Next, we compared the electronic and geometric parameters of 2a and 3a. In the 31 P NMR spectrum of 3a, the resonance corresponding to the N-phosphinoyl moiety is observed at P 82.0 in toluene-d8, which represents a significant downfield shift compared to that of 2a (P 68.0 in THF-d8), while it is almost identical to that of (-O-1a)Al(C6F5)3 (P 79.8 in CD2Cl2). These results indicate that the 1a moiety in 3a should adopt predominantly the anti-conformation. The geometric parameters of 3a obtained from the SC-XRD analyses are shown in Figure . As previously reported, the Ni center in 2a, which bear the -C,O-syn-1a ligand (C-N-P-O torsion angle: 8.5(1)°), adopts a tetrahedral geometry. In stark contrast, 3a features a trigonal-planar Ni center (sum of bond angles around Ni: 358.9°) bearing anti-1a (C1-N2-P-O1 torsion angle: 159.7(2)°), as shown in Figure . The Ni(CO)2 unit is located slightly out of ideal alignment with the carbene lone pair (Z1-C1-Ni angle: 169.9°; Z1 = centroid of the imidazolinylidene ring), most likely due to the high steric demand of the t Bu groups.