Toward Frameworks with Multiple Aligned and Interactive Fe(CO)3 Rotators: Syntheses and Structures of Diiron Complexes Linked by Two trans-Diaxial α,ω-Diphosphine Ligands Ar2P(CH2)nPAr2

Samuel R Zarcone; Gong M Chu; Andreas Ehnbom; Ashley Cardenal; Tobias Fiedler; Nattamai Bhuvanesh; Michael B Hall; John A Gladysz

doi:10.1021/acs.inorgchem.0c03737

Toward Frameworks with Multiple Aligned and Interactive Fe(CO)₃ Rotators: Syntheses and Structures of Diiron Complexes Linked by Two trans-Diaxial α,ω-Diphosphine Ligands Ar₂P(CH₂)_nPAr₂

Inorg Chem. 2021 Mar 1;60(5):3314-3330. doi: 10.1021/acs.inorgchem.0c03737. Epub 2021 Feb 11.

Authors

Samuel R Zarcone¹, Gong M Chu¹, Andreas Ehnbom¹, Ashley Cardenal¹, Tobias Fiedler¹, Nattamai Bhuvanesh¹, Michael B Hall¹, John A Gladysz¹

Affiliation

¹ Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012, United States.

PMID: 33571407
DOI: 10.1021/acs.inorgchem.0c03737

Abstract

Reactions of (η⁴-benzylideneacetone)Fe(CO)₃ and the α,ω-diphosphines Ar₂P(CH₂)_nPAr₂ afford the trigonal bipyramidal diiron tetraphosphorus complexes trans,trans-(CO)₃Fe[Ar₂P(CH₂)_nPAr₂]₂Fe(CO)₃ (n/Ar = 3/Ph 3, 4/Ph 4a, 4/p-tol 4b; 56-19%). Crystal structures establish essentially parallel P-Fe-P axes, iron-iron distances of 5.894(9)-5.782(1) Å (3) and 6.403(1)-6.466(1) Å (4a,b), and van der Waals radii of 4.45 Å for the Fe(CO)₃ rotators, the planes of which are offset by 0.029-1.665 Å. Analogous reactions of Ph₂P(CH₂)₆PPh₂ yield the square pyramidal monoiron complex trans-(CO)₃Fe[Ph₂P(CH₂)₆PPh₂] (6', 31%), a rare case where a diphosphine spans trans basal positions (∠P-Fe-P 147.4(2)°). Both 3 and 6' exhibit two CO ¹³C NMR signals at room temperature, indicating slow exchange on the NMR time scale, which in the former could entail Fe(CO)₃/Fe(CO)₃ gearing. Under analogous conditions, 4a,b exhibit one signal. Previously reported adducts of Fe(CO)₃ and Ph₂P(CH₂)_nPPh₂ are surveyed (1:1, n = 1-5; 2:2, n = 5), and the IR ν_C≡O band patterns and energies of all complexes 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.