Simple alkylcerium reagents are well known.  One example is .
Although they are described as RCeCl, their structures are far more complex.. Furthermore, the solvent seems to alter the solution structure of the complex, with differences noted between reagents prepared in diethyl ether and tetrahydrofuran. There is evidence that the parent chloride forms a polymeric species in THF solution, of the form [Ce(μ-Cl)(HO)(THF)], but whether this type of polymer exists once the organometallic reagent is formed is unknown.