Fluoro and Trifluoromethyl Derivatives of POCOP-Type Pincer Complexes of Nickel: Preparation and Reactivities in S_N2 Fluorination and Direct Benzylation of Unactivated Arenes

Abstract

This report describes the synthesis, characterization, and reactivities of the pincer-type complexes κ). These complexes were prepared by treating their Ni−Br analogues with excess AgF at rt (2a and 2b) or excess AgF and Me 3 SiCF 3 (3a and 3b) at 45 °C. The Ni−F derivative 2a was shown to be an intermediate for the formation of the Ni−CF 3 derivative 3a. Complexes 2a, 3a, and 3b were fully characterized by multinuclear NMR spectroscopy, cyclic voltammetry, and X-ray diffraction analysis. Variable temperature, multinuclear NMR analysis of 2a helped elucidate interaction of the fluoride ligand with hydrofluoric acid present in the reaction medium. The bromo complexes 1a or 1b catalyzed fluorination of benzyl halides at 90 °C in the presence of excess AgF, whereas the Ni−CF 3 complexes 3 failed to promote trifluoromethylation of benzyl bromide, leading instead to a direct benzylation of the aromatic reaction solvent (benzene, toluene, xylene, or bromobenzene). Possible mechanisms for this benzylation reaction have been probed and discussed.

The Reactivity of Mercapto Groups against Boron Hydrides in Pincer Ligated Nickel Mercapto Complexes

“…A distorted square‐planar geometry for the nickel centers of complexes 1 a , 1 b , 2 b and 3 a was observed; this is similar to other reported POCOP,,, or PCP pincer ligated nickel complexes. The C ipso –Ni bond lengths in 1 a and 1 b (1.942(2) and 1.937(5) Å) are slightly longer than those of 2 a , 2 b and 3 a (1.9009(17), 1.894(7) and 1.889(3) Å).…”

“…Multinuclear NMR, FTIR, X‐ray crystallography and elemental analysis were used to characterize these new complexes. The 1 H, 13 C{ 1 H} and 31 P{ 1 H} NMR spectra of complexes 1 a , 1 b , 2 b and 3 a (SI Figures S1–S12) were consistent with the structures shown in Scheme , and displayed the expected spectra features for POCOP,,, or PCP (PCP=2,6‐(R 2 PCH 2 ) 2 C 6 H 3 ) pincer ligated nickel complexes. Like complex 2 a , the 1 H NMR resonances of the mercapto protons of 1 a , 1 b , 2 b and 3 a appeared in a relatively high‐field region (−0.92 to −1.60 ppm) as virtual triplets with H‐P coupling constants of 17–20 Hz.…”

On the Stability of a POCsp3OP‐Type Pincer Ligand in Nickel(II) Complexes

“…The two Ni centers in the terminal {(allyl)NiP 2 } fragments adopt a square-planar geometry defined by h 3 -coordination of the allyl ligand and two monodentate phosphinite moieties; accordingly, the sum of angles defining the square plane adds up to approximately 3608. [18] A different but related decomposition of the POC sp3 OP ligand was also noted during the synthesis of the alkynyl derivatives, as follows. [17] The mechanism for the unusual transformation of 1-OSiMe 3 to 2 remains elusive, but the finding that ambient light plays a crucial role in initiating the decomposition process implies a radical-initiated reaction sequence.…”

d8 Nickel and palladium difluorocarbenes derived from trifluoromethyl POCOP-type pincer complexes

“…[17] Here, we report an alternative synthetic protocol for the preparation of nickel and palladium trifluoromethyl POCOP complexes. Treatment of both 1-Cl and 2-Cl with Me 3 SiCF 3 /CsF for 2 h at room temperature in DMF results in formation of the trifluoromethyl pincer complexes 1-CF3 (yellow solid, 80% isolated yield) and ( iPr POCOP)Pd(CF 3 ) (2-CF3) (white solid, 74% isolated yield), respectively (Scheme 2).…”