Unsaturated Organic Derivatives of Phosphaferrocene – Synthesis and Reactivity of Vinyl‐ and Alkynylphosphaferrocenes

Abstract

Starting from 2-formyl-3,4-dimethylphosphaferrocene, a series of vinyl-substituted phosphaferrocenes was prepared by Wittig and related olefination reactions. The parent 3,4dimethyl-2-vinylphosphaferrocene (2) could be selectively converted to either the terminal or branched alcohols 8b and 8a by hydroboration/oxidation or protonation in aqueous solution, respectively. Elimination of HBr from 2-bromovinylphosphaferrocene 9 provided access to the 2-ethynylphosphaferrocene derivative 10, which could be converted to other alkynes by deprotonation and electrophilic quench. Additionally, the syntheses of the 2-cyano-(15) and 2-Synthesis and Reactivity of Vinyl-and Alkynylphosphaferrocenes Scheme 1. Preparation of the vinylphosphaferrocene derivative 2.are easily accessible by Horner-Wadsworth-Emmons reactions (Scheme 2). [7] The desired phosphonates were obtained from triethyl phosphite and the respective bromo compound and were subsequently deprotonated with nBuLi or NaH prior to addition of the aldehyde. The acrylic ester 3 was obtained solely as the E isomer, whereas for the acrylonitrile 4 an E/Z ratio of 10:1 was observed. Scheme 2. Preparation of acrylic derivatives 3 and 4.The presence of the phosphorus atom affects the appearance of the 1 H NMR spectrum of the vinyl group in compound 2; the signal for the CH proton is additionally split due to a 3 J HP coupling of 10.5 Hz, whereas the trans proton of the CH 2 group experiences a 4 J HP coupling of 1.8 Hz.No H-P coupling was observed for the cis CH 2 proton. The acrylic ester 3 could be reduced to give the saturated compound 5 by treatment with NaBH 4 in the presence of CuCl [8] and was finally hydrolyzed to the propionic acid 6 (Scheme 3).Scheme 3. Preparation of propionic acid derivatives 5 and 6.Commencing from 2, the isomeric 2-(phosphaferrocenyl)ethanols 8a and 8b could be prepared. Thus, hydroboration of 2 yields the anti-Markownikow organoborane 7 as a mixture of diastereomers due to the racemic nature of compound 2. However, treatment with alkaline hydrogen peroxide cleanly afforded the linear alcohol 8b in 69 % overall yield, an alternative synthesis of which has been reported by our group before. [9] On the contrary, the branched isomer 8a was obtained by treatment of the vinyl derivative 2 with aqueous hydrochloric acid (Scheme 4). Presumably, the Eur.

1′-(Diphenylphosphino)-1-cyanoferrocene: A Simple Ligand with Complicated Coordination Behavior toward Copper(I)

“…14 Compounds of this type are not entirely unprecedented, even among ferrocene derivatives, being represented by 1-(diphenylphosphino)-2-(cyanomethyl)ferrocene 15 and its Cα-substituted derivatives, 16 1-(diphenylphosphino)-2-cyano-3-ethylferrocene, 17 and 2-cyano-1-phosphaferrocene. 18 However, only the last of these compounds has been studied as a ligand in transition-metal complexes, coordinating as a P-monodentate donor. 18 In this contribution, we report the synthesis and structural characterization of 1′-(diphenylphosphino)-1-cyanoferrocene (3) as a new ferrocene-based donor-asymmetric ligand and the copper(I) complexes resulting from its reactions with Cu(I) halides and [Cu(MeCN) 4 ] + salts or their synthetic equivalents.…”

“…18 However, only the last of these compounds has been studied as a ligand in transition-metal complexes, coordinating as a P-monodentate donor. 18 In this contribution, we report the synthesis and structural characterization of 1′-(diphenylphosphino)-1-cyanoferrocene (3) as a new ferrocene-based donor-asymmetric ligand and the copper(I) complexes resulting from its reactions with Cu(I) halides and [Cu(MeCN) 4 ] + salts or their synthetic equivalents. Because the stoichiometries of copper(I) complexes usually "give little clue to their structures, which can be very complicated", 19 we have focused mainly on the structural characterization of the prepared complexes and have thus identified both conventional and novel compound types.…”

“…Given the numerous reports dealing with the multifaceted coordination chemistry of 1′-functionalized ferrocene phosphines, , we decided to prepare and study the new ferrocene-based mixed-donor ligand 3 , which combines the soft cyano and phosphine donor groups and formally represents a congener of the ubiquitous 1,1′-bis(diphenylphosphino)ferrocene (dppf) . Compounds of this type are not entirely unprecedented, even among ferrocene derivatives, being represented by 1-(diphenylphosphino)-2-(cyanomethyl)ferrocene and its Cα-substituted derivatives, 1-(diphenylphosphino)-2-cyano-3-ethylferrocene, and 2-cyano-1-phosphaferrocene . However, only the last of these compounds has been studied as a ligand in transition-metal complexes, coordinating as a P-monodentate donor …”

“…Compounds of this type are not entirely unprecedented, even among ferrocene derivatives, being represented by 1-(diphenylphosphino)-2-(cyanomethyl)ferrocene and its Cα-substituted derivatives, 1-(diphenylphosphino)-2-cyano-3-ethylferrocene, and 2-cyano-1-phosphaferrocene . However, only the last of these compounds has been studied as a ligand in transition-metal complexes, coordinating as a P-monodentate donor …”

Oligo(metallocene)s Containing Keto‐Bridged Phospholyl Rings

“…As far as we are aware, the phosphorus atoms in such metallocene polymers are invariably present as exocyclic substituents of classical metallocenes, as in 1 , so that no examples exist of conjugated oligo(phosphametallocene)s 2 , whose phosphorus atom is incorporated into the metallocene skeleton rather than the bridge 20. Such phosphametallocenes have, however, been widely used as ligands for catalysis 21. The increased exposure of the phosphorus atom to the metal centre in oligomers such as 2 has the potential to generate properties that are quite different from those found in oligo(metallocenephosphine)s, and the presence of the phosphorus atoms buried within an extended metallocene chain in an aromatic carbon matrix also makes them attractive targets.…”