In this paper we study perturbed Ornstein-Uhlenbeck operatorsfor simultaneously diagonalizable matrices A, B ∈ C N,N . The unbounded drift term is defined by a skew-symmetric matrix S ∈ R d,d . Differential operators of this form appear when investigating rotating waves in time-dependent reaction diffusion systems. We prove under certain conditions that the maximal domain D(Ap) of the generator Ap belonging to the Ornstein-Uhlenbeck semigroup coincides with the domain of L∞ in L p (R d , C N ) given byOne key assumption is a new L p -dissipativity condition |z| 2 Re w, Aw + (p − 2)Re w, z Re z, Aw γA|z| 2 |w| 2 ∀ z, w ∈ C N for some γA > 0. The proof utilizes the following ingredients. First we show the closedness of L∞ in L p and derive L p -resolvent estimates for L∞. Then we prove that the Schwartz space is a core of Ap and apply an L p -solvability result of the resolvent equation for Ap. A second characterization shows that the maximal domain even coincides with D p max (L0) = {v ∈ W 2,p | S·, ∇v ∈ L p }, 1 < p < ∞. This second characterization is based on the first one, and its proof requires L p -regularity for the Cauchy problem associated with Ap. Finally, we show a W 2,p -resolvent estimate for L∞ and an L p -estimate for the drift term S·, ∇v . Our results may be considered as extensions of earlier works by Metafune, Pallara and Vespri to the vector-valued complex case.