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Effects of a Nonligating Pendant Hydrogen-Bonding Group in a Metal Complex:  Stabilization of an HF Complex

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journal contribution
posted on 02.04.1999, 00:00 authored by Dong-Heon Lee, Hye J. Kwon, Ben P. Patel, Louise M. Liable-Sands, Arnold L. Rheingold, Robert H. Crabtree
An amino group has been appended to a benzoquinolinato ligand (bq-NH2 or bq-NH(i-Pr)) in such a way that it can hydrogen bond to a ligand that is also bound to the metal. The effects of this two-point binding are studied. The complexes [(bq-NHR)IrH(L)(PPh3)2]BF4 (R = H, i-Pr) were synthesized where L = H2O, F. The hydrogen-bonding pattern in the water complex is probed by crystallographic, IR, and NMR studies. The fluoro complexes protonate at −90 °C to give unstable hydrogen fluoride complexes, characterized by NMR (1JHF = 440 Hz, bq-NH2; 430 Hz, bq-NH(i-Pr)). Comparison with results for the corresponding bq-H and bq-CH3 species suggests that the hydrogen bonding provided by the pendant amino group is the key factor that allows stabilization of the HF complex, a previously unknown species. Crystal structures of an aqua and a fluoro derivative are reported.