In a groundbreaking advancement that promises to reshape synthetic methodologies within organometallic chemistry, researchers from the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, have unveiled a highly selective cobalt-catalyzed anti-Markovnikov hydrosilylation of terminal alkynes utilizing tertiary silanes. This innovative catalytic system is centered around a dinuclear cobalt carbonyl complex coordinated by the bidentate phosphine ligand Xantphos, [(Xantphos)Co₂(CO)₆], which demonstrates unprecedented efficiency and selectivity in transforming simple alkynes into valuable alkenyl silicon compounds under mild reaction conditions.
The hydrosilylation of alkynes, an important transformation in organosilicon chemistry, typically confronts challenges related to regio- and stereoselectivity, especially when using tertiary silanes. These silanes, despite their commercial availability and cost-effectiveness, exhibit significant steric hindrance, which historically has impeded their effective utilization. More so, catalytic systems based on earth-abundant 3d transition metals like cobalt often struggle in maintaining high selectivity alongside broad substrate scope. This latest development addresses these critical issues, offering a remarkable solution through the elegant design of a dinuclear cobalt catalyst that leverages cooperative metal-ligand interactions.
The core of the catalytic activity lies within the unique architecture of the [(Xantphos)Co₂(CO)₆] complex. Here, the Xantphos ligand acts in a metalloligand capacity, serving not merely as a spectator but as an active participant in the catalytic cycle. This ligand environment enables one cobalt center designated as the (Xantphos)(CO)Co site to function effectively as a ligand entity, working synergistically with the adjacent Co(CO)_n site. This unusual cooperation facilitates activation and transformation of Si-H and C≡C bonds in a finely orchestrated manner, achieving selective anti-Markovnikov hydrosilylation with remarkable efficiency.
Experimental studies revealed that the in situ generated catalyst from the reaction of Co₂(CO)₈ with Xantphos showed comparable activity and selectivity to the preformed [(Xantphos)Co₂(CO)₆] complex. The incorporation of the Xantphos ligand was paramount in tuning the β/α selectivity of hydrosilylation products, favoring formation of linear alkenyl silanes via anti-Markovnikov addition. This functional tuning underscores the critical influence of ligand architecture in modulating catalytic pathways, reinforcing the importance of rational ligand design in transition metal catalysis.
The substrate scope explored in this study affirms the versatility and robustness of the catalytic system. A wide range of terminal alkynes bearing primary, secondary, and tertiary alkyl substituents underwent smooth hydrosilylation with triethylsilane, leading to high yields of linear alkenyl silicon products. Moreover, the system tolerated various functional groups including halogens, ethers, and hydroxyl functionalities, which often pose challenges in transition metal-catalyzed transformations. Even electron-rich and electron-deficient aryl alkynes displayed excellent reactivity and selectivity across ortho-, meta-, and para-substitutions, highlighting the broad applicability of this catalytic platform in complex molecular contexts.
Mechanistic insight was elucidated through a combination of experimental isolation of intermediates and deuterium labeling studies alongside advanced theoretical calculations performed by a collaborative team at the Institute of Chemistry, Chinese Academy of Sciences. Results demystified the catalytic cycle, pinpointing a dinuclear cobalt alkyne complex [(Xantphos)(CO)Co(μ-η²:η²-HCCCy)Co(CO)₃] as the pivotal active species (denoted as complex 2). This complex undergoes subsequent reaction steps involving silane coordination and bond rearrangements leading to selective anti-Markovnikov hydrosilylation products alongside the regeneration of the catalytically competent dinuclear cobalt species.
Density functional theory (DFT) computations revealed that the reaction pathway traverses a singlet-to-triplet spin state transition during an intramolecular hydrogen atom transfer, marking the regioselective and rate-determining step. The formation of a dinuclear cobalt vinylsilyl intermediate is central to catalytic efficiency and directs the observed selectivity. Subsequent reductive elimination establishes the crucial C–Si bond, leading to olefinic silicon intermediates before product release and catalyst regeneration. The dynamic interplay between the two cobalt centers allows for redox cycling and electron transfers fundamental to bond activation processes.
Electronic structure analysis exposed a fascinating mechanistic paradigm where one cobalt center undergoes oxidative addition of the Si–H bond, transforming from a zero-valent Co(0) site to a Co(I) species. Simultaneously, the adjacent cobalt center coordinated to Xantphos maintains a non-redox, ligand-like role. This bimetallic synergy facilitates multi-electron redox processes unattainable with mononuclear catalysts and underscores the emergent concept of redox-active metalloligands in catalysis. Such cooperative behaviors expand the boundaries of sustainable catalysis with earth-abundant metals.
The catalytic proficiency with various tertiary silanes beyond triethylsilane—including HSiBu₃, HSiMe₂Ph, HSiPh₃, and siloxane-substituted silanes—was demonstrated, albeit with a noted decline in selectivity correlated with decreasing numbers of substituents on silicon. This observation links steric and electronic factors of silane substrates directly to catalytic outcomes, inviting further investigation into optimizing ligand-catalyst-substrate interfaces.
This study highlights the transformative potential in applying dinuclear cobalt complexes featuring metalloligand functionality to achieve challenging bond formations with high regio- and stereocontrol. The ability to selectively produce anti-Markovnikov addition products tolerating diverse functional groups and substrate classes positions this catalytic platform as a valuable tool for the synthesis of functionalized alkenyl silanes. These compounds hold immense importance in organic synthesis, materials science, and pharmaceutical manufacturing, serving as versatile intermediates or building blocks.
The collaborative research effort, led by Liang Deng and Hui Chen with first authorship by Dongyang Wang, represents a major stride forward in the design principles of 3d metal-based catalysts. The findings underscore the unexplored potential of redox-active metal-ligand cooperation in achieving transformations previously deemed difficult with base metals. Furthermore, the research emphasizes the advantages of combining detailed mechanistic study with computational insights to rationally develop next-generation catalysts exhibiting enhanced selectivity and substrate compatibility.
Publication of this work in CCS Chemistry, the flagship English-language journal of the Chinese Chemical Society, marks a significant milestone in contemporary catalysis research. The open-access nature of the journal ensures broad dissemination and accessibility to the global scientific community. The discovery resonates beyond academic laboratories, encouraging industrial chemists to revisit cobalt catalysis as a cost-effective and environmentally benign alternative to precious metal systems for constructing carbon-silicon frameworks.
Looking forward, this breakthrough opens avenues for exploring other bimetallic complexes and metalloligand systems for diverse catalytic reactions. The synergy observed in the dinuclear cobalt catalyst could inspire analogous strategies across a spectrum of transition metals, potentially revolutionizing the field of metal-catalyzed bond activations. As demand for sustainable technologies escalates, innovations harnessing earth-abundant metals with intelligent ligand design hold unparalleled promise.
In conclusion, the reported dinuclear cobalt system demonstrates how judicious ligand engineering and exploitation of metal-metal cooperation can overcome intrinsic challenges in catalytic selectivity and reactivity. By illuminating a unique mechanistic pathway involving metalloligand-enabled activation and transformation steps, the study reshapes conceptual frameworks in organometallic chemistry. It stands poised to influence both fundamental research and practical applications in the synthesis of silicon-containing compounds, reinforcing cobalt’s emerging status as a versatile and powerful catalytic center.
Article Title: Metalloligand Enabling Cobalt-Catalyzed anti-Markovnikov Hydrosilylation of Alkynes with Tertiary Silanes
News Publication Date: 15-Jul-2025
Web References:
https://www.chinesechemsoc.org/journal/ccschem
http://dx.doi.org/10.31635/ccschem.025.202505983
Image Credits: CCS Chemistry
Keywords
Cobalt, Transition Metals, Hydrosilylation, Dinuclear Catalysis, Anti-Markovnikov Addition, Organometallic Chemistry, Metalloligand, Xantphos, Alkyne Functionalization, Tertiary Silanes, Redox-Active Ligands, Catalytic Mechanism
