligand Research Articles

Light-enhancing ketone transfer hydrogenation catalyzed by diphosphine phenanthroline ruthenium complexes

The cationic phenanthroline ruthenium derivatives [Ru(OAc)(dppb)(NN)]OAc (NN = phen 1, imidazo[4,5-f][1,10]phenanthroline 2) have been obtained in high yield by reaction of the acetate [Ru(OAc)2dppb] with the corresponding NN ligand. The dinuclear cyclometalated [(dppb)(η2-OAc)(Ru(µ-NN-phenimid-NC)Ru(η2-OAc)(dppb)]OAc (3) has been prepared from 2 with [Ru(OAc)2(dppb)] via elimination of acetic acid. The characterization of these compounds has been carried out by NMR, FT-IR, UV–Vis, conductivity and cyclic voltammetry measurements. These derivatives display catalytic activity in the transfer hydrogenation of aromatic and aliphatic cyclic ketones at S/C up to 2000 in presence of NaOiPr in 2-propanol. An increase of the rate (up to 8 times) has been observed upon irradiation at 30 and 60 °C (300 W Xenon Arc Lamp light source). Control experiments show that [Ru(OiPr)2(dppb)(phen)] (1A), formed from 1 by substitution of the acetate with the isopropoxide ligand, shows a stronger emission compared to 1 and that 1A is quenched by NaOiPr, affording the dihydride [Ru(H)2(dppb)(phen)] (1C) via a photo induced β-H elimination.

The structural, optical, electrical and radiation shielding properties of Co-doped ZnO thin films

Co:ZnO thin films are promising due to the similar ionic radii of cobalt and ZnO, and their potential for carrier spin injection, transfer, and detection. This study aims to investigate the structural, optical, electrical, and radiation shielding properties of Co-doped zinc oxide (Co:ZnO) thin films for potential applications in various fields such as semiconductors, solar cells, spintronics, and radiation shielding. The effect of commercially available Cobalt acetate tetrahydrate and Cobalt complex (Co with conjugated NN ligand) as cobalt additives on the synthesis of ZnO thin films is compared, aiming to discern their respective impacts. The dopants are incorporated in 2, 4, and 6 wt%, employing the sol-gel spin coating method.Applying cobalt complex additive as Co precursor resulted in ZnO:Co films with a superior enhancement of the electronic band gap of 2.84–3.00 eV compared to cobalt acetate precursor (2.62–2.84 eV). With the introduction of Cobalt, there is a notable change in the electrical conductivity, showcasing a decrease from 1.5x10−7 to 2.11x10−10 (S/cm). Also, radiation shielding parameters were experimentally measured in the energy range of 186.1–1764.5 keV within the scope of gamma ray spectral analysis. Exposure buildup factors (EBF) in the energy range of 15–15,000 keV were calculated up to 1–40 mean free path (mfp). Mass stopping power (MSP) and projected range values (PR) for nuclear safety applications were calculated for protons and alpha particles using the SRIM code. Thin film thicknesses were determined by using Lambert-Beer law. It was observed that the thin film thicknesses obtained from gamma spectrometry (2.090–2.628 μm) and SEM (2.157–2.725 μm) were compatible with each other.

Nitrile Substituents at the Conjugated Dipyridophenazine Moiety as Infrared Redox Markers in Electrochemically Reduced Heteroleptic Ru(II) Polypyridyl Complexes.

Ruthenium(II) complexes [Ru(tap)2(NN)]2+ (tap = 1,4,5,8-tetraazaphenanthrene, NN = 11-cyano-dipyrido[3,2-a:2',3'-c]phenazine (11-CN-dppz) and 11,12-dicyano-dipyrido[3,2-a:2',3'-c]phenazine (11,12-CN-dppz)) feature the C≡N groups as infrared (IR)-active redox markers. They were studied by cyclic voltammetry, UV-vis, and IR spectroelectrochemistry (SEC), and density functional theory calculations to assign the four 1e- reduction waves R1-R4 observed in dichloromethane. Generally, the NN ligands are reduced first (R1). For [Ru(tap)2(11,12-CN-dppz)]2+, R1 is sufficiently separated from R2 and delocalized over both tap ligands. Accordingly, IR SEC conducted at R1 shows a large red shift of the νs,as(C≡N) modes by -18/-28 cm-1, accompanied by a 4-fold enhancement of the νs(C≡N) intensity, comparably with reference data for free 11,12-CN-dppz. The first tap-based reduction of spin-doublet [Ru(tap)2(11,12-CN-dppz)]+ to spin-triplet [Ru(tap)2(11,12-CN-dppz)] at R2 decreased ν(C≡N) by merely -2 cm-1, while the intensity enhancement reached an overall factor of 8. Comparably, a red shift of ν(C≡N) by -27 cm-1 resulted from the 1e- reduction of [Ru(tap)2(11-CN-dppz)]2+ at R1 (poorly resolved from R2), and the intensity enhancement was roughly 3-fold. Concomitant 1e- reductions of the tap ligands (R2 and R3) caused only minor ν(C≡N) shifts of -3 cm-1 and increased the absorbance by overall factors of 6.5 and 8, respectively.

Cinchona-Alkaloid-Derived NN Ligands and Achiral Phosphines for Iridium-Catalyzed Asymmetric Hydrogenation of Heteroaromatic and α-Chloroheteroaryl Ketones.

A concise synthesis of cinchona-alkaloid-derived NN ligands bearing alkyl substituents on chiral nitrogen atoms was described. Iridium catalysts containing new chiral NN ligands and achiral phosphines were effective for the asymmetric hydrogenation of heteroaromatic ketones, which afforded corresponding alcohols in up to 99.9% ee. The same protocol was applicable to the asymmetric hydrogenation of α-chloroheteroaryl ketones. Most importantly, the gram-scale asymmetric hydrogenation of 2-acetylthiophene and 2-acetylfuran proceeded smoothly even under 1 MPa of H2.

Manganese(I)-catalyzed asymmetric (transfer) hydrogenation of ketones: An insight into the effect of chiral PNN and NN ligands

A new type of (RC,SP)-1-(2-diphenylphosphino)ferrocenylethylamine N-substituted with a (RC)-5,6,7,8-tetrahydroquinolinyl group (LPNN-1) was successfully employed as a chiral chelating ligand in both Mn-catalyzed asymmetric transfer hydrogenation (ATH) and asymmetric hydrogenation (AH) of a broad range of ketonic substrates (39 examples), leading to high conversions and excellent enantioselectivities for their product alcohols. In particular, PNN-pincer complex Mn-1 and its NN-bidentate analogue Mn-2 have been isolated and their comparative performance as catalysts studied with Mn-1 proving more effective in both ATH and AH. Moreover, Mn-1 generally imparted higher degrees of enantiomeric excess (ee) in both hydrogenation processes which can reach up to 99% in ATH and 93% in AH for propiophenone-type substrates. DFT calculations highlight the importance of π-π interactions and steric hindrance between catalyst and substrate which manifests itself in enhancements in ee for propiophenone over acetophenone substrates. Furthermore, a possible mechanism for the Mn-catalyzed ATH has been proposed on the basis of a joint DFT and experimental investigation.

Cinchona-alkaloid-derived NN ligands for ruthenium catalyzed asymmetric hydrogenation of ketones.

A range of cinchona-alkaloid-derived NN ligands bearing N-H were employed for the asymmetric hydrogenation of ketones. By substituting N-H of the ligands, we demonstrated that the N-H moiety was essential for asymmetric hydrogenation and that without the N-H moiety asymmetric hydrogenation could not proceed, based on which a proposed mechanism is discussed. The effectiveness of the optimal ligand was evaluated on various aromatic and α,β-unsaturated ketones, producing the corresponding alcohols with up to 98.8% ee and good yields.

Robust and efficient transfer hydrogenation of carbonyl compounds catalyzed by NN-Mn(I) complexes.

A series of manganese(I) carbonyl complexes bearing structurally related NN- and NNN-chelating ligands have been synthesized and assessed as catalysts for transfer hydrogenation (TH). Notably, the NN-systems based on N-R functionalized 5,6,7,8-tetrahydroquinoline-8-amines, proved the most effective in the manganese-promoted conversion of acetophenone to 1-phenylethanol. In particular, the N-isopropyl derivative, Mn1, when conducted in combination with t-BuONa, was the standout performer mediating not only the reduction of acetophenone but also a range of carbonyl substrates including (hetero)aromatic-, aliphatic- and cycloalkyl-containing ketones and aldehydes with especially high values of TON (up to 17 200; TOF of 3550 h-1). These findings, obtained through a systematic variation of the N-R group of the NN ligand, are consistent with an outer-sphere mechanism for the hydrogen transfer. As a more general point, this Mn-based catalytic TH protocol offers an attractive and sustainable alternative for producing alcoholic products from carbonyl substrates.

Three-center-four-electron halogen bond enables non-metallic complex catalysis for Mukaiyama-Mannich-type reaction

SummaryThe three-center-four-electron halogen bond (3c4e X-bond) presents a fundamental design concept for catalysis. By integrating halogen(I) (X+: I+ or Br+), the bis-pyridyl ligand NN, and a non-nucleophilic counteranion Y, we developed non-metallic complex catalysts, [N···X···N]Ys, that exhibited outstanding activity and facilitated the Mukaiyama-Mannich-type reaction of N-heteroaromatics with parts-per-million-level catalyst loading. The high activity of [N···X···N]SbF6 was clearly demonstrated. NMR titration experiments, CSI-MS, computations, and UV-vis spectroscopic studies suggest that the robust catalytic activity of [N···X···N]Y can be attributed to the unique ability of the 3c4e X-bond for binding chloride: i) the covalent nature transforms the [N···X···N]+ complexation to sp2 CH as a hydrogen-bonding donor site, and ii) the noncovalent property allows for the dissociation of [N···X···N]+ for the formation of [Cl···X···Cl]−. This study introduces the application of 3c4e X-bonds in catalysis via halogen(I) complexes.

Preparation of Neutral trans - cis [Ru(O2CR)2P2(NN)], Cationic [Ru(O2CR)P2(NN)](O2CR) and Pincer [Ru(O2CR)(CNN)P2] (P = PPh3, P2 = diphosphine) Carboxylate Complexes and their Application in the Catalytic Carbonyl Compounds Reduction.

The diacetate complexes trans-[Ru(κ1-OAc)2(PPh3)2(NN)] (NN = ethylenediamine (en) (1), 2-(aminomethyl)pyridine (ampy) (2), 2-(aminomethyl)pyrimidine (ampyrim) (3)) have been isolated in 76–88% yield by reaction of [Ru(κ2-OAc)2(PPh3)2] with the corresponding nitrogen ligands. The ampy-type derivatives 2 and 3 undergo isomerization to the thermodynamically most stable cationic complexes [Ru(κ1-OAc)(PPh3)2(NN)]OAc (2a and 3a) and cis-[Ru(κ1-OAc)2(PPh3)2(NN)] (2b and 3b) in methanol at RT. The trans-[Ru(κ1-OAc)2(P2)2] (P2 = dppm (4), dppe (5)) compounds have been synthesized from [Ru(κ2-OAc)2(PPh3)2] by reaction with the suitable diphosphine in toluene at 95 °C. The complex cis-[Ru(κ1-OAc)2(dppm)(ampy)](6) has been obtained from [Ru(κ2-OAc)2(PPh3)2] and dppm in toluene at reflux and reaction with ampy. The derivatives trans-[Ru(κ1-OAc)2P2(NN)] (7–16; NN = en, ampy, ampyrim, 8-aminoquinoline; P2 = dppp, dppb, dppf, (R)-BINAP) can be easily synthesized from [Ru(κ2-OAc)2(PPh3)2] with a diphosphine and treatment with the NN ligands at RT. Alternatively these compounds have been prepared from trans-[Ru(OAc)2(PPh3)2(NN)] by reaction with the diphosphine in MEK at 50 °C. The use of (R)-BINAP affords trans-[Ru(κ1-OAc)2((R)-BINAP)(NN)] (NN = ampy (11), ampyrim (15)) isolated as single stereoisomers. Treatment of the ampy-type complexes 8–15 with methanol at RT leads to isomerization to the cationic derivatives [Ru(κ2-OAc)P2(NN)]OAc (8a–15a; NN = ampy, ampyrim; P2 = dppp, dppb, dppf, (R)-BINAP). Similarly to 2, the dipivalate trans-[Ru(κ1-OPiv)2(PPh3)2(ampy)] (18) is prepared from [Ru(κ2-OPiv)2(PPh3)2] (17) and ampy in CHCl3. The pincer acetate [Ru(κ1-OAc)(CNNOMe)(PPh3)2] (19) has been synthesized from [Ru(κ2-OAc)2(PPh3)2] and HCNNOMe ligand in 2-propanol with NEt3 at reflux. In addition, the dppb pincer complexes [Ru(κ1-OAc)(CNN)(dppb)] (CNN = AMTP (20), AMBQPh (21)) have been obtained from [Ru(κ2-OAc)2(PPh3)2], dppb, and HAMTP or HAMBQPh with NEt3, respectively. The acetate NN and pincer complexes are active in transfer hydrogenation with 2-propanol and hydrogenation with H2 of carbonyl compounds at S/C values of up to 10000 and with TOF values of up to 160000 h–1.

Synthesis of Ethylene/1-Octene Copolymers with Ultrahigh Molecular Weights by Zr and Hf Complexes Bearing Bidentate NN Ligands with the Camphyl Linker

Ultrahigh molecular weight polyethylene (UHMWPE) is a class of high-performance engineering plastics, exhibiting a unique set of properties and applications. Although many advances have been achieved in recent years, the synthesis of UHMWPE is still a great challenge. In this contribution, a series of zirconium and hafnium complexes, [2,6-(R1)2-4-R2-C6H2-N-C(camphyl)=C(camphyl)-N-2,6-(R1)2-4-R2-C6H2]MMe2(THF) (1-Zr: R1 = Me, R2 = H, M = Zr; 2-Zr: R1 = Me, R2 = Me, M = Zr; 1-Hf: R1 = Me, R2 = H, M = Hf; 2-Hf: R1 = Me, R2 = Me, M = Hf), bearing bidentate NN ligands with the bulky camphyl backbone were synthesized by the stoichiometric reactions of α-diimine ligands with MMe4 (M = Hf or Zr). All Zr and Hf metal complexes were analyzed using 1H and 13C NMR spectroscopy, and the molecular structures of complexes 1-Zr and 1-Hf were determined by single-crystal X-ray diffraction, revealing that the original α-diimine ligand was selectively reduced into the ene-diamido form and generated an 1,3-diaza-2-metallocyclopentene ring in the metal complexes. Zr complexes 1-Zr and 2-Zr showed moderate activity (up to 388 kg(PE)·mol−1(M)·h−1), poor copolymerization ability, but unprecedented molecular weight capability toward ethylene/1-octene copolymerization. Therefore, copolymers with ultrahigh molecular weights (>600 or 337 × 104 g∙mol−1) were successfully synthesized by 1-Zr or 2-Zr, respectively, with the borate cocatalyst [Ph3C][B(C6F5)4]. Surprisingly, Hf complexes 1-Hf and 2-Hf showed negligible activity under otherwise identical conditions, revealing the great influence of metal centers on catalytic performances.

Heteroleptic NiII complexes: Synthesis, structural characterization, computational studies and amoebicidal activity evaluation

In this work, we present the synthesis, characterization, electrochemical studies, DFT calculations, and in vitro amoebicidal effect of seven new heteroleptic NiII coordination compounds. The crystal structures of [H2(pdto)](NO3)2 and [Ni(pdto)(NO3)]PF6 are presented, pdto = 2,2′-[1,2-ethanediylbis-(sulfanediyl-2,1-ethanediyl)]dipyridine. The rest of the compounds have general formulae: [Ni(pdto)(NN)](PF6) where N-N = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (44dmbpy), 5,5′-dimethyl-2,2′-bipyridine (55dmbpy), 1,10-phenanthroline (phen), 4,7-dimethyl-1,10-phenanthroline (47dmphen) and 5,6-dimethyl-1,10-phenanthroline (56dmphen). The size of NN ligand and its substituents modulate the compound electronic features and influence their antiproliferative efficiency against Entamoeba histolytica. 56dmphen derivative, shows the biggest molar volume and presents a powerful amoebicidal activity (IC50 = 1.2 μM), being seven times more effective than the first-line drug for human amoebiasis metronidazole. Also, increases the reactive oxygen species concentration within the trophozoites. This could be the trigger of the E. histolytica growth inhibition. The antiparasitic effect is described using NiII electron density, molar volume, estimated by DFT, as well as the experimental redox potential and diffusion coefficients. In general, amoebicidal efficiency is directly proportional to the increment of the molar volume and decreases when the redox potential becomes more positive.

Rhenium(I) polypyridine complexes coordinated to an ethyl-isonicotinate ligand: Luminescence and in vitro anti-cancer studies

In this work, fac-[Re(et-isonic)(NN)(CO)3]+ complexes, et-isonic = ethyl-isonicotinate, NN = 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (Ph2phen), 4,7-dichloro-1,10-phenanthroline (Cl2phen) or 4,7-dimethyl-1,10-phenanthroline (Me2phen), were synthesized to combine different substituent groups at coordinate phen ligand along with the coordination of a nicotinic acid derivative aiming the modulation of the photophysical and lipophilic properties. The electronic absorption spectra profile can be divided into two main regions: the high-energy region ascribed to the intraligand transition (IL), and the low-energy region assigned to the metal-to-ligand charge transfer transition (MLCT). Additionally, the complexes exhibited 3MLCT emission, sensitive to the nature of NN ligand, which can be used to photosensitize the generation of singlet oxygen as well as to localize them into the cell. The lipophilicity of the complexes increases as the substituent at coordinated phen ligand was changed from hydrogen to phenyl and these results reflected also in the same trend observed for the cytotoxicity results, in the absence of light, using breast cancer (MCF-7) and melanoma (SkMel-147 and SkMel-29) cell lines. In addition, the flow cytometry assay along with the Western Blotting analyses showed an overexpression on pro caspase-9, suggesting a Caspase proteolytic cascade through the intrinsic pathway in the apoptosis as the mechanism of action. In spite of the Re(I) complexes were capable of generating singlet oxygen in the presence of light, they were very effective in killing the cells by a different mechanism of action in the absence of light. Thus, these results provided a better understanding of the mechanism of anticancer action and highlight the potential application of rhenium(I) complexes in the development of a novel therapy process.

Half-Sandwich Ruthenium(II) Complexes with Bidentate NN Ligands:Active Catalysts for the Synthesis of Quinolines and Pyrroles by Acceptorless Dehydrogenative Cyclization

Half-Sandwich Ruthenium(II) Complexes with Bidentate NN Ligands:Active Catalysts for the Synthesis of Quinolines and Pyrroles by Acceptorless Dehydrogenative Cyclization

A series of blue-green-yellow-red emitting Cu(I) complexes: Molecular structure and photophysical performance.

In this work, we designed a series of [Cu(NN)(PPh3)2]BF4 complexes with different optical edge values and emission colors from blue to red, where NN and PPh3 denoted a diamine ligand and triphenylphosphine, respectively. Six NN ligands with various conjugation chains (short π chain, modest π chain and long π chain) were selected. A systematical comparison between these Cu(I) complexes was performed, so that the correlation between NN structure and [Cu(NN)(PPh3)2] photophysical performance was tentatively discussed. Their single crystal structure was found consistent with literature ones, forming a typical tetrahedral coordination geometry. Density functional theory calculation indicated that their onset electronic transition showed a mixed character of metal-to-ligand-charge-transfer and ligand-to-ligand-charge-transfer. Detailed analysis on photophysical parameters suggested that the absorption edge of [Cu(NN)(PPh3)2]BF4 complex was controlled by conjugation length in diamine ligand. A wide absorption edge needed a short conjugation chain in diamine ligand. Similar tendency was found for their emission spectra. In addition, a long conjugation chain in diamine ligand widened emission spectra obviously. Emission dynamics showed slim correlation with diamine ligand conjugation length since the excited state was controlled mainly by dynamic procedure and steric factor of diamine ligands.

Dinuclear Copper(I) Complexes Combining Bis(diphenylphosphanyl)acetylene with 1,10‐Phenanthroline Ligands

Dinuclear copper(I) complexes have been prepared starting from bis(diphenylphosphanyl)acetylene (dppa), [Cu(CH3CN)4](BF4) and various 1,10‐phenanthroline ligands (NN), namely 1,10‐phenanthroline (phen), neocuproine (dmp), bathophenanthroline (Bphen), bathocuproine (Bdmp) and 2‐phenyl‐1,10‐phenanthroline (mpp). The resulting [Cu2(µ‐dppa)2(NN)2](BF4)2 complexes have been thus obtained in excellent yields (88 to 94 %). X‐ray crystal structure analysis of four complexes revealed that the 10‐membered dimetallacycle adopts a chair‐like conformation in the solid state. Detailed variable temperature NMR investigations have evidenced dynamic coordination/decoordination of the NN ligands as well as ligand exchange reactions. At high temperature (100 °C), entropic effects tend to destabilize the dinuclear heteroleptic complexes. As a result, homoleptic mononuclear complexes, i.e. [Cu(NN)2]+ and undefined dppa copper(I) complexes, start to appear in solution. In contrast, the heteroleptic coordination scenario is almost exclusively favored at lower temperatures. For most of the dinuclear complexes, the 10‐membered dimetallacycle remains flexible and chair‐to‐chair interconversion occurs faster than the NMR timescale even at –70 °C. In the particular case of the mpp derivative, the bulky phenyl substituent prevents the isomerization of the metallacycle and thus contributes to rigidify the structure. This rigidification has a dramatic effect on the emission properties of this particular compound. The emission quantum yield of [Cu2(µ‐dppa)2(mpp)2](BF4)2 is effectively one order of magnitude higher when compared to all the other complexes in this series (20 % vs. 0.3–1.7 % in the solid state).

Topological and Steric Constraints to Stabilize Heteroleptic Copper(I) Complexes Combining Phenanthroline Ligands and Phosphines.

Heteroleptic copper(I) complexes combining phenanthroline derivatives (NN) and chelating bisphosphine ligands (PP) are an important class of luminescent materials for various applications. Although thermodynamically stable, [Cu(NN)(PP)]+ derivatives are also kinetically unstable. As a result, a dynamic ligand-exchange reaction is often observed in solution, leading to a dynamic mixture of heteroleptic and homoleptic complexes. To prevent the formation of the homoleptic species, macrocyclic phenanthroline ligands have been used for the preparation of [Cu(NN)(PP)]+ pseudorotaxanes. The topological constraint resulting from the macrocyclic structure of the NN ligand drives the thermodynamic equilibrium towards the exclusive formation of the heteroleptic complex as long as the macrocycle is large and flexible enough to allow for the threading of the PP ligand. Conversely, when the threading is prevented by steric constraints, unprecedented copper(I) complexes with a trigonal coordination geometry are obtained. These results are summarized in the present concept article.

Atom‐Transfer Radical Addition Photocatalysis Using a Heteroleptic Copper Complex

AbstractHerein, we describe a photocatalyzed atom‐transfer radical addition (ATRA) reaction using a heteroleptic copper(I) complex bearing a bipyridyl‐based NN ligand and a 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) based PP ligand. The selected heteroleptic complex was [Cu(BINAP)(cup)](PF6), which was used because of its intense absorption in the visible region and its long excited‐state lifetime. The reported copper photocatalyzed reactions of olefins with carbon tetrabromide afford the products in moderate‐to‐excellent yields under irradiation with a 3 W, 400 nm light emitting diode (LED).

Cycloneophylplatinum Chemistry: A New Route to Platinum(II) Complexes and the Mechanism and Selectivity of Protonolysis of Platinum–Carbon Bonds

A new route to cycloneophylplatinum(II) complexes is reported and the selectivity of protonolysis of the platinum–aryl and −alkyl bonds has been determined. Reaction of [PtCl2(SMe2)2] with neophylmagnesium chloride gives the binuclear cycloneophylplatinum(II) complex [Pt2(CH2CMe2C6H4)2(μ-SMe2)2], 1, which is shown to exist as a mixture of syn and anti isomers. Complex 1 reacts reversibly with SMe2 to give [Pt(CH2CMe2C6H4)(SMe2)2], 2, and irreversibly with bidentate ligands NN = 3,4,7,8-tetramethyl-1,10-phenanthroline (phen*) or 4,4′-di-t-butyl-2,2’bipyridine (bubipy) to give the corresponding complexes [Pt(CH2CMe2C6H4)(phen*)], 3, and [Pt(CH2CMe2C6H4)(bubipy)], 4, respectively. Complex 2 reacts with HCl initially by cleavage of the aryl–platinum bond to give mostly trans-[PtCl(CH2CMe2Ph)(SMe2)2], which then rearranges to an equilibrium mixture with trans-[PtCl(C6H4-2-t-Bu)(SMe2)2], while 3 and 4 react to give [PtCl(CH2CMe2Ph)(phen*)] and [PtCl(CH2CMe2Ph)(bubipy)], which do not undergo the isomerization re...

OsXCl(phosphine)2(diamine) and OsXCl(diphosphine)(diamine) (X = Cl, H) Complexes for Ketone Hydrogenation

The osmium complex trans-[OsCl2(PPh3)2(en)] (2) was prepared by reaction of [OsCl2(PPh3)3] (1a) with ethylenediamine (en), whereas the diphosphine derivatives trans-[OsCl2(dppf)(NN)] (NN = en (3), bn (4; bn = 1,4-butanediamine)) and trans-[OsCl2(dpbp)(en)] (5) were obtained from 1a, dppf or dpbp, and the corresponding NN ligand in CH2Cl2 or toluene. An X-ray diffraction study has been provided for 3. The isolation of the chiral derivatives trans-[OsCl2(diphosphine)((R,R)-dpen)] (diphosphine = dppf (6), dpbp (7), (R,R)-skewphos (8)) was achieved by reacting 1a with the diphosphine and (R,R)-dpen in toluene. Treatment of the precursor [Os2Cl4(P(m-tolyl)3)5] (1b) with en afforded [OsCl2(P(m-tolyl)3)2(en)] (9), while reaction of 1b with dppb and N,N-dmen gave [OsCl2(dppb)(N,N-dmen)] (10). The chiral derivatives [OsCl2(diphosphine)(NN)] (11–21; diphosphine = (S)-MeObiphep, (R)-MeObiphep, (R)-xylMeObiphep, (R)-binap, (S)-xylbinap, (R)-xylbinap, (R,S)-Josiphos*; NN = en, (R,R)-dpen, (R)-daipen, (R,R)-dppn) were ...

Probing Interligand Electron Transfer in the 1MLCT S1 Excited State of trans-Mo2L2L'2 Compounds: A Comparative Study of Auxiliary Ligands and Solvents.

The interligand charge dynamics of the lowest singlet metal-to-ligand charge-transfer states (1MLCT S1 states) of a series of quadruply bonded trans-Mo2(NN)2(O2C-X)2 paddlewheel compounds are investigated, where NN is a π-accepting phenylpropiolamidinate ligand and O2C-X (X = Me, tBu, TiPB, or CF3) is an auxiliary carboxylate ligand. The compounds show strong light absorption in the visible region due to MLCT transitions from the Mo2 center to the NN ligands. The transferred electron density was followed by femtosecond time-resolved infrared (fs-TRIR) spectroscopy with vibrational reporters such as the ethynyl groups on the NN ligands. The observed fs-TRIR spectra show that these compounds have asymmetric 1MLCT S1 excited states where the transferred electron mainly resides on a single NN ligand. The presence of interligand electron transfer (ILET) is suggested to explain the shape of the ν(C≡C) bands and the influence of auxiliary ligands and solvents on the interligand electronic coupling. The ILET in the 1MLCT S1 state is shown to be sensitive to the functional groups on the auxiliary ligands while being less responsive to changes in solvents.