This review is a comprehensive account of reactions with the participation of nickel complexes that result in the formation of carbon–phosphorus (C‒P) bonds. The catalytic and non-catalytic reactions with the participation of nickel complexes as the catalysts and the reagents are described. The various classes of starting compounds and the products formed are discussed individually. The several putative mechanisms of the nickel catalysed reactions are also included, thereby providing insights into both the synthetic and the mechanistic aspects of this phosphorus chemistry.

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Four metal halides of the ( tBu PCN)NiX family [X = F (1), Cl (2), Br (3), or I (4); methyl]phenyl]-1H-pyrazole] have been prepared through a direct reaction of the corresponding anhydrous NiX 2 salts and the unsymmetrical PCN pincer ligand. Structural information from single-crystal X-ray data, 19 F solution nuclear magnetic resonance, and combined electrochemical results [cyclic voltammetry (CV) and in situ electron paramagnetic resonance spectro-electrochemistry] reveal that the fluoride complex 1 is different from the other halides 2−4 in terms of electro-oxidation behavior (presence of three anodic peaks instead of one in the CV profile). 1 is also different from its symmetrical analogue ( tBu PCP)NiF in terms of halogen-bonding capability toward the halogen-bond donor, iodopentafluorobenzene (C 6 F 5 I, IPFB). The positive ΔS°value for the formation of the 1•••IPFB adduct inferred from the van't Hoff plots is in agreement with the existence of (1•H 2 O) aggregates in solution, not present in 2−4. The high nucleophilicity of the fluoride ligand and the simultaneous presence of electrophilic (acidic) protons on the sidearm of the pyrazole ligand are at the origin of the observed phenomena.

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Pincer complexes play an important role in organometallic chemistry; in particular, their use as homogeneous catalysts for organic transformations has increased dramatically in recent years. The high catalytic activity of such bis-cyclometallic complexes is associated with the easy tunability of their properties. Moreover, the phosphorus-based unsymmetrical pincers showed higher catalytic activity than the corresponding symmetrical analogues in several catalytic reactions. However, in modern literature, an increasing interest in the development of catalysts based on non-precious metals is observed. For example, nickel, which is an affordable and sustainable analogue of platinum and palladium, known for its low toxicity, has attracted increasing attention in the catalytic chemistry of transition metals in recent years. Thus, this mini-review is devoted to the recent advances in the chemistry of unsymmetrical phosphorus-based pincer nickel complexes, including the ligand design, the synthesis of nickel complexes and their catalytic applications.

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