The present invention relates to functionalizing agents that are particularly useful for functionalizing living rubbery polymers to make the polymer more compatible with fillers, such as carbon black and silica. These functionalizing agents are comprised of a boron containing compound having a structural formula selected from the group consisting of: wherein R is selected from the group consisting of hydrogen atoms, alkyl groups and aryl groups, wherein R1, R2, and R3 can be the same or different and are selected from the group consisting of alkyl groups, and aryl groups, and wherein R4 represents an alkylene group or a bridging aromatic group.