Open AccessInterplay between Terminal and Bridging Diiron Hydrides in Neutral and Oxidized States
Author(s) -
Xin Yu,
Chen Ho Tung,
Wenguang Wang,
Mioy T. Huynh,
Danielle L. Gray,
Sharon HammesSchiffer,
Thomas B. Rauchfuss
Publication year - 2017
Publication title -
organometallics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.231
H-Index - 172
eISSN - 1520-6041
pISSN - 0276-7333
DOI - 10.1021/acs.organomet.7b00297
Subject(s) - protonation , chemistry , hydride , electrochemistry , density functional theory , crystallography , medicinal chemistry , redox , stereochemistry , inorganic chemistry , computational chemistry , hydrogen , ion , electrode , organic chemistry
This study describes the structural, spectroscopic, and electrochemical properties of electronically unsymmetrical diiron hydrides. The terminal hydride Cp*Fe(pdt)Fe(dppe)(CO)H ([ 1 ( t -H)] 0 , Cp* - = Me 5 C 5 - , pdt 2- = CH 2 (CH 2 S - ) 2 , dppe = Ph 2 PC 2 H 4 PPh 2 ) was prepared by hydride reduction of [Cp*Fe(pdt)Fe(dppe)(CO)(NCMe)] + . As established by X-ray crystallography, [ 1 ( t -H)] 0 features a terminal hydride ligand. Unlike previous examples of terminal diiron hydrides, [ 1 ( t -H)] 0 does not isomerize to the bridging hydride [ 1 ( μ -H)] 0 . Oxidation of [ 1 ( t -H)] 0 gives [ 1 ( t -H)] + , which was also characterized crystallographically as its BF 4 - salt. Density functional theory (DFT) calculations indicate that [ 1 ( t -H)] + is best described as containing an Cp*Fe III center. In solution, [ 1 ( t -H)] + isomerizes to [ 1 ( μ -H)] + , as anticipated by DFT. Reduction of [ 1 ( μ -H)] + by Cp 2 Co afforded the diferrous bridging hydride [ 1 ( μ -H)] 0 . Electrochemical measurements and DFT calculations indicate that the couples [ 1 ( t -H)] +/0 and [ 1 ( μ -H)] +/0 differ by 210 mV. Qualitative measurements indicate that [ 1 ( t -H)] 0 and [ 1 ( μ -H)] 0 are close in free energy. Protonation of [ 1 ( t -H)] 0 in MeCN solution affords H 2 even with weak acids via hydride transfer. In contrast, protonation of [ 1 ( μ -H)] 0 yields 0.5 equiv of H 2 by a proposed protonation-induced electron transfer process. Isotopic labeling indicates that μ -H/D ligands are inert.