Half-Sandwich Aminorhenium Complexes: Preparation and Regioselective N-versus Re-Alkylations

The aminorhenium complex (CO) 2 ReNH(CH 3 )CH 2 CH 2 (η 5 -C 5 H 4 ) ( 3 ), in which the ligating amino group is connected to the cyclopentadienyl ligand, was prepared by irradiation of (η 5 -C 5 H 4 CH 2 CH 2 NHCH 3 )Re(CO) 3 ( 2 ) in THF. Alkylation of the corresponding anion [(CO) 2 ReN(CH 3 )CH 2 CH 2 (η 5 -C 5 H 4 )] - Li + ( 4 ) as well as the neutral aminorhenium complex 3 with a variety of electrophiles has been studied. The anion 4 reacted with electrophiles, such as CH 3 I, CH 2 CHCH 2 Br, C 6 H 5 CH 2 Br, and HC⋮CCH 2 Br, at the nitrogen center to provide (CO) 2 ReNR(CH 3 )CH 2 CH 2 (η 5 -C 5 H 4 ) ( 5a − d ). However, 4 reacted with electrophiles having a carbonyl group or a nitrile group next to the electrophilic carbon, such as BrCH 2 CO 2 CH 3, BrCH 2 CO 2 C 2 H 5, and BrCH 2 CN, to give rhenium alkylation compounds [(CO) 2 (R)ReNH(CH 3 )CH 2 CH 2 (η 5 -C 5 H 4 )] + Br - ( 7e − g ) after protonation. The neutral aminorhenium complex 3 reacted with the electrophiles mentioned above to provide exclusive Re-alkylation compounds 7a − g . The structure of the tetraphenylborate salt of 7c, [(CO) 2 (C 6 H 5 CH 2 )ReNH(CH 3 )CH 2 CH 2 (η 5 -C 5 H 4 )] + BPh 4 - ( 8 ), has been determined by X-ray diffraction.