Reactivity of -Phosphinoguanidines of the Formula (HNR)(PhPNR)C(NAr) toward Main Group Metal Alkyls: Facile Ligand Rearrangement from -Phosphinoguanidinates to Phosphinimine-Amidinates.

We report the reactivity of -phosphinoguanidines of the formula (HNR)(PhPNR)C(NAr) (R = Pr and Ar = 2,6-PrCH [Dipp] for , R = Pr and Ar = 2,4,6-MeCH [Mes] for , and R = Cy and Ar = Dipp for ), prepared in high yields from the corresponding trisubstituted guanidines, toward main group metal alkyls AlMe, ZnEt, MgBu, and BuLi to obtain novel phosphinoguanidinato and phosphinimine-amidinato compounds. Reactions of - with AlMe at room temperature led to the kinetic phosphinoguanidinato products [Al{κ-'-(NR)C(NAr)(NRPPh)}Me] (-), whereas the mild heating (60-80 °C) of solutions of - give the thermodynamic phosphinimine-amidinato products [Al{κ-'-(NR)C(NAr)(PPhNR)}Me] (-) after ligand rearrangement. The reactions of equimolar amounts of - and ZnEt initially give solutions containing unstable phosphinoguanidinato compounds [Zn{κ--(NR)C(NAr)(NRPPh)}Et] (-), which rearrange upon mild heating to the phosphinimine-amidinato derivatives [Zn{κ-'-(NR)C(NAr)(PPhNR)}Et] (-). Bis(phosphinoguanidinato) compounds [Zn{κ--(NR)C(NAr)(NRPPh)}] (-) can be obtained under mild conditions (<45 °C) in THF, whereas bis(phosphinimine-amidinato) compounds [Zn{κ-'-(NR)C(NAr)(PPhNR)}] (-) are also accessible under more forcing conditions (55-100 °C) from (i) ZnEt and , (2 equiv), (ii) and , or (iii) ,. Equimolar mixtures of MgBu and - in THF at room temperature give unstable phosphinimine-amidinato monoalkyl products [Mg{κ-'-(NR)C(NAr)(PPhNR)}Bu(THF)] (-), whereas 2 equiv of , are required to reach the bischelate compounds [Mg{κ-'-(NPr)C(NAr)(PPhNPr)}] (,). Finally, phosphinoguanidinato compounds [Li{κ--(NR)C(NDipp)(NRPPh)}(THF)] (,) were obtained in the reactions of , with BuLi in THF under ambient conditions. The removal of the solvent from solutions of , under partial vacuum leads to the dinuclear compounds [Li{μ-κ-':κ-(NR)C(NDipp)(NRPPh)}(THF)] (,) after the decoordination of one of the THF molecules in , and dimerization. Heating solutions of , at 60 °C triggers ligand rearrangement to give phosphinimine-amidinato compounds [Li{κ-'-(NR)C(NDipp)(PPhNR)}(THF)] (,). We also propose a mechanism for the ligand rearrangement reaction from to give , supported by DFT calculations, which fits nicely with our experimental results. It essentially involves a carbodiimide deinsertion reaction followed by a [3 + 2] cycloaddition between the resulting lithium phosphino-amide and the carbodiimide.