Hypercoordinate compounds of the group 14 elements containing κn-C,N-, C,O-, C,S- and C,P-ligands

Organohypervalent heterocycles

This review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine. Heterocyclic compounds of elements with double bonds are not categorized as hypervalent molecules owing to the zwitterionic nature of these bonds, resulting in the conventional 8-electron species. This review is focused on hypervalent heterocyclic derivatives of nonmetal main-group elements, such as boron, silicon, nitrogen, carbon, phosphorus, sulfur, selenium, bromine, chlorine, iodine(III) and iodine(V).

Stabilisation of the [SiH6]2- Anion within a Supramolecular Assembly

The hypercoordinate [SiH6]2- anion is not stable in solution. Here, we report the room temperature, solution stable molecular [SiH6]2- complex, [{KCa(NON)(OEt2)}2][SiH6] (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene)), where the [SiH6]2- anion is stabilised within a supramolecular assembly that mimics the solid-state environment of the anion in the lattice of K2SiH6. Solution-state reactivity of the complex towards carbon monoxide, benzaldehyde, azobenzene and acetonitrile is reported, yielding a range of reduction and C-C coupled products.

Hypercoordination by Multiple Dangling Benzylmethoxy Ligands in Highly Crowded Triaryltin Bromide [(2-MeOCH2 C6 H4 )]3 SnBr and Diaryltin Mixed Halides [(2-MeOCH2 C6 H4 )]2 SnBrCl, and a related Distannane and Distannoxane

The reaction between the Grignard reagent formed from Mg and 2-bromobenzylmethyl ether and SnCl4 produced four products: [2-(MeOCH2 )C6 H4 ]3 SnBr (1), [2-(MeOCH2 )C6 H4 ]2 SnX2 (2, X2 =Br2 (a) and BrCl (b)), [{2-(MeOCH2 )C6 H4 }3 Sn]2 (3), and [{2-(MeOCH2 )C6 H4 }2 SnBr]2 O (4). In the case of 1, two of the three dangling arm O atoms coordinate to the central tin atom with O-Sn internuclear distances of 2.53 (O1) and 2.91 (O2) Å, the shorter interaction being trans to the Br atom, the other trans to a phenyl carbon atom. In the case of 2a the resulting hexacoordinate structure exhibits two very short O-Sn interactions of 2.42 and 2.50 Å, well below the sum of the VdW radii of O and Sn, 3.69 Å. The sterically crowded ditin compound 3 was obtained in trace amounts and the structure demonstrates no dangling O-Sn interactions. General changes in structure compared to other distannane systems are reflective of the great steric crowding. Distannoxane 4, has a Sn-O-Sn bond angle of 148.1(2)° which is larger compared to other distannoxane structures. The intermolecular interactions between Sn-O 2.470(3) and 2.521(3)Å and 2.665(3) and 2.629(3)Å for Sn1 and Sn2 respectively are responsible for a distorted octahedral geometry around the two tin atoms. The various 119 Sn, 13 C and 1 H NMR spectra are in accord with their structural analysis for 1 and 2, and in the solid state 13 C NMR spectrum of 1 the dangling methylene group is observable whereas is solution there is a rapid dynamic equilibrium resulting in a single resonance for all methylene groups.

Hypercoordinated eka-tin materials with dangling aryl-methoxy and -methylthio ligands exhibiting intramolecular secondary bonding and aryl bond stabilization in reactions with organotin chlorides

The syntheses of [2-(CH₃ECH₂)C₆H₄]PbPh_3-nCl_n, (n = 0, E = O (4), E = S (5); n = 1, E = O (6), E = S (7); n = 2, E = O (8), are described. NMR and single crystal data illustrate significant Pb⋯E interactions increasing as n progresses from 0 to 2. The Pb⋯E interactions stabilize the Pb-aryl bonding to the extent that the reactions of 4 and 5 with Me₂SnCl₂ result in interchange of a Ph group and Cl to produce 6 and 7, respectively, together with Me₂PhSnCl.

Reactivity of a carbonyl moiety in organotin(iv) compounds: novel Pd(ii) and Cu(ii) complexes supported by organotin(iv) ligands

Converting the carbonyl moiety of an (aryl)organotin(iv) compound gives other functional groups that can act as metalloligands.

Preparation and DFT Studies of κ2C,N-Hypercoordinated Oxazoline Organotins: Monomer Constructs for Stable Polystannanes

Tetraorganotin tin(IV) compounds containing a flexible or rigid (4: Ph3Sn-CH2-C6H4-R; 7: Ph3SnC6H4-R, R = 2-oxazolinyl) chelating oxazoline functionality were prepared in good yields by the reaction of lithiated oxazolines and Ph3SnCl. Reaction of 7 with excess HCl resulted in the isolation of the tin monochlorido compound, 9 (ClSn[Ph2]C6H4-R). Conversion of the triphenylstannanes 7 and 4 into their corresponding dibromido species was successfully achieved from the reaction with Br2 to yield 10 (Br2Sn[Ph]C6H4-R) and 11 (Br2Sn[Ph]-CH2-C6H4-R), respectively. X-ray crystallography of 4, 7, 9, 10, and 11 reveal that all structures adopt a distorted trigonal bipyramidal geometry around Sn in the solid state. Compound 4, with an additional methylene spacer group, displays a comparatively long Sn–N bond distance compared to the dibromido tin species, 11. Several DFT methods were compared for accuracy in predicting the solid-state geometries of compounds 4, 7, 9–11. Compounds 10 and 11 were further converted into the corresponding dihydrides (12: H2Sn[Ph]C6H4-R, 13: H2Sn[Ph]-CH2-C6H4-R), via Br–H exchange, in high yield by reaction with NaBH4. Polymerization of 12 or 13 with a late transition metal catalyst produced a low molecular weight polystannane (14: –[Sn[Ph]C6H4-R]n–, Mw = 10,100 Da) and oligostannane (15: –[Sn[Ph]-CH2-C6H4-R]n–, Mw = 3200 Da), respectively.

A hypervalent and cubically coordinated molecular phase of IF8 predicted at high pressure

Up to now, the maximum coordination number of iodine is seven in neutral iodine heptafluoride (IF7) and eight in anionic octafluoride (IF8 -). Here, we explore pressure as a method for realizing new hypercoordinated iodine compounds. First-principles swarm structure calculations have been used to predict the high-pressure and T → 0 K phase diagram of binary iodine fluorides. The investigated compounds are predicted to undergo complex structural phase transitions under high pressure, accompanied by various semiconductor to metal transitions. The pressure induced formation of a neutral octafluoride compound, IF8, consisting of eight-coordinated iodine is one of several unprecedented predicted structures. In sharp contrast to the square antiprismatic structure in IF8 -, IF8, which is dynamically unstable under atmospheric conditions, is stable and adopts a quasi-cube molecular configuration with R3[combining macron] symmetry at 300 GPa. The metallicity of IF8 originates from a hole in the fluorine 2p-bands that dominate the Fermi surface. The highly unusual coordination sphere in IF8 at 300 GPa is a consequence of the 5d levels of iodine coming down and becoming part of the valence, where they mix with iodine's 5s and 5p levels and engage in chemical bonding. The valence expansion of iodine under pressure effectively makes IF8 not only hypercoordinated, but also hypervalent.