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Abstract Cooperativity among spin centres has long been the royal road in spin crossover (SCO) research to impose magnetic bistability in terms of thermal hysteresis. In this work we access magnetic multi-inert states of the iron(III) compound {FeL2[B(Ph)4]} ≡ FeB at low temperature, in addition to thermal bistability. The packing of the low-spin and high-spin forms of crystalline FeB differs only marginally what ultimately leads to structural conservatism. This indicates that the SCO-immanent breathing of the complex cation is almost fully compensated by the anion matrix. The unique cooling rate dependence of the residual low-temperature magnetisation in FeB unveils continuous switching between the trapped high-spin (ON) and the relaxed low-spin state (OFF). The macroscopic ratio of the spin states (ON:OFF) can be adjusted as a simple function of the cooling rate. That is, cooperative spin crossover can be the source of bistable and multi-inert system states in the very same material.

A new family of photochromic diarylethene-based ligands bearing a 2-(imidazol-2-yl)pyridine coordination unit has been developed. Four members of the new family have been synthesized. The photoactive ligands feature non-aromatic ethene bridges (cyclopentene, cyclopentenone, and cyclohexenone), as well as closely spaced photoactive and metal coordination sites aiming a strong impact of photocyclization on the electronic structure of the coordinated metal ion. The ligands with cyclopentenone and cyclohexenone bridges show good cycloreversion quantum yields of 0.20–0.32. The thermal stability of closed-ring isomers reveals half-lives of up to 20 days in solution at room temperature. The ligands were used to explore coordination chemistry with iron(II) targeting photoswitchable spin-crossover complexes. Unexpectedly, dinuclear and tetranuclear iron(II) complexes were obtained, which were thoroughly characterized by X-ray crystallography, magnetic measurements, and Mössbauer spectroscopy. The formation of multinuclear complexes is facilitated by two coordination sites of the diarylethene, acting as a bridging ligand. The bridging nature of the diarylethene in the complexes prevents photocyclization.

The synthesis of chelating N-heterocyclic carbene (NHC) complexes with considerable π-acceptor properties can be a challenging task. This is due to the dimerization of free carbene ligands, the moisture sensitivity of reaction intermediates or reagents, and challenges associated with the workup procedure. Herein, we report a general route using transmetalation from magnesium−NHCs. Notably, this route gives access to transition-metal complexes in quantitative conversion without the formation of byproducts. It therefore produces transition-metal complexes outperforming the conventional routes based on free or lithium-coordinated carbene, silver complexes, or in situ metalation in dimethyl sulfoxide (DMSO). We therefore propose transmetalation from magnesium−NHCs as a convenient and general route to obtain NHC complexes.

(S,S)-Ethylenediamine-N,N’-di-2-propanoic acid hydrochloride, (S,S)-H2eddp·HCl, was prepared and its crystal structure determined. The compound was characterized by infrared and 1H- and 13C-NMR spectroscopy. It forms P1 in the space group of a triclinic crystal system with a = 5.3902(2) Å, b = 5.8967(2) Å, c = 10.3319(2) Å, a = 99.625(2)°, b = 91.645(2)°, g = 109.995(2)° and Z = 1.

In the title compound, alternatively called α-hydroxy-γ-alkylidenebutenolide, C12H16O3, two independent molecules (A and B) crystallize in the asymmetric unit in each of which the 5,6-dihydrobenzo ring has an envelope conformation. The torsion angle along the butadiene chain in the γ-alkylidenebutenolide core is −177.9 (2)° for molecule A and 179.9 (2)° for molecule B. In the crystal, O—H...O hydrogen bonds between hydroxyl and carbonyl groups of adjacent independent molecules form dimers with R22(10) loops.

The new N,N,Oligand 2,2-bis(3,5-dimethylpyrazol-1-yl)propionic acid (2,2-Hbdmpzp) (2) and its transition metal complexes [Mn(2,2-bdmpzp)(CO)3] (3), [Re(2,2-bdmpzp)(CO)3] (4), [Cu(2,2-bdmpzp)2] (5), and [Ru(2,2-bdmpzp)Cl(L)(PPh3)] [L = PPh3(6), N2(7), CO (8a/b), SO2(9a/b)] have been synthesized, characterized and compared to analogous complexes bearing a bis(3,5-dimethylpyrazol-1-yl)acetic acid. It was found that the additional methyl group has a remarkable influence on the stability and reactivity of transition metal complexes. [ABSTRACT FROM AUTHOR]

The bis(acetyl)-bridged complex [{Pt(COMe)2}n] (2) has been prepared from the platina-β-diketone [Pt2{(COMe)2H}2(μ-Cl)2] (1) with hexamethyldisilazane. Reactions of complex 2with the monodentate P and N donors PPh3, pyrazole (Hpz), pyridine (py), 4-methylpyridine (4-Mepy), and benzylamine (BnNH2) resulted in the formation of the cis-diacetylplatinum(II) complexes cis-[Pt(COMe)2L2] (L = PPh3, 3; Hpz, 5; py, 6a; 4-Mepy, 6b; BnNH2, 7). Reactions with the bidentate N donors 2,2′-bipyridine (bpy), dimethylglyoxime (H2dmg), and pyridazine (pydz) resulted in formation of the complexes cis-[Pt(COMe)2(L∩L)] (L∩L = bpy, 4; H2dmg, 8) and [Pt2(COMe)4(μ-pydz)2] (9), respectively. Furthermore, complex 2has been found to react with acids such as HX (X = Cl, Br), generated in situ from Me3SiX/H2O, acetylacetone (Hacac), and hexafluoroacetylacetone (Hhfacac) to yield the known platina-β-diketone 1, the new dinuclear bromo-bridged platina-β-diketone [Pt2{(COMe)2H}2(μ-Br)2] (10), and new mononuclear platina-β-diketones [Pt{(COMe)2H}(L∩L)] (L∩L = acac, 11; hfacac, 12). All complexes were characterized by means of microanalysis and IR and NMR spectroscopy. X-ray diffraction analyses were performed for complexes 10−12, showing a two-dimensional network built up by closed-shell Pt···Pt (d8−d8) interactions and bifurcated hydrogen bonds in crystals of complex 10as well as infinite platinum chains built up by closed-shell Pt···Pt (d8−d8) interactions in crystals of complexes 11and 12. Complexes 8, 11, and 12have further been analyzed by UV/vis and luminescence spectroscopy in solution and in the solid state as well as time-resolved photo-emf measurements. Additionally, quantum chemical studies on the DFT level of theory revealed very strong O−H···O hydrogen bonds in the platina-β-diketones 10−12(25.6−27.9 kcal/mol). [ABSTRACT FROM AUTHOR]

A novel chiral phosphinite derivative was designed as a ligand for Ru 2+ions to give access to new enantiomerically pure or diastereomerically enriched [{σ( P):η 6-( ansa-phosphinite)benzene}Ru(II) complexes. We are interested in this class of compounds as potential catalysts for enantioselective transfer hydrogenation of organic carbonyl compounds. The preparation of enantiopure ( R)-[{σ( P):η 6-( ansa-phosphinite)benzene}Ru(II)Cl 2] ( 6) was achieved in good yeld on the basis of ( S)-mandelic acid. Four diastereomeric [{σ( P):η 6-( ansa-phosphinite)benzene}Ru(II)Cl(NH 2R)] +complex PF 6−salts were obtained from neutral 6by nucleophilic substitution of a chloride ligand with primary amines. For aniline and p-fluoroaniline salts 7and 8a significant excess of the ( SRu, RC)-diastereomers 7Sand 8Swas observed in the reaction mixtures as the kinetically preferred species, and 7Scould be isolated as a pure diastereomer. No diastereoselectivity was observed in the reaction mixtures of ( R)- and ( S)-1-phenylethylamine salts 9and 10right after preparation. 7, 8, and 9epimerize at the metal center. This leads to a loss of diastereoselectivity of 7Sand 8Sbut enrichment of ( RRu, RC)-diastereomer 9R. Pure diastereomers 7S,9R, and 10Sas well as a 1:1 diastereomeric mixture 8S/ 8Rhave been characterized structurally. The experimental setup allowed detailed insight into the specific X-ray crystallographic, CD, and NMR spectroscopic properties of defined stereoisomers of chiral Ru(II) complexes. The kinetic diastereoselectivities of 7Sand 8Sare explained by a H-bond delivery effect, while pure diastereomer salt 9Ris configuratively stable. [ABSTRACT FROM AUTHOR]

A general synthetic method has been designed to prepare a series of unsymmetrical cationic organo-diplatinum complexes each containing two bridging 2-diphenylphosphinopyridine (PN), PPh2py, ligands and a platinum–platinum donor–acceptor bond. Thus, reaction of cis-[PtR2(SMe2)2] (R = Ph, p-MeC6H4 or p-FC6H4), 1, or cis,cis-[R2Pt(µ-SMe2)2PtR2](R = Me) with 2 equiv. or 4 equiv., respectively, of PN in CH2Cl2 gave cis-[PtR2(PN-κ1P)2], 2. When complex 2 was reacted with 1 equiv. of HX (X = CF3COO) in CH2Cl2, an approximately 2 : 1 mixture of trans-[PtRX(PN-κ1P)2], 3, and [PtR(η2-PN)(PN-κ1P)]X, 4, was obtained. The reaction of one equiv. of the latter monomeric mixture with 0.5 equiv. of cis,cis-[R′2Pt(µ-SMe2)2PtR′2] (R′ = Me) or one equiv. of cis-[PtR′2(SMe2)2] (R′ = p-MeC6H4) in CH2Cl2 immediately gave the head-to-head (HH) stereoisomer of the diplatinum complex hh-[RPt(µ-PN)2PtR′2]X, 6. However, the same reaction in benzene gave the corresponding head-to-tail (HT) stereoisomer ht-[RPt(µ-PN)(µ-NP)PtR′2]X, 9, in pure form after a few hours. The conversion of the HH isomer 6 to the HT isomer 9 in CH2Cl2 took place very slowly during 10 d, while the conversion in C6H6 was much faster and took place over 5 h. Based on the observations, a mechanism for the conversion of the kinetic HH stereoisomer to the thermodynamic HT stereoisomer is suggested which involves association of X− with the N2PtR′2 center following by one-arm dissociation of one of the PN bridging ligands from the nitrogen terminal in the HH isomer, and subsequent exchange of the ligating atom and reformation of the HT arrangement. The methyl-di p-tolyl dimer ht-[MePt(µ-PN)(µ-NP)Pt(p-MeC6H4)2]X, 9e, in solution gradually isomerizes to ht-[(p-MeC6H4)Pt(µ-PN)(µ-NP)PtMe(p-MeC6H4)]X, 11, by an aryl ligand transfer. All the complexes were fully characterized using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and the complexes ht-[PhPt(µ-PN)(µ-NP)PtMe2]X, 9a, and ht-[(p-MeC6H4)Pt(µ-PN)(µ-NP)PtMe(p-MeC6H4)]X, 11, were further characterized by single crystal X-ray crystallography. [ABSTRACT FROM AUTHOR]

The semiconductor catalyzed photoaddition of cyclopentene or cyclohexene to various novel electron-poor imines of type p-XC6H4(CN)C=N(COPh) (X = H, F, Cl, Br, Me, MeO) was investigated as a function of the nature of the cadmium sulfide photocatalyst. Irradiation (λ≥ 350 nm) of silica supported cadmium sulfide surprisingly did not afford the expected olefin–imine adducts but an imine hydrocyanation product via an unprecedented dark reaction. However, when silica was replaced by zinc sulfide as the support for cadmium sulfide, the expected homoallylic N-benzoyl-α-amino cyanides were isolated in yields of 65–84%. Thus, chemoselectivity is introduced through replacing an insulating by a semiconducting support, a hitherto unknown effect in semiconductor photocatalysis. From the sign of the time resolved photovoltage it is found that the mixed metal sulfide interface CdS/ZnS increases the lifetime of photogenerated electron–hole pairs by about one order of magnitude as compared to the SiO2/CdS system. The reaction rate increases with increasing imine σ-Hammett constants and decreasing stability of intermediate benzyl radicals. [ABSTRACT FROM AUTHOR]

The equilibrium between the twist-boat (tb) and half-chair (hc) conformers of the central diamine chelate ring of [FeIII(tmdta)]− in solids and aqueous solution has been studied by Raman spectroscopy, supported by calculated Raman spectra using Density Functional Theory. [ABSTRACT FROM AUTHOR]

Reductive S–S bond cleavage of a disulfide precursor 3obtained from a pyridine-catalyzed Peterson-type reaction starting from camphorpyrazole 1, thionyl chloride and 2-methyl-2-(methyldithio)propionaldehyde yields 2,2′-bis(camphorpyrazol-1-yl)-2-methylpropane-2-thiol (HSiprbpm3cam, 4); the first zinc complexes bearing this ligand exhibit κ3coordination of the ligand. [ABSTRACT FROM AUTHOR]