Coordination-Induced Weakening of a C(sp³)–H Bond: Homolytic and Heterolytic Bond Strength of a CH–Ni Agostic Interaction

Abstract

The scission of a C­(sp3)–H bond to form a new metal–alkyl bond is a fundamental step in coordination chemistry and catalysis. However, the extent of C–H bond weakening when this moiety interacts with a transition metal is poorly understood and quantifying this phenomenon could provide insights into designing more efficient C–H functionalization catalysts. We present a nickel complex with a robust adamantyl reporter ligand that enables the measurement of C–H acidity (pKa) and bond dissociation free energy (BDFE) for a C­(sp3)–H agostic interaction, showing a decrease in pKa by dozens of orders of magnitude and BDFE decrease of about 30 kcal/mol upon coordination. X-ray crystallographic data is provided for all molecules, including a distorted square planar NiIII metalloradical and “doubly agostic” NiII(κ2-CH2) complex