Diverse Reactions of α-Diimine-Ligated Mg^I−Mg^I-Bonded Compound with Carbodiimides

The α-diimine-ligated dimagnesium(I) compound [K(thf)₃]₂[LMg−MgL] (1, L=[(2,6-iPr₂C₆H₃)NC(Me)]₂²⁻) displays diverse reactivities toward carbodiimides (RN=C=NR) with different R substituents. In the reaction of 1 with Me₃SiNCNSiMe₃, one of the easily leaving trimethylsilyl groups is lost to yield the Me₃SiNCN⁻ moiety that either bridges two Mg^II centers (2) or terminally coordinated (3). In contrast, with the similarly bulky tBuNCNtBu, the carbodiimide inserts into Mg−Mg bond with accompanying C−H activation of a ligand or solvent (products 4 and 5). In the case of dicyclohexyl or diisopropyl carbodiimide, reductive C−C coupling of two RNCNR molecules occurs to form the [C₂(NR)₄]²⁻ diamido moiety, which bridges two Mg centers, giving complexes [{K(dme)₂}₂LMg(μ-{C₂(NR)₄})MgL] (6, R=Cy; 7, R=iPr) and [L⋅⁻Mg(μ-{C₂(NR)₄})MgL⋅⁻] (8). Most interestingly, upon treating 1 with Me₃SiC≡CSiMe₃, the acetylide complex [K(dme)][LMg(C≡CSiMe₃)(dme)] (9) was prepared, which undergoes a rare “double insertion” with CyNCNCy to afford [K(solv)][K(dme)₂LMg(NCy)₂C−C≡C−C(NCy)₂MgL] (10) containing an acetylenediide-coupled bis(amidinate) ligand that bridges two Mg atoms.