Synthesis of Symmetric and Nonsymmetric Ni^II Thiophosphinito PECSP (E = S, O) Pincer Complexes and Their Applications in Kumada Coupling under Mild Conditions

Abstract

The reaction of 1,3‐dimercaptobenzene with iPr2PCl in the presence of the base NaH, furnishes the symmetric ligand [C6H4‐1,3‐(SPiPr2)2] (1a). The direct reaction of this ligand as well as of the literature‐known nonsymmetric ligand [C6H4‐1‐(SPiPr2)‐3‐(OPiPr2)] (1b) with NiCl2 affords the symmetric bis(thiophosphinito) PSCSP pincer complex [{C6H3‐2,6‐(SPiPr2)2}NiCl] (2a) as well as the phosphinito–thiophosphinito POCSP pincer complex [{C6H3‐2‐(SPiPr2)‐6‐(OPiPr2)}NiCl] (2b). Both complexes were fully characterised and their catalytic performance in Kumada coupling of aryl halides and p‐tolylmagnesium bromide under mild conditions was evaluated.

Study of the Reactivity of the [(PE1CE2P)Ni(II)] (E1, E2 = O, S) Pincer System with Acetonitrile and Base: Formation of Cyanomethyl and Amidocrotononitrile Complexes versus Ligand Decomposition by P–S Bond Activation

“…1 H NMR data of complex 2-ACN resemble those of the POCOP analogue 1-ACN (δ­(CH 3 ) = 1.90, δ­(CH) = 3.68 ppm); however, the NH resonance is found at much higher field (δ = 1.65 ppm). 31 P­{ 1 H} NMR spectra show two doublets at δ = 101.9 and 175.3 ppm, and both signals are again shifted to higher field compared to the cyanomethyl complex (δ = 121.1, 183.6 ppm) or the starting material, the chlorido complex 2-Cl (δ = 105.0, 179.7 ppm) …”

“…On the basis of Zargarian’s initial report, our group recently published the first Ni thiophosphinite [( i Pr POCSP i Pr )­NiCl] ( 2-Cl ) and Ni bis­(thiophosphinite) [( i Pr PSCSP i Pr )­NiCl] ( 3-Cl ) pincer complexes (POCSP = C 6 H 4 -2-(OP­( i Pr) 2 )-6-(SP­( i Pr) 2 ); PSCSP = C 6 H 4 -2,6-(SP­( i Pr) 2 ) 2 ) . Both complexes showed significantly better activity for Kumada cross-coupling than the well-known isostructural complex 1-Cl with activation of chlorobenzene even at room temperature.…”

Hybrid POCZP Aryl Pincer Metal Complexes and their Catalytic Applications

“…The precipitation of the formed salt promotes the latter reaction. Further addition of the metal source to the reaction mixture leads to regioselective bis ortho ‐cyclometalation affording the corresponding pincer metal complexes with Ni, [ 30–32 ] Pd, [ 33,34 ] Co, [ 35 ] Ir, [ 36,37 ] Fe, [ 38 ] and Ru, [ 39 ] in good to excellent yields. [ 20 ]…”

“…Nickel complexes 1a–c were also used as catalysts in Kumada C–C, [ 31 ] C–S and C–Se couplings (Scheme 7). [ 30,40 ] Complex 1b was used as catalyst in Kumada couplings of a series of phenyl halides and p ‐Me‐C 6 H 4 MgBr.…”

“…The precipitation of the formed salt promotes the latter reaction. Further addition of the metal source to the reaction mixture leads to regioselective bis ortho-cyclometalation affording the corresponding pincer metal complexes with Ni, [30][31][32] Pd, [33,34] Co, [35] Ir, [36,37] Fe, [38] and Ru, [39] in good to excellent yields. [20] Recently, Morales-Morales et al described an alternative route for the synthesis of POCSP pincer metal complexes, start-EurJIC European Journal of Inorganic Chemistry ing from a disulfide precursor instead of 3-mercaptophenol (Scheme 4).…”