Abstract
Na[cyclo‐(P~5~__t__Bu~4~)] (1) reacts with [NiCl~2~(PEt~3~)~2~] and [PdCl~2~(PMe~2~Ph)~2~] with elimination of __t__BuCl and formation of the corresponding metal(0) cyclopentaphosphene complexes [Ni{cyclo‐(P~5~__t__Bu~3~)}(PEt~3~)~2~] (2) and [Pd{cyclo‐(P~5~__t__Bu~3~)}(PMe~2~Ph)~2~] (3). In contrast, complexes with the more labile triphenylphosphane ligand, such as [MCl~2~(PPh~3~)~2~] (M=Ni, Pd), react with 1 with formation of [NiCl{cyclo‐(P~5~__t__Bu~4~)}(PPh~3~)] (4) and [Pd{cyclo‐(P~5~__t__Bu~4~)}~2~] (5), respectively, in which the cyclo‐(P~5~__t__Bu~4~) ligand is intact. In the case of palladium, the cyclopentaphosphene complex [Pd{cyclo‐(P~5~__t__Bu~3~)}(PPh~3~)~2~] (6) in trace amounts is also formed. However, [Ni{cyclo‐(P~5~__t__Bu~4~)}~2~] (7) is easily obtained by reaction of two equivalents of 1 and one equivalent of [NiCl~2~(bipy)] at room temperature. Complex 7 rearranges on heating in n‐hexane or toluene to the previously unknown [Ni{cyclo‐(P~5~__t__Bu~4~)P__t__Bu}{cyclo‐(P~4~__t__Bu~3~)}] (8), which presumably is formed via the intermediate [Ni{cyclo‐(P~5~__t__Bu~4~)}{cyclo‐(P~4~__t__Bu~3~)P__t__Bu}], which, after an unexpected and unprecedented phosphanediide migration, gives 8, but always as an inseparable mixture with 7. In the reaction of 1 with [PtCl~2~(PPh~3~)~2~], ring contraction and formation of [PtCl{cyclo‐(P~4~__t__Bu~3~)P__t__Bu}(PMe~2~Ph)] (9) is observed. Complexes 3–5 and 7–9 were characterised by ^31^P NMR spectroscopy, and X‐ray structures were obtained for 5–9.