Straightforward synthesis of iron cyclopentadienone N-heterocyclic carbene complexes

Abstract

Novel iron complexes bearing both cyclopentadienone and N-heterocyclic carbene ancillary ligands were obtained by a straightforward synthesis from Fe2(CO)9. The preparation represents a rare example of silver transmetallation involving iron. The reaction is general and occurs in the presence of variously functionalized NHC and cyclopentadienones.

Synthesis, reactivity and preliminary biological activity of iron(0) complexes with cyclopentadienone and amino‐appended N‐heterocyclic carbene ligands

“…The molecular structure of 4 is reported in Figure 1 and shows the 6-membered metallacycle involving iron and the chelating κ 2 -C,N-NHCCH 2 CH 2 NH 2 , as evidenced by the close Fe(1)-N(3) contact [2.0636(16) Å] (see Table S2 in SI for a complete list of bond distances and angles). [53] The Fe(1)-C(17) contact [1.945(2) Å] is in the typical range for the interaction between iron(0) and an N-heterocyclic carbene, [25,54] and the overall structure of 4 resembles that of previously reported [Fe(CpO)(CO) 2 (NHC)] analogue of 2a. [25] Analogous experiments were performed with 2b, bearing the propylene amino lateral chain.…”

“…The Fe(1)–C(2) distance [2.2926(17) Å] is significantly longer than Fe(1)–C(3–6) [2.0772(18)‐2.1598(19) Å], and C(2)–O(2) [1.271(2) Å] is essentially a double bond . The Fe(1)–C(17) contact [1.945(2) Å] is in the typical range for the interaction between iron(0) and an N ‐heterocyclic carbene, and the overall structure of 4 resembles that of previously reported [Fe(CpO)(CO) 2 (NHC)] analogue of 2a …”

“…The current state‐of‐the‐art reveals that the design of iron complexes containing ligands able to tune both their solubility in water and electronic properties is still a challenge for the development of bio‐active organometallic compounds. Within this field, our group recently developed a straightforward pathway toward the synthesis of a new family of iron(0) complexes where the combination of cyclopentadienone (CpO), N ‐heterocyclic carbene (NHC) and carbonyl ligands were exploited . The CpO moiety induces efficient tuning of electronic properties of the metal centers acting as a non‐innocent ligand in redox bifunctional catalysis .…”

“…Within this field, our group recently developed a straightforward pathway toward the synthesis of a new family of iron(0) complexes where the combination of cyclopentadienone (CpO), N-heterocyclic carbene (NHC) and carbonyl ligands were exploited. [25] The CpO moiety induces efficient tuning of electronic properties of the metal centers acting as a non-innocent ligand in redox bifunctional catalysis. [26,27] On the other hand, NHCs can nowadays be considered ubiquitous as ancillary ligands, since they are easy to prepare and can be variously functionalized in order to change steric, electronic and solubility properties of complexes.…”

“…[33][34][35][36][37][38][39][40][41] Herein we describe the functionalization of CpO-NHC-bis-carbonyl iron(0) complexes, by addition of lateral chains with a terminal amino group to the NHC ligand and yielding compounds of general formula [Fe(η 4 -CpO)(CO) 2 (κC-NHC(CH 2 ) n NH 2 )] with n = 2 (2a), 3 (2b), and [Fe(η 4 -CpO)(CO) 2 (κC-NHC(CH 2 ) 2 NMe 3 )](I) (3), which shows increasing solubility in water. This combination of ligands is useful in order to stabilize the iron(0) oxidation state, [25,42] and such type of complexes have never been assessed for potential biological applications. Nevertheless, these compounds bring both the metal-carbonyl fragment and the terminal lateral amino chain, which have shown to be able to enhance cytotoxicity.…”