X-ray crystallographic studies of three heterocyclic complexes of the type cis-Mo(CO)4{(R2PO)2Si(Me)R′} (R2 = OCH2CMe2CH2O; R′ = Me, But or R2 = Ph2; R′ = But)

X-Ray crystal structures for three complexes of the type cis-Mo(CO)4{(R2PO)2-Si(Me)R′} (I: R2 = OCH2CMe2CH2O, R′ = Me; II: R2 = OCH2CMe2CH2O, R′ = But; III: R2 = Ph2, R′ = But) are reported. Complex I crystallizes in the monoclinic space group P21/n (a 15.373(1), b 10.617(2), c 16.053(1) Å; β 110.336(6)°; V 2460(7) Å3; Z = 4), complex II crystallizes in the triclinic space group P1 (a 9.6203(9), b 10.6899(15), c 16.0098(25) Å; α 69.4716(2), β 68.8474(2), γ 66.7698(2)°; V 1368.7(3) Å3; Z = 2) and complex III crystallizes in the orthorhombic space group P212121 (a 11.500(2), b 16.430(2), c 17.892(3) Å; V 3380(2) Å3; Z = 4). The conformations of the chelate rings in these complexes are affected by the nature of the P and Si substituents. The conformations of the chelate rings in I, II and III are best described as a twist boat, a distorted chair and a chaise longue, respectively. In contrast, the conformations of the 1,3,2-dioxaphosphorinane rings in I and II do not appear to be affected by the nature of the Si substituents and are distorted chairs for both complexes. These studies indicate that the P and Si substituents have very different effects upon the steric and electronic properties of these ligands.