Sharon E. Spey

Substituent effects on aromatic stacking interactions

Synthetic supramolecular zipper complexes have been used to quantify substituent effects on the free energies of aromatic stacking interactions. The conformational properties of the complexes have been characterised using NMR spectroscopy in CDCl(3), and by comparison with the solid state structures of model compounds. The structural similarity of the complexes makes it possible to apply the double mutant cycle method to evaluate the magnitudes of 24 different aromatic stacking interactions. The major trends in the interaction energy can be rationalised using a simple model based on electrostatic interactions between the pi-faces of the two aromatic rings. However, electrostatic interactions between the substituents of one ring and the pi-face of the other make an additional contribution, due to the slight offset in the stacking geometry. This property makes aromatic stacking interactions particularly sensitive to changes in orientation as well as the nature and location of substituents.

Noncovalent Assembly of [2]Rotaxane Architectures

Reversible zinc-pyridine coordination and hydrogen-bonding interactions have been used to assemble a [2]rotaxane from three components. Cooperativity in the macrocyclization process that results in the porphyrin dimer makes the system exceptionally stable. However, the kinetic lability of the zinc-porphyrin interaction means the dimer is in dynamic equilibrium with its monomer, and this has been exploited in the construction of a [2]rotaxane.

A supramolecular system for quantifying aromatic stacking interactions.

A supramolecular complex for investigating the thermodynamic properties of intermolecular aromatic stacking interactions has been developed. The conformation of the complex is locked in a single well-defined conformation by an array of H-bonding interactions that force two aromatic rings on one end of the complex into a stacked geometry. Chemical double-mutant cycles have been used to measure an anthracene-aniline interaction (+0.6 +/- 0.8 kJ mol(-1)) and a pentafluorophenyl-aniline interaction (-0.4 +/- 0.9 kJ mol(-1)) in this system. Although the interactions are very weak, the pentafluorophenyl interaction is attractive, whereas the anthracene interaction is repulsive: this is consistent with the dominance of pi-electron electrostatic interactions. The nitropyrrole subunits used to control the conformation of these complexes lead to problems of aggregation and multiple conformational equilibria. The implications for the thermodynamic analysis are examined in detail, and the double-mutant-cycle approach is found to be remarkably robust with respect to such effects, since systematic errors in individual experiments are removed in a pair-wise fashion when the cycle is constructed.

Experimental Measurement of Noncovalent Interactions Between Halogens and Aromatic Rings

Chemical double mutant cycles have been used to quantify the interactions of halogens with the faces of aromatic rings in chloroform. The halogens are forced over the face of an aromatic ring by an array of hydrogen‐bonding interactions that lock the complexes in a single, well‐defined conformation. These interactions can also be engineered into the crystal structures of simpler model compounds, but experiments in solution show that the halogen–aromatic interactions observed in the solid state are all unfavourable, regardless of whether the aromatic rings contain electron‐withdrawing or electron‐donating substituents. The halogen–aromatic interactions are repulsive by 1–3 kJ mol−1. The interactions with fluorine are slightly less favourable than with chlorine and bromine.

[2,3]-Sigmatropic rearrangement of allylic sulfur ylides derived from trimethylsilyldiazomethane (TMSD)

Trimethylsilyldiazomethane reacts with allylic sulfides in the presence of catalytic quantities of Rh2(OAc)4 (1 mol%) to give homoallylic sulfides in good yields and with high diastereoselectivity.

Modification of the solid state structures of dithiadiazolyl radicals: crystal structure of p-iodophenyl-1,2,3,5-dithiadiazolyl

Abstract The solid state structure of the 1,2,3,5-dithiadiazolyl p -IC 6 H 4 CNSSN ( 3 ) is described. The molecules associate in dimer pairs, across an inversion centre, in an unusual trans -cofacial manner. The separation between the heterocyclic rings is 3.121 A. The intradimer sulfur contacts (3.696 A) are larger than those observed in dithiadiazolyls that associate in the more usual cis -cofacial manner. Individual p -IC 6 H 4 CNSSN molecules are linked into zigzag chains through weak I⋯S interactions (3.82 A); each half of a [ p -IC 6 H 4 CNSSN] 2 dimer is a member of separate chains that run in opposite directions.

The generation of a trinuclear nickel(II) core maintained by tridentate acetate bridges

Abstract The asymmetric compartmental proligand H L B bearing a tridentate N2O donor set and a bidentate NO donor set has given the novel trinuclear nickel(II) complex [ Ni 3 ( L B ) 2 ( OAc ) 2 ( NCS ) 2 ] in which there are two tridentate acetate bridges each having a μ3,η1,η2-bridging mode.

Stabilisation of alkynyl dithiocarboxylates at a ruthenium centre: X-ray crystal structures of [Ru(H)(CO)(S2CCCPh)(PPh3)2], [Ru(CO)(CPhCHPh)(S2CCCPh)(PPh3)2] and [Ru(CO)(CCMes)(S2CCCPh)(PPh3)2]

Abstract Solutions of the alkynyldithiocarboxylate anions RCC–CS 2 − (R=Mes, Ph, Bu t ), generated by treatment of the acetylides LiCCR with carbon disulfide, are sufficiently stable to allow reaction with haloruthenium(II) complexes. In this way, the complexes [Ru(H)(CO)(S 2 CCCR)(PPh 3 ) 2 ] and [Ru(CO)(CPhCHPh)(S 2 CCCR)(PPh 3 ) 2 ] (R=Mes, Ph, Bu t ) have been prepared and characterised. The vinyl complexes react with additional terminal alkynes R 1 CCH at room temperature to afford the acetylide complexes [Ru(CO)(CCR 1 )(S 2 CCCR)(PPh 3 ) 2 ]. The crystal structures of [Ru(H)(CO)(S 2 CCCPh)(PPh 3 ) 2 ], [Ru(CO)(CPhCHPh)(S 2 CCCPh)(PPh 3 ) 2 ] and [Ru(CO)(CCMes)(S 2 CCCPh)(PPh 3 ) 2 ] have been determined.

Oligonuclear nickel(II) complexes of asymmetric compartmental ligands bearing adjacent {N2O} and {N,S,O} donor sets

Abstract Asymmetric compartmental proligands bearing adjacent {N2O} and {NSO} donor sets have been prepared and used in complexation reactions with nickel(II). [4-Methyl-2-{[methyl-(2-pyridin-2-yl-ethyl)amino]methyl}-6-[(2-methylsulfanyl phenyl imino)methyl]phenol (HL3) and 2-{[(3-dimethylamino-propyl)methylamino]methyl}-4-methyl-6-[(2-methylsulfanylphenyl imino)methyl]phenol (HL4) gave the dinuclear nickel(II) complexes, [Ni2(L3)(AcO)(NCS)2(CH3CN)] (3), [Ni2(L4)(AcO)2(NCS)] (4), whereas 4-methyl-2-{[methyl(2-pyridin-2-yl-ethyl)amino]-methyl}-6-[(2-methylsulfanylethylimino)-methyl]-phenol (HL5) and 4-methyl-2-{[methyl(2-pyridin-2-yl-ethyl)amino]methyl}-6-[(3-methylsulfanylpropylimino) methyl]-phenol (HL6), gave the trinuclear nickel(II) complexes [Ni3(L5)2(OAc)2(NCS)2]·2H2O (5) and [Ni3(L6)2(OAc)2(NCS)2]·MeOH (6). The crystal structures of 3–6 are reported.

Diversity in the reactions of unsymmetric dinucleating Schiff base ligands with CuII and NiII

A diversity of reaction products have been found in the reactions of two related unsymmetrical Schiff base dinucleating ligands, HL1 and HL2, derived from 3-chloromethyl-5-methylsalicylaldehyde 1, with copper(II) and nickel(II) salts. The ligands remain intact in the copper(II) complexes to give the homodinuclear complexes [Cu2L1Br3] 2 and [Cu2L2(OH)(ClO4)]ClO43, the crystal structures of which have been solved. The reactions of HL1 and HL2 with nickel perchlorate led to hydrolysis of the imine bond. With HL1 the homodinuclear complex [NiLA(OH2)]2[ClO4]2·4H2O was formed and with HL2 hydrolysis was followed by elimination of C2H4 from the terminal NEt2 of the iminic side arm to leave an NHEt group and the dinuclear complex [NiLC(OH2)]2[ClO4]2·3CH3OH. The crystal structures of the two nickel complexes are also reported.