Observation of Internal Electron Transfer in Bulky Allyl Ytterbium Complexes with Substituted Terpyridine Ligands

A series of new bulky allyl terpyridyl−ytterbium complexes have been synthesized to determine the effect of allyl
ligands on the internal charge-transfer process that exists in these materials. Compared to the pentamethylcyclopentadienyl−ytterbocene compound Cp*2Yb(tpyCN) (νC⋮N = 2172 cm-1), the symmetrically substituted allyl complex
[1,3-(SiMe3)2C3H3]2Yb(tpyCN) possesses a markedly lowered C⋮N frequency of 2130 cm-1. Furthermore, the
electronic nature of these bulky allyl complexes can be tuned, as demonstrated by the C⋮N frequency of the
asymmetric derivatives [1-(SiMe3)C3H4]2Yb(tpyCN) and [1-(SiPh3)-3-(SiMe3)C3H3]2Yb(tpyCN) (2171 and 2164 cm-1,
respectively). The differences in these frequencies can be attributed to differences in the ligands' steric and electronic
character. Single-crystal X-ray characterization of [1,3-(SiMe3)2C3H3]2Yb(tpy) reveals that the allyl moiety possesses
shorter Yb−C and Yb−N bond distances than the Cp* analogue. The magnetic susceptibility data for
[1,3-(SiMe3)2C3H3]2Yb(tpy) departs dramatically from the Curie law, with a room-temperature magnetic moment of
2.95 μB.