Erik Wächtler

Stannylene or Metallastanna(IV)ocane: A Matter of Formalism

The s basicity of electron-rich transition metals (TMs) plays a crucial role in Brønsted acid–base reactions of TM complexes, such as [H2Fe(CO)4] and [HCo(CO)4] (strong acids, poor s-basicity of the corresponding conjugate bases) and was shown to increase upon coordination of good donor ligands L, such as phosphines; that is, lowered acidity of [H2Fe(CO)3(PPh3)] or [HCo(CO)3(PPh3)]. [2] Thus, P and/or S donors bearing electron-rich TM centers have been shown to support s donation towards other main-group-element (E) Lewis acidic centers, for example in the so-called metallaboratranes I and II and Be, Al, and Ga compounds of type III (Scheme 1). Very recently, we have described compounds IV–VII comprising {L5TM(d )} moieties that exhibit s donation towards electronically saturated Lewis acidic centers E, that is, Si and Sn. Gabba et al. have reported similar intermetallic interactions in the heterobimetallic complexes VIII–X (Scheme 1), which comprise d TM donor sites with an almost square-planar coordination sphere. Whereas compounds IV–X were obtained by a straightforward route starting from sources that comprise TM and E in the desired oxidation states, herein we present a (formal) redox approach, which involves a reaction sequence starting from a stannylene (SnCl2) and yielding hypercoordinate tin compounds that can be regarded as palladastanna(IV)ocanes. In a convenient one-pot synthesis, [PdCl2(PPh3)2] was treated with the potassium salt of 1-methyl-2-mercaptoimidazole (methimazole, Hmt) and [SnCl2(dioxane)] (Scheme 2) to afford compound 1. Substitution of the tin-bound chlorine atoms with a dianionic tridentate ligand afforded compound 2, which comprises a hexacoordinate tin atom (Scheme 2). Reference compounds 3 and 4 (comprising Sn and Sn, respectively, and the same tridentate ONN ligand as 2) were prepared as references for spectroscopic properties. The molecular structures of 1–4 were confirmed crystallographically (see Figure 1 and the Supporting Information). Scheme 1. Selected examples of TM–base complexes with electrophilic main-group-element sites (“Z-type ligands”). Cy = cyclohexyl.

Molecular structures of pyridinethiolato complexes of Sn(II), Sn(IV), Ge(IV), and Si(IV)

Abstract Complexes of Sn(II), Sn(IV), Ge(IV), and Si(IV) with the ambidentate pyridine-2-thiolato ligand (PyS-) were synthesized and characterized by multinuclear NMR spectroscopy and single-crystal X-ray diffractometry. Comparison of the structures of E(PyS)2Cl2 (E=Sn, Ge, Si) and E(PyS)4 (E=Sn, Si) allows for insights into the group 14 coordination chemistry of this ambidentate chelator in dependence of the thiophilicity of the central atom of the corresponding complex. Furthermore, the crystal structure of Sn(PyS)2 reveals two different coordination modes of its constituents, i.e., the crystal packing features cyclic dimers and polymeric chains of Sn(PyS)2. This compound was shown to undergo oxidative addition of 2,2′-dipyridyldisulfide and sulfur with the formation of Sn(PyS)4and (PyS)2Sn(μ-S)2Sn(PyS)2, respectively.

Metallophilic Contacts in 2-C6F4PPh2 Bridged Heterobinuclear Complexes: A Crystallographic and Computational Study

Treatment of the bis(chelate) complex trans-[Pd(κ(2)-2-C6F4PPh2)2] (7) with PMe3 gave trans-[Pd(κC-2-C6F4PPh2)2(PMe3)2] (13) as a mixture of syn- and anti-isomers. Reaction of 13 with CuCl, AgCl, or [AuCl(tht)] (tht = tetrahydrothiophene) gave the heterobinuclear complexes [(Me3P)2Pd(μ-2-C6F4PPh2)2MCl] [M = Cu (14), Ag (15), Au (16)], from which the corresponding salts [(Me3P)2Pd(μ-2-C6F4PPh2)2M]PF6 [M = Cu (17), Ag (18), Au (19)] could be prepared by abstraction of the chloro ligand with TlPF6; 18, as well as its triflato (20) and trifluoroacetato (21) analogues, were also prepared directly from 13 and the appropriate silver salt. Reaction of 13 with [AuCl(PMe3)] gave the zwitterionic complex [(Me3P)PdCl(μ-2-C6F4PPh2)2Au] (24) in which the 2-C6F4PPh2 ligands are in a head-to-head arrangement. In contrast, the analogous reaction with [AuCl(PPh3)] gave [(Ph3P)PdCl(μ-2-C6F4PPh2)2Au] (25) with a head-to-tail ligand arrangement. Single crystal X-ray diffraction studies of complexes 14-21 show short metal-metal separations [2.7707(11)-2.9423(3) Å] suggestive of attractive noncovalent (dispersion) interactions, a conclusion that is supported by theoretical calculations of the electron localization function and the noncovalent interactions descriptor.

New Insights into Hexacoordinated Silicon Complexes with 8- Oxyquinolinato Ligands: 1,3-Shift of Si-Bound Hydrocarbyl Substituents and the Influence of Si-Bound Halides on the 8-Oxyquinolinate Coordination Features

Abstract The transsilylation reaction between allyltrichlorosilane and 8-trimethylsiloxyquinoline in the molar ratio 1 : 3 yields the hexacoordinated silicon tris-chelate (oxinate)2Si(adho) (“oxinate” = 8- oxyquinolinate, “adho” = di-anion of 2-allyl-1,2-dihydro-8-oxyquinoline) comprising an SiO3N3 skeleton. The identity of this complex was established by single-crystal X-ray diffraction analysis and 29Si CP=MAS NMR spectroscopy of its chloroform solvate. Benzyltrichlorosilane and dibenzyldichlorosilane, comprising benzyl (Bn) as an “aromatically stabilized allyl moiety” did not undergo such rearrangement. Instead, the complexes (oxinate)2SiBnCl and (oxinate)2SiBn2 were obtained even upon using three molar equivalents of 8-trimethylsiloxyquinoline. We determined the crystal structure of a non-disordered bis-chelate (oxinate)2SiBnCl with Sibound hydrocarbyl and halogen substituents (the previously published (oxinate)2SiMeCl was disordered with alternative Me=Cl site occupancies). (Oxinate)2SiBnCl exhibits surprisingly poor response of the N-Si bonds to the different trans-disposed Si-X (X=Bn, Cl) bonds. For comparison and deeper insights into the coordination chemistry of oxinato silicon complexes with halide substituents, we determined the crystal structures of (oxinate)2SiPhCl·CHCl3, (oxinate)2SiCl2, (oxinate)2SiF2·1.5(CHCl3), and (8-oxyquinaldinate)2SiF2. Furthermore, the crystal structures of BnSiCl3 and Bn2SiCl2 (and its dibromo analog) are reported. The influence of the Si-C-C-C torsion angles of the benzyl group on the 29Si NMR shift of benzylsilanes (which is noticeably upfield with respect to analogous methyl silanes) was analyzed by quantum-chemical calculations.

Tin(IV) Compounds with 2-C6F4PPh2 Substituents and Their Reactivity toward Palladium(0): Formation of Tin–Palladium Complexes via Oxidative Addition

The tin(IV) compounds MexSn(2-C6F4PPh2)4-x (1, x = 1; 2, x = 2) and ClSn(2-C6F4PPh2)3 (3) were obtained from the reactions of 2-LiC6F4PPh2 with MeSnCl3 (3:1), Me2SnCl2 (2:1), or SnCl4 (3:1), respectively. The reactions of 2-LiC6F4PPh2 with SnCl4 in different stoichiometric ratios (4:1-1:1) gave 3 as the main product. Compound Cl2Sn(2-C6F4PPh2)2 (4) was formed in the transmetalation reaction of 3 and [AuCl(tht)] but could not be isolated. 1 and 2 react with palladium(0) sources {[Pd(PPh3)4] and [Pd(allyl)Cp]} by the oxidative addition of one of their Sn-CAryl bonds to palladium(0) with formation of the heterobimetallic complexes [MeSn(μ-2-C6F4PPh2)2Pd(κC-2-C6F4PPh2)] (5) and [Me2Sn(μ-2-C6F4PPh2)Pd(κ2-2-C6F4PPh2)] (6) featuring Sn-Pd bonds. The reaction of 3 with palladium(0) proceeds via the oxidative addition of the Sn-Cl bond to palladium(0), thus furnishing the complex [Sn(μ-2-C6F4PPh2)3PdCl] (7) featuring a Sn-Pd bond and a pentacoordinate Pd atom. Transmetalation of MexSn(2-C6F4PPh2)4-x (x = 1-3) with [Pd(allyl)Cl]2 gave MexClSn(2-C6F4PPh2)3-x and [Pd(allyl)(μ-2-C6F4PPh2)]2. For x = 1, the compound MeClSn(2-C6F4PPh2)2 (generated in situ) reacted with another 1 equiv of [Pd(allyl)Cl]2 by the oxidative addition of the Sn-Cl bond to palladium(0) and the reductive elimination of allyl chloride, thus leading to [MeSn(μ-2-C6F4PPh2)2PdCl] (8). The reductive elimination of allyl chloride was also observed in the reaction of 3 with [Pd(allyl)Cl]2, giving [Sn(μ-2-C6F4PPh2)3PdCl] (7). All compounds have been characterized by means of multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction, and selected compounds by 119Sn Mössbauer spectroscopy. Computational analyses (natural localized molecular orbital calculations) have provided insight into the Sn-Pd bonding of 5-8.

Synthesis and Oxidation of a Paddlewheel-Shaped Rhodium/Antimony Complex Featuring Pyridine-2-Thiolate Ligands

The paddlewheel-shaped complex [Sb(μ-pyS)4 Rh]2 (1) (pyS- = 2-S-C5 H4 N- ) was synthesized from [Rh(pyS)(cod)]2 (cod=1,5-cyclooctadiene) and Sb(pyS)3 . Upon oxidation with ONMe3 , the complex [(μ-O)Sb(μ-pyS)3 Rh(κ2 -pyS)]2 (2) is formed. Both 1 and 2 form dimers and feature short Rh-Sb bonds and bridging pyS ligands. 121 Sb Mössbauer spectro- scopy and computational studies were employed to elucidate the Rh-Sb bonding in 1 and 2. Both covalent (Rh-Sb, X-type Sb ligand) and dative (Rh→Sb, Z-type; Rh←Sb L-type Sb ligand) interactions have to be considered for the description of their bonding situations.