η1-Vinylidene to η2-Alkyne Isomerization of Tungsten and Molybdenum Complexes

✍ Scribed by Junes Ipaktschi; Javad Mohsseni-Ala; Sascha Uhlig

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 175 KB
• Volume: 2003
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/ejic.200300314

✦ Synopsis

Abstract

The thermal isomerizations of η^1^‐vinylidene complexes [(η^5^‐C~5~H~5~)(CO)(NO)W=C=CHR] [5a, R = Si(CH~3~)~2~C(CH~3~)~3~; 5c, R = C(CH~3~)~3~] as well as [(η^5^‐C~5~H~5~)(CO)(NO)Mo=C=CHC(CH~3~)~3~] (8), to the corresponding η^2^‐1‐alkyne complexes [(η^5^‐C~5~H~5~)(CO)(NO)W(η^2^‐H−C≡C−R)] [7a, R = Si(CH~3~)~2~C(CH~3~)~3~; 7c, R = C(CH~3~)~3~] and [(η^5^‐C~5~H~5~)(CO)(NO)Mo{η^2^‐H−C≡C−CHC(CH~3~)~3~}] (9) has been investigated. Activation parameters for the isomerization of 5a in [D~6~]benzene and 8 in [D~8~]toluene and [D~5~]ethanol were determined. In [D~8~]toluene η^1^‐vinylidene complex 5a undergoes a single step 1,2‐shift of the silyl group from C~β~ to C~α~. However, complex 8 shows dichotomous behavior. The isomerization 8 ⇄ 9, dependent upon the solvent applied, occurs by means of two different pathways: in a nonpolar solvent, 8 tautomerizes via the 1,2‐migration of the hydrogen atom to 9 and in ethanol this tautomerization proceeds by a multi‐step process via deprotonation‐protonation and subsequent reductive elimination. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)