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Intramolecular Dynamics of Five‐coordinate iron Carbonyl Complexes with olefinic ligands as studied by variable‐pressure 1 H‐NMR spectroscopy
Author(s) -
Ioset Jacques,
Helm Lothar,
Merbach André,
Roulet Raymond,
Grepioni Fabrizia,
Braga Dario
Publication year - 1988
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19880710609
Subject(s) - chemistry , triclinic crystal system , intramolecular force , crystallography , nuclear magnetic resonance spectroscopy , crystal structure , dissociation (chemistry) , 1,5 cyclooctadiene , tetragonal crystal system , stereochemistry , catalysis , organic chemistry
Variable‐pressure 1 H‐NMR Spectroscopy has been used to study the fluxionality of some five‐coordinated Fe complexes in solution. For [Fe(CO) 2 1,3‐cyclooctadiene (PPh 3 )], the CO site exchange is known (by analogy with [Fe(CO) 3 (1,3‐cyclooctadiene)]) to be a non‐dissociative process, and an activation volume of ca. 0 cm 3 .mol −1 was indeed obtained. However, for [Fe(CO 2 ){2,3‐η: O ‐σ‐(7,7‐dimethoxybicyclo[2.2.1]hept‐2‐ene)}(PPh 3 )], the activation volume of +5 cm 3 mol −1 suggests that an unprecedented dissociation process is responsible for the CO site exchange. The molecular structure of [Fe(CO) 2 (1,3‐cyclooctadiene)(PPh 3 )] was ascertained by single‐crystal X‐ray diffractometry. The crystals are triclinic, space group P 1 , a = 9.606(3), b = 16.795(2), c = 7.743(8) Å, α = 97.83(4), β = 109.63(4), γ = 83.37(2)°. The structure determination has shown that the complex possesses a tetragonal pyramidal coordination, with the endocyclic CC bond and PPh 3 occupying basal sites.