Synthesis and solid-state structures of three magnesium diamide complexes derived from RN(H)CH2CH2N(H)R diamine precursors (R = Ph or PHCH2)

Three new magnesium diamide complexes have been prepared by treating the diamine precursors N,N'-diphenylethylenediamine or N,N'-dibenzylethylenediamine with the commercial reagent dibutyl-magnesium in the presence of a donor solvent (THF or HMPA). Their crystal structures have been determined. Both [{MgN(Ph)CH2CH2N(Ph). 2THF(1.5 THF)}(2)] and [{MgN(CH2Ph)CH2CH2N(CH2Ph). HMPA}(2)] adopt dimeric arrangements based on trans-5.4.5-fused ring systems. The former structure is distinctive and noteworthy for exhibiting a five-coordinate, distorted trigonal bipyramidal Mg centre, instead of the more usual four-coordinate, distorted tetrahedral geometry found in the latter structure. Replacing the two THF ligands of the former structure by two HMPA molecules leads to deaggregation, 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.