The reactivity of phosphaalkynes, the isolobal and isoelectronic congeners to alkynes, with metal alkylidyne complexes is explored in this work. Treating the tungsten alkylidyne [
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Tethered Alkylidenes for REMP from Carbon Disulfide Cleavage
Reactions between tungsten alkylidyne [tBuOCO]W≡CtBu(THF)2 1 and sulfur containing small molecules are reported. Complex 1 reacts with CS2 to produce intermediate η2 bound CS2 complex [O2C(tBuC═)W(η2-(S,C)-CS2)(THF)] 8. Heating complex 8 provides a mixture of a monomeric tungsten sulfido complex 9 and a dimeric complex 10 in a 4:1 ratio, respectively. Heating the mixture does not perturb the ratio. Addition of excess THF in a solution of 9 and 10 (4:1) converts 10 to 9 (>96%) with concomitant loss of (CS)x. Both 9 and 10 can be selectively crystallized from the mixture. An alternative synthesis of exclusively monomeric 9 involves the reaction between 1 and PhNCS. Demonstrating ring expansion metathesis polymerization (REMP), tethered tungsten alkylidene 8 polymerizes norbornene to produce cis-selective syndiotactic cyclic polynorbornene (c-poly(NBE)).
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- Award ID(s):
- 2154377
- PAR ID:
- 10530900
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- Inorganic Chemistry
- Volume:
- 63
- Issue:
- 26
- ISSN:
- 0020-1669
- Page Range / eLocation ID:
- 12207 to 12217
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract t BuOCO]W≡Ct Bu(THF)2(1 ) with phosphaalkyne (10 ) results in the formation of [O2C(t BuC=)W{η 2‐(P ,C )−P≡C−Ad}(THF)] (13‐ t BuTHF ) and [O2C(AdC=)W{η 2‐(P ,C )−P≡C−t Bu}(THF)] (13‐AdTHF ); derived from the formal reductive migratory insertion of the alkylidyne moiety into a W−Carenebond. Analogous to alkyne metathesis, a stable phosphametallacyclobutadiene complex [t BuOCO]W[κ 2‐C(t Bu)PC(Ad)] (14 ) forms upon loss of THF from the coordination sphere of either13‐ t BuTHF or13‐AdTHF . Remarkably, the C−C bonds reversibly form/cleave with the addition or removal of THF from the coordination sphere of the formal tungsten(VI) metal center, permitting unprecedented control over the transformation of a tetraanionic pincer to a trianionic pincer and back. Computational analysis offers thermodynamic and electronic reasoning for the reversible equilibrium between13‐ t Bu/AdTHF and14 . -
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Abstract The reactivity of phosphaalkynes, the isolobal and isoelectronic congeners to alkynes, with metal alkylidyne complexes is explored in this work. Treating the tungsten alkylidyne [
t BuOCO]W≡Ct Bu(THF)2(1 ) with phosphaalkyne (10 ) results in the formation of [O2C(t BuC=)W{η 2‐(P ,C )−P≡C−Ad}(THF)] (13‐ t BuTHF ) and [O2C(AdC=)W{η 2‐(P ,C )−P≡C−t Bu}(THF)] (13‐AdTHF ); derived from the formal reductive migratory insertion of the alkylidyne moiety into a W−Carenebond. Analogous to alkyne metathesis, a stable phosphametallacyclobutadiene complex [t BuOCO]W[κ 2‐C(t Bu)PC(Ad)] (14 ) forms upon loss of THF from the coordination sphere of either13‐ t BuTHF or13‐AdTHF . Remarkably, the C−C bonds reversibly form/cleave with the addition or removal of THF from the coordination sphere of the formal tungsten(VI) metal center, permitting unprecedented control over the transformation of a tetraanionic pincer to a trianionic pincer and back. Computational analysis offers thermodynamic and electronic reasoning for the reversible equilibrium between13‐ t Bu/AdTHF and14 . -
null (Ed.)The exceptionally π-basic metal fragments {MoTp(NO)(DMAP)} and {WTp(NO)(PMe3)} (Tp = tris(pyrazolyl)borate; DMAP = 4-(N,N-dimethylamino)pyridine) form thermally stable η2-coordinated complexes with a variety of electron-deficient arenes. The tolerance of substituted arenes with fluorine-containing electron withdrawing groups (EWG; −F, −CF3, −SF5) is examined for both the molybdenum and tungsten systems. When the EWG contains a π bond (nitriles, aldehydes, ketones, ester), η2 coordination occurs predominantly on the nonaromatic functional group. However, complexation of the tungsten complex with trimethyl orthobenzoate (PhC(OMe)3) followed by hydrolysis allows access to an η2-coordinated arene with an ester substituent. In general, the tungsten system tolerates sulfur-based withdrawing groups well (e.g., PhSO2Ph, MeSO2Ph), and the integration of multiple electron-withdrawing groups on a benzene ring further enhances the π-back-bonding interaction between the metal and aromatic ligand. While the molybdenum system did not form stable η2-arene complexes with the sulfones or ortho esters, it was capable of forming rare examples of stable η2-coordinated arene complexes with a range of fluorinated benzenes (e.g., fluorobenzene, difluorobenzenes). In contrast to what has been observed for the tungsten system, these complexes formed without interference of C–H or C–F insertion.more » « less
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