ppm (ν½ = 290 Hz). We were unable to observe coupling to phosphorus, however, the width of the signal likely hides this coupling. This signal is quite downfield relative to many reported ytterbium alkyls, but still within typical regions (600-1200 ppm). There are no reported Yb NMR chemical shifts for ytterbium complexes with iminophosphoranomethanide ligands, however, Junk and co-workers reported 171 Yb NMR data for several Yb formamidinate complexes (e.g. [Yb(ArForm)I(THF)3], Form=ArNCHNAr, Ar = 2,6-Me2C6H3, 2,4,6-Me3C6H2). These typically exhibited resonances in their Yb NMR spectra around 400-600 ppm, although it should be noted that these also contained a halide atom additionally ligating the metal atom. Additionally, Lappert and co-workers reported several Yb homoleptic and heteroleptic β-diketiminate complexes. The homoleptic species ( With the same method, we also measured the magnetic susceptibilities for 2-Sm (2.98 μB) and 2-Pr (3.19 μB). In the case of 2-Sm, µeff is higher than the calculated value for the free ion (Sm 3+ 0.85 μB), though it is not uncommon for Sm(III) complexes to have higher magnetic moments owing to the presence of low-lying excited states that mix with the 6 H5/2 ground state. As mentioned above, NMR analysis of various samples of 2-La revealed the presence of residual proligand, NPC-H2, as a persistent impurity, likely obtained as the result of partial decomposition. Despite these impurities, the 31 P{ 1 H} NMR spectrum clearly shows resonances corresponding to 2-La at 27.8 ppm. In the case of 2-Y, the same restricted rotation as for 1-Mg was observed in its H spectrum (Figure ), P{ 1 H} (Figure ) and Si{ 1 H} (Figure ) NMR spectra. The ). It can also be seen from these studies that 2 JPY coupling is visible (8.2 Hz). JPY scalar coupling constants are typically around 40-50 Hz for neutral phosphine ligands, whereas in yttrium BIPM complexes the 2 JPY coupling constants are more in the region of 12-15 Hz. From this, it can be seen that the 2 JPY constant in 2-Y is relatively small, although plausible. In the is more than compensated for by the greater filling of the coordination sphere by the three NPC-H ligands.