Activation of Heteroatom-Functionalized Alkynes by d6 Transition-Metal Complexes


Student thesis: Doctoral Thesis

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Award date29 Jun 2021


Metallafuran complexes with a fused five-membered phosphonium ring (complexes: 1 and 2) were synthesized from reactions between terminal ynones HC≡C(C=O)R and cis-[Ru/Os(dppm)2Cl2] (dppm = 1,1-bis(diphenylphosphino)methane). A metal-vinylidene-involving pathway was found to be an energetically feasible formation mechanism for these complexes. Overall, this work provides structural and mechanistic insights for the rational design of functional metallacycles via activation of alkynes by RuII and OsII centers.

Two types of unexpected quinolizinium complexes were obtained from the reactions between pyridine-functionalized propargylic alcohol HCRCC(OH)(Ph)(CH2(2-py)) (L1) and cis-[M(L^L)2Cl2] (M = Ru, Os; L^L = 1,1-bis(diphenylphosphino)methane (dppm), 2,2’-bipyridine (bpy)). Their molecular structures revealed that L1 can be activated by Ru and Os via the conventional "vinylidene-involving" or unconventional "non-vinylidene-involving" pathways.

Indolizine-fused metallafuran and metal−quinolizinium complexes were synthesized from reactions between dipicolinyl-substituted propargylic alcohol HC≡CC(OH)(CH2(2-py))2 and cis-[Ru/Os(dppm)2Cl2] (dppm = 1,1-bis(diphenylphosphino)methane), revealing the operation of both non-vinylidene and vinylidene pathways regarding the Ru(II)/Os(II)−alkyne interactions. Strategies to control the selectivity of these two competitive pathways were successfully developed, paving ways to the rational design of Ru/Os-induced alkyne activations and new metallacycles.

A series of unprecedented ruthena-halo-cyclic complexes featuring five-membered Ru−X−C−N−C rings (X = F, Cl, Br) that are ortho- and peri-fused to quinolizinium skeletons were serendipitously prepared from the reactions between halo-substituted picolinyl propargylic alcohols and phosphine-ligated Ru(II) precursors. Preparation of analogous osma-bromo-cyclic complex suggested a vinylidene-involving pathway as the formation mechanism of these metalla-halo-cycles. Crystal structures of these metalla-halo-cycles revealed lateral interactions of the covalently bonded X with the electrophilic Ru(II)/Os(II) centers, consistent with the directional preference of halogen-bonding interactions. The X in the M−X−C bonds are prone to substitution as demonstrated by the facile formation of quinolizinium-fused ruthenaoxazole from the ruthena-halo-cyclic complexes in methanolic NaOH solution at room temperature.