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.

本研究合成了一系列新型大位阻烯丙基三联吡啶（terpyridyl）镱配合物，以探究烯丙基配体（allyl ligand）对这类材料中存在的分子内电荷转移过程（internal charge-transfer process）的影响。相较于二(五甲基环戊二烯基（pentamethylcyclopentadienyl）)镱茂化合物（ytterbocene）Cp*₂Yb(tpyCN)（其C≡N伸缩振动波数ν_C≡N=2172 cm⁻¹），对称取代的烯丙基配合物（symmetrically substituted allyl complex）二[1,3-二(三甲基硅基（SiMe3）)烯丙基](氰基三联吡啶)合镱{[1,3-(SiMe3)₂C₃H₃]₂Yb(tpyCN)}的C≡N伸缩振动频率显著降低至2130 cm⁻¹。进一步研究表明，这类大位阻烯丙基配合物的电子性质可通过配体取代进行调控：非对称衍生物（asymmetric derivatives）二[1-(三甲基硅基（SiMe3）)烯丙基](氰基三联吡啶)合镱{[1-(SiMe3)C₃H₄]₂Yb(tpyCN)}与二[1-(三苯基硅基（SiPh3）)-3-(三甲基硅基（SiMe3）)烯丙基](氰基三联吡啶)合镱{[1-(SiPh3)-3-(SiMe3)C₃H₃]₂Yb(tpyCN)}的C≡N伸缩振动频率分别为2171 cm⁻¹与2164 cm⁻¹。上述频率差异可归因于不同配体的位阻与电子特性（steric and electronic character）差异。对二[1,3-二(三甲基硅基（SiMe3）)烯丙基](三联吡啶)合镱{[1,3-(SiMe3)₂C₃H₃]₂Yb(tpy)}开展单晶X射线表征（single-crystal X-ray characterization）后发现，其烯丙基配体的Yb−C与Yb−N键长（bond distances）均短于五甲基环戊二烯基对应配合物。该配合物的磁化率数据（magnetic susceptibility data）与居里定律（Curie law）偏差显著，室温磁矩（room-temperature magnetic moment）为2.95 μ_B。