André DeCian

Induced Fit Selection of a Barbiturate Receptor from a Dynamic Structural and Conformational/Configurational Library

The selection of the receptor presenting the strongest affinity for a barbiturate substrate from a dynamic combinatorial library of constituents differing in structure and conformation/configuration is described. The gradual addition of the barbiturate to an equilibrating mixture of hydrazone isomers leads to the quantitative shift towards a single species, 3, which presents highest complementarity to the substrate and yields the supramolecular entity 3:4.

Efficient Homogeneous Hydrosilylation of Olefins by Use of Complexes of Pt0 with Selected Electron-Deficient Olefins as Ligands

Triolefinic platinum(0) complexes of the type {(η4-CH2CHSiMe2)2O}Pt(OlE) containing an electron-deficient olefin, (OlE), were synthesised from the Karstedt catalyst precursor [{(CH2CHSiMe2)2O}3Pt2] and studied as catalysts for the hydrosilylation of olefins (figure). Several of these complexes, particularly those with naphthoquinones as ligands, were very efficient catalysts, superior to the classical Karstedt systems. The nature of the catalytically active molecular species involved is discussed.

Synthesis of η3-allyl-Pd complexes and subsequent formation of N-heterocycles via the reaction of a cyclometallated compound with conjugated dienes

The Pdue5f8C bond of the cyclopalladated derivative of dimethylaminomethylferrocene (1) is fairly reactive to insertion of conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dimethylbutadiene or 1,3-cyclohexadiene. This reaction affords organopalladium complexes containing an η3-allyl-Pd moiety where the NMe2 unit of the starting material is still intramolecularly coordinated to Pd. These complexes are stable in solution but in MeOH in the presence of PPh3, reductive elimination of Pd is observed. This occurs whilst a nucleophilic intramolecular addition of the NMe2 group to the allylic fragment takes place, affording six-, seven- or eight-membered heterocyclic compounds. The importance of the steric effects of the substituents on the butenyl chain upon the course of the reaction has been investigated.

Axial structure of oxathiane benzyl sulfonium perchlorate

Abstract It is shown that the S-benzyl substituent, in the S-benzyl sulfonium perchlorate 2 derived from Eliels oxathiane, has an axial position in the solid state (X Ray analysis of a single crystal) as well as in solution (2D 1H NMR), probably due to 1-3-anomeric effect between the lone-pairs of oxygen and sulfur.

[2 + 2] Photocycloadditions of [(η5-C5H5) Ru(DMPP)2L]PF6 complexes

A series of [(η5-C5H5)Ru(DMPP)2L]PF6 complexes, DMPP = 1-phenyl-3,4-dimethylphosphole, L = CH3CN, Ph3P, PhS(O)2CHCH2, (CH3)2NC(O)CHCH2, PhNC, CO and (CH3O)3P, was found to undergo sunlight initiated [2 + 2] photodimerization of the coordinated phospholes only when L is a good π-acceptor ligand. These [2 + 2] dimerizations are accompanied by [4 + 2] dimerizations. The ratio of the [2 + 2] to [4 + 2] cycloaddition products is a function of the steric bulk of L. The nature of the photoexcited state has been probed by electron absorption and emission spectroscopy. The electron absorption spectra show high ɛ bands in the near UV region that are attributed to DMPP π → π* transitions. The emission spectral lifetimes are a function of L and their magnitude at 77 K (about 0.2 to 2.0 μs), together with large Stokes shifts, is indicative of phosphorescence from a triplet excited state. It is postulated that this triplet excited state undergoes cycloaddition by way of a biradical intermediate. The complexes have been characterized by elemental analyses, infrared, electronic, and 1H, 1H31P, 13C1H and 31P1H NMR spectroscopy and cyclic voltammetry. The structure of (η5-C5H5)Ru(DMPP)2[2 + 2](CO)PF6 was confirmed by X-ray crystallography. The complex cation possesses a non-crystallographic mirror plane, the two RuP distances (2.282(1) and 2.281(2) A) are equivalent and the cyclobutane ring has a long (1.607(8) A) and a short (1.550(8) A) CC bond.

Resolution of a cyclopalladated complex containing an asymmetric metallated carbon atom

Abstract Enantiomerically enriched cyclopalladated 8-ethylquinoline derivatives containing a stereogenic centre directly linked to palladium have been obtained by a resolution technique using (S)-leucine as chiral auxiliary.

A three-step synthesis of an enantiomerically pure halostachine analogic starting from η6 (o-tolualdehyde)-chromium-tricarbonyl.

Abstract An optically pure (+)-S-Halostachine analogue 5a was synthesized in 57% total yield and in three steps from optically pure (−)-aR-[o-tolualdehyde]-chromium-tricarbonyl complex 2b . Various optically pure Halostachine analogues having an ortho-substituted aromatic ring and of both configurations (R and S) are thus available by this route. An X-ray structure of the intermediate complexed oxazoline 3bI allowed to confirm the model we proposed for the approach of a nucleophile on these arene complexes.

Configuration and conformation of (−)-8-phenylmenthyl 3-amino-2-hydroxy-5-methylhexanoate

Abstract Conformations of 6aI in solution (NMR, IR) and in the solid state (X-ray) are, shown to be similar and it appears, from X-ray data, that the usually invoqued π-π electronic interaction is probably not responsable of the cis conformation. Conformation in solution of the major diastereomer obtained, 3aI , has been shown to be similar to that of 6aI and it is postulate that the asymmetric induction obtained might be due to formation of a bridged species.

Electrophilic additions to the bimetallic silyl complexes [(OC)3{(MeO)3Si}-Fe(μ-PR2)Pt(1,5-COD)] (R Ph, Cy). Crystal structure of [(OC)3Fe(μ-PCy2)(μ-Au(PPh3)2Pt-(1,5-COD)][PF6] (CY c-C6H11)

Abstract Reactions of the heterobimetallic complexes [(OC) 3 {(MeO) 3 Si} Fe(μ-PPh 2 )P t(PPh 3 ) 2 ] ( 1 ) and [(OC) 3 {(MeO) 3 Si} Fe(μ-PR 2 )P t(1,5-COD)] ( 3a , R ue5fb Ph) with HBF 4 ·Et 2 O result in cleavage of the Feue5f8Si bond and formation of the dihydrido complexes [(OC) 3 Fe(μ-PPh 2 )(μ-H) 2 P t(PPh 3 ) 2 ] [BF 4 ] ( 2 ) and [(OC) 3 ] Fe(μ-PR 2 )(μ-H) 2 P t(1,5-COD)] [BF 4 ] ( 4 ), respectively. Reactions of 3a or 3b (R ue5fb Cy) with [(Ph 3 P)Au] [PF 6 ] required 2 equiv. of the electrophile to give the clusters [(OC) 3 Fe(μ-0PR 2 ) {μ-Au(PPh 3 )}{ 2 P}t(1,5-COD)][PF 6 ] ( 5a , R ue5fb Ph; 5b , R ue5fb Cy). These were fully characterised and the structure of 5b was determined by X-ray diffraction: crystals are monoclinic, space group P 2 1 / n , a = 22.479(6), b = 26.781(8), c = 10.254(3) A, β = 102.94(2)° U = 6016.1 A 3 and Z = 4. This is the first structural determination of a heterobimetallic complex carrying two Au-fragments. The Feue5f8Pt bond (2.715(3) A) is bridged by a μ-PCy 2 group and by two Au(PPh 3 ) fragments. No Au-Au interaction is observed (4.333(1)A).