C?H Activation of Benzene by a Photoactivated NiII(azide): Formation of a Transient Nickel Nitrido Complex

Photochemical activation of nickel‐azido complex 2 [Ni(N₃)(PNP)] (PN^HP=2,2′‐di(isopropylphosphino)‐4,4′‐ditolylamine) in neat benzene produces diamagnetic complex 3 [Ni(Ph)(PN^PN^H)], which is crystallographically characterized. DFT calculations support photoinitiated N₂‐loss of the azido complex to generate a rare, transient Ni^IV nitrido species, which bears significant nitridyl radical character. Subsequent trapping of this nitrido through insertion into the Ni P bond generates a coordinatively unsaturated Ni^II imidophosphorane PN donor. This species shows unprecedented reactivity toward 1,2‐addition of a C H bond of benzene to form 3 . The structurally characterized chlorido complex 4 [Ni(Cl)(PN^PN^H)] is generated by reaction of 3 with HCl or by direct photolysis of 2 in chlorobenzene. This is the first report of aromatic C H bond activation by a trapped transient nitrido species of a late transition metal.     

Synthesis and molecular structure of Cr(salen)(μ‐N)RhCl(COD): the first example of a heterobimetallic nitride‐bridged complex containing chromium

Five‐coordinate Cr(N)(salen) {salen is 2,2′‐[ethane‐1,2‐diylbis(nitrilomethylidyne)]diphenolate} reacts with [RhCl(COD)]₂ (COD is 1,5‐cyclooctadiene) to yield the heterobimetallic nitride‐bridged title compound, namely chlorido‐2κCl‐[2(η⁴)‐1,5‐cyclooctadiene]{2,2′‐[ethane‐1,2‐diylbis(nitrilomethylidyne)]diphenolato‐1κ⁴O,N,N′,O′}‐μ‐nitrido‐1:2κ²N:N‐chromium(V)rhodium(I), [CrRh(C₁₆H₁₄N₂O₂)ClN(C₈H₁₂)]. The Cr—N bond of 1.5936 (14) Å is elongated by only 0.035 Å compared to the terminal Cr—N bond in the precursor. The nitride bridge is close to being linear [173.03 (9)°] and the Rh—N bond of 1.9594 (14) Å is very short for a monodentate nitrogen‐donor ligand, indicating significant π‐acceptor character of the Cr[triple‐bond]N group.     

An unusual partial occupancy of labile chloride and aqua ligands in cocrystallized isomers of a nickel(II) complex bearing a tripodal N4‐donor ligand

A novel Ni²⁺ complex with the N₄‐donor tripodal ligand bis[(1‐methyl‐1H‐imidazol‐2‐yl)methyl][2‐(pyridin‐2‐yl)ethyl]amine (L), namely, aqua{bis[(1‐methyl‐1H‐imidazol‐2‐yl‐κN³)methyl][2‐(pyridin‐2‐yl‐κN)ethyl]amine‐κN}chloridonickel(II) perchlorate, [NiCl(C₁₇H₂₂N₆)(H₂O)]ClO₄ or [NiCl(H₂O)(L)Cl]ClO₄ ( 1 ), was synthesized and characterized by spectroscopic and spectrometric methods. The crystal structure of 1 reveals an interesting and unusual cocrystallization of isomeric complexes, which are crystallographically disordered with partial occupancy of the labile cis aqua and chloride ligands. The Ni²⁺ centre exhibits a distorted octahedral environment, with similar bond lengths for the two Ni—N(imidazole) bonds. The bond length increases for Ni—N(pyridine) and Ni—N(amine), which is in agreement with literature examples. The bond lengths of the disordered labile sites are also in the expected range and the Ni—Cl and Ni—O bond lengths are comparable with similar compounds. The electronic, redox and solution stability behaviour of 1 were also evaluated, and the data obtained suggest the maintenance of structural integrity, with no sign of demetalation or decomposition under the studied conditions.     

Highly Active,Low‐Valence Molybdenum‐ and Tungsten‐Amide Catalysts for Bifunctional Imine‐Hydrogenation Reactions

The reactions of [M(NO)(CO)₄(ClAlCl₃)] (M=Mo, W) with (iPr₂PCH₂CH₂)₂NH, (PN^HP) at 90 °C afforded [M(NO)(CO)(PN^HP)Cl] complexes (M=Mo, 1a ; W, 1b ). The treatment of compound 1a with KOtBu as a base at room temperature yielded the alkoxide complex [Mo(NO)(CO)(PN^HP)(OtBu)] ( 2a ). In contrast, with the amide base Na[N(SiMe₃)₂], the PN^HP ligand moieties in compounds 1a and 1b could be deprotonated at room temperature, thereby inducing dehydrochlorination into amido complexes [M(NO)(CO)(PNP)] (M=Mo, 3a ; W, 3b ; PNP=(iPr₂PCH₂CH₂)₂N)). Compounds 3a and 3b have pseudo‐trigonal‐bipyramidal geometries, in which the amido nitrogen atom is in the equatorial plane. At room temperature, compounds 3a and 3b were capable of adding dihydrogen, with heterolytic splitting, thereby forming pairs of isomeric amine‐hydride complexes [Mo(NO)(CO)H(PN^HP)] ( 4a(cis) and 4a(trans) ) and [W(NO)(CO)H(PN^HP)] ( 4b(cis) and 4b(trans) ; cis and trans correspond to the position of the H and NO groups). H₂ approaches the Mo/W?N bond in compounds 3a , 3b from either the CO‐ligand side or from the NO‐ligand side. Compounds 4a(cis) and 4a(trans) were only found to be stable under a H₂ atmosphere and could not be isolated. At 140 °C and 60 bar H₂, compounds 3a and 3b catalyzed the hydrogenation of imines, thereby showing maximum turnover frequencies (TOFs) of 2912 and 1120 h^?1, respectively, for the hydrogenation of N‐(4 ‐ methoxybenzylidene)aniline. A Hammett plot for various para‐substituted imines revealed linear correlations with a negative slope of ?3.69 for para substitution on the benzylidene side and a positive slope of 0.68 for para substitution on the aniline side. Kinetics analysis revealed the initial rate of the hydrogenation reactions to be first order in c(cat.) and zeroth order in c(imine). Deuterium kinetic isotope effect (DKIE) experiments furnished a low k_H/k_D value (1.28), which supported a Noyori‐type metal–ligand bifunctional mechanism with H₂ addition as the rate‐limiting step.     

The Photochemistry of [FeIIIN3(cyclam‐ac)]PF6 at 266 nm

The photochemistry of iron azido complexes is quite challenging and poorly understood. For example, the photochemical decomposition of [Fe^IIIN₃(cyclam‐ac)]PF₆ ([ 1 ]PF₆), where cyclam‐ac represents the 1,4,8,11‐tetraazacyclotetradecane‐1‐acetate ligand, has been shown to be wavelength‐dependent, leading either to the rare high‐valent iron(V) nitrido complex [Fe^VN(cyclam‐ac)]PF₆ ([ 3 ]PF₆) after cleavage of the azide N_α? N_β bond, or to a photoreduced Fe^II species after Fe? N_azide bond homolysis. The mechanistic details of this intriguing reactivity have never been studied in detail. Here, the photochemistry of 1 in acetonitrile solution at room temperature has been investigated using step‐scan and rapid‐scan time‐resolved Fourier transform infrared (FTIR) spectroscopy following a 266 nm, 10 ns pulsed laser excitation. Using carbon monoxide as a quencher for the primary iron‐containing photochemical product, it is shown that 266 nm excitation of 1 results exclusively in the cleavage of the Fe? N_azide bond, as was suspected from earlier steady‐state irradiation studies. In argon‐purged solutions of [ 1 ]PF₆, the solvent‐stabilized complex cation [Fe^II(CH₃CN)(cyclam‐ac)]⁺ ( 2 red ) together with the azide radical (N₃^.) is formed with a relative yield of 80 %, as evidenced by the appearance of their characteristic vibrational resonances. Strikingly, step‐scan experiments with a higher time resolution reveal the formation of azide anions (N₃^?) during the first 500 ns after photolysis, with a yield of 20 %. These azide ions can subsequently react thermally with 2 red to form [Fe^IIN₃(cyclam‐ac)] ( 1 red ) as a secondary product of the photochemical decomposition of 1 . Molecular oxygen was further used to quench 1 red and 2 red to form what seems to be the elusive complex [Fe(O₂)(cyclam‐ac)]⁺ ( 6 ).     

Synthesis,Structure, and Reactivity of Hydridoiridium Complexes Bearing a Pincer‐Type PSiP Ligand

A series of iridium tetrahydride complexes [Ir(H)₄(PSiP‐R)] bearing a tridentate pincer‐type bis(phosphino)silyl ligand ([{2‐(R₂P)C₆H₄}₂MeSi]⁻, PSiP‐R, R=Cy, iPr, or tBu) were synthesized by the reduction of [IrCl(H)(PSiP‐R)] with Me₄N ⋅ BH₄ under argon. The same reaction under a nitrogen atmosphere afforded a rare example of thermally stable iridium(III)–dinitrogen complexes, [Ir(H)₂(N₂)(PSiP‐R)]. Two isomeric dinitrogen complexes were produced, in which the PSiP ligand coordinated to the iridium center in meridional and facial orientations, respectively. Attempted substitution of the dinitrogen ligand in [Ir(H)₂(N₂)(PSiP‐Cy)] with PMe₃ required heating at 150 °C to give the expected [Ir(H)₂(PMe₃)(PSiP‐Cy)] and a trigonal bipyramidal iridium(I)–dinitrogen complex, [Ir(N₂)(PMe₃)(PSiP‐Cy)]. The reaction of [Ir(H)₄(PSiP‐Cy)] with three equivalents of 2‐norbornene (nbe) in benzene afforded [Ir^I(nbe)(PSiP‐Cy)] in a high yield, while a similar reaction of [Ir(H)₄(PSiP‐R)] with an excess of 3,3‐dimethylbutene (tbe) in benzene gave the C H bond activation product, [Ir^III(H)(Ph)(PSiP‐R)], in high yield. The oxidative addition of benzene is reversible; heating [Ir^III(H)(Ph)(PSiP‐Cy)] in the presence of PPh₃ in benzene resulted in reductive elimination of benzene, coordination of PPh₃, and activation of the C H bond of one aromatic ring in PPh₃. [Ir^III(H)(Ph)(PSiP‐R)] catalyzed a direct borylation reaction of the benzene C H bond with bis(pinacolato)diboron. Molecular structures of most of the new complexes in this study were determined by a single‐crystal X‐ray analysis.     

Binuclear Aromatic C−H Bond Activation at a Dirhenium Site

The electronically unsaturated dirhenium complex [Re₂(CO)₈(μ‐H)(μ‐Ph)] ( 1 ) has been found to exhibit aromatic C?H activation upon reaction with N,N‐diethylaniline, naphthalene, and even [D₆]benzene to yield the compounds [Re₂(CO)₈(μ‐H)(μ‐η¹‐NEt₂C₆H₄)] ( 2 ), [Re₂(CO)₈(μ‐H)(μ‐η²‐1,2‐C₁₀H₇)] ( 3 ), and [D₆]‐ 1 , respectively, in good yields. The mechanism has been elucidated by using DFT computational analyses, and involves a binuclear C?H bond‐activation process.     

[Ni(terpy)(H2O)]‐trans‐[Ni‐(μ‐CN)2‐(CN)2]n,a one‐dimensional linear tetra­cyano­nickelate chain

The one‐dimensional chain catena‐poly­[[aqua(2,2′:6′,2′′‐terpyridyl‐κ³N)­nickel(II)]‐μ‐cyano‐κ²N:C‐[bis­(cyano‐κC)nickelate(II)]‐μ‐cyano‐κ²C:N], [Ni(terpy)(H₂O)]‐trans‐[Ni‐μ‐(CN)₂‐(CN)₂]_n or [Ni₂­(CN)₄­(C₁₅H₁₁N₃)(H₂O)], consists of infinite linear chains along the crystallographic [10] direction. The chains are composed of two distinct types of nickel ions, paramagnetic octahedral [Ni(terpy)(H₂O)]²⁺ cations (with twofold crystallographic symmetry) and diamagnetic planar [Ni(CN)₄]^2? anions (with the Ni atom on an inversion center). The [Ni(CN)₄]^2? units act as bidentate ligands bridging through two trans cyano groups thus giving rise to a new example of a trans–trans chain among planar tetra­cyano­nickelate complexes. The coordination geometry of the planar nickel unit is typical of slightly distorted octahedral nickel(II) complexes, but for the [Ni(CN)₄]^2? units, the geometry deviates from a planar configuration due to steric interactions with the ter­pyridine ligands.     

Syntheses and Structures of Coordination Polymers Constructed by Semi‐Rigid Bicarboxylic Acid Ligands

The complexes [Co(L¹)(mpy)] ( 1 ), [Ni(L¹)(mpy)] ( 2 ), [Co(L¹)(tbpy)] · 2H₂O ( 3 ), [Ni₂(L¹)₂(tbpy)₂] · 5H₂O ( 4 ), [Mn₂(L¹)₂(tbpy)₂] · 3H₂O ( 5 ), [Mn(L¹)(biim‐3)] ( 6 ), [Ni₂(L¹)₂(btb)₂(H₂O)] · 2H₂O ( 7 ), [Cu(L²)(mpy)] · 7H₂O ( 8 ), [Co(L²)(tbpy)(H₂O)] ( 9 ), [Ni(L²)(tbpy)(H₂O)] · H₂O ( 10 ), [Cu(L²)(bib)] · 2H₂O ( 11 ), and [Cu(L²)(btb)] · 2H₂O ( 12 ) [H₂L¹ = (3‐carboxyl‐phenyl)‐(4‐(2′‐carboxyl‐phenyl)‐benzyl)ether, H₂L² = 3‐carboxy‐1‐(4′‐carboxybenzyl)‐2‐oxidopyridinium, mpy = 2‐(4‐(4′‐methylphenyl)‐6‐(pyrindin‐2‐yl)pyridin‐2‐yl)pyridine), tbpy = 2‐(4‐(4′‐tert‐butylphenyl)‐6‐(pyrindin‐2‐yl)pyridin‐2‐yl)pyridine), biim‐3 = 1,3‐bis(imidazol‐1′‐yl)propane, btb = 1,4‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene, bib = 1,4‐bis(imidazol‐1′‐ylmethyl)benzene] were synthesized. Compounds 1 – 6 have similar 1D chain structures, which are further linked by π–π interactions to generate supramolecular double chains for 1 and 2 , and supramolecular layers for 3 – 6 . Compound 7 displays a 3D 6‐connected framework with (4⁴ · 6¹¹) topology. Compound 8 features a monomolecular structure, which is further linked by hydrogen bonds between the lattice water molecules and carboxylate oxygen atoms of L² anions to form a 2D supramolecular layer. The monomolecular structures of 9 and 10 are connected by hydrogen bonds and π–π interactions simultaneously to generate supramolecular layers. Compounds 11 and 12 show layer structures.     

Two nickel(II) bis[(pyridin‐2‐yl)methyl]amine complexes with homophthalic and benzene‐1,2,4,5‐tetracarboxylic acids

Two new Ni^II complexes involving the ancillary ligand bis[(pyridin‐2‐yl)methyl]amine (bpma) and two different carboxylate ligands, i.e. homophthalate [hph; systematic name: 2‐(2‐carboxylatophenyl)acetate] and benzene‐1,2,4,5‐tetracarboxylate (btc), namely catena‐poly[[aqua{bis[(pyridin‐2‐yl)methyl]amine‐κ³N,N′,N′′}nickel(II)]‐μ‐2‐(2‐carboxylatophenyl)aceteto‐κ²O:O′], [Ni(C₉H₆O₄)(C₁₂H₁₃N₃)(H₂O)]_n, and (μ‐benzene‐1,2,4,5‐tetracarboxylato‐κ⁴O¹,O²:O⁴,O⁵)bis(aqua{bis[(pyridin‐2‐yl)methyl]amine‐κ³N,N′,N′′}nickel(II)) bis(triaqua{bis[(pyridin‐2‐yl)methyl]amine‐κ³N,N′,N′′}nickel(II)) benzene‐1,2,4,5‐tetracarboxylate hexahydrate, [Ni₂(C₁₀H₂O₈)(C₁₂H₁₃N₃)₂(H₂O)₂]·[Ni(C₁₂H₁₃N₃)(H₂O)₃]₂(C₁₀H₂O₈)·6H₂O, (II), are presented. Compound (I) is a one‐dimensional polymer with hph acting as a bridging ligand and with the chains linked by weak C—H...O interactions. The structure of compound (II) is much more complex, with two independent Ni^II centres having different environments, one of them as part of centrosymmetric [Ni(bpma)(H₂O)]₂(btc) dinuclear complexes and the other in mononuclear [Ni(bpma)(H₂O)₃]²⁺ cations which (in a 2:1 ratio) provide charge balance for btc⁴⁻ anions. A profuse hydrogen‐bonding scheme, where both coordinated and crystal water molecules play a crucial role, provides the supramolecular linkage of the different groups.     

Facile P−C/C−H Bond‐Cleavage Reactivity of Nickel Bis(diphosphine) Complexes

Unusual cleavage of P?C and C?H bonds of the P₂N₂ ligand, in heteroleptic [Ni(P₂N₂)(diphosphine)]²⁺ complexes under mild conditions, results in the formation of an iminium formyl nickelate featuring a C,P,P‐tridentate coordination mode. The structures of both the heteroleptic [Ni(P₂N₂)(diphosphine)]²⁺ complexes and the resulting iminium formyl nickelate have been characterized by NMR spectroscopy and single‐crystal X‐ray diffraction analysis. Density functional theory (DFT) calculations were employed to investigate the mechanism of the P?C/C?H bond cleavage, which involves C?H bond cleavage, hydride rotation, Ni?C/P?H bond formation, and P?C bond cleavage.     

Physicochemical Characterization of Four Gadolinium(III) DTPA‐like Complexes

The analysis of ¹⁷O NMR transverse relaxation rates and EPR transverse electronic relaxation rates for aqueous solutions of the four DTPA‐like (DTPA = diethylenetriamine‐N,N,N′,N″,N″‐pentaacetic acid) complexes, [Gd(DTPA‐PY)(H₂O)]^? (DTPA‐PY = N′‐(2‐pyridylmethyl)), [Gd(DTPA‐HP)(H₂O)₂]^? (DTPA‐HP = N′‐(2‐hydroxypropyl)), [Gd(DTPA‐H1P)(H₂O)₂]^? (DTPA‐H1P = N′‐(2‐hydroxy‐1‐phenylethyl)) and [Gd(DTPA‐H2P)(H₂O)₂] (DTPA‐H2P = N′‐(2‐hydroxy‐2‐phenylethyl)), at various temperatures allows us to understand the water exchange dynamics of these four complexes. The water‐exchange lifetime (τM) parameters for [Gd(DTPA‐PY)(H₂O)]^?, [Gd(DTPA‐HP)(H₂O)₂]^?, [Gd(DTPA‐H1P)(H₂O)₂]^? and [Gd(DTPA‐H2P)(H₂O)₂] are of 585, 98, 163, and 69 ns, respectively. Compared with [Gd(DTPA)(H₂O)]^2? (τM = 303 ns), the τM value of [Gd(DTPA‐PY)(H₂O)]^? is slightly higher, but the other three complexes values are significantly lower than those of [Gd(DTPA)(H₂O)]^2?. This difference is explained by the fact that the gadolinium(III) complexes of DTPA‐HP, DTPA‐H1P, and DTPA‐H2P have two inner‐sphere waters. The ²H longitudinal relaxation rates of the labeled diamagnetic lanthanum complex allow the calculation of its rotational correlation time (τR). The τR values calculated for DTPA‐PY, DTPA‐HP, DTPA‐H1P, and DTPA‐H2P are of 127, 110, 142 and 147 ps, respectively. These four values are higher than the value of [La(DTPA)]^2? (τR = 103 ps), because the rotational correlation time is related to the magnitude of its molecular weight.     

Different intermolecular interactions in azido[2‐(diphenylphosphino)benzaldehyde semicarbazonato‐κ2P,N1,O]nickel(II)

The title compound, [Ni(C₂₀H₁₇N₃OP)(N₃)], is the first complex with a semicarbazide‐based ligand having a P atom as one of the donors. The influence of the P atom on the deformation of the coordination geometry of the Ni^II ion is evident but less expressed than in the cases of complexes with analogous seleno‐ and thiosemicarbazide ligands. The torsion angles involving the two bonds formed by the P atom within the six‐membered chelate ring have the largest values [C—P—Ni—N = 24.3 (2)° and C—C—P—Ni = −24.2 (4)°], suggesting that the P atom considerably influences the conformation of the ring. Two types of N—H...N hydrogen bond connect the complex units into chains.     

Synthesis,crystal structure and magnetic properties of (acetato‐κ2O,O′)bis(5,5′‐dimethyl‐2,2′‐bipyridine‐κ2N,N′)nickel(II) perchlorate monohydrate

The title hydrated ionic complex, [Ni(CH₃COO)(C₁₂H₁₂N₂)₂]ClO₄·H₂O or [Ni(ac)(5,5′‐dmbpy)₂]ClO₄·H₂O (where 5,5′‐dmbpy is 5,5′‐dimethyl‐2,2′‐bipyridine and ac is acetate), (1), was isolated as violet crystals from the aqueous ethanolic nickel acetate–5,5′‐dmbpy–KClO₄ system. Within the complex cation, the Ni^II atom is hexacoordinated by two chelating 5,5′‐dmbpy ligands and one chelating ac ligand. The mean Ni—N and Ni—O bond lengths are 2.0628 (17) and 2.1341 (15) Å, respectively. The water solvent molecule is disordered over two partially occupied positions and links two complex cations and two perchlorate anions into hydrogen‐bonded centrosymmetric dimers, which are further connected by π–π interactions. The magnetic properties of (1) at low temperatures are governed by the action of single‐ion anisotropy, D, which arises from the reduced local symmetry of the cis‐NiO₂N₄ chromophore. The fitting of the variable‐temperature magnetic data (2–300 K) gives g_iso = 2.134 and D/hc = 3.13 cm⁻¹.     

Hydrothermal Syntheses and Crystal Structures of Two Layered Nickel(II) Coordination Polymers Based on 1,2,3‐Benzenetricarboxylic Acid

The hydrothermal reactions of Ni(II), 1,2,3‐benzenetricarboxylic acid (1,2,3‐H₃btc) and 4,4′‐bipyridine (4,4′‐bpy)/1,2‐bis(4‐pyridyl)ethane (bpa) yield two layered nickel(II) coordination polymers, [Ni₂(1,2,3‐btc)(OAc)‐(4,4′‐bpy)₂(H₂O)]·2H₂O ( 1 ) and [Ni(ip)(bpa)] ( 2 ) (ip=isophthalate), respectively. Both complexes are 2‐D coordination network based on 1‐D Ni‐carboxylate chains. The 1,2,3‐btc ligand adopts 3‐bridging mode in complex 1 , but transformed to isophthalate (ip) ligand through decarboxylation in 2 . The formation of the two complexes indicates that hydrothermal conditions andin‐situ ligand reaction have significant effect on constructing coordination polymers.     

Assembly,Structures, and Properties of a Series of Metal‐Organic Coordination Polymers Derived from a Semi‐rigid Bis‐pyridyl‐bis‐amide Ligand

Four metal‐organic coordination polymers [Cd(4‐bpcb)_1.5Cl₂(H₂O)] ( 1 ), [Cd(4‐bpcb)_0.5(mip)(H₂O)₂] · 3H₂O ( 2 ), [Co(4‐bpcb)(oba)(H₂O)₂] ( 3 ), and [Ni(4‐bpcb)(oba)(H₂O)₂] ( 4 ) [4‐bpcb = N,N′‐bis(4‐pyridinecarboxamide)‐1, 4‐benzene, H₂mip = 5‐methylisophthalic acid, and H₂oba = 4, 4′‐oxybis(benzoic acid)] were synthesized under hydrothermal conditions and characterized by single‐crystal X‐ray diffraction, elemental analyses, IR spectroscopy, powder X‐ray diffraction, and TG analysis. In complex 1 , two Cl^– anions serve as bridges to connect two Cd‐(μ₁‐4‐bpcb) subunits forming a dinuclear unit, which are further linked by μ₂‐bridging 4‐bpcb to generate 1D zigzag chain. Complex 2 shows a 2D 6³ network constructed by [Cd‐mip]_n zigzag chains and μ₂‐bridging 4‐bpcb ligands. Complexes 3 and 4 are isostructural 2D (4, 4) grid networks derived from [M‐oba]_n (M = Co, Ni) zigzag chains and [M‐(4‐bpcb)]_n linear chains. The 1D chains for 1 and the 2D networks for 2 – 4 are finally extended into 3D supramolecular architectures by hydrogen bonding interactions. The roles of dicarboxylates and central metal ions on the assembly and structures of the target compounds were discussed. Moreover, the thermal stabilities, photoluminescent properties, and photocatalytic activities of complexes 1 – 4 and the electrochemical properties of complexes 3 and 4 were investigated.     

Tritopic NHC Precursors: Unusual Nickel Reactivity and Ethylene Insertion into a C(sp3)–H Bond

The imidazolium chloride [C₃H₃N(C₃H₆NMe₂)N{C(Me)(=NDipp)}]Cl ( 1 ; Dipp=2,6‐diisopropyl phenyl), a potential precursor to a tritopic N^imineC^NHCN^amine pincer‐type ligand, reacted with [Ni(cod)₂] to give the Ni^I‐Ni^I complex 2 , which contains a rare cod‐derived η³‐allyl‐type bridging ligand. The implied intermediate formation of a nickel hydride through oxidative addition of the imidazolium C−H bond did not occur with the symmetrical imidazolium chloride [C₃H₃N₂{C(Me)(=NDipp)}₂]Cl ( 3 ). Instead, a Ni−C(sp³) bond was formed, leading to the neutral N^imineCHN^imine pincer‐type complex Ni[C₃H₃N₂{C(Me)(=NDipp)}₂]Cl ( 4 ). Theoretical studies showed that this highly unusual feature in nickel NHC chemistry is due to steric constraints induced by the N substituents, which prevent Ni−H bond formation. Remarkably, ethylene inserted into the C(sp³)−H bond of 4 without nickel hydride formation, thus suggesting new pathways for the alkylation of non‐activated C−H bonds.     

[N,N′‐Bis­(salicyl­idene)‐2,2‐di­methyl‐1,3‐propane­diaminato]­nickel(II) and [N,N′‐bis­(salicyl­idene)‐2,2‐di­methyl‐1,3‐propane­diaminato]copper(II)

In the title compounds, {2,2′‐[2,2‐di­methyl‐1,3‐propane­diyl­bis­(nitrilo­methyl­idyne)]­diphenolato‐κ⁴N,N′,O,O′}nickel(II), [Ni(C₁₉H₂₀N₂O₂)], and {2,2′‐[2,2‐di­methyl‐1,3‐propane­diyl­bis­(nitrilo­methyl­idyne)]­diphenolato‐κ⁴N,N′,O,O′}copper(II), [Cu(C₁₉H₂₀N₂O₂)], the Ni^II and Cu^II atoms are coordinated by two iminic N and two phenolic O atoms of the N,N′‐bis­(salicyl­idene)‐2,2‐di­methyl‐1,3‐propane­diaminate (SALPD^2?, C₁₇H₁₆N₂O₂^2?) ligand. The geometry of the coordination sphere is planar in the case of the Ni^II complex and distorted towards tetrahedral for the Cu^II complex. Both complexes have a cis configuration imposed by the chelate ligand. The dihedral angles between the N/Ni/O and N/Cu/O coordination planes are 17.20 (6) and 35.13 (7)°, respectively.     

Controlled Synthesis of Heterotrimetallic Single‐Chain Magnets from Anisotropic High‐Spin 3 d–4 f Nodes and Paramagnetic Spacers

By using the node‐and‐spacer approach in suitable solvents, four new heterotrimetallic 1D chain‐like compounds (that is, containing 3d–3d′–4f metal ions), {[Ni(L)Ln(NO₃)₂(H₂O)Fe(Tp*)(CN)₃] ? 2 CH₃CN ? CH₃OH}_n (H₂L=N,N′‐bis(3‐methoxysalicylidene)‐1,3‐diaminopropane, Tp*=hydridotris(3,5‐dimethylpyrazol‐1‐yl)borate; Ln=Gd ( 1 ), Dy ( 2 ), Tb ( 3 ), Nd ( 4 )), have been synthesized and structurally characterized. All of these compounds are made up of a neutral cyanide‐ and phenolate‐bridged heterotrimetallic chain, with a {? Fe? C?N? Ni(? O? Ln)? N?C? }_n repeat unit. Within these chains, each [(Tp*)Fe(CN)₃]^? entity binds to the Ni^II ion of the [Ni(L)Ln(NO₃)₂(H₂O)]⁺ motif through two of its three cyanide groups in a cis mode, whereas each [Ni(L)Ln(NO₃)₂(H₂O)]⁺ unit is linked to two [(Tp*)Fe(CN)₃]^? ions through the Ni^II ion in a trans mode. In the [Ni(L)Ln(NO₃)₂(H₂O)]⁺ unit, the Ni^II and Ln^III ions are bridged to one other through two phenolic oxygen atoms of the ligand (L). Compounds 1 – 4 are rare examples of 1D cyanide‐ and phenolate‐bridged 3d–3d′–4f helical chain compounds. As expected, strong ferromagnetic interactions are observed between neighboring Fe^III and Ni^II ions through a cyanide bridge and between neighboring Ni^II and Ln^III (except for Nd^III) ions through two phenolate bridges. Further magnetic studies show that all of these compounds exhibit single‐chain magnetic behavior. Compound 2 exhibits the highest effective energy barrier (58.2 K) for the reversal of magnetization in 3d/4d/5d–4f heterotrimetallic single‐chain magnets.