Unusual ligand rearrangement: from N-phosphinoguanidinato to phosphinimine-amidinato compounds

Abstract

N,N′-Phosphinoguanidinate Al compounds rearrange under mild conditions to phosphinimine-amidinato derivatives via an unprecedented carbodiimide de-insertion followed by [3+2] cycloaddition.

Mono- and Dinuclear Asymmetric Aluminum Guanidinates for the Catalytic CO2 Fixation into Cyclic Carbonates

“…Continuing our interest in the chemistry of guanidines and their derivatives, some of us have studied the reaction of trimethylaluminum (AlMe 3 ) with N-phosphinoguanidine ligands, which yields stable phosphinimine-amidinato compounds, after the rearrangement of the Nphosphinoguanidinato intermediates initially detected. 61,62 Very recently, we have also described the use of aromatic guanidines such as those depicted in Scheme 2, as catalysts for the preparation of cyclic carbonates. In these compounds, the presence of two N−H groups represented a substantial improvement in the activity, as hydrogen-bond donor systems, compared to what was previously found with other types of guanidines.…”

Reactivity of N-Phosphinoguanidines of the Formula (HNR)(Ph2PNR)C(NAr) toward Main Group Metal Alkyls: Facile Ligand Rearrangement from N-Phosphinoguanidinates to Phosphinimine-Amidinates

“…2j,3b,d,f Aiming to fill the lack of examples of anionic Nphosphinoguanidinato ligands, our group recently communicated the high-yield straightforward preparation of two novel N-phosphinoguanidines, (HN i Pr)(Ph 2 PN i Pr)C(NAr) (Ar = 2,6-i Pr 2 C 6 H 3 [Dipp] for 1a and Ar = 2,4,6-Me 3 C 6 H 2 [Mes] for 1b). 4 These were confronted with Al and Zn alkyls targeting new N-phosphinoguanidinato compounds with κ 2 -N,N′ and κ 2 -N,P coordination modes (Figure 1A and B). Interestingly, kinetic κ 2 -N,N′-phosphinoguanidinato products initially detected in the reactions with AlMe 3 transformed upon mild heating to stable κ 2 -N,N′-phosphinimine-amidinato complexes (Figure 1C).…”

“…Compound 1c was synthesized following the same high-yield two-step procedure described for compounds 1a,b. 4 As starting materials, we used trisubstituted guanidines of the formula (NHR) 2 C(NAr), which were previously prepared on a multigram scale by an efficient catalytic method reported in our group. 7 Thus, the first step involved the in situ monolithiation of the guanidine using n BuLi, followed by the addition of chlorophosphine ClPPh 2 (Scheme 2).…”

“…A variable temperature 31 P{ 1 H} NMR study conducted for 1a suggested the existence of up to three different species at −80 °C, most likely different E conformers, as supported by DFT calculations. 4 Therefore, fast equilibria between some of these species may be taking place in solution. As for the 1 H and 13 C{ 1 H} NMR spectra for 1a−c recorded at 25 °C, they are all in agreement with the presence of an apparent symmetry plane containing the planar CN 3 core of the N-phosphinoguanidines, a circumstance to be expected if we allow for the usual fast rotation processes in the NMR time scale (i.e., C−N sigma bonds, etc.).…”

“…Further confirmation for the structure of 1a came from its diffractometric analysis (Figure 2). 4 The structure of 1c was also determined by X-ray diffraction of poor-quality crystals of the compound (Figure S26), so only the former will be commented on in detail. As can be seen, the molecule of 1a is built around a trigonal-planar "CN 3 " core, which is characteristic of guanidines (∑ angles of 360°).…”