Ambidentate Ligand Reactivity with the Rhenium(I) Compounds [BrRe(CO)4 ]2 and cis -BrRe(CO)4 L: A Kinetic and Mechanistic Study: Ambidentate Ligand Reactivity with the Rhenium(I) Compounds [BrRe(CO)4 ]2 and cis -BrRe(CO)4 L: A Kinetic and Mechanistic Study