Disupersilylmetalle (tBu3Si)2M und SupersilylmetallhalogenidetBu3SiMX mit M ? Zn, Cd, Hg: Synthesen, Strukturen, Eigenschaften

Synthesis, crystal structure, thermal and spectroscopic properties of ZnX2-2-methylpyrazine (X = Cl, Br, I) coordination compounds

Reaction of zinc(II) chloride, bromide and iodide with 2-methylpyrazine (2-Mepyz) leads to the formation of coordination compounds with the composition ZnX2(2-Mepyz)2 (X = Cl; 1-Cl, Br; 1-Br and I; 1-I). In the compounds each Zn cation is tetrahedrally coordinated by two halide anions and two 2-methylpyrazine ligands forming discrete complexes. TG-DTA and temperature dependent PXRD measurements prove that upon heating compounds 1 transform into new compounds with the composition ZnX2(2-Mepyz) (2), that are subsequently converted into compounds with the composition (ZnX2)3(2-Mepyz) (3) upon further heating. It was also found that compounds 2 can be prepared directly in solution. For ZnI2(2-Mepyz) (2-I) crystals were obtained and characterized by single crystal X-ray diffraction, whereas the crystal structures of 2-Cl and 2-Br were determined ab initio from PXRD data. In these compounds the Zn cations are also tetrahedrally coordinated and linked into chains by bridging 2-methylpyrazine ligands. The (ZnX2)3(2-Mepyz) compounds can only be obtained by thermal decomposition, and the products are of poor crystallinity and extremely hygroscopic, which prevented structure determinations.

Zinc and Cadmium Complexes of Chelating N-Heterocyclic Silylene and Their Reactivity toward Elemental Chalcogens

The reactions of the pyridine-functionalized silylene L^NSi [L = PhC(NtBu)₂; N = 2-(methylamido)pyridine] with zinc and cadmium halides are described. These resulted in the formation of a series of zinc and cadmium silylene complexes: [L^NSi-ZnX₂] (X = Cl, Br, I) and [{L^NSi-CdI₂}₂], which is the first cadmium silylene compound. Subsequent reaction of these silylene complexes with elemental sulfur and selenium under mild conditions at room temperature afforded under activation of these elements the corresponding silanethione-stabilized zinc [(L^NSi═S)-ZnX₂] (X = Cl, I) and cadmium [(L^NSi═S)-CdI₂] complexes and the silaneselenone-stabilized zinc species [(L^NSi═Se)-ZnCl₂]. A selective insertion of the group 16 elements into the M-Si bond of the silylenes was observed. Because of metal coordination, the Si-chalcogen bond lengths in the silanethiones and silaneselenones are enlarged and thus range between a single and a double bond. All new compounds were fully characterized by single-crystal X-ray diffraction analyses, multinuclear NMR spectroscopy, elemental analyses, and IR spectroscopy.

Generation and EPR Spectroscopy of the First Silenyl Radicals, R2 C=Si. -R: Experiment and Theory

The first two persistent silenyl radicals (R₂ C=Si^. -R), with a half-life (t_1/2 ) of about 30 min, were generated and characterized by electron paramagnetic resonance (EPR) spectroscopy. The large hyperfine coupling constants (hfccs) (a(²⁹ Si_α )=137.5-148.0 G) indicate that the unpaired electron has substantial s character. DFT calculations, which are in good agreement with the experimentally observed hfccs, predict a strongly bent structure (∡C=Si-R=134.7-140.7°). In contrast, the analogous vinyl radical, R₂ C=C^. -R (t_1/2 ≈3 h), exhibits a small hfcc (a(¹³ C_α )=26.6 G) and has a nearly linear geometry (∡C=C-R=168.7°).

Unprecedented solvent induced inter-conversion between monomeric and dimeric silylene–zinc iodide adducts

The reaction of silylene [PhC(NtBu)₂SiN(SiMe₃)₂] with ZnI₂leads to both monomeric [PhC(NtBu)₂Si{N(SiMe₃)₂} → ZnI₂]·THF (1) and dimeric [PhC(NtBu)₂Si{N(SiMe₃)₂} → ZnI₂]₂(2) adducts which are inter-convertible.

Activation of Homolytic Si-Zn and Si-Hg Bond Cleavage, Mediated by a Pt(0) Complex, via Novel Pt-Zn and Pt-Hg Compounds

The thermally stable [(tBuMe2 Si)2 M] (M=Zn, Hg) generate R3 Si(.) radicals in the presence of [(dmpe)Pt(PEt3 )2 ] at 60-80 °C. The reaction proceeds via hexacoordinate Pt complexes, (M=Zn (2 a and 2 b), M=Hg (3 a and 3 b)) which were isolated and characterized. Mild warming or photolysis of 2 or 3 lead to homolytic dissociation of the Pt-MSiR3 bond generating silyl radicals and novel unstable pentacoordinate platinum paramagnetic complexes (M=Zn (5), Hg (6)) whose structures were determined by EPR spectroscopy and DFT calculations.

1-(Bromomercurio)ferrocene

The asymmetric unit of the title compound, [Fe(C₅H₅)(C₅H₄BrHg)], contains two independent mol­ecules, A and B, in which the Hg—C bond lengths are 2.045 (6) and 2.046 (6) Å, the Hg—Br bond lengths are 2.4511 (9) and 2.4562 (7) Å, and the C—Hg—Br angles are 176.42 (17) and 177.32 (17)°. The two cyclo­penta­dienyl rings of mol­ecule A are eclipsed, while those of mol­ecule B are almost staggered. The HgBr groups are connected by inter­molecular Hg⋯Br contacts of 3.3142 (9)–3.4895 (11) Å, forming layers parallel to (001). These layers contain both four-membered (HgBr)₂ and eight-membered (HgBr)₄ rings. Ferrocene–ferrocene C—H⋯π contacts connect the mol­ecular layers along the c-axis direction.

Synthesis and structures of some bimetallic (Li/Ca, Li/Zn, Li/Li) diamides derived from 1,2-bis(neopentylamino)benzene and of Li2[{N(SiMe2NPri2)}2C6H4-1,2](thf)3

The following crystalline, or microcrystalline (4), metal diamides have been prepared under mild conditions from the N,N'-disubstituted 1,2-diaminobenzene [{N(R)H}2C6H4-1,2] (H(2): R = CH2But; H2L': R = SiMe2NPri2): [Li(thf)(mu-L)(mu-I)Ca(thf)] (1), [Li(thf)4][{Zn(mu-L)}3(mu3-Cl)] (2), [Li(thf)4][Zn(L)2] (3), [{Li(OEt2)(mu-L)Zn}2(mu-L)] (4), [Li(OEt2)(mu-L)Zn(mu-L)Zn(LH)] (5) and [Li(thf)(mu-L')Li(thf)2] (6). Compounds 1-5 were obtained from [Li2(L)] and CaI2 (1) or ZnCl2 (2-5) while 6 was derived from H2(L') and LiBun. Compound 5 was isolated as a very minor by-product from the synthesis of 4, and is assumed to have been formed therefrom by adventitious hydrolysis. The green salt 3 was paramagnetic with the negative charge uniformly delocalised on the two ligands. The other compounds were colourless and diamagnetic. The X-ray structures of each, except 4, are reported and discussed.