REACTIONS OF COORDINATED PHOSPHINES AND ARSINES - STEREOSELECTIVE REACTIONS AT THE FLUOROARSINE-AS STEROCENTRE IN THE COMPLEX [(R-ASTERISK),(R-ASTERISK,R-ASTERISK)]-(+ (5)-C5H5)(1,2-C6H4(PMEPH)2)FE(ASFMEPH)]PF6.CH2CL2/

The reaction of (+/-)-AsFMePh, freshly prepared from (+/-)-AsBrMePh an d AgF in acetone, with )-(+/-)-[(eta5-C5H5){1,2-C6H4(PMePh)2}Fe(NCMe)] PF6 in boiling dichloromethane affords a separable mixture of two dias tereomeric iron complexes, epimeric at arsenic, viz. [(R),(R*,R*)]-(/-)- and /-)-[(eta5-C5H5){1,2-C6H4(PMePh)2)Fe(AsFMePh)]PF6, with the d iastereomeric ratio(R),(R*,R*)/(S*), (R*,R*)= 3:1. The major diastere omer of the complex crystallizes as a 1:1-dichloromethane solvate, the crystal structure of which has been determined. The minor (S),(R*,R* ) diastereomer crystallizes from acetone/diethyl ether as a 1:1 aceton e solvate. Reactions of the two diastereomers with RMgBr (R = Bn or Et ) are stereospecific giving the corresponding tertiary arsenic complex es with predominant inversion of configuration at arsenic. Hydrolysis of either diastereomer of the fluoroarsine complex affords the corresp onding hydroxyarsine (arsinous acid) derivative stereospecifically wit h complete inversion at arsenic.