Synthesis and Catalytic Evaluation of Phosphanylferrocene Ligands with Cationic Guanidinium Pendants and Varied Phosphane Substituents

Abstract

This contribution expands the still narrow class of functional ferrocene phosphanes with polar cationic groups, focusing on the synthesis and catalytic use of a series of phosphanylferrocene ligands bearing positively charged guanidinium tags, [R 2 PfcCH 2 NHC(NH 2 ) 2 ]Cl (3a-d), where fc = ferrocene-1,1′-diyl, R = isopropyl (a), cyclohexyl (b), phenyl (c), and 2-furyl (d). To probe the influence of phosphane substituents, these compounds were studied as supporting ligands in Pd-catalyzed Suzuki-Miyaura cross-coupling of acyl chlorides with arylboronic acids, in analogous coupling of aryl bromides with arylboronic acids, and in Rh-catalyzed hydroformylation of 1-hex- [a] 4846 ene using trans-[RhCl(CO){R 2 PfcCH 2 NHC(NH 2 ) 2 -κP} 2 ]Cl 2 complexes (4a-d) as pre-catalysts. The outcome of the cross-coupling reactions strongly depended on the starting materials, and no ligand generated a universally applicable catalyst when combined with Pd(OAc) 2 . In the hydroformylation reactions, the catalyst based on 4d led to lower conversions than all others, which performed rather similarly. Overall, the phenyl-substituted phosphane 3c emerged as a good compromise, giving rise to reasonably efficient and stable catalysts in most cases (except for Suzuki-Miyaura biaryl cross-couplings, wherein electron-rich alkylphosphanes performed better than 3c). Scheme 1. Phosphinoferrocene ligands bearing guanidinium pendants. Note: among compounds 3, only 3c has been reported before.

Forever young: the first seventy years of ferrocene

“…Representative recent examples, shown in Scheme 5, include the phosphinoferrocene nitriles 10 73 and 11 , 74 isocyanide 12 , 75 homologous alcohols 13 76 and 14 77 and their corresponding ethers 15 78 and 16 , 79 “acyl” derivatives 17 , 77,80 18 81 and 19 , 82 phosphino-amines 20 , 75,83 21 84 and 22 , 80 a ,85 P-protected phosphino-alkynes ( 23 and 24 86 ) and an azide 25 . 75 Departing from this series are the ambiphilic phosphine-boranes 26 , 87 27 88 and 28 , 89 and polar ferrocene phosphines bearing sulfonate ( 29 90 ), phosphonic acid ( 30 , 91 31 , 92 and 32 93 ) or guaninidium substituents ( 33 94 ).…”

Rh(I) Complexes in Catalysis: A Five-Year Trend

“…Another example of phosphino-ferrocenes is given by the series of derivatives carrying a highly polar and positively charged guanidinium moiety onto the 1 -position, with the aim of increasing their affinity towards polar solvents. The hydrophobic phosphino group at the 1-position, on the other hand, was modified with both alkyl or aryl substituents [69] (Figure 3). The relative Rh(I) species, to which two ligands are bonded in a monodentate fashion (Scheme 7), were tested in the hydroformilation of 1-hexene, with yields going from moderate (42%) to high (98%) according to the substituent on the phosphorus atom.…”

Synthesis of Hydrophilic Phosphorus Ligands and Their Application in Aqueous‐Phase Metal‐Catalyzed Reactions

“…Guanidinium Groups . Recently, the guanidine moiety as hydrophilic entity was revisited by the group of Štěpnička for the preparation of phosphinylferrocene ligands [58–60] . Taking advantage of a carboxyl group, which can be transformed into its acylbenzotriazole derivative, an acylguanidinium moiety could be efficiently installed (Scheme 23).…”

“…The same protocol was employed for the preparation of similar ligands ( 69 b – d ) differing in the alkyl/aryl groups at the phosphorus atom (Scheme 25). [60] …”

“…In general the best yields were achieved when electron‐rich boronic acids are reacted with electron‐poor benzoyl chlorides. [34],[45] Recently, a related catalyst system derived from ligands 69 b – d was introduced for CF 3 ‐substituted derivatives [60] …”