Codex @codex  0

 Incoming links: Triphenyl phosphite

The all-carbonyl hydride, HCo(CO) $_{4}$ , is more acidic. Loss of

H^{+}

gives

[Co (CO)_{4}]^{-}

, whose negative charge is stabilized by pi backbonding into four carbonyl ligands. Replacing one CO by triphenyl phosphite reduces the net electron-withdrawing character of the ligand set relative to four carbonyls. The substituted hydride is more electron rich and its conjugate-base anion is less stabilized against protonation.

HCo (CO)_{3} L ⇌ H^{+} + [Co (CO)_{3} L]^{-}, L = CO or P (OPh)_{3} .

Both conjugate bases have a conventional 18-electron count, so the difference is not a missing-electron argument. It is the relative stabilization of acid and base by the ligands in coordination chemistry. This concerns heterolytic deprotonation, not the homolytic Co–H bond-dissociation energy.

P (OPh)_{3}