Preparation of Complexes Bearing N‐Alkylated, Anionic or Protic CAACs Through Oxidative Addition of 2‐Halogenoindole Derivatives

CAAC precursors 2‐chloro‐3,3‐dimethylindole 1 and 2‐chloro‐1‐ethyl‐3,3‐dimethylindolium tetrafluoroborate 2BF4 have been prepared and oxidatively added to [M(PPh3)4] (M=Pd, Pt). Salt 2BF4 reacts with [Pd(PPh3)4] in toluene at 25 °C over 4 days to yield complex cis‐[3]BF4 featuring an N‐ethyl substituted CAAC, two cis‐arranged phosphines and a chloro ligand. Compound trans‐[3]BF4 was obtained from the same reaction at 80 °C over 1 day. Salt 2BF4 reacts with [Pt(PPh3)4] to give cis‐[4]BF4. The neutral indole derivative 1 adds oxidatively to [Pt(PPh3)4] to give trans‐[5] featuring a CAAC ligand with an unsubstituted ring‐nitrogen atom. This nitrogen atom has been protonated with py⋅HBF4 to give trans‐[6]BF4 bearing a protic CAAC ligand. The PdII complex trans‐[7]BF4 bearing a protic CAAC ligand was obtained in a one‐pot reaction from 1 and [Pd(PPh3)4] in the presence of py⋅HBF4.
Cyclic (alkyl)(amino)carbene (CAAC) precursor salt 2BF4 reacts with [M(PPh3)4] (M=Pd, Pt) to give cis/trans‐[3]BF4 and cis‐[4]BF4, in which the CAAC ligand bears an unusual N‐alkyl substituent. trans‐[5] has a unique anionic CAAC ligand with an unsubstituted ring‐nitrogen atom which can be protonated to give trans‐[6]BF4 bearing a protic CAAC (pCAAC) ligand.