NICKEL(I) OCTAETHYLISOBACTERIOCHLORIN ANION - AN EXCEPTIONAL NUCLEOPHILE - REDUCTION AND COUPLING OF ALKYL-HALIDES BY ANIONIC AND RADICAL PROCESSES - A MODEL FOR FACTOR-F-430

Nickel(I)octaethylisobacteriochlorin anion (Ni(I)OEiBC-) reacts extremely rapidly with aliphatic halides and methyl tosylate in homogeneous DMF solution. The reactivity sequence, CH3 > primary > secondary greater than or similar to tertiary, and the rate law accord with an S(N)2-like process for the carbon-halogen bond scission. However, the main products of the reactions derive from free radicals. The rate for methyl chloride is 2000 times faster than the corresponding reaction with the super nucleophile CoIB12s- and the rate constant for isopropyl bromide is 350 times greater than that observed with CpFe(CO)2-. The results indicate NiOEiBC- is the fastest nucleophile on record. Studies of the influence of solvent and reactant deuteration and the influence of anion and radical scavengers upon the product distribution suggest the intermediacy of at least one and possibly two nickel alkyls of fleeting lifetime. A novel explanation for the unusual speed of these reactions is put forward. It entails the participation of three metal electrons in the initial and rate-limiting bond-breaking process. The reactions observed are consistent with the activity of methanogenic bacteria to dehalogenate a broad range of substrates via the participation of factor F-430.