Tetranuclear complexes from the reaction of tetraphosphorus triselenide with cyclopentadienylchromium tricarbonyl dimer. Synthesis, thermal degradation, and x-ray crystal structures of Cp4Cr4(CO)(9)(P4Se3)center dot 1/2C(6)H(6) and Cp4Cr4(CO)(8)(P2Se2)

The reaction of [CpCr(CO)(3)](2) with P4Se3 has been investigated. Under mi ld conditions, Cp4Cr4(CO)(9)(P4Se3) (4) was the main product (48% yield), a longside low yields of CpCr(CO)(3)H (5), CpCr(CO)(2)P-3 (6), [CpCr(CO)(2)]( 2)P-2 (7), and Cp4Cr4(CO)(8)(P2Se2) (8). Product isolation under various re action conditions, together with H-1 NMR spectral monitoring of the reactio n and thermolytic studies of the complexes 4 and 8, indicates that 4 and 5 were the primary products of the reaction. Thermolysis of 4 led to 8, which in turn degraded to give 6, 7, and Cp4Cr4Se4 (9). The complexes 4 and 8 we re also obtained from the reaction of [CpCr(CO)(2)](2)Se (3) with P4Se3 or P4S3; the reaction with the latter also gave [CpCr(CO)(2)](2)S (10), the su lfur analogue of 3, as an additional product. Mechanistic pathways via the monomeric CpCr(CO)(3) species and the Cr2Se complex 3 are proposed. The cot hermolysis of [CpCr(CO)(2)](2) (Cr=Cr) (2) with P4Se3 led to the isolation of 5, 6, 7, and 9. All the complexes have been characterized spectroscopica lly, while 4 and 8 have also been studied by X-ray diffraction analysis. Th e complex 8 possesses an unusual open-book framework with a P-P bond as its backbone and a 2-fold symmetry axis passing through its midpoint.