Reactions of coordinated phosphines and arsines: stereoselective reactions at the chlorophosphine- P stereocentre in the complex [( R★), ( R★, R★)]-(±)-[(η 5-C 5H 5){1,2-C 6H 4(PMePh) 2}-Fe(PClMePh)]PF 6·CH 2Cl 2

Abstract

The reaction of ( R ★, R ★)-(±)-[(η 5-C 5H 5){1,2-C 6H 4(PMePh)2}Fe(NCMe)]PF 6 with (±)-chloromethylphenylphosphine in boiling dichloromethane affords a separable mixture of two diastereomeric iron complexes, epimeric at the chlorophosphine- P stereocentre, viz. [( R ★), ( R ★, R(su★)]-(±)- and [( S ★), ( R ★, R ★)±)-[(η 5-C 5H 5){1,2-C 6H 4(PMePh) 2}Fe(PClMePh)]PF 6, with the diastereomeric ratio ( R ★), ( R ★, R ★)/( S ★), ( R ★, R(su★) = 3/1. The crystal structure of the ( R ★), ( R ★, R ★) diastereomer (with one molecule of solvation of dichloromethane) has been determined. By use of the optically active acetonitrile complex, optically pure [R-[( S ★), ( R ★, R ★)]]-(+) 589-(η 5-C 5H 5){1,2-C 6H 4(PMePh) 2}Fe(PClMePh)]PF 6·Me 2CO was obtained, the first complex to be isolated containing resolved (±)-PClMePh. Alkylations of the diastereomeric chlorophosphine-iron complexes with Grignard reagents in tetrahydrofuran at 20°C are highly stereoselective, with predominant retention of configuration at phosphorus. The reaction of ethylmagnesium bromide with the ( R ★), ( R ★, R ★) diastereomer of the (±)-chloromethylphenylphosphine-iron complexes gives the (±)-ethylmethylphenylphosphine-iron complex with ( R ★), ( R ★, R ★)I(S*), ( R ★, R ★) = 1/3; benzylmagnesium bromide gives the (±)-benzylmethylphenylphosphine iron complex with ( R ★), ( R ★, R ★)/( S ★), ( R ★, R ★) = 1/8. Sodium borohydride reductions of the (±)-chloromethylphenylphosphine- iron complexes are also stereoselective, with predominant retention of configuration at phosphorus in each case. Thallium(I) phenoxide, however, when allowed to react with the ( R ★), ( R ★, R ★) diastereomer of the (±)-chloromethylphenyl-phosphine- iron complex in boiling tetrahydrofuran, gives the corresponding (±)-methylpheno-xyphenylphosphine-iron complex, with predominant inversion of configuration at phosphorus (( R ★), ( R ★, R ★)I(S*), ( R ★, R ★) = 1/6).