# Why do the protons in pentacarbonylmethylmanganese show up at –0.21 ppm?

The $\ce{^1H}$ NMR of $\ce{Mn(CO)5CH3}$ shows a resonance at –0.21 ppm, which has to be due to the methyl group. Why are the protons so shielded?

I would have thought that all the pi backdonation from the Mn to the carbonyl would reduce the electron density on the $\ce{CH3}$, hence increasing the chemical shift.

• Agostic interactions can also shift H resonances upfield in OM compounds with alpha protons – StevieD Apr 22 '16 at 22:53
• ilpi.com/organomet/agostic.html – StevieD Apr 22 '16 at 22:57
• I thought of an agostic interaction, too. However, to me, Mn(CO)5Me doesn't seem to be a prime candidate for an agostic interaction, being coordinatively and electronically saturated. That said, I wouldn't know. – orthocresol Aug 8 '17 at 18:15