Dominic S. Wright

Synergic sedation of sensitive anions: alkali-mediated zincation of cyclic ethers and ethene.

Zinc-Based Bases Conventional methods of stripping a proton from a hydrocarbon yield an alkali metal-coordinated carbanion as the preliminary product. In certain cases, however, this preliminary product falls apart before it can be used for further constructive synthetic purposes. Kennedy et al. (p. 706; see the Perspective by Marek) show that in such cases, zinc ions can act as potent stabilizers. Specifically, a bimetallic base incorporating both sodium and zinc ions was used to deprotonate the common cyclic ethers tetrahydrofuran and tetrahydropyran. Zinc coordination to the carbanion inhibited an otherwise rapid ring-opening decomposition pathway. Similarly, a zinc-potassium combination facilitated deprotonation of ethylene to a stabilized product. Tandem coordination by zinc and an alkali metal increases the reactivity of carbon-hydrogen bonds of organic molecules. Deprotonation of alkyl and vinyl carbon-hydrogen bonds for synthetic purposes is often hindered not merely by the need for an exceptionally strong base, but by the inherent instability of the resultant anion. Metalation of cyclic ethers adjacent to oxygen, for example, has invariably initiated a ring-opening decomposition pathway. Here, we show that the use of a bimetallic base can overcome such instability through a cooperative combination of zinc-carbon and sodium-oxygen bonding. Both tetrahydrofuran and tetrahydropyran reacted cleanly over days at room temperature to yield α-zinc–substituted products that were sufficiently stable to be isolated and crystallographically characterized. A related zincation-anion trapping strategy, with sodium replaced by potassium, induced clean deprotonation of ethene to yield a stable product. Preliminary electrophilic quenching experiments with the α-zinc–substituted cyclic ethers and benzoyl chloride gave satisfactory yields of the tetrahydrofuran-derived ketone but only trace amounts of the tetrahydropyran-derived ketone.

Synthetic applications of p block metal dimethylamido reagents

The reactions of dimethylamido p block metal reagents with primary amines (RNH2) and primary amido and phosphido alkali metal complexes ([REHM]; E=N, P; M=alkali metal) furnish direct routes to a range of imido and phosphinidene compounds. In particular, novel p block metal polyimido and phosphinidene anions are readily accessible from these reactions. These function as versatile ligands to a variety of main group and transition metals, giving a structured approach to the assembly of heterometallic complexes containing a broad spectrum of mixed-metal stoichiometries. This review describes the synthetic applications of p block metal dimethylamido reagents to a range of p block metal compounds and the structures and reactivities of the imido and phosphinidene complexes produced.

Efficient visible light-active N-doped TiO2 photocatalysts by a reproducible and controllable synthetic route.

A reproducible and controllable method allows the synthesis of practical quantities of efficient, visible light active TiO(2)(N) photocatalysts in which the nitrogen content may be varied to achieve optimum performance.

Ab initio structure search and in situ 7Li NMR studies of discharge products in the Li-S battery system.

The high theoretical gravimetric capacity of the Li–S battery system makes it an attractive candidate for numerous energy storage applications. In practice, cell performance is plagued by low practical capacity and poor cycling. In an effort to explore the mechanism of the discharge with the goal of better understanding performance, we examine the Li–S phase diagram using computational techniques and complement this with an in situ 7Li NMR study of the cell during discharge. Both the computational and experimental studies are consistent with the suggestion that the only solid product formed in the cell is Li2S, formed soon after cell discharge is initiated. In situ NMR spectroscopy also allows the direct observation of soluble Li+-species during cell discharge; species that are known to be highly detrimental to capacity retention. We suggest that during the first discharge plateau, S is reduced to soluble polysulfide species concurrently with the formation of a solid component (Li2S) which forms near the beginning of the first plateau, in the cell configuration studied here. The NMR data suggest that the second plateau is defined by the reduction of the residual soluble species to solid product (Li2S). A ternary diagram is presented to rationalize the phases observed with NMR during the discharge pathway and provide thermodynamic underpinnings for the shape of the discharge profile as a function of cell composition.

Catalytic dehydrocoupling of Me2NHBH3 with Al(NMe2)3.

The catalytic dehydrocoupling reaction of Me(2)NHBH(3) with Al(NMe(2))(3) gives the dimer [Me(2)NBH(2)](2) and the chain [(Me(2)N)(2)BH], involving the thermally-stable Al(III) hydride catalyst [{(Me(2)N)(2)BH(2)}(2)AlH].

Templating and Selection in the Formation of Macrocycles Containing [{P(μ-NtBu)2}(μ-NH)]n Frameworks: Observation of Halide Ion Coordination

Amination of [ClP(micro-NtBu)](2) (1) using NH(3) in THF gives the cyclophospha(III)zane dimer [H(2)NP(micro-NtBu)](2) (2), in good yield. (31)P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et(3)N show that almost quantitative formation of the cyclic tetramer [[P(micro-NtBu)](2)(micro-NH)](4) (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre-organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58-67 % using various reaction scales. The isolation of the major by-product of the reaction (ca. 0.5-1 % of samples of 3), the pentameric, host-guest complex [[P(micro-NtBu)(2)](2)(micro-NH)](5)(HCl).2 THF] (4.2 THF), gives a strong indication of the mechanism involved. In situ (31)P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl(-) ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent- and anion-dependent. The X-ray structures of 2 and 4.2 THF are reported.

Recent perspectives on main group-mediated dehydrocoupling of P–P bonds

Transition metal-mediated dehydrocoupling is a developing synthetic tool for the preparation of an extensive range of main group element-element bonded species, with broad applications to molecular and polymeric materials. Recent results have stressed the relationship between this class of transition metal reagents and their entirely main group counterparts. But what are the similarities and differences between transition metal and main group systems?

A seeded synthetic strategy for uniform polymer and carbon nanospheres with tunable sizes for high performance electrochemical energy storage

We established a novel and facile strategy to synthesize uniform polymer and carbon nanospheres, the diameters of which can be precisely programmed between 35-105 and 30-90 nm, respectively, via time-controlled formation of colloidal seeds. The carbon nanospheres show promising prospects in high rate performance electrochemical energy storage.

Single-source materials for metal-doped titanium oxide: Syntheses, structures, and properties of a series of heterometallic transition-metal titanium oxo cages

Titanium dioxide (TiO(2)) doped with transition-metal ions (M) has potentially broad applications in photocatalysis, photovoltaics, and photosensors. One approach to these materials is through controlled hydrolysis of well-defined transition-metal titanium oxo cage compounds. However, to date very few such cages have been unequivocally characterized, a situation which we have sought to address here with the development of a simple synthetic approach which allows the incorporation of a range of metal ions into titanium oxo cage arrangements. The solvothermal reactions of Ti(OEt)(4) with transition-metal dichlorides (M(II)Cl(2), M = Co, Zn, Fe, Cu) give the heterometallic transition-metal titanium oxo cages [Ti(4)O(OEt)(15)(MCl)] [M = Co (2), Zn (3), Fe (4), Cu (5)], having similar MTi(4)(μ(4)-O) structural arrangements involving ion pairing of [Ti(4)O(OEt)(15)](-) anion units with MCl(+) fragments. In the case of the reaction of MnCl(2), however, two Mn(II) ions are incorporated into this framework, giving the hexanuclear Mn(2)Ti(4)(μ(4)-O) cage [Ti(4)O(OEt)(15)(Mn(2)Cl(3))] (6) in which the MCl(+) fragments in 2-5 are replaced by a [ClMn(μ-Cl)MnCl](+) unit. Emphasizing that the nature of the heterometallic cage is dependent on the metal ion (M) present, the reaction of Ti(OEt)(4) with NiCl(2) gives [Ti(2)(OEt)(9)(NiCl)](2) (7), which has a dimeric Ni(μ-Cl)(2)Ni bridged arrangement arising from the association of [Ti(2)(OEt)(9)](-) ions with NiCl(+) units. The syntheses, solid-state structures, spectroscopic and magnetic properties of 2-7 are presented, a first step toward their applications as precursor materials.

Dipole‐Induced Band‐Gap Reduction in an Inorganic Cage

Metal-doped polyoxotitanium cages are a developing class of inorganic compounds which can be regarded as nano- and sub-nano sized molecular relatives of metal-doped titania nanoparticles. These species can serve as models for the ways in which dopant metal ions can be incorporated into metal-doped titania (TiO2 ), a technologically important class of photocatalytic materials with broad applications in devices and pollution control. In this study a series of cobalt(II)-containing cages in the size range ca. 0.7-1.3 nm have been synthesized and structurally characterized, allowing a coherent study of the factors affecting the band gaps in well-defined metal-doped model systems. Band structure calculations are consistent with experimental UV/Vis measurements of the Tix Oy absorption edges in these species and reveal that molecular dipole moment can have a profound effect on the band gap. The observation of a dipole-induced band-gap decrease mechanism provides a potentially general design strategy for the formation of low band-gap inorganic cages.