Density functional theory calculations on the conformational preferences in the two fused five-membered rings of anionic N(SiR2CH2PR'(2))(2) chelated to RuX+ are compared to several experimental structures (X = halide). The calculations consider the structures of both singlet and triplet states and reveal that both the four Bu-t groups and the crowded juncture (N(SiMe2)(2)) of the two rings must be included computationally to understand the observed structures. Computational experiments with different substituents R and R' show the reality of N -> Ru pi donation. The cases where X = H and CH3 are also studied.