Crystal structures of trans-acetyl­dicarbon­yl(η(5)-cyclo­penta­dien­yl)(di­methyl­phenyl­phosphane)molybdenum(II) and trans-acetyl­dicarbon­yl(η(5)-cyclo­penta­dien­yl)(ethyl­diphenyl­phosphane)molybdenum(II)

The title compounds, [Mo(C(5)H(5))(COCH(3))P(CH(3))(2)(C(6)H(5))(CO)(2)], (1), and [Mo(C(5)H(5))(COCH(3))P(C(2)H(5))(C(6)H(5))(2))(CO)(2)], (2), have been prepared by phosphine-induced migratory insertion from [Mo(C(5)H(5))(CO)(3)(CH(3))]. Both complex mol­ecules exhibit a four-legged piano-stool geometry with trans-disposed carbonyl ligands along with Mo—P bond lengths and C—Mo—P angles that reflect the relative steric pressure of the respective phosphine ligand. The structure of compound (1) exhibits a layered arrangement parallel to (100). Within the layers mol­ecules are linked into chains along [001] by non-classical C—H⋯O inter­actions between the acetyl ligand of one mol­ecule and the phenyl and methyl phosphine substituents of another. In the structure of complex (2), a chain motif of centrosymmetrical dimers is found along [010] through C—H⋯O inter­actions.