Comparison of MgYb and Mg-Ca bonding: structures, electronic analyses and reactivities.

Reaction of [(BDI*)MgNa]2 with (Am*YbI)2 in methylcyclohexane led to the precipitation of NaI and quantitative formation of (BDI*)Mg-Yb(Am*) (1-Yb); BDI* = HC[C(tBu)N(DIPeP)]2, DIPeP = 2,6-Et2CH-phenyl; Am* = tBuC(N-DIPP)2, DIPP = 2,6-iPr-phenyl. Complex 1-Yb features a long unsupported 2c-2e Mg-Yb bond of 3.302 Å and crystallizes isomorphous to (BDI*)Mg-Ca(Am*) (1-Ca). The formal Mg0-YbII oxidation states in 1-Yb are confirmed by effective-oxidation-state analysis but the low reliability index of 68.0% indicates that this description is not fully representative of the electron distribution. Analysis of the electron density shows significant Mg0 → YbII electron transfer and therefore the complex has partial MgI-YbI character. EDA-NOCV analysis suggests that bonding in 1-Yb is best pictured as a combination of neutral open-shell radicals (BDI*)Mg˙/(Am*)Yb˙. Accordingly, (BDI*)Mg acts as an X-type ligand for Yb(Am*). The long, polarized Mg δ--Yb δ+ bond in 1-Yb is highly reactive. The thermal decomposition and reactivity of 1-Yb with N2O, NH3, 1,1-diphenylethylene, trans-stilbene and anthracene have been studied. Comparison with the reactivity of 1-Ca shows strong similarities, but also important differences. Most reactants oxidize the Mg0 centre in 1-Yb and 1-Ca and produce similar complexes that generally crystallize isomorphous. However, N2O can also oxidize the YbII centre, resulting in paramagnetic YbIII products. In all cases, the Mg-Yb and Mg-Ca bonds in 1-Yb and 1-Ca are considerably more reactive than the unpolarized Mg-Mg bond in complexes of type (BDI)Mg-Mg(BDI).