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

Abstract

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.

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

“…Generally, all resonances in the NMR spectra shift downfield upon the transformation of trans- [5] to trans- [6]BF 4 attributable to the introduction of a positive charge in trans- [6] + . X-Ray diffraction studies with crystals of trans- [5]•CH 2 Cl 2 •C 6 H 14 and trans- [6]BF 4 •CH 2 Cl 2 ( Figure 3) [16] confirmed the conclusions drawn from NMR spectroscopy.…”

“…The 13 C NMR spectrum exhibits the resonance for the carbene carbon atom at d(C2) = 232.9 as the expected doublet of doublets ( 2 J CPtrans = 126.7 and 2 J CPcis = 8.2 Hz) for a cis-diphosphine complex. (Figure 2) and of cis- [4]BF 4 (see the SI, Figure S1) [16] have been determined by X-ray diffraction, confirming the composition and coordination geometry of the complex cations. The metal atoms in the complexes are Hydrogen atoms have been omitted for clarity.…”

“…Compound trans- [7]BF 4 was fully characterized by NMR spectroscopy, ESI-MS spectrometry and an X-ray diffraction analysis (see the SI). [16] The 13 C NMR spectrum shows the resonance for the C pCAAC carbon atom at d(C2) = 241.6 (t, 2 J CP = 6.3 Hz) and the resonance for the N-H proton was found at d(H1) = 12.45 in the 1 H NMR spectrum. Comparable metric parameters in trans-[3]BF 4 (N-ethyl substitution) and trans- [7]BF 4 (N-H Scheme 3.…”

“…Thermal ellipsoids are set at 50 % probability. [16] Selected bond lengths [] and angles (8) for trans- [5] [trans- [6] + ]: Pt-Cl 2.4056 5[2.361(2)], Pt-P1 2.3205 (5) [2.3207(14)], Pt-P2 2.3257 5[2.332(2)], Pt-C2 1.997(2) [1.974(8)], N-C2 1.295(3) [1.302(10)], N-C5 1.422(2) [1.428(10)], C2-C3 1.561(3) [1.534(11)]; Cl-Pt-P1 87.17 2[86. 10(6)], Cl-Pt-P2 88.01(2) [87.01 7], Cl-Pt-C2 174.09 6…”

“…Thermal ellipsoids are set at 50 % probability. [16] 7[95.83- (10)], P2-Pd-C2 92.56 7[94.79 (10)], C2-N-C5 113. 4(2) [112.…”