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

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. 13C NMR coupling to 119/117Sn, observed in both
SnMe and SnPh, was used to make 13C NMR resonance assignments. Qualitative results of semiempirical molecular
orbital calculations support the 13C 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, α = 99.91(1)°, β = 106.33(1)°, γ = 77.80(1)° with Z = 2
in space group P1̄. 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.