Researchers in the Johnson group at MIT are synthesizing biodegradable thermoset polymers to be used in drug delivery. A common example of polymerization is done through 1-alkenes via a radical propagation step, though these methods can be prone to severe branching and their stereochemistry is difficult to control. What d^0 organometallic catalysts can be used to synthesize linear polymers of 1-alkenes while also controlling the stereochemistry of the product?