183W–1H long-range shift correlation and 1H NOESY studies on tungsten(II) hydrido–pyrazolylborate complexes
✍ Scribed by Joseph L. Templeton; Craig C. Philipp; Paul S. Pregosin; Heinz Rüegger
- Publisher
- John Wiley and Sons
- Year
- 1993
- Tongue
- English
- Weight
- 450 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
^183^W NMR spectra for several tungsten carbonyl complexes were recorded using heteronuclear multiple‐quantum spectroscopy. The measurements involved the use of both one‐bond and long‐range coupling constants, with the latter technique demonstrating a general approach to obtaining ^183^W spectra in Tp′ [Tp′ = tris(3,5‐dimethylpyrazolyl)borohydride] and Cp tungsten compounds. Differences in the ^183^W chemical shifts between the Tp′ and Cp complexes are explained in terms of σ‐donor and π‐acceptor capabilities of the ligands. It is suggested that the very small ^1^J(^183^W,^1^H) value of 7 Hz in WH(Tp′)(CO)~3~ arises from an interaction of an H^+^ with a [W(Tp′)(CO)~3~]^−^ orbital with a relatively large d‐component. For WH(Tp′)(CO)(PHCCMe) (3), the very lowfield hydride chemical shift, δ = 10.8, is suggested to arise, in part, from anisotropic effects. ^1^H NOESY measurements on 3 show that the hydride lies in a deshielding region with respect to both the acetylene and two pyrazolylborate rings, the acetylene is bent such that the CH~3~ and Ph groups move toward one another and there is a second isomer of 3, presumably related to the geometry of the coordinated acetylene with respect to the WCO bond.