Isolation and Structural Characterization of Eightfold Protonated Octacyanometalates [M(CNH)8 ]4+ (M=MoIV , WIV ) from Superacids.

Malte Sellin,Moritz Malischewski,Valérie Marvaud

doi:10.1002/anie.202002366

Abstract

Octacyanometalates K4[Mo(CN)8] and K4[W(CN)8] are completely protonated in superacidic mixtures of anhydrous hydrogen fluoride and antimony pentafluoride. The resulting hydrogen isocyanide complexes [Mo(CNH)8]4+ [SbF6]− 4 and [W(CNH)8]4+ [SbF6]− 4 are the first examples of eight‐coordinate homoleptic metal complexes containing hydrogen isocyanide (CNH) ligands. The complexes were crystallographically characterized, revealing hydrogen‐bonded networks with short N⋅⋅⋅H⋅⋅⋅F contacts. Low‐temperature NMR measurements in HF confirmed rapid proton exchange even at −40 °C. Upon protonation, ν(C≡N) increases of about 50 cm−1 which is in agreement with DFT calculations.

Highlights

Octacyanometalates K4[Mo(CN)8] and K4[W(CN)8] are completely protonated in superacidic mixtures of anhydrous hydrogen fluoride and antimony pentafluoride
Advantage that even the formed AsF6À or SbF6À anions are very weak nucleophiles and much weaker ligands than the containing hydrogen isocyanide (CNH) ligands that are formed upon protonation
The comparison between the calculations for [M(CNH)8]4+, [M(NCH)8]4+, [M(CNH)8]4+·8 HF, and [M(NCH)8]4+·8 HF (M = Mo, W) with the reaction products was inconclusive. This is caused by the high ionic charges and strong hydrogen bonding which are insufficiently modeled in the calculations

Summary

Introduction

Octacyanometalates K4[Mo(CN)8] and K4[W(CN)8] are completely protonated in superacidic mixtures of anhydrous hydrogen fluoride and antimony pentafluoride. The fully protonated species [M(CNH)8] [SbF6]4 (M = Mo, W) are only The central metal is coordinated by eight (crystallographically different) protonated cyanide/ hydrogen isocyanide ligands (MÀCNH), resulting in a slightly distorted square-antiprismatic coordination geometry.

Results

Conclusion