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One‐Step Synthesis and Schlenk‐Type Equilibrium of Cyclopentadienylmagnesium Bromides
Author(s) -
Schüler Philipp,
Görls Helmar,
Krieck Sven,
Westerhausen Matthias
Publication year - 2021
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.202102636
Subject(s) - chemistry , equilibrium constant , tetrahydropyran , homoleptic , magnesium bromide , enthalpy , diethyl ether , adduct , medicinal chemistry , ligand (biochemistry) , magnesium , organic chemistry , thermodynamics , receptor , ring (chemistry) , biochemistry , physics , metal
In the in situ Grignard metalation method (iGMM), the addition of bromoethane to a suspension of magnesium turnings and cyclopentadienes [C 5 H 6 (HCp), C 5 H 5 ‐Si( i Pr) 3 (HCp TIPS )] in diethyl ether smoothly yields heteroleptic [(Et 2 O)Mg(Cp R )(μ‐Br)] 2 (Cp R =Cp ( 1 ), Cp TIPS ( 2 )). The Schlenk equilibrium of 2 in toluene leads to ligand exchange and formation of homoleptic [Mg(Cp R ) 2 ] ( 3 ) and [(Et 2 O)MgBr(μ‐Br)] 2 ( 4 ). Interfering solvation and aggregation as well as ligand redistribution equilibria hamper a quantitative elucidation of thermodynamic data for the Schlenk equilibrium of 2 in toluene. In ethereal solvents, mononuclear species [(Et 2 O) 2 Mg(Cp TIPS )Br] ( 2’ ), [(Et 2 O) n Mg(Cp TIPS ) 2 ] ( 3’ ), and [(Et 2 O) 2 MgBr 2 ] ( 4’ ) coexist. Larger coordination numbers can be realized with cyclic ethers like tetrahydropyran allowing crystallization of [(thp) 4 MgBr 2 ] ( 5 ). The interpretation of the temperature‐dependency of the Schlenk equilibrium constant in diethyl ether gives a reaction enthalpy ΔH and reaction entropy ΔS of −11.5 kJ mol −1 and 60 J mol −1 , respectively.