Nickel phosphite complexes dissociation

All the reactions of the hydrocyanation process are catalyzed by zero-valent nickel phosphine or phosphite complexes. These are used in combination with Lewis acid promoters such as zinc chloride, trialkyl boron compounds, or trialkyl borate ester. The ability of the precatalyst to undergo ligand dissociation... 

Ligand size determines coordination numbers as well as reactivity. Thus phosphine complexes of Pd°, frequently used as precursors in palladium catalyzed reactions, may be 4-, 3-, or 2-coordinate, as in Pd(PMe3)4, Pd(PPr )3, and Pd(PPhBu 2)2, respectively. For nickel phosphine and phosphite complexes, the dissociation constant Kd for the equilibrium... 

Some complexes dissociate fully in solution (e.g., 7r-allyl nickel tri-fluoroacetate) whence [63] Rp cc [C2][M]. Donor solvents (triphenyl-phosphite, nitrobenzene) can also coordinate with the metal and influence catalyst dissociation with effects on rate and polymer molecular weight the structure of the polymer may also be affected [173]. 

Certain reaction conditions and properties of the nickel complexes promote hydrocyanation. The oxidative addition of HCN requires an open coordination site. Catalysts containing P(0-o-Tol)3 as ligand are particularly reactive because the imsatu-rated L Ni complex is the most stable form of the Ni(0) complex, whereas the saturated 18-electron L Ni complex is the most stable form of the catalysts containing smaller phosphite ligands. The need to imderstand the steric and electronic properties of the ligand on the dissociation of phosphine led to the classic work of Tolman on cone angles and electronic parameters. ... 

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