Unprecedented rearrangement during the formation of P–P homoatomic N-phosphino formamidine complexes
摘要:
A variety of homoatomic P-P donor-acceptor homoleptic (R=R') and heteroleptic (R not equal R') N-phosphino formamidine complexes [iPr(2)N-C(H)=N-PR2-PR'(2)]Cl were synthesized from the addition of N-phosphino formamidine (phosfam) donor reagent iPr(2)N-C(H)=N-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 [iPr(2)N-C(H)=N-PPh2-PPh2]Cl by changing the solvent or by varying the temperature. Activation parameters of Delta S-not equal = (-130 +/- 7.2) J mol K-1 (1), Delta H-not equal = (8.4 +/- 0.6) kJ mol (1) and Delta G(not equal) (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 Delta H-not equal 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 [iPr(2)N-C(H)=N-PR2 -> PR'(2)](+), but the P-31 NMR chemical shift and the calculated electronic charges are more in favor of a phosphinophosphonium Lewis drawing [iPr(2)N-C(H)=N-PR2-PR'(2)](+). Formation of the homoatomic P - P heteroleptic formamidine complexes [iPr(2)N-C(H)=NPR'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 iPr(2)N-C(H)=N-PR2. Computed data are in agreement with the transient formation of a heteroatomic N-P intermediate [iPr(2)N-C(H)=N(PR2)PR'(2)]Cl, which then rearranges to the more thermodynamically favored homoatomic P-P compound [iPr(2)N-C(H)=N-PR2-PR'2] Cl. (C) 2008 Elsevier B. V. All rights reserved.
Unprecedented rearrangement during the formation of P–P homoatomic N-phosphino formamidine complexes
摘要:
A variety of homoatomic P-P donor-acceptor homoleptic (R=R') and heteroleptic (R not equal R') N-phosphino formamidine complexes [iPr(2)N-C(H)=N-PR2-PR'(2)]Cl were synthesized from the addition of N-phosphino formamidine (phosfam) donor reagent iPr(2)N-C(H)=N-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 [iPr(2)N-C(H)=N-PPh2-PPh2]Cl by changing the solvent or by varying the temperature. Activation parameters of Delta S-not equal = (-130 +/- 7.2) J mol K-1 (1), Delta H-not equal = (8.4 +/- 0.6) kJ mol (1) and Delta G(not equal) (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 Delta H-not equal 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 [iPr(2)N-C(H)=N-PR2 -> PR'(2)](+), but the P-31 NMR chemical shift and the calculated electronic charges are more in favor of a phosphinophosphonium Lewis drawing [iPr(2)N-C(H)=N-PR2-PR'(2)](+). Formation of the homoatomic P - P heteroleptic formamidine complexes [iPr(2)N-C(H)=NPR'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 iPr(2)N-C(H)=N-PR2. Computed data are in agreement with the transient formation of a heteroatomic N-P intermediate [iPr(2)N-C(H)=N(PR2)PR'(2)]Cl, which then rearranges to the more thermodynamically favored homoatomic P-P compound [iPr(2)N-C(H)=N-PR2-PR'2] Cl. (C) 2008 Elsevier B. V. All rights reserved.