Redox Reactions between Phosphines (R3P; R = nBu, Ph) or Carbene (iPr2IM) and Chalcogen Tetrahalides ChX4 (iPr2IM = 2,5-diisopropylimidazole-2-ylidene; Ch = Se, Te; X = Cl, Br)

Evidence for C-F Bond Formation through Formal Reductive Elimination from Tellurium(VI)

The fundamental challenge of C-F bond formation by reductive elimination has been met by compounds of select transition metals and fewer main group elements. The work detailed herein expands the list of main group elements known to be capable of reductively eliminating a C-F bond to include tellurium. Surprising and novel modes of both sp² and sp³ C-F bond formation were observed alongside formation of Te^IV cations during two separate attempts to synthesize/characterize fluorinated organotellurium(VI) cations in superacidic media (SbF₅ /SO₂ ClF). Following detailed low-temperature NMR experiments, the mechanisms of the two unique reductive elimination reactions were probed and investigated using density functional theory (DFT) calculations. Ultimately, we found that an "indirect" reductive elimination pathway is likely operative whereby Sb plays a key role in fluoride abstraction and C-F bond formation, as opposed to unimolecular reductive elimination from a discrete Te^VI cation.

Reactions of N-heterocyclic carbene-based chalcogenoureas with halogens: a diverse range of outcomes

We have investigated the reactions of chalcogenoureas derived from N-heterocyclic carbenes, referred to here as [E(NHC)], with halogens. Depending on the structure of the chalcogenourea and the identity of the halogen, a diverse range of reactivity was observed and a corresponding range of structures was obtained. Cyclic voltammetry was carried out to characterise the oxidation and reduction potentials of these [E(NHC)] species; selenoureas were found to be easier to oxidise than the corresponding thioureas. In some cases, a correlation was found between the oxidation potential of these compounds and the electronic properties of the corresponding NHC. The reactivity of these chalcogenoureas with different halogenating reagents (Br₂, SO₂Cl₂, I₂) was then investigated, and products were characterised using NMR spectroscopy and single-crystal X-ray diffraction. X-ray analyses elucidated the solid-state coordination types of the obtained products, showing that a variety of possible adducts can be obtained. In some cases, we were able to extrapolate a structure/activity correlation to explain the observed trends in reactivity and oxidation potentials.

Reactions of PhIX2 I(iii) oxidants with heavy triphenyl pnictines

The reactions of [PhI(pyridine)2]2+, PhI(OAc)2 and PhI(OTf)(OAc) with Ph3As, Ph3Sb and Ph3Bi are described. The reactions of [PhI(pyridine)2]2+ with Ph3Sb and Ph3Bi afford dicationic Pn(v) complexes ligated by pyridine in one step. These were previously reported by Burford in multi-step syntheses. Reactions with PhI(OAc)2, which were already known for Sb and Bi giving Pn(v) diacetates, were confirmed to give the same type of compound for As. Reactions with PhI(OAc)(OTf) were less selective, resulting in the isolation of iodonium cations [Ph-I-Ph]+ for As and Bi, while Ph3Sb gave an oxobridged di-antimony species characteristic of the decomposition of a high valent triflate bound species.

NHCs in Main Group Chemistry

Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

Transition metal mediated formation of dicationic diselenides stabilised by N-heterocyclic carbenes: designed synthesis

Designed syntheses of dicationic diselenides have been developed by (i) reduction of dihaloselones (routes A and B) and (ii) by oxidation of selone adducts of metal halides (route C).

Triphenylphosphine promoted regio and stereoselective α-halogenation of ynamides

Metal free α-halogenation of ynamides at room temperature.

A 2,2′-bipyridine coordination complex of [ICl2]+

A straightforward synthesis of a new type of iodine(iii) complex is presented – anN′Nchelated [ICl₂]⁺cation.

Diverse reactions of PhI(OTf)2 with common 2-electron ligands: complex formation, oxidation, and oxidative coupling

The crystal structures of bis-pyridine stabilized iodine dications [PhI(pyr)(2)](2+) are reported as triflate salts, representing the first ligand supported iodine dications to be structurally characterized. The pyridine complexes are susceptible to ligand exchange in reaction with stronger N-based donors such as 4-dimethylaminopyridine. Attempts to extend this reactivity to N-heterocyclic carbene and phosphine ligands, as has been accomplished in the earlier p-block groups, resulted in redox chemistry, with oxidation of the ligands rather than coordination.

Structural isomerism in tris-tolyl halo-phosphonium and halo-arsonium tri-halides, [(CH3C6H4)3EX][X3], (E = P, As; X = Br, I)

The group 15 ligands (o-CH(3)C(6)H(4))(3)P, (m-CH(3)C(6)H(4))(3)P, (p-CH(3)C(6)H(4))(3)P, Ph(3)As, (o-CH(3)C(6)H(4))(3)As and (p-CH(3)C(6)H(4))(3)As have been reacted with two equivalents of di-iodine or di-bromine to yield complexes of formula R(3)EX(4) (E = P, As; X = I, Br). These halogenated group 15 compounds are ionic, [R(3)EX][X(3)] consisting of halo-phosphonium or halo-arsonium cations and trihalide anions. These adducts exhibit structural isomerism and may exist either as simple 1:1 ion pairs, [R(3)EX][X(3)], isomer (A), which display a weak XX interaction between cation and anion, or as a 2:1 complex, which consists of a [{R(3)EX}(2)X(3)](+) cationic species made up of two [R(3)EX](+) cations interacting with one [X(3)](-) anion. The overall charge is balanced by a second [X(3)](-) anion. These 2:1 species also exhibit structural isomerism due to subtle differences in the connectivity of the [{R(3)EX}(2)X(3)](+) fragment, as the {R(3)EX}(+) units may either interact at the same end of the [X(3)](-) ion, to give a Y-shaped motif, isomer (B), or at opposite ends, giving a Z-shaped motif, isomer (C). The type of structural isomer formed is related to the way in which [Ar(3)EX](+) cations pack together via aryl embraces. Isomer (A) and (C) structures form chains of side-to-side, anti-parallel embracing cations. In (A) and (C) structures a square-like stacking motif of cations is observed. In contrast, isomer (B) structures feature side-to-side, parallel embracing cations, and do not exhibit the square motif.

N-(2-Bromo-benz-yl)-N'-(2-pyrid-yl)benzene-1,2-diamine

In the title compound, C₁₈H₁₆BrN₃, mol­ecules are linked into dimers by co-operative inter­molecular N—H⋯N hydrogen bonding. Only one N—H group is involved in hydrogen bonding. The planes of the pyridine and bromo­phenyl rings are twisted by 61.49 (3) and 79.11 (8)°, respectively, from the plane of the central phenyl ring.