J. A. Kanters

Organopalladium complexes with bidentate phosphorus and nitrogen containing ligands.

Organopalladium complexes containing the potentially P,N-bidentate ligands o-diphenylphosphino-N, N-dimethylbenzylamine (PN) and o-diphenylphosphino-amethyl-N, N-dimethylbenzylamine (PN*) have been studied. The palladium(O) complexes Pd(P-N), (P-N = PN or PN*) have been prepared; the ligands coordinate to the metal primarily through phosphorus, with the amine function coordinating not at all or only very weakly. Oxidative addition of several organic halides to these palladium(O) complexes afforded the corresponding monoorganopalladium(I1) complexes Pd(R)(X)(P-N) in which the donor ligands are P,N-bidentate coordinated. In solution the divalent species possess a Pd-N bond, and even in the presence of either free ligand, CO or X- there is no evidence for dissociation or displacement of the amine function from the metal centre. Complexes PdMe,(P-N) have been prepared from the corresponding dihalopalladium complexes by treatment with MeLi. Reaction of these dimethylpalladium species with the electrophiles MeI, MeBr and PhCH,Br resulted in replacement of one methyl group by halogen. The structures of Pd(Me)(Br)(PN) and Pd(C=CSiMe,)(Br)(PN) have been determined by X-ray diffraction studies. Pd(Me)(Br)o(PN) crystallizes in space group Cc with a 8.379(g), b 17.363(7) and c 14.818(6) A, /3 99.34(5)O, and 2 = 4; the structure was refined to Rf = 0.030. Pd(C=CSiMe,)(Br)(PN) ~stallizes in space group P2,/c with a 13.478(3), b 10.848(2) and c 19.212(3) A, j3 102.59(2)“, and 2 = 4; the structure was refined to R, = 0.038. Both complexes have a square planar configuration around palladium, with the organic group (Me, C+&SiMe3) trans to the amine function and the six-membered chelate ring in a boat conformation.

Conformation of some carboxylic acids and their derivatives

The conformation in the crystalline state of some aliphatic carboxylic acids and their derivatives has been analysed. This analysis, based upon the results of structure determinations by means of X-ray diffraction, seems to support the concept that the conformation of a molecule is governed chiefly by intramolecular interactions.

Spectroscopic evidence for CH⋯ interaction in crystalline steroids and reference compounds

Abstract The attractive interaction between CH donors and oxygen acceptors is demonstrated for a number of compounds measured as liquid, solid and in non-polar solution. Reference values for the “free” (isolated) molecules are derived from gas-phase or solution measurements. Infrared spectral data for the CH stretching mode of a series of compounds with geminal-substituted hydroxyl and ethynyl groups, are reported. Both the Δν SC ( ν CCl 4 − ν solid ) and Δν T ( ν 300 K − ν 100 K ) values are shown to be indicative of the strength of the CH⋯O interaction. For a limited number of steroids an attempt is made to correlate the H⋯O distance with the frequency shift, Δν SC . The steric effect of neighbouring alkyl groups is shown for some cyclohexanol and adamantanol derivatives.

Stereochemistry of charged nitrogen-aromatic interactions and its involvement in ligand-receptor binding.

SummaryRecently, new evidence was found for the involvement of charged nitrogen-aromatic interactions in ligand-receptor binding. In this study we report two favourable orientations of a phenyl ring with respect to a R-N+(CH3)3 group, based on crystal structure statistics from the Cambridge Structural Database. In the first orientation, the phenyl ring is situated in between the substituents at about 4.5 Å from the nitrogen atom, and the ring is approximately oriented on the sphere around the nitrogen atom. In the second orientation, the phenyl ring is situated in the same direction as one of the N-C bonds at about 6.0 Å from the nitrogen atom, and the ring is tilted with respect to the sphere around the nitrogen atom. The same two orientations were also found in the crystal structures of three ligand-receptor complexes, which implies that these orientations probably play a major role in molecular recognition mechanisms.

Weak hydrogen bonding. Part 5. Experimental evidence for the long-range nature of CC–H ⋯π interactions: crystallographic and spectroscopic studies of three terminal alkynes

In the crystal structures of three terminal alkynes, long CC–H ⋯ CC contacts with H ⋯ C separations in the range 2.7–3.1 A are observed. Despite the long distances, these contacts possess the characteristic infrared spectroscopic features of weak hydrogen bonds. This provides direct evidence that the range of C–H ⋯π interactions donated by sufficiently acidic C–H groups extends beyond van der Waals separation. In two of the crystal structures, the C–H ⋯π interactions form interconnected systems CC–H ⋯ CC–H ⋯ CC–H.

Conformational polymorphism of d-sorbitol (d-glucitol): the crystal and molecular structures of d-glucitol 2/3-hydrate and epsilon d-glucitol

Abstract The crystal structures of d -glucitol 2/3-hydrate (1) and epsilon d -glucitol (2) were determined by X-ray crystallography and refined to final conventional parameters of R=0.034 and 0.050, respectively. The conformations of the three independent molecules of 1 and one of the two independent molecules of 2 are similar and exhibit, bent-chain, sickle conformations of the carbon chain, thus avoiding the unfavourable 1,3-parallel O//O interactions. However, the orientation of a terminal hydroxyl group differs from the one observed in the bent-chain conformation of the known A form. An even more striking observation is the unexpected, extended, zigzag conformation of the second independent molecule of 2, which results in a 1,3-parallel interaction between O-2 and O-4. Thus in the class of alditols, the crystals of the epsilon and A forms of d -glucitol constitute the rarely occurring type of conformational polymorphism.

Acceptor directionality of sterically unhindered C–H⋯OC hydrogen bonds donated by acidic C–H groups

Crystal correlation study of acidic and sterically unhindered C–H groups (chloroform, dichloromethane and terminal alkynes) forming short contacts with carbonyl acceptors, reveals a soft but significant preference for the conventional carbonyl lone-pair direction.

The crystal structure of [1-lithio-2-methoxybenzene]8·TMEDA

Abstract The structure of 1-lithio-2-methoxybenzene(2-methoxyphenyllithium) in the presence of N , N , N ′, N ′-tetramethylethylenediamine (TMEDA) has been determined by single crystal X-ray diffraction techniques. The compound crystallizes in the triclinic system with space group P 1¯. The cell dimensions are determined as follows: a 9.035(1), b 11.896(1), c 15.219(2)A˚, α 92.55(1), β 92.03(1) and γ 110.11(1)°. The structure was refined by least-squares techniques to R ( F ) 6.1% and R ( wF ) 3.9%. The structure consists of two centrosymmetrically related tetrameric units of lithiomethoxybenzene connected to each other by a bridging TMEDA ligand which has a center of inversion in the middle of the C-C bond. The nature of the highly asymmetric tetrameric unit is discussed and compared to that of other organolithium compounds with intramolecular coordination through an ether function.

2-Ethynyladamantan-2-ol: a model compound with distinct OH ··· π and CH ··· O hydrogen bonds

Abstract Vibrational spectroscopy has been used to demonstrate that the extremely short OH ··· π and ≡CH ··· O intermolecular contacts in crystalline 2-ethynyladamantan-2-ol are due to strong interactions, which may unambiguously be typified as hydrogen bonding in view of the behaviour of OH and ≡CH stretching and bending modes. The XH stretching vibration shifts to lower frequency, becomes broader and more intense and has a positive frequency-temperature coefficient, whereas the XH bending modes shift to higher values and show a negative frequency-temperature coefficient. Solution spectra of the title compound in apolar solvents served as a reference for the “free” molecule. Variable-temperature measurements together with deuteration experiments have been performed to establish the correct assignment of these characteristic modes.

The structure of 2-(diphenylphosphino)phenyllithium: the significance of PLi bonding

Abstract The solid state structure of 2-(diphenylphosphino)phenyllithium·Et 2 O has been determined by a single crystal X-ray diffraction study. The crystal consists of dimeric aggregates in which the Li atoms are solvated by an additional diethyl ether molecule. The compound retains the dimeric structure in an apolar solvent (toluene) but in THF it exists in monomeric form. Ab initio calculations indicate a small but significant influence of PLi interaction on the stability and structure of P-containing organolithium compounds.