Bulky cationic β-diketiminate magnesium complexes
Friedrich A, Pahl J, Elsen H, Harder S (2019)
Publication Type: Journal article
Publication year: 2019
Journal
Book Volume: 48
Pages Range: 5560-5568
Journal Issue: 17
DOI: 10.1039/c8dt03576h
Abstract
Cationic β-diketiminate Mg complexes with the bulky
tBu
BDI ligand and the weakly coordinating anion B(C
6
F
5
)
4
-
have been prepared by the reaction of (
tBu
BDI)MgnBu with [Ph
3
C]
+
[B(C
6
F
5
)
4
]
-
;
tBu
BDI = CH[C(tBu)N-Dipp]
2
and Dipp = 2,6-diisopropylphenyl. Their structures are compared to the previously reported cationic (
Me
BDI)Mg
+
complexes;
Me
BDI = CH[C(Me)N-Dipp]
2
. Crystallization of [(
tBu
BDI)Mg]
+
[B(C
6
F
5
)
4
]
-
from chlorobenzene gave a unique (
tBu
BDI)Mg
+
·ClC
6
H
5
cation with a rather short Mg⋯Cl and consequently long C-Cl bond. Crystallization from chlorobenzene/arene solvent mixtures gave (
tBu
BDI)Mg
+
·arene complexes (arene = benzene, toluene, m-xylene) but in the presence of mesitylene the chlorobenzene complex was formed. Due to the greater shielding of the metal, none of these complexes display Mg⋯(F
5
C
6
)
4
B
-
interactions. Crystal structures of the arene complexes show in all cases η
2
-coordination of the arene ligands. Ring slippage from a more favorable η
2
-coordination can be explained by the steric bulk of the
tBu
BDI ligand. The smaller arenes, benzene and toluene, also bind to (
tBu
BDI)Mg
+
in bromobenzene solution. The Lewis acidity of these cationic Mg complexes was determined by the Gutmann-Beckett test. The acceptor number for (
tBu
BDI)Mg
+
(AN = 76.0) is substantially higher than that estimated for (
Me
BDI)Mg
+
(AN = 70.3). Calculation of the atomic NPA charges by DFT shows that the Mg
2+
ion in (
tBu
BDI)Mg
+
is slightly more positively charged than the metal in (
Me
BDI)Mg
+
, confirming its higher Lewis acidity. The lower benzene complexation energy calculated for (
tBu
BDI)Mg
+
versus (
Me
BDI)Mg
+
is due to steric congestion of the metal in the (
tBu
BDI)Mg
+
cation which allows only for Mg⋯(η
1
)C
6
H
6
instead of Mg⋯(η
6
)C
6
H
6
bonding. This ring slippage, however, results in a significant polarization of the electron density in the benzene ring, making it susceptible for nucleophilic attack..
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How to cite
APA:
Friedrich, A., Pahl, J., Elsen, H., & Harder, S. (2019). Bulky cationic β-diketiminate magnesium complexes. Dalton Transactions, 48(17), 5560-5568. https://dx.doi.org/10.1039/c8dt03576h
MLA:
Friedrich, Alexander, et al. "Bulky cationic β-diketiminate magnesium complexes." Dalton Transactions 48.17 (2019): 5560-5568.
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