Synthesis of substituted oligothiophenes and X-ray crystal structures of 3'-methyl-22' :5'2'' - terthiophene and 5'-(2-thienyl)-22' :3'2''-terthiophene

A range of substituted oligothiophenes has been prepared and characterised. Crystal structures were determined for three substituted terthiophenes. Both in solution and in the solid state, syn-conformers were found to be populated to a greater extent than expected

Synthesis and structural determination of the stable dinuclear carbonyl-phosphite rhodium(0) complex: (CO)2(P(O-o-tBuPh)3)Rh-Rh(P(O-o-tBuPh)3)(CO)3

[Rh(μ-OMe)(COD)]2 reacts with tris-ortho-tert-butylphenylphosphite in the presence of carbon monoxide to provide the first example of a stable dinuclear carbonyl-phosphite rhodium(0) complex with a metal–metal bond distance of 2.73(1) Å. The geometry at the metals is different: square planar and distorted trigonal bipyramid. The crystallographic data indicate that two of the carbonyl ligands are semi-bridged between the two rhodium atoms

Group 9 metal 1,1′-bis(phosphino)ferrocene complexes: synthesis, structures, solution conformation and unusual reactivity

The crystal structure of [Ir(cod)(L–L)]+3[cod = cycloocta-1,5-diene, L–L = 1-(diisopropylphosphino)-1′-(diphenylphosphino)ferrocene] can be related to those of the analogous complexes with L–L = 1,1′-bis(diphenylphosphino)ferrocene (dppf)1 and 1,1′-bis(diisopropylphosphino)ferrocene (disppf), 2, all the complexes being readily synthesized from [Ir(cod)(py)2]+(py = pyridine). An optimum diphosphine bite angle of approximately 99° is maintained in all three complexes by varying the twist of the ferrocene, which decreases with increasing steric profile of the phosphine, and by distortion of the geometry at the iridium atom away from square planar towards tetrahedral. The twist about the ferrocene moiety induces chirality at the iridium atom in all three complexes and the interchange of stereoisomers can be followed by variable-temperature 1H NMR spectroscopy. Application of the Eyring equation gave approximate values of ΔG‡ for this process of 36.1 ± 0.2, 39.3 ± 0.2 and 34.3 ± 0.2 kJ mol–1 for 1–3 respectively. The ligand disoppf also induces considerable distortion away from square-planar geometry in the complex [Rh(nbd)(disoppf)][BF4]4{nbd = norbornadiene (bicyclo[2.2.1]hepta-2,5-diene)}, as found in a crystal structure determination, which may account for the unusual lability of the chelating diphosphine. This is demonstrated by its reactions with Ph2P(CH2)nPPh2(n= 1 or 2) both of which give [Rh(L–L)2]+. More surprisingly, considering its lability in [Rh(nbd)(dppf)]+, dppf also readily displaced disoppf from 4, to give [Rh(nbd)(dppf)][BF4]5. The nbd ligand in this complex is not displaced by reaction with an excess of dppf

X-Ray diffraction and phosphorous-31 NMR studies of the dynamically disordered 3:2 phenol-triphenylphosphine oxide complex

The 3:2 phenol–triphenylphosphine oxide (phenol–TPPO) adduct was studied by means of X-ray diffraction together with high-resolution solid-state 31P NMR spectroscopy. The X-ray results showed that the crystalline structure, which belongs to the triclinic P[1 with combining macron] space group, involves disorder. There are two molecules of TPPO and three phenol molecules per unit cell. One of the latter is disordered across an apparent inversion centre. Analysis of NMR data in conjunction with the crystal structure allowed the origin of such disorder to be established, showing that it is dynamic in nature. Variable-temperature NMR experiments were performed and a coalescence temperature was found at 247 K. Spectra recorded below this temperature showed two phosphorus signals. The kinetics for the phenol residue exchanging between two different TPPO moieties (two-site exchange with equal populations) were determined. Thermodynamic parameters for the motion were calculated from Eyring plots. For temperatures ranging from 262.9 to 221.5 K, the bandshape analysis technique was used to derive the required data. For lower temperatures, the selective polarisation inversion experiment (SPI) was performed, whilst high temperature values were derived from variable-temperature T1ρ studies. The activation enthalpy (ΔH‡), calculated using the results obtained by bandshape analysis, T1ρ and SPI, was determined as 38 kJ mol−1, while the activation entropy (ΔS‡) was found to be −23 J mol−1 K−1 (assuming the transmission coefficient is ½). Phosphorus-31 shielding tensor anisotropies have been derived for this system by spinning sideband analysis at both fast and slow-exchange limits and it has been shown that the tensor is axially symmetric. Single-crystal experiments show that the symmetry axis of the tensor is along the P[double bond, length half m-dash]O bond (within experimental error)