Heterobimetallic complexes with ferrocenyl-substituted phosphaheterocycles

doi:10.1016/j.jorganchem.2013.07.064

Journal of Organometallic Chemistry

Volume 751, 1 February 2014, Pages 670-677

https://doi.org/10.1016/j.jorganchem.2013.07.064 Get rights and content

Highlights

•
A synthetic route to ferrocenyl-substituted heterophosphorinanes was developed.
•
They act as bidentate P,N ligands towards Mo⁰ and as monodentate ligands towards Ru^II and Au^I.
•
Preliminary studies in the Rh^I-catalysed hydroformylation were performed.
•
Hydroformylation of ethyl methacrylate showed a preference for the branched aldehyde.

Abstract

The ferrocenyl-substituted phosphaheterocycles racemic 1-(1,3,2-dithiaphosphorinan-2-yl)-2-N,N-dimethylaminomethylferrocene (rac-4) and racemic 1-(1,3,2-dioxaphosphorinan-2-yl)-2-N,N-dimethylaminomethylferrocene (rac-5) have been prepared and their coordination chemistry has been studied. Compounds rac-4 and rac-5 act as bidentate P,N ligands in rac-[Mo(CO)₄(4-κP,N)] (rac-6) and rac-[Mo(CO)₄(5-κP,N)] (rac-7), and as monodentate ligands in rac-[RuCl₂(5-κP)(η⁶-cymene)] (rac-8) and rac-[AuCl(4-κP)] (rac-9). Compounds rac-4 to rac-9 were fully characterised by NMR (¹H, ¹³C, ³¹P) and IR spectroscopy, mass spectrometry, single-crystal X-ray crystallography, and elemental analysis. Furthermore, preliminary studies on rac-5 in the rhodium(I)-catalysed hydroformylation of ethyl methacrylate were carried out and showed a preference for the branched aldehyde.

Graphical abstract

Substitution of N,N-dimethylaminomethylferrocene (1) with phosphorinanes 2 and 3 leads to 1-(1,3,2-dithia- (rac-4) and 1-(1,3,2-dioxaphosphorinan-2-yl)-2-N,N-dimethylaminomethylferrocene (rac-5). Transition metal complexes of molybdenum, gold and ruthenium were obtained. Additionally, preliminary catalytic studies on rac-5 in the rhodium(I)-catalysed hydroformylation of ethyl methacrylate were carried out.

Introduction

Phosphorus-containing heterocycles have been known for more than one century and have always attracted much interest [1], [2], [3]. The development of new and effective synthetic methods for cyclic, rigid, bulky phosphorus(III) ligands which might offer improved performance in homogeneous catalysis is one of the current challenges in organophosphorus chemistry [4]. Among these heterocycles, five-(phospholanes) [5], [6], [7] and six-membered (phosphorinanes) rings [8], [9], [10] are the best studied. 1H-Phosphorinane was first obtained in 1962 by Wagner [11], [12] and Braid [13] by a multistep synthesis which included an intramolecular Michaelis–Arbuzov reaction, a Grignard reaction, hydrolysis, and reduction. Lambert et al. developed a simplified synthesis of phosphorinanes and described their conformation [14], [15]. Heteroatom-containing phosphorinanes, so-called heterophosphorinanes, containing two oxygen [16], [17], [18], [19], sulfur [16], [19], [20] or nitrogen [16] atoms or two different donor atoms (O,S [21] or O,N [16], [17], [22], [23]) can be synthesised from bifunctional linear precursors and trichlorophosphine via HCl elimination [24], [25], [26]. Like phosphorinanes, they exhibit the chair, boat and twist conformations typical of six-membered rings. The preferred conformation depends on the incorporated heteroatoms and the substituent on the phosphorus atom. Axial positions are typically favoured for substituents at phosphorus due to interaction of the lone pair of electrons of the phosphorus atom with the σ* orbitals of the C–X bond (n(P) → σ*(C–X)) [27]. Compounds with equatorial orientation of the substituents are rare [27], [28]. Phosphorinanes are applied in therapeutic agents and pesticides as well as in catalysis [29].

Ferrocene has proved to be a versatile substituent for phosphines due to its rich chemistry, stability and redox properties [2], [3], [30], [31]. In the last decades, ferrocene-substituted phosphaheterocycles such as FerroTANEs (1,1′-bis(phosphetano)ferrocenes) [32], [33] and FerriESPHOS (diazaphospholane) [34] (Fig. 1) have attracted much interest. The combination of a chiral bis-phosphine with the characteristics of ferrocene in FerroTANEs and FerriESPHOS derivatives makes them suitable for a wide range of applications [30], [35].

We now report the synthesis of ferrocenyl-substituted heterophosphorinanes (rac-4 and rac-5) and transition metal complexes thereof (rac-6, rac-7, rac-8 and rac-9) as well as some preliminary studies on the catalytic activity of the corresponding rhodium(I) complexes in hydroformylation.

Section snippets

General considerations

All manipulations were carried out by using standard Schlenk techniques under an atmosphere of dry, high-purity nitrogen. Solvents were dried with an MB SPS-800 Solvent Purification System and stored over activated 4 Å molecular sieves. Deuterated solvents for NMR spectroscopy were purchased from Euriso-Top and Chemotrade GmbH. CDCl₃ was distilled from P₂O₅ and stored over activated 4 Å molecular sieves. C₆D₆ was dried with sodium, filtered and stored over potassium mirror. N,N

Synthesis of ferrocenyl-substituted phosphorinanes

The ferrocenyl-substituted heterophosphorinanes rac-4 and rac-5 were prepared in a facile two-step synthesis starting with the selective ortho-lithiation of aminoalkylferrocene (1) [36] followed by reaction with 2-chloro-1,3,2-dithiaphosphorinane (2) [37], [38] or 2-chloro-1,3,2-dioxaphosphorinane (3) [39] (Scheme 1).

The phosphorus-containing heterocycles 2 and 3 were prepared from linear diols or dithiols and PCl₃ according to literature procedures [37], [38], [39]. Although

Conclusion

The ferrocenyl-substituted phosphorinanes rac-4 and rac-5 were prepared and their coordination chemistry studied. Compounds rac-4 and rac-5 act as bidentate P,N ligands towards Mo(CO)₄ (rac-6, rac-7), and as monodentate ligands towards ruthenium(II) and gold(I) in complexes rac-8 and rac-9. Furthermore, preliminary studies of rac-5 in the rhodium(I)-catalysed hydroformylation of ethyl methacrylate showed a preference for the branched aldehyde.

Acknowledgements

We gratefully acknowledge generous donations of chemicals of Umicore AG & Co. KG, Chemetall GmbH and BASF SE and thank Dr. Jörg Linke und Dr. Daniel Lässig for data collection of rac-8. We also thank Regina Zäbe, Frank Seifert and Ramona Oehme for analytical measurements.

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¹: Crystal structure determination.

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Heterobimetallic complexes with ferrocenyl-substituted phosphaheterocycles

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

General considerations

Synthesis of ferrocenyl-substituted phosphorinanes

Conclusion

Acknowledgements

Modern Heterocyclic Chemistry

Angew. Chem. Int. Ed.

Ferrocenes. Homogeneous Catalysis, Organic Synthesis, Material Science

Ber. Dtsch. Chem. Ges.

Phosphorus Ligands Asymmetric Catal.

Top. Phosphorus Chem.

Uspekhi Khimii

Sci. Synth.

Tetrahedron Lett.

Tetrahedron: Asymmetry

Tetrahedron

J. Org. Chem.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Phys. Chem.

Phosphorus, Sulfur, Silicon Relat. Elem.

Tetrahedron

Phosphorus, Sulfur, Silicon Relat. Elem.

Russ. Chem. Rev.

J. Am. Chem. Soc.

Phosphorus, Sulfur, Silicon Relat. Elem.

J. Am. Chem. Soc.

Phosphorus, Sulfur, Silicon Relat. Elem.

Chem. Heterocycl. Compd.

Chiral Ferrocenes in Asymmetric Catalysis. Synthesis and Applications