Aromaticity in Group 14 Metalloles:  Structural, Energetic, and Magnetic Criteria

Abstract

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 (C 2 v ), C4H4EH- (C s and C 2 v ; C, D 5h ), C4H4EH+ (singlet, C 2 v ), C4H4EHLi (C s ; C, C 5v ), and C4H4ELi2 (C 2 v ). In addition, structural trends are established for C4H4ELi- (C s ) and for C4H4E2- (C 2 v ) as well as for the singlet and triplet C4H4E (C 2 v ) sets. The increased pyramidality at E down group 14 results in strongly decreased aromaticity of metallolyl anions C4H4EH- (C s ). In contrast, all planar C4H4EH- (C 2 v ) geometries are significantly more aromatic. Although all C4H4EH+ (C 2 v ) 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 singlets C4H4E exhibit nearly as localized geometries as the C4H4EH+ ions, but the C4H4E triplets are more delocalized. As in the free anions, pyramidally coordinated E's lead in C4H4EHLi (C s ) to reduced aromaticity, but stabilizing Li−H interactions are apparent in these structures. The metallole dianions and their Li+ complexes (e.g. C4H4ELi2, C 2 v ) are the most aromatic among the species studied. The aromaticity in these dianionic metalloles is remarkably constant in going from E = C to E = Pb.

Synthesis and NMR-Study of the 2,3,4,5-Tetraethylsilole Dianion [SiC4Et4]2−•2[Li]+

“…These chemical shifts of 29 Si and 13 C resonances are consistent with delocalization of the negative charge into the silole ring, which is supported by the calculated negative NICS value of dilithiumsilole dianion [9,10]. In addition the signals of the ethyl groups in the 1 H- and 13 C-NMR spectra of 3 shift downfield due to the anisotropic effect of the ring current from the delocalization {Δδ( 13 C of CH 2 CH 3 ) = 1.42–7.83 ppm and Δδ( 1 H of CH 2 ) = 0.16–0.19 ppm)} (Table 3).…”

“…Since the first silole dianion, 2,3,4,5-tetraphenyl-1-silacyclopentadienide dianion, was prepared in 1990 by Joo and Hong [1], the aromaticity of the silole dianion [2] and germole dianion [3] was suggested by NMR study and it was confirmed by X-ray crystallography of the structures [4,5,6,7,8] and by theoretical study [9,10]. The chemistry of group 14 metallole dianions has been developed enormously [11,12], and recently the stannole dianion [SnC 4 Ph 4 ] 2− was also reported [13,14,15,16].…”

Quantum‐chemical analyses of aromaticity, UV spectra, and NMR chemical shifts in plumbacyclopentadienylidenes stabilized by Lewis bases

“…Magnetic criteria including NICS of Silole dianions and metaloles containing Si, Ge, Sn, and Pb have been reported. [9,10] Pioneering theoretical calculations of metal NMR [11,12] were helpful for the present analyses. The relativistic correction, especially the spinorbit effect, is essentially required in heavy-element NMR chemical shifts.…”

Aggregation-Induced Emission in Group 14 Metalloles (Siloles, Germoles, and Stannoles): Spectroscopic Considerations, Substituent Effects, and Applications

“…The luminescence quantum yields of the germole analogs of DMTPS and HPS are 0.28 and 0.63%, respectively, compared with 0.24 and 0.42% for the siloles. Compared with the siloles, relatively few germoles or reports of their AIE behavior have been described in the literature [4,8,104,[107][108][109][110].…”