Disclosed are metallocene compounds, catalyst compositions comprising a metallocene compound, processes for polymerizing olefins, methods for making catalyst compositions, olefin polymers and articles made from olefin polymers. In an aspect, a metallocene compounds contain a fluorenyl ligand and a cyclopentadienyl ligand which are bridged by a linking group, in which the metallocene is characterized by [1] the cyclopentadienyl ligand being substituted with a C2-C18 heterohydrocarbyl group having an oxygen atom positioned 5 atoms distance or less from the cyclopentadienyl ligand and [2] the linking group having a pendant C3-C12 alkenyl group having a terminal C═C double bond. It has been discovered that a catalyst composition comprising a metallocene compound having these features can produce polyethylene having a low melt index in the absence of a second metallocene.