OXIDATIVE ADDITION-REDUCTIVE ELIMINATION SUPPORTED BY A LIGAND-ELEMENT COOPERATION AT THE ARSINIDENE AND STIBINIDENE CENTER.

Abstract

The treatment of pnictinidenes [2-(RNHCH2)-6-(RN=CH)C6H3]E (1As/Sb) (where E = As or Sb) with benzoyl peroxide provided compounds [2-(DippNCH2)-6-(DippN=CH)C6H3]E(O2CPh) (2As/Sb) as a result of two step procedure, i.e. oxidation of the pnictogen centre followed by the elimination of benzoic acid. The reaction between 1As and diphenyl disulfide proceeded in the same vein yielding thiophenol and [2-(DippNCH2)-6-(DippN=CH)C6H3]As(SPh) (3As). Analogous reaction of 1Sb furnished a mixture of [2-(DippNHCH2)-6-(DippN=CH)C6H3]Sb(SPh)2 (3´Sb), [2-(DippNCH2)-6-(DippN=CH)C6H3]Sb(SPh) (3Sb) and PhSH, while NMR studies proved the existence of a dynamic equilibrium between all three compounds in solution and removal of incipient PhSH was necessary for the isolation of 3Sb. Both 1As/Sb smoothly reacted with 2-nitrosotoluene leading to [2-(DippNCH2)-6-(DippN=CH)C6H3]E(O-NH-2-Me-Ph) 4As/Sb and with 4-phenyl-1,2,4-triazoline-3,5-dione giving [2-(DippNCH2)-6-(DippN=CH)C6H3]E[(N(CO)-NH(CO))N-Ph] 5As/Sb. All compounds were characterized by IR, Raman, NMR spectroscopy, and the molecular structures, except for 3As and 5Sb, were determined by single-crystal X-ray diffraction. Furthermore, we scrutinized the thermally induced reductive elimination of benzoic acid and thiophenol from 2-3As/Sb, respectively, and that of 4-phenylurazole from 5As. These eliminations involve C-H activation at the CH2N group, and the recovery of the pnictinidene center in [2,6-(RN=CH)2C6H3]E (6As/Sb). Using DFT calculations a plausible mechanism was suggested for all investigated reactions, which are in good agreement with the experimental observations.