Conventional and unconventional alkyne activations by Ru and Os for unprecedented dimetalated quinolizinium complexes

Abstract

<p>Two types of unexpected quinolizinium complexes were obtained from the reactions between pyridine-functionalized propargylic alcohol HCCC(OH)(Ph)(CH₂(2-py)) (<bold>L1</bold>) and <italic>cis</italic>-[M(L^L)₂Cl₂] (M = Ru, Os; L^L = dppm, bpy).</p>

Ruthenafuran Complexes Supported by the Bipyridine-Bis(diphenylphosphino)methane Ligand Set: Synthesis and Cytotoxicity Studies

“…Although the formation of metal–vinylidene species via alkyne–vinylidene rearrangement has been regarded as a key step in Ru(II)-induced alkyne transformations, a number of our synthetic studies revealed that Ru(II) can also activate alkynes via “non-vinylidene” pathways [ 31 , 32 ]. With the aim to gain control on the modes of alkyne activation, we initiated research activities on probing and isolating intermediates and products from the reactions between functionalized alkynes and a variety of Fe(II), Ru(II) and Os(II) complexes [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. In 2015, we reported the synthesis of metallafuran complexes in the form of [M(bpy) 2 (C^O)] + from the reactions between cis -[M(bpy) 2 Cl 2 ] (M = Ru, Os; bpy = 2,2′-bipyridine) and ynone HC≡C(C=O)Ph in MeOH ( Scheme 1 a; C^O represents an anionic bidentate [ C (OMe)CHC(Ph) O ] − chelate, coordinating atoms in italics) [ 38 ].…”

“…In 2015, we reported the synthesis of metallafuran complexes in the form of [M(bpy) 2 (C^O)] + from the reactions between cis -[M(bpy) 2 Cl 2 ] (M = Ru, Os; bpy = 2,2′-bipyridine) and ynone HC≡C(C=O)Ph in MeOH ( Scheme 1 a; C^O represents an anionic bidentate [ C (OMe)CHC(Ph) O ] − chelate, coordinating atoms in italics) [ 38 ]. Later in 2019, we discovered that reactions between cis -[M(κ 2 -dppm) 2 Cl 2 ] (M = Ru, Os; dppm = 1,1-bis(diphenylphosphino)methane) and HC≡C(C=O)Ph in MeOH gave the phosphonium-ring-fused bicyclic metallafuran complexes in the form of [M(κ 2 -dppm)(P^C^O)Cl] + , but not [M(κ 2 -dppm) 2 (C^O)] + ( Scheme 1 b; P^C^O represents a neutral tridentate [(Ph) 2 P CH 2 P(Ph) 2 C CHC(Ph) O ] chelate) [ 44 ]. This striking difference in reactivity suggested the participation of dppm in the reaction and led us to examine the reactions between HC≡C(C=O)Ph and [Ru(κ 2 -L^L)(bpy)Cl 2 ], where L^L represents bidentate phosphine or arsine ligands.…”

Controlled Activation of Dipicolinyl-Substituted Propargylic Alcohol by Ru(II) and Os(II) for Unprecedented Indolizine-Fused Metallafuran Complexes

“…3,4 More recently, we reported the formation of 2methylpyridinium-functionalized metallafuran and M−quinolizinium complexes from the reactions between Ru(II)/Os(II) precursors and picolinyl-substituted propargylic alcohol HC CC(OH)(Ph)(CH 2 (2-py)), in which the former complexes were derived from non-vinylidene pathways. 5 Evidently, the presence and the nature of nucleophilic functionality on alkynes diversify the mode of Fe(II)/Ru(II)/Os(II)−alkyne interactions, and it is essential to control the selectivity of these modes (vinylidene vs non-vinylidene pathways) for rational molecular and catalytic designs.…”

“…The Ru−C bond distances (2.086( 6) and 2.113( 6) Å) and the bite angle of the κ 2 (C4,C6)-quinolizinium (64.2°) are comparable with the Ru−quinolizinium complex we reported recently. 5 Notably, complexes 1f and 2f represent new family members of the metallafuran family. In the last three decades, metallaaromatic compounds have been subjected to intensive synthetic, reactivity and theoretical studies by pioneers including Roper,Bleeke,Wright,Jia,Xia,and Zhu.…”

“…Similar elimination of the picoline group from picolinyl-substituted propargylic alcohol was recently reported. 5 However, the formation of q is established to go through a combination of vinylidene rearrangement, dehydration, and then 6-exo-dig cyclization to give a monometalated quinolizinium species and finally metalation at C6 of the quinolizinium to give dimetalated quinolizinium complexes (Scheme 3b). 5 Evidently, dipicolinyl-substituted propargylic alcohol L OH could be activated by cis-[Ru/Os(dppm) 2 Cl 2 ] via both non-vinylidene and vinylidene pathways.…”