N, N′, N′-trimethylethylenediamine as a substituent group at main group centers: intramolecular donor-acceptor interactions and unusual modes of coordination in compounds of silicon and phosphorus and their transition metal complexes

Abstract

This review is concerned with the role of the N, N′, N′-trimethylethylenediamine group as a substituent at phosphorus atoms in different coordination and/or oxidation numbers. A few examples for silicon are also presented. Intramolecular donor-acceptor interactions between the nitrogen atom of the dimethylamino group and Si or P as the central atom were first noted in some N, N′, N′-trimethylethylenediamine-substituted fluorosilanes (LSiF 3, PhSiF 2L) and P(III)Cl systems, e.g. LPCl 2 and PhP(Cl)L (L = N, N′, N′-trimethylethylenediamine group). These observations gave rise to a more detailed study of the coordinating behavior, especially of further phosphorus compounds of different substitution pattern. Spontaneous intramolecular coordination with formation of salt-like products was observed, especially, for compounds in which a phosphorus-bonded halogen atom is available to dissociate as an anion. A dependence both on the nature of the halogen atom and on the nature of other ligands at P(III) [or P(V)] was noted and will be discussed. Through the action of Lewis acids, e.g. AlCl 3 of PF 5, or in the reaction with tetraphenylborate as a non-coordinating anion, halide abstraction and consequent formation of the Me 2N → P coordinative bond from cyclic N, N′, N′-trimethylethylenediamine-substituted halophosphines or trimethylethylenediamine-substituted fluorophosphoranes could be induced. No such Me 2N → P coordination took place during oxidation of N, N′, N′-trimethylethylenediamine-substituted phosphorus(III) compounds with oxidizing agents, e.g. sulfur, selenium, o-quinones or hexafluoroacetone. Numerous oxidation reactions were conducted on intramolecularly stabilized phospholidin-1-ium salts. They furnished the expected oxidation/addition products. This was accompanied in some cases (depending on the nature of the substituents at P(III)) by a scission of the coordinative Me 2N → P bond. The reaction of phospholidin-1-ium salts with phenyl azide, dimethyl sulfoxide and sulfur furnished phosphonic acid diamides and substituted λ 4-phospholidin-1-ium salts, as well as substituted diazadiphosphetidines, as a result of the dimerization of PN species. Intramolecular donor-acceptor interaction in N, N′, N′-trimethylethylenediamine-substituted fluorophosphoranes was only observed in the presence of the Lewis acid, phosphorus pentafluoride leading to the formation of hexafluorophosphate salts. The reaction of dialkylamino-substituted tetrafluorophosphoranes with N, N′, N′-trimethylethylenediamine took an unusual course. Instead of the expected PF cleavage and formation of an N, N′, N′-trimethylethylenediamine-substituted dialkylaminotrifluorophosphorane, cyclic tetrafluorophosphates with a λ 6P atom, and dialkylaminotrimethylsilane were formed. The reaction of phosphorus(III)- N, N′, N′-trimethylethylenediamine compounds with transition metal compounds [Fe(0), Cr(0), Mo(0), Pt(II)] furnished mono-, di- or trisubstituted coordination compounds, depending on the nature of the metal. The P(III) ligand was bonded in some cases via P(III) only (as a monodentate ligand) and in other cases as a chelating ligand coordinated via P(III) and N. A variety of variable-temperature NMR experiments have examined the dynamic processes occurring at room temperature in solution, and X-ray single-crystal structure determinations have been conducted in many cases to characterize these new and unusual compounds.