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183W NMR study of alkenylcarbyne– and alkenylvinylidene–tungsten complexes

✍ Scribed by Rodrigo J. Carbajo; Lei Zhang; Fernando López-Ortiz

Publisher
John Wiley and Sons
Year
1998
Tongue
English
Weight
307 KB
Volume
36
Category
Article
ISSN
0749-1581

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✦ Synopsis

183W NMR data are reported for a series of alkenylvinylideneÈ and alkenylcarbyneÈtungsten complexes of the type and [(dppe)(CO) 3 WxCxCHR], [(dppe)(CO) 3 WyCwCHxCR 2 ]`BF 4 [dppe \ 1,2-bis(diphenylphosphino)ethane]. Spectra were recorded using [(dppe)(CO) 2 LWyCwCHxCR 2 ] inverse 2D 1H,183Wand 31P,183WM1HN-HMQC NMR spectroscopy without 183W decoupling.

In some examples of the alkenylcarbyne series minor amounts of the propenylcarbyne isomer were present and the corresponding 183W chemical shifts could also be characterized. For a given complex and measuring time the proton-detected correlation spectra based on the existing long-range coupling to the metal a †ords a higher signal-to-noise ratio than the phosphorus-detected correlation via 1J(183W,31P). Additionally, the tilt of cross peaks in the 1H,183W HMQC spectra reveals the relative sign of the coupling of these nuclei with phosphorus. 183W chemical shift variations for compounds (L \ CO, or halogen) are rational-

, CH 3 CN ized in terms of the n-acceptor ability of the ligand. Halogen derivatives show shielding decreases in the order F \ Cl \ Br \ I. For carbyne complexes a deshielding of the metal is observed with increase in the size of the carbocyclic ring substituent as a result of steric e †ects. For complexes (L \ CO, [(dppe)(CO) 2 LWyCwCHxCR 2 ] the phosphorusÈtungsten scalar coupling is also determined by the p-donor/n-acceptor ability and PMe 3 , CH 3 CN) bulkiness of the ligands.

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