1,1'-Bis(diphenylphosphino)ferrocene: Properties and Coupling Reactions in Materials Syntheses

General Description

1,1'-Bis(diphenylphosphino)ferrocene is a versatile diphosphine ligand essential in transition metal catalysis, particularly in coupling reactions for synthesizing functional materials like polyphenylenes and oligothiophenes. Its ease of synthesis, thermal stability, and conformational flexibility enhance its effectiveness in stabilizing catalytic intermediates. The ligand's optimal P–M–P bite angle of approximately 95.60° facilitates coordination with various metal centers, leading to higher yields and regioselectivity in coupling reactions. Notably, 1,1'-Bis(diphenylphosphino)ferrocene improves polymerization of phenylacetylene and the synthesis of branched oligothiophenes, demonstrating its critical role in advancing materials science and catalysis.

Figure 1. 1,1'-Bis(diphenylphosphino)ferrocene

Properties

Fundamental Properties

1,1'-Bis(diphenylphosphino)ferrocene, a prominent diphosphine ligand, plays a pivotal role in various transition metal-catalyzed reactions owing to its unique properties. One of the primary advantages of 1,1'-bis(diphenylphosphino)ferrocene is its ease of synthesis, which can be achieved from the relatively inexpensive ferrocene. This accessibility contributes to its widespread application in both catalysis and materials science. Furthermore, 1,1'-bis(diphenylphosphino)ferrocene exhibits remarkable stability under air and moisture, as well as thermal stability, making it a reliable choice for various experiments and processes. The ligand's conformational flexibility allows it to adapt in coordination environments, enhancing its functionality in catalysis. ¹

Coordination and Catalytic Versatility

Moreover, the structural characteristics of 1,1'-bis(diphenylphosphino)ferrocene contribute to its effectiveness as a ligand. Its ferrocenyl backbone enables a larger natural bite angle, facilitating effective coordination with metal centers. The calculated preferred P–M–P bite angle of 1,1'-bis(diphenylphosphino)ferrocene is approximately 95.60°, which allows for greater flexibility during catalytic cycles. This flexibility permits the stabilization of various geometries, accommodating different transition states with minimal energy penalties. Consequently, both the stabilization of catalytic intermediates and the formation of a diverse range of metal–1,1'-bis(diphenylphosphino)ferrocene complexes are achievable, underlining the ligand's versatility in facilitating numerous catalytic transformations across a spectrum of metal centers. ¹

Coupling Reactions in Materials Syntheses

Coupling Reactions in the Synthesis of Poly- and Oligo-phenylenes

1,1'-Bis(diphenylphosphino)ferrocene is a highly effective stabilizing ligand in various coupling reactions crucial for synthesizing functional materials such as polyphenylenes. These materials, known for their applications in organic light-emitting diodes (OLEDs) and other electronic devices, benefit significantly from the controlled synthesis of oligoarenes via chemoselective Suzuki–Miyaura coupling reactions. Using 1,1'-bis(diphenylphosphino)ferrocene provides higher yields during the cross-coupling of arylboronic acids with aryl triflates, effectively tempering reactivity and ensuring that each step in the oligomerization is more quantitative. This property is particularly advantageous, as the precise control of each coupling step minimizes the complications associated with isolating closely related products. ²

Role in Synthesizing Oligothiophenes

1,1'-Bis(diphenylphosphino)ferrocene is also instrumental in synthesizing oligothiophenes, which serve as critical components in electro-optical materials like dye-sensitized solar cells. In this regard, achieving regioselective C–C coupling reactions is essential, and the superior performance of palladium catalysts, notably those coordinated with 1,1'-bis(diphenylphosphino)ferrocene, has been demonstrated. For example, using [PdCl2(diphosphine)] as a catalyst in conjunction with thienylzinc substrates yielded higher product yields and improved regioselectivity in the synthesis of branched oligothiophenes. The unique bite angle and sterics provided by 1,1'-bis(diphenylphosphino)ferrocene enhance the rate of reductive elimination, facilitating more effective coupling processes and yielding desired products over undesired by-products. ²

Advancements in Polyacetylenes

In the realm of polyacetylenes, 1,1'-Bis(diphenylphosphino)ferrocene catalyzes polymerization reactions effectively, showcasing its adaptability and utility. The cationic palladium complexes derived from reactions involving 1,1'-bis(diphenylphosphino)ferrocene demonstrate considerable activity in the polymerization of phenylacetylene. These active species, typically generated through the abstraction of chloride ions and subsequent coordination of acetonitrile, exhibit variations in activity based on the ligand employed. Specifically, the polymerization involving the complex [PdCl(CH3)(1,1'-bis(diphenylphosphino)ferrocene)] stands out due to its steric bulk and the inherent flexibility imparted by the ferrocene backbone. This flexibility is instrumental in stabilizing intermediates during the insertion mechanism of polymerization, underscoring the pivotal role of 1,1'-bis(diphenylphosphino)ferrocene in driving forward significant advancements in materials synthesis through its involvement in coupling reactions. ²

Reference

1. Aziz F, Hierso JC, Meunier P. Performances of symmetrical achiral ferrocenylphosphine ligands in palladium-catalyzed cross-coupling reactions: A review of syntheses, catalytic applications and structural properties. Coordination Chemistry Reviews. 2007; 251(15): 2017-2055.

2. Young DJ, Chien SW, Hor TS. 1,1'-Bis(diphenylphosphino)ferrocene in functional molecular materials. Dalton Trans. 2012; 41(41): 12655-12665.

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