Abstract

The trimethylenemethane ligand is found in the experimentally known and structurally characterized mononuclear iron carbonyl derivative (CH2)3CFe(CO)3, which may be regarded as a substitution product of Fe(CO)5. The structures of trinuclear trimethylenemethane iron carbonyl derivatives similarly related to the well-known doubly bridged Fe3(CO)12 structure have now been investigated by density functional theory. The lowest energy [(CH2)3C]Fe3(CO)10 structures likewise have two CO bridges and can be derived from the known Fe3(CO)12 structure by replacement of two terminal CO groups with either an unsymmetrical edge-bridging or face-bridging trimethylene methane ligand while preserving the central Fe3 triangle. However, replacing four CO groups in Fe3(CO)12 with two trimethylenemethane ligands to give [(CH2)3C]2Fe3(CO)8 is predicted unexpectedly to give a very different type of structure. In this structure one edge of the Fe3 triangle in Fe3(CO)12 is broken to form a bent Fe–Fe–Fe chain with the trimethylenemethane ligands bonded to the end iron atoms of this triiron chain. This [(CH2)3C]2Fe3(CO)8 structure appears to be very favorable, since it lies ∼22kcal/mol below alternative structures. We anticipate that both [(CH2)3C]Fe3(CO)10 and [(CH2)3C]2Fe3(CO)8 should be sufficiently stable to be synthesized from the known (CH2)3CFe(CO)3 by thermolysis or photolysis with suitable iron carbonyls.

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