Stefan D. Nogai

Tetrazolyl and tetrazolylidene complexes of gold: a synthetic and structural study

Lithiation of 1-benzyl-1H-tetrazole followed by transmetallation with [AuCl(PPh3)], [Au(C6F5)(tht)] or [AuCl(tht)] (tht = tetrahydrothiophene) and subsequent alkylation afforded cationic 1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene(triphenylphosphine)gold(I), 1, neutral 1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene(pentafluorophenyl)gold(I), 2, and a cationic biscarbene complex, bis(1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene)gold(I), 3. The first complex underwent a homoleptic rearrangement in solution to form 3. Reaction of [Au(N3)PPh3] with the three isocyanides (CH3)2C6H3NC, tBuNC and CyNC, respectively, yielded the corresponding neutral tetrazolyl(phosphine) complexes of gold, [1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(I), 4, [1-(tert-butyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(I), 6, and [1-(cyclohexyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(I), 7. Alkylation of 4 with methyl triflate on N4 allowed isolation of the crystalline carbene complex 1-(2,6-dimethylphenyl)-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene)(triphenylphosphine)gold(I), 5. Complex 7 was not isolable in pure form but converts by isocyanide substitution of triphenylphosphine into [1-cyclohexylisocyanide][1-(cyclohexyl)-1H-tetrazol-5-yl]gold(I), 8. From a product mixture of 7 and 8 the transformed molecules [(cyclohexylamino)(ethoxy)carbene](1-cyclohexyl-1H-tetrazol-5-yl)gold(I), 9, and [bis(cyclohexylamino)carbene](1-cyclohexyltetrazol-5-yl)gold(I), 10, co-crystallised spontaneously after a long time at −20 °C.

Preparation of tris(azolyl)phosphine gold(I) complexes: digold(I) coordination and variation in solid state intermolecular interactions

Various tris(azolyl)phosphines R3P (R = 1-methylimidazol-2-yl, thiazol-2-yl, 4-methylthiazol-2-yl or 4,5-dimethylthiazol-2-yl) (1a–d) were utilised to prepare complexes of the type R3PAuCl (2a–d). The donor strength of the nitrogen atoms was assessed with natural-abundance 15N{1H} NMR of 1a–c and 2a–c. The chloride of 2c could be successfully substituted by the anions BzS– and NCS–. Further utilisation of the imine nitrogens of the tris(azole)phosphines to coordinate additional AuI centres was successful only for 2a where treatment with 3 mole equivalents of C6F5Au(tht) (tht = tetrahydrothiophene) afforded bis(pentafluorophenyl)-µ-[tris(1-methylimidazol-2-yl)phosphine-κ2P,N]digold(I) (4). A hydrolysis product consisting of two bis(1-methylimidazol-2-yl)phosphinite ligands bridging a Au24+ centre and further coordination to two AuC6F5 moieties (5) was formed during this reaction. The crystal and molecular structures were determined of compounds 1d, 2a–d and 3b. Intriguingly, 2b and 2c crystallise in a total of seven polymorphs and solvates exhibiting different modes of intermolecular association. Compound 2b crystallises in three polymorphs; two of them and the solvate 2b·0.5CH2Cl2 exhibit aurophilic interaction while the third one is stabilised by a short Au⋯Cl interaction of 3.2660(9) A. In 2c, one polymorph exhibits a strong aurophilic interaction of 3.0393(4) A, but the other, as well as the solvate 2c·thf, lack such contacts. Product 2b is the first simple gold compound known to have both Au⋯Au or Au⋯Cl contacts in different crystals. Calculations at the B3LYP and MP2 levels of theory using quasi-relativistic basis sets show that for 2b2 the Au⋯Cl interaction is between 2.6 and 12.2 kJ mol–1 greater than the Au⋯Au interaction, depending on the level of theory and basis set. This contrasts with a model (PH3AuCl)2 dimer, where the Au⋯Au interaction is found to be stronger.

1,3-Dimesitylimidazolidinium tetra-chloridogold(III) dichloro-methane solvate

The title ionic compound, (C21H27N2)[AuCl4]·CH2Cl2, was obtained from the reaction of 1,3-dimesitylimidazolidinium chloride with t-BuOK and a solution of AuCl3 in tetrahydrofuran. In the crystal structure, numerous weak C—H⋯Cl hydrogen bonds form double layers parallel to (100), which are further stabilized by π–π interactions between mesitylene rings [centroid–centroid distance = 4.308 (4) Å], resulting in the formation of a three-dimensional supramolecular assembly.

Titanoxycarbene complexes of Ti(IV) with O- and N-donor ligands

Heterobimetallic complexes of the general formula [{(OC)5MC(Me)OTi(OiPr)2}(µ-OiPr)]2 with M = Cr (1), W (2) were synthesized by reacting (OC)5MC(Me)OLi (M = Cr, W) with ClTi(OiPr)3. X-Ray crystallography revealed dimeric molecular structures based on four-membered Ti2O2-rings for both compounds. Most intriguingly crystals of 1 virtually “shattered” upon cooling below −60 °C. Treatment of 1 and 2 with an excess of pyridine did not effect symmetric cleavage of the dimers, but afforded the unique rearrangement products [(OC)5MC(Me)O]2Ti(OiPr)2(C5H5N)2 with M = Cr (3) and W (4). The isomorphous structures, determined by means of X-ray diffraction, are only the second examples of an unrestrained titanium center coordinated by four OR and two N-donor ligands. Complexes 3 and 4 were also accessible from Cl2Ti(OiPr)2(C5H5N)2 (5) and (OC)5MC(Me)OLi. Owing to the inherent dynamic behaviour of all complexes, low-temperature NMR studies were undertaken. The formation of nanoparticles upon thermolysis of complex 2 lends support to the notion that the presented (or related) compounds could be useful as single source precursors for nano-sized mixed metal oxides or oxo nitrides.

1,1,2,2-Tetra­kis(1,3-benzoxazol-2-yl)ethene

The title compound, C30H16N4O4, reveals crystallographic and molecular symmetry and accordingly the asymmetric unit comprises one half-molecule. The dihedral angle between the planes of the two geminal benzoxazole rings is 74.39 (5)°. The packing features weak C—H⋯N and π–π interactions [centroid–centroid distance = 3.652 (1) Å].

1,1,2,2-Tetra-kis(1,3-benzothia-zol-2-yl)ethene chloro-form disolvate.

The asymmetric unit of the title solvate, C30H16N4S4·2CHCl3, contains one half-molecule of tetrakis(2-benzothiazolyl)ethene, the complete molecule being generated by inversion symmetry, and one molecule of chloroform. Pairs of the benzothiazole rings attached to the same carbon atom are almost perpendicular to each other, with an angle between planes of 85.74 (4)°. In the crystal, weak C—H⋯N and C—H⋯Cl interactions generate a three-dimensional network.

1,3-Benzothia­zolium tetra­chlorido­aurate(III) tetra­hydro­furan solvate

In the crystal structure of the title ionic compound (C7H6NS)[AuCl4]·C4H8O, the [AuCl4]− anion shows a typical square-planar geometry. Numerous weak C—H⋯Cl hydrogen bonds between [AuCl4]− and the 1,3-benzothiazolium units form layers comprised of 24-membered rings in which hydrogen-bonded tetrahydrofuran (THF) solvent molecules are accommodated. C—H⋯Cl interactions between THF and [AuCl4]− from adjacent layers result in bilayers. These are further stabilized by π–π interactions between the thiazole and benzene rings [centroid–centroid distance = 3.971 (3) Å], resulting in the formation of a three-dimensional supramolecular assembly.