In this work, we investigate whether such a species can be supported by a tridentate phosphine ligand. We present the synthesis of a well-defined tetracoordinated nickel carbene complex bearing a triphosphine pincer ligand and study its reactivity. DFT calculations and Energy Decomposition Analyses (EDA) within the framework of quantitative Kohn-Sham molecular orbital theory are used to shine light onto the bonding situation of the tetracoordinated nickel carbene. Reduction of the previously reported PPP p-tol Ni I Br complex with sodium naphthalenide afforded well-defined Ni(0) complex 1 bearing only nitrogen as coligand (Figure and Figures ). Treating complex 1 with 1 equivalent of N2C(p-anisyl)2 resulted in instantaneous complete conversion to two new species detected by 31 P{ 1 H} NMR analysis (Figure ). The IR spectrum of the reaction mixture showed a strong signal at 2030 cm -1 , supporting the presence of a Ni(0) diazo complex as major species (Figure ), which is associated with broad 31 P NMR signals at 20 and 75 ppm. This species cleanly converted into the initially minor product 2 over five days at room temperature. The latter displayed a clear triplet and doublet at 57.9 and 47.6 ppm in 31 P NMR (Figure ). Gratifyingly, 13 C{ 1 H} NMR analysis revealed that compound 2 is a Ni-carbene complex with a diagnostic signal at 288.8 ppm (Figure and S10). The doublet of triplet multiplicity (dt, 2 JC,P = 30 Hz, 2 JC,P = 17 Hz) confirms that all three phosphine moieties are bound to Ni. The assignment is additionally confirmed by the observation of three-bond 1 H-13 C coupling by HMBC analysis (Figure ). Complex 2 was isolated in 61 % yield as a black solid. NMR and IR analysis show the total conversion of complex 2 to free 2,2-bis(4-methoxyphenyl)ethen-1-one and complex (PPP p-tol )Ni 0 (CO) (3, Figures S16 and S18), which could also be independently generated from complex 1 with CO (Figures and). This result demonstrates the ability of 2 to transfer the carbene fragment to a small molecule in milder conditions than reported for (dtbpe)NiCPh2. The reaction of complex 2 with CO2 led to the formation of a metallalactone complex 4 via a possible [2+2] sequential cycloaddition of two CO2 equivalents (Figures ). Strong IR ester signals at 1602 cm -1 and 1643 cm -1 , similar to those reported by Hillhouse, 8 testify the presence of two ester groups in the metallacycle. In addition, the reaction complex 4 with HCl in ether leads to the formation of 2,2-bis(4-methoxyphenyl)acetic acid, the expected product of protolysis of the dicarboxylate ligand in 4 (Figure ). 24 Scheme 1. (A) Reactivity of complex 2 with CO and CO2. (B) Reaction of complex 2 with Brookhart's acid (C) Reaction of complex 2 with HCl.