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Dilithiostannoles, which are aromatic tin-containing ring compounds, were proposed to have stannylene character, as judged from their NMR analysis. We herein report on the synthesis of silyl-substituted dilithiostannoles, which were characterized by NMR spectroscopy and X-ray diffraction analysis. The silyl-substituted derivatives also exhibit features characteristic of aromatic dilithiostannoles such as 7Li NMR signals at high-field area and no C–C bond alternation in the stannole rings. Theoretical calculations and the 119Sn NMR chemical shifts revealed that the stannylene character in the silyl-substituted dilithiostannoles is enhanced due to greater interaction between 5p (Sn) and LUMO (butadiene) in comparison to those in alkyl and aryl derivatives. The 119Sn Mossbauer spectra of dilithiostannoles were measured for the first time, indicating that each of the tin atoms in dilithiostannoles can be characterized as having Sn(II) character.

Reaction of a dilithiostannole with Cp2HfCl2 (Cp = cyclopentadienyl anion, C5H5–) afforded a dinuclear hafnium complex bridged by a stannole dianion ligand, (Cp2ClHf)2[μ-η1;η1-{SnC4(SitBuMe2)2Ph2}]. The product was fully characterized by NMR, elemental analysis, and X-ray diffraction analysis. The product adopts a new coordination pattern in the coordination chemistry of metallole dianion ligands, μ-η1;η1-fashion. Unlike aromatic μ-η5;η5-stannole dianion ligands in triple-decker-type sandwich complexes we previously reported, the stannole ring of the product has 1,3-diene character, revealing its nonaromatic nature. Electronic structures of stannole dianion ligands are therefore strongly affected by their coordination modes.

The reaction mechanism of the [2 + 2 + 1] cycloaddition of two ethynes and one stannylene, SnR‘2 (R‘ = H, CH(SiMe3)2), to produce stannole catalyzed by the transition-metal complexes M(PR3)2 (1; M = Ni, Pd, Pt; R = H, Me, i-Pr, t-Bu) has been theoretically investigated by means of both density functional theory (DFT) and ONIOM methods. The DFT calculations of the model molecule with R and R‘ = H showed that the catalytic reaction proceeds via the 1,2-metallastannete intermediate 4, as experimentally proposed. The starting complex 1 first reacts with stannylene to from the stannylene complex 5, which is followed by ethyne addition to the M−Sn double bond with a small energy barrier of less than 10 kcal/mol for all three metals to form 4. The subsequent ethyne insertion into the M−Sn bond and the C−C bond formation, which require the larger energy barrier, take place to produce stannole. For Ni and Pd, the ethyne insertion needs the largest energy barrier of 11.3 and 16.4 kcal/mol, respectively. On the othe...

A series of group 14 metalloles, from silole to stannole, together with cyclopentadiene, having two thienyl groups at the 2,5-positions, have been prepared. Their crystal structures, UV−vis absorpt...

Various structural (C−C bond length equalization, D), energetic (isodesmic stabilization energies, ISE), and magnetic (diamagnetic susceptibility exaltations, Λ and nucleus-independent chemical shifts, NICS) criteria are employed (using B3LYP, CSGT, and GIAO ab initio methods) to assess the aromaticity and antiaromaticity of a variety of group 14 (E = C, Si, Ge, Sn, Pb) metalloles: C4H4EH2 (C2v), C4H4EH- (Cs and C2v; C, D5h), C4H4EH+ (singlet, C2v), C4H4EHLi (Cs; C, C5v), and C4H4ELi2 (C2v). In addition, structural trends are established for C4H4ELi- (Cs) and for C4H4E2- (C2v) as well as for the singlet and triplet C4H4E (C2v) sets. The increased pyramidality at E down group 14 results in strongly decreased aromaticity of metallolyl anions C4H4EH- (Cs). In contrast, all planar C4H4EH- (C2v) geometries are significantly more aromatic. Although all C4H4EH+ (C2v) structures are planar, the antiaromaticity in singlet C5H5+ is much higher than that of the heavier congeners (E = Si to Pb). The four-π-electron ...

Reaction of 1,1-dichloro-TEGeCp (TEGeCp = 2,3,4,5-tetraethyl-1-germacyclopentadiene) with excess Li in tetrahydrofuran (THF) at room temperature gave [TEGeCp2-]·2[Li+] quantitatively. X-ray structure determination of this germole dianion shows three lithium cations around one germole ring in η1, η5, and η5 sites to give the composition [η5-Li·TMEDA][η5-Li]1/2[η1-Li]1/2[Et4C4Ge] (TMEDA = N,N,N‘,N‘-tetramethylethylenediamine). Nearly equal C−C bond distances in the Et4C4Ge ring indicate a delocalized π-system. Reactions of this germole dianion with trimethylchlorosilane provided 1,1-bis(trimethylsilyl)-TEGeCp, in high yields.

Structural, energetic, and magnetic criteria confirm that the silole dianion (CH)4Si2- (7) and its alkali-metal ion pairs, e.g. (CH)4SiLi- (7a), (CH)4SiLi2 (7b), (CH)4SiNa2 (13), and (CH)4SiK2 (14), are highly aromatic. Inverse sandwich structures and strongly delocalized silole rings are prefered by 7b, 13, and 14. The degree of aromaticity in [η5-(CH)4Si]Li- (7a) exceeds that of the isoelectronic third-period heterocycles (CH)4PLi (5a) and (CH)4SLi+ (6a) and even approaches that of (CH)5Li (3a).