HOMOLEPTIC ACTINIDE COMPLEXES WITH CHELATING DIPHOSPHINOPHOSPHIDO LIGANDS - NEW MODE OF REACTIVITY WITH CARBON-MONOXIDE AND THE X-RAY CRYSTAL-STRUCTURE OF U(P(CH(2)CH(2)PME(2))(2))(4)

The tetrakis(dialkylphosphido) complexes M{P(CH(2)CH(2)PMe(2))(2)}(4) (M = Th, U) are isolated in high yield from the reaction of MCl(4) with 4 mol equiv of (Li+ or K+)P--(CH(2)CH(2)PMe(2))(2) ((Li/K)PPP). The uranium and thorium compounds are isostructural, although the thorium compound exhibits dimorphism. Detailed shape analysis indicates the structures of the three tetraphosphides conform to triangulated dodecahedra distorted toward bicapped trigonal prisms. The thorium compound is shown to be labile, exhibiting facile exchange of coordinated with uncoordinated tertiary phosphine functions, by P-31{H-1} NMR spectroscopy The thorium compound reacts readily with CO to give a unique double-insertion product where CO is incorporated into a diphosphacarbinol (diphospha secondary alcohol) derivative with two phosphido phosphorus atoms becoming bonded to the inserted carbon atom and the new P2CO unit being eta(3)-bonded to thorium. Structural and spectroscopic data indicate a reduction in C-O bond order from 3 to 1 upon insertion. Hydrolysis liberates the free diphospha secondary alcohol, which is unstable with respect to P-C cleavage and aldehyde formation under mass-spectroscopic conditions. Alkenes with vinylic protons and phenols also react with the thorium tetraphosphide, which eliminates HPPP. The new compounds were characterized by analytical and spectroscopic techniques and by X-ray crystallography for the uranium complex.