Hauptinhalt

Beiträge in begutachteten Fachzeitschriften

2024

70. D. Rottschäfer, S. Reith, J. Schwarzmann, F. Tambornino, C. Lichtenberg*
Chem. Eur. J. 2024, 30, e202303363.
Cyclic Hydrocarbon Frameworks Containing Two Bismuth Atoms:
Towards 9,10-Dibismaanthracene
2023

69. D. Rottschäfer, A. Pachkovska, X. Xie, K. Oberdorf, S. Reith, A. Stoy, C. Lichtenberg*
      Inorg. Chem. 2023, 62, 18228-18238.
      Fusing Triphenylbismuth and PnPh₃ (Pn = P–Bi):
      Synthesis, Isolation, and Characterization of 9-Bisma-10-Pnictatriptycenes
      *** Hervorgehoben in ChemistryViews ***

68. S. Martínez, C. Lichtenberg*
       Synlett 2023, DOI: 10.1055/a-2187-0455.
       Bismuth-centered radical species: access and applications in organic synthesis

67. M. Maier, V. Zeh, N. Munker, J. Glock, K. Oberdorf, O. Ayhan, C. Lichtenberg, H. Helten*
       Eur. J. Inorg. Chem. 2023, e202300490.
      1,2,5-Azadiborolane as a Building Block for Inorganic–Organic Hybrid Polymers
*** Hervorgehoben auf dem "front cover" ***

66. F. Geist, S. Martínez, J. Ramler, K. Oberdorf, L. Brändler, S. Reith, C. Lichtenberg*
      Eur. J. Inorg. Chem. 2023, e202300415.
      A Dibismuthane with Olefin Functional Groups:
      towards Tridentate Hybrid Chalcogen/Olefin Ligands
     *** Hervorgehoben in ChemistryViews ***
     *** Hervorgehoben auf dem "front cover" ***
   *** Hervorgehoben als "editor's choice" ***

65. A. Stoy, M. Jürgensen, C. Millidoni, C. Berthold, J. Ramler, S. Martínez, M. Buchner,
      C. Lichtenberg*
      Angew. Chem. Int. Ed. 2023, 62, e202308293.
      Bismuth in Dynamic Covalent Chemistry: Access to a Bowl-Type Macrocycle
      and a Barrel-Type Heptanuclear Complex Cation

64. K. Oberdorf, C. Lichtenberg*
      Chem. Commun. 2023, 59, 8043-8058.
      Small molecule activation by well-defined compounds of heavy p-block elements

63. K. Oberdorf, P. Pfister, P. Grenzer, J. Ramler, A. Hanft, A. Stoy, X. Xie,
      C. Lichtenberg*
      Organometallics 2023, 42, 885-895.
      Cationic Bismuth Amides Add across Activated C=X Bonds (X = C, N, and S):
      Pronounced Solvent Effects on Reactivity and Selectivity

62. K. Oberdorf, A. Hanft, X. Xie, F. M. Bickelhaupt, J. Poater,* C. Lichtenberg*
      Chem. Sci. 2023, 14, 5214-5219.
      Insertion of CO₂ and CS₂ into Bi–N bonds enables catalyzed CH-activation
      and light-induced bismuthinidene transfer
     *** Hervorgehoben in: "Trendberichte 2024: Anorganische Chemie",
M. Fischer, D. Heift, Nachr. Chem. 2024, 72, 46-57. ***

61. E. Karaev, M. Gerlach, L. Faschingbauer, J. Ramler, I. Krummenacher,
      C. Lichtenberg,* P. Hemberger,* I. Fischer*
      Chem. Eur. J. 2023, 29, e202300637.
      Bonding in Low-Coordinated Organoarsenic and Organoantimony Compounds:
      A Threshold Photoelectron Spectroscopic Investigation
      *** Hervorgehoben als "hot paper" ***
      *** Hervorgehoben durch ein "cover feature" ***

60. T. Dunaj, J. Schwarzmann, J. Ramler, A. Stoy, S. Reith, J. Nitzsche, L. Völlinger,
      C. von Hänisch,* C. Lichtenberg*
      Chem. Eur. J. 2023, 29, e202204012.
      Bismuth Cations: Fluoride Ion Abstraction, Isocyanide Coordination,
      and Impact of Steric Bulk on Lewis Acidity
      *** Hervorgehoben als "hot paper" ***
      *** Hervorgehoben auf dem "front cover" ***
      *** "cover story" ***

59. J. Heine,* B. Peerless, S. Dehnen,* C. Lichtenberg*
      Angew. Chem. Int. Ed. 2023, 62, e202218771.
      Charge Makes a Difference: Molecular Ionic Bismuth Compounds

58. K. Oberdorf, P. Grenzer, P. Pfister, A. Hanft, A. Rempel, C. Lichtenberg*
      ChemPlusChem 2023, 88, e202200455.
      Reactivity of a Cationic Bismuth Amide towards Unsymmetric Heterocumulenes
     *** Hervorgehoben auf dem "front cover" ***
      *** "cover story" ***

57. F. Lindl, A. Lamprecht, M. Arrowsmith, E. Khitro, A. Rempel, M. Dietz, T. Wellnitz,
      G. Bélanger-Chabot, A. Stoy, V. Paprocki, D. Prieschl, C. Lenczyk, J. Ramler,
      C. Lichtenberg, H. Braunschweig*
      Chem. Eur. J. 2023, 29, e202203345.
      Aromatic 1,2-Azaborinin-1-yls as Electron-Withdrawing Anionic Nitrogen Ligands
      for Main Group Elements
2022

56. J. Ramler, A. Stoy, T. Preitschopf, J. Kettner, I. Fischer, B. Rohling, F. Fantuzzi*,
      C. Lichtenberg*
      Chem. Commun. 2022, 58, 9826-9829.
      Dihalo bismuth cations:
      unusual coordination properties and inverse solvent effects in Lewis acidity

55. A. Hanft, D. Rottschäfer, V. Müller, P. Weinberger, K. Radacki, X. Xie, C. Lichtenberg*
      Dalton Trans. 2022, 51, 10809-10817.
      Sulfinyl-aminotroponiminates: alkali- (Li, Na, K) and heavy-metal (Bi) complexes

54. S. Reith, S. Demeshko, B. Battistella, A. Reckziegel, C. Schneider, A. Stoy, C. Lichtenberg,
      F. Meyer, D. Munz,* C. G. Werncke*
      Chem. Sci. 2022, 13, 7907-7913.
      Between Imide, Imidyl and Nitrene – An Imido Iron Complex in Two Oxidation States

53. J. Ramler, J. Schwarzmann, A. Stoy, C. Lichtenberg*
      Eur. J. Inorg. Chem. 2022, e202100934.
    Two Faces of the Bi–O Bond: Photochemically- and Thermally-Induced
      Dehydrocoupling for Si–O Bond Formation
      *** Hervorgehoben auf dem "front cover" ***
2021

52. K. Oberdorf, P. Grenzer, N. Wieprecht, J. Ramler, A. Hanft, A. Rempel, A. Stoy,
      K. Radacki, C. Lichtenberg*
      Inorg. Chem. 2021, 60, 19086-19097.
CH Activation of Cationic Bismuth Amides:
      Heteroaromaticity, Derivatization, and Lewis Acidity

51. J. Ramler, F. Fantuzzi, F. Geist, A. Hanft, H. Braunschweig, B. Engels,
     C. Lichtenberg*
      Angew. Chem. Int. Ed. 2021, 60, 24388-24394.
      The Dimethylbismuth Cation:
      Entry into Dative Bi–Bi Bonding and Unconventional Methyl Exchange
      *** Hervorgehoben als "hot paper" ***
      *** Hervorgehoben durch ein "frontispiece" ***
      *** Hervorgehoben in: "Trendbericht Anorganik 2022",
              M. Fischer, D. Heift, Nachr. Chem. 2022, 70, 40-51. ***

50. A. Hanft, D. Rottschäfer, N. Wieprecht, F. Geist, K. Radacki, C. Lichtenberg*
        Chem. Eur. J. 2021, 27, 14250-14262.
        Aminotroponiminates: Impact of the NO₂ Functional Group
        on Coordination, Isomerisation, and Backbone Substitution
        *** Hervorgehoben als "hot paper" ***

49. J. Ramler C. Lichtenberg*
       Dalton Trans. 2021, 50, 7120-7138.
       Bismuth Species in the Coordination Sphere of Transition Metals:
   Sythesis, Bonding, Coordination Chemistry, and Reactivity of
   Molecular Complexes    (perspective article)
       *** Hervorgehoben durch ein "cover feature" ***
       *** Auszeichnet als "hot article" ***

48. C. Lichtenberg*
        Chem. Commun. 2021, 57, 4483-4495.
        Molecular Bismuth(III) Monocations:
        Structure, Bonding, Reactivity, and Catalysis     (feature article)

47. J. Ramler, L. Wüst, A. Rempel, L. Wolz, C. Lichtenberg*
       Organometallics 2021, 40, 832–837.
   Bismuth Atoms in Hydrocarbon Ligands:
       Bismepines as Rigid, Ditopic Arene Donors in Coordination Chemistry
       *** Hervorgehoben durch ein "cover feature" ***

46. C. Brunecker, M. Arrowsmith, J. Muessig, J. Böhnke, A. Stoy, M. Heß, A.
        Hofmann, C. Lenczyk, C. Lichtenberg, A. Rempel, J. Ramler, H. Braunschweig*
        Dalton. Trans. 2021, 50, 3506-3515.
        Synthesis and characterisation of boranediyl- and diboranediyl-bridged
      diplatinum A-frame complexes

45. A. Hanft, K. Radacki, C. Lichtenberg*
        Chem. Eur. J. 2021, 27, 6230-6239.
        Cationic Bismuth Aminotroponiminates: Charge Controls Redox Properties
    *** Hervorgehoben durch ein "cover feature" ***

44. K. Oberdorf, A. Hanft, J. Ramler, I. Krummenacher, F. M. Bickelhaupt,
        J. Poater,* C. Lichtenberg*
        Angew. Chem. Int. Ed. 2021, 60, 6441-6445.
        Bismuth Amides Mediate Facile and Highly Selective Pn-Pn Radical Coupling
        Reactions (Pn = N, P, As)
2020

43.   A. Hanft, M. Jürgensen, L. Wolz, K. Radacki, C. Lichtenberg*
        Inorg. Chem. 2020, 59, 17678-17688.
        Salicylaldimines: Formation via Ring Contraction and Synthesis
        of Mono- and Heterobimetallic Alkali Metal Heterocubanes

42.   J. Ramler, I. Krummenacher, C. Lichtenberg*
       Chem. Eur. J. 2020, 26, 14551-14555.
       Well-defined, molecular bismuth compounds:
       catalysts in photochemically-induced radical dehydrocoupling reactions

41.   J. Ramler, K. Radacki, J. Abbenseth,* C. Lichtenberg*
       Dalton Trans. 2020, 49, 9024-9034.
       Combined experimental and theoretical studies
       towards mutual Osmium–Bismuth donor/acceptor bonding

40.   D. P. Mukhopadhyay, D. Schleier, S. Wirsing, J. Ramler, D. Kaiser, E. Reusch, P. Hemberger,
        T. Preitschopf, I. Krummenacher, B. Engels,* I. Fischer,* C. Lichtenberg*
        Chem. Sci. 2020, 11, 7562-7568.
        Methylbismuth: an Organometallic Bismuthinidene Biradical
*** Hervorgehoben auf dem "front cover" ***
        *** Hervorgehoben in "HOT article collection 2020" ***
        *** Hervorgehoben in "Chemistry Views" ***
        *** Hervorgehoben in: "Notizen aus der Chemie", Nachr. Chem. 2020, 68 (Sept), 54. ***
        *** Hervorgehoben in: "Trendberichte 2020: Anorganische Chemie",
              C. Hering-Junghans, C. Sindlinger, Nachr. Chem. 2021, 69, 52-66. ***

39.   J. Ramler, C. Lichtenberg*
       Chem. Eur. J. 2020, 26, 10250-10258.
       Molecular Bismuth Cations: Assessment of Soft Lewis Acidity
       *** Hervorgehoben durch ein "cover feature" ***
       *** Hervorgehoben als "very important paper" ***

38.   A. Hanft, C. Lichtenberg*
        Z. Kristallogr. NCS 2020, 235, 963-966.
        Dimerization of 2-[(2-((2-Aminophenyl)thio)phenyl)amino]-cyclohepta-2,4,6-trien-1-one
        through Hydrogen Bonding

37.   C. Lichtenberg*
        Chem. Eur. J. 2020, 26, 9674-9687.
        Main Group Metal Complexes in Selective Bond Formations through Radical Pathways
        (Übersichtsartikel)
        *** Hervorgehoben im "Showcase" für ausgezeichnete Übersichtsartikel ***

36.   J. Ramler, K. Hofmann, C. Lichtenberg*
        Inorg. Chem. 2020, 59, 3367-3376.
      Neutral and Cationic Bismuth Compounds:
      Structure, Hetero-Aromaticity, and Lewis Acidity of Bismepines
        *** Hervorgehoben durch ein "cover feature" ***
2019

35.   J. Ramler, I. Krummenacher, C. Lichtenberg*
        Angew. Chem. Int. Ed. 2019, 58, 12924-12929.
      Bismuth Compounds in Radical Catalysis: Transition Metal Bismuthanes
      Facilitate Thermally-Induced Cyclo-Isomerizations

34.   A. Hanft, I. Krummenacher, C. Lichtenberg*
        Chem. Eur. J. 2019, 25, 11883-11891.
    Alkali Metal Aminotroponiminates: Selectivities and Equilibria
in Reversible Radical Coupling of Delocalized π-Electron Systems
      *** Hervorgehoben als "hot paper" ***
        *** Hervorgehoben durch ein "cover feature" ***

33. J. Ramler, J. Poater, F. Hirsch, B. Ritschel, I. Fischer, F. M. Bickelhaupt,* C. Lichtenberg*
        Chem. Sci. 2019, 10, 4169-4176.
        Carbon Monoxide Insertion at a Heavy p-Block Element:
        Unprecedented Formation of a Cationic Bismuth Carbamoyl
        *** Hervorgehoben als "pick of the week". ***
        *** Hervorgehoben in "HOT article collection 2019" ***
        *** Hervorgehoben in "Chemistry World" ***
        *** Hervorgehoben in: "Trendberichte 2019: Anorganische Chemie",
               C. Hering-Junghans, C. Sindlinger, Nachr. Chem. 2020, 68, 50-64. ***
2018

32.   A. Hanft, C. Lichtenberg*
        Eur. J. Inorg. Chem. 2018, 3361-3373.
New Perspectives for Aminotroponiminates: Coordination
        Chemistry, Redox Behavior, Cooperativity, and Catalysis
      (Übersichtsartikel)
*** Hervorgehoben als "very important paper" ***

31.   B. Ritschel, C. Lichtenberg*
        Synlett 2018, 29, 2213-2217.
Cationic Bismuth Compounds in Organic Synthesis and Catalysis:
        New Prospects for CH Activation
*** Hervorgehoben auf dem front cover ***

30.   A. Hanft, C. Lichtenberg*
        Organometallics 2018, 37, 1781-1787.
Rationalizing the Effect of Ligand Substitution Patterns
        on Coordination and Reactivity of Alkali Metal Aminotroponiminates

29.   A. Hanft, M. Jürgensen, R. Bertermann, C. Lichtenberg*
        ChemCatChem 2018, 10, 4018-4027.
Sodium Aminotroponiminates: Ligand-Induced Disproportionation,
        Mixed-Metal Compounds, and Exceptional Activity in Polymerization Catalysis

28.   A. Hanft, C. Lichtenberg*
        Dalton Trans. 2018, 47, 10578-10589.
      Aminotroponiminates: ligand-centred, reversible redox events
      under oxidative conditions in sodium and bismuth complexes

27.   B. Ritschel, J. Poater, H. Dengel, F. M. Bickelhaupt,* C. Lichtenberg*
        Angew. Chem. Int. Ed. 2018, 57, 3825-3829.
        Double CH Activation of a Masked Cationic Bismuth Amide
    *** Hervorgehoben in: "Trendberichte 2018: Anorganische Chemie",
               C. Hering-Junghans, C. Sindlinger, Nachr. Chem. 2019, 67, 46-64. ***
2017

26.   H. Braunschweig*, I. Krummenacher, C. Lichtenberg, J. D. Mattock, M. Schäfer, U.
        Schmidt, C. Schneider, T. Steffenhagen, S. Ullrich, A. Vargas
        Angew. Chem. Int. Ed. 2017, 56, 889-892.
        Dibora[2]ferrocenophane: A Carbene-Stabilized Diborene
in a Strained cis-Configuration
2016

25.   H. Dengel, C. Lichtenberg*
        Chem. Eur. J. 2016, 22, 18465-18475.
        Cationic Bismuth Amides: Accessibility, Structure, and Reactivity

24.   C. Lichtenberg*, I. Krummenacher
        Chem. Commun. 2016, 52, 10044-10047.
        Aminotroponiminates as tunable, redox-active ligands: reversible single
    electron transfer and reductive dimerisation

23.   C. Lichtenberg*
        Organometallics 2016, 35, 894-902.
        Aminotroponiminates: Alkali Metal Compounds Reveal Unprecedented
        Coordination Modes

22.   C. Lichtenberg*
        Angew. Chem. Int. Ed. 2016, 55, 484-486.
        Well-Defined, Mononuclear Bi^I and Bi^II Compounds: Towards Transition-
    Metal-Like Behavior
2015-2014 (Arbeiten mit Prof. H. Grützmacher)

21. C. Lichtenberg, J. Bloch, T. L. Gianetti, T. Büttner, J. Geier, H. Grützmacher*
        Dalton Trans. 2015, 44, 20056-20066.
        Diolefins with an Ether/Thioether Functionality as Potentially Hemilabile Ligands in
        the Coordination Sphere of Ni and Rh

20.   C. Lichtenberg*, M. Adelhardt, T. L. Gianetti, K. Meyer, B. de Bruin, H. Grützmacher*
        ACS Catal. 2015, 5, 6230-6240.
        Low-Valent Iron Mono-Diazadiene Compounds: Electronic Structure and Catalytic
        Application

19.   C. Lichtenberg*, D. E. Prokopchuk, M. Adelhardt, L. Viciu, K. Meyer, H.
        Grützmacher*
        Chem. Eur. J. 2015, 21, 15797-15805.
        Reactivity of an All-Ferrous Iron-Nitrogen Heterocubane under Reductive and
        Oxidative Conditions

18.   C. Lichtenberg*, I. Garcia Rubio, L. Viciu, M. Adelhardt, K. Meyer, G. Jeschke, H.
        Grützmacher*
        Angew. Chem. Int. Ed. 2015, 54, 13012-13017.
        A Low-Valent Iron Imido Heterocubane Cluster: Reversible Electron Transfer and
        Catalysis of Selective C-C couplings

17.   C. Lichtenberg*, L. Viciu, M. Vogt, R. E. Rodríguez-Lugo, M. Adelhardt, J. Sutter, M.
        M. Khusniyarov, K. Meyer, B. de Bruin, E. Bill, H. Grützmacher*
        Chem. Commun. 2015, 51, 13890-13893.
        Low-valent iron: an Fe(I) ate compound as a building block for a linear trinuclear Fe
        cluster
      *** Hervorgehoben als Rückseitentitelbild. ***
    *** Hervorgehoben in: Chimia 2015, 12, 805. ***

16.   C. Lichtenberg*, M. Adelhardt, M. Wörle, T. Büttner, K. Meyer, H. Grützmacher*
        Organometallics 2015, 34, 3079-3089.
        Mono- and Dinuclear Neutral and Cationic Iron(II) Compounds Supported by an
        Amidinato-diolefin Ligand: Characterization and Catalytic Application

15.   C. Lichtenberg*, L. Viciu, M. Adelhardt, J. Sutter, K. Meyer, B. de Bruin*, H.
        Grützmacher*
        Angew. Chem. Int. Ed. 2015, 54, 5766-5771.
        Low-Valent Iron(I) Amido Olefin Complexes as Promotors for Dehydrogenation
        Reactions
        *** Hervorgehoben in: "Trendberichte 2015: Anorganische Molekülchemie, T. Böttcher,
               R. Kretschmer, Nachr. Chem. 2016, 64, 217-232. ***
2013-2010 (Arbeiten mit Prof. J. Okuda)

14.   C. Lichtenberg, J. Okuda*
      Angew. Chem. Int. Ed. 2013, 52, 5228-5246.
        Structurally Defined Allyl Compounds of Main Group Metals: Coordination and
        Reactivity

13. C. Lichtenberg, T. P. Spaniol, I. Peckermann, T. P. Hanusa*, J. Okuda*
        J. Am. Chem. Soc. 2013, 135, 811-821.
      Cationic, Neutral, and Anionic Allyl Magnesium Compounds: Unprecedented Ligand
        Conformations and Reactivity toward Unsaturated Hydrocarbons
        Hervorgehoben in: "Trendberichte 2013: Anorganische Molekülchemie", R. C.
        Fischer, J. J. Weigand, Nachr. Chem. 2014, 62, 219-236.

12.   C. Lichtenberg, F. Pan, T. P. Spaniol, U. Englert, J. Okuda*
        Angew. Chem. Int. Ed. 2012, 51, 13011-13015.
      The Bis(allyl)bismuth Cation: A New Reagent for Direct Allyl Transfer by Lewis Acid
        Activation and Controlled Radical Polymerization

11. C. Lichtenberg, T. P. Spaniol, J. Okuda*
        Angew. Chem. Int. Ed. 2012, 51, 8101-8105.
        Dimerization of the Allylzinc Cation: Selective Coupling of Allyl Anions in a Metallo-
        Ene-Reaction

10. C. Lichtenberg, J. Engel, T. P. Spaniol, U. Englert, G. Raabe, J. Okuda*
        J. Am. Chem. Soc. 2012, 134, 9805-9811.
      Bis(allyl)zinc Revisited: Sigma versus Pi Bonding of Allyl Coordination

9.     C. Lichtenberg, T. P. Spaniol, L. Perrin, L. Maron*, J. Okuda*
Chem. Eur. J. 2012, 18, 6448-6452.
        Reversible 1,4-Insertion of Pyridine Into A Highly Polar Metal Carbon Bond:
        Effect of the Second Metal

8.     C. Lichtenberg, T. P. Spaniol, J. Okuda*
      Inorg. Chem. 2012, 51, 2254-2262.
      Bis(allyl)gallium Cation, Tris(allyl)gallium, and Tetrakis(allyl)gallate: Synthesis,
        Characterization, and Reactivity

7.     C. Lichtenberg, T. P. Spaniol, J. Okuda*
        Organometallics 2011, 30, 4409-4417.
        Reactivity of Tris(allyl)aluminum toward Pyridine:
        Coordination versus Carbometalation

6.     C. Lichtenberg, P. Jochmann, T. P. Spaniol, J. Okuda*
        Angew. Chem. Int. Ed. 2011, 50, 5753-5756.
        The Allylcalcium Monocation: A Bridging Allyl Ligand with a Non-Bent Coordination
        Geometry
        *** Hervorgehoben in: "Trendberichte 2011: Anorganische Molekülchemie", R. C.
          Fischer, J. J. Weigand, Nachr. Chem. 2012, 60, 216-232. ***

5.     C. Lichtenberg, D. Robert, T. P. Spaniol, J. Okuda*
        Organometallics 2010, 29, 5714-5721.
      Bis(allyl)aluminum Cation, Tris(allyl)aluminum, and Tetrakis(allyl)aluminate:
        Synthesis, Characterization, and Reactivity
2010 (Arbeiten mit Prof. J. Sundermeyer)

4.     F. G. Schröder, C. Lichtenberg, M. Elfferding, J. Sundermeyer*
        Organometallics 2013, 32, 5082-8091.
        Deprotonated P-ylides As Templates for Novel Cyclopentadienyl Phosphonioalkyl,
        alkylidene, and -alkylidyne (CpPC) Constrained-Geometry Complexes

3.     C. Lichtenberg, N. S. Hillesheim, M. Elfferding, B. Oelkers, J. Sundermeyer*
      Organometallics 2012, 31, 4259-4266.
        New Lithium Phosphonium Diylides: A Methylene and a Cyclopentadienyl Moiety as
        Ylidic Coordination Sites

2.     C. Lichtenberg, M. Elfferding, L. Finger, J. Sundermeyer*
        J. Organomet. Chem. 2010, 695, 2000-2006.
      Investigation of Novel and Reinvestigation of Known Cyclopentadienylphosphanes:
        News on [1,5] Sigmatropic Rearrangements

1.     C. Lichtenberg, M. Elfferding, J. Sundermeyer*
        Eur. J. Inorg. Chem. 2010, 2010, 3117-3124.
        Unexpected Oxidative Dimerisations of a Cyclopentadienyl-Phosphane -
        Formation of Unprecedented, Structurally Remarkable Phosphacyclic Compounds