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) wit h 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 st ructures of the three tetraphosphides conform to triangulated dodecahe dra distorted toward bicapped trigonal prisms. The thorium compound is shown to be labile, exhibiting facile exchange of coordinated with un coordinated tertiary phosphine functions, by P-31{H-1} NMR spectroscop y The thorium compound reacts readily with CO to give a unique double- insertion product where CO is incorporated into a diphosphacarbinol (d iphospha secondary alcohol) derivative with two phosphido phosphorus a toms becoming bonded to the inserted carbon atom and the new P2CO unit being eta(3)-bonded to thorium. Structural and spectroscopic data ind icate a reduction in C-O bond order from 3 to 1 upon insertion. Hydrol ysis liberates the free diphospha secondary alcohol, which is unstable with respect to P-C cleavage and aldehyde formation under mass-spectr oscopic conditions. Alkenes with vinylic protons and phenols also reac t with the thorium tetraphosphide, which eliminates HPPP. The new comp ounds were characterized by analytical and spectroscopic techniques an d by X-ray crystallography for the uranium complex.