The recently reported 1,2-di-tert-butylcyclopentadienyl ligand has been used to prepare new Group 6 metal complexes. Lithium 1,2-di-tert-butylcyclopentadienide (1) reacts cleanly with M(CO) 6 (M = Mo, W) and following acidification and oxidation gives, depending upon reaction conditions, [M(η 5 -1,2-C 5 H t 3 Bu 2 )(CO) 3 ] 2 (M = Mo (2), W (3)) or [Mo(η 5 -1,2-C 5 H t 3 Bu 2 )O] 2 (μ 2 -O) 2 (4). The hexacarbonyl dimer 2 is easily oxidized by Br 2 to the tricarbonyl bromide complex, [Mo(η 5 -1,2-C 5 H t 3 Bu 2 )(CO) 3 Br] (5). Crystal data for2 with Mo K α (λ = 0.7107 a) radiation at 296 K: Mo 2 C 3 2 H 4 2 O 6 , a = 7.470(3) a,b = 8.658(3) a, c = 13.319(6) a, α = 84.16(3) o , β = 80.26(3) o , γ = 75.04(3) o ; triclinic space group P1 (No. 2), Z = 1, R = 3.44%,R w = 3.61%. Crystal data for 4 with Mo K α (λ = 0.7107 a) radiation at 296 K: Mo 2 C 2 6 H 4 2 O 4 , a = 12.886(3) a, b = 16.877(5) a, c = 12.316(3) a, orthorhombic space group Pccn (No. 56), Z = 4, R = 3.46%, R w = 5.00%.