| Abstract
| - The steric constraints of the linear tetraphosphine ligand P4 (meso-o-C6H4(PPhCH2CH2PPh2)2) impose the uncommon trigonal-prismatic coordination geometry on [MX2(κ4-P4)] (2, MX = MoCl, MoBr, WBr). Reactions of the 16-electron complex 2 with diazoalkanes promoted catalytic carbenoid-group coupling to give diethyl maleate and fumarate, or they yielded the diazoalkane complexes trans-[MX(NNCHSiMe3)(κ4-P4)]+ and cis,mer-[MoCl2(NNCHSiMe3)(κ3-P4)].
- New Mo and W tetraphosphine−dihalide complexes [MX2(κ4-P4)](2, MX = MoCl, MoBr, WBr; P4 = meso-o-C6H4(PPhCH2CH2PPh2)2) with uncommon trigonal-prismatic geometries have beenprepared. Treatment of ethyl diazoacetate with 2 (MX = MoCl)resulted in catalytic carbenoid-group coupling to give diethyl maleateand fumarate, whereas reactions of 2 with trimethylsilyldiazoalkaneformed the diazoalkane complexes trans-[MX(NNCHSiMe3)-(κ4-P4)]+ (3+) and cis,mer-[MoCl2(NNCHSiMe3)(κ3-P4)]. Themolecular structures of 2 (MX = MoCl) and 3[PF6] (MX = WBr)were crystallographically determined.
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