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

Abstract

A series of η2-aldehyde complexes of pentaammineosmium(II) of the form [Os(NH3)5(L)](OTf)2 (L = formaldehyde (1), acetaldehyde (2), trimethylacetaldehyde (3), benzaldehyde (4), and crotonaldehyde (5), OTf = trifluoromethanesulfonate) are prepared and characterized. Treatment of these η2-bound aldehyde complexes with CH3OTf affords Fischer carbyne complexes 14−18 with typical yields ranging from 25−92%. Protonation (HOTf/MeCN) or methylation (MeOTf/DME) of many of these aldehyde complexes afford O-protonated or O-methylated η2-aldehydium intermediates, respectively, which over time convert to the corresponding carbyne complex. The chemistry of olefin-coordinated α,β-unsaturated aldehyde complexes is also explored.

Nitrilium ions – synthesis and applications

“…48 Other O-nucleophiles can also be used, such as olefin-bound η 2 -acrolein osmium(II) complexes in which the carbonyl oxygen attacks the nitrilium ion, resulting in a η 3 -vinyl osmium complex. 49 The reaction of N-aryl-1-SbCl 6 , 43a N-alkyl-1-FeCl 4 , 50 and 1-OTf, 27b with primary or secondary amines gives amidines 29 upon deprotonation of the amidinium intermediate (Scheme 4b). The power of this method was demonstrated by Gordon et al for the high-yield synthesis of otherwise inaccessible N-tert-butylamidines as precursors for bulky amidinate ligands.…”

Coordination of α,β-unsaturated aldehydes on d6 Ru and Rh complexes: A DFT study

“…Depending on the number of ligands, the coordination can change from g 2 CC to g 4 [18][19][20]. In rare cases the g 2 CO coordination has been found with Re and Os complexes [21,22]. In these cases, the g 2 CO complex is the kinetic one, which means that it is produced first and is transformed into the thermodynamic complex g 2 CC.…”

The Asymmetric π-Bases fac-{Re(dien)(PPh3)(PF3)}+ and fac-{Re(dien)(PPh3)(CO)}+: Evidence for Formation of an η2-Furan Complex

“…Each of these compounds exhibits a cyclic voltammogram (DMAc at 100 mV/s) with a broad, chemically irreversible anodic peak between 0.6 and 0.9 V (NHE) as well as a methine resonance between 70 and 75 ppm in their 13 C NMR spectrum. These signals are shifted upfield by approximately 5−10 ppm relative to the analogous {Os(NH 3 ) 5 } 2+ complexes . The acetaldehyde complex 7 exhibits the most diagnostic 1 H NMR spectrum, since the bound aldehyde proton (which overlaps with dien resonances) is easily distinguished by its coupling to the methyl group.…”

“…The identification of the bound aldehyde proton for the benzaldehyde complex 8 (4.5 ppm) was accomplished by deuterating the amine protons with ( i Pr) 2 (Et)N in MeOD. Attempts to generate the olefin-bound isomer of fac -[Re(η 2 -crotonaldehyde)(dien)(PPh 3 )(PF 3 )][OTf] ( 9 ) by a protonation/deptotonation sequence similar to that used for osmium(II) failed for the rhenium system . Coordination of 2-thiophenecarboxaldehyde also occurs through the carbonyl group, although this compound was not obtained in an analytically pure form.…”