Tris borates with chromium

CHROMIUM ALKYLS WITH NITROGEN- AND OXYGEN-LIGANDS 3.1. Tris(pyrazolyl)borate complexes... 

In an attempt to change the electronics of the chromium atom, we are replacing the carbon based cyclopentadienyl ring with ligands containing harder donor atoms. For example, we have employed the tris(pyrazolyl)borate moiety, an isoclectronic replacement for Cp featuring tridentate N-coordination.[9] Figure 2 shows the molecular structure of Tp SU Cr-Ph, a representative Cr° alkyl. It will be noted, that this complex is mononuclear, due to the steric protection of the extremely bulky tris(pyrazolyl)borate. 

R = Me, Et, -Bu, CH2SiMc3, Ph). They feature short Cr-Cr distances ( 2.26A), low effective magnetic moments, and attenuated reactivity, all consistent with strong metal-metal bonding. Steric saturation of chromium with a sterically encumbered tris(pyrazolyl)borate ligand (i. e. =... 

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