Unprecedented rearrangement during the formation of P-P homoatomic N-phosphino formamidine complexes

T.D. Le (1) , D. Arquier (2) , Karinne Miqueu (3) , Jean-Marc Sotiropoulos (4) , Yannick Coppel (2) , S. Bastin (2) , Alain Igau (2)

1 DRS-IPHC - Département Recherches Subatomiques
2 LCC - Laboratoire de chimie de coordination
3 IPREM - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux
4 IPREM - Institut pluridisciplinaire de recherche sur l'environnement et les matériaux

A variety of homoatomic P-P donor-acceptor homoleptic (R = R′) and heteroleptic (R ≠ R′) N-phosphino formamidine complexes [iPr2N-C(H)double bond, longN-PR2-PR′2]Cl were synthesized from the addition of N-phosphino formamidine (phosfam) donor reagent iPr2N-C(H)double bond, longN-PR2 on halogenophosphane compounds R′2PCl which are synthetic sources for the corresponding phosphenium derivatives R2P+. We have demonstrated that the dynamic equilibrium observed between the different species is shifted either completely to the side of the free species or to the side of the donor-acceptor adduct [iPr2N-C(H)double bond, longN-PPh2-PPh2]Cl by changing the solvent or by varying the temperature. Activation parameters of ΔS≠ = (-130 ± 7.2) J mol-1 K-1, ΔH≠ = (8.4 ± 0.6) kJ mol-1 and ΔG≠ (298.15 K) = (53.6 ± 2.3) kJ mol-1 were determined by an Eyring analysis over the temperature range of 193-293 K. The negative entropy of activation is consistent with an associative pathway and the low value of ΔH≠ suggests that the energy barrier for this reaction is entropically controlled. Phosphine-phosphenium adducts is the most appropriate term to describe the dynamic process observed at variable temperature for complexes [iPr2N-C(H)double bond, longN-PR2 → PR′2]+, but the 31P NMR chemical shift and the calculated electronic charges are more in favor of a phosphinophosphonium Lewis drawing [iPr2N-C(H)double bond, longN-PR2-PR′2]+. Formation of the homoatomic P-P heteroleptic formamidine complexes [iPr2N-C(H)double bond, longNPR′2PR2]Cl (R = Ph, R′ = Et, iPr) results in the formal insertion of the phosphino group of the corresponding alkyl chlorophosphanes R′2PCl into the N-P bond of the starting phosfam ligand iPr2N-C(H)double bond, longN-PR2. Computed data are in agreement with the transient formation of a heteroatomic N-P intermediate [iPr2N-C(H)double bond, longN(PR2)PR′2]Cl, which then rearranges to the more thermodynamically favored homoatomic P-P compound [iPr2N-C(H)double bond, longN-PR2-PR′2]Cl. © 2008 Elsevier B.V. All rights reserved.

Domaines: Catalyse; Chimie de coordination; Chimie organique; Polymères; Chimie théorique et/ou physique

T.D. Le, D. Arquier, Karinne Miqueu, Jean-Marc Sotiropoulos, Yannick Coppel, et al.. Unprecedented rearrangement during the formation of P-P homoatomic N-phosphino formamidine complexes. Journal of Organometallic Chemistry, 2009, 694 (2), pp.229-236. ⟨10.1016/j.jorganchem.2008.10.033⟩. ⟨hal-01613254⟩