Synthesis, Characterization, and Crystal Structures of {Me2Al(μ-i-Pr2N)2Mg[(R)NC(Me)N(R)]} (R = i-Pr, t-Bu):  Insertion of a Carbodiimide (RNCNR) into a Mg−C Bond

A series of amidino-bridged mixed-metal aluminum−magnesium complexes, {[R2Al(μ-R‘2N)2Mg[(R‘‘)NC(R)N(R‘‘)]} (R = Me, R‘ = i-Pr, R‘‘ = i-Pr, 1a; R = Me, R‘ = i-Pr, R‘‘ = t-Bu, 1b; R = Me, R‘ = i-Pr, R‘‘ = p-tolyl, 1c; R = Me, R‘ = Et, R‘‘ = i-Pr, 2a; R = Me, R‘ = Et, R‘‘ = t-Bu, 2b; R = Et, R‘ = i-Pr, R‘‘ = i-Pr, 3a; R = Et, R‘ = i-Pr, R‘‘ = t-Bu), were prepared by insertion reactions of the aluminum−magnesium complexes [R2Al(μ-R‘2N)2Mg(μ-R)]n (R = Me, Et; R‘ = Et, i-Pr) (n = 2, 4) with various substituted carbodiimides and characterized by mass spectra, IR spectra, elemental analysis, and 1H and 13C NMR data. The structures of two of the compounds 1a,b have been determined by single-crystal X-ray diffraction analysis. The structural data show that the bonding of the two nitrogens of the carbodiimide to the magnesium atom is (σ, σ) symmetric and indicate a weak interaction between Mg and C(15).