Design and synthesis of versatile ligand precursors based on phosphonium ylides for palladalactam formation and catalytic investigation.

A new series of ligand precursors designed for the synthesis of palladalactams has been developed. These precursors are easily accessible through a one-step reaction involving 2-chloro-N-phenylacetamide and a wide choice of various monophosphines, offering tunable electronic and steric properties within the ligand framework. The stability of both ligand precursors and resulting palladalactams in ambient air enhances their practical applicability. A newly synthesized palladalactam, featuring an electron-donating triethylphosphine moiety on the anionic phosphonium ylide ligand scaffold exhibited promising catalytic activities in the Mizoroki-Heck coupling reaction between aryl chlorides and alkenes. Theoretical calculations further affirmed that the ligand system in the complex is the most electron-donating, forming the strongest Pd-C bond compared to other complexes with alternative phosphine moieties.

Nitron-derivative-based palladium carbene complexes: structural characterization, theoretical calculations, and catalytic applications in the Mizoroki-Heck coupling reaction.

New palladium(0) and palladium(ii) complexes with N-heterocyclic carbene (NHC) ligands derived from nitron and its derivatives were synthesized. The structures of most of these complexes were established by single-crystal X-ray diffraction studies. Among the new complexes, the palladium complex with a monodentate NHC ligand derived from nitron demonstrated the highest efficacy as a catalyst precursor in the Mizoroki-Heck coupling reaction of aryl chlorides with alkenes. Theoretical calculations provide valuable insights into the electronic parameters of both the ligands and the palladium complexes, highlighting the significance of a robust Pd-C bond and the π-accepting property of the NHC ligand in achieving enhanced catalytic activity. Notably, catalyst activation occurred much more rapidly with the preformed palladium(0) complex compared to its palladium(ii) counterpart.

Direct arylation reaction catalyzed by a PEPPSI-type palladium complex with an amido-functionalized triazole-based mesoionic carbene ligand.

Ligand precursors for amido/amidate-functionalized triazole-based MIC ligands were synthesized. An initial theoretical calculation confirmed that triazole-based MIC ligands were promising ligands in terms of their σ-donating and π-acidic properties. Based on these ligand precursors, three different types of palladium complexes were successfully obtained, namely (1) a PEPPSI-type MIC complex, (2) a complex containing both a bidentate ligand of a MIC and an amidate donor and a mondentate NHC derived from nitron, and (3) a complex featuring a tridentate ligand of a MIC, an amidate, and a phenoxy donor. The structures of all these complexes were established by single-crystal X-ray diffraction studies. Imidazole derivatives are important heterocycles with enormous medicinal value. The catalytic activities of these new palladium complexes in the green direct C-H arylation of imidazoles with aryl halides were investigated and compared to those delivered from palladium complexes with IMes and triazole-based normal NHC ligands. Among the new complexes, the PEPPSI-type palladium complex with the monodentate triazole-based MIC ligand was found to be a very promising precatalyst which was capable of utilizing electron-deficient aryl chlorides as coupling partners in the reaction.

Nickel(II) complexes containing tridentate ONCi ligands (i = abnormal N-heterocyclic carbene donors) and their catalytic application in Suzuki-Miyaura coupling reaction.

New nickel complexes with tridentate phenoxy-amidate-aNHC donor groups were synthesized from the reactions between nickel acetate and imidazolium ligand precursors in net pyridine. An unusual degradation pathway was observed, leading to imidazole derivatives occupying the fourth coordination sites in these square planar complexes. A new imidazole-coordinated nickel complex was found to be efficient in catalyzing Suzuki-Miyaura cross-coupling with aryl chlorides under 3 mol% of catalyst loading. The catalytic activities were superior to those of its reported normal NHC counterpart. Instead of the common procedure of using additional phosphine, the addition of IMes·HCl significantly enhances the product yields of the catalytic reaction.

Mono- and dinuclear oxidovanadium(v) complexes of an amine-bis(phenolate) ligand with bromo-peroxidase activities: synthesis, characterization, catalytic, kinetic and computational studies.

The mono- and dinuclear oxidovanadium(v) complexes [VVO(L1)(Cl)] (1) and [L1VVO(µ2-O)VO(L1)] (2) of ONNO donor amine-bis(phenolate) ligand (H2L1) were readily synthesized by the reaction between H2L1 and VCl3.(THF)3 or VO(acac)2 in MeOH or MeCN, respectively, and then characterized through mass spectroscopy, 1H-NMR and FTIR techniques. Both the complexes possess distorted octahedral geometry around each V centre. Upon the addition of 1 equivalent or more acid to a MeCN solution of complex 1, it immediately turned into the protonated form, which might be in equilibrium as: [L1ClVV[double bond, length as m-dash]OH]+ ↔ [L1ClVV-OH]+ (in the case of [L1ClVV[double bond, length as m-dash]OH]+ oxo-O is just protonated, whereas in [L1ClVV-OH]+ it is a hydroxo species), with the shift in λmax from 610 nm to 765 nm. Similar was the case for complex 2. The complexes 1 and 2 could efficiently catalyze the oxidative bromination of salicylaldehyde in the presence of H2O2 to produce 5-bromo salicylaldehyde as the major product with TONs of 405 and 450, respectively, in the mixed solvent system (H2O : MeOH : THF = 4 : 3 : 2, v/v). The kinetic analysis of the bromide oxidation reaction indicated a first-order mechanism in the protonated peroxidovanadium complex and a bromide ion and limiting first-order mechanism on [H+]. The evaluated kBr and kH values were 5.78 ± 0.20 and 11.01 ± 0.50 M-1 s-1 for complex 1 and 6.21 ± 0.13 and 20.14 ± 0.72 M-1 s-1 for complex 2, respectively. The kinetic and thermodynamic acidities of the protonated oxido species of complexes 1 and 2 were pKa = 2.55 (2.35) and 2.16 (2.19), respectively, which were far more acidic than those reported by Pecoraro et al. for peroxido-protonation instead of oxido protonation. On the basis of the chemistry observed for these model compounds, a mechanism of halide oxidation and a detailed catalytic cycle are proposed for the vanadium haloperoxidase enzyme and these were substantiated by detailed DFT calculations.

Well-defined palladium(0) complexes bearing N-heterocyclic carbene and phosphine moieties: efficient catalytic applications in the Mizoroki-Heck reaction and direct C-H functionalization.

Two series of well-defined palladium(0) complexes with phosphine-functionalized N-heterocyclic carbene ligands were prepared. These complexes featured six- and seven-membered chelate rings in the two series. Among the seven-membered chelate complexes, those featuring the PCy2 moiety exhibited observable fluxional behavior on the NMR time scale, corresponding to the interchange between two sets of conformations. Most of these novel complexes were successfully structurally characterized by single-crystal X-ray diffraction studies. These two series of palladium(0) complexes were tested for their potential catalytic applications in two mechanistically distinct reactions, namely, Mizoroki-Heck coupling and direct C-H functionalization reactions. One of the six-membered chelate complexes was found to be an efficient pre-catalyst for mediating the coupling reactions between aryl chlorides and alkenes. The palladium(0) complex could also be effectively applied in the direct C-H functionalization reactions of aryl bromides with 1,2-dimethylimidazole.

1-(10-Bromo-anthracen-9-yl)-1H-imidazole.

In the title mol-ecule, C17H11BrN2, the planes of the anthracene ring system [maximum deviation from the mean plane = 0.036 (3) Å] and the imidazole ring form a dihedral angle of 85.14 (14)°. In the crystal, weak C-H⋯N and C-H⋯Br hydrogen bonds link the mol-ecules into double chains propagating along [01-1]. In addition, π-π stacking inter-actions between pairs of benzene rings are observed, with centroid-centroid distances of 3.7968 (17) and 3.8496 (16) Å.

One-step synthesis of isocoumarins and 3-benzylidenephthalides via ligandless Pd-catalyzed oxidative coupling of benzoic acids and vinylarenes.

A straightforward synthetic method for the preparation of isocoumarins and 3-benzylidenephthalides via C-H olefination and oxidative coupling of readily available benzoic acids and vinylarenes was developed. The directing effect of the substituents on the benzoic acid allows for the synthesis of both types of lactone in pure form.

Efficient Pd-catalyzed direct arylations of heterocycles with unreactive and hindered aryl chlorides.

A highly electron-rich Pd complex can efficiently catalyze the direct arylation of heteroaromatics with unreactive and sterically congested aryl chlorides.

Pd(0)-catalyzed decarboxylative coupling and tandem C-H arylation/decarboxylation for the synthesis of heteroaromatic biaryls.

An effective Pd(0) carbene complex was successfully employed in the decarboxylative coupling of the heteroaromatic carboxylic acids (imidazo[1,2-a]pyridine and isoxazole) with aryl halides. For carboxyindoles, either decarboxylative coupling or tandem C-H arylation and decarboxylation occurred, leading to the formation of C2-monoarylated indoles.

N-[2-(Methyl-sulfan-yl)phen-yl]-2-sulfanylbenzamide.

In the title compound, C(14)H(13)NOS(2), the S atom with the methyl group is involved in an intra-molecular hydrogen bond with the amido H atom. In the crystal, the sulfanyl H atoms form inter-molecular hydrogen bonds with the O atoms, connecting the mol-ecules into zigzag chains along the c axis. The two aromatic rings exhibit a small interplanar angle of 16.03 (9)°.

N,N'-Bis[(1H-imidazol-1-yl)meth-yl]-2,2'-(disulfanedi-yl)dianiline.

The symmetrical title compound, C(20)H(20)N(6)S(2), contains a disulfide bond of 2.0884 (6) Å. The C-S-S-C torsion angle is -59.57 (7)°. In the crystal, classical N-H⋯N and non-classical C-H⋯N hydrogen bonds link the compounds into chains along the a axis.

1,3-Bis(2-anilino-2-oxoeth-yl)-1H-imidazol-3-ium chloride.

In the cation of the title salt, C(19)H(19)N(4)O(2) (+)·Cl(-), the dihedral angles between the imidazole ring and the phenyl rings are 70.39 (8) and 86.26 (9)°. The chloride anion inter-acts with the cation through an N-H⋯Cl hydrogen bond. In the crystal, classical N-H⋯O hydrogen bonds link the cations into chains parallel to the b axis. Non-classical C-H⋯Cl and C-H⋯O hydrogen bonds further connect the chains into a three-dimensional network.

Formation of CC-type palladacycles with assistance from an apparently innocent NH(CO) functional group.

A novel cyclometalation pathway to form CC-type palladacycles is reported. Unlike common donor-assisted cyclometalation, the NH(CO) auxiliary group undergoes a deprotonation step to form a palladalactam intermediate. The coordinating nitrogen atom functions as an intramolecular base promoting selective C-H bond cleavage. Without the NH proton, the ortho-N-phenyl C-H is activated instead.

An order-disorder phase transition in the structure of C60·4benzene.

A reversible, broad, order-disorder phase transition in the structure of C(60)·4benzene has been observed to take place with an inflection point at 134 K. In the low-temperature structure fullerene disorder is removed, although the average atomic displacement parameters differ for the two C(60) molecules in the asymmetric unit. Some benzene disorder persists, even at 13 K.

1,3-Bis(2-anilino-2-oxoeth-yl)-1H-imidazol-3-ium chloride dimethyl-formamide monosolvate.

In the imidazolium cation of the title compound, C19H19N4O2(+)·Cl(-)·C3H7NO, the dihedral angles between the imidazole ring and the phenyl rings are 85.86 (4) and 70.26 (5)°. In the crystal, N-H⋯Cl hydrogen bonds link the imdiazo-lium cations and chloride anions into zigzag chains along [110] and together with C-H⋯Cl and C-H⋯O hydrogen bonds, which involve also the dimethyl-formamide solvent mol-ecule, form a two-dimensional network extending across the ab plane.

1,3-Bis(2-anilino-2-oxoeth-yl)-1H-imidazol-3-ium chloride acetonitrile monosolvate.

In the title compound, C(19)H(19)N(4)O(2) (+)·Cl(-)·C(2)H(3)N, the dihedral angle between the two phenyl rings is 69.57 (8)° while the dihedral angles between the imidazole ring and the phenyl rings are 70.61 (7) and 82.11 (7)°. In the crystal, N-H⋯Cl, C-H⋯O, C-H⋯Cl and C-H⋯N hydrogen bonds link the imidazolium cations, chloride anions and acetonitrile solvent mol-ecules into a two-dimensional hydrogen-bonded network parallel to (001); an intra-molecular C-H⋯O hydrogen bond is also observed.

3,3'-Bis(3-meth-oxy-benz-yl)-1,1'-(ethane-1,2-diyl)-diimidazolium dibromide dihydrate.

In the title compound, C(24)H(28)N(4)O(2) (2+)·2Br(-)·2H(2)O, the diimid-azo-lium cation is located on an inversion center. The imidazole and the benzene rings make a dihedral angle of 68.08 (04)°. In the crystal, O-H⋯Br, C-H⋯O and C-H⋯Br hydrogen bonds link the diimidazolium cations, the bromide anions and the water mol-ecules into a two-dimensional network.

trans-Bis[1-(2-anilino-2-oxoeth-yl)-3-benzyl-1H-imidazol-2-yl]palladium(II) methanol disolvate.

In the title compound, [Pd(C(18)H(16)N(3)O)(2)]·2CH(3)OH, the Pd(II) atom is located on a crystallographic inversion center. It has a square-planar coordination geometry, with the two bidentate ligands coordinated in a trans fashion via the carbene C atom and the amido N atoms. The methanol solvent mol-ecules form O-H⋯O hydrogen bonds with the complex. Additional non-classical inter-molecular C-H⋯O hydrogen bonds link the complexes into a two-dimensional network parallel to (001).