Electrochemistry of Late Transition Metal Complexes Containing the Ligand 1,1′-Bis(diisopropylphosphino)ferrocene (dippf) # Joyce H. L. Ong, † Chip Nataro,* ,† James A. Golen, ‡,§,⊥ and Arnold L. Rheingold ‡,§ Department of Chemistry, Lafayette College, Easton, Pennsylvania 18042, and Department of Chemistry & Biochemistry, University of Delaware, Newark, Delaware 19716 Received July 2, 2003 The chemically reversible oxidation of 1,1′-bis(diisopropylphosphino)ferrocene (dippf) was investigated using cyclic voltammetry. In addition, seven new compounds with general formulas of [(MCl n ) m (dippf)] (M ) Co, Ni, Pt, Zn, Cd or Hg, n ) 2, m ) 1; M ) Au, n ) 1, m ) 2) have been prepared. The Ni and Co compounds were found to be paramagnetic, and the Evans method was used to determine the magnetic moment for these compounds. The remaining compounds were characterized by 1 H, 13 C, and 31 P NMR. As an additional means of characterization, the molecular structures of [PtCl 2 (dippf)] and [ZnCl 2 (dippf)] were determined. The electrochemistry of the new compounds and the previously synthesized [PdCl 2 (dippf)] was investigated using cyclic voltammetry. The results of this investigation show that coordination of the dippf ligands leads to more positive oxidation potentials for the ferrocene backbone. Introduction Although both are commercially available, 1,1′-bis- (diphenylphospino)ferrocene (dppf) 1 has been studied more thoroughly than the analogous isopropyl com- pound, 1,1′-bis(diisopropylphosphino)ferrocene (dippf). One means of evaluating this difference is to look at the number of reported structures that contain either of these phosphines. At the time of this report, there are approximately 320 structures containing dppf registered in the Cambridge Crystallographic Data Centre, while there are only 13 structures containing dippf. The structure of dippf has apparently been determined, but not yet reported. 2 Of the 13 published dippf-containing structures, three are of the phosphine chalcogenides, dippfE 2 (E ) O, S, or Se). 3 One structure has dippfS 2 bridging two Te centers. 4 Of the remaining structures, six have dippf coordinated to a square-planar Pd(II) center. 5 Many of the reports of compounds containing dippf have focused on catalytic processes, particularly using Pd(II) catalysts. For the cooligomerization of butadiene and carbon monoxide in the presence of Pd(acac) 2 , dippf was found to be far superior to dppf in selectivity. 5b In the catalysis of the Heck reaction, [PdCl 2 (dippf)] was determined to be a superior catalyst to the analogous dppf compound. 5a However, in hydroamination reactions using Pd(II) catalysts, higher yields were obtained using dppf as a ligand for the catalyst as compared to dippf. 5f Steric and electronic properties are often cited as the reasons for the variation in activity of dppf and dippf. However, compounds containing dppf and dippf have been compared only sterically. 6 It is surprising that the electronic nature of dippf has not been investigated. Since dippf contains a redox- active ferrocene backbone, studying the electrochemistry of dippf may provide insight into its electronic nature. The electrochemistry of dppf has been thoroughly studied, and, unlike ferrocene, the oxidation is compli- cated by a chemical follow-up reaction. 7 However, upon coordination, the oxidation of dppf is frequently but not always reversible. 8 The property that seems to govern the reversibility of the oxidation of dppf is the lone pair of electrons on the phosphorus atoms. If the phosphorus atoms are strongly bound to a metal center such as [PdCl 2 (dppf)] or oxidized to phosphorus(V) as in dppfO 2 , # Presented in part at the 226th National Meeting of the American Chemical Society, New York, NY, September 7-11, 2003; see: Ab- stracts of Papers, INOR 409. * Corresponding author. E-mail: nataroc@lafayette.edu. † Lafayette College. ‡ University of Delaware. § Current address: Department of Chemistry and Biochemistry, University of San Diego, La Jolla, CA 92093. ⊥ Permanent address: Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, MA 02747. (1) Gan, K.-S.; Hor, T. S. A. In Ferrocenes. From Homogeneous Catalysis to Material Science; Togni, A., Hayashi, T., Eds.; VCH: New York, 1995; p 3. (2) Elsagir, A. R.; Gassner, F.; Gorls, H.; Dinjus, E. J. Organomet. Chem. 2000, 597, 139. Ref 8 makes note of the dippf structure, but it has yet to be published. (3) Necas, M.; Beran, M.; Woolins, J. D.; Novosad, J. Polyhedron 2001, 20, 741. (4) Necas, M.; Novosad, J.; Husebye, S. J. Organomet. Chem. 2001, 623, 124. (5) (a) Boyes, A. L.; Butler, I. R.; Quayle, S. C. Tetrahedron Lett. 1998, 39, 7763. (b) Elsagir, A. R.; Gassner, F.; Gorls, H.; Dinjus, E. J. Organomet. Chem. 2000, 597, 139. (c) Guzei, I. A.; Maisela, L. L.; Darkwa, J. Acta Crystallogr. Sect. C: Cryst. Struct. Commun. 2000, 56, 564. (d) Maisela, L. L.; Crouch, A. N.; Darkwa, J.; Guzei, I. A. Polyhedron 2001, 20, 3189. (e) Culkin, D. A.; Hartwig, J. F. J. Am. Chem. Soc. 2002, 124, 9330. (f) Kelin, L.; Horton, P. N.; Hursthouse, M. B.; Hii, K. K. J. Organomet. Chem. 2003, 665, 250. (6) Avent, A. G.; Bedford, R. B.; Chaloner, P. A.; Dewa, S. Z.; Hitchcock, P. B. J. Chem. Soc., Dalton Trans. 1996, 4633. (7) (a) Pilloni, G.; Longato, B.; Corain, B. J. Organomet. Chem. 1991, 420, 57. (b) Nataro, C.; Campbell, A. N.; Ferguson, M. A.; Incarvito, C. D.; Rheingold, A. L. J. Organomet. Chem. 2003, 673, 47. (8) Corain, B.; Longato, B.; Favero, G.; Ajo `, D.; Pilloni, G.; Russo, U.; Kreissl, F. R. Inorg. Chim. Acta 1989, 157, 259. 5027 Organometallics 2003, 22, 5027-5032 10.1021/om0340138 CCC: $25.00 © 2003 American Chemical Society Publication on Web 10/31/2003