Diverse Reactions of α-Diimine-Ligated MgI -MgI -Bonded Compound with Carbodiimides.

ABSTRACT

The α-diimine-ligated dimagnesium(I) compound [K(thf)3 ]2 [LMg-MgL] (1, L=[(2,6-iPr2 C6 H3 )NC(Me)]2 2- ) displays diverse reactivities toward carbodiimides (RN=C=NR) with different R substituents. In the reaction of 1 with Me3 SiNCNSiMe3 , one of the easily leaving trimethylsilyl groups is lost to yield the Me3 SiNCN- moiety that either bridges two MgII 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 }2 LMg(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 Me3 SiC≡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)2 LMg(NCy)2 C-C≡C-C(NCy)2 MgL] (10) containing an acetylenediide-coupled bis(amidinate) ligand that bridges two Mg atoms.