Chemistry of [CpCr(CO)3]2. Synthesis of Cp2Cr2(CO)4S, Cp2Cr2(CO)4S2, and Cp2Cr2(CO)5S2. Crystal structure and reactivity of Cp2Cr2(CO)4S2 and Cp2Cr2(CO)5S2

Article abstract of DOI:10.1021/om00148a024

The instantaneous reaction of [CpCr(CO)₃]₂ (Cp = η⁵-C₅H₅) in tetrahydrofuran or toluene with stoichiometric amounts of elemental sulfur produced Cp₂Cr₂(CO)₄S (1) and Cp₂Cr₂(CO)₅S₂ (2) in near quantitative yields. A solution of 2 on standing 1 h at ambient temperature gave a mixture of Cp₂Cr₂(CO)₄S₂ (3) (76%) and 1. The transformation of the very labile complex 2 to 3 with the cleavage of a CO ligand thence to the linear multiple bonded Cr-S-Cr complex 1 with extrusion of a S atom and finally to Cp₄Cr₄S₄ was demonstrated by a time-dependent NMR study at 30°C. When 2 was treated with CF₃SO₃CH₃, one of the S atoms was immediately methylated, giving [Cp₂Cr₂(CO)₅S₂(CH ₃)](SO₃CF₃) (4) as a fine black unstable solid, which decomposed in solution to give 1 and [Cp₄Cr₄S₄(CH₃)](SO ₃CF₃) (5). Complexes 1-3 have been characterized by elemental, spectral, and crystal structure analyses. The structure of 1 has been reported previously. Crystals of 2 are monoclinic, P2₁/n, with a = 11.638 (4) A?, b = 15.508 (5) A?, c = 9.825 (3) A?, β = 111.56 (2)°, and Z = 4. Crystals of 3 are monoclinic, P2₁/c, with a = 8.214 (1) A?, b = 11.464 (2) A?, c = 16.182 (3) A?, β = 92.44 (1)°, and Z = 4. The disulfur ligand bridges the two chromium centers asymmetrically μ-η¹,η² in 2 and symmetrically μ-η² in 3. S-S distances [2.010 (4) A?, 2; 1.990 (1) A?, 3] are similar to those found in other transition-metal μ-S₂ complexes. Metal atoms in both complexes exhibit 4:3, 7-coordination.