Iron Complexes Derived from {nacnac-(CH2py)2}− and {nacnac-(CH2py)(CHpy)}n Ligands: Stabilization of Iron(II) via Redox Noninnocence

Valerie A. Williams †, Peter T. Wolczanski *†, Jörg Sutter ‡, Karsten Meyer ‡, Emil B. Lobkovsky †, andThomas R. Cundari §

† Baker Laboratory, Department of Chemistry & Chemical Biology, Cornell University, Ithaca, New York 14853, United States

‡ Department of Chemistry & Pharmacy, University of Erlangen-Nuremberg, Egerlandstrasse 1. D-91058 Erlangen, Germany

§ Department of Chemistry, Center for Advanced Scientific Computing and Modeling (CASCaM),University of North Texas, Box 305070, Denton, Texas 76203-5070, United States

Inorg. Chem., Article ASAP

DOI: 10.1021/ic5001123

Publication Date (Web): April 24, 2014

Copyright © 2014 American Chemical Society

*E-mail: ptw2@cornell.edu. Fax: 607 255 4173.

Synopsis

Nanac-based tetradentate chelates, {nacnac-(CH2py)2}− ({nn(PM)2}−) and {nacnac-(CH2py)(CHpy)}n ({nn(PM)(PI)}n), have been applied to iron, and the latter exhibits redox noninnocent behavior (n = 2−) in {nn(PM)(PI)}FeLL′ [2-L,L′; L,L′ = (PMe3)2, (PMe2Ph)2, PMe3(CO)] and {nn(PM)(PI)}FeL (3-L; L = CO, PMe3, PMePh2, PPh3).

Abstract

Nacnac-based tetradentate chelates, {nacnac-(CH2py)2}− ({nn(PM)2}−) and {nacnac-(CH2py)(CHpy)}n ({nn(PM)(PI)}n) have been investigated in iron complexes. Treatment of Fe{N(TMS)2}2(THF) with {nn(PM)2}H afforded {nn(PM)2}FeN(TMS)2 [1-N(TMS)2], which led to {nn(PM)2}FeCl (1-Cl) from HCl and to {nn(PM)2}FeN3 (1-N3) upon salt metathesis. Dehydroamination of 1-N(TMS)2 was induced by L (L = PMe3, CO) to afford {nn(PM)(PI)}Fe(PMe3)2 [2-(PMe3)2] and {nn(PM)(PI)}FeCO (3-CO). Substitution of 2-(PMe3)2 led to {nn(PM)(PI)}Fe(PMe3)CO [2-(PMe3)CO], and exposure to a vacuum provided {nn(PM)(PI)}Fe(PMe3) (3-PMe3). Metathesis routes to {nn(PM)(PI)}FeL2 (2-L2; L = PMe3, PMe2Ph) and {nn(PM)(PI)}FeL (3-L; L = PMePh2, PPh3) from [{nn(PM)(PI)}2–]Li2 and FeBr2(THF)2 in the presence of L proved feasible, and 1e– and 2e– oxidation of 2-(PMe3)2 afforded 2+-(PMe3)2 and22+-(PMe3)2 salts. Mössbauer spectroscopy, structural studies, and calculational assessments revealed the dominance of iron(II) in both high-spin (1-X) and low-spin (2-L2 and 3-L) environments, and the redox noninnocence (RNI) of {nn(PM)(PI)}n [2-L2, 3-L, n = 2–; 2+-(PMe3)2, n = 1–; 22+-(PMe3)2, n = 0]. A discussion regarding the utility of RNI in chemical reactivity is proffered.