Karl W. Klinkhammer

The Formation of Heteroleptic Carbene Homologues by Ligand Exchange— Synthesis of the First Plumbanediyl Dimer

Double bond—yes or no? The centrosymmetic trans-bent dimers 1 and 2 crystallize from a mixture of the corresponding monomeric carbene analogues Rf2Sn/Sn(SiR3)2 or Rf2Sn/Pb(SiR3)2. The question whether the plumbanediyl dimer 2 contains a double bond and therefore becomes the last member of the series of ethene homologues R4E2 (E = Si, Ge, Pb) remains open. R = SiMe3, Rf = 2,4,6-(CF3)3C6H2.

The Synthesis and Molecular Structure of the First Two-Coordinate, Dinuclear σ-Bonded Mercury(I) RHgHgR Compound.

A linear Si-Hg-Hg-Si arrangement and a Hg-Hg distance of 265.69 pm are exhibited by the first two-coordinate, dinuclear σ-bonded organomercury(I) compound 1. It was formed unexpectedly in the reaction of two equivalents of the silane (Me3 SiMe2 Si)3 SiH with tBu2 Hg. In contrast if the reagents are allowed to react in a 1:1 ratio the expected mercury(II) compound (Me3 SiMe2 Si)3 SiHgtBu is obtained.

Ligand exchange between arylcopper compounds and bis(hypersilyl)tin or bis(hypersilyl)lead: Synthesis and characterization of hypersilylcopper and a stannanediyl complex with a Cu-Sn bond

Bis(hypersilyl)tin (1) and bis(hypersilyl)lead (2) [hypersilyl= Hyp = tris(trimethylsilyl)silyl] undergo ligand exchange reactions with other carbene homologues to yield heteroleptic distannenes or diplumbenes. Here we report the extension of this reaction principle to coordinatively unsaturated arylcopper(I) compounds. The primary reaction products are probably adducts with the carbene homologues as Lewis base and the arylcopper compounds as Lewis acids. This is followed by rearrangement to the adducts HypCu-E-(Hyp)Ar* (E = Sn (6) and Pb (7); Ar* = C(6)H(3)Mes(2)-2,6,) of hypersilylcopper (9) and the heteroleptic stannanediyl or plumbanediyl. The complex may be the final product or may dissociate into its component parts, free hypersilylcopper (9) and the appropriate heteroleptic carbene homologue. The colorless hypersilylcopper forms a trimer (9), in the solid state with short Cu Cu contacts (238.4-241.5 pm). All observed Cu-Si bonds are relatively long. However, shorter distances (234.9-237.4pm) alternate with longer ones (249.2 pm), such that quasi-monomeric hypersilylcopper units can be identified. The dark green complex 6 exhibits a shorter Cu-Si bond (227.3 pm), The Sn-Cu bond length was determined to be 249.9 pm. The turquoise plumbanediyl Pb(Hyp)Ar* (8) is the first strictly monomeric mixed aryl silyl derivative, even in the solid state. The steric repulsions are obviously less than in the parent homoleptic compounds because the Pb-C bond in 8 is shorter (229.0 pm) and the C-Pb-Si angle (109.2 degrees) is markedly smaller.

Persistent Radicals of Trivalent Tin and Lead

In this report we present synthetic, crystallographic, and new electron paramagnetic resonance (EPR) spectroscopic work that shows that the synthetic route leading to the recently reported, first persistent plumbyl radical *PbEbt3 (Ebt = ethylbis(trimethylsilyl)silyl), that is, the oxidation of the related PbEbt3-anion, was easily extended to the synthesis of other persistent molecular mononuclear radicals of lead and tin. At first, various novel solvates of homoleptic potassium metallates KSnHyp3 (4a), KPbHyp3 (3a), KSnEbt3 (4b), KPbIbt3 (3c), and KSnIbt3 (4c) (Hyp = tris(trimethylsilyl)silyl, Ibt = isopropylbis(trimethylsilyl)silyl), as well as some heteroleptic metallates, such as [Li(OEt2)2][Sn(n)BuHyp2] (3d), [Li(OEt2)2][Pb(n)BuHyp2] (4d), [Li(thf)4][PbPhHyp2] (3e), and [K(thf)7][PbHyp2{N(SiMe3)2}] (3f), were synthesized and crystallographically characterized. Through oxidation by tin(II) and lead(II) bis(trimethylsilyl)amides or the related 2,6-di-tert-butylphenoxides, they had been oxidized to yield in most cases the corresponding radicals. Five novel persistent homoleptically substituted radicals, that is, *SnHyp3 (2a), *PbHyp3 (1a), *SnEbt3 (2b), *SnIbt3 (2c), and *PbIbt3 (1c), had been characterized by EPR spectroscopy. The stannyl radicals 2a and 2c as well as the plumbyl radical 1c were isolated as intensely colored crystalline compounds and had been characterized by X-ray diffraction. Persistent heteroleptically substituted radicals such as *PbHyp2Ph (1e) or *PbHyp2Et (1g) had also been generated, and some selected EPR data are given for comparison. The plumbyl radicals *PbR3 exhibit a clean monomolecular decay leading to the release of a temperature-dependent stationary concentration of branched silyl radicals. They may thus serve as tunable sources of these reactive species that may be utilized as reagents for mild radical silylations and/or as initiators for radical polymerizations. We present EPR-spectroscopic investigations for the new tin- and lead-containing compounds giving detailed insights into their electronic and geometric structure in solution, as well as structural studies on the crystalline state of the radicals, some of their anionic precursors, and some side-products.

LIGANDENAUSTAUSCH ALS WEG ZU HETEROLEPTISCHEN CARBENHOMOLOGEN : SYNTHESE DES ERSTEN PLUMBANDIYL-DIMERS

Doppelbindung – ja oder nein? Zentrosymmetrische, trans-gewinkelte Dimere 1 und 2 kristallisieren aus Mischungen der entsprechenden einheitlich substituierten monomeren Carbenanaloga RSn/Sn(SiR3)2 bzw. RSn/Pb(SiR3)2. Ob im Plumbandiyl-Dimer 2 eine Doppelbindung vorliegt und damit das letzte Glied aus der Reihe der Ethen-Homologe R4E2 (E = Si, Ge, Pb) hergestellt wurde, mus noch offen bleiben. R = SiMe3, Rf = 2,4,6-(CF3)3C6H2.

Kinetic and Thermodynamic Stability of the Group 13 Trihydrides

The kinetic and thermodynamic stabilities of the group 13 hydrides EH(3) (E = B, Al, Ga, In, Tl, E113) are investigated by relativistic density functional and wave function based theories. The unimolecular decomposition of EH(3) --> EH + H(2) becomes energetically more favorable going down the Group 13 elements, with the H(2)-abstraction of InH(3), TlH(3), and (E113)H(3) (E113: element with nuclear charge 113) being exothermic. In accordance with the Hammond-Leffler postulate, the activation barrier for the dissociation process decreases accordingly going down the group 13 elements in the periodic table shifting to an early transition state, with activation energies ranging from 88.4 kcal/mol for BH(3) to 41.3 kcal/mol for TlH(3) and only 21.6 kcal/mol for (E113)H(3) at the scalar relativistic coupled cluster level of theory. For both TlH(3) and (E113)H(3) we investigated spin-orbit effects using Dirac-Hartree-Fock and second-order Møller-Plesset theory to account for electron correlation. For (E113)H, spin-orbit coupling results in a chemically inert closed 7p(1/2)-shell, thus reducing the stability of the higher oxidation state even further. We also investigated the known organothallium compound Tl(CH(3))(3), which is thermodynamically unstable similar to TlH(3), but kinetically very stable with an activation barrier of 57.1 kcal/mol.

Aminoallenylidene complexes of ruthenium(II) from the regioselective addition of secondary amines to butatrienylidene intermediates: a combined experimental and theoretical study of the hindered rotation around the CN-bond

Aminoallenylidene complexes trans-[Cl(dppm)2RuC3(NRR′)(CH3)]+ are obtained from the regioselective addition of secondary amines to trans-[Cl(dppm)2RuCCCCH2]+. Unsymmetrically substituted amines give rise to Z/E isomeric mixtures. Dynamic 31P NMR spectroscopy gave an energy barrier of about 85 kJ mol−1 for rotation around the CN-bond pointing to a large contribution of the iminium alkynyl resonance form trans-[Cl(dppm)2Ru–CC–C(NRR′)(CH3)]+. This is also indicated by the pronounced bond length alternation within the RuC3N-chain as is revealed by X-ray structure analysis of the Z isomer of the (benzylmethyl)methylamine derivative 2d. The issue of NR2 rotation was also addressed by DFT calculations on the trans-[Cl(dhpm)2RuC3{N(CH3)2}(CH3)]+ model complex (dhpm = H2PCH2PH2). Upon rotation around the iminium type CN bond, the nitrogen lone pair and the π-system of the allenylidene ligand are decoupled, resulting in a significantly longer CN bond and a tetrahedrally coordinated nitrogen atom.