Mendeleev Communications Electronic Version, Issue 1, 2002 1 Reactions of the pentaphospholide anion with half-sandwich complexes of iron: a new route to pentaphosphaferrocenes Vasily A. Miluykov,*a Oleg G. Sinyashin,a Otto Schererb and Evamarie Hey-Hawkinsc a A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre of the Russian Academy of Sciences, 420088 Kazan, Russian Federation.Fax: +7 8432 76 7424; e-mail: miluykov@iopc.knc.ru, oleg@iopc.knc.ru b Universität Kaiserslautern, Fachbereich Chemie, D-67663 Kaiserslautern, Germany. Fax: +49 631 205 2432; e-mail: oscherer@rhrk.uni-kl.de c Universität Leipzig, Institut für Anorganische Chemie, D-04103 Leipzig, Germany. Fax: +49 0341 973 9319; e-mail: hey@rz.uni-leipzig.de DOI: 10.1070/MC2002v012n01ABEH001517 Pentaphosphaferrocenes were prepared in good yields by the reaction of the pentaphospholide anion P5 – with half-sandwich complexes of iron containing carbonyl groups or tertiary phosphine ligands.The pentaphospholide anion P5 –, which is an isolobal analogue of the cyclopentadienyl anion,1 is of interest as a convenient reagent in organometallic and coordination chemistry.2,3 However, only a few organometallic compounds with P5 fragments were synthesised from NaP5 1.4,5 In particular, pentamethylpentaphosphaferrocene 2 was prepared in 12% yield by the reaction of 1 with iron(II) chloride and lithium pentamethylcyclopentadienide. 4 Recently, we reported a new method for preparing 1 by the reaction of sodium metal with white phosphorus under the conditions of phase-transfer catalysis.6 This simple method makes it possible to study the chemical behaviour of 1 towards various organometallic compounds.It was also of interest to develop a general high-yield route to pentaphosphaferrocenes and to determine the factors affecting the product yields. We based our approach on the well-known reaction of half-sandwich iron complexes with sodium cyclopentadienide.7 The reaction of 1 with pentamethylcyclopentadienyl(dicarbonyl) iron bromide† 3 in diglyme at 110 °C for 2 h gave pentamethylpentaphosphaferrocene 2 in ~70% yield.The structure of 2 was determined by 1H and 31P NMR spectroscopy and by a comparison with the published data.8,9 The reaction of 1 with 1,3-di-tert-butylcyclopentadienyl- (dicarbonyl)iron bromide 4† under similar conditions gave compound 5 in a yield of at most 5%.The structure of 5 was determined by 1H and 31P NMR spectroscopy and mass spectrometry. This compound also was prepared by the interaction of Cr(CO)5PCl3 with Cp''Fe(CO)2K in a yield of about 10%.10 The 31P NMR spectrum exhibits a singlet at 167 ppm, and the 1H NMR spectrum exhibits a singlet at 1.06 ppm due to methyl groups and a broad singlet at 3.71 ppm due to the protons of the cyclopentadienyl ring.Relative to tetra-tert-butylferrocene, the 1H NMR signals are shifted by an average of 0.26 ppm.11,12 The mass spectrum showed a peak of the molecular ion (m/z 388). The main product of this reaction was 1,1',3,3'-tetra-tertbutylferrocene 6, which was identified by 1H NMR spectroscopy and by a comparison of the physical properties with published data.9 Clearly, at a reaction temperature of 110 °C, pentaphosphaferrocene 5 decomposes to give compound 6.We postulated that a decrease in the reaction temperature increases the yield of 5. It is known that the replacement of CO ligands in organometallic compounds with better leaving groups, such as tertiary phosphines, facilitates the process of ligand exchange.Therefore, we treated 1 with 1,3-di-tert-butylcyclopentadienyl[ bis(trimethylphosphine)]iron bromide 7.‡ This reaction was conducted at 70 °C to form compound 5 in high yield (about 80%). Thus, we developed a new route to pentaphosphaferrocenes based on the reaction of the pentaphospholide anion with halfsandwich iron compounds containing carbonyl or tertiary phosphine ligands. V.Miluykov thanks the Deutsche Akademische Austauschdienst (A/00/06361) and the Sächsisches Ministerium für Wissenschaft und Kunst (SMWK, Az. 4-7531.50-04-0361-00) for financial support. † A solution of pentamethylcyclopentadienyl(dicarbonyl)iron bromide (260 mg, 0.8 mmol) in diglyme (20 ml) was added to a solution of NaP5 in diglyme (40 ml, 0.02 mol dm–3) at room temperature.The reaction mixture was stirred for 2 h at 110 °C. After cooling, the solvent was evaporated and the residue was purified by chromatography with light petroleum to give 2 (190 mg, 70%) as green crystals. 1H NMR, d: 1.08. 31P NMR, d: 153. A solution of 1,3-di-tert-butylcyclopentadienyl(dicarbonyl)iron bromide (295 mg, 0.8 mmol) in diglyme (20 ml) was added to a solution of NaP5 in diglyme (40 ml, 0.02 mol dm–3) at room temperature.The reaction mixture was stirred for 2 h at 110 °C. After cooling, the solvent was evaporated and the residue was purified by chromatography with light petroleum to give 5 (15 mg, 5%) as green crystals and 1,1',3,3'-tetra-tertbutylferrocene 6 (215 mg, 65%) as a yellowish orange powder (mp 193 °C; lit.,9 196 °C).P P P P P Me Me Me Me Me Fe CO OC Br + NaP5 110 °C – 2CO, – NaBr Me Me Me Me Me Fe 1 3 2 (~70%) ‡ A solution of 1,3-di-tert-butylcyclopentadienyl[bis(trimethylphosphine)]- iron bromide 7 (295 mg, 0.8 mmol) in diglyme (20 ml) was added to a solution of NaP5 in diglyme (40 ml, 0.02 mol dm–3) at room temperature. The reaction mixture was stirred for 2 h at 70 °C.After cooling, the solvent was evaporated and the residue was purified by chromatography with light petroleum to afford 5 (250 mg, 80%) as green crystals. P P P P P Fe CO OC Br + NaP5 110 °C – 2CO, – NaBr Fe 1 4 5 (~5%) P P P P P Fe PMe3 Br PMe3 + NaP5 70–80 °C – 2PMe3, – NaBr Fe 1 7 5Mendeleev Communications Electronic Version, Issue 1, 2002 2 References 1 R.Hoffmann, Angew. Chem., 1982, 94, 752 (Angew. Chem., Int. Ed. Engl., 1982, 21, 711). 2 O. Scherer, Angew. Chem., 1990, 102, 1137 (Angew. Chem., Int. Ed. Engl., 1990, 29, 1104). 3 M. Scheer and E. Herrmann, Z. Chem., 1990, 30, 41. 4 M. Baudler, S. Akpapoglou, D. Ouzounis, F. Wasgestian, B. Meinigke, H. Budzikiewicz and H. Münster, Angew. Chem., 1988, 100, 288 (Angew. Chem., Int.Ed. Engl., 1988, 27, 280). 5 M. Baudler and T. Etzbach, Angew. Chem., 1991, 103, 590 (Angew. Chem., Int. Ed. Engl., 1991, 30, 580). 6 V. Miluykov and O. Sinyashin, Russ. Patent, no. 2000106504/12 (006673). 7 A. N. Nesmeyanov and Yu. A. Chapovskii, Izv. Akad. Nauk SSSR, Ser. Khim., 1967, 223 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1967, 16, 224). 8 O. Scherer and T. Brück, Angew. Chem., 1987, 99, 59 (Angew. Chem., Int. Ed. Engl., 1987, 26, 59). 9 O. Scherer, T. Brück and G. Wolmershaüser, Chem. Ber., 1988, 121, 935. 10 M. Scheer, G. Friedrich and K. Schuster, Angew. Chem., 1993, 105, 641 (Angew. Chem., Int. Ed. Engl., 1993, 32, 593). 11 T. Leigh, J. Chem. Soc., 1964, 3294. 12 A. N. Nesmeyanov, N. S. Kotshetkova, S. V. Vitt, V. B. Bondarev and E. I. Kovshov, Dokl. Akad. Nauk SSSR, 1964, 156, 99 [Dokl. Chem. (Engl. Transl.), 1964, 156, 464]. Received: 17th September 2001; Com. 01/1843