Iron‐Catalyzed Decarboxylative (4+1) Cycloadditions: Exploiting the Reactivity of Ambident Iron‐Stabilized Intermediates

The first example of iron‐catalyzed decarboxylative (4+1) cycloaddition reactions is described in this publication. By using this method, a wide range of functionalized indoline products were prepared from easily available vinyl benzoxazinanones and sulfur ylides in high yields and selectivities. A possible reaction pathway involving an allylic iron intermediate is discussed based on a series of control experiments and density‐functional theory calculations.     

Organosulfur phosphonium salt-mediated synthesis of functionalized thiopyran derivatives

Methyl 4-oxotetrahydro-2H-thiopyran-3-carboxylate as a CH-acid undergoes a mild reaction with acetylenic esters in the presence of triphenylphosphine to produce phosphorus ylides possessing thiopyran-4-one ring moiety. The resulted phosphorus ylides when heated in toluene afforded functionalized thiopyran derivatives through intramolecular Wittig reaction.     

A Ten‐membered Dimetallacycle with an [Ag···Ag]2+ Dication Bridged by Two P,N Ligands

The reaction of silver hexafluoridoantimonate with Ph₂PCH₂PPh₂NSiMe₃ ( 1 ) in dichloromethane produces the dimeric complex [Ag(μ‐Ph₂PCH₂PPh₂NSiMe₃)]₂[SbF₆]₂ ( 2 ), in which two heterobifunctional ligands 1 in the dication are N, P‐chelated in a head‐to‐tail fashion to a [Ag ··· Ag]²⁺ unit that exhibits an Ag ··· Ag contact of 2.8530(6) Å. Quantum theory of atoms‐in‐molecules (QTAIM) analysis of the bonding revealed an attractive interaction between the two silver atoms.     

Alkenyl Arenes as Dipolarophiles in Catalytic Asymmetric 1,3‐Dipolar Cycloaddition Reactions of Azomethine Ylides

The use of alkenyl arenes as dipolarophiles in the catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides is reported. Under appropriate reaction conditions with a Cu^I or Ag^I catalyst either the exo or the endo adduct was obtained with high stereoselectivity. This process provides efficient access to highly enantiomerically enriched 4‐aryl proline derivatives. The observed results are compatible with the blockage of one prochiral face of the 1,3‐dipole, as well as with the efficient transmission of electrophilicity towards the terminal carbon atom of the dipolarophile. This polarization results in a change from a concerted to a stepwise mechanism.     

Anab initio study of the molecules P2O and P2O+

Summary This paper presents a detailedab initio study of the molecules P₂O and P₂O⁺ at the Hartree-Fock, and Multi-Reference Single and Double Excitation Configuration Interaction levels. An analysis of the geometries and relative stabilities of both molecules is presented, together with a discussion of the dissociation channels and of the electronic spectrum of linear P₂O. The results for the ionic species P₂O⁺ suggest a cyclic geometry for this molecule, as indicated by the calculated vibrational frequencies. The calculations also indicate a surface crossing at a relatively low energy which might lead to P₂O dissociation and may hence be one of the factors contributing to the failure to detect it at room temperatures.     

Die Kristallstruktur des Oxophosphazens [Ph3PNPPh2NP(O)Ph2]

Crystal Structure of the Oxophosphazene [Ph₃PNPPh₂NP(O)Ph₂] Single crystals of [Ph₃PNPPh₂NP(O)Ph₂] were obtained as a by‐product from the synthesis of [NaNPPh₃]₆ as a result of partial hydrolysis. According to the crystal structure determination the compound forms a molecular structure with a PNPNP chain with PN distances between 155.3(6) and 159.8(5) pm and PNP bond angles of 143.2(4) and 140.7(4)°. Space group P1¯, Z = 2, lattice dimensions at 213 K: a = 922.7(1); b = 1040.1(1); c = 1908.0(1) pm; α = 90.55(1)°; β = 103.01(1)°; γ = 92.87(1)°; R = 0.0859.     

Novel unsymmetrical PCP′ pincer ligands and their palladium(II) complexes

Synthetic routes towards novel PCP′ pincer ligands were devised. Ligand 1-(Pr₂ⁱPOCH₂)-3-(Bu₂^tPCH₂)(C₆H₄) is prepared in a three step synthesis from 1,3-benzenedimethanol and 1-(Pr₂ⁱPO)-3-(Bu₂^tPCH₂)(C₆H₄) is accessible in three steps from 3-hydroxybenzylalcohol. Both their palladium(II) complexes are prepared in good yields but are distinctly different since [PdCl{(C₆H₃)(OPPr₂ⁱ)-2-(CH₂PBu₂^t)-6}] possesses two five-membered palladacycles, whereas [PdCl{(C₆H₃)(CH₂PBu₂^t)-2-(CH₂OPPr₂ⁱ)-6}] is unusual for a pincer complex in that it contains both five- and six-membered palladacycles. Both compounds also represent the first examples of pincer complexes where one donor is a phosphinite and the other is a phosphine. The X-ray structures of these complexes were solved and are discussed. The data reveal that an increase in the metallacycle ring-size leads to changes in bond lengths, but more importantly to significant increases in the bond angles.     

From neutral iminophosphoranes to multianionic phosphazenates. The coordination chemistry of imino-aza-P(V) ligands

This review deals with the chemistry and coordination behaviour of imino-aza phosphorus(V) ligands focussing on s- and p-block as well as Group 11 and 12 metal complexes. Imino phosphorus(V) ligands contain one or more terminal RNP-units, which include iminophosphoranes R₃PNR′, monoanionic diiminophosphinates [R₂P(NR′)₂]⁻, dianionic triiminophosphonates [RP(NR′)₃]²⁻ and trianionic tetraiminophosphates [P(NR′)₄]³⁻. Aza-phosphorus(V) ligands feature bridging PNP units, which include cyclic and polymeric phosphazenes [R₂PN]_n. Imino-aza- phosphorus(V) ligands containing both imino and aza functions include linear diiminodiphosphazenates [N{R₂P(NR′)₂}₂]⁻ and multianionic poly(imino) cyclophosphazeantes such as [N₄{RP(NR′)}₄]⁴⁻ and [N₃{P(NR′)₂}₃]⁶⁻. Imino-aza phosphorus(V) ligands are assembled of three basic building blocks: the cationic tetravalent phosphonium centre (P), the anionic divalent amido function (N) and the terminally arranged R-group. The overall negative charge Z of the resulting ligand system is equal to the difference between the number of P and the number of N-centres: Z=n(P)n(N). Imino-aza phosphorus(V) ligands are electron rich N-donor ligands which co-ordinate via both N(imino) and N(aza) functions and have been applied in numerous metal complexes in order to stabilise low coordination numbers, unusual oxidation states and bonding modes or serve as ligands in homogeneous catalysis. The R-group provides both steric bulk and solubility in non-polar solvents. Multianionic phosphazenates feature a polydentate ligand surface, which facilitates an extremely high metal load. PN units of iminophosphoranes and phosphazenes have acceptor properties and enhance the acidity of α-alkyl and ortho-aryl protons. Deprotonation of P-alkyl and P-aryl iminophosphoranes give ligand systems featuring C,N chelating sites, which are also discussed.     

A study of influence of temperature and <Emphasis Type="Italic">N</Emphasis>, <Emphasis Type="Italic">N</Emphasis>-acyl protected keto ylides structure on their predominant transformations

The effect of temperature and keto ylides structure on preference of their intramolecular cyclization leading to N-containing heterocyclic compounds or linear products formation has been investigated at the B3LYP/6-31G(d,p) level of theory. It has been determined that the thermodynamic advantage of the cyclization reactions of ylides increases with temperature, while Gibbs free energies of linear products formation reactions depend insignificantly on temperature. The Wittig and the Corey–Chaykovsky reactions are least probable in the case of the sulfonium and ammonium ylides considered. However, for phosphonium ylides the Wittig reaction must be considerably preferable in comparison with other routes, while behavior of the arsonium ylides is predicted to be more complex. Research of S-ylides transformations shows that formation of methylthio-substituted heterocycles with five-, six- or seven- membered rings is possible from a thermodynamic standpoint, while conversion of the corresponding ylide to a four-membered heterocycle is disadvantageous. Presence of a methyl substituent and its position in the ylide carbon chain depends ambiguously on the behavior of sulfur keto ylides.     

Reaction of chromone-3-carbaldehyde with α-amino acids—syntheses of 3- and 4-(2-hydroxybenzoyl)pyrroles

Azomethine ylides generated from the reaction of chromone-3-carbaldehyde with α-amino acids undergo 1,5-electrocyclization reactions to afford 3- and 4-(2-hydroxybenzoyl)pyrroles. These ylides can be trapped with dipolarophiles in 1,3-dipolar cycloaddition reactions to yield chromonyl pyrrolidines. The reaction of chromone-3-carbaldehyde with methyl glycinate gives a mixture of pyrrole, pyridine, and 3-aza-9-xanthenone derivatives.