OR Phosphinidenoid Complexes

COMMUNICATION pubs.acs.org/Organometallics

Generation and Decomposition of Li/OR Phosphinidenoid Complexes Lili Duan, Gregor Schnakenburg, and Rainer Streubel* Institut f€ur Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universit€at Bonn, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany

bS Supporting Information ABSTRACT: Reaction of the P-bifunctional phosphane complex 2 with LDA and 12-crown-4 yielded complex 4, featuring the unprecedented combination of a P
H and P
O
Li unit, via an unknown decomposition pathway. Strong spectroscopic evidence for the transient Li/OC(O)CH3 phosphinidenoid complex 5 possessing a P
Li bond was obtained through reaction of 2 with LDA in the absence of 12-crown-4.

P

hosphanides I and their complexes II (Scheme 1) are valuable synthetic building blocks for the formation of multiple bonds between phosphorus and carbon and/or metal atoms.1 In contrast, phosphinidenoids III were proposed only as intermediates and/or precursors for phosphinidenes2 but were never firmly established, although their synthetic potential could be very important. Recently, the first protocol to generate Li/X phosphinidenoid complexes IV (X = F,3a Cl;3b R = CH(SiMe3)2) via deprotonation at low temperature using lithium diisopropylamide (LDA) in the presence of 12-crown-4 was developed. Although the protocol was successfully exploited to generate a P-C5Me5 substituted derivative of IV (X = Cl),3c the bonding remained unclear as all attempts to identify a P
Li or X
Li interaction were unsuccessful. Preliminary results on the reactivity of IV (X = Cl) toward nitriles, alkynes, and aldehydes pointed to a phosphinidene complex like behavior,3b but a nucleophilic reactivity4,5 toward organic iodides was also observed. Recently, the first account on the redox chemistry of IV (X = Cl) appeared, which revealed an access to P-centered P-functional phosphanyl complexes.6 Despite these investigations and results, the structure
reactivity relationship of M/X phosphinidenoid complexes is largely not understood. Here, we report preliminary results on the synthesis and deprotonation of the P-bifunctional phosphane complex 2 and its selective transformation into complex 4, which features the unprecedented combination of a P
H and P
O
Li unit,7
10 and 31P NMR spectroscopic evidence for the Li/OC(O)CH3 phosphinidenoid complex 3 as transient species. In the absence of 12-crown-4 the transient Li/OC(O)CH3 phosphinidenoid complex 5 featuring a P
Li bond was formed, but also decomposed upon warming. Deprotonation of the 1,10 -bifunctional phosphane complex 2, obtained from reaction of chlorophosphane complex 111 with silver acetate (Scheme 2), at low temperature using LiNiPr2 (LDA) in the presence of 12-crown-4 yielded complex 4 as the final product. 31P{1H} NMR spectroscopic monitoring showed a broad signal at 224.4 ppm at
78 °C; the value is close to that of r 2011 American Chemical Society

Scheme 1. Phosphanides I, Phosphinidenoids III, and Their Complexes II and IVa

R, R0 = organic substituents, X = halogen, M = main-group metal, MLn = transition-metal complex. a

Scheme 2. Synthesis of Complexes 2 and 4a

a

12-c-4 = 12-crown-4.

the transient P-Cl phosphinidenoid derivative (212.9 ppm).3b Therefore, we tentatively assign it to the transient P-OAc phosphinidenoid complex 3 (OAc = OC(O)CH3). When 3 was warmed, a selective conversion into complex 4 took place. The resonance signal of 4 (δ 43.8, 1JWP = 244.1 Hz, 1JPH = 302.6 Hz) varied from 43.8 ppm at
78 °C to 46.0 ppm at 25 °C. As no Li
P interaction was spectroscopically discovered for complex 3, it seemed interesting to perform the deprotonation in the absence of 12-crown-4 but under the same conditions Received: April 7, 2011 Published: May 31, 2011 3246

dx.doi.org/10.1021/om200300m | Organometallics 2011, 30, 3246–3249

Organometallics

COMMUNICATION

Scheme 3. Reaction of Complex 2 in the Absence of 12-c-4 To Form Intermediate 5 and Complex 6

Figure 1. 31P{1H} NMR spectrum (
30 °C) in Et2O of the reaction intermediate complex 5.

(Scheme 3). The 31P{1H} NMR spectroscopic monitoring (
78 °C) revealed a broad resonance at 219 ppm, a resonance at 55.1 ppm (1JWP = 255.6 Hz, 1JPH = 306.4 Hz), and a small signal at 46.0 ppm (1JWP = 241.6 Hz, 1JPH = 301.4 Hz); because of the great similarity of the latter data (to those of 4), they were assigned to complex 6. The signal at 219 ppm vanished above
60 °C, while a signal at 182 ppm appeared (
30 °C) displaying a phosphorus
lithium coupling (JP,Li = 66.1 Hz)12 (Figure 1). Although the constitution could not be further supported, we tentatively assign this to the phosphinidenoid complex 5. When the temperature was raised, the intermediate vanished to yield complex 6 as the final phosphorus-containing product. Complexes 2 and 4 were fully characterized by multinuclear NMR and IR spectroscopy and mass spectrometry and confirmed by single-crystal X-ray diffractometry. The structures of complexes 2 and 4 (Figures 2 and 3) showed similar P
C distances and phosphorus centers that have a trigonal-pyramidal geometry (sums of bond angles at P: 335.7° (2) and 346.4° (4)). The P
O bond in complex 2 is about 0.17 Å longer than in complex 4, which is remarkably short (1.505(6) Å) in the latter case. The P
O1
Li unit in complex 4 showed an approximately linear arrangement (166.7(5)°), which is surprising if compared to the P
O1
C1 value in 2 (118.5(2)°) and/or related complexes of the latter.13 When the elongated P
W bond (2.5483(17) Å) is taken into account, this points to an increased negative charge density at the phosphorus atom and, thus, the overall situation might be explained simply by the two anionic ligand resonance structures RP(H)
O
and RHP
dO— thereby bringing some PdO double-bond character to the fore. A supporting argument can be deduced from the decrease of the wavenumbers for the ν(CO) A1 mode of complex 4, which is 2054 vs 2075 cm
1 in complex 2. In summary, the first generation and NMR spectroscopic evidence for Li/OR phosphinidenoid complexes was reported. Obviously, coordination of lithium to 12-crown-4 prevent strong P
Li interactions, an observation made before by other authors12 in lithium phosphanide chemistry, which may even lead to ion pair formation and/or ion separation. In the absence of 12-crown-4 two intermediates were detected at different (low) temperatures, an observation which points to aggregation and/or coordination isomerism phenomena. Despite the presence or absence of 12-crown-4, both Li/OR phosphinidenoid complexes

Figure 2. Molecular structure of complex 2 in the crystal state (50% probability level; hydrogen atoms omitted for clarity). Selected bond lengths (Å) and angles (deg): P
H(10) = 1.35(3), P
C(3) = 1.813(3), P
O(1) = 1.676(2), P
W = 2.4780(8), O(1)
C(1) = 1.375(4), C(1)
O(2) = 1.191(4); H(10)
P
C(3) = 101.3(13), H(10)
P
W = 118.9(13), H(10)
P
O(1) = 96.8(13), C(3)
P
O(1) = 99.66(14), C(3)
P
W = 120.37(11), O(1)
P
W = 115.68(8), P
O(1)
C (1) = 118.5(2).

Figure 3. Molecular structure of complex 4 in the crystal state (50% probability level; hydrogen atoms omitted for clarity). Selected bond lengths (Å) and angles (deg): P
H(17) = 1.50(8), P
O(1) = 1.505(6), P
C(1) = 1.822(7), P
W = 2.5483(17), O(1)
Li = 1.777(14); H(17)
P
W = 103(3), H(17)
P
C(1) = 99(3), H(17)
P
O(1) = 104(3), W
P
C(1) = 115.9(3), W
P
O(1) = 121.4(2), C(1)
P
O(1) = 109.1(3), P
O(1)
Li = 166.7(5).

decomposed in ways different from those of Li/X derivatives (X = F, Cl).3a,b Experimental Section. General Procedures. All manipulations involving air- and moisture-sensitive compounds were carried out under an atmosphere of dry argon by using modified Schlenk line techniques. The solvents were dried over sodium before use. The 1H, 13C{1H}, and 31P{1H} NMR spectroscopic data were recorded on a Bruker Avance 300 MHz spectrometer. Elemental analyses were recorded on an Elementar Vario EL analytical gas chromotagraph. Melting points were measured in a 3247

dx.doi.org/10.1021/om200300m |Organometallics 2011, 30, 3246–3249

Organometallics sealed glass tube with a B€uchi capillary apparatus. Infrared spectra were recorded on a Thermo-Nicolet 380 spectrophotometer. Mass spectra (EI) were recorded on a Kratos MS 50 spectrometer (70 eV). Synthesis of Complex 2. To a solution of AgOCOCH3 (184 mg, 1.1 mmol) in 10 mL of Et2O was added complex 2 (551 mg, 1 mmol) in 10 mL of Et2O at 0 °C. Then the reaction mixture was stirred overnight while being gently warmed to room temperature. The liquid was filtered from the solid and the solvent removed in vacuo. The raw product was purified by washing with n-pentane at low temperature, and crystals suitable for an X-ray study were obtained from diethyl ether. Characterization data for 2 are as follows. Pale yellow solid. Yield: 322 mg (56%). Mp: 50
51 °C. IR (KBr; νmax/cm
1): 2369 (w, P
H), 2075 (s, CO), 1988 (s, CO), 1941 (vs, CO), 1929 (vs, CO), 1915 (vs, CO), 1740 (s, COCH3). 1H NMR (300.1 MHz, CDCl3): δH 0.22 (9H, s, Si(CH3)3), 0.31 (9H, s, Si(CH3)3), 0.98 (1H, d, 2JPH = 2.8 Hz, PCH), 2.18 (3H, d, 4JPH = 1.3 Hz, COCH3), 8.21 (1H, dd, 1J(P,H) = 354.8 Hz, 3J(H,H) = 2.5 Hz, P
H). 13C{1H} NMR (75.5 MHz, CDCl3): δC 1.0 (s, Si(CH3)3), 2.1 (d, 3J(P,C) = 2.6 Hz, Si(CH3)3), 21.7 (d, 1J(P,C) = 9.1 Hz, PCH), 22.3 (s, COCH3), 168.5 (d, 2J(P,C) = 7.8 Hz, COCH3), 195.9 (d, 2J(P,C) = 7.5 Hz, cis-CO), 198.8 (d, 2J(P,C) = 28.8 Hz, trans-CO). 31P NMR (121.5 MHz; 85% H3PO4): δ 88.6 (d, 1JWP = 275.8, 1JPH = 354.2 Hz). MS (EI, 184W m/z (%)): 573.9 [(M)þ, 55], 545.9 [(M
CO)þ, 50], 489.9 [(M
3CO)þ, 100], 462.0 [(M
4CO)þ, 31], 434.0 [(M
5CO)þ, 42], 73.1 [SiMe3þ, 90]. Anal. Calcd for C20H36LiO10PSi2W: C, 29.33; H, 4.15. Found: C, 29.28; H, 4.04. Synthesis of Complex 4. A solution of 115 mg (0.22 mmol) of 2 in 2 mL of Et2O was added to a solution of LDA, freshly prepared from 0.14 mL (1.6 M, 0.22 mmol) of n-butyllithium in n-hexane and 30 μL (0.22 mml) of diisopropylamine in 2 mL of Et2O, at
78 °C, and the reaction solution was stirred for 2 h. The solvent was evaporated in vacuo, and the residue was washed with small amounts of n-pentane at
30 °C. The yellow powder was dried in vacuo. Characterization data for 4 are as follows. Yellow solid. Yield: 51 mg (36%). Mp: 84
86 °C. IR (KBr; νmax/cm
1): 2185 (w, P
H), 2054 (s, CO), 1959 (vs, CO), 1909 (vs, CO). 1H NMR (300.1 MHz, [D8]THF): δH 0.15 (9H, s, Si(CH3)3), 0.25 (9H, s, Si(CH3)3), 0.82 (1H, br, PCH), 1.29 (3H, d, 4JPH = 7.0 Hz, i Pr2NCOCH3), 3.66 (16H, s, 12-crown-4), 8.59 (1H, d, 1JPH = 301.8 Hz, PH). 13C{1H} NMR (75.5 MHz, [D8]THF): δC 1.3 (d, 3JPC = 1.9 Hz, Si(CH3)3), 3.1 (d, 3JPC = 2.6 Hz, Si(CH3)3), 29.7 (d,1JPC = 3.2, PCH), 70.1 (s, 12-crown-4), 202.1 (d, 2JPC = 9.1 Hz, cis-CO), 205.1 (d, 2JPC = 13.6 Hz, trans-CO). 31P{1H} NMR (121.5 MHz, [D8]THF): δP 46.0, (ssat, 1JWP = 244.1 Hz, 1 JPH = 302.6 Hz). Anal. Calcd for C20H36LiO10PSi2W: C, 33.62; H, 5.08. Found: C, 33.14; H, 4.77. X-ray Crystallography. Suitable yellow single crystals of 2 and 4 were grown from concentrated diethyl ether solutions by decreasing the temperature from ambient temperature to þ4 °C (4) or
30 °C (2). Data were collected on a Nonius KappaCCD diffractometer equipped with a low-temperature device at 123 K using graphite-monochromated Mo KR radiation (λ = 0.710 73 Å). The structures were solved by Patterson methods (SHELXS-97) and refined by full-matrix least squares on F2 (SHELXS-97). All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were included isotropically using the riding model on the bound atoms. Absorption corrections were carried out semiempirically from equivalents.

COMMUNICATION

Crystal structure data for complex 2 are as follows: colorless single crystals of 2 were obtained from a concentrated diethyl ether solution at
30 °C, C14H23O7PSi2W, crystal size 0.47  0.24  0.20 mm, orthorhombic, a = 9.1768(3) Å, b = 16.9657(6) Å, c = 27.8831(11) Å, β = 90°, V = 4341.1(3) Å3, Z = 8, 2θmax = 56°, 11 916 (5203) collected (independent) reflections, Rint = 0.0357, μ = 5.535 mm
1, 237 refined parameters, 0 restraints, R1 (for I > 2σ(I)) = 0.0201, wR2 (for all data) = 0.0442, maximum/minimum residue electron density 0.746/
0.732 e Å
3. Crystal structure data for complex 4 are as follows: yellow single crystals of 4 were obtained from a concentrated diethyl ether solution upon slow cooling to 4 °C, C20H36LiO10PSi2W, crystal size 0.68  0.17  0.16 mm, monoclinic, P21/n, a = 10.2454(4) Å, b = 16.2432(7) Å, c = 17.7500(6) Å, β = 93.788(2)°, V = 2947.5(2) Å3, Z = 4, 2θmax = 55.74°, 27 067 (6838) collected (independent) reflections, Rint = 0.0577, μ = 4.100 mm
1, 363 refined parameters, 54 restraints, R1 (for I > 2σ(I)) = 0.0490, wR2 (for all data) = 0.1319, maximum/ minimum residue electron density 1.972/
1.909 e Å
3. Crystallographic data of complex 2 and 4 have been deposited at the Cambridge Crystallographic Data Centre. The CCDC numbers are 803717 (4) and 803718 (2). This data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

’ ASSOCIATED CONTENT Supporting Information. CIF files giving crystallographic data for compounds 2 and 4. This material is available free of charge via the Internet at http://pubs.acs.org.

bS

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT We thank the Deutsche Forschungsgemeinschaft (STR 411/ 26-1) and the COST action CM0802 “PhoSciNet” for financial support. ’ REFERENCES (1) (a) Fritz, G.; Sch€afer, H.; H€ olderich, W. Z. Anorg. Allg. Chem. 1974, 407, 266. (b) Fritz, G.; H€ olderich, W. Z. Anorg. Allg. Chem. 1976, 422, 104. (c) Fritz, G.; Scheer, P. Chem. Rev. 2000, 100, 3341. (d) Blair, S.; Izod, K.; Clegg, W.; Harrington, R. W. Inorg. Chem. 2004, 43, 8526. (e) Westerhausen, M.; Rotter, T.; G€orls, H.; Birg, C.; Warchhold, M.; N€oth, H. Z. Naturforsch. 2005, 60b, 766. (2) (a) Huttner, G.; M€uller, H. D.; Frank, A.; Lorenz, H. Angew. Chem., Int. Ed. 1975, 14, 705–706. (b) Li, X.; Lei, D.; Chiang, M. Y.; Gaspar, P. P. J. Am. Chem. Soc. 1992, 114, 8526. (c) Li, X.; Weissman, S. I.; Lin, T. S.; Gaspar, P. P. J. Am. Chem. Soc. 1994, 116, 7899. (d) Keck, H.; Kuchen, W.; Terlouw, J. K.; Tommes, P. Phosphorus, Sulfur, Silicon Relat. Elem. 1999, 149, 23. (e) Lammerstma, K. Top. Curr. Chem. 2003, 229, 95–119. (f) Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578. € (3) (a) Ozbolat, A.; Frantzius, G. v.; Perez, J. M.; Nieger, M.; € Streubel, R. Angew. Chem., Int. Ed. 2007, 46, 9327. (b) Ozbolat, A.; Frantzius, G. v.; Hoffbauer, W.; Streubel, R. Dalton Trans. 2008, 2674. (c) Bode, M.; Daniels, J.; Streubel, R. Organometallics 2009, 28, 4636. € (4) Streubel, R.; Ozbolat-Sch€ on, A.; Bode, M.; Daniels, J.; Schnakenburg, G.; Teixidor, F.; Vinas, C.; Vaca, A.; Pepoil, A.; Farras, P. Organometallics 2009, 28, 6031. 3248

dx.doi.org/10.1021/om200300m |Organometallics 2011, 30, 3246–3249

Organometallics

COMMUNICATION

(5) Nesterov, V.; Duan, L.; Schnakenburg, G.; Streubel, R. Eur. J. Inorg. Chem. 2011, 567–572. € (6) Ozbolat-Sch€ on, A.; Bode, M.; Schnakenburg, G.; Anoop, A.; van Gastel, M.; Neese, F.; Streubel, R. Angew. Chem., Int. Ed. 2010, 49, 6894. (7) For a recent example on lithiation of phosphonates and phosphinates and POLi intermediates, see: Xu, Q.; Zhao, C. Q.; Han, L. B. J. Am. Chem. Soc. 2008, 130, 12648 and references cited therein. (8) A related ligand (RP(H)O-BR3) was reported recently: Panichakul, D.; Mathey, F. Organometallics 2011, 30, 348. (9) For ligands of the type RP(H)OH, see: (a) Marinetti, A.; Mathey, F. Organometallics 1982, 1, 1488. (b) Malish, W.; Angerer, W.; Cowley, A. H.; Norman, N. C. J. Chem. Soc., Chem. Commun. 1985, 1811. (c) Malish, W.; Hirth, U. A.; Gruen, K.; Schmeusser, M.; Fey, O.; Weis, U. Angew. Chem., Int. Ed. 1995, 34, 2500. (d) Alonso, M.; Alvarez, M. A.; Garcia, M. E.; Vivo, D. G.; Ruiz, M. A. Inorg. Chem. 2010, 49, 8962. (10) For noncoordinated ligands such as RP(H)ONa, see: Prishchenko, A. A.; Livantsov, M. V.; Novikova, O. P.; Livantsova, L. I.; Pol’shchikov, D. G.; Krut’ko, D. P. Russ. J. Gen. Chem. 2004, 74, 1943. (11) Khan, A. A.; Wismach, C.; Jones, P. G.; Streubel, R. Dalton Trans. 2003, 2483. (12) (a) Colquhoun, I. J.; McFarlane, H. C. E.; McFarlane, W. J. Chem. Soc., Chem. Commun. 1982, 220. (b) Colguhoun, I. J.; McFarlane, H. C. E.; McFarlane, W. Phosphorus Sulfur Relat. Elem. 1983, 18, 61. (c) Hope, H.; Olmstead, M. M.; Power, P. P.; Xu, X. J. J. Am. Chem. Soc. 1984, 106, 819–821. (d) Bartlett, R. A.; Olmstead, M. M.; Power, P. P.; Sigel, G. A. Inorg. Chem. 1987, 26, 1941–1946. (e) Power, P. P. Acc. Chem. Res. 1988, 21, 147. (f) Bartlett, R. A.; Dias, H. V. R.; Feng, X. D.; Power, P. P. J. Am. Chem. Soc. 1989, 111, 1306. (g) Reich, H. J.; Dykstra, R. R. Organometallics 1994, 13, 4578. (h) Fernandez, I.; Viviente, E. M.; Pregosin, P. S. Inorg. Chem. 2004, 43, 4555. (13) Duan, L.; Schnakenburg, G.; Streubel, R. Manuscript in preparation.

3249

dx.doi.org/10.1021/om200300m |Organometallics 2011, 30, 3246–3249