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.

Various 8-halogenotheophyllines (halogen = Cl, Br, I) were selectively C8 metalated by an oxidative addition of the C8–halogen bond to [Pd­(PPh3)4] to give the PdII azolato complexes [1]–[3]. The complexes were protonated at the N9 nitrogen atom to yield the NH,NH-NHC (pNHC) complexes [4]­BF4–[6]­BF4. Due to the unsymmetrical nature of the backbone of the theophylline-derived pNHC ligands, two NH resonances were observed by 1H NMR spectroscopy. In addition, 8-bromoadenine was also regioselectively C8 metalated via an oxidative addition of the C8–Br bond to [Pd­(PPh3)4] in the presence of the proton source pyridinium tetrafluoroborate to give [7]­BF4.

The synthesis of the new vicinal frustrated Lewis pair 5 containing (C6F5)2P-Lewis base and (C6F5)BH-Lewis acid functionality is described. It forms a unique cyclotrimer (5)3 which was structurally characterized by X-ray crystallography and high-resolution solid-state NMR spectroscopy. The relevant NMR Hamiltonian parameters ((11)B and (31)P chemical shielding tensors, (11)B quadrupolar coupling tensors, and (31)P-(11)B spin-spin coupling constants) indicate significant intramolecular covalent BP interactions, consistent with results from density functional theory (DFT) calculations. In addition, the (11)B/(31)P and (31)P/(31)P three-spin geometries are accurately reproduced by suitable high-resolution hetero- and homonuclear dipolar NMR experiments. As predicted from the bonding character portrayed by the solid-state NMR results, the cyclotrimer (5)3 possesses only moderate catalytic activity. However, it undergoes an addition reaction with pyridine and hydroboration reactions with benzaldehyde and tert-butylacetylene. The products of the hydroboration reactions form stable adducts with pyridine.

The Ir III hydrido complexes [ 1 ] and [ 2 ] have been synthesized by the regioselective oxidative addition of the N7–H bond of 8-halogenotheophyllines to [IrCl(coe) 2 ] 2 in the presence of PPh 3 . The use of dppf in this reaction yielded the bimetallic Ir III /Fe II hydrido complexes [ 3 ] and [ 4 ]. X-ray diffraction studies confirmed that complexes [ 1 ]–[ 4 ] feature a theophyllinato ligand coordinated to the metal center in the rarely observed, chelating fashion via the N7 and O1 atoms. In addition, 8-bromoadenine reacts with [IrCl(coe) 2 ] 2 in the presence of PPh 3 to form the Ir III hydrido complex [ 5 ] which features one anionic 8-bromoadeninato and one neutral 8-bromoadenine ligand linked by an intramolecular hydrogen bond. Complex [ 5 ] was characterized by high-resolution mass spectrometry and an X-ray diffraction analysis but could not be analyzed by nuclear magnetic resonance spectroscopy because of its low solubility.