Role of cluster size and substrate in the gas phase C [sbnd]C bond coupling reactions of allyl halides mediated by Ag n+ and Ag n−1 H + cluster cations

Abstract

Previous studies have demonstrated that the silver hydride cluster cation Ag 4H + promotes C C bond coupling of allylbromide [G.N. Khairallah, R.A.J. O’Hair, Angewandte Chemie International Edition 44 (2005) 728]. Here the influence of both the nature and the size of the silver cluster cation and the substrate on C C bond coupling are examined. Thus each of the cations Ag 2H +, Ag 4H +, Ag 3 +, and Ag 5 + were allowed to react with three different halides: allyl chloride, allyl bromide and allyl iodide. No C C bond coupling is observed in the reactions of the cluster cations with allyl chloride. There are four main reaction sequences that result in C C bond coupling for allyl bromide and allyl iodide mediated by Ag n + and Ag n−1 H + clusters: (i) A sequence involving the reactions of silver cluster cations with two molecules of C 3H 5X: Ag n + → Ag n (C 3H 5X) + → Ag n X 2 +. This only occurs in the cases of: n = 3 and X = I; n = 5 and X = Br. (ii) A sequence involving the reactions of silver cluster cations with two molecules of C 3H 5X via an organometallic intermediate: Ag n + → Ag n−1 (C 3H 5) + → Ag n−1 X +. This only occurs in the cases of: n = 5 and X = Br and I. (iii) A sequence involving the reactions of silver hydride cluster cations with three molecules of C 3H 5X: Ag n−1 H + → Ag n−1 X + → Ag n−1 X(C 3H 5X) + → Ag(C 3H 5) 2 + and Ag n−1 X 3 +. This only occurs in the cases of: n = 5 and X = Br and I. (iv) A sequence involving the reactions of silver hydride cluster cations with three molecules of C 3H 5X via an organometallic intermediate: Ag n−1 H + → Ag n−1 X + → Ag n−3 (C 3H 5) + → Ag(C 3H 5) 2 + and Ag n−3 X +. This only occurs in the cases of: n = 5 and X = I.