Syntheses, Structures, Reactivities, and Basicities of Quinolinyl and Isoquinolinyl Complexes of an Electron Rich Chiral Rhenium Fragment and Their Electrophilic Addition Products

Reactions of Li + [( η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )] − with 2‐ and 4‐chloroquinoline or 1‐chloroisoquinoline give the corresponding σ quinolinyl and isoquinolinyl complexes 3 , 6 , and 8 . With 3 and 8 there is further protonation to yield HCl adducts, but additions of KH give the free bases. Treatment of 3 with HBF 4 ⋅OEt 2 or H(OEt 2 ) 2 + BAr f − gives the quinolinium salts [( η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(C(NH) C(CH) 4 C (CH)(CH))] + X − ( 3‐H + X − ; X − =BF 4 − /BAr f − , 94–98 %). Addition of CF 3 SO 3 CH 3 to 3 , 6 , or 8 affords the corresponding N ‐methyl quinolinium salts. In the case of [( η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(C(NCH 3 ) C(CH) 4 C (CH)(CH))] + CF 3 SO 3 − ( 3‐CH 3 + CF 3 SO 3 − ), addition of CH 3 Li gives the dihydroquinolinium complex ( S Re R C , R Re S C )‐[( η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(C(NCH 3 ) C(CH) 4 C (CHCH 3 )(CH 2 ))] + CF 3 SO 3 − (( S Re R C , R Re S C )‐ 5 + CF 3 SO 3 − , 76 %) in diastereomerically pure form. Crystal structures of 3‐H + BAr f − , 3‐CH 3 + CF 3 SO 3 − , ( S Re R C , R Re S C )‐ 5 + Cl − , and 6‐CH 3 + CF 3 SO 3 − show that the quinolinium ligands adopt Re ⋅⋅⋅ C conformations that maximize overlap of their acceptor orbitals with the rhenium fragment HOMO, minimize steric interactions with the bulky PPh 3 ligand, and promote various π interactions. NMR experiments establish the Brønsted basicity order 3 > 8 > 6 , with K a (BH + ) values >10 orders of magnitude greater than the parent heterocycles, although they remain less active nucleophilic catalysts in the reactions tested. DFT calculations provide additional insights regarding Re ⋅⋅⋅ C bonding and conformations, basicities, and the stereochemistry of CH 3 Li addition.