Synthesis, structure, and reactivity of palladacycles that contain a chiral rhenium fragment in the backbone: New cyclometalation and catalyst design strategies

The bromocyclopentadienyl complex [(eta(5)-C5H4Br)Re(CO)(3)] is Converted to racemic [(eta(5)-C5H4Br)Re(NO)(PPh3)(CH2PPh2)] (1b) similarly to a published sequence for cyclopentadienyl analogues. Treatment of enantiopure (S)-[(eta(5)-C5H5)Re(NO)(PPh3)- (CH3)] with nBuLi and I-2 gives (S)[(eta(5)-C5H4I)Re(NO)(PPh3)(CH3)] ((S)-6c; 84%) which is converted (Ph3C+ PF6-, PPh2H, tBuOK) to (S)f(eta(5)-C5H4I)Re(NO)(Pph(3))(CH2PPh2)] ((S)-1c). Reactions of 1b and (S)-1c with Pd[P(tBu)(3)](2) yield [(eta(5)-C5H4)Re(NO)(PPh3)(mu-CH2PPh2)Pd(mu-X)](2)] (10;X = b, Br, raclmeso, 88%: c. I, S,S, 22%). Addition of PPh3 to 10b gives [eta(5)-C5H4)Re(NO)(PPh3)(mu-CH2PPh2)Pd(PPh3)(Br)] (11b: 92%). Reaction of (S)-[(eta(5)-C5H5)Re(NO)(PPh3)(CH2PPh2)] ((S)-2) and Pd(OAc)(2) (1.5 equiv: toluene. RT) affords the novel Pd-3,(OAc)(4)-based palladacycle (S,S)- (eta(5)-C5H4)Re(NO)(PPh3)(mu- CH2PPh2)Pd(mu-OAc)(2)Pd(mu-OAC)(2)Pd(mu-PPh2CH2)(Ph3P)(ON)Re(eta(5)-C5H4)] ((S S)-13: 71-90%). Addition of LiCl and LiBr yields (S.S)-10a,b (73%). and Na(acac-F-6) gives C5H4)Re(NO)(PPh3)(mu-CH2PPh2)Pd-(acac-F-6)] ((S)-16, 72%). Reaction of (S,S)-10b and pyridine affords (S)-[(eta(5)-C5H4)Re(NO)(PPh3)(mu-CH2\PPh3)(mu-CH2PPh2)Pd-(NC5H5)(BR)] ((S) 17b. 72%): other Lewis bases yield similar adducts. Reaction of (S)-2 and Ps(OAc)(2) (0.5 equiv: benzene. 80 degrees C) gives the spiropalladacycle trans-(S,S)-[{(eta(5)- C5H4)Re(NO)(PPh3)(mu-CH2PPh2)}(2)Pd] (39%). The crystal structures of (S)-6c. 11b (S,S)- and (R,R)-13(.)2C(7)H(s). (S.S)-10b. and (S)-17b aid the preceding assignments. Both 10b (racemic or S,S) and (S)-16 are excellent catalyst precursors for Suzuki and Heck couplings.