Isomerization of Internal Alkynones to Vinylidenes in Tris(pyrazolyl)borate Ruthenium Complexes. Solution and Solid-State Kinetics

DFT calculations bring insight to internal alkyne-to-vinylidene transformations at rhodium PNP- and PONOP-pincer complexes

Through DFT calculations, the equilibrium between Rh–alkyne and Rh–vinylidene species of PXNXP pincer ligated Rh cationic complexes is shown to be tuned by the P–Rh–P bite angle, which in turn is dictated by the nature of the X moiety of the pincer ligand.

Synthesis of lactone-fused pyrroles by ruthenium-catalyzed 1,2-carbon migration-cycloisomerization

A ruthenium-catalyzed cycloisomerization of 3-amino-4-alkynyl-2H-chromen-2-ones via 1,2-carbon migration was developed. Various 1-arylchromeno[3,4-b]pyrrol-4(3H)-ones were synthesized in good to excellent yields. The reaction was applied to the formal total synthesis of marine natural products Ningalin B and Lamellarin H. The efficient synthesis of γ-butyrolactone-fused pyrrole derivatives was also achieved.

Isolation of a C3-metalated indolizine complex and a phosphonium ring-fused bicyclic metallafuran from the osmium-induced transformation of pyridine-tethered alkynes

The first C3-metalated indolizine complex was prepared from the reaction between cis-[Os(dppm)2Cl2] (dppm = 1,1-bis(diphenylphosphino)methane) and propargylic pyridine, HC[triple bond, length as m-dash]CC(OH)(2-py)2. A phosphonium ring-fused bicyclic osmafuran complex was also prepared from the reaction between cis-[Os(dppm)2Cl2] and pyridyl ynone, HC[triple bond, length as m-dash]C(C[double bond, length as m-dash]O)(2-py). The formation of these two products revealed the intermediacy of metal-vinylidene species regarding [Os(dppm)2Cl]+-mediated alkyne transformations. Comparison of the d6 transition-metal precursors employed to activate HC[triple bond, length as m-dash]CC(OH)(2-py)2 suggests that precursors with higher π-basicity favor the vinylidene-involving pathway.

Intermolecular Dehydrative Coupling and Intramolecular Cyclization of Ruthenium Vinylidene Complexes Formed from Aromatic Propynes Containing Carbonyl Functionalities

A remarkable intermolecular dehydrative coupling reaction with the formation of a C-C bond was found for the vinylidene complex 2 a, yielding the dinuclear bisvinylidene complex 4 a. Complex 2 a containing 1-hydroxyindan moiety was first formed from the reaction of o-propynyl benzaldehyde 1 a with [Ru]-Cl ([Ru]=Cp(PPh₃ )₂ Ru) by a cyclization process. For analogous aldehyde 1 b containing an additional 1,3-dioxolane group on the aryl ring, similar intermolecular coupling yields the dinuclear bisvinylidene complex 4 b. However, the fluoro group on the aryl ring in aldehyde 1 c inhibits the coupling reaction, giving only the vinylidene complex 2 c. For the reactions of [Ru]-Cl in MeOH with compounds 1 f, 1 g and 1 h, each with a ketone functionality, cyclization gives vinylidene complexes 2 f, 2 g and 2 h, respectively. However, no similar intermolecular coupling was observed, instead, the intramolecular dehydration yields 8 f, 8 g and 8 h, respectively. In CDCl₃ , catalytic cyclization is observed for the o-propynylphenyl ketone 1 h with [Ru]-Cl at 50 °C giving the isochromene products 14 h. Furthermore, treatment of the o-propynylaryl α,β-unsaturated ketones 1 k-m and 1 n with [Ru]-Cl in MeOH affords the corresponding vinylidene complexes 10 k-m and 11 n each with 1-benzosuberone moiety in the presence of NH₄ PF₆ . These intramolecular cyclization products were formed by the addition of Cβ onto the terminal carbon of the alkene moiety. All these reaction products were characterized by spectroscopic methods. In addition, structures of complexes 4 a, and 10 l were confirmed by single crystal X-ray diffraction analysis.

Aromatic alkyne insertion into six-membered cyclometalated pyridine complexes of iridium: different insertion modes and structurally novel products

Reactions of 2-benzoylpyridine or 2-benzylpyridine with [Cp*MCl₂]₂ (M = Ir, Rh) have been carried out in the presence of NaOAc in refluxing methanol, which form the corresponding six-membered cyclometalated products (1–3) except for the reaction of 2-benzylpyridine with [Cp*RhCl₂]₂. Insertion reactions of two six-membered cyclometalated pyridine iridium complexes (1 and 2) with terminal or internal aromatic alkynes were studied. Terminal alkynes p-XC₆H₄C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH (X = H, MeO, and F) with 1 give the corresponding five- and seven-membered doubly cycloiridated complexes 4a–c, internal alkynes p-XC₆H₄CCC₆H₄X-p (X = H, MeO, and Br) form the similar five- and seven-membered doubly cycloiridated complexes (5a,b) and/or di-insertion products (6a,c), whereas the acyl alkyne PhCCCOPh affords the novel spiro-metalated complex 7. For complex 2, internal alkynes p-XC₆H₄CCC₆H₄X-p (X = H, MeO, and Br) form similar five- and seven-membered doubly cycloiridated complexes (8a–c). However, in the case of PhCCCOPh, the reaction gives the novel four-membered cyclometalated complex 9. These results suggest that the products formed by alkyne insertion reactions of the six-membered cycloiridated pyridine complexes are very diverse. Plausible pathways for the formation of these novel insertion products were proposed. Molecular structures of seven cyclometalated complexes were determined by X-ray diffraction.

Insertion reactions of aromatic alkynes into the Ir–C bond of six-membered cycloiridated complexes formed various novel products via different insertion modes.

Ruthenium-Catalyzed Cycloisomerization of 2-Alkynylanilides: Synthesis of 3-Substituted Indoles by 1,2-Carbon Migration

We developed ruthenium-catalyzed cycloisomerization of alkynylanilides that gave 3-substituted indoles in high yields. The reaction proceeded via the disubstituted vinylidene ruthenium complex that was formed by the 1,2-carbon migration.

Allenyl esters as quenching agents for ruthenium olefin metathesis catalysts

In the attempt to synthesize substituted allenyl esters through a metathesis coupling of unsubstituted allenyl esters and alkenes using a variety of ruthenium catalysts, it was discovered that allenyl esters themselves cleanly arrested the activity of the catalysts. Further studies suggests possible utility of allene esters as general quenching agents for metathesis reactions. To explore this idea, several representative olefin metathesis reactions, including ring closing, were successfully terminated by the addition of simple allenyl esters for more convenient purification.

Amide-Directed Formation of Five-Coordinate Osmium Alkylidenes from Alkynes

The amide-directed synthesis of five-coordinate osmium alkylidene derivatives from alkynes is reported. These types of complexes, which have been elusive until now because of the tendency of osmium to give hydride alkylidyne species, are prepared by reaction of the dihydride OsH₂Cl₂(PⁱPr₃)₂ (1) with terminal alkynes containing a distal amide group. Complex 1 reacts with N-phenylhex-5-ynamide and N-phenylhepta-6-ynamide to give OsCl₂{=C(CH₃)(CH₂)_nNH(CO)Ph}(PⁱPr₃)₂ (n = 3 (2), 4 (3)). The relative position of carbonyl and NH groups in the organic substrates has no influence on the reaction. Thus, treatment of 1 with N-(pent-4-yn-1-yl)benzamide leads to OsCl₂{=C(CH₃)(CH₂)₃NHC(O)Ph}(PⁱPr₃)₂ (4). The new compounds are intermediate species in the cleavage of the C–C triple bond of the alkynes. Under mild conditions, they undergo the rupture of the C_α–CH₃ bond of the alkylidene, which comes from the alkyne triple bond, to afford six-coordinate hydride–alkylidyne derivatives. In dichloromethane, complex 2 gives a 10:7 mixture of OsHCl₂{≡C(CH₂)₃C(O)NHPh}(PⁱPr₃)₂ (5) and OsHCl₂{≡CCH(CH₃)(CH₂)₂C(O)NHPh}(PⁱPr₃)₂ (6). The first complex contains a linear separation between the alkylidyne C_α atom and the amide group, whereas the spacer is branched in the second complex. In contrast to the case for 2, complex 4 selectively affords OsHCl₂{≡C(CH₂)₃NHC(O)Ph}(PⁱPr₃)₂ (7). In spite of their instability, these compounds give the alkylidene–allene metathesis, being a useful entry to five-coordinate vinylidene complexes, including the dicarbon-disubstituted OsCl₂(=C=CMe₂)(PⁱPr₃)₂ (8) and the monosubstituted OsCl₂(=C=CHCy)(PⁱPr₃)₂ (9).

Organometallic synthesis, reactivity and catalysis in the solid state using well-defined single-site species

Acting as a bridge between the heterogeneous and homogeneous realms, the use of discrete, well-defined, solid-state organometallic complexes for synthesis and catalysis is a remarkably undeveloped field. Here, we present a review of this topic, focusing on describing the key transformations that can be observed at a transition-metal centre, as well as the use of well-defined organometallic complexes in the solid state as catalysts. There is a particular focus upon gas-solid reactivity/catalysis and single-crystal-to-single-crystal transformations.

Organometallic chemistry of ethynyl boronic acid MIDA ester, HCCB(O2CCH2)2NMe

The reactions of HCCBMIDA (BMIDA = B(O₂CCH₂)₂NMe) with a range of ruthenium complexes examples of σ-alkynyl, σ-alkenyl and vinylidene complexes bearing 4-coordinate boron substituents.

Competition between vinylidene rearrangement and 1,2-insertion of carbon-disubstituted internal alkynes at a Cp*Ir(iii) complex

Competition between vinylidene rearrangement/1,1-insertion and 1,2-alkyne insertion into the Ir–Ar bond of [Cp*Ir(ppy-F₄)]⁺ was observed on reaction with diarylacetylenes. The former process afforded the 9-membered iridacycle via the subsequent 1,4-Ir migration.

Picolyl-NHC hydrotris(pyrazolyl)borate ruthenium(II) complexes: synthesis, characterization, and reactivity with small molecules

Ruthenium(II) hydrotris(pyrazolyl)borate chloro complexes bearing picolyl-functionalized N-heterocyclic carbenes [TpRu(κ(2)-C,N-picolyl-(R)I)Cl] (picolyl-(Me)I = 3-methyl-1-(2-picolyl)imidazol-2-ylidene) (1a), picolyl-(iPr)I = 3-isopropyl-1-(2-picolyl)imidazol-2-ylidene (1b), picolyl-(Me)45DClI = 3-methyl-1-(2-picolyl)-4,5-dichloroimidazol-2-ylidene (1c), picolyl-(Ph)I = 3-phenyl-1-(2-picolyl)imidazol-2-ylidene (1d), picolyl-(Me)BI = 3-methyl-1-(2-picolyl)benzoimidazol-2-ylidene (1e)) have been synthesized and characterized. Furthermore, cationic carbonyl derivatives 2a-e have been prepared, characterized, and used to study the donor properties of the picolylcarbene ligands (picolyl-(R)I) via infrared spectroscopy. Also, the reactivity of the 16-electron species [TpRu(κ(2)-C,N-picolyl-(R)I)](+), in situ generated using NaBAr(F)4 (Ar(F) = 3,5-bis(trifluoromethyl)phenyl) as a halide scavenger, toward N2, CH3CN, H2, CH2CH2, S8, and O2 was studied indicating a strong influence of the NHC wingtip and backbone substituents in the product distribution. The crystal structures of [TpRu(κ(2)-C,N-picolyl-(iPr)I)Cl] (1b), [TpRu(κ(2)-C,N-picolyl-(Me)I)CO][BAr(F)4] (2a), [TpRu(κ(2)-C,N-picolyl-(Ph)I)CO][BAr(F)4] (2d), [{TpRu(κ(2)-C,N-picolyl-(Me)I}2(μ-N2)][BAr(F)4]2 (3'a), [{TpRu(κ(2)-C,N-picolyl-(Ph)I)}2(μ-N2)][BAr(F)4]2 (3'd), [TpRu(κ(2)-C,N-picolyl-(iPr)I)(η(2)-CH2CH2)][BAr(F)4] (5b), and [{TpRu(κ(2)-C,N-picolyl-(Me)I)}2(μ-S2)][BAr(F)4]2 (6) are reported.

Reactions of ruthenium-allenylidene complexes tethering a cyclopropyl group

Two cyclopropyl allenylidene complexes [Ru]=C=C=C(R)(C(3)H(5)) ([Ru]=[RuCp(PPh(3))(2)], Cp=Cyclopentadienyl; R=thiophene (2a) and R=Ph (2b)) are prepared from the reactions of [Ru]Cl with the corresponding 1-cyclopropyl-2-propyn-1-ol in the presence of KPF(6). Thermal treatment, halide-anion addition, and palladium-catalyzed reactions of 2a and 2b all lead to a ring expansion of the cyclopropyl group, giving the vinylidene complexes 4a and 4b, respectively, each with a five-membered ring. This ring expansion proceeds by C-C bond formation between Cβ of the cumulative double bond and a methylene group of the cyclopropyl ring. In the reaction of 2a with pyrrole, consecutive formation of two C-C bonds, one between C-2 of pyrrole and Cγ of 2a and the other between C-3 of pyrrole and Cα, results in the formation of 6a. The reaction proceeds by addition of pyrrole and 1,3-proton shifts. The hydrogenation of 2a by NaBH(4) is carried out in different solvents. The cumulative double bonds are reduced regioselectively to give a mixture of 7a and 8a. Interestingly, use of different solvents leads to different ratios of 7a and 8a. Presence of a protic solvent like methanol in dichloromethane or chloroform solution increases the yield of 8a, thus revealing that both the rates of hydroboration and deboronation increase. The structures of two new complexes 4a and 6a have been firmly established by X-ray diffraction analysis.