Tetranuclear complexes from the reaction of tetraphosphorus triselenide with cyclopentadienylchromium tricarbonyl dimer. Synthesis, thermal degradation, and X-ray crystal structures of Cp4Cr4(CO)9(P4Se 3)·1/2C6H6 and Cp4Cr4(CO)8(P2Se2)

Abstract

The reaction of [CpCr(CO)3]2 with P4Se3 has been investigated. Under mild conditions, Cp4Cr4(CO)9(P4Se3) (4) was the main product (48% yield), alongside low yields of CpCr(CO)3H (5), CpCr(CO)2P3 (6), [CpCr(CO)2]2P2 (7), and Cp4Cr4(CO)8(P2Se2) (8). Product isolation under various reaction conditions, together with 1H NMR spectral monitoring of the reaction 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 were also obtained from the reaction of [CpCr(CO)2]2Se (3) with P4Se3 or P4S3; the reaction with the latter also gave [CpCr(CO)2]2S (10), the sulfur analogue of 3, as an additional product. Mechanistic pathways via the monomeric CpCr(CO)3 species and the Cr2Se complex 3 are proposed. The cothermolysis 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 spectroscopically, while 4 and 8 have also been studied by X-ray diffraction analysis. The 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.