Synthesis, Spectroscopic and Theoretical Studies of Ruthenafuran and Osmafuran Prepared by Activation of Ynone in Alcohol

Abstract

Ruthenafuran and osmafuran monocationic complexes [Ru([14]aneS4)(C ∧ O)] + or [M(bpy) 2 (C ∧ O)] + (C ∧ O = anionic bidentate chelate [C(OR)CHC(Ph)O] − ; [14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane; M = Ru, Os; bpy = 2,2′-bipyridine) have been prepared from reactions between phenylynone HCC(CO)Ph and [Ru ([14]aneS4)Cl 2 ] or [M-(bpy) 2 Cl 2 ] in alcoholic solvents ROH. The formation of metal− vinylidene intermediate, followed by nucleophilic attack by RO − , and carbonyl group coordination to the metal center are believed to be the key steps in the formation of these metallafurans. The nature of the anionic C ∧ O ligand was investigated by electrochemical, spectroscopic, and theoretical means. ■ INTRODUCTIONActivation of alkynes for functional and novel organic products by transition-metal complexes is one of the most important topics in organometallic chemistry. 1 It is well documented that alkynes generally interact with d6-transition-metal centers through the formation of reactive yet sometimes isolable metal−vinylidene intermediates, which can further transform into other carbon-rich organometallic species including metal− acetylide, −acyl, −allenylidene, −alkoxycarbene, and −carbyne complexes, depending on the functionality of the alkynes and the reactants available in the reaction mixture. 2, 3 Our group has been scrutinizing the reactivity between a variety of organic substrates and structurally well-defined d6-transition-metal complexes, and the spectroscopic properties of the derived organometallic complexes. 4 As an extension of this research direction, we now present the reactivity of a specific type of alkyne, phenyl-ynone HCC(CO)Ph, toward [Ru([14]aneS4)Cl 2 ] and [M(bpy) 2 Cl 2 ] (M = Ru and Os; [14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane; bpy = 2,2′-bipyridine) in alcoholic solvents ROH. Our results reveal that the resultant products are metallafuran monocationic complexes [Ru([14]aneS4)(C ∧ O)] + and [M(bpy) 2 (C ∧ O)] + , where C ∧ O represents an anionic bidentate [C(−OR)CHC(−Ph) O] − chelate. It is worth mentioning that metallafuran and other members of metallacycles have received extensive attention in the field of organometallic and theoretical chemistry, 5,6 and the reactivity reported in this work may represent a general synthetic approach for different metallafurans. Moreover, the electronic properties of the ruthenafurans and osmafuran have been probed by electrochemical, spectroscopic, and theoretical studies. ■ RESULTS AND DISCUSSION Synthesis and Characterizations. Ruthenafuran and osmafuran monocationic complexes 1−3 have been prepared in high yield (50−80%) from reactions between phenyl-ynone HCC(CO)Ph and metal precursors [Ru([14]aneS4)Cl 2 ] or [M(bpy) 2 Cl 2 ] (M = Ru, Os) in alcoholic solvents (Scheme 1).These metallafuran complexes are air stable in both solution and solid forms. The alkoxy group attached to the C α is determined by the alcoholic solvent used (cf. synthesis of 1 and 1′). The carbenoid character for the M−C bonds is indicated by the low-field 13 C NMR ...

Ruthenium‐Induced Alkyne Cycloisomerization: Construction of Metalated Heterocycles, Revelation of Unconventional Reaction Pathways, and Exploration of Functional Applications

“…The first successful synthesis of metal-indolizine complexes 1a-1c was accomplished by reactionb etween the Ru II precursor [Ru( [9]aneS3)(bpy)(H 2 O)] 2 + and pyridine-substituted propargylic alcohols HCCC(OH)(2-py)R in water (Scheme 2a; [9]aneS3 = 1,4,7-trithiacyclononane). [4] It should be pointed out that the term "indolizine" here actually refers to "1,1-disubstituted 1H-indolizinium-2-yl" zwitterion.…”

“…The first metalated indolizinonec omplexes 3-5 were prepared from reactions between [Ru( [9]aneS3)(bpy)(H 2 O)] 2 + or [Ru( [14]aneS4)Cl 2 ]a nd pyridine-substituted ynones RCC(C= O)(2-py) (Scheme4;t he term "indolizinone" here referst o" 3monosubstituted 1-indolizinonium-2-yl" zwitterion). [7] As shown in the crystal structures,t he ynones cycloisomerize into indolizinones and behavea sm onodentate ligands coordinating through the C-2 ( Figure 2).…”

“…Reactions between the Ru II precursors and non-pyridine-substituteda lkyne substrates were performed to gain more mechanistic insight (Scheme6): (a) reaction between [Ru([9]-aneS3)(bpy)(H 2 O)] 2 + and HCCC(OH)Ph 2 in H 2 Oa fforded aR uacyl complex 6; [4] (b) reacting [Ru( [14]aneS4)Cl 2 ]w ithH C CC(OH)Ph 2 in MeOH yieldedaRu-methoxycarbene complex 7; [5] (c) ar uthenafuran complex 8 was obtained from reaction between [Ru( [14]aneS4)Cl 2 ]a nd HCC(C=O)Ph in MeOH. [9] Importantly, these reactions were reported to proceed via vinylidene-involving pathways. Given that reactions between the Ru precursors and the pyridine-substituted alkyne substrates shown in Schemes 2a nd 4y ielded Ru-indolizine or -indolizinone complexes 1-5 but not any Ru-vinylidened erived products according to Scheme 6, it is reasonable to postulate that 1-5 are formed from non-vinylidene-involving pathways exhibiting lower activation barriers.…”

“…Therefore, the vinylidene intermediacy should not be taken for granted regarding the mechanism in any Ru-mediated alkyne transformations. Scheme6.Reactions between [Ru( [9]aneS3)(bpy)(H 2 O)] 2 + or [Ru( [14]a-neS4)Cl 2 ]and non-pyridine substituted alkynes reportedw ith vinylidenei ntermediacy.…”

“…Some Ru-heterocyclic complexes also display interesting photoluminescent behavior.F or example, Ru-indolizine complex 1c exhibits luminescence in severalc ommon organic solvents (CH 3 CN, MeOH,a cetone) at approximately 630 nm upon photoexcitation (Figure 8), and its quantum yields (F)a nd lifetimes (t)a t2 98 Ka re approximately 10 À3 and 0.5 ms, respectively.T heoretical calculations suggested that the photoluminescenceo riginates from ad p (Ru II )!p*(bpy) triplet metal-toligand charge transfer ( 3 MLCT) excited state. Interestingly, 1c exhibits improved F andl onger t than its alkynyl analog [Ru( [9]aneS3)(bpy)(CCPh)] + (F = 5.44 10 À4 , t = 59 ns in degassed CH 3 CN), [16] presumablyb ecause the indolizine zwitterion serves as as tronger s-donor than the alkynyl ligand and thus elevate the metal-centered 3 dd quenching state at a greater extent. This example opens up opportunities of utiliz-Scheme10.…”