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).