Reactions of (4-benzylideneacetone)Fe(CO)3 complexes and α,ω-diphosphines Ar2P(CH2)nPAr2 afford diiron complexes shown in Figure 1 carrying different methylene linker bridges (n), and forming complexes of varying inter(iron)atomic distances. Crystal structures establish essentially parallel P−Fe−P axes, Fe−Fe distances of 5.8−6.5 Å, and van der Waals radii of 4.5 Å for the Fe(CO)3 rotators. Analogous reactions of Ph2P(CH2)6PPh2 yield square pyramidal monoiron complexes trans-(CO)3Fe[Ph2P(CH2)6PPh2], a rare case where a diphosphine spans trans basal positions. The IR ν(C≡O) diagnostic band patterns and energies of all complexes (mono- and bimetallic species with linker lengths n = 3−6) are analyzed with the aid of DFT calculations. The diiron complexes are preferred thermodynamically. Attention is given to limiting types of Fe(CO)3/Fe(CO)3 interactions in the diiron complexes and steric models are constructed to discuss potential gearing between the diiron rotators.

Steric models and computations to investigate gearing in diiron complexes featuring interactive Fe(CO)3 rotators

ACS Fall 2021

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