Hydrogen scrambling processes in [Ta(η-C5Me5)(η-C5H5){(µ-H)2BH2}]: a surprising observation

Abstract

Quantitative phase-sensitive two-dimensional exchange n.m.r. spectra of [Ta(η-C₅Me₅)(η-C₅H₅)-{(µ-H)₂BH₂}] show that the observed scrambling of the terminal and bridging hydrogens of the (µ-H)₂BH₂ ligand proceeds by a dominant mechanism in which there is no direct exchange between the two terminal hydrogens. This has been interpreted in terms of an associative mechanism proceeding via an Ta{(µ-H)₃BH} intermediate accompanied by η⁵↔η³ shifts of the C₅ rings.