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C–N Bond Coupling Reactions of Ammonia with Acetone Promoted by Iridium and Rhodium Complexes: Experimental and DFT Studies
Author(s) -
Pilar Betoré M.,
GarcíaOrduña Pilar,
Lahoz Fernando J.,
Casado Miguel A.,
Polo Víctor,
Oro Luis A.
Publication year - 2016
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201600925
Subject(s) - chemistry , deprotonation , ligand (biochemistry) , protonation , medicinal chemistry , rhodium , metallacycle , iridium , imine , nucleophile , enamine , stereochemistry , organic chemistry , catalysis , ion , biochemistry , x ray crystallography , receptor , physics , diffraction , optics
Treatment of acetone solutions of the known chlorido‐bridged complexes [{M(µ‐Cl)(cod)} 2 ] (M = Ir, Rh; cod = 1,5‐cyclooctadiene) under an ammonia atmosphere afforded the cationic complexes {M(cod)[κ N ,κ N ‐NH 2 –C(CH 3 ) 2 –CH 2 –C(CH 3 )=NH]}Cl [M = Ir ( 3 ), Rh ( 4 )]. The molecular structures of 3 and 4 showed the formation of six‐membered metallacycles due to the presence of a 4‐imino‐2‐methylpentan‐2‐amine‐κ N ,κ N ‐chelated ligand. Alternatively, the cations [M(cod)(NCCH 3 ) 2 ]BF 4 (M = Ir, Rh) reacted with gaseous ammonia at atmospheric pressure affording bis(ammine) complexes [M(cod)(NH 3 ) 2 ]BF 4 [M = Ir ( 5 ), Rh ( 6 )], which were found to react with acetone, forming cations [M(cod)(κ N ,κ N ‐NH 2 –C(CH 3 ) 2 –CH 2 –C(CH 3 )=NH)]BF 4 [M = Ir ( 7 ), Rh ( 8 )]. DFT studies reveal that the transformation of 6 into 8 is mediated by NH 3 molecules acting as an external base. The reaction is triggered by deprotonation of an ammonia ligand forming a amido–metal intermediate, which further transforms into an acetimino ligand through aldol condensation. The terminal methyl group of one acetimino ligand is deprotonated by NH 3 yielding an enamine ligand, which can react with the imine ligand through concerted nucleophilic addition to afford the metallacycle, which is stabilized by protonation.