Aytaç Gürhan Gökçe

N-benzyl substituted N-heterocyclic carbene complexes of iridium(I): assessment in transfer hydrogenation catalyst.

Iridium(I) complexes of N-heterocyclic carbenes (NHCs) (1a-3a) were obtained by transmetalation reactions from the corresponding Ag(I)-NHC complexes. These complexes have been fully characterized by (1)H, (13)C, heteronuclear multiple-bond correlation NMR spectroscopies, and elemental analysis. X-ray diffraction studies on single crystals of 1a and 2a confirm the square planar geometry at the metal center. [IrCl(CO)2(NHC)] complexes 1b-3b were also synthesized to compare σ-donor/π-acceptor strength of NHC ligands. Transfer hydrogenation (TH) reactions of various ketones and imines have been studied using complexes 1a-3a as precatalysts. N-Benzyl substituted NHC complexes of Ir(I) proved to be highly efficient precatalysts in the reduction of aromatic and aliphatic ketones to afford the corresponding alcohol products with turnover frequencies values up to 24,000 h(-1).

Hydroxyl and ester functionalized N-heterocyclic carbene complexes of iridium(I): efficient catalysts for transfer hydrogenation reactions†

Hydroxyl and ester-functionalized iridium(I) complexes of N-heterocyclic carbenes (3a–e) were obtained by transmetalation reactions from the in situ prepared silver(I)–NHC complexes and characterized by IR, NMR, mass spectroscopies, and elemental analysis. X-ray diffraction studies on single crystals of 3a, 3c and 3d verify the square planar geometry at the iridium center. Ester functionalized iridium(I)–NHC complexes were found to be highly active and selective catalysts for the transfer hydrogenation reactions of various aldehydes and ketones. The influence of different ester substituents on the reactivity of the complexes was studied and the complex with a pivaloyl substituent (3d) showed the best activity (TON up to 10 000).

The synthesis and structural characterization of a N -heterocyclic carbene-substituted palladacycle

Reaction of {[Pd(dmba)(μ-Cl)]2} (dmba = (CH3)2NCH2C6H4) with an in situ generated N-heterocyclic carbene (NHC = 1,3-dimesitylimidazolidin-2-ylidene) afforded crystals containing [chloro-(1,3-dimesitylimidazolidin-2-ylidene)(N,N-dimethylaminobenzyl-C1,N)palladium(II)] (VII). Molecular and crystal structures of the title compound have been determined by single crystal X-ray diffraction technique. Complex VII crystallizes in space group P 1, with a = 13.685(3) Å, b = 13.590(2) Å, c = 16.229(3) Å, α = 87.162(13)°, β = 70.514(15)°, γ = 84.153(16)°, Z = 4, D Calcd = 1.367 g cm−3. There are two independent molecules in the asymmetric unit.

trans-Bis[1-benzyl-3-(2,3,4,5,6-pentafluorobenzyl)benzimidazol-2-ylidene]dibromopalladium(II).

The title compound, [PdBr2(C21H13F5N2)2], crystallizes with two independent centrosymmetric conformational isomers having a square-planar coordination at the Pd atom. The conformational isomers differ by the ligands having a cis or trans orientation of their benzyl and pentafluorobenzyl rings with respect to the benzimidazole ring plane. The benzimidazole rings are rotated with respect to the coordination plane of the metal by 79.1 (2) and 75.2 (1) degrees for molecules A and B, respectively. The Pd-Br bond lengths are 2.4218 (8) and 2.4407 (10) A for molecules A and B, respectively, and the Pd-C bond lengths are 2.030 (8) and 2.018 (9) A. The crystal structure contains two types of C-H...F and one type of C-H...Br intramolecular contact, as well as C-H...pi interactions.

The two‐dimensional coordination polymer poly[[bis(3‐methyl­pyridine)­cadmium(II)]‐tetra‐μ‐cyano‐nickel(II)]

The title complex, [CdNi(CN)4(C6H7N)2]n, adopts a slightly distorted octahedral geometry around the Cd centre. Four cyanide N atoms occupy the equatorial coordination sites around the Cd centre. The structure consists of corrugated and cyanide-bridged polymeric networks made up of tetracyanonickelate ions coordinated to cadmium, with the Ni ion coordinated by four cyanide ligands in a square-planar arrangement. The Cd and Ni atoms occupy special positions of 2/m site symmetry. The 3-methylpyridine group, except for two methyl H atoms, lies on a crystallographic mirror plane. The 3-methylpyridine molecules, bound to cadmium in trans positions, are located on both sides of the network. The bonding in the networks occurs because of a departure of the Ni-C-N-Cd sequence of atoms from linearity at the C and N atoms.

Adsorption of alkali and alkaline earth metal atoms and dimers on monolayer germanium carbide

First-principles plane wave calculations have been performed to study the adsorption of alkali and alkaline earth metals on monolayer germanium carbide (GeC). We found that the favourable adsorption sites on GeC sheet for single alkali and alkaline earth adatoms are generally different from graphene or germanene. Among them, Mg, Na and their dimers have weakly bounded to GeC due to their closed valence electron shells, so they may have high mobility on GeC. Two different levels of adatom coverage ( and ) have been investigated and we concluded that different electronic structures and magnetic moments for both coverages owing to alkali and alkaline earth atoms have long range electrostatic interactions. Lithium atom prefers to adsorbed on hollow site similar to other group-IV monolayers and the adsorption results in metallisation of GeC instead of semiconducting behaviour. Na and K adsorption can induce 1 total magnetic moment on GeC structures and they have shown semiconductor property which may have potential use in spintronic devices. We also showed that alkali or alkaline earth metal atoms can form dimer on GeC sheet. Calculated adsorption energies suggest that clustering of alkali and alkaline earth atoms is energetically favourable. All dimer adsorbed GeC systems have nonmagnetic semiconductor property with varying band gaps from 0.391 to 1.311 eV which are very suitable values for various device applications.

Synthesis and Structural Characterization of trans-Bis[1,3-bis(methoxyethyl)- 4,5-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene]dichloropalladium( II)

A Pd(II) complex of a new N-heterocyclic carbene (NHC) ligand with bulky substituents and functionalized methoxy-donor side arms has been synthesized and characterized by elemental analyses, 1H and 13C NMR, and IR spectroscopy. Molecular and crystal structures of the title complex have been determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P21/c, with a = 15.927(2), b = 8.489(2), c = 20.309(5) Å, β = 99.213(2)°, Z = 2, Dx = 1.253 g cm−3. The palladium atom is situated on an inversion center. There are several weak intramolecular C-H ··· N/O interactions.

Supramolecular structure of racemic 5-hydroxy-4-(4-methoxyphenyl)-10-oxa-4-azatricyclo[5.2.1.0^2,6^]dec-8-en-3-one

The structure of the title compound, C(15)H(15)NO(4), comprises a racemic mixture of chiral molecules containing five stereogenic centres. The cyclohexane ring tends towards a boat conformation and the two tetrahydrofuran rings adopt envelope conformations. Molecules are linked into sheets parallel to (100) by a combination of O-H...O, C-H...O and C-H...pi hydrogen bonds, leading to a two-dimensional supramolecular structure.