James C. Fettinger

Reversible Reactions of Ethylene with Distannynes Under Ambient Conditions

Tin Two-Step Doubly and triply bonded carbon compounds have a well-studied tendency to link up with one another and form rings. The rates of these reactions and their relative susceptibilities to acceleration by heat versus light are encapsulated in the decades-old Woodward-Hoffmann rules. More recently, alkene and alkyne analogs have been prepared with heavier elements such as silicon and tin substituted for carbon. Peng et al. (p. 1668; see the Perspective by Sita) have now discovered that two distannynes (compounds with triply bonded tins) react readily with ethylene to form cycloadducts, with tin-carbon σ bonds taking the place of C-C and Sn-Sn π bonds. These products, characterized spectroscopically and crystallographically, are only loosely bound at room temperature, easily reverting to their multiply bonded precursors on gentle heating. Ethylene reacts reversibly with triply bonded tin, contrasting with its reactivity toward carbon triple bonds. Ethylene’s cycloadditions to unsaturated hydrocarbons occupy well-established ground in classical organic chemistry. In contrast, its reactivity toward alkene and alkyne analogs of carbon’s heavier-element congeners silicon, germanium, tin, or lead has been little explored. We show here that treatment of the distannynes AriPr4SnSnAriPr4 [AriPr4 = C6H3-2,6(C6H3-2,6-iPr2)2, 1] or AriPr8SnSnAriPr8 [AriPr8 = C6H-2,6(C6H2-2,4,6-iPr3)2-3,5-iPr2, 2] with ethylene under ambient conditions affords the cycloadducts ArPir4Sn(μ2:η1:η1-C2H4)2Sn⎴ArPir4 (3) or ArPir8Sn(μ2:η1:η1-C2H4)2Sn⎴ArPir8 (4) that were structurally and spectroscopically characterized. Ethylene incorporation in 3 and 4 involves tin-carbon σ bonding and is shown to be fully reversible under ambient conditions; hydrocarbon solutions of 3 or 4 revert to the distannynes 1 or 2 with ethylene elimination under reduced pressure or upon standing at ~25°C. Variable-temperature proton nuclear magnetic resonance studies showed that the enthalpies of reaction were near –48 (3) and –27 (4) kilojoules per mole.

Isolation of a stable, acyclic, two-coordinate silylene.

The synthesis and characterization of a stable, acyclic two-coordinate silylene, Si(SAr(Me(6)))(2) [Ar(Me(6)) = C(6)H(3)-2,6(C(6)H(2)-2,4,6-Me(3))(2)], by reduction of Br(2)Si(SAr(Me(6)))(2) with a magnesium(I) reductant is described. It features a V-shaped silicon coordination with a S-Si-S angle of 90.52(2)° and an average Si-S distance of 2.158(3) Å. Although it reacts readily with an alkyl halide, it does not react with hydrogen under ambient conditions, probably as a result of the ca. 4.3 eV energy difference between the frontier silicon lone pair and 3p orbitals.

The closo-[Sn9M(CO)3]4− Zintl Ion Clusters where M=Cr, Mo, W: Two Structural Isomers and Their Dynamic Behavior

The closo-[Sn9M(CO)3]4-ions where M = Cr (1), Mo (2), W (3) were prepared from [LM(CO)3] precursors (L=mesitylene, cycloheptatriene), K4Sn9. and 2,2,2-cryptand in ethylenediamine/toluene solvent mixtures. The [K(2,2,2-cryptand)]+ salts are very air and moisture sensitive and have been characterized by IR, 119Sn, and 13C NMR spectroscopy and single-crystal X-ray diffraction studies. Complexes 1-3 form bicapped square-antiprismatic 10-vertex 22-electron closo structures in which the [M(CO)3] units occupy cluster vertices. For 1 and 2, the clusters have C4. symmetry in the solid state in which the [M(CO)A] fragments occupy capping positions with Sn9(4-) ions that are bound to the metal in an 4 fashion. For 3, the [M(CO)3] fragment occupies a position in the square plane with an eta/5-Sn9(4-) ion and C(s) point symmetry. For 1-3, a dynamic equilibrium exists between the eta4 and eta5 structures yielding three 119Sn NMR signals that reflect the three chemically distinct Sn environments of the higher symmetry C(4v) structure. The 119Sn NMR chemical shifts and coupling constants show solvent and temperature dependencies due to the equilibrium process. A triangular-face rotation mechanism is proposed to describe the dynamic behavior.

Substituent effects in ditetrel alkyne analogues: multiple vs. single bonded isomers

The synthesis and characterization of a series of digermynes and distannynes stabilized by terphenyl ligands are described. The ligands are based on the Ar′ (Ar′ = C6H3-2,6(C6H3-2,6-iPr2)2) or Ar* (Ar* = C6H3-2,6(C6H2-2,4,6-iPr3)2) platforms which were modified at the meta or para positions of their central aryl rings to yield 4-X-Ar′ (4-X-Ar′ = 4-X-C6H2-2,6(C6H3-2,6-iPr2)2, X = H, F, Cl, OMe, tBu, SiMe3, GeMe3) and 3,5-iPr2-Ar′ or Ar* and 3,5-iPr2-Ar*. The compounds were synthesized by reduction of the terphenyl germanium(II) or tin(II) halide precursors with a variety of reducing agents. The precursors were obtained by the reaction of one equivalent of the lithium terphenyl with GeCl2 dioxane or SnCl2. For germanium, their X-ray crystal structures showed them to be either Ge–Ge bonded dimers with trans-pyramidal geometries or V-shaped monomers. In contrast, the terphenyl tin halides had no tin–tin bonding but existed either as halide bridged dimers or V-shaped monomers. Reduction with a variety of reducing agents afforded the digermynes ArGeGeAr (Ar = 4-Cl-Ar′, 4-SiMe3-Ar′ or 3,5-iPr2-Ar*) or the distannynes ArSnSnAr (Ar = 4-F-Ar′, 4-Cl-Ar′, 4-MeO-Ar′, 4-tBu-Ar′, 4-SiMe3-Ar′, 4-GeMe3-Ar′, 3,5-iPr2-Ar′, 3,5-iPr2-Ar*), which were characterized structurally and spectroscopically. The digermynes display planar trans-bent core geometries with Ge–Ge distances near 2.26 A and bending angles near 128° consistent with Ge–Ge multiple bonding. In contrast, the distannynes had either multiple bonded geometries with Sn–Sn distances that averaged 2.65 A and an average bending angle near 123.8°, or single bonded geometries with a Sn–Sn bond length near 3.06 A and a bending angle near 98°. The 3,5-iPr2-Ar*SnSnAr*-3,5-iPr2 species had an intermediate structure with a longer multiple bond near 2.73 A and a variable torsion angle (14–28°) between the tin coordination planes. Mossbauer data for the multiple and single bonded species displayed similar isomer shifts but had different quadrupole splittings.

Direct Spectroscopic Observation of Large Quenching of First Order Orbital Angular Momentum with Bending in Monomeric, Two-Coordinate Fe(II) Primary Amido Complexes and the Profound Magnetic Effects of the Absence of Jahn- and Renner-Teller Distortions in Rigorously Linear Coordination

The monomeric iron(II) amido derivatives Fe{N(H)Ar*}(2) (1), Ar* = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Pr(i)(3))(2), and Fe{N(H)Ar(#)}(2) (2), Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2), were synthesized and studied in order to determine the effects of geometric changes on their unusual magnetic properties. The compounds, which are the first stable homoleptic primary amides of iron(II), were obtained by the transamination of Fe{N(SiMe(3))(2)}(2), with HN(SiMe(3))(2) elimination, by the primary amines H(2)NAr* or H(2)NAr(#). X-ray crystallography showed that they have either strictly linear (1) or bent (2, N-Fe-N = 140.9(2) degrees ) iron coordination. Variable temperature magnetization and applied magnetic field Mossbauer spectroscopy studies revealed a very large dependence of the magnetic properties on the metal coordination geometry. At ambient temperature, the linear 1 displayed an effective magnetic moment in the range 7.0-7.50 mu(B), consistent with essentially free ion magnetism. There is a very high internal orbital field component, H(L) approximately 170 T which is only exceeded by a H(L) approximately 203 T of Fe{C(SiMe(3))(3)}(2). In contrast, the strongly bent 2 displayed a significantly lower mu(eff) value in the range 5.25-5.80 mu(B) at ambient temperature and a much lower orbital field H(L) value of 116 T. The data for the two amido complexes demonstrate a very large quenching of the orbital magnetic moment upon bending the linear geometry. In addition, a strong correlation of H(L) with overall formal symmetry is confirmed. ESR spectroscopy supports the existence of large orbital magnetic moments in 1 and 2, and DFT calculations provide good agreement with the physical data.

Dispersion Forces and Counterintuitive Steric Effects in Main Group Molecules: Heavier Group 14 (Si–Pb) Dichalcogenolate Carbene Analogues with Sub-90° Interligand Bond Angles

The synthesis and spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M(ChAr)2 (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky m-terphenyl ligand, including two new acyclic silylenes) are described. They were found to possess several unusual features-the most notable of which is their strong tendency to display acute interligand, Ch-M-Ch, bond angles that are often well below 90°. Furthermore, and contrary to normal steric expectations, the interligand angles were found to become narrower as the size of the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including corrections for dispersion effects, led to the conclusion that dispersion forces play an important role in stabilizing their acute interligand angles.

Ion‐Pair Recognition by Nucleoside Self‐Assembly: Guanosine Hexadecamers Bind Cations and Anions

G-Quartets can bind anions as well as cations: Solid-state and solution data indicate that self-assembled ion-pair receptors are formed from 16 guanosine monomers, 2 divalent cations, and 4 picrate anions. Hydrogen-bonding, ion-dipole, and base-stacking interactions combine to give a tubular complex with a cation-loaded interior. An array of hydrogen-bond donors on the receptors surface then enables anion coordination (see schematic representation, shaded rectangles=G-quartets, shaded circles=cations).

Glycoluril derivatives form hydrogen bonded tapes rather than cucurbit[n]uril congeners

Abstract The synthesis and X-ray crystallographic characterization of diphenylglycoluril derivatives ( 1–4 ) that possess one or two alkyl groups on their N- or O-atoms is reported. Compounds 1–4 preferentially form linear hydrogen bonded tapes in the crystal by heterochiral recognition processes. We do not observe cyclic hydrogen bonded cucurbit[n]uril congeners that would result from homochiral recognition processes. The high propensity of alkylated derivatives of diphenylglycoluril to form hydrogen bonded tapes stands in stark contrast to the reported X-ray crystal structures of other known alkylated derivatives of glycoluril. We attribute this high propensity to form tapes to the phenyl and alkyl substituents that impart good solubility in non-polar aprotic solvents which do not compete for H-bonds. These results suggest that suitably functionalized glycoluril derivatives have untapped potential in studies of crystal engineering.

Dispersion Force Stabilized Two-Coordinate Transition Metal???Amido Complexes of the ???N({SiMe}

A series of high spin, two-coordinate first row transition metal-amido complexes, M{N(SiMe3)Dipp}2 {M = Fe (1), Co (2), or Ni (3); Dipp = C6H3-2,6-Pr(i)2} and a tetranuclear C-H activated chromium amide, [Cr{N(SiMe2CH2)Dipp}2Cr]2(THF) (4), were synthesized by reaction of their respective metal dihalides with 2 equiv of the lithium amide salt. They were characterized by X-ray crystallography, electronic and infrared spectroscopy, SQUID magnetic measurements, and computational methods. Contrary to steric considerations, the structures of 1-3 display planar eclipsed M{NSiC(ipso)}2 arrays and short M-N distances. DFT calculations, corrected for dispersion effects, show that dispersion interactions involving C-H-H-C moieties likely stabilize the structures by 21.1-29.4 kcal mol(-1), depending on the level of the calculations employed. SQUID measurements confirm high spin electron configurations for all the complexes and substantial orbital contributions for 1 and 2.

_{\textrm{3}}

We report the synthesis and characterization of 12 C-shaped methylene-bridged glycoluril dimers (1-12) bearing H-bonding groups on their aromatic rings. Compounds 1, 2, (+/-)-4a, (+/-)-5, (+/-)-7, and 8 form tightly associated homodimers in CDCl3, due to the combined driving force of pi-pi and H-bonding interactions. Compounds 2, (+/-)-5, and 8, having disparate spatial distribution of their H-bonding groups, display the ability to efficiently distinguish between self and nonself even within three-component mixtures in CDCl3. When the spatial distributions of the H-bonding groups of the molecular clips are similar (e.g., 1 and 2), a mixture of homodimers and heterodimers is formed. The effect of various structural modifications (e.g., chirality, side chain steric bulk, number and pattern of H-bonds) on the strength of self-assembly and the fidelity of self-sorting are presented. On the basis of these results we prepared self-sorting systems comprising three (e.g., 1, (+/-)-5, and (+/-)-7) and even four ( 2, (+/-)-5, 9, and 10) components. The potential of molecular clips 1-12 as robust, functionalizable, self-sorting modules to control the noncovalent interaction network in systems chemistry studies is described.