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Organometallics 2009, 28, 4636–4638 DOI: 10.1021/om900331g
Formation of a Novel P,C-Cage Ligand via a P-C5Me5-Substituted Li/Cl Phosphinidenoid Complex Maren Bode, J€ org Daniels, and Rainer Streubel* Institut f€ ur Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universit€ at Bonn, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany Received April 28, 2009 Summary: The novel P,C-cage ligand in the dinuclear tungsten complex 3 was obtained by reaction of the Li/Cl phosphinidenoid complex 2, characterized by NMR spectroscopy, at low temperature; complex 3 was characterized by elemental analysis and NMR, IR, and MS studies and by single-crystal X-ray diffraction. Carbenoids I1 and silylenoids II2 are versatile reactive intermediates in organic synthesis (Scheme 1). In contrast, phosphinidenoids III are still unknown, although some authors had speculated3 about their existence. Scheme 1. Carbenoids, Silylenoids, Phosphinidenoids, and Complexes Thereofa
a Legend: R = common organic substituents; M0 = main-groupelement metal; X = halogen; MLn = transition-metal complex.
Recently, we reported the generation of the first Li/Cl phosphinidenoid transition-metal complex (IV) and chemical evidence through various reactions. With methyl iodide the PMe-substituted phosphine complex was selectively obtained, thus showing the nucleophilic reactivity of IV, while π-systems afforded three-membered heterocyclic complexes such as *To whom correspondence should be addressed. Fax: (49)228739616. Tel: (49)228-735345. E-mail:
[email protected]. (1) (a) K€ obrich, G. Angew. Chem. 1967, 79, 15; Angew. Chem., Int. Ed. 1967, 6, 41. (b) Kirmse, W. Angew. Chem. 1965, 77, 1; Angew. Chem., Int. Ed. 1965, 4, 1. (c) Boche, G.; Lohrenz, J. W. Chem. Rev. 2001, 101, 697. (2) (a) Tamao, K.; Kawashi, A. Angew. Chem. 1995, 107, 886; Angew. Chem., Int. Ed. 1995, 34, 818. (b) Tamao, K.; Kawashi, A.; Asahara, M.; Toshimitsu, A. Pure Appl. Chem. 1999, 71, 393. (c) Lee, M. E.; Cho, H. M.; Lim, Y. M.; Choi, J. K.; Park, C. H.; Jeong, S. E.; Lee, U. Chem. Eur. J. 2004, 10, 377. (d) Antolini, F.; Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun. 2005, 5112. (e) Flock, M.; Marschner, C. Chem. Eur. J. 2005, 11, 4635. (f) Weidenbruch, M. Angew. Chem. 2006, 118, 4347; Angew. Chem., Int. Ed. 2006, 45, 4241. (g) Molev, G.; BravoZhivotovskii, D.; Karni, M.; Tumanski, B.; Botoshansky, M.; Apeloig, Y. J. Am. Chem. Soc. 2006, 128, 2784. (3) For the proposal of a transient ClMg/Cl-phosphinidenoid, see: Yoshifuji, M. Dalton Trans. 1998, 3343. (4) O¨zbolat, A.; von Frantzius, G.; Marinas Perez, J.; Nieger, M.; Streubel, R. Angew. Chem. 2007, 119, 9488; Angew. Chem., Int. Ed. 2007, 46, 9327. (5) Bode, M.; Jones, P. G.; Schnakenburg, G.; Streubel, R. Organometallics 2008, 27, 2664. (6) Streubel, R.; Bode, M.; Marinas Perez, J.; Schnakenburg, G.; Daniels, J.; Nieger, M.; Jones, P. G. Z. Allg. Anorg. Chem. 2009, 635, 1163. pubs.acs.org/Organometallics
Published on Web 07/23/2009
oxaphosphirane complexes,4-6 thus revealing the terminal phosphinidene complex like reactivity of IV. This new and selective access to oxaphosphirane complexes not only enabled access to novel O,P,C-cage complexes5 but also created interest in investigating this ring system theoretically.7-9 Although characterization of the first Li/F phosphinidenoid tungsten complex of type IV10 was achieved recently, Li/Cl phosphinidenoid complexes have not yet been identified. Here, investigations on the generation of a P-C5Me5-substituted phosphinidenoid complex in the absence of trapping reagents will be reported. Deprotonation of the chloro(pentamethylcyclopentadienyl)phosphine complex 111 at -78 °C with lithium diisopropylamide in diethyl ether in the presence of 12-crown-4 afforded a single product, which was characterized by low-temperature NMR spectroscopy and assigned as the Li/Cl phosphinidenoid complex 2 (Scheme 2). The Li/Cl phosphinidenoid complex displays a 31P NMR resonance at low field with a small tungsten-phosphorus coupling (δ 279.4, 1J(W,P)=80 Hz), which seems to be a characteristic feature of Li/X phosphinidenoid complexes.cf.10 Furthermore, 2 exhibits a small 2 J(P,C) coupling of about 14 Hz for the trans-CO ligand; a comparably small value was observed in the case of the Li/F phosphinidenoid complex.10 The latter provides evidence for a negatively charged phosphorus center in 2, which seems to somehow contradict the observation of a phosphorus resonance at low field but points to an unknown interaction of the lithium cation. 31P{1H} NMR spectroscopic monitoring of the warming-up process did not reveal a terminal phosphinidene complex as the expected formal 1,1-elimination product. Instead, the dinuclear polycyclic P,C-cage complex 3 was formed selectively upon warming to -25 °C (Scheme 2), subsequently isolated by column chromatography and fully characterized including singlecrystal X-ray diffraction analysis (Figure 1). Complex 3 shows 31P NMR data characteristic of an AB spin system (PA, δ -101.6, 1J(W,P)=234.0 Hz, 1J(P,P)=142.4 Hz; PB, δ 41.4, 1J(W,P) = 225.1 Hz, 1J(P,P) = 142.4 Hz) that nicely illustrates the difference in chemical shielding of a (7) For calculations on σ3λ3-oxaphosphiranes, see: Goumans, T. P. M.; Ehlers, A. W.; Lammertsma, K.; W€ urthwein, E.-U. Eur. J. Org. Chem. 2003, 2941. 3 3 (8) For more recent calculations on σ λ -oxaphosphiranes and chromium complexes thereof, see: Krahe, O.; Neese, F.; Streubel, R. Chem. Eur. J. 2009, 15, 2594. (9) For calculations on σ5λ5-oxaphosphirane, see: Chesnut, D. B.; Quin, L. D. Tetrahedron 2005, 61, 12343. (10) O¨zbolat, A.; von Frantzius, G.; Hoffbauer, W.; Streubel, R. Dalton Trans. 2008, 2674. (11) 1: Streubel, R.; Rohde, U.; Jeske, J.; Ruthe, F.; Jones, P. G. Eur. J. Inorg. Chem. 1998, 2005. r 2009 American Chemical Society
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Scheme 2. Formation of P,C-Cage Complex 3 via Reaction of Li/Cl Phosphinidenoid Complex 2
Scheme 3. Plausible Reaction Pathway i for the Formation of 3
Scheme 4. Plausible Reaction Pathway ii for the Formation of 3
Figure 1. Structure of complex 3 (50% probability level; hydrogen atoms are omitted for clarity). Selected bond lengths (A˚) and angles (deg): W1-P1=2.591(1), W2-P2=2.516(1), P1P2=2.193(1), P1-C1=1.937(3), P1-C11=1.902(3), P2-C2= 1.880(3), P2-C3 = 1.909(3), C1-C2 = 1.571(4), C2-C3 = 1.508(4), C3-C4 = 1.498(4), C4-C5 = 1.330(4), C5-C1 = 1.511(4); C2-P2-C3 = 46.9(1), C2-C3-P2 = 65.5(2), P2C2-C3=67.6(2), P1-P2-C2=78.7(1), P1-P2-C3=99.4(1), P1-C1-C2 = 94.7(2), C1-P1-P2 = 80.7(1), C1-C2-P2 = 101.6(2), P2-P1-C11 = 112.6(1), C1-P1-C11 = 115.5(1), C1-C2-C3=101.9(2), C2-C3-C4=107.2(2), C3-C4-C5= 110.3(2), C4-C5-C1=110.6(2), C5-C1-C2=103.6(2).
phosphorus(III) nucleus incorporated into a three-membered ring (PA) and into a four-membered ring (PB) of a polycyclic P-heterocycle. Two reaction pathways might be envisaged for the formation of 3: the dinuclear diphosphene complex 64 forms via dimerization of the transient terminal phosphinidene complex 4, which undergoes rapid intramolecular [4 þ 2] cycloaddition to yield 3 (Scheme 3, path i); complex 5, which is a structural isomer of 4, undergoes ring expansion by insertion of one [W(CO)5(PC5Me5)] unit into one of the two
outer edge bonds of the strained phosphirane subunit in 5 (Scheme 4, path ii). Recently, we showed by DFT calculations that the gasphase structure of 5 is energetically slightly favored over 4 and has two long (outer edge) P-C bonds.12 The latter indicates a weak interaction (in 5) that might change in solution as Lewis acid/base interactions between the electrophilic phosphorus in 4 and the solvent donor center might be present and thus stabilizing 4 over 5; we recently showed that weak donors such as aldehydes interact with the phosphorus center in 4.5 Discussion of the Structure. The molecular structure of 3 (Figure 1) unambiguously confirms the molecular constitution of the P,C-cage ligand, which shows a relatively short P-P single bond length of 2.193(1) A˚; this is surprising, as two neighboring P-bonded W(CO)5 groups should create steric repulsion and thus lead to a bond lengthening. It should be noted that a comparably short P-P bond (2.185(9) A˚) was recently determined as a characteristic feature of a different P,C-cage.12 It is also interesting to note that the distance W2-P2=2.516(1) A˚ is much shorter than W1-P1 (2.591(1) A˚), thus providing further evidence for the significantly different steric environments at the two phosphorus nuclei. All P-C bond lengths in 3 (1.88-1.94 A˚) are more in the upper region of the typical P-C single-bond range (ca. 1.80-1.92 A˚), and here the P1-C1 bond length of 1.937(3) A˚ deserves special mention, as it might reflect steric repulsion between the two five-membered-ring units. (12) Streubel, R.; Bode, M.; von Frantzius, G.; Hrib, C.; Jones, P. G.; Monsees, A. Organometallics 2007, 26, 1371.
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Acknowledgment. Financial support by the DFG (No. STR 411/26-1) and the COST action CM0802 “PhoSciNet” is gratefully acknowledged. Supporting Information Available: Text giving detailed experimental procedures and product characterization data of new compounds and a CIF file giving X-ray crystallographic
Bode et al. data for 3. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data of 3 have also been deposited at the Cambridge Crystallographic Data Centre under the number CCDC-729015. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif.
