Synthesis and characterization of non-symmetric Ni(II)- and Pd(II)-POCOP pincer complexes derived from 1,7-naphthalenediol. Evaluation of their catalytic activity in Suzuki-Miyaura couplings

Schiff Bases as Inspirational Motif for the Production of Ni(II) and Pd(II) Coordination and Novel Non‐Symmetric Ni(II)‐POCOP Pincer Complexes

“…The Ni−C (1.876 Å) and Ni−Cl (2.1903 Å) bond lengths are comparable to those reported for related Ni(II)‐POCOP pincer complexes, whereas the M−P distances exhibited values in the range of 2.1432–2.1633(10) Å. The distances and angles of Ni(II)‐POCOP‐1 and Ni(II)‐POCOP‐2 are comparable with the interatomic distances and angles in closely related structures [13a,21] . Attempts to synthesize the corresponding Pd‐POCOP pincer complexes under different reaction conditions were unsuccessful.…”

“…This was followed by treatment with the chlorodiisopropylphosphine in refluxing toluene for 24 h under nitrogen atmosphere. Unexpectedly, the 31 P{ 1 H} NMR analysis of the POCOP‐ligands showed three signals (P b , P a and P c ): two singlets between δ 144–155 ppm (P b and P a ), similar to those reported for analogous non‐symmetric POCOP ligands [13b,c,21] and a third signal (P c ) at lower field assigned to a phosphorous nuclei from a phosphine oxide: [22] POCOP‐1 δ 144.2 (P a ), 154.6 (P b ) and 66.6 (P c ) ppm; POCOP‐2 : δ 147.9 (P a ), 154.7 (P b ) and 62.6 (P c ) ppm. Noteworthy, the fact that the phosphorous of the chlorodiisopropylphosphine oxide (Cl(iPr) 2 P=O) appears at δ 65.4 ppm in the 31 P{ 1 H} NMR spectrum.…”

“…Palladium and nickel complexes are among the most efficient catalysts for cross-coupling reactions leading to the formation of new CÀ C bonds. [21,27] In this context, the Suzuki-Miyaura reaction is amongst the best-studied metal-catalysed coupling process due to its relevance for the synthesis of active pharmaceutical ingredients, materials and others industrial relevant intermediates. [27a,28] Likewise, the applications of these metal systems and the use of alternative energy sources, such as microwave irradiation (MW) to generate more eco-friendly, economical and sustainable protocols are themes of great relevance nowadays.…”

“…[29] The use of microwave irradiation has undeniable advantages compared to conventional heating affording shorter reaction times, faster reaction kinetics and cleaner products. Thus, we evaluated the catalytic activity of the series of newly synthesized coordination and organometallic complexes in Suzuki-Miyaura couplings using microwave irradiation in a model reaction between bromobenzene and phenylboronic acid under optimized reaction conditions previously established in our laboratory [21] for analogous catalytic systems (Na 2 CO 3 , DMF/H 2 0, 4 : 1 (5 mL), 150 W, 20 min) as summarized in Table 3 (Entries 1-6). Among all screened complexes, palladium complex 4 was the most efficient catalyst affording the coupled product in 58.6 % yield (Entry 4).…”

Recent Advances in Chemistry of Unsymmetrical Phosphorus-Based Pincer Nickel Complexes: From Design to Catalytic Applications

“…More recently, the synthesis of a series of unsymmetrical Ni(II)-POCOP pincer complexes ( 54a – 54c ) derived from 1,7-naphthalenediol were described ( Scheme 30 ) [ 150 ]. The molecular structures of two complexes were determined by single-crystal X-ray diffraction analysis.…”