Phosphine ligands synthetic properties

Adduct 18 may be considered as model intermediate for reactions of the palladium complex with other electrophiles. For example, strong Bronsted acids like HCl, which reacted with the abnormal complex 15 but not with its normal counterpart, induced Ccarbene Pd bond cleavage to yield the imidazo-lium salt 20. However, the rates of this acidolysis were too fast to allow the detection of an intermediate similar to 18. Notably, the coordination of two abnormal carbenes inverts the electronic properties of the palladium centre. While palladium(II) is generally considered to be electrophilic, it is obviously nucleophilic in complex 15 and related species. This fact offers a plethora of new synthetic possibilities and unprecedented reactivity schemes, which cannot be accessed by using classical carbene or phosphine ligands. 

Selected nickel(I) complexes with phosphines and arsines, together with relevant properties and synthetic routes, are reported in Table 21. In general, these nickel(I) complexes are air-unstable, especially when dissolved in solution consequently their preparation and handling require the exclusion of oxygen and, often, of moisture. The synthetic routes which afford nickel(I) complexes are strictly dependent on the nature of the phosphines and arsines and are not of general application, except in the case of some tripodal ligands. Most of the nickel(I)... 

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