Quantitative Determination of the Regioselectivity of Nucleophilic Addition to η-Propargyl Rhenium Complexes and Direct Observation of an Equilibrium Between η-Propargyl Rhenium Complexes and Rhenacyclobutenes. - Casey CP; Boller TM; Samec JS; Reinert-Nash JR (Organometallics, 2009)