SYNTHESIS AND SOLID-STATE STRUCTURES OF 3 MAGNESIUM DIAMIDE COMPLEXESDERIVED FROM RN(H)CH2CH2N(H)R DIAMINE PRECURSORS (R = PH OR PHCH2)

Three new magnesium diamide complexes have been prepared by treating t he diamine precursors N,N'-diphenylethylenediamine or N,N'-dibenzyleth ylenediamine with the commercial reagent dibutyl-magnesium in the pres ence of a donor solvent (THF or HMPA). Their crystal structures have b een determined. Both [{MgN(Ph)CH2CH2N(Ph). 2THF(1.5 THF)}(2)] and [{Mg N(CH2Ph)CH2CH2N(CH2Ph). HMPA}(2)] adopt dimeric arrangements based on trans-5.4.5-fused ring systems. The former structure is distinctive an d noteworthy for exhibiting a five-coordinate, distorted trigonal bipy ramidal Mg centre, instead of the more usual four-coordinate, distorte d tetrahedral geometry found in the latter structure. Replacing the tw o THF ligands of the former structure by two HMPA molecules leads to d eaggregation, in the form of the monomeric complex [MgN(Ph)CH2CH2N(Ph) . 2HMPA], which also displays an unremarkable distorted tetrahedral Mg coordination. Comparisons are made with other dimeric and monomeric, magnesium-amide and related complexes. (C) 1998 Elsevier Science Ltd. All rights reserved.