Functionalized cobalt bis(dicarbollide) ions as selective extraction reagents for removal of M2+ and M3+ cations from nuclear waste, crystal and molecular structures of the [8,8′-μ-CIP(O)(O)2(1,2-C2B9H10)2-3,3′-Co]HN(C2H5)3 and [8,8′-μ-Et2NP(O)(O)2 (1,2-C2B9H10)2-3,3′-Co](HN(CH3)3)

New reliable synthetic methods leading to derivatives of the closo-[(1,2-C2B9H11)(2)-3,3'-Co](-) (1) anion 1 with phosphorus containing substituents on the cage boron atoms have been successfully developed, starting from its 8-OH (2) and 8,8'-(OH)(2) (3) hydroxyderivatives. Reactions of 2 with either Cl3PO or PhCl2PO followed by hydrolysis gave 8-(HO)(2)PO-O- (4) and [(8-PhPO(OH) -O)- 1,2-C2B9H10)(1,2-C2B9H11)-3,3'-Co](-) (5) phosphorylated species, respectively. Analogous reactions Of Cl3PO with 3 provided a chlorine bearing bridged product [8,8'-mu-ClP(O)(O)(2) < (1,2-C2B9H10)(2)-3,3'-Co](-) (6) with surprisingly high hydrolytic stability. The anticipated anion [8,8'-mu-(HO)(O)-P(O)(2) < (1,2-C2B9H10)(2)-3,3'-Co](-) (7) with phosphoric acid as the bridging substituent was obtained after alkaline hydrolysis of compound 6. The related [8,8'-mu-Ph(O)P(O)(2) < (1,2-C2B9H10)(2)-3,3'-Co](-) (8) derivative was prepared by similar reaction of 3 with PhCl2PO and subsequent hydrolysis. Further developments starting from versatile precursor 6 led to synthesis of a derivative containing an asymmetric bridging diethylphosporamide moiety [8,8'-mu-(Et2N)P(O)(O)(2) < (1,2-C2B9H10)(2)-3,3'-Co](-) (9). A crystal of the compound 9 containing a pure enantiomer was selected, and its absolute configuration was determined by X-ray diffraction. Molecular structure of the compound 6 was also determined by X-ray diffraction analysis and the crystallographic results for both compounds are presented. Compounds 6 and 7 represent efficient Eu3+ extractants, enabling metal extraction even from highly acidic solutions (up to 1 M HNO3) to aromatic solvents. The novel compounds thus amalgamate in the single molecule good extraction properties of cobalta bis(dicarbollide) anion and the complexation ability of alkylphosphates. (C) 2002 Elsevier Science B.V. All rights reserved.