Novel Polycyclic Phosphane-to Metal Coordination. Reaction of [CpCr(CO)₃]₂ with Elemental Phosphorus and Structure and Paramagnetism of the Odd-electron Complex [CpCr(CO)₂]₅P₁₀

The cothermolysis of [CpCr(CO)3]2 (Cp = η5-C5H5 with 1.5 mol equiv of P4 at 85°C for 4 h resulted in the isolation of Cp2Cr2(CO)4(μ-η2-P 2) (2), CpCr(CO)2(η3-P3) (3), Cp2Cr2(CO)4 (4), and [CpCr(CO)2]5P10 (5) in 34, 34, 17, and 13% yields, respectively. The reaction of 4 with P4 for 1.5 h, gave a similar mixture of 2, 3, and 5. The structure of the P10 unit in 5 is unique in polyphosphane chemistry. Its novel mode of coordination to organotransition metal groups is the first known instance of its kind. A further unusual feature is that 5 forms an odd-electron molecule, which is therefore paramagnetic; the 35-GHz EPR spectrum of an arbitrarily oriented single crystal at 6.1 K shows a complex 30-peak signal. The magnetic moment is 1.75 μB. The NMR spectrum shows that delocalization of unpaired spin density onto the Cp ligands is negligible. The complex undergoes three one-electron processes at 200 K: a quasi-reversible reduction at -1.29 V and two reversible oxidations at 0.61 and 1.03 V, respectively. 5 crystallizes as dark brown chunky polyhedra; crystal data: space group P1 with Z = 2, a = 12.339 (3) Å, b = 13.993 (3) Å, c = 16.115 (6) Å, α = 94.52 (2)°, β = 92.93 (4)°, γ = 114.20 (3)°. R = 6.1% for 6884 reflections. © 1993 American Chemical Society