Unexpected formal [1+3] cycloadditions between azides and alpha-zirconated phosphanes: a route to unprecedented phosphazide and iminophosphorane complexes

Polycyclic zwitterionic complexes that incorporate one or two phosphonium unit(s) as cationic center(s) and zirconocene-ate moiety(ies) as the anionic counterpart(s) can be easily prepared by either [1+3] or [1+3] and [2+3] cycloadditions which involve bi- or tricyclic alpha-zirconated phosphanes 3 or 4 and various azides. Some of these species exhibit unprecedented phosphazide chelation with bonding between the zirconium and a nitrogen atom in the alpha position relative to phosphorus. When heated, the phosphazide complexes lose dinitrogen to form stable polycyclic zwitterionic phosphonium mono- or dinuclear complexes. The solid-state structure of the two zwitterionic complexes 5 and 8 was determined by X-ray crystallography.     

N-phosphanylamidine ligands and their catalytic activity in the hydroformylation of 1-octene and styrene

Pyridine-based N-phosphanylamidine ligands i-Pr₂N-C(pyr)N-PR₂ (R = Ph (3), i-Pr (4)) were synthesized and fully characterized by NMR spectroscopy and X-ray crystallography. Mononuclear rhodium complexes 7 and 8 were obtained in one step from the [RhCl(COD)]₂ dimer and the monodentate ligands 1 and 2. Their single-crystal X-ray diffraction studies revealed the structural adaptive behavior of the monodentate N-phosphanylamidine ligands 1 and 2 upon k¹-P coordination mode in rhodium(I) complexes with the imino nitrogen atom of the amidine function which behaves as a “universal joint”. Compounds 1-4 were evaluated as ligands in the 1-octene and styrene hydroformylation reactions. The results obtained are encouraging and represent the first report on the use of N-phosphanylamidine ligands of the type R″₂N-C(R′)N-PR₂ in catalytic reactions.     

Can a functionalized phosphine ligand promote room temperature luminescence of the [Ru(bpy)(tpy)]2+ core?

Unexpected room temperature luminescence is observed and rationalized by highly challenging excited state calculations for a functionalized phosphine ligand coordinated on the [Ru(bpy)(tpy)](2+) core.     

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

A variety of homoatomic P-P donor-acceptor homoleptic (R = R′) and heteroleptic (R ≠ R′) N-phosphino formamidine complexes [iPr₂N-C(H)N-PR₂-PR′₂]Cl were synthesized from the addition of N-phosphino formamidine (phosfam) donor reagent iPr₂N-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 [iPr₂N-C(H)N-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)N-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)N-PR₂-PR′₂]⁺. Formation of the homoatomic P-P heteroleptic formamidine complexes [iPr₂N-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 iPr₂N-C(H)N-PR₂. Computed data are in agreement with the transient formation of a heteroatomic N-P intermediate [iPr₂N-C(H)N(PR₂)PR′₂]Cl, which then rearranges to the more thermodynamically favored homoatomic P-P compound [iPr₂N-C(H)N-PR₂-PR′₂]Cl.     

X-H (X = C, N, O, P, S) bond activations induced by beta-heterosubstituted zirconaindenes

The azazirconacyclopentene-substituted phosphines 3 and 4 have been found to activate the C-H bonds of acetylenic systems, such as methylpropiolate, diphenylphosphinoacetylene and phenylacetylene, or of methylene compounds, such as malonitrile and diethylmalonate, to give complexes 5a-c, 6a and 6b. C-H bond activation also takes place with vinylacetate. Similar reactions with amines, alcohols, enolisable ketones, phenols, phosphonates, thiols and a second-generation SH-terminated dendrimer lead through X-H bond activation (X = N, O, P, S) to new complexes 8a-c, 9, 12 a,b, 13, 14a-c, 15, 16a and 16b. The azazirconacyclopentene-substituted amine 20 reacts to form analogous complexes. Zr-X bonds of these complexes (X = C, N, O, S) can be cleaved with diphenylchlorophosphine to give P-X phosphorus derivatives in high yield.