Curious Case of Cobaltocenium Carbaldehyde

Abstract

Cobaltocenium carbaldehyde (formylcobaltocenium) hexafluoridophosphate, a long sought-after functionalized cobaltocenium salt, is accessible from cobaltocenium carboxylic acid by a three-step synthetic sequence involving (i) chlorination to the acid chloride, (ii) copper-borohydride reduction to the hydroxymethyl derivative, and (iii) Dess–Martin oxidation to the title compound. Due to the strongly electron-withdrawing cationic cobaltocenium moiety, no standard aldehyde reactivity is observed. Instead, nucleophilic addition followed by haloform-type cleavage prevails, thereby ruling out common useful aldehyde derivatization. One-electron reduction of cobaltocenium carbaldehyde hexafluoridophosphate affords the deep-blue, isolable cobaltocene carbaldehyde 19-valence-electron radical whose spin density is located fully at cobalt and not at the formyl carbon atom. 1H/13C NMR, IR, EPR spectroscopy, high-resolution mass spectrometry, cyclic voltammetry, single crystal structure analysis (XRD), and density functional theory are applied to characterize these unusual formyl-cobaltocenium/cobaltocene compounds.

A Versatile Comproportionation Route to Construct Mono‐Imido Trichlorido Complexes of Molybdenum(V) and Tungsten(V)

“…Compared to oxo complexes, the M−N distance in 5 is similar to (thio−)ether‐coordinated mono‐oxo complexes of tungsten(V) (1.729(12) Å [35] and 1.725(5) Å [36] ) or related complexes. However, BDI coordinated W V complexes show substantially shorter W−O distances (1.693(4) Å) [37] . Notably, a tert‐butylamine analogue of 5 , namely [W(N t Bu)Cl 3 (NH 2 t Bu)], [38] has been prepared by the reaction between WCl 6 and four equivalents of TMS‐NH t Bu however, the product could only be obtained in single crystal quantities contrasting the bulk preparation reported herein.…”