Synthesis and characterization of new mixed allyl–alkoxo-complexes of uranium(IV). The crystal and molecular structure of di-µ-isopropoxo-bis[di(η-allyl)isopropoxouranium(IV)]

Abstract

New complexes of general formula [U(η-C₃H₅)₂(OR)₂][R = Et(1), Prⁱ(2), or Bu^t(3)] have been prepared by reaction of [U(η-C₃H₅)₄] with ROH. The crystal structure of (2) has been determined from single-crystal X-ray diffraction data (Mo-K_α radiation). The complex crystallizes in the space group P2₁/c with unit-cell dimensions a= 12.324(7), b= 8.535(1), c= 17.897(9)Å, β= 126.71(3)°, Z= 4, and R 0.030 for 1 408 independent observations. In the dimeric molecular structure, with crystallographic site symmetry, two uranium atoms are joined by two alkoxide bridges. The co-ordination polyhedron of the uranium can be regarded as a distorted pentagonal bipyramid, whose equatorial plane is defined by the terminal carbons of the η-allyl ligands and by a bridging oxygen. The axial positions of the bipyramid are occupied by the remaining bridging oxygen and by a terminal oxygen. The latter shows a linear co-ordination [U–O–C 178.0(10)°]. Other relevant bond distances are: U–O(bridging) 2.271(10) and 2.413(10); U–O(terminal) 2.056(13); and U–C(mean) 2.679(14)Å. Infrared data for (1)–(3) suggest that the uranium–allyl π bond is predominantly ionic; this is consistent with some structural peculiarities of the allyl ligands in (2). Hydrogen-1 n.m.r. results indicate monomeric structures in tetra-hydrofuran [(1)–(3)] and dimeric ones in toluene solution for (1) and (2).