Characterization of Ar‘Sn(μ-Br)Sn(Ar‘)CH2C6H4-4-Pri (Ar‘ = C6H3-2,6-Dipp2; Dipp = C6H3-2,6-Pri2): A Stable Structural Analogue for a Heavier Group 14 Element Monobridged Alkene Isomer HM(μ-H)MH2 (M = Sn or Pb)

Investigating the structural chemistry of organotin(IV) compounds: recent advances

Organotin(IV) compounds have been considered for their outstanding industrial, medical and specific applications in the synthesis of various types of chemical compounds. In this review, we have focused on the structural chemistry of organotin(IV) compounds, including coordination chemistry, the effect of structure on reactions, bond formations from the perspective of structure and investigation of the structure of organotin(IV) compounds in different phases. The structural chemistry of organotin(IV) compounds is subject to interest due to their major impact on predicting the properties and drumming up support for pushing back the frontiers of synthesis of organotin(IV) compounds with advanced properties.

Cyclic Distannene or Bis(stannylene) with a Ferrocenyl Backbone: Synthesis, Structure, and Coordination Chemistry

1,1'-Dilithioferrocene was reacted with 2 equiv of isopropyl (Ar*) or methyl (Ar') substituted terphenyl tin(II) chloride. Reaction product 1, carrying the bulkier terphenyl substituent Ar*, displays a bis(stannylene) structure in the solid state without formation of a tin-tin bond. Temperature-dependent solution ¹¹⁹Sn NMR spectroscopy, however, revealed a dynamic interplay between bis(stannylene) (100 °C) and cyclic distannene (-80 °C). In contrast to 1, the less bulky Ar' substituent results in a cyclic distannene 2. On the basis of temperature-dependent ¹¹⁹Sn NMR spectroscopy the Sn-Sn bond of compound 2 was preserved up to 100 °C. Both compounds were further characterized by solid-state ¹¹⁹Sn NMR spectroscopy as well as ¹¹⁹Sn and ⁵⁷Fe Mössbauer spectroscopy. 1 reacted as a chelating ligand with nickel and palladium complexes [Ni(cod)₂] and [Pd(nbe)₃] (nbe = norbornene). In the resulting coordination compounds the nonstabilized stannylene acts as a donor as well as an acceptor ligand and shows a dynamic switch from donor to acceptor behavior in the monopalladium complex.

New Insight into the Nature of Bonding in the Dimers of Lappert's Stannylene and Its Ge Analogs: A Quantum Mechanical Study

The strength and nature of the connection in Lappert's stannylene dimer ({Sn[CH(SiMe3)2]2}2) and its smaller analogs, simplified stannylenes, as well as similar Ge complexes were studied by means of DFT-D3 calculations, energy decomposition analysis (EDA), electrostatic potential (ESP), and natural population analysis. The trans-bent structure of the investigated molecules was rationalized by means of EDA, ESP, and molecular orbital (MO) analyses. The different ESPs for the monomers studied are a result of different hybridization of the Sn (Ge) atoms. The comparably strong stabilization in the largest and the smallest systems with a dramatically different substituent size is explained by the different nature of the binding between monomers. For all complexes, it has been found that the total attractive interaction is mostly provided by the electrostatic component (>50%), followed by orbital interaction and dispersion. In the largest molecule (Lappert's stannylene), the dispersion interaction plays a more significant role in stabilization and its magnitude is comparable to that of orbital interaction; on the other hand in the smallest molecule (SnH2), where bulky substituents are replaced by H only, the dispersion energy is less important and the E-E bond is more of a charge-transfer character, caused by donor-acceptor orbital interactions. The charge transfer in Ge dimers is greater than in the Sn ones due to shorter distances between monomers, which cause better ⟨HOMO/LUMO⟩ overlaps. The easier dimerization of Lappert's stannylene as compared to Kira's ({Sn[(Me3Si)2CHCH2CH2CH(SiMe3)2-κ(2)C,C']}) stannylene is explained by the different orientation of their substituents-asymmetry promotes dimerization.

Reversibility in Reactions of Linker-Bridged Distannenes with Terminal Alkynes at Ambient Temperature

The linker-bridged distannene [(2,6-Mes2)C6H3Sn]2C12H8 (1) featuring an acenaphthene linker and the sterically demanding terphenyl substituent Ar(Me) (= C6H3-2,6-Mes2; Mes = C6H2-2,4,6-Me3) was prepared and characterized by single-crystal analysis, NMR spectroscopy, as well as elemental analysis. Furthermore, the reactivity of distannene 1 and previously reported distannenes 2 and 3, bearing either a naphthalene or a 9,9-dimethylxanthene backbone and the terphenyl substituent Ar(Me), as well as bis(stannylene) 4, featuring a 9,9-dimethylxanthene backbone and the terphenyl substituent Ar(iPr) (= C6H3-2,6-Trip2; Trip = C6H2-2,4,6-i-Pr3), toward terminal alkynes at ambient temperature was investigated, leading to the formal [2 + 2] cycloaddition products 5-9. The reactions of distannene 1 with trimethylsilylacetylene and phenylacetylene, the reaction of distannene 2 with trimethylsilyl-acetylene, as well as the reaction of bis(stannylene) 4 with phenylacetylene show reversibility, while distannenes 2 and 3 react irreversibly with phenylacetylene at room temperature. A van't Hoff analysis of variable-temperature (1)H NMR spectra of the cycloadduct of the reaction of distannene 1 with trimethylsilylacetylene afforded a dissociation enthalpy (ΔHdiss) of 71.6 kJ·mol(-1), which is in surprisingly good agreement with the results of accompanying DFT calculations (ΔHdiss = 70.9 kJ·mol(-1)).

Impact of a rigid backbone on the structure of an agostically-stabilised dialkylstannylene: isolation of an unusual bridged stannyl-stannylene

The reaction between the phosphine-borane-stabilised dicarbanion complex [1,2-C6H4{CHP(BH3)Cy2}2][Li(THF)n]2 and Cp2Sn gives the unusual stannyl-stannylene [[1,2-C6H4{CHP(BH3)Cy2}2]Sn]2·1½PhMe, in which one dicarbanion ligand chelates a tin centre, while the other bridges a tin-tin bond. The stannylene centre is stabilised by an agostic-type B-H···Sn interaction.

The role of group 14 element hydrides in the activation of C-H bonds in cyclic olefins

Formally, triple-bonded dimetallynes ArEEAr [E = Ge (1), Sn (2); Ar = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)] have been previously shown to activate aliphatic, allylic C-H bonds in cyclic olefins, cyclopentadiene (CpH), cyclopentene (c-C(5)H(8)) and 1,4-cyclohexadiene, with intriguing selectivity. In the case of the five-membered carbocycles, cyclopentadienyl species ArECp [E = Ge (3), Sn (4)] are formed. In this study, we examine the mechanisms for activation of CpH and c-C(5)H(8) using experimental methods and describe a new product found from the reaction between 1 and c-C(5)H(8), an asymmetrically substituted digermene ArGe(H)Ge(c-C(5)H(9))Ar (5), crystallized in 46% yield. This compound contains a hydrogenated cyclopentyl moiety and is found to be produced in a 3:2 ratio with 3, explaining the fate of the liberated H atoms following triple C-H activation. We show that when these C-H activation reactions are carried out in the presence of tert-butyl ethylene (excess), compounds {ArE(CH(2)CH(2)tBu)}(2) [E = Ge(8), Sn(9)] are obtained in addition to ArECp; in the case of CpH, the neohexyl complexes replace the production of H(2) gas, and for c-C(5)H(8) they displace cyclopentyl product 5 and account for all the hydrogen removed in the dehydroaromatization reactions. To confirm the source of 8 and 9, it was demonstrated that these molecules are formed cleanly between the reaction of (ArEH)(2) [E = Ge(6), Sn(7)] and tert-butyl ethylene, new examples of noncatalyzed hydro-germylation and -stannylation. Therefore, the presence of transient hydrides of the type 6 and 7 can be surmised to be reactive intermediates in the production of 3 and 4, along with H(2), from 1 and 2 and CpH (respectively), or the formation of 3 and 5 from 1. The reaction of 6 or 7 with CpH gave 3 or 4, respectively, with concomitant H(2) evolution, demonstrating the basic nature of these low-valent group 14 element hydrides and their key role in the 'cascade' of C-H activation steps. Additionally, during the course of these studies a new polycyclic compound (ArGe)(2)(C(7)H(12)) (10) was obtained in 60% yield from the reaction of 1,6-heptadiene and 1 via double [2 + 2] cycloaddition and gives evidence for a nonradical mechanism for these types of reactions.

Reversible Valence Equilibrium Reactions in Main Group Compounds. A Theoretical Study

The potential energy surface for the intramolecular reaction of singlet state RR'E=ERR' (E = C, Si, Ge, Sn, and Pb) has been explored using density functional theory. All the stationary points, including the unsymmetrical reactant (R'R(2)E-ER'), the transition state, the symmetric product (R'RE=ERR'), and the monomer (R'RE) were completely optimized at the B3LYP/LANL2DZdp level of theory. Our theoretical findings suggest the following: (1) Both double-bonded RR'C=CRR' and RR'Si=SiRR' species are true minima on their potential energy surfaces and should be the only compounds existing at all temperatures. (2) The germanium system will occur either in the dimeric R(2)R'Ge-GeR' and RR'Ge=GeRR' structures or the monomeric RR'Ge structure, depending on the temperature. (3) If the size of the substituent (R) is small, then the unsymmetrical single-bonded R(2)R'Sn-SnR' molecule can exist at low temperatures. At room temperature, the unsymmetrical R(2)R'Sn-SnR' species can exist in equilibrium with its RR'Sn monomer. (4) The unsymmetrical R(3)Pb-PbR compound may be kinetically stable at low temperatures. On the other hand, it is predicted that both the unsymmetrical R(3)Pb-PbR and the symmetric R(2)Pb=PbR(2) species will spontaneously dissociate into R(2)Pb monomers at room temperature. Our theoretical results are in good agreement with available experimental observations (J. Am. Chem. Soc. 2003, 125, 7520), and the results obtained allow a number of predictions to be made.

Tuning of Electronic Structures of Poly(p-phenylenevinylene) Analogues of Phenyl, Thienyl, Furyl, and Pyrrolyl by Double-Bond Linkages of Group 14 and 15 Elements

We investigated electronic structures of four sets of monomers and polymers comprising of phenyl rings and five-membered hetero(aromatic) moieties connected with double-bond -X=X- linkages (X = CH, SiH, GeH, N, P, As) by density functional theory, time-dependent density functional theory, and periodic boundary condition calculations with B3LYP functional. Electronic structures of poly(p-phenylenevinylene) (PPV) analogues are primarily dominated by central double-bond moieties. The introduction of ethylene homologues with group 14 and 15 elements was demonstrated to be a promising approach to modify electronic structures of conjugated oligomers and polymers. Excitation energies of monomers with double-bond linkages were reduced by around 13-50% with respect to corresponding dimers of phenyl, thienyl, furyl, and pyrrolyl rings. Similarly, band gaps of poly(p-phenylene) and polythiophene were decreased by 0.3-0.9 eV upon the insertion of double-bond linkages. Furthermore, excitation energies of monomers presented decreasing trends when descending through groups 14 and 15. For group 14 ethylene homologues, the decreasing trend in the lowest excitation energies was rationalized by a progressively favoring of pi-sigma* interactions as descending X = CH, SiH, and GeH. Increasing p contents of central bonds along X = N, P, and As accounted for geometry features and the lowest excitation energies of group 15 species. A decrease in the extent of electronic communications between aromatic rings and -X=X- linkages within higher congeners was also revealed.