Premium
Binding Cooperativity of Two Different Lewis Acid Groups at the Edge of Ferrocene
Author(s) -
Boshra Ramez,
Sundararaman Anand,
Zakharov Lev N.,
Incarvito Christopher D.,
Rheingold Arnold L.,
Jäkle Frieder
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400968
Subject(s) - chemistry , pyridine , diastereomer , lewis acids and bases , moiety , adduct , ferrocene , stereochemistry , denticity , nucleophile , heteronuclear molecule , fluorine 19 nmr , intramolecular force , medicinal chemistry , nuclear magnetic resonance spectroscopy , crystallography , crystal structure , organic chemistry , catalysis , electrode , electrochemistry
The binding properties of heteronuclear bidentate Lewis acids, in which an organoboron and an organotin moiety are attached adjacent to each other at one of the Cp rings of ferrocene, have been studied. Treatment of [1,2‐fc(SnMe 2 Cl)(BClMe)] ( 1‐Cl ) (fc = ferrocenediyl) with one equivalent of pyridine or 4‐dimethylaminopyridine (DMAP) resulted in diastereoselective complexation of boron. Adducts 2 and 3 have been studied by multinuclear NMR, and the stereoselectivity of complexation was further confirmed by single crystal X‐ray diffraction of 2 . The importance of cooperative effects that involve an intramolecular B‐Cl⋅⋅⋅Sn interaction on the diastereoselectivity is evident from comparison with binding studies on the phenyl‐substituted analogue [1,2‐fc(SnMe 2 Cl)(BPhMe)] ( 1‐Ph ). Complexation of 1‐Ph led to diastereomeric mixtures of adducts 4 and 5 , respectively, which were identified by multinuclear NMR including NOESY experiments. The solid‐state structure of one of the diastereomers of 5 was confirmed by X‐ray crystallography. Facile isomerization was found in solution and the barrier of activation was determined by VT NMR studies ( 4 : Δ ${G{{\,{\ne}\hfill \atop 298\hfill}}}$ = 54.9±0.4 kJ mol −1 ; 5 : Δ ${G{{\,{\ne}\hfill \atop 298\hfill}}}$ = 70.3±0.1 kJ mol −1 ). Competitive binding of pyridine to 1‐Cl and [FcB(Cl)Me] (Fc = ferrocenyl) showed that cooperative effects between tin and boron lead to significant Lewis acidity enhancement. Binding of a second nucleophile in the presence of excess of base occurred also at boron. The novel zwitterionic complexes [1,2‐fc(BMe(py) 2 )(SnMe 2 Cl 2 )] ( 6 ) and [1,2‐fc(BMe(dmap) 2 )(SnMe 2 Cl 2 )] ( 7 ) formed, which consist of boronium cation and stannate anion moieties. The structure of 7 in the solid‐state was confirmed by X‐ray crystallography. Multinuclear NMR data and competition experiments indicate weak binding of chloride to tin in 7 and partial dissociation in solution.