The observed isotropic 1 H hyperfine couplings that are even smaller than those observed for d 1 metal alkyls suggest that, in contrast to the case of Cp 3 Yb, there is no significant charge and spin density transfer to the ligands in Yb[CH(SiMe 3 ) 2 ] 3 . This is also consistent with the preferential presence of the unpaired electron in the 4f orbital rather than in the valence 5d orbital, which would result in more significant distribution of the spin density into the ligands of Yb(III). A difficulty of promoting 4f electrons of Yb(III) to the 5d orbital, which effectively prevents the formation of double Yb --C bonds, was previously discussed based on CASSCF calculations. Taking into account the results of magnetic susceptibility measurements (vide supra), we propose that the ground state of the Yb[CH(SiMe 3 ) 2 ] 3 complex has a single electronic configuration of 4f 13 (S = 1/2), close to the one of Yb(III) free ion.