meso-Bis{[eta]⁵-1-[1-(dimethyl­amino)­ethenyl]-3-(trimethyl­silyl)cyclo­penta­dienyl}iron(II) and the cobalt(II) analogue

The two title crystalline compounds, viz. meso-bis­{[eta]⁵-1-[1-(dimethyl­amino)­ethenyl]-3-(trimethyl­silyl)cyclo­penta­dienyl}iron(II), [Fe(C₁₂H₂₀NSi)₂], (II), and meso-bis­{[eta]⁵-1-[1-(dimethyl­amino)­ethenyl]-3-(trimethyl­silyl)cyclo­penta­dienyl}cobalt(II), [Co(C₁₂H₂₀NSi)₂], (III), were obtained by the reaction of lithium 1-[1-(dimethyl­amino)­ethenyl]-3-(tri­methyl­silyl)cyclo­penta­dienide with FeCl₂ and CoCl₂, respectively. For (II), the trimethyl­silyl- and dimethyl­amino­ethenyl-substituted cyclo­penta­dienyl (Cp) rings present a nearly eclipsed conformation, and the two pairs of trimethyl­silyl and dimethyl­amino­ethenyl substituents on the Cp rings are arranged in an inter­locked fashion. In the case of (III), the same substituted Cp rings are perfectly staggered leading to a crystallographically centrosymmetric mol­ecular structure, and the two trimethyl­silyl and two dimethyl­amino­ethenyl substituents are oriented in opposite directions, respectively, with the trimethyl­silyl group of one Cp ring and the dimethyl­amino­ethenyl group of the other Cp ring arranged more closely than in (II).