Hilary A. Jenkins

Supramolecular macrocycles reversibly assembled by Te … O chalcogen bonding

Organic molecules with heavy main-group elements frequently form supramolecular links to electron-rich centres. One particular case of such interactions is halogen bonding. Most studies of this phenomenon have been concerned with either dimers or infinitely extended structures (polymers and lattices) but well-defined cyclic structures remain elusive. Here we present oligomeric aggregates of heterocycles that are linked by chalcogen-centered interactions and behave as genuine macrocyclic species. The molecules of 3-methyl-5-phenyl-1,2-tellurazole 2-oxide assemble a variety of supramolecular aggregates that includes cyclic tetramers and hexamers, as well as a helical polymer. In all these aggregates, the building blocks are connected by Te…O–N bridges. Nuclear magnetic resonance spectroscopic experiments demonstrate that the two types of annular aggregates are persistent in solution. These self-assembled structures form coordination complexes with transition-metal ions, act as fullerene receptors and host small molecules in a crystal.

Preparation and Magnetic Properties of Iron(3+) Spin-Crossover Complexes Bearing a Thiophene Substituent: Toward Multifunctional Metallopolymers

The synthesis of a new 3-ethynylthienyl-substituted QsalH ligand (QsalH is the short form for N-(8-quinolyl)salicylaldimine) (ThEQsalH 3), and the preparation, electronic, and magnetic properties of three homoleptic and cationic iron(3+) complexes containing this ligand with PF(6)(-) 4, SCN(-) 5, and ClO(4)(-) 6 counteranions are reported. In all three complexes a spin-crossover is observed in the solid state by variable temperature magnetic susceptibility measurements and Mossbauer spectroscopy, indicating that the synthetic modification of the QsalH ligand has not significantly altered the electronics at the metal center. This includes the observation of a very rare S = 5/2 to 3/2 spin-crossover in a non-porphyrin iron(3+) complex 5. The molecular structure and magnetic properties of an unusual iron(2+) complex 7 generated by reduction of complex 6 serendipitously during a recrystallization attempt in aerobic acetone solution is also reported. Complexes 4-6 feature iron(3+) reduction and oxidation of the thiophene ring at potentials of approximately -0.7 and +1.2 V (vs Fc), respectively.

Oxidation of meso-tetraphenyl-2,3-dihydroxychlorin: simplified synthesis of β,β′-dioxochlorins

DDQ Oxidation of meso-tetraphenyl-cis-2,3-dihydroxychlorins leads to an efficient synthesis of the corresponding 2,3-dioxochlorins. This alternative synthesis of these known chromophores is simple and likely to be more general as compared to established syntheses. A single crystal structure of [meso-tetraphenyl-cis-2,3-dihydroxychlorinato]Ni(II) proves the ruffled structure of the chromophore. The reduction of the free base dioxochlorin allows the preparation of the meso-tetraphenyl-trans-2,3-dihydroxychlorin.

Diversity of metal-ligand interactions in halide (X = I, Br, Cl, F) and halide-free ambiphilic ligand rhodium complexes.

Reaction of the neutral ambiphilic ligand 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPB) with [{Rh(mu-Cl)(CO)(2)}(2)] yields [RhCl(CO)(TXPB)] (1) (Emslie et al. Organometallics 2006, 25, 5835). Complex 1 is square planar with the TXPB ligand bound to rhodium via the phosphine and thioether donors (these are features common to complexes 2-5, vide infra). Treatment of 1 with Me(3)SiBr and Me(3)SiI allowed for halide substitution to afford [RhBr(CO)(TXPB)] (2) and [RhI(CO)(TXPB)] (3), respectively. The halide co-ligands in complexes 1 and 2 form a strong bridging interaction between rhodium and the borane group in TXPB. The presence of stronger borane-halide coordination in 1 is clearly illustrated by an (11)B NMR chemical shift of 12 ppm versus 27 ppm in 2. In contrast, the iodide ligand in 3 forms only a weak bridging interaction to boron, leading to a B...I distance of 3.125(7) A, and an (11)B NMR chemical shift of 56 ppm (versus 69 ppm for free TXPB). A lower carbonyl stretching frequency in 3 (2002 cm(-1)) versus 1 or 2 (2008 and 2013 cm(-1), respectively) could be attributed to weakening of the Rh-X bond in 1 and 2 as a consequence of halide-borane coordination and/or a shorter Rh-S bond in complex 3. [Rh(CO)(TXPB-F)] (4) and the halide-free cation [Rh(CO)(TXPB)][PF(6)] (5) were accessed by reaction of 1 with [NMe(4)]F and Tl[PF(6)], respectively. Complex 4 is zwitterionic with fluoride bound to boron [(11)B NMR delta 4 ppm; B-F = 1.445(6) A; Rh...F = 3.261(3) A] and an eta(2)-interaction between the cationic rhodium center and the ipso- and ortho-carbon atoms of a B-phenyl ring in TXPB-F. By contrast, rhodium in 5 engages in an eta(2)-interaction with boron and the ipso-carbon of one B-phenyl ring; Rh-B and Rh-C(ipso) bond lengths in 5 are 2.557(3) and 2.362(2) A, respectively. The long Rh-B distance and an (11)B NMR chemical shift of 57 ppm are consistent with only a weak Rh-B interaction in 5, and a CO stretching frequency of 2028 cm(-1) (Nujol), versus 2004-2013 cm(-1) for complexes 1-4, is indicative of greatly reduced electron density in 5, relative to 1-4.

Tetranuclear Ag(I) complexes with an octagonal Ag4S4 core: building large structures from small macrocycles

Abstract Reaction of the thioether macrocycles TT[9]OC and Me 2 TT[9]OC with Ag + salts in a 1:1 ratio produces unique tetrameric cations containing an octagonal [Ag 4 S 4 ] 4+ cavity. The X-ray crystal structures of three of these aggregates {[AgL][X]}4 (X =BF 4 − , L = TT[9]OC; X = CF 3 SO 3 − , L = TT[9]OC; X = BF 4 − , L = Me 2 TT[9]OC) were determined. In each case, the thiacyclophane ligand bonds in a facial coordination mode to one Ag(I) ion with the central S-donor bridging to the next Ag(I) ion. This completes a pseudotetrahedral geometry and results in cyclic tetramers with a [AgS] 4 4+ octagonal core. Each structure has two symmetry related anions (BF 4 − or CF 3 SO 3 − included over the opposing faces of the large tetracationic cavity. {[Ag(TT[9]OC)][BF 4 ]} 4 ·2(MeCN): C 52 H 70 B 4 F 16 N 2 S 12 , P2 1 c , a=14.525(7), b=16.703(11), c = 16.250(6) A, β = 115.54(3)°, V = 3557(6)A 3 and Z=2. {[Ag(TT[9]OC)][CF 3 SO 3 ]} 4 : C 52 H 64 Ag 4 F 12 O 12 S 16 , P2 1 c , a=12.308(2), b=23.381(4), c=14.018(2) A, β = 113.30(1)°, V = 3705(5)A 3 and Z=2. {[Ag(Me 2 [9]OC)][BF 4 ]} 4 ·2(MeCN): C 60 H 86 Ag 4 B 4 F 16 N 2 S 12 , P2 1 c , a=14.878(8), b=17.356(7), c = ]6.804([1) A, P = 114.95(4)°, V = 3934(4) A3 and Z = 2.

Rigid NON- and NSN-ligand complexes of tetravalent and trivalent uranium: comparison of U–OAr2 and U–SAr2 bonding

A rigid NSN-donor proligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylthioxanthene (H(2)[TXA(2)], 1) was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylthioxanthene. Deprotonation of 1 using (n)BuLi provided Li(2)(DME)(2)[TXA(2)] (2), and subsequent reaction with UCl(4) afforded [Li(DME)(3)][(TXA(2))UCl(3)] (4). The analogous NON-donor ligated complex [(XA(2))UCl(3)K(DME)(3)] [3; XA(2) = 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene] was prepared by the reaction of K(2)(DME)(x)[XA(2)] with UCl(4). A cyclic voltammogram (CV) of 3 in THF/[NBu(4)][B(C(6)F(5))(4)] at 200 mV s(-1) showed an irreversible reduction to uranium(III) at E(pc) = -2.46 V versus FeCp(2)(0/+1), followed by a product wave at E(1/2) = -1.83 V. Complex 4 also underwent irreversible reduction to uranium(iii) [E(pc) = -2.56 V], resulting in an irreversible product peak at E(pa) = -1.83 V. One-electron reduction of complexes 3 and 4 using K(naphthalenide) under an argon atmosphere in DME yielded 6-coordinate [(XA(2))UCl(DME)] (5) and the thermally unstable 7-coordinate [(TXA(2))U(DME)Cl(2)Li(DME)(2)] (6), respectively. The U-S distances in 4 and 6 are uncommonly short, the C-S-U angles are unusually acute, and the thioxanthene backbone of the TXA(2) ligand is significantly bent. By contrast, the xanthene backbone in XA(2) complexes 3 and 5 is planar. However, κ(3)-coordination and an approximately meridional arrangement of the ancillary ligand donor atoms is maintained in all complexes. DFT and Atoms in Molecules (AIM) calculations were carried out on 3, 4, 5, 6, [(XA(2))UCl(3)](-) (3B), [(TXA(2))UCl(2)(DME)](-) (6B) and [(TXA(2))UCl(DME)] (6C) to probe the extent of covalency in U-SAr(2) bonding relative to U-OAr(2) bonding.

A thermally robust di-n-butyl thorium complex with an unstable dimethyl analogue

Methyl and n-butyl thorium complexes of a rigid 2,6-bis(anilidomethyl)pyridine ligand have been prepared; the n-butyl complex is thermally stable, even at 60 degrees C, while the methyl complexes exhibit a high tendency to eliminate methane via sigma-bond metathesis.

The molecular quadrupole moment: solid state architectures containing organic and organometallic molecules

Abstract The preparation and X-ray crystal structures of co-crystals containing octafluoronaphthalene with organic and organometallic compounds is reported. The type of association, namely, alignment of molecular quadrupole moments, that is observed in these systems provides an easy method of preparing well-ordered arrays of organic/organometallic molecules.

iPSC Neuronal Assay Identifies Amaryllidaceae Pharmacophore with Multiple Effects against Herpesvirus Infections.

The Amaryllidaceae alkaloid trans-dihydrolycoricidine 7 and three analogues 8-10 were produced via asymmetric chemical synthesis. Alkaloid 7 proved superior to acyclovir, the current standard for herpes simplex virus, type 1 (HSV-1) infection. Compound 7 potently inhibited lytic HSV-1 infection, significantly reduced HSV-1 reactivation, and more potently inhibited varicella zoster virus (VZV) lytic infection. A configurationally defined (3R)-secondary alcohol at C3 proved crucial for efficacious inhibition of lytic HSV-1 infection.

Dimethyl(hydrido)platinum(IV) chemistry related to methane activation: the effect of a tetradentate ligand

The complex [PtMe2(TPMA)] (1), TPMA=tris(2-pyridylmethyl)amine, contains bidentate TPMA with two free pyridyl groups. It reacts with HX (X=CF3CO2, CF3SO3, BF4) at room temperature to yield [PtHMe2(TPMA)][X], which exists as an equilibrium mixture of two isomeric forms, each containing fac-tridentate TPMA. The major product has the hydride trans to a pyridyl group, but an equilibrium exists with the isomer in which the hydride is trans to amine. These cationic methyl(hydrido)platinum(IV) complexes are stable at room temperature for several hours, but undergo slow reductive elimination of CH4 to yield [PtMe(TPMA)][X], in which TPMA is mer-tridentate. The reaction of 1 with CF3SO3D in CD3OD gives only CH3D, with no deuterium incorporation into the remaining methylplatinum group, and with MeI it yields [PtMe3(TPMA)][I].