Data analysis for kinetic profiles: Kinetic profiles were monitored by 1 H NMR spectroscopy using mesitylene as internal standard. Proton peaks used in quantification (d The aromatic peak of the internal standard (6.67 ppm) was used for quantification in all profiles except for the isomerization at 25 ºC, where the aliphatic peak was used (2.13 ppm). The data was processed with MestReNova program with the data analysis on arrayed spectra. The information was extracted by peak area integration for all kinetic profiles except the catalysis analysis. For the kinetic profiles involving semihydrogenation a background correction was applied on (E)-stilbene by withdrawing the first value of the integration to all the points (to withdraw some intensity corresponding to the resting state). In case of the catalysis analysis in the semihydrogenation profile this was extracted based on the peak height, recommended if peaks of interest have some degree of overlapping. To decrease the effect of noise in the spectra, a background correction was applied on the resting state and self-hydrogenated products. The average of the value of the last 6 points for the resting state was subtracted from all points. In case of the self-hydrogenated products, the average of the value of the first 6 points was subtracted. C67H58NiP2 • C6H14, Fw = 1069.95, red needle, 0.39 ´ 0.06 ´ 0.06 mm 3 , monoclinic, P21/n (no. 14), a = 10.2716 (6), b = 24.0789 (12), c = 46.997(3) Å, β = 92.130(3) °, V = 11615.7(12) Å 3 , Z = 8, Dx = 1.224 g/cm 3 , µ = 0.43 mm -1 . The diffraction experiment was performed on a Bruker Kappa ApexII diffractometer with sealed tube and Triumph monochromator (l = 0.71073 Å) at a temperature of 150(2) K up to a resolution of (sin q/l)max = 0.57 Å -1 . The Eval15 software was used for the intensity integration. The crystal structure is characterized by pseudo-translational symmetry (pseudo-I centered Bravais lattice). Consequently many reflections are weak or very weak. A numerical absorption correction and scaling was performed with SADABS 77 (correction range 0.84-0.98). A total of 114418 reflections was measured, 18328 reflections were unique (Rint = 0.223), 8209 reflections were observed [I>2s(I)]. The structure was solved with Patterson superposition methods using SHELXT. Structure refinement was performed with SHELXL-2018 79 on F 2 of all reflections. Non-hydrogen atoms were refined freely with anisotropic displacement parameters. The n-hexane solvent molecules were refined with a disorder model. The hydrogen atoms of the metal complexes were located in difference Fourier maps, the hydrogen atoms of the solvent were introduced in calculated positions. Hydrogens H71 and H73 were kept fixed at their located position. All other hydrogen atoms were refined with a riding model. 1483 Parameters were refined with 2242 restraints (distances, angles and displacement parameters of all atoms, distances and angles in the disordered n-hexane molecules). R1/wR2 [I > 2s(I)]: 0.0682 / 0.1363. R1/wR2 [all refl.]: 0.1865 / 0.1793. S = 0.996. Residual electron density between -0.51 and 0.79 e/Å 3 . Geometry calculations and checking for higher symmetry was performed with the PLATON program. Computational methods: DFT calculations were performed using the Gaussian 16 software package version C.01. The tolyl groups in the structure were substituted by phenyl groups for simplicity. Geometry optimizations were carried out in vacuum at the B3LYP-GDB3J/6-31g(d,p) level of theory on all atoms. Frequency analyses on all stationary points were used to ensure that they are minima (no imaginary frequency) or transition states (one imaginary frequency). Transition states were calculated using the QST3 (synchronous transit-guided quasi-Newton number 3) method or using the opt=TS (Berny algorithm) keyword. The guess structure proposed for each TS calculation was based on the results of relaxed potential energy surface scans (PES). ∆Gº was calculated by single point calculation at B3LYP-GDB3J/def2TZVP/SMD(toluene) level of theory adjusting the value with the thermal correction obtained at the B3LYP-GDB3J/6-31g(d,p) level of theory with temperature 298.15 K and pressure 1 atmosphere. QTAIM analysis was perfomed on the single point calculation at B3LYP-GDB3J/def2TZVP/SMD(toluene) level of theory with the Multiwfn program. 60