Electrochemical and Photophysical Properties of a Series of Group-14 Metalloles

Abstract

A series of six group-14 dimethyl-or diphenyl-tetraphenylmetallacyclopentadienes were synthesized and characterized by their spectroscopic and electrochemical properties. The group-14 elements investigated were silicon, germanium, and tin. (The compounds are designated according to the heteroatom and the substituent on the heteroatom, i.e., SiMe, SiPh, ..., SnPh.) Five of the six compounds luminesce in both the solid state and in solution. The emission maxima of SiPh, GePh, and SnPh are invariant to a change in the heteroatom, while for SiMe, GeMe, and SnMe there is a strong dependence of the emission maxima on the identity of the heteroatom. SiMe emits at a longer wavelength than GeMe, while SnMe is not luminescent. The dramatic luminescence difference between the two tin compounds was investigated. 13 C NMR coupling to 119/117 Sn, observed in both SnMe and SnPh, was used to make 13 C NMR resonance assignments. Qualitative results of semiempirical molecular orbital calculations support the 13 C NMR assignments. The crystal structure data for SnPh was obtained at 20°C: a ) 10.353(2) Å, b ) 16.679(2) Å, c ) 9.482(1) Å, R ) 99.91(1)°, ) 106.33(1)°, γ ) 77.80(1)°with Z ) 2 in space group P 1 h . It is proposed that the increased electron density at tin in SnMe is responsible for the deactivation of the emissive state. The presence of phenyl substituents in SnPh serves to stabilize the emissive state and luminescence is observed.

Synthesis and Structures of Bi(1,1‐stannole)s

“…The latter band can be assigned to the π-π* transition of the stannole ring because a similar absorption band is found in 1,1,2,3,4,5-hexaphenylstannole (1; λ max = 355 nm). [21] The π-π* transition of group 14 metalloles is observed in the same region, at around 360 nm, because the contributions of the diene moiety to both HOMO and LUMO are predominant rather than that of the metal moiety. [21] The shorter wavelength band can be assigned to the transition from σ(Sn-Sn) to π*(diene) because the corresponding band is absent in 1.…”

“…[21] The π-π* transition of group 14 metalloles is observed in the same region, at around 360 nm, because the contributions of the diene moiety to both HOMO and LUMO are predominant rather than that of the metal moiety. [21] The shorter wavelength band can be assigned to the transition from σ(Sn-Sn) to π*(diene) because the corresponding band is absent in 1. This absorption (320 nm) is red-shifted compared to that of a bi(1,1-silole) (300 nm) [7] because of the higher energy level of a σ(Sn-Sn) bond than that of a σ(Si-Si) bond.…”

Synthesis and Reactions of Stannole Anions

“…Namely, the absorption is derived from the π-π* transition of the stannole ring. [18] The π-π* transitions of group 14 metaloles are observed in the same region at about 360 nm because the contribution of the diene moiety to both HOMO and LUMO is more predominant than that of the metal moiety. [18] This spectral feature suggests no significant through-space interaction between the two stannole rings in solution.…”

Stepwise Oxidation of the Stannole Dianion

“…In the 119 Sn NMR spectrum, two signals were observed at d = À87.5 and À205.5 ppm with an intensity ratio of 2:1, resulting from the two terminal and single central tin atoms, respectively. The signal assignable to the central tin atom was accompanied by a pair of satellite signals owing to the ter- UV/Vis spectra of stannoles, 4-7: UV/Vis absorption spectra of monostannole 5, [14] oligo-and poly(1,1-stannole)s in toluene are shown in Figures 2 and 3. The bi-and ter(1,1-stannole)s, 6 and 7, have two absorption maxima at around l = 310 and 370 nm.…”

“…The CÀC bond lengths within the middle stannole ring (the bond distances of C(5) À C(6) and C(6) À C(6)* are 1.356(4) and 1.498(7) , respectively) are similar to these of typical stannoles. [14] Bond alternation in the C À C bonds in the five-membered terminal stannole rings is observed (the bond distances of C(1) À C(2), C(2) À C(3) and C(3) À C(4) are 1.36(4), 1.473(4) and 1.378(4) , respectively), indicating that the terminal stannole rings have considerable diene character and the negative charges of 1,3-dianion 3 would localize on both terminal tin atoms, as seen previously in other group 14 metallole anions. [12,15] Pyramidalization at the tin center is clearly evident from the angle between the C 4 Sn plane and the Sn À Sn bond (1068).…”