Craig R. Rice

Catechol as an efficient anchoring group for attachment of ruthenium–polypyridine photosensitisers to solar cells based on nanocrystalline TiO2 films

The Ru(II)–polypyridyl complexes [Ru(H2L)(terpy)][PF6]2 (1) and [Bu4N][Ru(H2L)(NCS)3] (2) (H2L=4′-(3,4-dihydroxyphenyl)-2,2′:6′,2″-terpyridine), in which H2L is coordinated as a terpyridyl fragment with a catechol site pendant from the C4′ position, adhere effectively to nanocrystalline TiO2 (anatase) surfaces via the pendant catechol group; incident photon-to-current conversion efficiency values of up to 50% were obtained in their photocurrent action spectra, suggesting that the catechol unit may be a convenient and effective anchoring group for attaching dyes to TiO2-based photovoltaic cells.

The Coordination Chemistry of 3,3′-Diamino-2,2′-bipyridine and Its Dication: Exploring the Role of the Amino Groups by X-ray Crystallography

The synthesis and structural chemistry of a series of new divalent transition metal complexes of the bis-bidentate ligand 3,3-diamino-2,2-bipyridine (L1) and its dication L1H2 are described. Ligand L1 reacts with salts of divalent transition metals to afford the (1:1) metal-ligand complexes (2a-2d) as well as the tris complexes (3a-3f). All complexes were fully characterised by spectroscopic methods and the following compounds [Cu(L1)Cl2]2 (2a), [Cu(L1)(OAc)2] (2b), [Zn(L1)3][OTf]2 (3a), and [Zn(L1)3][ZnCl4] (3e and 3f) were structurally characterised. Results from single crystal X-ray diffraction measurements indicate that formation of an intramolecular hydrogen bond between the two amino groups allows the ligand to coordinate divalent metal ions through their diimine binding sites. Furthermore, the structure of compound 2a reveals that it crystallises as a dimer in which each copper ion is bound to two pyridine nitrogen atoms and two chloride ions in a distorted square planar arrangement, with a long axial contact from a neighbouring amino group completing the approximately square-pyramidal geometry at CuII. Complexation of this ligand in acidic conditions afforded the compound [Cu(L1H2)Cl4] (4), as well as the two salts [L1H2][CuCl4] (5a) and [L1H2][ZnCl4] (5b). All three compounds have been structurally characterised and results indicate that the dication (L1H2) displays a different coordination preference for the chelation of metal ions. In all three cases, both of the heterocyclic N atoms of the ligand are protonated, thus preventing chelation to the metal ion, although for compound 4 crystallographic studies reveal that the two amino functionalities coordinate the copper(II) ion. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

A wavelength and lifetime responsive cryptate-containing fluorescent probe for zinc ions in water

A diamino-functionalised cryptate can react irreversibly with butanal in water, in the presence of an excess of a metal ion, to form a cyclised bis-aminal complex, which displays metal-dependent luminescence properties.

Head‐To‐Tail and Heteroleptic Pentanuclear Circular Helicates

Everybody form a circle: Careful design of ligand strands and their reaction with Cu2+ ions leads to the formation of the title helicates. Incorporation of differing numbers of N-donor units within a ligand strand containing a phenyl spacer results in a pentanuclear head-to-tail circular helicate, whereas reaction of two different ligands results in a heteroleptic pentanuclear circular helicate (see picture; green: Cu, red and blue: ligands).

Pyridines from azabicyclo[3.2.0]hept-2-en-4-ones through a proposed azacyclopentadienone

Pyridines have been formed by heating azabicyclo[3.2.0]hept-2-en-4-ones in toluene. The generation of a 3-azacyclopentadienone intermediate via a [2 + 2]-cycloreversion is proposed as the key step. A Diels-Alder reaction of a styrene, extrusion of carbon monoxide, and loss of hydrogen then gives the pyridine. The process parallels the well-known synthesis of benzenes from cyclopentadienones. The azabicyclo[3.2.0]hept-2-en-4-ones were synthesized from the reaction between readily available cyclopropenones and 1-azetines, in which the cyclopropenones behave as all-carbon 1,3-dipolar equivalents.

New hybrid ditopic ligands containing fused phenanthroline and crown ether units

Reaction of 5,6-dihydroxy-1,10-phenanthroline with various poly(ethylene)glycol-ditosylates affords, in good yield, a series of ligands in which a phenanthroline binding site is attached to an adjacent crown ether unit; the NN chelating site may be coordinated to {Ru(bipy)2}2+ units to afford [Ru(bipy)3]2+ derivatives with pendant crown ether units, which can bind alkali metal ions.

Diborane(4) compounds incorporating thio- and seleno-carboranyl groups

The reaction between B2(NMe2)4 and the carborane dithiol C2B10H10(SH)2, followed by addition of HCl affords the [NH2Me2]+ salt of the dianion [B2Cl2(S2C2B10H10)2]2−, which has been characterised by X-ray crystallography. A similar reaction utilising the carborane diselenol C2B10H10(SeH)2 (generated in situ) afforded a compound containing the dianion [B2(Se2C2B10H10)3]2−.

Controlling the formation of metallosupramolecular assemblies by metal ionic radii

The formation of either dinuclear double-stranded or pentanuclear circular helicates from a ligand containing two tridentate domains separated by a phenylene unit can be controlled by inter-ligand steric interactions which themselves are governed by the size of the metal ion.

Cadmium-containing pyridyl–thiazole complexes: crystal structures and solution behaviour of mononuclear, dinuclear double helicate and dinuclear triple helicate complexes

Reaction of Cd(ClO4)2 with the potentially tetra- (L1), penta- (L2) and hexadentate (L3) pyridine–thiazole-containing ligands gives [Cd2(L1)3(H2O)][ClO4]4 (a dinuclear triple helicate), mononuclear [Cd(L2)(ClO4)2], and [Cd2(L3)2(ClO4)(CH3CN)][ClO4]3 (a dinuclear double helicate), respectively. In [Cd2(L1)3(H2O)][ClO4]4 two of the ligands L1 partition into two bidentate pyridyl–thiazole domains whereas the remaining ligand partitions into a bidentate (pyridyl–thiazole) and monodentate (coordinating pyridyl unit with a pendant thiazole) unit; one Cd(II) centre is coordinated by three bidentate ligand fragments, whereas the other is coordinated by two bidentate and one monodentate ligand fragments as well as a water molecule. This low-symmetry arrangement is retained in solution. In [Cd(L2)(ClO4)2], L2 acts as a planar pentadentate equatorial ligand with perchlorate anions coordinated at the axial sites; the ligand has a shallow helical twist to minimise steric interactions between the terminal pyridyl H6 protons, which are directed towards each other. In [Cd2(L3)2(ClO4)(CH3CN)][ClO4]3, the potentially hexadentate ligand L3 is partitioned into terdentate (pyridyl–thiazole–pyridyl) and bidentate (pyridyl–thiazole) coordination domains with a non-coordinated terminal pyridyl unit; each Cd(II) centre is coordinated by one terdentate and one bidentate ligand fragment, with the sixth site being occupied by MeCN at one Cd(II) site and a perchlorate anion at the other. Again, the low symmetry coordination mode of the ligands is retained in solution although the two metal centres become equivalent.

Platinum catalysed 1,4-diboration of α,β-unsaturated ketones

Diborane(4) compounds react with α,β-unsaturated ketones to give the 1,4-addition product in the presence of a platinum catalyst at 80 °C.