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)-[(eta(5)-C5H5)Re(NO)(PPh3)(=CH2)](+) PF6- [(S)-2] and PH2CH2(CH2)(n)CH2PH2 (0.5 equiv.) give (SRReSRe)-[(eta(5)-C5H5)Re(NO)(PPh3){CH2PH2CH2(CH2)(n)-CH2PH2CH2}(Ph3P)(ON)Re(eta(5)-C5H5)](2+) 2PF(6)- [n = 0/1, (SRReSRe)-3/4; 65-62/77-58 %]. Reaction of racemic 2 (BF4- salt) and PH2(CH2)(2)PH2 (0.5equiv.) gives the meso and rac diastereomers of 3 (BF4- salts) in 28 % and 38 % yields after crystallization. Treatments of (SReSRe)-3/4 with tBuOK and then (S)-2 give the tetrarhenium complexes (SRReSReSReSRe) [{(eta(5)-C5H5)Re(NO)(PPh3)(CH2)}(2){PHCH2(CH2)(n)-CH2PH}{CH2)(Ph3P)(ON)Re(eta(5)-C5H5)}(2+) 2PF(6)(-) [n = 0/1, (SReSReSReSRe)7/8; 89-88/98-87 %]. The crystal structure of (SReSReSReSRe)-7 is determined and its conformation analyzed. Reactions of (SReSReSReSRe)-7/8 and tBuOK give air-sensitive diphosphanes (SReSReSReSRe)-{(eta(5)-C5H5)Re(NO)-(PPh3)(CH2)}(2)PCH2(CH2) CH2P){(CH2)(Ph3P)(ON)Re(eta(5)-C5H5)}(2) [n = 0/1, (SReSReSReSRe-9/10; 92/62 %]. Additions of (a) PhIO give the corresponding dioxides (72/62 %), and (b) [Rh(NBD)(2)](+) PF6- give the corresponding chelates [(P-P)Rh(NBD)]+ PF6- (75/82 %) (NBD = norbornadiene). These catalyze hydrogenations of protected dehydroamino acids and hydrosilylations of propiophenone with only modest enantioselectivities. Similar results are obtained when (SReSReSReSRe)-9/10 are applied in rhodium-catalyzed conjugate additions of aryl boronic acids, or palladium-catalyzed allylic alkylations. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).