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
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AbstractReactions of enantiopure (S)[(5C5H5)Re(NO)(PPh3)(=CH2)]+ PF6 [(S)2] and PH2CH2(CH2)nCH2PH2 (0.5 equiv.) give (SReSRe)[(5C5H5)Re(NO)(PPh3){CH2PH2CH2(CH2)nCH2PH2CH2}(Ph3P)(ON)Re(5C5H5)]2+ 2PF6 [n = 0/1, (SReSRe)3/4; 6562/7758%]. Reaction of racemic 2 (BF4 salt) and PH2(CH2)2PH2 (0.5 equiv.) 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 (SReSReSReSRe)[{(5C5H5)Re(NO)(PPh3)(CH2)}2{PHCH2(CH2)nCH2PH}{(CH2)(Ph3P)(ON)Re(5C5H5)}2]2+ 2PF6 [n = 0/1, (SReSReSReSRe)7/8; 8988/9887%]. The crystal structure of(SReSReSReSRe)7 is determined and its conformation analyzed. Reactions of (SReSReSReSRe)7/8 and tBuOK give airsensitive diphosphanes (SReSReSReSRe){(5C5H5)Re(NO)(PPh3)(CH2)}2{PCH2(CH2)nCH2P}{(CH2)(Ph3P)(ON)Re(5C5H5)}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 [(PP)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 rhodiumcatalyzed conjugate additions of aryl boronic acids, or palladiumcatalyzed allylic alkylations. ( WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
