ZINTL ANIONS AS STARTING COMPOUNDS FOR THE SYNTHESIS OF POLYNUCLEAR TRANSITION-METAL COMPLEXES

The Zintl anion P-7(3-) reacts with complexes of transition metal hali des to form multinuclear metal phosphorus clusters. Reaction of Li3P7 . 3 DME with [FeCp(CO)(2)Br] or [NiCl2(PBu(3))(2)] leads to the format ion of [P-7{FeCp(CO)(2)}(3)] (1) and [{Ni(PBu(3))(2)}P-4(14)] (2), res pectively. X-ray structure determinations show that in 1 the P-7 cage of Li3P7 remains intact, but in 2 a P-14 framework is formed by linkag e of two norbornadiene-like P-7 units. The P-14 skeleton coordinates t o four Ni(PBu(3))(2) groups. LiCp and CoCl2 react with P-7(SiMe(3))(3 ) to give [(CpCo)(3)-(P-2)(3)] (3) with three Cp*Co groups bridged by P-2 units. Reaction of FeCl2 and LiCp with P-7(SiMe(3))(3) yields [( CpFe)(3)P-6]-[FeCl3(thf)] (4) or [(Cp*Fe)(3){(eta(3)-P-3)Fe}-P-6] (5) , depending on the reaction conditions. In 4 the structure of the Fe3P 6 core of the [(CpFe)(3)P-6](+) cation is comparable to closo-B9H92-, while in 5 the Fe4P6 core does not obey the Wade rules. The unusual G o-As cluster [Co6As12(PEt(2)Ph)(6)] (6),prepared from K, As, and [CoCl 2(PEt(2)-Ph)(2)], can be described as a Co6As6 heteroicosahedron linke d to two Co3As3 octahedra by common Co-3 faces. A theoretical treatmen t within the density functional approximation reproduces the experimen tal structures of 2 and 6 and allows an interpretation of molecular el ectronic structures. In 2 one finds P-P double bonds that are delocali zed to some extent into vacant Ni AOs. For the cage compound 6 the Co 3d AOs participate in case bonding and 38 electrons can be assigned to cage bonds; this is in accord with the (2N + 2) rule for 18-atom cage s but not with the usual electron counting rules.