David A. McMorran

The First Coordinatively Saturated, Quadruply Stranded Helicate and Its Encapsulation of a Hexafluorophosphate Anion.

Incarcerated in a helical prison: The encapsulation of a PF6- ion within a quadruply stranded helicate (shown schematically) results from the self-assembly of four molecules of 1,4-bis(3-pyridyloxy)benzene and two PdII ions. This represents not only the first example of a coordinatively saturated quadruple helicate, but also the first example of the encapsulation of a complex anion by a helicate.

“Click-Triazole” Coordination Chemistry: Exploiting 1,4-Disubstituted-1,2,3-Triazoles as Ligands

Access to readily functionalized ligand architectures is of crucial importance in a range of different areas including catalysis, metallopharmaceuticals, bioimaging, metallosupramolecular chemistry, mechanically interlocked architectures, and molecular machines. The mild and modular Cu(I)-catalyzed 1,3-cycloaddition of terminal alkynes with organic azides (the CuAAC “click” reaction) allows the ready formation of functionalized 1,4-disubstituted-1,2,3-triazole scaffolds, and this has led to an explosion of interest in the coordination chemistry of these heterocycles. The parent 1,4-disubstituted-1,2,3-triazole units can potentially act as monodentate or bridging ligands. Examples of both the monodentate (through either the N3 nitrogen or C5 carbon positions of the 1,2,3-triazole) and bridging (through the N2 and N3 nitrogen atoms) coordination modes have been structurally characterized. A diverse array of bi-, tri-, and polydentate ligands incorporating 1,4-disubstituted-1,2,3-triazole units have also been synthesized and characterized. When the chelate pocket involves coordination through the N3 nitrogen atom of the 1,2,3-triazole, these are called “regular” click ligands. While these are the most common type of “click” chelate, “inverse” ligands in which the 1,2,3-triazole unit coordinates through the less electron-rich N2 nitrogen atom have also been synthesized and characterized. The resulting “click” complexes are beginning to find applications in catalysis, metallosupramolecular chemistry, photophysics, and as metallopharmaceuticals and bioimaging agents.

A self-complementary molecular cleftElectronic supplementary information (ESI) available: assignment of the 1H NMR spectrum of [Ag21](BF4)2 in CD3CN solution. See http://www.rsc.org/suppdata/cc/b2/b205831f/

Reaction of silver(I) salts with a new octadentate ligand generates a novel self-complementary molecular cleft which forms dimers in the solid state, stabilised by pi-stacking interactions and intermolecular C-H...M interactions.

Syntheses and X-ray crystal structures of poly(pyridylsulfanylmethyl)arenes: new multi-armed molecules

Abstract The synthesis of a series of seven new poly(pyridylsulfanylmethyl)arenes is reported. These are readily prepared from either 2- or 4-mercaptopyridine and a poly(bromomethyl)arene in the presence of triethylamine. Compounds with three, four, six and eight pyridylsulfanylmethyl arms are reported. These have been fully characterised and, in four cases, the relative orientations of the pyridylsulfanylmethyl arms have been ascertained by X-ray structural analysis.

Synthesis, Characterization, and Photocatalytic H2-Evolving Activity of a Family of [Co(N4Py)(X)]n+ Complexes in Aqueous Solution

A series of [Co(III)(N4Py)(X)](ClO4)n (X = Cl(-), Br(-), OH(-), N3(-), NCS(-)-κN, n = 2: X = OH2, NCMe, DMSO-κO, n = 3) complexes containing the tetrapyridyl N5 ligand N4Py (N4Py = 1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine) has been prepared and fully characterized by infrared (IR), UV-visible, and NMR spectroscopies, high-resolution electrospray ionization mass spectrometry (HRESI-MS), elemental analysis, X-ray crystallography, and electrochemistry. The reduced Co(II) and Co(I) species of these complexes have been also generated by bulk electrolyses in MeCN and characterized by UV-visible and EPR spectroscopies. All tested complexes are catalysts for the photocatalytic production of H2 from water at pH 4.0 in the presence of ascorbic acid/ascorbate, using [Ru(bpy)3](2+) as a photosensitizer, and all display similar H2-evolving activities. Detailed mechanistic studies show that while the complexes retain the monodentate X ligand upon electrochemical reduction to Co(II) species in MeCN solution, in aqueous solution, upon reduction by ascorbate (photocatalytic conditions), [Co(II)(N4Py)(HA)](+) is formed in all cases and is the precursor to the Co(I) species which presumably reacts with a proton. These results are in accordance with the fact that the H2-evolving activity does not depend on the chemical nature of the monodentate ligand and differ from those previously reported for similar complexes. The catalytic activity of this series of complexes in terms of turnover number versus catalyst (TONCat) was also found to be dependent on the catalyst concentration, with the highest value of 230 TONCat at 5 × 10(-6) M. As revealed by nanosecond transient absorption spectroscopy measurements, the first electron-transfer steps of the photocatalytic mechanism involve a reductive quenching of the excited state of [Ru(bpy)3](2+) by ascorbate followed by an electron transfer from [Ru(II)(bpy)2(bpy(•-))](+) to the [Co(II)(N4Py)(HA)](+) catalyst. The reduced catalyst then enters into the H2-evolution cycle.

New U-shaped Components for Metallosupramolecular Assemblies: Synthesis and Coordination Chemistry of 2,6-bis(4-(3-pyridyloxy)phenoxy)pyrazine

The new ligand 2,6-bis(4-(3-pyridyloxy)phenoxy)pyrazine ( L ) has been prepared and characterised. Reaction with a palladium (II) precursor yields a discrete complex of formula [Pd( L ) 2 ](ClO 4 ) 2 , in which the ligand coordinates in a U-shaped fashion through the pyridine groups only, resulting in the complex containing two 22-membered chelate rings ( a =15.288(9), b =10.118(4), c = 22.720(12), g =95.450(12), P 2 1 / n , Z =2, calcd =1.413 g cm m 3 , 507 parameters, R =0.0433). Reaction with silver nitrate yields a metallocyclic complex of formula [Ag 2 ( L ) 2 (NO 3 )](NO 3 ), in which each silver is bound to one pyridine group of two different ligands, each of which is again in a U-shaped configuration ( a = 12.215(9), b =12.759(9), c =19.461(14), f =90.949(10), g =103.214(10), n =110.327(11), P m 1, Z =2, calcd = 1.591 g cm m 3 , 755 parameters, R =0.0287).

Tetrakis(pyrazol-1-ylmethyl)methane and its hypodentate binuclear complex with silver(I) nitrate

Abstract The preparation and X-ray crystal structure of tetrakis(pyrazol-1-ylmethyl)methane are described. This new ligand reacts with silver(I) nitrate to give a M2L2 complex, in which the ligand bridges two trigonal silver atoms with bidentate and monodentate coordination domains. As such the ligand is hypodentate with one non-coordinated pyrazole group.

New multinuclear zinc complexes with N4O2 coordination spheres

Abstract The preparation and characterisation of the new, potentially octadentate, ligand 1,2,4,5-tetrakis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzene ( L 2 ) is reported. This and two related ligands, 1,2-bis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzene ( L 1 ) and hexakis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzene ( L 3 ) were reacted with zinc(II) acetate to give complexes in which pairs of ligand arms chelate to Zn(OAc) units. The X-ray crystal structures of [Zn( L 1 )(OAc)]PF6 and [ Zn 2 ( L 2 )( OAc ) 2 ]( BPh 4 ) 2 are reported.

Chelating and Bridging Modes of Coordination by 1,3-Bis(pyrazol-1-yl)propane; Coexistence of Discrete and Polymeric Metallosupramolecular Isomers within the Same Crystal

1,3-Bis(pyrazol-1-yl)propane (1) reacts with zinc acetate and cadmium nitrate to give tetrahedral [Zn(1)(OAc)2] and eight-coordinate [Cd(1)2(NO3)2] mononuclear complexes (2) and (3), respectively. Reaction with silver nitrate results in the formation of an intriguing complex (4) that consists of discrete M2L2 binuclear units stacked between [ML]n polymeric chains.

Application of electrospray mass spectrometry to the characterisation of tertiary arsine ligands

Abstract The use of silver (1) nitrate provides a convenient ionisation method for the analysis of a wide range of mono- bi- and tridentate tertiary arsines by electrospray mass spectrometry. Eleven different arsines (L) were investigated, of which four were newly prepared and characterised hybrid arsines. Species commonly observed include [LAg] − , [L 2 Ag] − and, at higher Ag concentrations, [LAg 2 (NO 3 )] − and [L 2 Ag 2 (NO 3 )] − . Impurity arsine species can also be readily identified in many cases, dependding on the amount of silver employed. Comparable results for a monodentate and a bidentate arsine were obtained when copper(I) ions (from Cu(MeCN) 4 BF 4 ) were used in place of silver(I). Oxidisation and methylation of selected arsine ligands was also investigated, giving analogous results to those reported previously for tertiary phosphines.