Zintl Anions as Starting Compounds for the Synthesis of Polynuclear Transition Metal Complexes

The Zintl anion P 3− 7 reacts with complexes of transition metal halides to form multinuclear metal phosphorus clusters. Reaction of Li 3 P 7 ·3 DME with [FeCp(CO) 2 Br] or [NiCl 2 (PBu 3 ) 2 ] leads to the formation of [P 7 {FeCp(CO) 2 } 3 ] ( 1 ) and [{Ni(PBu 3 ) 2 } 4 P 14 ] ( 2 ), respectively. X‐ray structure determinations show that in 1 the P 7 cage of Li 3 P 7 remains intact but in 2 a P 14 framework is formed by linkage of two norbornadiene‐like P 7 units. The P 14 skeleton coordinates to four Ni(PBu 3 ) 2 groups. LiCp * and CoCl 2 react with P 7 (SiMe 3 ) 3 to give [(Cp * Co) 3 ‐(P 2 ) 3 ] ( 3 ) with three Cp * Co groups bridged by P 2 units. Reaction of FeCl 2 and LiCp * with P 7 (SiMe 3 ) 3 yields [(Cp * Fe) 3 P 6 ][FeCl 3 (thf)] ( 4 ) or [(Cp * Fe) 3 { n 3 ‐P 3 )Fe}P 6 ] ( 5 ), depending on the reaction conditions. In 4 the structure of the Fe 3 P 6 core of the [(Cp * Fe) 3 P 6 ] + cation is comparable to closo ‐B 9 H 9 2− , while in 5 the Fe 4 P 6 core does not obey the Wade rules. The unusual Co‐As cluster [Co 6 As 12 (PEt 2 Ph) 6 ] ( 6 ), prepared from K, As, and [CoCl 2 (PEt 2 ‐Ph) 2 ], can be described as a Co 6 As 6 heteroicosahedron linked to two Co 3 As 3 octahedra by common Co 3 faces. A theoretical treatment within the density functional approximation reproduces the experimental structures of 2 and 6 and allows an interpretation of molecular electronic structures. In 2 one finds P‐P double bonds that are delocalized to some extent into vacant Ni AOs. For the cage compound 6 the Co 3 d AOs participate in cage bonding and 38 electrons can be assigned to cage bonds; this is in accord with the (2 N + 2) rule for 18‐atom cages but not with the usual electron counting rules.