Structures and Spectroscopic Properties of Polysulfide Radical Anions: A Theoretical Perspective.

The potential involvement of polysulfide radical anions Sn•- is a recurring theme in discussions of the basic and applied chemistry of elemental sulfur. However, while the spectroscopic features for n = 2 and 3 are well-established, information on the structures and optical characteristics of the larger congeners (n = 4-8) is sparse. To aid identification of these ephemeral species we have performed PCM-corrected DFT calculations to establish the preferred geometries for Sn•- (n = 4-8) in the polar media in which they are typically generated. TD-DFT calculations were then used to determine the number, nature and energies of the electronic excitations possible for these species. Numerical reliability of the approach was tested by comparison of the predicted and experimental excitation energies found for S2•- and S3•-. The low-energy (near-IR) transitions found for the two acyclic isomers of S4•- (C2h and C2v symmetry) and for S5•- (Cs symmetry) can be understood by extension of the simple HMO π-only chain model that serves for S2•- and S3•-. By contrast, the excitations predicted for the quasi-cyclic structures Sn•- (n = 6-8) are better described in terms of σ → σ* processes within a localized 2c-3e manifold.

Temperature-Assisted Generation of Arylmethyl Radicals from Bis(arylmethyl)tin Dichlorides: Efficient Reagents for C s p 3 ${{{\bf C}}_{{{\bf s p}}

The oxidative-addition reaction between an arylmethyl chloride (RCH2 Cl; R=1-C10 H7 , 2,4,6-Me3 C6 H2 , 4-MeC6 H4 , 3-MeC6 H4 , C6 H5 , 4-ClC6 H4 ) and tin powder in boiling toluene produces bis(arylmethyl)tin dichlorides, [(RCH2 )2 SnCl2 ] in good yields. At 160 °C in mesitylene bis(1-naphthylmethyl)tin dichloride undergoes Sn-C homolytic cleavage to generate two 1-naphthylmethyl radicals (1-C10 H7 CH2 ⋅) which were trapped by TEMPO (C9 H8 NO⋅). Subsequently, the radicals (RCH2 ⋅) produced in this manner were utilized for efficient substitution reactions with electron-rich arenes (R'H; R'=2,4,6-Me3 C6 H2 , 1,2,4,5-Me4 C6 H, 1,2,3,4,5-Me5 C6 ) to obtain a variety of unsymmetrical diarylmethanes (RR'CH2 ). The addition of one equivalent of iodine (I2 ) to the reaction mixture resulted in a significant increase in the yields of coupled products.

Correction: Tellurium: a maverick among the chalcogens.

Correction for 'Tellurium: a maverick among the chalcogens' by Tristram Chivers and Risto S. Laitinen, Chem. Soc. Rev., 2015, 44, 1725-1739, DOI: 10.1039/C4CS00434E.

Neutral binary chalcogen-nitrogen and ternary S,N,P molecules: new structures, bonding insights and potential applications.

Early theoretical and experimental investigations of inorganic sulfur-nitrogen compounds were dominated by (a) assessments of the purported aromatic character of cyclic, binary S,N molecules and ions, (b) the unpredictable reactions of the fascinating cage compound S4N4, and (c) the unique structure and properties of the conducting polymer (SN)x. In the last few years, in addition to unexpected developments in the chemistry of well-known sulfur nitrides, the emphasis of these studies has changed to include nitrogen-rich species formed under high pressures, as well as the selenium analogues of well-known S,N compounds. Novel applications have been established or predicted for many binary S/Se,N molecules, including their use for fingerprint detection, in optoelectronic devices, as high energy-density compounds or as hydrogen-storage materials. The purpose of this perspective is to evaluate critically these new aspects of the chemistry of neutral, binary chalcogen-nitrogen molecules and to suggest experimental approaches to the synthesis of target compounds. Recently identified ternary S,N,P compounds will also be considered in light of their isoelectronic relationship with binary S,N cations.

Catenated and spirocyclic polychalcogenides from potassium carbonate and elemental chalcogens.

The reaction of potassium carbonate with elemental sulfur or selenium in acetone in the presence of [PPN]Cl (PPN = (Ph3P)2N) produces catena-[S12]2-, the longest structurally characterised polysulfide dianion, or spiro-[Se11]2- as ion-separated [PPN]+ salts.

Correction: The role of polysulfide dianions and radical anions in the chemical, physical and biological sciences, including sulfur-based batteries.

Correction for 'The role of polysulfide dianions and radical anions in the chemical, physical and biological sciences, including sulfur-based batteries' by Ralf Steudel et al., Chem. Soc. Rev., 2019, 48, 3279-3319.

The role of polysulfide dianions and radical anions in the chemical, physical and biological sciences, including sulfur-based batteries.

The well-known tendency of sulfur to catenate is exemplified by an extensive series of polysulfide dianions [Sn]2- (n = 2-9) and related radical monoanions [Sn]˙-. The dianions can be isolated as crystalline salts with appropriate cations and structurally and spectroscopically characterized. Although the smaller radical monoanions may be stabilized in zeolitic matrices, they are usually formed in solution via disproportionation or partial dissociation of the dianions as well as by electrochemical reduction of elemental sulfur. An understanding of the fundamental chemistry of these homoatomic species is key to unravelling their behaviour in a broad variety of chemical environments. This review will critically evaluate the techniques used to characterize polysulfide dianions and radical anions both in solution and in the solid state, i.e. Raman, UV-visible, EPR, NMR and X-ray absorption spectroscopy, X-ray crystallography, mass spectrometry, chromatography and high-level quantum-chemical calculations. This is followed by a discussion of recent advances in areas in which these anionic sulfur species play a crucial role, viz. alkali-metal-sulfur batteries, organic syntheses, biological chemistry, geochemical processes including metal transport, coordination complexes, atmospheric chemistry and materials science.

s-Block metal complexes of PC(H)P-bridged chalcogen-centred methanides: comparisons with isoelectronic PNP-bridged monoanions.

The chemistry of the chalcogen-centred methanides [HC(PR2E)2]- (E = S, Se, Te; R = alkyl, aryl) (PC(H)P-bridged anions) is less well-developed than that of the isoelectronic imidodiphosphinates [N(PR2E)2]-, which are PNP-bridged analogues. The objective of this Perspective is to compare the chemistry of s-block metal complexes of the PC(H)P- and PNP-bridged anions in the context of synthetic approaches, X-ray (solid-state) structures, multinuclear NMR spectra, redox behaviour, and applications in coordination and inorganic heterocyclic chemistry. The related monochalcogeno-centred anions [HC(PR2)(PR2E)]- and [N(PR2)(PR2E)]- (E = S, Se, Te; R = alkyl, aryl) are also included in the discussion. Consideration of the similarities and, especially, the differences in the properties and reactions of the methanides with those of their imidodiphosphinate analogues reveals a number of areas in which the significance of the PC(H)P-bridged anions could be advanced.

Fundamental chemistry of binary S,N and ternary S,N,O anions: analogues of sulfur oxides and N,O anions.

Binary S,N anions, e.g., NSN2- and SSNSS-, and related ternary S,N,O anions such as the structural isomers NSO-/SNO- and SSNO- are rarely mentioned in inorganic chemistry textbooks, despite the fact that their salts were synthesised and structurally characterised more than 30 years ago. These fundamentally important species and their conjugate acids, e.g. HNSO and HSNO, have been the focus of numerous investigations in recent years in view of their significance in disciplines as diverse as atmospheric chemistry and cell biology. This Tutorial Review provides a consolidated account of the fundamental chemistry including synthesis, spectroscopic characterisation, molecular and electronic structures, and properties of these intriguing species, and compares these aspects of their behaviour with those of isoelectronic sulfur oxides and N,O anions. A final section draws attention to the significance and applications of these simple S-N species in a broader context.

Insights into the formation of inorganic heterocycles via cyclocondensation of primary amines with group 15 and 16 halides.

Cyclocondensation is a major preparative route for the generation of inorganic heterocycles especially in the case of ring systems involving a Group 15 or 16 element linked to nitrogen. This Perspective will consider recent experimental and computational studies involving the reactions of primary amines (or their synthetic equivalents) with pnictogen and chalcogen halides. The major focus will be a discussion of the identity and role of acyclic intermediates in the reaction pathways to ring formation, as well as the nature of the heterocycles so formed. The similarities and differences between the chemistry of group 15 and 16 systems are emphasised with a view to providing signposts for further investigations.

Synthesis of a labile sulfur-centred ligand, [S(H)C(PPh2S)2](-): structural diversity in lithium(i), zinc(ii) and nickel(ii) complexes.

A high-yield synthesis of [Li{S(H)C(PPh2S)2}]2 [Li2·(3)2] was developed and this reagent was used in metathesis with ZnCl2 and NiCl2 to produce homoleptic complexes 4 and 5b in 85 and 93% yields, respectively. The solid-state structure of the octahedral complex [Zn{S(H)C(PPh2S)2}2] (4) reveals notable inequivalence between the Zn-S(C) and Zn-S(P) contacts (2.274(1) Å vs. 2.842(1) and 2.884(1) Å, respectively). Two structural isomers of the homoleptic complex [Ni{S(H)C(PPh2S)2}2] were isolated after prolonged crystallization processes. The octahedral green Ni(ii) isomer 5a exhibits the two monoprotonated ligands bonded in a tridentate (S,S',S'') mode to the Ni(ii) centre with three distinctly different Ni-S bond lengths (2.3487(8), 2.4500(9) and 2.5953(10) Å). By contrast, in the red-brown square-planar complex 5b the two ligands are S,S'-chelated to Ni(ii) (d(Ni-S) = 2.165(2) and 2.195(2) Å) with one pendant PPh2S group. DFT calculations revealed that the energetic difference between singlet and triplet state octahedral and square-planar isomers of the Ni(ii) complex is essentially indistinguishable. Consistently, VT and (31)P CP/MAS NMR spectroscopic investigations indicated that a mixture of isomers exists in solution at room temperature, while the singlet state square-planar isomer 5b becomes favoured at -40 °C.

The role of imidoselenium(II) chlorides in the formation of cyclic selenium imides via cyclocondensation.

The third member of the series of imidoselenium(II) chlorides ClSe[N(tBu)Se]nCl (n = 3) (9) has been isolated from the cyclocondensation reaction of tBuNH2 and SeCl2 in THF in a molar ratio of ca. 3:1 and characterized in the form of two polymorphs 9a and 9b by single crystal X-ray analysis. The unusual structural features of this nine-atom chain are explained satisfactorily in terms of a bonding model that invokes intra-molecular secondary bonding interactions and hyperconjugation. The reaction of the bifunctional reagent ClSe[N(tBu)Se]2Cl (8) with tBuNH2 in THF occurs via concurrent pathways to give 1,3,5-Se3(NtBu)3 (1) and 1,3-Se3(NtBu)2 (3a). The energetics of the reactions of tBuNH2 and SeCl2 in THF have been calculated at the PBE0/def2-TZVPP level of theory in order to assess the feasibility of ClSe[N(tBu)Se]nCl (7­9, n = 1­3) as intermediates in the formation of known cyclic selenium imides. DFT calculations were also employed to explore the energy profile of the pathway of the formation of the first member of the series ClSeN(tBu)SeCl (7) from tBuNH2 and SeCl2 in THF at 298 K. The neutral ligand ClSeN(tBu)SeCl (7) is Se,Se'-coordinated to the metal centre in the unusual adduct [PdCl2{Se,Se'-(SeCl)2N(tBu)}]·[PdCl2{Se,Se'-Se4(NtBu)3}]·MeCN (10·MeCN), which is the first metal complex of an imidoselenium(II) chloride.

Mercury- and cadmium-assisted [2 + 2] cyclodimerization of tert-butylselenium diimide.

The complexes [MCl2{N,N'-(t)BuNSe(µ-N(t)Bu)2SeN(t)Bu}] [M = Cd (1), Hg (2)] were obtained in high yields by the reaction of tert-butylselenium diimide Se(IV)(N(t)Bu)2 with CdCl2 or HgCl2 in tetrahydrofuran. Recrystallization of 1 and 2 from acetonitrile (MeCN) afforded yellow crystals of 1·MeCN and 2·MeCN, respectively. Isomorphic 1·MeCN and 2·MeCN contain an unprecedented dimeric selenium diimide ligand, which is N,N'-chelated to the metal through exocyclic imido groups. In addition to the complexes 1 and 2, the (77)Se NMR spectra of acetonitrile solutions of 1·MeCN and 2·MeCN indicated the presence of the dimeric (t)BuNSe(µ-N(t)Bu)2SeN(t)Bu, monomeric Se(IV)(N(t)Bu)2, and cyclic selenium imides. Density functional theory calculations at the PBE0/def2-TZVPP level of theory were used to assign the (77)Se resonances of the dimer. A comparison of Gibbs energies of formation of some metal dichloride complexes [MCl2{N,N'-Se(IV)(N(t)Bu)2}] and [MCl2{N,N'-(t)BuNSe(µ-N(t)Bu)2SeN(t)Bu}] (M = Zn, Cd, Hg) indicated that the formation of complexes containing a dimeric selenium diimide ligand is favored over those containing a monomeric ligand for the group 12 metals. In the case of the group 10 metal halogenides (M = Ni, Pd, Pt), the Gibbs energies of the complexes with monomeric Se(IV)(N(t)Bu)2 ligands are close to those containing dimeric (t)BuNSe(µ-N(t)Bu)2SeN(t)Bu ligands. A plausible reaction pathway with a low activation energy involves the initial formation of [MCl2{N,N'-Se(IV)(N(t)Bu)2}] (M = Zn, Cd, Hg), which then reacts with another molecule of Se(N(t)Bu)2, leading to the final [MCl2{N,N'-(t)BuNSe(µ-N(t)Bu)2SeN(t)Bu}] complex. Without the presence of group 12 metal halogenides, the [2 + 2] cyclodimerization of Se(IV)(N(t)Bu)2 is virtually thermoneutral, but the activation energy is relatively high, which accounts for the kinetic stability of (t)BuNSe(µ-N(t)Bu)2SeN(t)Bu in solution. A minor byproduct, [Cd7Cl14{N,N'-Se(II)(NH(t)Bu)2}6]·4CH2Cl2, was identified by X-ray crystallography as a heptanuclear cluster with selenium(II) diamide ligands N,N'-chelated to the cadmium centers.

A square-planar tellurium(II) complex with Te,Te'-chelating ligands.

While exploring the chemistry of tellurium-containing dichalcogenidoimidodiphosphinate ligands, the first all-tellurium member of a series of related square-planar E(II)(E')4 complexes (E and E' are group 16 elements), namely bis(P,P,P',P'-tetraphenylditelluridoimidodiphosphinato-κ(2)Te,Te')tellurium(II) (systematic name: 2,2,4,4,8,8,10,10-octaphenyl-1λ(3),5,6λ(4),7λ(3),11-pentatellura-3,9-diaza-2λ(5),4λ(5),8λ(5),10λ(5)-tetraphosphaspiro[5.5]undeca-1,3,7,9-tetraene), C48H40N2P4Te5, was obtained unexpectedly. The formally Te(II) centre is situated on a crystallographic inversion centre and is Te,Te'-chelated to two anionic [(TePPh2)2N](-) ligands in an anti conformation. The central Te(II)(Te)4 unit is approximately square planar [Te-Te-Te = 93.51 (3) and 86.49 (3)°], with Te-Te bond lengths of 2.9806 (6) and 2.9978 (9) Å.

Experimental and Computational (77)Se NMR Investigations of the Cyclic Eight-Membered Selenium Imides 1,3,5,7-Se4(NR)4 (R = Me, (t)Bu) and 1,5-Se6(NMe)2.

The cyclocondensation reaction of equimolar amounts of SeCl2 and (Me3Si)2NMe in THF affords 1,3,5,7-Se4(NMe)4 (5b) [δ((77)Se) = 1585 ppm] in excellent yield. An X-ray structural determination showed that 5b consists of cyclic, puckered crown-shaped molecules with a mean Se-N bond length of 1.841 Å typical of single bonds. A minor product of this reaction was isolated as unstable orange-red crystals, which were identified by X-ray analysis as the adduct 1,5-Se6(NMe)2·(1)/2Se8 (1b·(1)/2Se8), composed of cyclic 1,5-Se6(NMe)2 and disordered cyclo-Se8 molecules. A detailed reinvestigation of the cyclocondensation reaction of SeCl2 and (t)BuNH2 as a function of molar ratio and time by multinuclear ((1)H, (13)C, and (77)Se) NMR spectroscopy revealed that the final product exhibits one (77)Se resonance at 1486 ppm and equivalent N(t)Bu groups. The shielding tensors of 28 selenium-containing molecules, for which the (77)Se chemical shifts are unambiguously known, were calculated at the PBE0/def2-TZVPP level of theory to assist the spectral assignment of new cyclic selenium imides. The good agreement between the observed and calculated chemical shifts enabled the assignment of the resonance at 1486 ppm to 1,3,5,7-Se4(N(t)Bu)4 (5a). Those at 1028 and 399 ppm (intensity ratio 2:1) could be attributed to 1,5-Se6(NMe)2 (1b).

Tellurium: a maverick among the chalcogens.

The scant attention paid to tellurium in both inorganic and organic chemistry textbooks may reflect, in part, the very low natural abundance of the element. Such treatments commonly imply that the structures and reactivities of tellurium compounds can be extrapolated from the behaviour of their lighter chalcogen analogues (sulfur and selenium). In fact, recent findings and well-established observations clearly illustrate that this assumption is not valid. The emerging importance of the unique properties of tellurium compounds is apparent from the variety of their known and potential applications in both inorganic and organic chemistry, as well as materials science. With reference to selected contemporary examples, this Tutorial Review examines the fundamental concepts that are essential for an understanding of the unique features of tellurium chemistry with an emphasis on hypervalency, three-centre bonding, secondary bonding interactions, σ and π-bond energies (multiply bonded compounds), and Lewis acid behaviour.

Main group tellurium heterocycles anchored by a P(2)(V)N(2) scaffold and their sulfur/selenium analogues.

A comprehensive investigation of reactions of alkali-metal derivatives of the ditelluro dianion [TePV(NtBu)(µ-NtBu)]22­ (L2­, E = Te) with p-block element halides produced a series of novel heterocycles incorporating P2VN2 rings, tellurium, and group 13­16 elements. The dianion engages in Te,Te'-chelation to the metal center in Ph2Ge and R2Sn (R = tBu, nBu, Ph) derivatives; similar behavior was noted for group 14 derivatives of L2­ (E = S, Se). In the case of group 13 trihalides MCl3 (M = Ga, In), neutral spirocyclic complexes (L)M[NtBu(Te)PV(µ-NtBu)2PIIIN(H)tBu)] (M = Ga, In) comprised of a Te,Te'-chelated ligand L2­ and a N,Te-bonded ligand resulting from loss of Te and monoprotonation were obtained. In reactions with RPCl2 (R = tBu, Ad, iPr2N) a significant difference was observed between Se- and S-containing systems. In the former case, Se,Se'-chelated derivatives were formed in high yields, whereas the N,S-chelated isomers predominated for sulfur. All complexes were characterized by multinuclear (1H, 31P, 77Se, 119Sn, and 125Te) NMR spectroscopy; this technique was especially useful in the analysis of the mixture of (L)(Se) and (L)(SeSe) obtained from the reaction of Se2Cl2 with L2­ (E = Te). Single-crystal X-ray structures were obtained for the spirocyclic In complex (9), (L)GePh2 (E = Te, 10), (L)SntBu2 (E = Te, 12a); E = Se, 12aSe, E = S, 12aS) and (L)(µ-SeSe) (E = Te, 16).

Spirocyclic, macrocyclic and ladder complexes of coinage metals and mercury with dichalcogeno P2N2-supported anions.

Metathetical reactions of alkali-metal derivatives of the dianion [(t)BuN(Se)P(µ-N(t)Bu)2P(Se)N(t)Bu](2-) ((2Se2-)) with Ag(NHC)Cl, Ag[BF4], AuCl(THT) and HgCl2, as well as the reaction of 2S(2-) with AuCl(THT) were investigated. The observed products all incorporate the monoprotonated ligands 2SeH(-) or 2SH(-) in a variety of structural arrangements around the metal centres, including tetrameric and trimeric macrocycles [Ag and Au (E = Se)], a ladder (Au, E = S) and a spirocycle (Hg); the ladder contains both the dianion 2S(2-) and the monoanion 2SH(-) as ligands linking three Au2 units. All complexes have been characterised in the solid state by single crystal X-ray analyses and in solution by multinuclear ((1)H, (31)P and (77)Se) NMR spectra.

Sodium and rhodium complexes of a spirocyclic Te5 dianion supported by P2N2 rings.

Reactions of the dianion [Te((t)BuN)P(µ-N(t)Bu)2P(N(t)Bu)Te](2-) with I2 or [Cp*RhCl2]2 unexpectedly produced complexes of the novel spirocyclic Te5 dianion [{(t)BuN(Te)P(µ-N(t)Bu)2P(Te)N(t)Bu}2µ-Te](2-), which is N,N'-coordinated to two Na(+) ions in the disodium derivative and adopts a Te,Te',Te''-bonding mode in the Cp*Rh complex.