Reaction of Carbodiphosphorane Ph3PCPPh3 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 Ph 3 P C PPh 3 ( 1 ) readily reacts with Ni(CO) 4 in toluene to give the substitution product (CO) 3 NiC(PPh 3 ) 2 ( 2 ). If the reaction is carried out in THF solution, additionally red crystals of the dicarbonyl complex (CO) 2 NiC(PPh 3 ) 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 PH 3 ligands instead of PPh 3, 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(PH 3 ) 2 bond energy of 3a ( D 0 = 33.7 kcal/mol) is nearly the sum of the Ni−C(PH 3 ) 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(PH 3 ) 2 in 2a . Donation and back-donation become stronger and back-donation becomes more important in 3a than in 2a .