Synthesis and Reactivity of 1,2‐ and 1,3‐Diphosphanes that Contain Four Chiral Rhenium Fragments: Architecturally Novel Tetrametallo‐DMPE and ‐DMPP Species that are Unprivileged Ligands for Enantioselective Catalysis

Reactions of enantiopure ( S )‐[(η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(=CH 2 )] + PF 6 – [( S )‐ 2 ] and PH 2 CH 2 (CH 2 ) n CH 2 PH 2 (0.5 equiv.) give ( S Re S Re )‐[(η 5 ‐C 5 H 5 )Re(NO)(PPh 3 ){CH 2 PH 2 CH 2 (CH 2 ) n CH 2 PH 2 CH 2 }(Ph 3 P)(ON)Re(η 5 ‐C 5 H 5 )] 2+ 2PF 6 – [ n = 0/1, ( S Re S Re )‐ 3 / 4 ; 65–62/77–58 %]. Reaction of racemic 2 (BF 4 – salt) and PH 2 (CH 2 ) 2 PH 2 (0.5 equiv.) gives the meso and rac diastereomers of 3 (BF 4 – salts) in 28 % and 38 % yields after crystallization. Treatments of ( S Re S Re )‐ 3 / 4 with t BuOK and then ( S )‐ 2 give the tetrarhenium complexes ( S Re S Re S Re S Re )[{(η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(CH 2 )} 2 {PHCH 2 (CH 2 ) n CH 2 PH}{(CH 2 )(Ph 3 P)(ON)Re(η 5 ‐C 5 H 5 )} 2 ] 2+ 2PF 6 – [ n = 0/1, ( S Re S Re S Re S Re )‐ 7 / 8 ; 89–88/98–87 %]. The crystal structure of( S Re S Re S Re S Re )‐ 7 is determined and its conformation analyzed. Reactions of ( S Re S Re S Re S Re )‐ 7 / 8 and t BuOK give air‐sensitive diphosphanes ( S Re S Re S Re S Re )‐{(η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(CH 2 )} 2 {PCH 2 (CH 2 ) n CH 2 P}{(CH 2 )(Ph 3 P)(ON)Re(η 5 ‐C 5 H 5 )} 2 [ n = 0/1, ( S Re S Re S Re S Re )‐ 9 / 10 ; 92/62 %]. Additions of (a) PhIO give the corresponding dioxides (72/62 %), and (b) [Rh(NBD) 2 ] + PF 6 – give the corresponding chelates [(P–P)Rh(NBD)] + PF 6 – (75/82 %) (NBD = norbornadiene). These catalyze hydrogenations of protected dehydroamino acids and hydrosilylations of propiophenone with only modest enantioselectivities. Similar results are obtained when ( S Re S Re S Re S Re )‐ 9 / 10 are applied in rhodium‐catalyzed conjugate additions of aryl boronic acids, or palladium‐catalyzed allylic alkylations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)