Aminoalkylferrocenyldichlorophosphanes: facile synthesis of versatile chiral starting materials

A series of racemic and optically pure aminoalkylferrocenyldichlorophosphanes has been prepared by reaction of phosphorus trichloride with the corresponding lithiated aminoalkylferrocene precursors. Crystal structures of racemic 1-dichlorophosphanyl-2-N,N-dimethylaminomethylferrocene, racemic 1-dichlorophosphanyl-2-N,N-dimethylaminomethyl-3-triphenylsilylferrocene and (S)-N,N-dimethyl-1-[(R)-2-(dichlorophosphanyl)ferrocenyl]ethylamine reveal short intramolecular N[dot dot dot]P distances, which are suggestive of weak N --> P dative bonds. The aminoalkylferrocenyldichlorophosphanes can be used for the preparation of the corresponding primary phosphanes, one of which was characterised by X-ray crystallography. Optically pure (R)-N,N-dimethyl-1-[(S)-2-(phosphanyl)ferrocenyl]ethylamine can easily be lithiated twice to give the first enantiomerically pure lithium-phosphorus closo cluster compound, which was also structurally characterised.