om9b00481_si_002.xyz (46.33 kB)
Molybdenum and Tungsten Alkylidyne Complexes Containing Mono‑, Bi‑, and Tridentate N‑Heterocyclic Carbenes
dataset
posted on 2019-10-18, 15:36 authored by Iris Elser, Jonas Groos, Philipp M. Hauser, Maximilian Koy, Melita van der Ende, Dongren Wang, Wolfgang Frey, Klaus Wurst, Jan Meisner, Felix Ziegler, Johannes Kästner, Michael R. BuchmeiserNew tungsten and
molybdenum alkylidyne complexes bearing mono-,
bi-, and tridentate N-heterocyclic carbenes (NHCs)
have been synthesized. Formation of unprecedented structures in complexes
bearing N-tert-butyl substituents
on the imidazol(in)-2-ylidene was observed, leading to molybdenum
complexes containing an abnormal carbene (Mo-4) and a
bridging O,C,C-pincer ligand (Mo-10) and to a tungsten
complex containing a cationic imidazolinium-tagged alkoxide forming
an inner salt with an anionic tungsten center (W-5).
Both the abnormal carbene binding in Mo-4 and the O,C,C-pincer-type
structure of Mo-10 were confirmed by single-crystal X-ray
analysis, and the proposed structure of W-5 is supported
by the single-crystal X-ray structure of a minor byproduct (W-8) formed during the synthesis of W-4, displaying
the aforementioned inner-salt-like structure. The novel alkylidyne
complexes were also investigated for their capability to form a previously
postulated quasi-cationic species with a weakly coordinating anion
(WCA) during the alkyne homometathesis of 1-phenyl-1-propyne. Overall,
incorporation of bidentate and strongly σ donating NHCs as well
as introduction of better leaving groups did not lead to the expected
increase in catalytic activity. Despite identical ligand spheres,
changing from molybdenum to tungsten led to complete loss of activity
in the bidentate systems.