Carbonyl Ligands Research Articles

Bridging Carbonyl and Carbyne Complexes of Weak-Field Iron: Electronic Structure and Iron-Carbon Bonding.

Carbon monoxide inhibited forms of nitrogenases have carbonyl (CO) and carbide (C4-) bridges, which are common in synthetic iron complexes with strong-field ligand environments but rare in iron sites with weak-field ligand environments analogous to the enzyme. Here, we explore the fundamental bonding description of bridging CO in high-spin iron systems. We describe the isolation of several diiron carbonyls and related species, and elucidate their electronic structures, magnetic coupling, and characteristic structural and vibrational parameters. These high-spin iron complexes exhibit equivalent π-backbonding abilities to low-spin iron complexes. Sequential reduction and silylation of a formally diiron(I) bridging CO complex ultimately gives a formally diiron(IV) bridging carbyne complex. Despite the large range of formal oxidation states across this series, X-ray absorption spectroscopy and density functional theory calculations indicate that the electron density at the iron sites does not change. Thus, the [Fe(μ-CO)]2 core undergoes redox changes at the bridging carbonyls rather than the metal centers, rendering the metal's formal oxidation state misleading. The ability of the Fe2C2 core to easily shift charge between the metals and the ligands has implications for nitrogenases, and for other multinuclear systems for redox catalysis.

Crystal structures of two polymorphs for fac-bromidotricarbonyl[4-(4-methoxyphenyl)-2-(pyridin-2-yl)thiazole-κ2 N,N′]rhenium(I)

Crystallization of the title compound, fac-[ReBr(ppt-OMe)(CO)3] (ppt-OMe = C15H12N2OS), from CH2Cl2/n-pentane (1:5 v/v) at room temperature gave two polymorphs, which crystallize in monoclinic (P21/c; α form) and orthorhombic (Pna21; β form) space groups. The ReI complex molecules in either polymorph adopt a six-coordinate octahedral geometry with three facially-oriented carbonyl ligands, one bromido ligand, and two nitrogen atoms from one chelating ligand ppt-OMe. In the crystal, both polymorph α and β form di-periodic sheet-like architectures supported by multiple hydrogen bonds. In polymorph α, two types of hydrogen bonds (C—H...O) are found while, in polymorph β, four types of hydrogen bonds (C—H...O and C—H...Br) exist.

Bismuth Bound to Transition Metals: Visible-Light-Induced Olefin Coordination, Reductive Elimination, and Oxidative Addition.

A series of dibenzobismepinyl (C14H10Bi) substituted transition metal complexes of the type [(C14H10Bi)M(CO)x(L)] (M = Mn, Co, Fe) was prepared in salt elimination reactions from a halobismepine and sodium metallates. Irradiation of these complexes with visible light has been investigated, aiming at the elimination of one carbonyl ligand and the concomitant coordination of the bismepine's olefin moiety to the transition metal center. The resulting complexes of the type [{κ2C,κ1Bi-(C14H10)Bi}M(CO)x-1(L)] (M = Co, Fe) have been isolated and fully characterized. When two dibenzobismepinyl units are positioned in the coordination sphere of an iron carbonyl complex fragment, reductive elimination / oxidative addition events of the dibismuthane (C14H10Bi)2 have been shown to be relevant. The analytical techniques applied in this work include (heteronuclear) NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction analysis, UV/Vis spectroscopy, IR spectroscopy and (TD)-DFT calculations.

Structural and Solution Speciation Studies on fac-Tricarbonylrhenium(I) Complexes of 2,2'-Bipyridine Analogues.

In this study, we report the synthesis and characterization of 12 novel rhenium(I) complexes with the general formula fac-[Re(CO)3(NN)X]n+ where (NN) is a 2,2'-bipyridine analogue ligand, X = Cl-, Br-, or H2O, and n = 0 or 1, focusing on their speciation in an aqueous solution. The prepared organorhenium complexes are stable in a wide pH range in an aqueous solution, and no release of the bidentate ligands or the carbonyl ligands was observed. The stability of the complexes in various biologically relevant matrices (cell culture medium and real blood serum) was also demonstrated. However, the simultaneous substitution of the halido ligand by water and slow hydrolysis of the ester bonds in the ligands were observed, affecting both the solubility and the lipophilicity of the compounds. The aqua complexes became more lipophilic in the presence of chloride ions, while the hydrophilicity increased significantly with time due to the hydrolysis of the ester bonds, which probably contributed to their weak pharmacological activity. The results also showed kinetically hindered aqueous solvation of the halido complexes and low chloride ion affinity of the aqua complexes. The deprotonation of the coordinated aqua ligand in the complexes occurs in the pH = 7-10 range, leading to significant formation (18-30%) of hydroxido species at pH = 7.4. The halido complexes showed somewhat higher cytotoxicity (IC50 = 60-99 μM) on human colon adenocarcinoma cancer cells (Colo205 and Colo320) than the corresponding aqua complexes (IC50 > 100 μM). In all cases, no antibacterial effect was observed (MIC > 100 μM), but some of the complexes showed moderate antiviral activity (IC50 ∼ 50 μM) on Herpes simplex virus 2.

Iron Complexes of 4,5-Bis(diorganophosphinomethyl)acridine Ligands.

The search for an iron analog of the established ruthenium-based catalysts containing methylene-extended 4,5-bis(diorganophosphinomethyl)acridine ligands, [FeHCl(CO)(LR)], resulted in the discovery of a bidentate coordination mode of these usually tridentate pincer ligands toward iron. The acridines nitrogen atom does not coordinate to iron, leading to the formation of iron diphos-type complexes with unusually large cis bite angles of up to 124° as well as trans bite angles around 155°. The iron-containing complexes [FeCl2(κ2-LR)] (R = iPr, Ph), [FeX2(κ2-LCy)] (X = Cl, Br) and [Fe(CO)3(κ2-LR)] (R = iPr, Cy) have been isolated in crystalline form and characterized by spectroscopic methods and mass spectrometry. Their structures were verified unambiguously through X-ray diffraction. The stability of the iron(II) complexes decreased in the order Cy > Ph > iPr and Cl > Br > I, although all iron(II) complexes were found to be relatively stable enough for short-term handling in air in the solid state. Notably, no iron(0) complex of the phenyl derivative could be isolated. The iron(0) complex [Fe(CO)3(κ2-LCy)] was found to be significantly more stable toward hydrolysis and oxygen compared to [Fe(CO)3(κ2-LiPr)] and can be stored in air for months without significant decomposition in the solid state, while [Fe(CO)3(κ2-LiPr)] decomposes in air within seconds. The decomposition products [FeI2(κ2-O2LCy)], [{Fe(CO)3(κ2-HLR)}2] (R = iPr, Cy) and [FeCl2(CO)2(κ1-LCy)(κ1-OLCy)] were identified and characterized crystallographically. The iron(0) complex [Fe(CO)3(κ2-LCy)] is oxidized by [Fe(Cp)2](BPh4) to give the paramagnetic, low-spin iron(I) cation [Fe(CO)3(κ2-LCy)]+. The electron paramagnetic resonance spectrum of the highly sensitive cation as well as density functional theory calculations suggest a partial delocalization of the unpaired electron over the three carbonyl ligands and the acridines aromatic ring system. The catalytic activity and photophysical properties of the complexes have been preliminarily investigated.

New Metal Complexes with Mannich -β-amino carbonyl ligand; Preparation, spectral Characterisation and Biological Activity.

New metal complexes and a new beta-amino maniche carbonyl ligand were prepared and characterized. (((4-(tert-butyl)-2-((S)- (phenylamino) (p-tolyl) methyl)cyclohexan-1-one)) (HL) was formed from the reaction of aniline and 4-methylbesaldehyde with 4- (tert-butyl)cyclohexane-1-one at a 1:1:1 mol ratio respectively reaction of (4-methyl-2-((R)-(phenylamino)(p-tolyl) methyl)cyclohexan-1-one (HL) and MnII, CoII, NiII, CuII, ZnII and CdII metal ions in a 2:1 (L:M) ratio led to the isolation of monomeric complexes from analytical and spectroscopic techniques including; elemental microanalysis, magnetic susceptibility, conductivity, TGA, and FTIR, electronic and mass spectra and 1 H, 13C-NMR characterization data indicated to a four- and six-coordinate isolate.Complexes Many bacterial and fungal strains were tested, and the data obtained showed that these complexes are more active against a variety of organisms, under experiment, than free associations.

Trinuclear and Tetranuclear Ruthenium Carbonyl Nitrosyls: Oxidation of a Carbonyl Ligand by an Adjacent Nitrosyl Ligand.

Trinuclear and tetranuclear ruthenium carbonyls of the types Ru3(CO)n(NO)2, Ru3(N)(CO)n(NO), Ru3(N)2(CO)n, Ru3(N)(CO)n(NCO), Ru3(CO)n(NCO)(NO), Ru4(N)(CO)n(NO), Ru4(N)(CO)n(NCO), and Ru4(N)2(CO)n related to species observed experimentally in the chemistry of Ru3(CO)10(µ-NO)2 have been investigated using density functional theory. In all cases, the experimentally observed structures have been found to be low-energy structures. The low-energy trinuclear structures typically have a central strongly bent Ru-Ru-Ru chain with terminal CO groups and bridging nitrosyl, isocyanate, and/or nitride ligands across the end of the chain. The low-energy tetranuclear structures typically have a central Ru4N unit with terminal CO groups and a non-bonded pair of ruthenium atoms bridged by a nitrosyl or isocyanate group.

Crystal structure of bis-[(η5-tert-butyl-cyclo-pentadien-yl)tri-carbonyl-molybdenum(I)](Mo-Mo).

The dinuclear mol-ecule of the title compound, [Mo2(C9H13)2(CO)6] or [Mo( t BuCp)(CO)3]2 where t Bu and Cp are tert-butyl and cyclo-penta-dienyl, is centrosymmetric and is characterized by an Mo-Mo bond length of 3.2323 (3) Å. Imposed by inversion symmetry, the t BuCp and the carbonyl ligands are in a transoid arrangement to each other. In the crystal, inter-molecular C-H⋯O contacts lead to the formation of layers parallel to the bc plane.

Synthesis, spectroscopic analysis and crystal structure of (N-{2-[(2-amino-eth-yl)amino]-eth-yl}-4'-methyl-[1,1'-biphenyl]-4-sulfonamidato)tri-carb-on-ylrhenium(I).

The title compound, [Re(C17H22N3O2S)(CO)3] is a net neutral fac-Re(I)(CO)3 complex of the 4-methyl-biphenyl sulfonamide derivatized di-ethyl-enetri-amine ligand. The NNN-donor monoanionic ligand coordinates with the Re core in tridentate fashion, establishing an inner coordination sphere resulting in a net neutral complex. The complex possesses pseudo-octa-hedral geometry where one face of the octa-hedron is occupied by three carbonyl ligands and the other faces are occupied by one sp 2 nitro-gen atom of the sulfonamide group and two sp 3 nitro-gen atoms of the dien backbone. The Re-Nsp 2 bond distance, 2.173 (4) Å, is shorter than the Re-Nsp 3 bond distances, 2.217 (5) and 2.228 (6) Å, and is similar to the range reported for typical Re-Nsp 2 bond lengths (2.14 to 2.18 Å).

Infrared Photodissociation Spectroscopy of Dinuclear Vanadium-Group Metal Carbonyl Complexes: Diatomic Synergistic Activation of Carbon Monoxide.

The geometric structure and bonding features of dinuclear vanadium-group transition metal carbonyl cation complexes in the form of VM(CO)n+ (n = 9-11, M = V, Nb, and Ta) are studied by infrared photodissociation spectroscopy in conjunction with density functional calculations. The homodinuclear V2(CO)9+ is characterized as a quartet structure with CS symmetry, featuring two side-on bridging carbonyls and an end-on semi-bridging carbonyl. In contrast, for the heterodinuclear VNb(CO)9+ and VTa(CO)9+, a C2V sextet isomer with a linear bridging carbonyl is determined to coexist with the lower-lying CS structure analogous to V2(CO)9+. Bonding analyses manifest that the detected VM(CO)9+ complexes featuring an (OC)6M-V(CO)3 pattern can be regarded as the reaction products of two stable metal carbonyl fragments, and indicate the presence of the M-V d-d covalent interaction in the CS structure of VM(CO)9+. In addition, it is demonstrated that the significant activation of the bridging carbonyls in the VM(CO)9+ complexes is due in large part to the diatomic cooperation of M-V, where the strong oxophilicity of vanadium is crucial to facilitate its binding to the oxygen end of the carbonyl groups. The results offer important insight into the structure and bonding of dinuclear vanadium-containing transition metal carbonyl cluster cations and provide inspiration for the design of active vanadium-based diatomic catalysts.

Zerovalent ruthenium complexes of secondary alkoxyphosphines

The reaction of [RuHCl(CO)L3] (L = PPh3) with cyclohexylphosphine (PH2Cy) affords [RuHCl(CO)L2(PH2Cy)], protonation of which in acetonitrile with HX affords [RuCl(NCMe)(CO)L2(PH2Cy)]X (X = ClO4, OTf, PF6) salts while HCl provides [RuCl2(CO)L2(PH2Cy)]. The labile chloride and/or acetonitrile ligands are replaced by CO, CNC6H2Me3-2,4,6, [Et2NCS2]– or [Tp]– (Tp = hydrotris(pyrazolyl)borate) to provide [RuCl(CO)2L2(PH2Cy)]+, [Ru[Cl(CO)(CNC6H2Me3-2,4,6)L2(PH2Cy)]+, [Ru(S2CNEt2)(CO)L2(PH2Cy)]+ and [Ru(CO)L(Tp)(PH2Cy)]+ salts. Deprotonation of [RuCl(CO)2L2(PH2Cy)]OTf in benzene affords [RuCl(PHCy)(CO)2L2], but in methanol the secondary methoxyphosphine complex [Ru(CO)2L2{PH(OMe)Cy}] is obtained, as is [Ru(CO)(CNC6H2Me3-2,4,6)L2{PH(OMe)Cy}] from [Ru[Cl(CO)(CNC6H2Me3-2,4,6)L2(PH2Cy)]OTf. The reactions of [Ru(CO)2L2{PH(OMe)Cy}] with CO, CNC6H2Me3-2,4,6 or dppe afford [Ru(CO)3L{PH(OMe)Cy}], [Ru(CO)2(CNC6H2Me3-2,4,6)L2{PH(OMe)Cy}] or [Ru(CO)2(dppe){PH(OMe)Cy}], resectively, in each case demonstrating a preference for dissociation of PPh3 rather than PH(OMe)Cy. Aerial oxidation of [Ru(CO)2L2{PH(OMe)Cy}] results in oxidation of one carbonyl ligand with formation of the carbonato complex [Ru(O2CO)(CO)L2{PH(OMe)Cy}]. The reaction of [Ru(CO)2L2{PH(OMe)Cy}] with ethynyl benzene provides two diastereomers of [RuH(CCPh)(CO)2L{PH(OMe)Cy}], while with anhydrous HCl, the cyclohexyl phosphine complex [RuCl2(CO)L2(PH2Cy)] is observed.

From the Iron Pentacarbonyl Cation to Heteroleptic η6-arene Carbonyls and bis-η6-arene Cations.

Partial ligand substitution at the iron pentacarbonyl radical cation generates novel half-sandwich complexes of the type [Fe(η6-arene)(CO)2]⋅+ (arene=1,3,5-tri-tert-butylbenzene, 1,3,5-trimethylbenzene, benzene and fluorobenzene). Of those, the bulkier 1,3,5-tri-tert-butylbenzene (mes*) derivative [Fe(mes*)(CO)2]⋅+ was fully characterized by XRD analysis, IR, NMR, cw-EPR, Mössbauer spectroscopy and cyclic voltammetry as the [Al(ORF)4]- (RF=C(CF3)3) salt. Chemical electronation, i. e., the single electron reduction, with decamethylferrocene generates neutral [Fe(mes*)(CO)2], whereas further deelectronation under CO-pressure leads to a dicationic three-legged [Fe(mes*)(CO)3]2+ salt with [Al(ORF)4]- counterion. The full substitution of the carbonyl ligands in [Fe(CO)5]⋅+[Al(ORF)4]- mainly resulted in disproportionation reactions, giving solid Fe(0) and the dicationic bis-arene salts [Fe(η6-arene)2]2+([Al(ORF)4]-)2 (arene=1,3,5-trimethylbenzene, benzene and fluorobenzene). Only by employing the very large fluoride bridged anion [F-{Al(ORF)3}2]-, it was possible to isolate an open shell bis-arene cation salt [Fe(C6H6)2]⋅+[F-{Al(ORF)3}2]-. The highly reactive cation was characterized by XRD analysis, cw-EPR, Mössbauer spectroscopy and cyclic voltammetry. The disproportionation of [Fe(C6H6)2]⋅+ salts to give solid Fe(0) and [Fe(C6H6)2]2+ salts was analyzed by a suitable cycle, revealing that the thermodynamic driving force for the disproportionation is a function of the size of the anion used and the polarity of the solvent.

Acetylene ligands stabilize atomically dispersed supported rhodium complexes under harsh conditions

Facile sintering of atomically dispersed supported noble metal catalysts at catalytically relevant temperatures, particularly under reducing conditions, poses a challenge for their practical applications. Some ligands, such as carbonyls, aid in improving the stability at the expense of severely suppressing the catalytic activity. Here, we demonstrate that substitution of the carbonyl ligands with reactive acetylene ligands can maintain the atomic dispersion of the supported mononuclear rhodium complex under harsh reducing conditions (>573 K), as confirmed by in-situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. In contrast, the supported rhodium carbonyl complex aggregates into nanoclusters under identical conditions. Furthermore, our results indicate that the acetylene ligands provide this anti-sintering ability while retaining the hydrogenation activity.

Pressure Induced Alteration and Stabilization of Intermolecular Stacking in Square-planar Osmium tetracarbonyl.

Osmium carbonyls are well known to form stable 18-electron complexes like Os(CO)5 , Os2 (CO)9 and Os3 (CO)12 having both bridging and terminal carbonyls. For osmium tetra-carbonyl, Os(CO)4 solid-state packing significantly alters the ground-state structure. The gas-phase stable see-saw geometry converts to a square-planar structure in solid state. Highly efficient intermolecular stacking between Os(CO)4 units assists this transformation. Each Os(CO)4 molecule is stacked in a staggered orientation with respect to each other. Pressure induces a [Xe]4f14 5d6 6s2 (S=2)→[Xe]4f14 5d8 (S=0) electronic transition in osmium stabilize a square planar osmium tetra-carbonyl. Under the influence of isotropic pressure, the molecules not only come closer to each other but their relative orientations also get significantly altered. Calculations show that at P=1 GPa and above, the eclipsed orientation for the intermolecular stacking gets preferred over the staggered form. The staggered→eclipsed intermolecular stacking orientation under pressure is shown to be controlled by London dispersion interactions.

Vibrational Coupling Infrared Nanocrystallography.

Coupling between molecular vibrations leads to collective vibrational states with spectral features sensitive to local molecular order. This provides spectroscopic access to the low-frequency intermolecular energy landscape. In its nanospectroscopic implementation, this technique of vibrational coupling nanocrystallography (VCNC) offers information on molecular disorder and domain formation with nanometer spatial resolution. However, deriving local molecular order relies on prior knowledge of the transition dipole magnitude and crystal structure of the underlying ordered phase. Here we develop a quantitative model for VCNC by relating nano-FTIR collective vibrational spectra to the molecular crystal structure from X-ray crystallography. We experimentally validate our approach at the example of a metal organic porphyrin complex with a carbonyl ligand as the probe vibration. This framework establishes VCNC as a powerful tool for measuring low-energy molecular interactions, wave function delocalization, nanoscale disorder, and domain formation in a wide range of molecular systems.

Is Mn(I) More Promising Than Fe(II)-A Comparison of Mn vs Fe Complexes for Olefin Metathesis.

Olefin metathesis is one of the most significant transformations in organic chemistry and is an excellent example for efficient homogeneous catalysis. Although most currently used catalysts are primarily based on 4d and 5d metals, cycloaddition and cycloreversion reactions can also be attributed to first-row transition metals, such as Fe. Surprisingly, the potential of Mn(I)-based catalysts for olefin metathesis has been unexplored despite their prominence in homogeneous catalysis and their diagonal relationship to Ru(II). In the present study, we have investigated the prospective capabilities of Mn complexes for cycloaddition and reversion reactions using density functional theory. Therefore, we have initially compared the literature known iron model systems and their isoelectronic Mn counterparts regarding their reactivity and electronic structure. Next, we constructed potential Mn complexes derived from synthetically accessible species, including carbonyl ligands and obeying octahedral geometry. Based on thermodynamic parameters and the calculation of electronic descriptors, we were able to validate the isodiagonal relationship. Our study serves as guidance for the experimental chemist.

Friedel–Crafts Acylation for Accessing Multi‐Bridge‐Functionalized Large Pillar[n]arenes

AbstractPillar[n]arenes can be constructed using a Friedel–Crafts alkylation process. However, due to the reversible nature of the alkylation, mixture of large pillar[n]arenes (n≥7) are obtained as minor products, and thus laborious purification are necessary to isolate the larger pillar[n]arenes. Moreover, inert methylene bridges are introduced during the alkylation process, and the multi‐functionalization of the bridges has never been investigated. Herein, an irreversible Friedel–Crafts acylation is used to prepare pillar[n]arenes. Due to the irreversible nature of the acylation, the reaction of precursors bearing carboxylic acids and electron‐rich arene rings results in a size‐exclusive formation of pillar[n]arenes, in which the ring‐size is determined by the precursor length. Because of this size‐selective formation, laborious separation of undesired macrocycles is not necessary. Moreover, the bridges of pillar[n]arenes are selectively installed with reactive carbonyl groups using the acylation method, whose positions are determined by the precursor used. The carbonyl bridges can be easily converted into versatile functional groups, leading to various laterally modified pillar[n]arenes, which cannot be accessed by the alkylation strategy.

Friedel-Crafts Acylation for Accessing Multi-Bridge-Functionalized Large Pillar[n]arenes.

Pillar[n]arenes can be constructed using a Friedel-Crafts alkylation process. However, due to the reversible nature of the alkylation, mixture of large pillar[n]arenes (n≥7) are obtained as minor products, and thus laborious purification are necessary to isolate the larger pillar[n]arenes. Moreover, inert methylene bridges are introduced during the alkylation process, and the multi-functionalization of the bridges has never been investigated. Herein, an irreversible Friedel-Crafts acylation is used to prepare pillar[n]arenes. Due to the irreversible nature of the acylation, the reaction of precursors bearing carboxylic acids and electron-rich arene rings results in a size-exclusive formation of pillar[n]arenes, in which the ring-size is determined by the precursor length. Because of this size-selective formation, laborious separation of undesired macrocycles is not necessary. Moreover, the bridges of pillar[n]arenes are selectively installed with reactive carbonyl groups using the acylation method, whose positions are determined by the precursor used. The carbonyl bridges can be easily converted into versatile functional groups, leading to various laterally modified pillar[n]arenes, which cannot be accessed by the alkylation strategy.

Cobalt-catalyzed synthesis of amides from alkenes and amines promoted by light.

Catalytic methods to couple alkene and amine feedstocks are valuable in synthetic chemistry. The direct carbonylative coupling of alkenes and amines holds promise as a perfectly atom-economical approach to amide synthesis, but general methods remain underdeveloped. Herein, we report an alkene hydroaminocarbonylation catalyzed by unmodified, inexpensive cobalt carbonyl under mild conditions and low pressure promoted by light. Silane addition after the reaction enables sequential cobalt-catalyzed amide reduction, constituting a formal alkene hydroaminomethylation. These methods exhibit exceptional scope across both alkene and amine components with high chemo- and regioselectivity and proceed efficiently even in the absence of solvent. The formation of a hydridocobalt through photodissociation of a carbonyl ligand is proposed to enable catalytic activity under mild conditions, which addresses a long-standing challenge in catalysis.

Sensory improvement and antioxidant enhancement in silver carp hydrolysate using prebiotic oligosaccharides: insights from the Maillard reaction.

Our previous studies have highlighted the potential of silver carp hydrolysate (SCH) in managing chronic diseases. Unfortunately, its fishy smell and bitter taste limited consumer acceptance. Prebiotic oligosaccharides are often used as dietary supplements, ignoring their role as carbonyl ligands in the Maillard reaction to enhance food's sensory and antioxidant properties. This study aimed to improve SCH's sensory attributes and investigate its physicochemical properties and antioxidant activities using prebiotic oligosaccharides via the Maillard reaction. The results showed that xylo-oligosaccharide (XOS) had the highest reactivity among the oligosaccharides tested, and it greatly enhanced the taste and flavor of SCH, as well as its antioxidant activities (0.45 to 16.5 times). Specifically, XOS effectively reduced the fishy smell and bitter taste, imparting a caramel-like flavor and overall acceptability to SCH. The improved flavor profile was attributed to the increased presence of sulfur-containing and nitrogen oxide volatile flavor compounds, such as benzothiazole, methional, and furans, which also contributed to antioxidant effects. Sensory evaluation results indicated that SCH obtained from papain exhibited a stronger bitter taste than that obtained from alcalase. Additionally, XOS imparted a reddish-brown color to SCH due to the higher browning intensity. This study is the first to demonstrate that XOS in the Maillard reaction can effectively improve the undesirable flavor and taste of SCH while enhancing its antioxidant activities, providing a theoretical basis for developing SCH as a market-acceptable functional food ingredient.