Reaction of Carbodiphosphorane Ph3PCPPh3 with Ni(CO)4. Experimental and Theoretical Study of the Structures and Properties of (CO)3NiC(PPh3)2 and (CO)2NiC(PPh3)2

The carbodiphosphorane Ph3PCPPh3 (1) readily reacts with Ni(CO)4 in toluene to give the substitution product (CO)3NiC(PPh3)2 (2). If the reaction is carried out in THF solution, additionally red crystals of the dicarbonyl complex (CO)2NiC(PPh3)2 (3) are formed. 2 smoothly converts into 3 when dissolved in THF. The compounds have been characterized by single-crystal X-ray diffraction. Quantum chemical calculations at the DFT level of theory (B3LYP) are given for the geometries of model compounds 1a−3a with PH3 ligands instead of PPh3, which are in good agreement with the experimental results for 1−3. The metal−ligand bond energies are also predicted at B3LYP. The calculated Ni−C(PH3)2 bond energy of 3a (D 0 = 33.7 kcal/mol) is nearly the sum of the Ni−C(PH3)2 (D 0 = 20.9 kcal/mol) and first Ni−CO bond energy of 2a (D 0 = 16.3 kcal/mol). The analysis of the metal−ligand bonding using the CDA method shows that there is mainly ligand → metal donation and much less metal → ligand back-donation between Ni and C(PH3)2 in 2a. Donation and back-donation become stronger and back-donation becomes more important in 3a than in 2a.