Stereospecific Ligand Substitutions in Manganese(I) Complexes

Treatment of fac ‐[( P 2 SPh ‐ P,P ')Mn(CO) 3 Br] and fac ‐[( PS 2 Ph ‐ P,S )Mn(CO) 3 Br] [ P 2 SPh : Z = PPh 2 ; PS 2 Ph : Z = SPh in CH 3 C‐(CH 2 PPh 2 )(CH 2 SPh)(CH 2 Z)] with silver hexafluorophosphate yields the η 3 ‐tripodal manganese complexes [( P 2 SPh ‐ P,P',S )Mn(CO) 3 ]PF 6 ( 7 ) and [( PS 2 Ph ‐ P,S,S' )Mn(CO) 3 ]PF 6 ( 9 ), respectively, whereas the reaction of CH 3 C(CH 2 PPh 2 ) 2 ‐(CH 2 SH) with Mn(CO) 5 Br gives directly [CH 3 C(Ph 2 ‐PCH 2 ) 2 (CH 2 S)‐ P,P',S ]Mn(CO) 3 ( 11 ). Both ionic complexes 7 and 9 undergo stereospecifically ligand substitution upon treatment with Br − , I − , N − 3 , SCN − and CN − to give syn‐fac ‐[( P 2 SPh ‐ P,P' )Mn(CO) 3 X] and syn‐fac ‐[( PS 2 Ph ‐ P,S )Mn(CO) 3 X] (X = Br, I, SCN, N 3 , CN) respectively, but the neutral complex 11 fails to undergo such a substitution reaction with these ions. However, reaction of I − with the complex [( PSMe )‐ P,P',S ]Mn(CO) 3 ]BF 4 ( 20 ) [ P 2 SMe = CH 3 C(CH 2 ‐PPh 2 ) 2 (CH 2 SCH 3 )), which is obtained from the S ‐alkylation of 11 with (CH 3 ) 3 OBF 4 , affords syn‐fac ‐[( P 2 SMe )‐ P,P' ]Mn(CO) 3 I ( 22s ) exclusively. The possible reaction mechanism of this ligand substitution is discussed.