(Dimethylamino) borylene and related complexes of electron-rich metal fragments : generation of nucleophile-resistant cations by spontaneous halide ejection
Author
Addy, David A.
Phillips, Nicholas
Pierce, Glesni A.
Vidović, Dragoslav
Krämer, Tobias
Mallick, Dibyendu
Jemmis, Eluvathingal D.
Reid, Gill
Aldridge, Simon
Date of Issue
2012School
School of Physical and Mathematical Sciences
Abstract
Spontaneous halide ejection from a three-coordinate Lewis acid has been shown to offer a remarkable new route to cationic metal complexes featuring a linear, multiply bonded boron-donor ligand. The exploitation of electron-rich [CpM(PR3)2] fragments within boryl systems of the type LnMB(hal)NR2 leads to the spontaneous formation in polar solvents of chemically robust borylene complexes, [LnM(BNR2)]+, with exceptionally low electrophilicity and short M–B bonds. This is reflected by M–B distances (ca. 1.80 Å for FeB systems) which are more akin to alkyl-/aryl-substituted borylene complexes and, perhaps most strikingly, by the very low exothermicity associated with the binding of pyridine to the two-coordinate boron center (ΔH = −7.4 kcal mol–1, cf. −40.7 kcal mol–1 for BCl3). Despite the strong π electron release from the metal fragment implied by this suppressed reactivity and by such short M–B bonds, the barrier to rotation about the Fe═B bond in the unsymmetrical variant [CpFe(dmpe)(BN{C6H4OMe-4}Me)]+ is found to be very small (ca. 2.9 kcal mol–1). This apparent contradiction is rationalized by the orthogonal orientations of the HOMO and HOMO-2 orbitals of the [CpML2]+ fragment, which mean that the M–B π interaction does not fall to zero even in the highest energy conformation.
Subject
DRNTU::Science::Physics
Type
Journal Article
Series/Journal Title
Organometallics
Collections
http://dx.doi.org/10.1021/om201144e
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