Highly Strained Heterocycles Constructed from Boron-Boron Multiple Bonds and Heavy Chalcogens.

The reactions of a diborene with elemental selenium or tellurium are shown to afford a diboraselenirane or diboratellurirane, respectively. These reactions are reminiscent of the sequestration of subvalent oxygen and nitrogen in the formation of oxiranes and aziridines; however, such reactivity is not known between alkenes and the heavy chalcogens. Although carbon is too electronegative to affect the reduction of elements with lower relative electronegativity, the highly reducing nature of the B-B double bond enables reactions with Se(0) and Te(0) . The capacity of multiple bonds between boron atoms to donate electron density is highlighted in reactions where diborynes behave as nucleophiles, attacking one of the two Te atoms of diaryltellurides, forming salts consisting of diboratellurenium cations and aryltelluride anions.

Peri-substituted phosphorus-tellurium systems-an experimental and theoretical investigation of the P···Te through-space interaction.

A series of peri-substituted phosphorus-tellurium systems R'Te-Acenap-PR2 (R' = Ph, p-An, Nap, Mes, Tip; Acenap = acenaphthene-5,6-diyl (-C12H8); R = (i)Pr, Ph) exhibiting large "through-space" spin-spin coupling constants and the "onset" of three-center four-electron type interactions is presented. The influence of the substituents at the phosphorus and tellurium atoms as well as their behavior upon oxidation (with S, Se) or metal-coordination (Pt, Au) is discussed using NMR spectroscopy, single-crystal X-ray diffraction, and advanced density functional theory studies including NBO, AIM, and ELI-D analyses.

Conformational dependence of through-space tellurium-tellurium spin-spin coupling in peri-substituted bis(tellurides).

Three related series of peri-substituted bis(tellurides) bearing naphthalene, acenaphthene and acenaphthylene backbones (Nap/Acenap/Aceyl(TeY)2 (Nap = naphthalene-1,8-diyl N; Acenap = acenaphthene-5,6-diyl A; Aceyl = acenaphthylene-5,6-diyl Ay; Y = Ph 1; Fp 2; Tol 3; An-p- 4; An-o- 5; Tp 6; Mes 7; Tip 8) have been synthesised and their solid-state structures determined by X-ray crystallography. Molecular conformations were classified as a function of the two C9-C-Te-C(Y) dihedral angles (θ); in the solid all members adopt AB or CCt configurations, with larger Te(aryl) moieties exclusively imposing the CCt variant. Exceptionally large J((125)Te,(125)Te) spin-spin coupling constants between 3289-3848 Hz were obtained for compounds substituted by bulky Te(aryl) groups, implying these species are locked in a CCt-type conformation. In contrast, compounds incorporating smaller Te(aryl) moieties are predicted to be rather dynamic in solution and afford much smaller J values (2050-2676 Hz), characteristic of greater populations of AB conformers with lower couplings. This conformational dependence of through-space coupling is supported by DFT calculations.

Sterically encumbered tin and phosphorus peri-substituted acenaphthenes.

A group of sterically encumbered peri-substituted acenaphthenes have been prepared, containing tin moieties at the 5,6-positions in 1-3 ([Acenap(SnR3)2], Acenap = acenaphthene-5,6-diyl; R3 = Ph3 (1), Me3 (2); [(Acenap)2(SnMe2)2] (3)) and phosphorus functional groups at the proximal peri-positions in 4 and 5 ([Acenap(PR2)(P(i)Pr2)] R2 = Ph2 (4), Ph((i)Pr) (5)). Bis(stannane) structures 1-3 are dominated by repulsive interactions between the bulky tin groups, leading to peri-distances approaching the sum of van der Waals radii. Conversely, the quasi-linear CPh-P···P three-body fragments found in bis(phosphine) 4 suggest the presence of a lp(P)-σ*(P-C) donor-acceptor 3c-4e type interaction, supported by a notably short intramolecular P···P distance and notably large JPP through-space coupling (180 Hz). Severely strained bis(sulfides) 4-S and 5-S, experiencing pronounced in-plane and out-of-plane displacements of the exocyclic peri-bonds, have also been isolated following treatment of 4 and 5 with sulfur. The resulting nonbonded intramolecular P···P distances, ∼4.05 Å and ∼12% longer than twice the van der Waals radii of P (3.60 Å), are among the largest ever reported peri-separations, independent of the heteroatoms involved, and comparable to the distance found in 1 containing the larger Sn atoms (4.07 Å). In addition we report two metal complexes with square planar [(4)PtCl2] (4-Pt) and octahedral cis-[(4)Mo(CO)4] (4-Mo) geometries. In both complexes the bis(phosphine) backbone is distorted, but notably less so than in bis(sulfide) 4-S. All compounds were fully characterized, and except for bis(phosphine) 5, crystal structures were determined.

Probing interactions through space using spin-spin coupling.

The series of eight 5-(TeY)-6-(SePh)acenaphthenes (Y = Fp (2), Tol (3), An-p (4), An-o (5), Tp (6), Mes (7), Tip (8), Nap (9)) were prepared and structurally characterised by X-ray crystallography, solution and solid-state NMR spectroscopy and density functional theory (DFT/B3LYP) calculations. All members of the series, except 5, adopt a BA type configuration comparable to the parent compound 1 (Y = Ph), aligning the Te-C(Y) bond along the mean acenaphthene plane and promoting a nonbonded Se···Te-C(Y) 3c-4e type interaction to form to stabilise the molecule (G-dependence). 5 (Y = An-o) adopts a BC type conformation in the solid but DFT calculations show this optimises to BA. Indication of strong through-space peri-interactions between Te and Se are observed in the (77)Se and (125)Te NMR spectra, with J(Te,Se) spin-spin coupling constants (SSCCs) in the range -688 to -748 Hz. Evidence supporting the presence of this interaction was also found in solid-state NMR spectra of some of the compounds which exhibit an indirect spin-spin coupling on the same order of magnitude as observed in solution. In order to quantify the steric bulk of the aryl groups (Y), we introduce the crystallographic steric parameter (θ), the cone angle measured from the furthest H atoms lying on the edges of the cone to the Te atom located at its vertex. Modification to Y has no apparent influence over the conformation of the molecule, the degree of molecular distortion occurring in the acenaphthene backbone or the extent of 3c-4e interaction; peri-distances for all eight compounds are within 0.08 Å and no apparent correlation is observed between the steric bulk of Y (θ) and the (77)Se chemical shifts or J(Te,Se) SSCCs. In contrast, a good correlation is found between θ and (125)Te chemical shifts. DFT calculations performed on all members of the series confirm the comparable covalent bonding between Te and Se in the series, with WBIs of ca. 0.1 obtained. Natural bond orbital analysis shows a noticeable donor-acceptor interaction between a p-type lone pair on Se and a σ*(Te-C) antibonding orbital, confirming the onset of 3c-4e type bonding.

Electrochemically informed synthesis: oxidation versus coordination of 5,6-bis(phenylchalcogeno)acenaphthenes.

Chalcogen dications: Facile synthesis of E--E bonded dications can be readily achieved. Radical cations are identified as the intermediates.

Weak Te,Te interactions through the looking glass of NMR spin-spin coupling.

Across the bay: J((125)Te, (125)Te) spin-spin coupling is a highly sensitive probe into the electronic and geometric structure of 1,8-peri-substituted naphthalene tellurium derivatives. The coupling is related to the onset of multicenter bonding in these systems.

Silver(I) coordination complexes and extended networks assembled from S, Se, Te substituted acenaphthenes.

Six related organo­chalconium silver(I) coordination complexes, including two examples of rare organotellurium-silver coordination, have been prepared and structurally characterised by X-ray crystallography. The series of 5-bromo-6-(phenylchalcogeno)acenaphthene ligands L1­L3 [Acenap(Br)(EPh)] (Acenap = acenaphthene-5,6-diyl; E = S, Se, Te) were independently treated with silver(I) salts (AgBF4, AgOTf). In order to keep the number of variables to a minimum, all reactions were carried out using a 1:1 ratio of Ag/L and run in dichloromethane. The nature of the donor atoms and the coordinating ability of the respective counter-anion affects the structural architecture of the final silver(I) complex, generating a monomeric dinuclear complex {[(AgBF4(L1)2)2] 1}, monomeric, mononuclear, two-coordinate silver(I) complexes {[AgBF4(L)2] (2 L = L2; 3 L = L3)}, a monomeric three-coordinate silver(I) complex {[AgOTf(L2)2] 5}, a monomeric four-coordinate silver(I) complex {[AgOTf(L1)3] 4} and a 1D extended helical chain polymer {[AgOTf(L3)]n 6}. The organic acenaphthene ligands L1­L3 all adopt the same ligation mode with the central silver atom (classical monodentate coordination), which employs a variety of coordination geometries (linear, trigonal planar, see-saw, tetrahedral).

Investigating silver coordination to mixed chalcogen ligands.

Six silver(I) coordination complexes have been prepared and structurally characterised. Mixed chalcogen-donor acenaphthene ligands L1-L3 [Acenap(EPh)(E'Ph)] (Acenap = acenaphthene-5,6-diyl; E/E' = S, Se, Te) were independently treated with silver(I) salts (AgBF4/AgOTf). In order to keep the number of variables to a minimum, all reactions were carried out using a 1:1 ratio of Ag/L and run in dichloromethane. The nature of the donor atoms, the coordinating ability of the respective counter-anion and the type of solvent used in recrystallisation, all affect the structural architecture of the final silver(I) complex, generating monomeric, silver(I) complexes {[AgBF4(L)2] (1 L = L1; 2 L = L2; 3 L = L3), [AgOTf(L)3] (4 L = L1; 5 L = L3), [AgBF4(L)3] (2a L = L1; 3a L = L3)} and a 1D polymeric chain {[AgOTf(L3)](n) 6}. The organic acenaphthene ligands L1-L3 adopt a number of ligation modes (bis-monodentate µ2-η²-bridging, quasi-chelating combining monodentate and η6-E(phenyl)-Ag(I) and classical monodentate coordination) with the central silver atom at the centre of a tetrahedral or trigonal planar coordination geometry in each case. The importance of weak interactions in the formation of metal-organic structures is also highlighted by the number of short non-covalent contacts present within each complex.

Noncovalent interactions in peri-substituted chalconium acenaphthene and naphthalene salts: a combined experimental, crystallographic, computational, and solid-state NMR study.

Twelve related monocation chalconium salts [{Nap(EPh)(E'Ph)Me}(+){CF(3)SO(3)}(-)] 2-4, [{Acenap(Br)(EPh)Me}{CF(3)SO(3)}(-)] 5-7, and [{Acenap(EPh)(E'Ph)Me}(+){CF(3)SO(3)}(-)] 8-13 have been prepared and structurally characterized. For their synthesis naphthalene compounds [Nap(EPh)(E'Ph)] (Nap = naphthalene-1,8-diyl; E/E' = S, Se, Te) N2-N4 and associated acenaphthene derivatives [Acenap(X)(EPh)]/[Acenap(EPh)(E'Ph)] (Acenap = acenaphthene-5,6-diyl; E/E' = S, Se, Te; X = Br) A5-A13 were independently treated with a single molar equivalent of methyl trifluoromethanesulfonate (MeOTf). In addition, reaction of bis-tellurium compound A10 with 2 equiv of MeOTf afforded the doubly methylated dication salt [{Acenap(TePhMe)(2)}(2+){(CF(3)SO(3))(2)}(2-)}] 14. The distortion of the rigid naphthalene and acenaphthene backbone away from ideal was investigated in each case and correlated in general with the steric bulk of the interacting atoms located at the proximal peri positions. Naturally, introduction of the ethane linker in acenaphthene compounds increased the splay of the bay region compared with equivalent naphthalene derivatives resulting in greater peri distances. The conformation of the aromatic rings and subsequent location of p-type lone pairs has a significant impact on the geometry of the peri region, with anomalies in peri separations correlated to the ability of the frontier orbitals to take part in attractive or repulsive interactions. In all but one of the monocations a quasi-linear three-body C(Me)-E···Z (E = Te, Se, S; Z = Br/E) fragment provides an attractive component for the E···Z interaction. Density functional studies confirmed these interactions and suggested the onset of formation of three-center, four-electron bonding under appropriate geometric conditions, becoming more prevalent as heavier congeners are introduced along the series. The increasingly large J values for Se-Se, Te-Se, and Te-Te coupling observed in the (77)Se and (125)Te NMR spectra for 1, 3, 4, 9, 10, and 13 give further evidence for the existence of a weakly attractive through-space interaction.

Exploring hypervalency and three-centre, four-electron bonding interactions: reactions of acenaphthene chalcogen donors and dihalogen acceptors.

Sterically crowded peri-substituted selenium and tellurium acenaphthene donors D1-D7 [Acenap(EPh)(Br) E = Se, Te; Acenap(SePh)(EPh) E = Se, S; Acenap(TePh)(EPh) E = S, Se, Te] react with dibromine and diiodine acceptors to afford a group of structurally diverse addition products 1-12, comparable in some cases to previously reported naphthalene analogues. Tellurium donors D4-D6 react conventionally with the dihalogens to afford insertion adducts 6-11 (X-R(2)Te-X) exhibiting molecular see-saw geometries, characterised by hypervalent X-Te-X quasi-linear fragments. The reactions of selenium donors D1-D3 with diiodine afford expected neutral charge-transfer (CT) spoke adducts 1, 4 and 5 (R(2)Se-I-I) containing quasi-linear Se-I-I alignments. Conversely, treatment of D2 and D3 with dibromine results in the formation of two tribromide salts 2 and 3 containing bromoselanyl cations [R(2)Se-Br](+)···[Br-Br(2)](-), each exhibiting a quasi-linear three-body Br-Se···E (E = Se, S) fragment. The peri-bonding in these species can be thought of as a weak hypervalent G···Se-X three-centre, four-electron (3c-4e) type interaction, closely related to the T-shaped 3c-4e interaction. Density-functional calculations performed on 2 and 3 and their bare cations (2a and 3a) reveal Wiberg bond indices of 0.25-0.37, suggesting substantial 3c-4e character in these systems. The presence of such an interaction operating in 2 and 3 alleviates steric strain within the peri-region and minimises the degree of molecular distortion required to achieve a relaxed geometry. Ditellurium donor D7 reacts with dibromine to afford an unorthodox insertion adduct 12 containing a Te-O-Te bridge and two quasi-linear Br-Te-O fragments, with the central tellurium atoms assuming a molecular see-saw geometry. Whilst DFT calculations indicate 12 is thermodynamically unfavourable, its formation is viable under experimental conditions.

Onset of three-centre, four-electron bonding in peri-substituted acenaphthenes: a structural and computational investigation.

Two series of sterically crowded peri-substituted acenaphthenes have been prepared, containing mixed halogen-chalcogen functionalities at the 5,6-positions in A1-A6 (Acenap[X][EPh] (Acenap = acenaphthene-5,6-diyl; X = Br, I; E = S, Se, Te) and chalcogen-chalcogen moieties in A7-A12 (Acenap[EPh][E'Ph] (Acenap = acenaphthene-5,6-diyl; E/E' = S, Se, Te). The related dihalide compounds A13-A16 Acenap[XX'] (XX' = BrBr, II, IBr, ClCl) have also been prepared. Distortion of the acenaphthene framework away from the ideal was studied as a function of the steric bulk of the interacting halogen and chalcogen atoms occupying the peri-positions. The acenaphthene series experiences a general increase in peri-separation for molecules accommodating heavier congeners and maps the trends observed previously for the analogous naphthalene compounds N1-N12 (Nap[X][EPh], Nap[EPh][E'Ph] (X = Br, I; E/E' = S, Se, Te). The conformation of the aromatic ring systems and subsequent location of p-type lone-pairs dominates the geometry of the peri-region. The differences in peri-separations observed for compounds adopting differing conformations of the peri-substituted phenyl group can be correlated to the ability of the frontier orbitals of the halogen or chalcogen atoms to take part in attractive or repulsive interactions. Density-functional studies have confirmed these interactions and suggested the onset of formation of three-centre, four-electron bonding under appropriate geometric conditions.

Naphthalene and related systems peri-substituted by Group 15 and 16 elements.

Synthetic and bonding aspects of heavier Group 15 (P, As, Sb, Bi) and 16 (S, Se, Te) peri-substituted naphthalenes, are discussed in this review. An important and unifying feature of the chemistry of these systems is the lively discussion about the nature of the interaction between peri-atoms. Are atoms bonded when they are closer than the sum of their van der Waals radii? Is there any (weak) bonding, or just a strained repulsive interaction? Positioning atoms of Group 15 and 16 at the naphthalene 1,8-positions provides leading systems with which to study these bonding issues.

Hypervalent adducts of chalcogen-containing peri-substituted naphthalenes; reactions of sulfur, selenium, and tellurium with dihalogens.

A range of structurally diverse compounds 1-15 {Nap[SPh](2).Br(4) (Nap = naphthalene-1,8-diyl); Nap[SePh][EPh].Br(4) (E = Se, S); Nap[SePh](2).I(2); Nap[SePh][EPh].3/2I(2) (E = Se, S); Nap[TePh][G].X(2) (G = SePh, SPh, Br, I; X = Br, I); and [Nap(PPh(2)OH)(SPh)](+)Br(3)(-)} formed from the reactions between peri-substituted naphthalene chalcogen donors D1-D8 {Nap[ER][E'R] (ER/E'R = SPh, SePh, TePh); Nap[TePh][X] (X = Br, I); and Nap[PPh(2)][SPh]} and dibromine and diiodine were characterized by X-ray crystallography and where possible by multinuclear NMR, IR, and MS. X-ray data for 1-15 were analyzed by naphthalene ring torsions, peri-atom displacement, splay angle magnitude, peri-distance, aromatic ring orientations, and quasi-linear three-body arrangements. The hypervalent linear moieties are considered in the context of the charge-transfer model and the 3c-4e model introduced by Pimentel and Rundle. In general, the conformation of the final products obeyed the rule based on charge-transfer that "seesaw" (X-ER(2)-X, 10-E-4) adducts arise when the halogen (X) is more electronegative than the chalcogen (E), and if the converse is true then, CT "spoke" (X-X-ER(2), 8-E-3) adducts are formed. Upon treatment with dibromine, selenium donor compounds D2 {Nap[SePh](2)} and D3 {Nap[SePh][SPh]} afford unusual tribromide salts of bromoselenyl cations containing a hypervalent X-E...E' 3c-4e type interaction. Upon treatment with diiodine, D2 and D3 form "Z-shaped", "extended spoke" adducts containing an uncommon 2:3 donor/chalcogen ratio and incorporating chains of I(2) held together by rare I...I interactions. As expected, "seesaw" 10-E-4 adducts are formed following the reaction of Te donors D4-D7 {Nap[TePh][X] (X = Br, I); Nap[TePh][EPh] (E = Se, S)} with the dihalogens. Naphthalene distortion in general is comparable between respective donor compounds and products 1-15. Ionic species 2 and 3 display a noticeable reduction in molecular distortion explained by the relief of steric strain via weak peri-interactions and the onset of 3c-4e bonding.

Synthetic and structural studies of 1,8-chalcogen naphthalene derivatives.

Four novel 1,8-disubstituted naphthalene derivatives 4-7 that contain chalcogen atoms occupying the peri positions have been prepared and fully characterised by using X-ray crystallography, multinuclear NMR spectroscopy, IR spectroscopy and MS. Molecular distortion due to noncovalent substituent interactions was studied as a function of the bulk of the interacting chalcogen atoms and the size and nature of the alkyl group attached to them. X-ray data for 4-7 was compared to the series of known 1,8-bis(phenylchalcogeno)naphthalenes 1-3, which were themselves prepared from novel synthetic routes. A general increase in the E...E' distance was observed for molecules containing bulkier atoms at the peri positions. The decreased S...S distance from phenyl-1 and ethyl-4 analogues is ascribed to a weaker chalcogen lone pair-lone pair repulsion acting in the ethyl analogue due to the presence of two equatorial S(naphthyl) ring conformations. Two novel peri-substituted naphthalene sulfoxides of 1, Nap(O=SPh)(SPh) 8 and Nap(O=SPh)(2) 9, which contain different valence states of sulfur, were prepared and fully characterised by using X-ray crystallography and multinuclear NMR spectroscopy, IR spectroscopy and MS. Molecular structures were analysed by using naphthalene ring torsions, peri-atom displacement, splay angle magnitude, S...S interactions, aromatic ring orientations and quasi-linear O=S...S arrangements. The axial S(naphthyl) rings in 8 and 9 are unfavourable for S...S contacts due to stronger chalcogen lone pair-lone pair repulsion. Although quasi-linear O=S...S alignments suggest attractive interaction is conceivable, analysis of the B3LYP wavefunctions affords no evidence for direct bonding interactions between the S atoms.

Synthetic and structural studies of 1-halo-8-(alkylchalcogeno)naphthalene derivatives.

A series of eight 1-halo-8-(alkylchalcogeno)naphthalene derivatives (1-8; halogen=Br, I; alkylchalcogen=SEt, SPh, SePh, TePh) containing a halogen and a chalcogen atom occupying the peri positions have been prepared and fully characterised by using X-ray crystallography, multinuclear NMR spectroscopy, IR spectroscopy and MS. Naphthalene distortion due to non-covalent substituent interactions was studied as a function of the bulk of the interacting chalcogen atoms and the size and nature of the alkyl group attached to them. X-ray data for 1, 2, 4 and 5-8 were compared. Molecular structures were analysed in terms of naphthalene ring torsions, peri-atom displacement, splay angle magnitude, X...E interactions, aromatic ring orientations and quasi-linear X...E-C arrangements. A general increase in the X...E distance was observed for molecules that contain bulkier atoms at the peri positions. The I...S distance of 4 is comparable with the I...Te distance of 8, and is ascribed to a stronger lone pair-lone pair repulsion due to the presence of an axial S(naphthyl) ring conformation. Density functional theory (B3LYP) calculations performed on 5-8 revealed Wiberg bond index values of 0.05-0.08, which indicate minor interactions taking place between the non-bonded atoms in these compounds.

Sterically crowded peri-substituted naphthalene phosphines and their PV derivatives.

Three sterically crowded peri-substituted naphthalene phosphines, Nap[PPh(2)][ER] (Nap=naphthalene-1,8-diyl; ER=SEt, SPh, SePh) 1-3, which contain phosphorus and chalcogen functional groups at the peri positions have been prepared. Each phosphine reacts to form a complete series of P(V) chalcogenides Nap[P(E')(Ph(2))(ER)] (E'=O, S, Se). The novel compounds were fully characterised by using X-ray crystallography and multinuclear NMR spectroscopy, IR spectroscopy and MS. X-ray data for 1, 2, nO, nS, nSe (n=1-3) are compared. Eleven molecular structures have been analysed by naphthalene ring torsions, peri-atom displacement, splay angle magnitude, X...E interactions, aromatic ring orientations and quasi-linear arrangements. An increase in the congestion of the peri region following the introduction of heavy chalcogen atoms is accompanied by a general increase in naphthalene distortion. P...E distances increase for molecules that contain bulkier atoms at the peri positions and also when larger chalcogen atoms are bound to phosphorus. The chalcogenides adopt similar conformations that contain a quasi-linear E...P-C fragment, except for 3O, which displays a twist-axial-twist conformation resulting in the formation of a linear O...Se-C alignment. Ab initio MO calculations performed on 2O, 3O, 3S and 3Se reveal Wiberg bond index values of 0.02 to 0.04, which indicates only minor non-bonded interactions; however, calculations on radical cations of 3O, 3S and 3Se reveal increased values (0.14-0.19).

Controlling Cu...Cu distances using halides: (8-phenylthionaphth-1-yl)diphenylphosphine copper halide dimers.

In the isomorphous binuclear Cu2X2L2 systems (L = (8-phenylthionaphth-1-yl)diphenylphosphine the Cu...Cu separation is reduced as the halide size increases.

8-Bromo-naphthalen-1-amine.

The title compound, C(10)H(8)BrN, was obtained by slow addition of sodium azide to 8-bromo-1-naphthoic acid, followed by addition of aqueous ammonia. The crude product was crystallized from petroleum ether to give pink crystals. Compared to other 1,8-disubstituted naphthalene compounds, this compound exhibits less strain between the 1 and 8 substituents. Additionally, the NH protons form both intra- and inter-molecular hydrogen bonds. The naphthalene units are arranged in a herring-bone stacking motif.