Syntheses, rearrangements, and structural analyses of unsaturated nitrogen donor ligands derived from diphenyldiazomethane and the chiral rhenium Lewis acid [(η5-C5H5)Re(NO)(PPh3)]+

Abstract

Diphenyldiazomethane and a labile chlorobenzene complex of [(η⁵-C₅H₅)Re(NO)(PPh₃)]⁺ BF₄⁻ react to give the η¹ adduct [(η⁵-C₅H₅)Re(NO)(PPh₃)(NNCPh₂)]⁺ BF₄⁻ (73%). When this is conducted in the presence of copper powder, a 3-phenyl-1H-indazole complex derived from carbon–hydrogen bond activation, [(η⁵-C₅H₅)Re(NO)(PPh₃)(NC(Ph)CCHCHCHCHCNH)]⁺ BF₄⁻, is obtained (65%). Subsequent reaction with NaOCH₃ gives indazolyl complex (η⁵-C₅H₅)Re(NO)(PPh₃)(NCCHCHCHCHCC(Ph)N) (85%), derived from NH deprotonation and a 1,2-rhenium shift. Crystal structures of the three new complexes are determined. DFT calculations are used to probe the mechanism of the 1,2-shift and energetics of alternative Re–N rotamers and linkage isomers, and assign bond orders and dominant resonance formulations.