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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 ...

A palladium-catalyzed (2 + 2 + 1) cycloaddition reaction of two C2H2 and one SnR2 to form C-unsubstituted stannoles (C4H4)SnR2 [R = CH(SiMe3)2 2a, R2 = {C(SiMe3)2CH2}2 2c] is described. Catalysts are (R‘2PC2H4PR‘2)Pd complexes (slow reaction) and (R‘3P)2Pd complexes (fast reaction). The mechanism of the catalysis has been elucidated in detail from stoichiometric reactions based on R = CH(SiMe3)2. For the [(R‘2PC2H4PR‘2)Pd]-catalyzed system, the starting Pd(0)−ethene complexes (R‘2PC2H4PR‘2)Pd(C2H4) (R‘ = iPr (3), tBu (4)) react both with ethyne to give the Pd(0)−ethyne derivatives (R‘2PC2H4PR‘2)Pd(C2H2) (R‘ = iPr (5), tBu (6)) and with SnR2 to yield the Pd(0)−Sn(II) adducts (R‘2PC2H4PR‘2)PdSnR2 (R‘ = iPr (7), tBu (8)). The Pd−Sn bond [2.481(2) A] of 7 is very short, indicative of partial multiple bonding. Subsequent reactions of the Pd(0)−ethyne complexes 5 and 6 with SnR2 or of the Pd(0)−Sn(II) complexes 7 and 8 with ethyne afford the 1,2-palladastannete complexes (R‘2PC2H4PR‘2)Pd(CHCH)SnR2 (Pd−Sn) (R‘ =...

Synthetic routes to the metallole species C4Me4E(H)R (9, E = Si, R = Si(SiMe3)3; 10, E = Si, R = Mes (mesityl); 11, E = Ge, R = Si(SiMe3)3; 12, E = Ge, R = Mes), C4R4E(SiMe3)2 (13, E = Si, R = Me; 14, E = Ge, R = Me; 19, E = Si, R = Et; 20, E = Ge, R = Et), and C4Me4E(R)E(R)Me4C4 (15, E = Si, R = SiMe3; 16, E = Si, R = Me; 17, E = Ge, R = SiMe3; 18, E = Ge, R = Me) are described. In the presence of 18-crown-6, dihalides 1 and 2 are reduced by potassium in tetrahydrofuran to give crystalline samples of the silole dianion [K(18-crown-6)+]2[C4Me4Si2-] (21) and the germole dianion [K4(18-crown-6)3][C4Me4Ge]2 (22). Compound 21 adopts an inverse-sandwich geometry, while 22 is a dimer with a bridging [K(18-crown-6)K]2+ group and η5-binding modes for all of the potassium atoms. The metallole dianions in these structures appear to possess delocalized π-systems, as evidenced by nearly equivalent C−C bond lengths in the five-membered rings. Silolyl and germolyl anions have been obtained by various methods involving ...

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).

The reversible redox behavior between the stannole dianion and the bistannole-1,2-dianion is demonstrated. Reaction of the stannole dianion with oxygen (1 eq) gives the 1,2-bistannole-1,2-dianion which is a tin-analogue of the cyclopentadienyl anion in 94% yield. Reaction of the stannole dianion with ferrocenium tetrafluoroborate (1 eq) also gives the 1,2-dianion. The 1,2-bistannole-1,2-dianion has a nonaromatic nature as evidenced by X-ray and NMR analysis. Reduction of the 1,2-dianion with lithium gives the starting dianion.

1,1-Dibromo- and 1,1-diiodo-2,3,4,5-tetraphenyl-1-stannacyclopentadiene, dihalotetraphenylstannoles, XYSnC4(C6H5)4, can be derivatized to form a series of disubstituted products in which X = Y = N3, iso-NCO, iso-SCN, OC(O)CH3, SC(S)N(C2H5)2, N(CH3)2 and P(C6H5)2. Fluorination by KF in acetone results in the X = F, Y = Br or Y = I product only, and lithioamination by LiN(Si(CH3)3)2 yields the X = N(Si(CH3)3)2, Y = Br product only. Attempted synthesis of the dihalostannoles by halogenation of the intermediate tin(II) stannole from 1,4-dilithio-1,2,3,4-tetraphenyl-1,3-butadiene and tin(II) chloride yields only the ring-opened products (4-bromo-1,2,3,4-tetraphenylbutadienyl)tin tribromide or (4-iodo-1,2,3,4-tetraphenylbutadienyl)tin triiodide. Even gentle chlorination of hexaphenylstannole by elemental chlorine cleaves the ring tin-carbon bonds to form cis-cis-1,4-dichloro-1,2,3,4-tetraphenylbutadiene-1,3 and diphenyltin dichloride, while the action of a glacial acetic acid/acetic anhydride mixture yields tetraphenylfuran and diphenyltin diacetate.