Jean Paul Declercq

Synthesis and characterization of cyclometallated complexes of benzalazines. Crystal and molecular structure of [{Pd(p-ClC6H3CHN–)Cl(PEt3)2}2]

The reaction of benzalazines, (p-RC6H4CHN–)2(R = H, Cl, NO2, or NMe2), with PdCl2 leads in the the first two cases to the formation of cyclometallated polymeric species that react with phosphines to yield dimetallated compounds [{Pd(p-RC6H3CHN–)Cl(PR′3)2}2](R′= Et or Ph) and/or [{[graphic omitted]–)Cl(PPh3)}2]. Phosphine exchange reactions give the complex [{Pd(p-RC6H3CHN–)Cl(PEt3)(PPh3)}2]. The molecular structure of [{Pd(p-ClC6H3CHN–)Cl(PEt3)2}2] has been determined by a single-crystal X-ray analysis. The crystals are monoclinic, space group P21/n, a= 11.124(3), b= 10.062(2), c= 22.566(5)A, β= 102.95(3)°, and Z= 2; R= 0.052 for 3 306 reflections. Palladium atoms are five-co-ordinated, the Pd–N distance being 2.743 A. However, n.m.r. spectra show that, in solution, free rotation around the C(aromatic)–C(azomethine) bonds does occur even at –100 °C.

‘O-phosphobiotine analogues.’ Isolation, X-ray strurcture, and reactivity of the intermediate of the addition of hindered phosphuric esters and thioesters on the carbodi-imide group. O → N phosphoryl migration versus P–O–P bond formation

Addition reactions to carbodi-imides using oxy- and thio-phosphoric diesters crowded around phosphorus have been carried out in order to obtain a better understanding of this reaction, and to trap the intermediate, an O-phosphobiotin analogue. Oxy-compounds give a mixture of pyrophosphate and rearranged N-Phosphorylated urea or react poorly if steric hindrance at phosphorus is important. The same type of addition with thiophosphoric esters has made possible the first isolation of the intermediate of this general reaction which is relevant to pyro-phosphate and to nucleotide synthesis. This difference is rationalized in terms of the C–X–P bond lengths (X = O or S) in the intermediate, as shown by an X-ray crystallorgraphic determination of the structure of the thio-compound. With oxy-compounds, the reaction is very sensitive to steric effects, because of the short C–O–P distances involved. Formation of the intermediate is only likely if the oxyphosphorus nucleophile does not contain bulky groups, and this leads quickly to the pyrophosphate. With thio-compounds, the analogus intermediate is formed even when bulky thiophosphorus groups are present, because of the longer C–S–P distances, and is protected against intermolecular rearrangement both by the poor overlap between the nitrogen and phosphorus orbitals and by protonation if a suitable ratio of ester to dicylohexylcarbodi-imide (DCCD) is used. Moreover this intermediate is not easily attacked by the bulky (RO)2P(S)S– nucleophile and therefore accumulates. With a less favourable ratio of ester to DCCD, the reaction gives only the rearranged N-phosphorylated product. Crystals of the isolated intermediate are monoclinic, space group P21/a with four molecules in a cell of dimensions a= 15.802(3), b= 13.409(2), c= 15.050(5)A, β= 96.82(1)°. The structure was solved by direct methods and refined by full-matrix least-squares calculations to an R value of 0.055 for 3 144 observed reflections. Several features of this molecular structure are discussed. Finally, a kinetic study of the rearrangement from C–S–P to N–P compounds shows that this reaction proceeds without the formation of any kinetically significant intermediate.

Eight-membered heterocycles containing two phosphorus atoms. X-ray diffraction and nuclear magnetic resonance studies of 2,6-dimethyl-1,3-dioxa-2,6-diphosphacyclo-octane 2,6-disulphides and 2,6-diselenides

trans- and cis-2,6-dimethyl-1,3-dioxa-2,6-diphosphacyclo-octane 2,6-disulphides (1) and (2), and trans- and cis-2,6-diselenides (3) and (4), have been investigated by means of 1H (2D,J-resolved), 13C, and 31P n.m.r. spectroscopy and X-ray diffraction. In the solid state the cis-isomers adopt a crown conformation and the trans-isomers a boat-chair conformation. The orientations of P–X (X = S or Se) and P–Me bonds are quasi-axial and quasi-equatorial, respectively. Room-temperature n.m.r. data can be interpreted on the basis of the X-ray data. A fast enantiomerization between two boat-chair conformations of opposite chirality characterizes the trans-isomers, whereas the cis-isomers exist mainly in a crown conformation similar to that observed in the crystal.

Epoxy-epimination of Cyclic Conjugated Dienes .7. Cycloaddition of Nitroso-halogenobenzenes To Cyclopentadiene Followed By Rearrangement To Epoxy-epimino-pentadienal and Gamma-delta-epimino-pentadienal Derivatives Via N-o and C-c Bond Breaking

[4+2] Cycloaddition of halogenated nitroso benzenes to cyclopentadiene followed by isomerisation of the intermediate adduct occurs already at room temperature to furnish the epoxy-epimine 1 and the epiminopentadienal 2. The structure proof of 1 is based on X-ray analysis.

Structure du bis(p‐chlorophényl)‐1,3 bis(triméthyl‐2,4,6 phényl)‐2,4 diaza‐1,3 diphosphétidine

C 30 H 30 Cl 2 N 2 P 2 cristallise dans P2 1 /a avec a=11.947, b=14.067, c=8.557A, β=98.08°, Z=2; affinement jusqua R=0.051. La molecule est centrosymetrique. lheterocycle a une planeite parfaite. Latome de phosphore tricoordine σ 3 λ 3 est fortement pyramidalise

Surprising electrochemical reduction product from a dihydrodiazepinium salt

Electrochemical reduction of 6-phenyldihydrodiazepinium perchlorate provides unexpectedly, in high yield, a pyrrolodiazepine; an interesting base–salt equilibrium between pyrrole and dihydrodiazepinium systems is observed.