Magnesium Stung by Nonclassical Scorpionate Ligands: Synthesis and Cone-Angle Calculations.

A series of tris(pyrazolyl)alkane (RCTp) scorpionate ligands of the type RCTp (R=Me, nBu, SiMe ; R'=H, Me, Ph, iPr, tBu) were synthesized and their ability to coordinate methylmagnesium moieties was examined. The reaction of Mg(AlMe ) with neutral proligands HCTp or Me SiCTp , containing a non-innocent backbone methine moiety, led to deprotonation/rearrangement and SiMe /AlMe exchange to afford [(Me AlCTp ) Mg] and [(Me AlCTp )Mg(AlMe )], respectively, with monoanionic tripodal ligands. Treatment of sterically less demanding RCTp with Mg(AlMe ) produced isostructural dicationic "metal-in-a-box" complexes of the type [(RCTp ) Mg][AlMe ] (R=Me, nBu; R'=H, Me). Utilization of the superbulky ligands MeCTp and MeCTp gave monocationic complexes [(MeCTp )MgMe][AlMe ] and [(MeCTp )MgMe][Al Me ] as separated ion pairs. The reaction of Mg(AlMe ) with nBuCTp led to the formation of the dimagnesium complex [{(nBuCTp )Mg(AlMe )} (μ-CH )], which features a bridging methyl moiety and terminal η -coordinated tetramethylaluminato ligands. Isopropyl-substituted ligand MeCTp emerged from further fine-tuning of the steric and electronic parameters and, upon reaction with Mg(AlMe ) , gave (MeCTp )Mg(AlMe ) ; this represents the first example of a magnesium bis(alkyl) complex with an intact RCTp ligand. The exact ligand cone angles Θ of all magnesium complexes were determined according to the mathematical analysis developed by Allen et al. [J. Comput. Chem. 2013, 34, 1189-1197].