Electrophilic Attack on the Carbon Terminus of a Niobium-Bound Formaldehyde Ligand

Abstract

The niobocene formaldehyde complex Cp′ 2 Nb-(Cl)(η 2 -CH 2 O) (1, Cp′ ) η 5 -C 5 H 4 SiMe 3 ) reacts with [Ph 3 C][BF 4 ] to give an alkoxide (2) of formula [Cp′ 2 Nb-(Cl)(OCH 2 CPh 3 )][BF 4 ] and with HBF 4 ‚OEt 2 to give analogue 4 ([Cp′ 2 Nb(Cl)(OMe)][BF 4 ]); these processes constitute examples of electrophilic attack on the formaldehyde carbon, instead of the more typical addition at oxygen. Compound 2 is hydrolyzed to Cp′ 2 Nb(Cl)-(OBF 3 ) (3), a Lewis acid adduct of the corresponding metal oxide; both 2 and 3 have been characterized by X-ray crystallography.

Effects of the Niobium(V) Center on the Energetics of Ligand-Centered Proton and Hydrogen Atom Transfer Reactions in Acyl and Alkoxide Complexes

“…This is consistent with structural data on an alkoxide analogue, which shows a Nb−O−C bond angle of 148.26(12)° 14b…”

“…The cationic methoxy−niobium compound 3 was prepared by protonation of the known η 2 -formaldehyde complex 4 …”

Trapping Unstable Terminal Ta−O Multiple Bonds of Monocyclopentadienyl Tantalum Complexes with a Lewis Acid

“…The O−B bond distance of 1.546(4) Å is within the range observed for neutral oxo−borane compounds (1.496−1.591 Å) , and the Ta−O−B angle deviates slightly from linearity (169.6(2)°), probably due to the steric requirements of the Cp* and B(C 6 F 5 ) 3 ligands. This value contrasts with the Nb−O−B angle in [NbCp 2 ‘Cl(O·BF 3 )] (140.07°), where a bond order of 2 was proposed to abide by the 18-electron rule.

1 ORTEP diagram of [TaCp*Cl 2 {O·B(C 6 F 5 ) 3 }] ( 1 ).

…”

Electrophilic Addition to η2-Aldehyde Complexes of Pentaammineosmium(II): The Formation of Fischer Carbyne Complexes via η2-Aldehydium Intermediates

“…Thus, aldehyde complexes and those reactions which link these species to other proposed intermediates of the Fischer−Tropsch process have been the subject of numerous investigations . While nucleophiles generally add to the carbonyl carbon of η 1 -aldehyde complexes, electrophilic addition can occur in η 2 -aldehyde complexes either at the carbonyl oxygen or the carbon . Significantly, several groups have observed cleavage of the metal−oxygen bond upon treatment of an η 2 -formaldehyde complex with an electrophile.…”