Jan L. M. Dillen

An empirical force field. I. Alkanes

A new empirical force field for saturated hydrocarbons is presented. It is applicable to gaseous and crystalline alkanes that do not contain four‐ or three‐membered rings. The force field allows the calculation of structural, thermodynamic, and vibrational properties of both simple and highly strained molecules to an accuracy comparable to experiment. Vibrational frequencies are improved considerably as compared to MM3.

Benzo[b]thiophenium S,C-ylides: Preparation, structure and comparison with thiophenium analogues

Abstract A series of new S,C-ylides derived from benzo[b]thiophene and β-dicarbonyldiazocompounds were prepared and characterised. NMR ( 1 H, 13 C) studies revealed that ylides substituted additionally at position 2 of the thiophene ring can exist as pairs of diastereoisomers, not interchangeable at room temperature. The slow exchange between two sites was attributed to the restricted rotation about the ylidic SC bond. The crystal structure determined for one ylide demonstrated different molecular environment for two parts of the β-dicarbonyl ylidic substituent with respect to the benzothiophene ring. The prepared ylides were found to be much less reactive than the previously studied thiophenium S,C-ylides.

Trimethylstannane derivatives of cobalt(I); synthesis and NMR spectroscopy. The crystal structures of [Co(Me3Sn)(CO)3L] (L = PPh3, AsPh3)

Abstract The Na/Hg reductive cleavage of the cobaltcobalt bond in CO2(CO)6L2 (L = PPh3 P(OPh)3 AsPh3) and subsequent reaction with Me3SnCl, afforded the five coordinate complexes Co(Me3Sn)(CO)3L (L = PPh3, P(OPh)3, AsPh3). The intermediate sodium salts Na[CO(CO)3L] are unstable and were not isolated. The 31P, 119Sn, 13C and 1H NMR spectra were recorded and are discussed. Crystal structure analyses of [Co(Me3Sn) (CO)3L] (L = PPh3, AsPh3) revealed, in both cases, a trigonal bipyramidal geometry with the trimethyl tin and the triphenyl phosphine/arsine in the two axial positions.

Conformational deformation of ring C in 14β-estra-1,3,5(10),15-tetraen-17-ones

Abstract High-field n.m.r. analysis of four 3-methoxy-14β-estra-1,3,5(10), 15-tetraen-17-ones provides evidence for conformational deformation of ring C to a twist-boat form in solution. These observations are supported by molecular mechanics (MM2) calculations, which predict that the ring C chair and ring C twist-boat conformers have similar steric energies, slightly favouring the latter. An X-ray crystal structure determination on 3-methoxy-14-methyl-14β-estra-1,3,5(10), 15-tetraen-17-one revealed that ring C does indeed adopt a twist-boat conformation in the solid state.

Intramolecular condensation of steroidal 17α-formyl 17β-acetates : synthesis of 14-functionalised 17-spirolactones

Abstract 17β-Acetoxy-3-methoxyestra-1,3,5(10)-triene-14,17α-dicarbaldehyde (1) undergoes base-mediated intramolecular condensation to give a mixture of the (141R)- and (141S)-141,20-hemiacetals of(20R)-14-formyl-20-hydroxy-3-methoxy-19-nor-17α- pregna-1,3,5(10)-triene-21,17-carbolactone (2). The synthesis of derived 19-nor 17-spirolactones is described, and it is shown that 14-functionality participates in unusual intramolecular rearrangements.

Iron carbene complexes: II. Syntheses and characterization of the iron carbene complexes [Fe(CO)3(L){C(OEt)R}] (L CO, PPh3; R C6H4NMe2, Bu, CH(Sph)CH2Bu)

Abstract The o-lithiated reagent of N,N -dimethylaniline reacts with Fe(CO) 4 L (L  CO, PPh 3 ) to yield, after alkylation with [Et 3 O][BF 4 ], [Fe(PPh 3 )(CO) 3 {C(OEt)C 6 H 4 N-Me 2 }] (L  PPh 3 ), the methylene bridged diiron complex [(CO) 2 (L)Fe{μ-C(OEt)-η 2 C 6 H 4 NMe 2 }Fe(L)(CO) 2 ] (L  CO) and the monoiron butylcarbene complexes [Fe(L)(CO) 3 {C(OEt)Bu}] (L  CO, PPh 3 ). The corresponding reaction with lithiated phenylvinylsulphide leads to the formation of iron acyl anions which, after alkylation wit [Et 3 O][BF 4 , affords the monoiron carbene complexes [Fe(CO) 3 (L){C(OEt)CH(Sph)CH 2 Bu}]. The structure of the complex with L  PPh 3 was confirmed by X-ray crystallogrphy. The crystals are monoclinic, space group P 2 1 / n with a = 11.212(2), b = 20.004(3), c = 15.600(3) A, β 107.81(2)° and Z = 4.

Metallocyclic carbene complexes of chromium(0). The crystal and molecular structure of a chronium(0) complex with an aminoarylcarbene chelating ligand

Summaryo-Lithiated reagents,o-LiC6H4XMe (X=O, S, or NMe), react with [Cr(CO)6] to yield, after alkylation with [Et3O][BF4], the pentacarbonyl carbene complexes [Cr{C(OEt)C6H4XR}(CO)5] and tetracarbonyl metallocyclic carbene complexes. An analogous five-membered chelate is obtainable from the lithiated vinylsulphide PhSCHCH2. The x-ray structure of was determined by single crystal x-ray diffraction. It crystallizes in the monoclinic space groupP21/n witha=7.054(3),b=11.746(1),c=19.443(3) Å,β = 95.35(2)c and Z = 4. The final R-factors were R = 0.099 and Rw=0.044. Bond distances of 1.990(7) Å for Cr−C(carbene) and 2.240(6) Å for Cr−N were found.