Organouranium chemistry with phosphorus ylides

Abstract

A new and novel class of organouranium complexes containing phosphorus ylides as ligands have been prepared and characterized. The phosphorus ylides used in this study were of the general formula: Although the preparation of several of these lithiated phosphoylides (R = CH3 or C6H5) had previously been reported, no data on their characterization was available. Accordingly we have done so. The addition of one equivalent of lithiated phosphoylide to one equivalent of (C5H5)3UCl results in dark green complexes of the These triscyclopentadienyluraniumphosphoylide complexes rapidly react with carbon monoxide at room temperature to give carbon monoxide where R = C2H5, CH3 or C6H5. On the basis of infrared data ( υ co = 1660 cm^-1) a side-bonded or dihapto coordination of the acyl group is assigned for these complexes. This is only the second example of a triscyclopentadienyluranium complex expanding its coordination number from ten to eleven. When two equivalents of lithiated phosphorus ylide are added to (C5H5)3UC1, dark red dimeric complexes of the formula (p-(CH) (CH2)P(C6H5) (R)U(C5H5)2)2 (where R = CH3 or C6H5) result. Crystallization from diethyl ether produces deep red crystals of space group P21/c containing four molecules per unit cell of dimensions a = 12.675(8) Å, b = 16.462(8) Å, c = 25.837(25) Å and β = 124.43(5)°. Refinement converged for 3993 reflections with I ≥ 3(I) at R1 = 0.092 and Rw = 0.110. Sohx1et extraction of this compound with pentane belonging to the orthorhombic space group P212121 with a = 16.026(12) Å, b = 23.453(13) Å, c = 12.679(3) Å and four molecules per unit cell. Refinement converged at R1= 0.047 and Rw = 0.052 for 1874 independent reflections with I ≥ 3(I). The complex is a biscyclopentadienyluranium dimer bridged by two phosphorus ylide ligands. In addition to being the first nine-coordinate organouranium compound it is the first example of a complex in which a phosphorus ylide both chelates a single metal atom and bridges two metal atoms through a methine bridge. The 1H nmr of (µ-(CH)(CH2)P(C6H5)2U(C5H5)2)2is temperature dependent. At ambient temperature enantiomerization and interchange of diastereotopic cyclopentadienyl groups occurs at a rapid rate on the nmr time scale. At low temperature these processes slow and an estimated ΔG^+253 = 10 ± 1 kcal/mole in toluene-d8 and ΔG^+234 = 10 ± 1 kcal/mole in THF-d8 are obtained. At lower temperatures another process begins to slow which is ascribed to the slowing of the rotation of one-half of the cyclopentadienyl groups. The addition of three equivalents of lithiated phosphoylide to one equivalent of either (C5H5)3UCl or (C5H5)UCl3.2THF produces gold R = CH3 or C6H5. These monomeric complexes consist of a uranium bound to one cyclopentadienyl group and three chelating phosphorus ylides. These are the second example of nine-coordinated organouranium compounds. In addition, they contain six U-C σ bonds which is the most observed to date for any organouranium compound.