James A. S. Howell

Synthesis and reactions of tetracarbonyl- and tricarbonyliron complexes of α,β-unsaturated ketones

Abstract A series of iron tricarbonyl derivatives of α,β-unsaturatedketones have been prepared. These are of special interest toorganometallic chemists concerned with the production of irontricarbonyl derivatives since they offer not only a convenientsource of the Fe(CO) 3 moiety but also several advantages overthe more conventional methods employing the iron carbonyls.

Enzymatic generation of planar chirality in the (arene)tricarbonylchromium series

Abstract Hydrolysis using pig liver esterase of the meso diesters [ortho-C 6 H 6 (CH 2 CO 2 R) 2 ]-Cr(CO) 3 (R = Me,Et) yields the half ester in good yield and high enantiomeric excess.

Asymmetric biochemical reduction, acylation and hydrolysis in the (diene)Fe(CO)3 series: Experimental results and molecular modelling studies

Abstract Asymmetric reduction using bakers yeast and asymmetric acyl transfer using porcine pancreatic lipase may be used in the kinetic resolution and desymmetrization of acyclic (diene)Fe(CO) 3 complexes bearing CHO and CH 2 OH substituents respectively. The results may be interpreted in terms of current active site models for these biotranformations.

Synthesis of new ferrocenyl aminoalcohols and aminonitriles and catalytic properties of the aminoalcohols in the ethylation of benzaldehyde

Abstract Chiral ferrocenyl aminoalcohols possessing either OH or NR 2 functionality α to the ferrocenyl ring were prepared and exhibit modest enantioselectivities for the addition of diethylzinc to benzaldehyde. Chiral ferrocenyl aminonitriles exhibit a facile inversion process in protonic solvents.

The solution structure and fluxional behaviour of cyclic and acyclic (diene) Fe(CO)2L complexes (L = phosphine, phosphite, isonitrile)

Variable temperature 13C and 31P NMR spectroscopy has been used to establish solution structures and conformer populations for a variety of cylic and acyclic (diene)Fe(CO)2L complexes (L = phosphine, phosphite, isonitrile). The solid state structures of (2,3-dimethylbutadiene)Fe(CO)2PPh3 and (trans,trans-2,4-hexadiene)Fe(CO)2PPh3 have been determined and used as a basis for molecular modelling of steric effects in these complexes.

The effect of fluorine, trifluoromethyl and related substitution on the donor properties of triarylphosphines towards [Fe(CO)4]

Abstract Infrared and crystallographic studies of [(CO)4FePAr3] complexes have been used to quantify the decreasing σ-donor/π-acceptor character of the ligand with increasing fluorine or trifluoromethyl substitution of the aryl ring. The poor coordinating ability of o-CF3 substituted phosphines may be mimicked by o-tBu substitution in the alkyl series.

Biochemical resolution and generation of planar chirality in formyl substituted (diene)Fe(CO)3 complexes

Abstract Kinetic resolution of (2,4-hexadien-1-al)Fe(CO) 3 and asymmetric reduction of (2,4-hexadien-1,6-dial)Fe(CO) 3 using bakers yeast proceed with high efficiency and enantioselectivity.

Carbon-13 nuclear magnetic resonance studies of isonitrile derivatives of tetracarbonylbis-(η-cyclopentadienyl)di-iron

Variable temperature 13C n.m.r. studies on [(η-C5H5)2Fe2(CO)3(CNR)](II; R = But) and (III; R = Ph) show that (II), which contains a terminally bonded CNR ligand, exhibits fluxional properties while (III), which contains a bridging CNR ligand, does not; it is also shown that 13C resonances of isonitrile ligands are diagnostic of the presence of bridging or terminal CNR groups.

Acyclic O- and N-substituted Pentadienyl Cations: Structural Characterisation, Cyclisation and Computational Results

Abstract A number of 1- and 3-hydroxy and 1-amino substituted acyclic pentadienyl cations have been characterised by NMR spectroscopy in situ at low temperature. Some of the 3-hydroxy cations undergo cyclisation to give 1-hydroxycyclopentenyl cations which on deprotonation give substituted cyclopentenones.

The kinetics and mechanism of diene exchange in (η4-enone) Fe(CO)2L complexes (L = phosphine, phosphite)

Abstract Kinetic data for the exchange of 1,3-cyclohexadiene with (η4-benzylideneacetone)Fe(CO)2L complexes (L = CO, PPh3-xMex (x = 0-2) or P(OPh)3) to give (η4-1,3-cyclohexadiene)Fe(CO)2L derivatives indicate a mechanism involving stepwise competing D and Id opening of the ketonic M-CO π-bond. Rates increase in the order CO ⪢ PPh3 ≈ P(OPh)3 > PPh2Me ⪢ PPhMe2, and both steric and electronic factors appear to be important. (η4-1,3-cyclohexadiene)Fe(CO)2L complexes of potential use in enantioselective synthesis (L=(+)-Ph2P(menthyl) or (+)-Ph2PCH2CH(Me)Et) may be prepared via their (η4-benzylideneacetone)Fe(CO)2L complexes.