Multi-Pathway Consequent Chemoselectivities of CpRuCl(PPh3)2/MeI-Catalysed Norbornadiene Alkyne Cycloadditions

Chemoselectivities of five experimentally realised CpRuCl(PPh3)(2)/MeI-catalysed couplings of 7-azabenzo-norbornadienes with selected alkynes were successfully resolved from multiple reaction pathway models. Density functional theory calculations showed the following mechanistic succession to be energetically plausible: ( 1) CpRuI catalyst activation; ( 2) formation of crucial metallacyclopentene intermediate; ( 3) cyclobutene product ( P2) elimination (Delta G(Rel(RDS)) approximate to 11.9-17.6 kcal mol(-1)). Alternative formation of dihydrobenzoindole products (P1) by isomerisation to azametalla-cyclohexene followed by subsequent CpRuI release was much less favourable (Delta G(Rel(RDS)) approximate to 26.5-29.8 kcal mol(-1)). Emergent stereoselectivities were in close agreement with experimental results for reactions a, b, e. Consequent investigations employing dispersion corrections similarly support the empirical findings of P1 dominating in reactions c and d through P2 -> P1 product transformations as being probable (Delta G approximate to 25.3- 30.1 kcal mol(-1)).