Jens Beckmann

Stannasiloxanes: from rings to polymers

Abstract A review is given with 140 references on the recent progress in the chemistry of cyclo-stannasiloxanes of different ring size, such as cyclo-R2Sn(OSiR′2)2O, cyclo-R2Sn(OSiPh2O)2SnR2, cyclo-R2Sn(OSiPh2O)2SiPh2, cyclo-R2Sn(OSiPh2)2SiPh2 and cyclo-R2Sn(OSiPh2)2 (R=alkyl, aryl, intramolecularly coordinating built-in ligand, transition metal fragment; R′=Me, i-Pr, Ph); and their potential in ring-opening polymerization reactions is critically evaluated and compared with that of related cyclo-borasiloxanes, cyclo-germasiloxanes, and cyclo-siloxanes.

How to Make the Ionic Si―O Bond More Covalent and the Si―O―Si Linkage a Better Acceptor for Hydrogen Bonding

Variation of a bond angle can tune the reactivity of a chemical compound. To exemplify this concept, the nature of the siloxane linkage (Si-O-Si), the most abundant chemical bond in the earths crust, was examined using theoretical calculations on the molecular model compounds H(3)SiOSiH(3), (H(3)Si)(2)OHOH, and (H(3)Si)(2)OHOSiH(3) and high-resolution synchrotron X-ray diffraction experiments on 5-dimethylhydroxysilyl-1,3-dihydro-1,1,3,3-tetramethyl-2,1,3-benzoxadisilole (1), a molecular compound that gives rise to the formation of very rare intermolecular hydrogen bonds between the silanol groups and the siloxane linkages. For theoretical calculations and experiment, electronic descriptors were derived from a topological analysis of the electron density (ED) distribution and the electron localization function (ELF). The topological analysis of an experimentally obtained ELF is a newly developed methodology. These descriptors reveal that the Si-O bond character and the basicity of the siloxane linkage strongly depend on the Si-O-Si angle. While the ionic bond character is dominant for Si-O bonds, covalent bond contributions become more significant and the basicity increases when the Si-O-Si angle is reduced from linearity to values near the tetrahedral angle. Thus, the existence of the exceptional intermolecular hydrogen bond observed for 1 can be explained by its very small strained Si-O-Si angle that adopts nearly a tetrahedral angle.

Well-Defined Stibonic and Tellurinic Acids

The first stibonic acids RSb(O)(OH)2 [1] and tellurinic acids RTe(O)(OH) (R = aryl, alkyl) were extensively investigated more than 90 years ago in the context of pharmacological studies on arsonic acids RAs(O)(OH)2 and the closely related remedies atoxyl and salvarsan, marking the beginning of modern chemotherapy. Unlike their lighter Group 15 and 16 congeners, all hitherto described stibonic and tellurinic acids are ill-defined, amorphous, high-melting compounds that are poorly soluble in most organic solvents. Molecular weight determinations and Sb M ssbauer spectroscopic studies confirm a high degree of aggregation and a trigonalbipyramidal structure for PhSb(O)(OH)2. By contrast, all phosphonic and arsonic acids RE(O)(OH)2 (E = P, As), as well as sulfinic and seleninic acids RE(O)(OH) (E = S, Se), are well-defined molecular compounds with tetrahedrally coordinated central atoms E, polar (formal) E=O double bonds and E OH groups that are usually involved in intermolecular hydrogen bonding in the solid state. Aggregation was also observed for related triarylantimony oxides and diaryltellurium oxides, which exist in two distinctively different structures, namely as asymmetric dimers, for example (Ph3SbO)2 [6] and (Ph2TeO)2 , [7] and as one-dimensional polymers, for example, (Ph3SbO)n [8] and (pAns2TeO)n (Ans = MeOC6H4). [9]

Intramolecularly Coordinated Telluroxane Clusters and Polymers

The stoichiometrically controlled chlorination of the diarylditelluride (8-Me(2) NC(10) H(6) Te)(2) with SO(2) Cl(2) afforded the aryltellurinyl chloride 8-Me(2) NC(10) H(6) TeCl (1) and the aryltellurium trichloride 8-Me(2) NC(10) H(6) TeCl(3) (2). Alternatively, 1 was obtained by the reaction of the aryltellurenyl diethyldithiacarbamate 8-Me(2) NC(10) H(6) Te(S(2) CNEt(2) ) with hydrochloric acid. The base hydrolysis of 2 provided the novel telluroxanes (8-Me(2) NC(10) H(6) Te)(2) OCl(4) (3), (8-Me(2) NC(10) H(6) Te)(6) O(5) Cl(8) (4), (8-Me(2) NC(10) H(6) Te)(6) O(8) Cl(2) (5), [(8-Me(2) NC(10) H(6) Te)(2) O(3) ](n) (6) and (8-Me(2) NC(10) H(6) Te)(6) O(8) (OH)(2) (7) depending on the reaction conditions applied. The reaction of 7 with ClTe(OiPr)(3) in the presence of water gave rise to the telluroxane (8-Me(2) NC(10) H(6) Te)(6) Te(2) O(12) Cl(2) (8). The crystal and molecular structures of 1-3 and 5-8 were determined by X-ray crystallography. The telluroxane clusters and polymers 6-8 hold potential as model compounds for alkali tellurite glasses (M(2) O)(x) (TeO(2) )(1-x) (M=Li, Na, K) for which no precise structural data are available.

Mesityltellurenyl Cations Stabilized by Triphenylpnictogens [MesTe(EPh3)]+ (E = P, As, Sb)

The homoleptic 1:1 Lewis pair (LP) complex [MesTe(TeMes2)]O3SCF3 (1) featuring the cation [MesTe(TeMes2)](+) (1a) was obtained by the reaction of Mes2Te with HO3SCF3. The reaction of 1 with Ph3E (E = P, As, Sb, Bi) proceeded with substitution of Mes2Te and provided the heteroleptic 1:1 LP complexes [MesTe(EPh3)]O3SCF3 (2, E = P; 3, E = As) and [MesTe(SbPh3)][Ph2Sb(O3SCF3)2] (4) featuring the cations [MesTe(EPh3)](+) (2a, E = P; 3a, E = As; 4a, E = Sb) and the anion [Ph2Sb(O3SCF3)2](-) (4b). In the reaction with Ph3Bi, the crude product contained the cation [MesTe(BiPh3)](+) (5a) and the anion [Ph2Bi(O3SCF3)2](-) (5b); however, the heteroleptic 1:1 LP complex [MesTe(BiPh3)][Ph2Bi(O3SCF3)2] (5) could not be isolated because of its limited stability. Instead, fractional crystallization furnished a large amount of Ph2BiO3SCF3 (6), which was also obtained by the reaction of Ph3Bi with HO3SCF3. The formation of the anions 4b and 5b involves a phenyl group migration from Ph3E (E = Sb, Bi) to the MesTe(+) cation and afforded MesTePh as the byproduct, which was identified in the mother liquor. The heteroleptic 1:1 LP complexes 2-4 were also obtained by the one-pot reaction of Mes2Te, Ph3E (E = P, As, Sb) and HO3SCF3. Compounds 1-4 and 6 were investigated by single-crystal X-ray diffraction. The molecular structures of 1a-4a were used for density functional theory calculations at the B3PW91/TZ level of theory and studied using natural bond order (NBO) analyses as well as real-space bonding descriptors derived from an atoms-in-molecules (AIM) analysis of the theoretically obtained electron density. Additionally, the electron localizability indicator (ELI-D) and the delocalization index are derived from the corresponding pair density.

On the reaction of [Ph2(OH)Si]2O with t-Bu2SnCl2: Synthesis and characterization of the first well defined polystannasiloxane [(t-Bu2SnO)(Ph2SiO)2]n

Abstract The high yield synthesis of [(t-Bu 2 SnO)(Ph 2 SiO) 2 ], 1 is reported. Compound 1 is a linear polymer in the solid state but a six-membered ring in solution.

Peri-Substituted (Ace)Naphthylphosphinoboranes. (Frustrated) Lewis Pairs

The synthesis and molecular structures of 1-(diphenylphosphino)-8-naphthyldimesitylborane (1) and 5-(diphenylphosphino)-6-acenaphthyldimesitylborane (2) are reported. The experimentally determined P-B peri distances of 2.162(2) and 3.050(3) Å allow 1 and 2 to be classified as regular and frustrated Lewis pairs. The electronic characteristics of the (non)bonding P-B contacts are determined by analysis of a set of real-space bonding indicators (RSBIs) derived from the theoretically calculated electron and pair densities. These densities are analyzed utilizing the atoms-in-molecules (AIM), stockholder, and electron-localizability-indicator (ELI-D) space partitioning schemes. The recently introduced mapping of the electron localizability on the ELI-D basin surfaces is also applied. All RSBIs clearly discriminate the bonding P-B contact in 1 from the nonbonding P-B contact in 2, which is due to the fact that the acenaphthene framework is rather rigid, whereas the naphthyl framework shows sufficient conformational flexibility, allowing shorter peri interations. The results are compared to the previously known prototypical phosphinoborane Ph3PB(C6F5)3, which serves as a reference for a bonding P-B interaction. The most prominent features of the nonbonding P-B contact in 2 are the lack of an AIM bond critical point, the unaffected Hirshfeld surfaces of the P and B atomic fragments, and the negligible penetration of the electron population of the ELI-D lone pair basin of the P atom into the AIM B atomic basin.

Synthesis and structures of new oligomethylene-bridged double ladders. How far can the layers be separated?

The synthesis of the α,ω-bis[dichloro(trimethylsilylmethyl)stannyl]alkanes, (Me3SiCH2)Cl2Sn(CH2)nSnCl2(CH2SiMe3) (13, n = 5; 14, n = 6; 15, n = 7; 16, n = 8; 17, n = 10; 18, n = 12) and the corresponding oligomethylene-bridged diorganotin oxides [(Me3SiCH2)(O)Sn(CH2)nSn(O)(CH2SiMe3)]m (19, n = 5; 20, n = 6; 21, n = 7; 22, n = 8; 23, n = 10; 24; n = 12) is reported. The reaction of the diorganodichlorostannanes 13–18 with the corresponding diorganotin oxides 19–24 provided the spacer-bridged tetraorganodistannoxanes {[(Me3SiCH2)ClSn(CH2)nSnCl(CH2SiMe3)]O}4 (25, n = 5; 26, n = 6; 27, n = 7; 28, n = 8; 29, n = 10; 30, n = 12). Compounds 13–30 have been identified by elemental analyses and multinuclear NMR spectroscopy. Compounds 25, 27, 29 and 30 have also been characterised by single crystal X-ray diffraction analysis and electrospray mass spectrometry. For the latter the essential double ladder motif is maintained for all n in the solid state, but subtle changes in alignment of the ladder planes occur. Separation between the two layers of the double ladder ranges from approx. 8.7 A (for 25, n = 5) to approx. 15 A (for 30, n = 12). In solution there is some dissociation of the double ladders into the corresponding dimers. The degree of dissociation is favoured by increasing oligomethylene chain length n.

6-Diphenylphosphinoacenaphth-5-yl-mercurials as Ligands for d10 Metals. Observation of Closed-Shell Interactions of the Type Hg(II)···M; M = Hg(II), Ag(I), Au(I)

The salt metathesis reaction of ArLi with HgCl2 produced Ar2Hg (1, Ar = 6-Ph2P-Ace-5), which underwent complex formation with d(10)-configurated transition metal chlorides and triflates to give the complexes 1·HgCl2, 1·Hg(O3SCF3)2, 1·AgCl, 1·Ag(O3SCF3), [1·Ag(NCMe)2](O3SCF3), 1·AuCl, and [1·Au](O3SCF3) comprising significant metallophilic interactions between Hg(II) and Hg(II), Ag(I), and Au(I), respectively. The transmetalation reaction of ArSnBu3 with HgCl2 afforded ArHgCl (2) that also forms a complex with additional HgCl2, namely, 2·HgCl2, which however lacks metallophilic interactions. Compounds 2 and 1·HgCl2 possess the same elemental composition and can be interconverted in solution by choice of the solvent. In the presence of tetrahydrothiophene (tht), the complexes 1·AuCl and [1·Au](O3SCF3) underwent rearrangement into the Au(III) cation [cis-Ar2Au](+) ([3](+), which was isolated as Cl(-) and (O3SCF3)(-) salts) and elemental Hg. The reaction of 1·Hg(O3SCF3)2 with ArH produced the complex ArHg(ArH)(O3SCF3) (4). The metallophilic interactions are theoretically analyzed by a set of real-space bonding indicators derived from the atoms-in-molecules (AIM) and electron localizability indicator (ELI) space-partitioning schemes.

Observation of Te…π and X…X Bonding in para-Substituted Diphenyltellurium Dihalides, (p-Me2NC6H4)(p-YC6H4)TeX2 (X = Cl, Br, I; Y = H, EtO, Me2N)

The supramolecular association of the previously described para-dimethylaminophenyl-substituted diorganotellurium dihalides (p-Me2NC6H4)2TeX2 (X = Cl (1), Br (2), I (3)) and (p-Me2NC6H4)RTeCl2 (R = Ph (4), p-EtOC6H4 (5)), was investigated by X-ray crystallography. Unlike almost all other structurally characterized diorganotellurium dihalides, (p-Me2NC6H4)2TeX2 (X = Cl (1), Br (2), I (3)) reveal no secondary Te∙∙∙X interactions, but X∙∙∙X interactions. The structure of (p-Me2NC6H4)PhTeCl2 (4) resembles that of Ph2TeCl2 and shows one secondary Te∙∙∙Cl contact, whereas (p-Me2NC6H4)(p-EtOC6H4)TeCl2 (5) exhibits neither secondary Te∙∙∙Cl nor Cl∙∙∙Cl interactions. The unusual structural characteristics of 1–5 are attributed to the occurrence of intermolecular Te∙∙∙π and π∙∙∙π contacts associated with quinoid π-electron delocalization across the para-dimethylaminophenyl (1–5) and para-ethoxyphenyl (5) groups.