Synthesis and Characterization of Dysprosium and ... - ACS Publications

Apr 20, 2010 - D. L.; Maddox, P. J.; Br`es, P.; Bochmann, M. Dalton Trans. 2000, 4247. (27) Appel ..... wing filtration and workup, colorless crystals...
0 downloads 0 Views 2MB Size
Download PDF
Organometallics 2010, 29, 2315–2321 DOI: 10.1021/om100104s

2315

Synthesis and Characterization of Dysprosium and Lanthanum Bis(iminophosphorano)methanide and -methanediide Complexes Ashley J. Wooles, Oliver J. Cooper, Jonathan McMaster, William Lewis, Alexander J. Blake, and Stephen T. Liddle* School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, U.K. Received February 10, 2010

Attempts to prepare [Dy{C(PPh2NSiMe3)2}(I)(THF)2] (1) from in situ prepared “[Dy(Bn)2(I)(THF)3]” (“2”; Bn = C6H5CH2) and H2C(PPh2NSiMe3)2 resulted in the isolation of [Dy{CH(PPh2NSiMe3)2}(I)2(THF)] (3) and, on one occasion, a small quantity of [{Dy(CH[PPh2NSiMe3]2)(I)}2(μ-O)] (4). However, attempts to prepare 3 from [K{CH(PPh2NSiMe3)2}(THF)n] and [Dy(I)3(THF)3.5] were unsuccessful. The corresponding reactions with [La(I)3(THF)4] were unsuccessful, and the reaction of [{Li2(C[PPh2NSiMe3]2)}2] and [La(I)3(THF)4] in a 1:1 ratio resulted in the isolation of [{La(μ-I)3Li(THF)2}2{μ-C(PPh2NSiMe3)2}] (5). However, the potassium methanide complex [K{CH(PPh2NMes)2}] (Mes = 2,4,6-Me3C6H2) was found to react with [La(I)3(THF)4] to give [La{CH(PPh2NMes)2}(I)2(THF)2] (6). Complex 6 reacts with 1 equiv of [K(Bn)] to afford the methanediide complex [La{C(PPh2NMes)2}(I)(THF)3] (7). A DFT study of 6 and 7 revealed an increased accumulation of charge at the endocyclic carbon following deprotonation and conversion of 6 to 7, and although the La-C bond indices increase substantially upon a second deprotonation, the bonding remains highly ionic and is dominated by carbon 2p contributions with little orbital contribution from lanthanum. Compounds 1-7 have been variously characterized by X-ray crystallography, NMR spectroscopy, FTIR spectroscopy, CHN microanalyses, room-temperature solution magnetic moments, and, for 6 and 7, DFT calculations.

Introduction The chemistry of bis(phosphorus-stabilized)methanides and -methanediides1 has received increasing attention over the past decade, due in part to the broad utility these anions offer as ancillary ligands for a wide range of metal centers.2-7 The first rare-earth bis(iminophosphorano)methanediide complex [Sm{C(PPh2NSiMe3)2}(NCy2)(THF)] was reported by Cavell in 20008 and was prepared using forcing reaction conditions. Mezailles, Le Floch, Nief, and Ephritikhine have demonstrated that bis(diphenylthiophosphinoyl)methanediide *To whom correspondence should be addressed. E-mail: stephen. [email protected]. (1) In this contribution we refer to the geminal dianion form of this compound as a methanediide. Use of the term carbene is entirely appropriate, but we restrict our nomenclature to methanediide to highlight the ionic nature of the lanthanum-carbon linkages described in this work and also to emphasize the relationship to the methanide form. (2) Liddle, S. T.; Mills, D. P.; Wooles, A. J. Organomet. Chem. 2010, 36, 29. (3) Panda, T. K.; Roesky, P. W. Chem. Soc. Rev. 2009, 38, 2782. (4) Cantat, T.; Mezailles, N.; Auffrant, A.; Le Floch, P. Dalton Trans. 2008, 1957. (5) Roesky, P. W. Z. Anorg. Allg. Chem. 2006, 632, 1918. (6) Jones, N. A.; Cavell, R. G. J. Organomet. Chem. 2005, 690, 5485. (7) Cavell, R. G.; Kamalesh Babu, R. P.; Aparna, K. J. Organomet. Chem. 2001, 617-618, 158. (8) Aparna, K.; Ferguson, M.; Cavell, R. G. J. Am. Chem. Soc. 2000, 122, 726. (9) Cantat, T.; Jaroschik, F.; Nief, F.; Ricard, L.; Mezailles, N.; Le Floch, P. Chem. Commun. 2005, 5178. (10) Cantat, T.; Jaroschik, F.; Ricard, L.; Le Floch, P.; Nief, F.; Mezailles, N. Organometallics 2006, 25, 1329. r 2010 American Chemical Society

rare-earth9,10 and actinide11,12 complexes can be obtained from the corresponding dilithium methanediide,13 and they have recently begun to explore the application of N-alkyl bis(iminophosphorano)methanides and -methanediides to neodymium.14 We initiated a study into the chemistry of rare-earth methanediide chemistry in 2008 with the synthesis of [Y{C(PPh2NSiMe3)2}(CH2SiMe3)(THF)],15 which was prepared by the straightforward reaction between the parent N-silyl methane and [Y(CH2SiMe3)3(THF)2]16 at or below room temperature. We have since extended this chemistry to include the benzyl derivatives [Ln{C(PPh2NSiMe3)2}(Bn)(THF)] (Ln = Dy, Er, Y; Bn = C6H5CH2),17,18 iodide derivatives [Ln{C(PPh2NSiMe3)2}(I)(THF)2] (Ln = Er, Y),19 (11) Cantat, T.; Arliguie, T.; No€el, A.; Thuery, P.; Ephritikhine, M.; Le Floch, P.; Mezailles, N. J. Am. Chem. Soc. 2009, 131, 963. (12) Tourneux, J.-C.; Berthet, J.-C.; Thuery, P.; Mezailles, N.; Le Floch, P.; Ephritikhine, M. Dalton Trans. 2010, 39, 2484. (13) Cantat, T.; Ricard, L.; Le Floch, P.; Mezailles, N. Organometallics 2006, 25, 4965. (14) Buchard, A.; Auffrant, A.; Ricard, L.; Le Goff, X. F.; Platel, R. H.; Williams, C. K.; Le Floch, P. Dalton Trans. 2009, 10219. (15) Liddle, S. T.; McMaster, J.; Green, J. C.; Arnold, P. L. Chem. Commun. 2008, 1747. (16) Hultzsch, K. C.; Okuda, J.; Voth, P.; Beckerle, K.; Spaniol, T. P. Organometallics 2000, 19, 228. (17) Mills, D. P.; Cooper, O. J.; McMaster, J.; Lewis, W.; Liddle, S. T. Dalton Trans. 2009, 4547. (18) Wooles, A. J.; Mills, D. P.; Lewis, W.; Blake, A. J.; Liddle, S. T. Dalton Trans. 2010, 39, 500. (19) Mills, D. P.; Wooles, A. J.; McMaster, J.; Lewis, W.; Blake, A. J.; Liddle, S. T. Organometallics 2009, 28, 6771. Published on Web 04/20/2010

pubs.acs.org/Organometallics

2316

Organometallics, Vol. 29, No. 10, 2010

and the gallyl derivative [Y{C(PPh2NSiMe3)2}{Ga(NArCH)2}(THF)2] (Ar = 2,6-diisopropylphenyl).20 However, using rare-earth tribenzyls results in the formation of [Ln{C(PPh2NSiMe3)2}{CH(PPh2NSiMe3)2}] complexes for the larger rare earths,18 and for maximum synthetic utility the synthesis of iodide derivatives is synthetically preferential but is limited to erbium and yttrium, as this relies on the use of [Ln(Bn)2(I)(THF)3] (Ln = Er, Y), which were only recently reported.19 An apparently straightforward approach would be to utilize the potassium methanide complex [K{CH(PPh2NSiMe3)2}]21,22 in reactions with rareearth triiodides.23 However, as we previously noted,20 and to our surprise, [K{CH(PPh2NSiMe3)2}]21,22 does not react with yttrium triiodide at room temperature in THF. The reaction mixture must be heated to reflux for 4 h to optimize the yield of [Y{CH(PPh2NSiMe3)2}(I)2(THF)]; shorter reaction times give considerable quantities of unreacted [K{CH(PPh2NSiMe3)2}(THF)n], and longer reaction times result in the formation of significant quantities of the free parent methane. Since [Y{CH(PPh2NSiMe3)2}(I)2(THF)]20 can be converted to [Y{C(PPh2NSiMe3)2}(I)(THF)2]19 by treatment with [K(Bn)],24 we explored the synthesis of [Ln{CH(PPh2NSiMe3)2}(I)2(THF)] complexes, where Ln = dysprosium, lanthanum. We have also investigated the use of N-arylsubstituted bis(iminophosphorano)methanes in f-element chemistry; we have successfully employed a N-Mes (Mes =2,4,6Me3C6H2) bis(iminophosphorano)methanediide as a ligand for uranium, resulting in the isolation of the first homoleptic uranium carbene complex to exhibit two formal UdC double bonds.25 Herein, we report our efforts to prepare dysprosium and lanthanum methanediides, the successful preparation of lanthanum methanide and methanediide derivatives of a bis(iminophosphorano)methane, H2C(PPh2NMes)2,26 which is less sterically demanding than H2C(PPh2NSiMe3)2,27 and a comparative DFT study of the lanthanum methanide and methanediide complexes.

Wooles et al.

Figure 1. Molecular structure of 3 3 THF with selective atom labeling. Thermal ellipsoids are set at the 30% probability level, and minor disorder components, hydrogen atoms, and lattice solvent are omitted for clarity. Scheme 1

Results and Discussion We initially attempted to prepare [Dy{C(PPh2NSiMe3)2}(I)(THF)2] (1) from “[Dy(Bn)2(I)(THF)3]” (“2”; Bn = C6H5CH2) and H2C(PPh2NSiMe3)2,27 as the corresponding erbium and yttrium iodide dibenzyls exhibited remarkable stability and were found to react cleanly with H2C(PPh2NSiMe3)2 to give [Ln{C(PPh2NSiMe3)2}(I)(THF)2] (Ln = Er, Y).19 However, whereas the erbium and yttrium iodide dibenzyls can be isolated as crystalline solids, the reaction between [Dy(I)3(THF)3.5]23 and 2 equiv of [K(Bn)]24 afforded a viscous, yellow oil (Scheme 1). While the isolation of an oil could indicate a mixture of products was formed, it could also (20) Liddle, S. T.; Mills, D. P.; Gardner, B. M.; McMaster, J.; Jones, C.; Woodul, W. D. Inorg. Chem. 2009, 48, 3520. (21) Kamalesh Babu, R. P.; Aparna, K.; McDonald, R.; Cavell, R. G. Organometallics 2001, 20, 1451. (22) Gamer, M. T.; Roesky, P. W. Z. Anorg. Allg. Chem. 2001, 627, 877. (23) Izod, K.; Liddle, S. T.; Clegg, W. Inorg. Chem. 2004, 43, 214. (24) Schlosser, M.; Hartmann, J. Angew. Chem., Int. Ed. Engl. 1973, 12, 508. (25) Cooper, O. J.; McMaster, J.; Lewis, W.; Blake, A. J.; Liddle, S. T. Dalton Trans. DOI: 10.1039/C0DT00152J. (26) Al-Benna, S.; Sarsfield, M. J.; Thornton-Pett, M.; Ormsby, D. L.; Maddox, P. J.; Bres, P.; Bochmann, M. Dalton Trans. 2000, 4247. (27) Appel, R.; Ruppert, I. Z. Anorg. Allg. Chem. 1974, 406, 131.

indicate that “2” does not contain the ideal ratio of metal size to ligands for optimal crystal growth.28 Treatment of the yellow oil of “[Dy(Bn)2(I)(THF)3]” (“2”) with H2C(PPh2NSiMe3)227 gave, after workup and recrystallization from THF, yellow crystals of the methanide complex [Dy{CH(PPh2NSiMe3)2}(I)2(THF)] (3) in 11.9% yield (Scheme 1). NMR data were very broad and uninformative due to the paramagnetic nature of f9 Dy(III), but analytical and room-temperature solution magnetic moment data were consistent with the proposed formulation. The identity of 3 was confirmed by an X-ray diffraction study of a crystal of 3 3 THF; the structure is shown in Figure 1, and selected bond lengths and angles are given in Table 1. The dysprosium center adopts a distorted-octahedral geometry where C(1) and I(1) can be considered to be occupying axial sites. The structure is essentially isostructural with the yttrium analogue20 but is in contrast with the structure of the dysprosium chloride complex reported by Roesky,29 which is dimeric in the solid state. The Dy(1)-C(1) (28) Evans, W. J.; Lee, D. S.; Rego, D. B.; Perotti, J. M.; Kozimor, S. A.; Moore, E. K.; Ziller, J. W. J. Am. Chem. Soc. 2004, 126, 14574. (29) Gamer, M. T.; Dehnen, S.; Roesky, P. W. Organometallics 2001, 20, 4230.

Article

Organometallics, Vol. 29, No. 10, 2010

2317

Table 1. Selected Bond Lengths (A˚) and Angles (deg) for 3-7 3 3 THF Dy(1)-C(1) Dy(1)-N(2) Dy(1)-I(2) C(1)-P(1) P(1)-N(1) P(1)-C(1)-P(2)

2.614(3) 2.350(3) 3.0228(4) 1.755(4) 1.602(3)

Dy(1)-N(1) Dy(1)-I(1) Dy(1)-O(1) C(1)-P(2) P(2)-N(2)

2.390(3) 2.9932(4) 2.359(3) 1.745(4) 1.604(3)

123.4(2)

N(1)-Dy(1)-N(2)

93.94(10)

4 3 4toluene Dy(1)-C(1) Dy(1)-N(2) Dy(1)-O(1) C(1)-P(2) P(2)-N(2) P(1)-C(1)-P(2)

2.680(3) 2.355(3) 2.03499(19) 1.743(3) 1.603(3)

Dy(1)-N(1) Dy(1)-I(1) C(1)-P(1) P(1)-N(1)

128.7(2)

2.350(3) 3.0009(3) 1.749(3) 1.603(3)

N(1)-Dy(1)-N(2)

104.17(9)

La(2)-C(1) La(2)-N(2) La(2)-I(3) La(2)-I(4) La(2)-I(5) La(2)-I(6) Li(2)-I(3) Li(2)-I(4) Li(2)-O(3) Li(2)-O(4) C(1)-P(2) P(2)-N(2)

2.704(14) 2.376(11) 3.1804(13) 3.2091(14) 3.2391(13) 3.2533(13) 2.79(3) 2.80(3) 1.91(3) 1.88(3) 1.718(13) 1.635(12)

5 La(1)-C(1) La(1)-N(1) La(1)-I(1) La(1)-I(2) La(1)-I(5) La(1)-I(6) Li(1)-I(1) Li(1)-I(2) Li(1)-O(1) Li(1)-O(2) C(1)-P(1) P(1)-N(1) P(1)-C(1)-P(2) N(2)-P(2)-C(1)

2.754(13) 2.372(11) 3.2034(13) 3.1236(13) 3.2475(13) 3.2642(13) 2.76(3) 2.82(3) 1.88(3) 1.93(3) 1.724(14) 1.614(10) 122.4(8) 105.7(6)

N(1)-P(1)-C(1) La(1)-C(1)-La(2)

107.0(6) 92.6(4)

6 3 2.5(toluene) La(1)-C(1) La(1)-N(2) La(1)-I(2) La(1)-O(2) C(1)-P(2) P(2)-N(2) P(1)-C(1)-P(2)

2.833(4) 2.535(3) 3.1988(4) 2.610(3) 1.723(4) 1.622(3)

La(1)-N(1) La(1)-I(1) La(1)-O(1) C(1)-P(1) P(1)-N(1)

133.8(2)

2.539(3) 3.2096(4) 2.574(3) 1.728(4) 1.612(3)

N(1)-La(1)-N(2)

109.49(10)

La(1)-N(1) La(1)-I(1) La(1)-O(2) C(1)-P(1) P(1)-N(1)

2.531(8) 3.2387(7) 2.575(6) 1.674(8) 1.647(7)

7 La(1)-C(1) La(1)-N(2) La(1)-O(1) La(1)-O(3) C(1)-P(2) P(2)-N(2) P(1)-C(1)-P(2)

2.505(8) 2.584(7) 2.696(6) 2.663(6) 1.652(8) 1.638(7) 145.1(5)

N(1)-La(1)-N(2)

120.4(2)

bond length of 2.614(3) A˚ in 3 is shorter than the corresponding Dy-C bond distance of 2.641(3) A˚ in the chloride congener,29 but the Dy(1)-N(1) and Dy(1)-N(2) bond lengths of 2.390(3) and 2.350(3) A˚, respectively, are longer than those observed in the chloride analogue,29 which taken together reflects the terminal binding of the iodide ligands in 3 compared to the bridging/terminal mix of chloride ligands in Roesky’s chloride complex.29 The bite angle of the methanide ligand of 93.94(10)° compares to an angle of 93.99(6)° in the yttrium analogue of 3. Given the ill-defined nature of the yellow oil of “2”, we attempted the reaction of “2” with H2C(PPh2NSiMe3)227 several times. On all occasions 3 was isolated in varying yield.

Figure 2. Molecular structure of 4 3 4(toluene) with selective atom labeling. Thermal ellipsoids are set at the 30% probability level, and minor disorder components, hydrogen atoms, and lattice solvent molecules are omitted for clarity. Symmetry operation: -x, -y, -z.

However, by varying the recrystallization conditions a small crop of colorless crystals was isolated and characterized by X-ray crystallography to ascertain their identity. The product was identified as [{Dy(CH[PPh2NSiMe3]2)(I)}2(μ-O)] (4) (Scheme 1) and was characterized by the Evans method solution magnetic moment and FTIR spectroscopy, but the low yield precluded full analysis. Routine precautions to exclude air and moisture were taken, but we cannot exclude the possibility that these are the source of oxygen in 4. However, given the ill-defined nature of “2”, we also cannot exclude the possibility that “2” contains oxo species. The molecular structure of 4 3 4(toluene) is illustrated in Figure 2, and selected bond lengths and angles are given in Table 1. Complex 4 is dimeric in the solid state and consists of two methanide dysprosium iodide fragments which are bridged by an oxo center. The oxo center resides on a crystallographic inversion center, and the Dy(1)-O(1)Dy(1A) angle is therefore 180°. Each dysprosium center adopts a distorted-trigonal-bipyramidal geometry such that I(1) and C(1) can be considered to adopt the axial sites. The Dy(1)-C(1) bond length of 2.680(3) A˚ is longer than the corresponding distance in 3 and reflects the replacement of one iodide ligand for an oxo group. The Dy(1)-N(1) and Dy(1)-N(2) bond lengths of 2.350(3) and 2.355(3) A˚, respectively, reflect the lower coordination number of 5 for 4, compared to 6 for 3, and the Dy(1)-O(1) distance of 2.03499(19) A˚ is short, as would be expected. The isolation of 3 and 4 rather than 1 suggests that dysprosium is too large to be stable with an iodide-dibenzyl ligand combination and that the yellow oil is a result of the formation of a mixture of products. However, the formation of Dy-C bonds in 3 and 4 suggests that a dysprosium benzyl complex of some kind is formed, possibly [Dy(Bn)(I)2(THF)3], but since dysprosium is larger than erbium and yttrium, complex Schlenk-type equilibria most likely result, giving unpredictable product formation. Two types of structural motif have been identified for the THF adducts of rare earth triiodides, namely molecular [Ln(I)3(THF)4] (Ln = La-Pr) and separated ion pair [Ln(I)4(THF)2][Ln(I)2(THF)5] (Ln = Nd-Lu) complexes. The solubility in THF of the molecular species is far greater than for the separated ion pairs.23 Consequently, to test whether the solubility of the rare-earth halide had any bearing on the sluggish reactivity observed with

2318

Organometallics, Vol. 29, No. 10, 2010

Wooles et al.

Scheme 2

[K{CH(PPh2NSiMe3)2}(THF)n],21,22 we tested the reactivity of this potassium methanide with lanthanum. No lanthanum methanide derivatives were formed, and heating solutions resulted in quantitative decomposition to give the free bis(iminophosphorano)methane, as evidenced by inspection of 31 P NMR reaction spectra. In light of the problems discussed above, attention then turned to the use of the dilithium methanediide complex [{Li2(C[PPh2NSiMe3]2)}2] reported by Cavell30 and Stephan,31 as it has been shown to be an effective ligand transfer reagent with group 4 tetrahalides.32 Accordingly, [La(I)3(THF)4]23 was treated with 1 molar equiv of [{Li2(C[PPh2NSiMe3]2)}2]30,31 in a toluene/diethyl ether mixture to maximize the solubility of the reagents without protonating the methanediide center as occurs in THF. After workup and recrystallization from toluene, colorless crystals of the compound subsequently identified as [{La(μ-I)3Li(THF)2}2{μ-C(PPh2NSiMe3)2}] (5) were isolated as the sole lanthanum-containing product in 15% yield (Scheme 2). Crystal crops of 5 were contaminated with crystals of the unreacted equivalent of [{Li2(C[PPh2NSiMe3]2)}2] 3 toluene30,31 in a 1:1 ratio, which could not be separated by fractional crystallization due to their similar solubilities. The reason 5 forms is not clear, but its formation may be due to sluggish reactivity of the methanediide with [La(I)3(THF)4],23 due to the low solubility of the latter in toluene/diethyl ether, which would account for the low yield of 5. Thus, once [La(I)3(THF)4]23 has reacted to form a soluble methanediide complex, it may be more favorable for unreacted [La(I)3(THF)4]23 to react with the newly formed lanthanum methanediide complex than the sterically crowded dilithium methanediide. The formulation of 5 was supported by the spectroscopic (31P NMR δ 1.50 ppm; 13C NMR δmethanediide 74.21 (t, JPC = 189.20 Hz)) and analytical data and by X-ray crystallography performed on a crystal selected from the 1:1 mixture and identified as a new compound from a unit cell determination. The molecular structure of 5 is illustrated in Figure 3, and selected bond lengths and angles are given in Table 1. Despite the 1:1 reaction ratio of [La(I)3(THF)4] to [{Li2(C[PPh2NSiMe3]2)}2], the crystal structure reveals a 2:1 product, accounting for the cocrystallization of unreacted dilithium methanediide, which was also confirmed by a unit cell determination. The methanediide center bridges two lanthanum centers, which in turn bond to one nitrogen center each to form two four-membered CPLaN rings with bite angles of 107.0(6) and 105.7(6)° for La(1) and La(2), respectively. Each lanthanum center is bridged by two iodide ligands to the other lanthanum center and by a further two iodide ligands to a lithium center, which is in turn coordinated by two molecules of THF. The La(1)-C(1) and La(2)-C(1) (30) Kasani, A.; Kamalesh Babu, R. P.; McDonald, R.; Cavell, R. G. Angew. Chem., Int. Ed. 1999, 38, 1483. (31) Ong, C. M.; Stephan, D. W. J. Am. Chem. Soc. 1999, 121, 2939. (32) Cavell, R. G.; Kamalesh Babu, R. P.; Kasani, A.; McDonald, R. J. Am. Chem. Soc. 1999, 121, 5805.

Figure 3. Molecular structure of 5 with selective atom labeling. Thermal ellipsoids are set at the 30% probability level, and minor disorder components and hydrogen atoms are omitted for clarity.

bond lengths of 2.754(13) and 2.704(14) A˚, respectively, are shorter than in [La{CH(PPh2NSiMe3)2}{N(SiHMe2)2}2] (2.875(4) A˚)33 and [La{CH(PPh2NSiMe3)2}(Cl){N(PPh2)2}] (2.845(2) A˚).34 Additionally, the La(1)-N(1) and La(2)-N(2) bond lengths of 2.372(11) and 2.376(11) A˚, respectively, are longer than the La-N bond lengths of 2.531(2) and 2.503(2) A˚ observed in [La{CH(PPh2NSiMe3)2}(Cl){N(PPh2)2}]34 The average La-I bond distance of 3.2151(13) A˚ is slightly longer than the average La-I bond length in [La(I)3(THF)4]23 (average 3.154(4) A˚), consistent with the bridging rather than terminal nature of the iodide ligands in 5. Subsequent attempts to react [{Li2(C[PPh2NSiMe3]2)}2]30,31 with [Ln(I)3(THF)n] (Ln = Ce, n = 4; Ln = Pr, n = 4; Ln = Er, n = 3.5)23 yielded only the unreacted dilithium methanediide. We postulated that the barrier to substituting the {C(PPh2NSiMe3)2}2- methanediide onto rare-earth centers was steric in origin, and since the use of [K{CH(PPh2NSiMe3)2}(THF)n]21,22 and [{Li2(C[PPh2NSiMe3]2)}2]30,31 as ligand transfer reagents had proven problematic with [Ln(I)3(THF)n]23 salts, we investigated the use of the N-Mes-substituted methane.26 The N-Mes variant is less sterically demanding than the N-silyl variant and has been successfully installed onto samarium(II) in its methanide form35 and uranium in its methanediide state.25 Furthermore, the potassium salt [K{CH(PPh2NMes)2}] has been demonstrated to be an effective ligand transfer reagent in group 2 chemistry by Hill.36 Treatment of [La(I)3(THF)4]23 with [K{CH(PPh2NMes)2}]36 in THF afforded the anticipated precipitate of KI. Following filtration and workup, colorless crystals of the complex [La{CH(PPh2NMes)2}(I)2(THF)2] (6) were isolated in 77% yield from toluene (Scheme 3). The spectroscopic and analytical data for 6 support its formulation. The 31P NMR spectrum of 6 exhibits a singlet at 11.46 ppm, which compares to 5.51 ppm for [K{CH(PPh2NMes)2}] and -15.1 ppm for CH2(PPh2NMes)2,26 and the methanediide resonates as a triplet in the 13C NMR spectrum at 5.73 ppm (33) Rast€atter, M.; Zulys, A.; Roesky, P. W. Chem. Commun. 2006, 874. (34) Gamer, M. T.; Rast€atter, M.; Roesky, P. W.; Steffens, A.; Glanz, M. Chem. Eur. J. 2005, 11, 3165. (35) Hill, M. S.; Hitchcock, P. B. Dalton Trans. 2003, 4570. (36) Ahmed, S. A.; Hill, M. S.; Hitchcock, P. B. Organometallics 2006, 25, 394.

Article

Organometallics, Vol. 29, No. 10, 2010

Figure 4. Molecular structure of 6 3 2.5(toluene) with selective atom labeling. Thermal ellipsoids are set at the 30% probability level, and minor disorder components, hydrogen atoms, and lattice solvent molecules are omitted for clarity. Scheme 3

(JPC = 136.8 Hz). An X-ray diffraction experiment was carried out to confirm the structure of 6 in the solid state. The molecular structure of 6 3 2.5(toluene) is illustrated in Figure 4, and selected bond lengths and angles are given in Table 1. Complex 6 crystallizes as a monomer, and the lanthanum center adopts a distorted-pentagonal-bipyramidal geometry with the two iodide ligands occupying the axial sites. The La(1)-C(1) bond distance of 2.833(4) A˚ is longer than the La-C bond lengths in 5 but compares well to [La{CH(PPh2NSiMe3)2}{N(SiHMe2)2}2] (2.875(4) A˚)33 and [La{CH(PPh2NSiMe3)2}(Cl){N(PPh2)2}] (2.845(2) A˚).34 The La(1)-I(1) and La(1)-I(2) bond lengths of 3.2096(4) and 3.1988(4) A˚, respectively, are slightly longer than the average La-I bond length of 3.154(4) A˚ in [La(I)3(THF)4],23 reflecting the presence of the sterically bulky methanediide ligand. The La(1)-N(1) and La(1)-N(2) bond distances of 2.539(3) and 2.535(3) A˚ are longer than in 5 and in [La{CH(PPh2NSiMe3)2}(Cl){N(PPh2)2}] (2.517(2) A˚).34 Encouraged by the synthesis of 6, and noting that [Y{CH(PPh2NSiMe3)2}(I)2(THF)]20 can be converted to [Y{C(PPh2NSiMe3)2}(I)(THF)2]19 by treatment with [K(Bn)],24 we attempted the analogous reaction with 6. Treatment of crystalline 6, or 6 prepared in situ, with [K(Bn)]24 in THF afforded, after workup and recrystallization from toluene, colorless crystals of the methanediide complex [La{C(PPh2NMes)2}(I)(THF)3] (7) in 53% yield (Scheme 3). The 31 P NMR spectrum of 7 exhibits a singlet at 4.81 ppm, which compares to a chemical shift of 11.46 ppm for 6. The methanediide resonates as a triplet in the 13C NMR spectrum at 58.76 ppm (JPC = 148.4 Hz), which compares to 5.73 ppm for 6. All other spectroscopic and analytical data support the proposed formulation. In order to determine the structure and nature of the lanthanum methanediide bond and directly

2319

Figure 5. Molecular structure of 7 with selective atom labeling. Thermal ellipsoids are set at the 30% probability level, and minor disorder components and hydrogen atoms are omitted for clarity.

compare to the methanide complex 6, we carried out an X-ray crystallographic study. The molecular structure of 7 is illustrated in Figure 5, and selected bond lengths and angles are given in Table 1. As observed in the crystal structure of 6, complex 7 is a monomer in the solid state and the lanthanum adopts a pentagonalbipyramidal geometry. However, the axial sites are now occupied by one iodide ligand, and the other has been replaced by a THF molecule. The La(1)-C(1) bond length of 2.505(8) A˚ in 7 is considerably shorter than the La(1)C(1) bond of 2.833(4) A˚ in 6, reflecting the methanediide versus methanide nature of 7 and 6, respectively. However, the La(1)-N(1) and La(1)-N(2) bond distances of 2.531(8) and 2.584(7) A˚ are essentially the same and longer, respectively, than the corresponding distances in 6. The La(1)-I(1) bond length of 3.2387(7) A˚ is longer than the La-I bond distances in 6, perhaps reflecting the presence of the methanediide center. In 6, the CP2N2La ring is arranged in a distorted-boat conformation, as evidenced by the P(1)C(1)-P(2) angle of 133.8(2)°. However, in 7 the CP2N2La ring is much flatter. Indeed, only the methanediide center deviates from the mean plane to any significant degree (0.196 A˚) and the P(1)-C(1)-P(2) angle is more obtuse at 145.1(5)°. In our previous study of [Y{C(PPh2NSiMe3)2}(CH2SiMe3)(THF)]15 we were able to directly compare the methanide- and methanediide-yttrium bonds in the same molecule by DFT calculations. The determination of the crystal structures of 6 and 7 and the similar distorted-pentagonal-bipyramidal structures for these lanthanum centers provides an excellent opportunity to directly compare the nature of the lanthanummethanide and -methanediide bonding in 6 and 7. We therefore carried out DFT calculations on the full structures of 6 and 7 using the ADF2009.01 code37,38 to determine the electronic structures of both complexes. The calculated structures of 6 and 7 closely match the experimentally derived structures. The bond lengths and (37) Fonseca Guerra, C.; Snijders, J. G.; te Velde, G.; Baerends, E. J. Theor. Chem. Acc. 1998, 99, 391. (38) te Velde, G.; Bickelhaupt, F. M.; van Gisbergen, S. J. A.; Fonseca Guerra, C.; Baerends, E. J.; Snijders, J. G.; Ziegler, T. J. Comput. Chem. 2001, 22, 931.

2320

Organometallics, Vol. 29, No. 10, 2010

Figure 6. Kohn-Sham orbital representations of 7 at the 0.05 e A˚-3 isosurface level: (a) HOMO (167A), -4.218 eV; (b) HOMO-1 (166A), -4.525 eV.

angles of the calculated structures are within (0.05 A˚ and (0.2° of the experimental values, respectively. We therefore conclude that the calculations provide a qualitative representation of the electronic structures of 6 and 7. The calculated La-C bond distance of 2.883 A˚ in 6 shortens considerably on conversion to 7, resulting in a calculated La-C bond length of 2.5284 A˚ in 7. The calculated La-N bond lengths remain largely unchanged (2.6021 A˚ (av) in 6 and 2.5836 A˚ (av) in 7), but as expected, the endocyclic P-C and P-N bond lengths shorten and lengthen, respectively, on moving from 6 to 7 (P-C = 1.746 A˚ (av) and P-N = 1.644 A˚ (av) for 6; P-C = 1.687 A˚ (av) and P-N = 1.660 A˚ (av) for 7). These trends are confirmed by inspection of the Nalewajski-Mrozek bond indices.39 For 6, the La-C, La-N, La-I, P-C, and P-N bond indices are 0.325, 0.547 (av), 0.921 (av), 1.091 (av), and 1.159 (av), respectively, whereas for 7 the corresponding bond indices are 0.767, 0.574 (av), 0.966, 1.257 (av), and 1.085 (av), respectively. The replacement of a “soft” polarizable iodide ligand with a “hard” methanediide is reflected by calculated Mulliken charges of þ0.70 and þ1.09 for the lanthanum centers in 6 and 7, respectively. This is accompanied by an accumulation of negative charge at the endocyclic carbon center, underscored by the calculated Mulliken charges of -0.868 for 6 and -1.089 for 7. As for related yttrium methanediides,15,17-20 a La-C bond order of less than 1 for a formal double bond illustrates the polar, ionic nature of rareearth bonding. Furthermore, this is exemplified by visual inspection of the Kohn-Sham molecular orbital representations of the HOMO and HOMO-1 of 7 (Figure 6), whose compositions (HOMO, 43.56% 2p C, 23.09% 2p N, 2.12% 3dxz P, 1.17% 5dyz La, 1.20% 3dz2 P; HOMO-1, 43.19% 2p C, 2.47% 5dx2-y2 La, 2.39% 3dxz P, 2.38% 3dxy P, 2.22% 6s La, 2.08 3dxy P, 1.72% 5dz2 La) reveal a combined contribution to the LadC “double bond” of only 7.58% from lanthanum.

Wooles et al.

[{Dy(CH[PPh2NSiMe3]2)(I)}2(μ-O)] (4) from attempts to prepare [Dy{C(PPh2NSiMe3)2}(I)(THF)2] (1). The formation of Dy-C bonds in 3 and 4 indicates that Dy-Bn linkages of some kind are present in “2”. This is supported by the observation that treating [K{CH(PPh2NSiMe3)2}(THF)n] with [Dy(I)3(THF)3.5] does not give 3. Attempts to utilize [{Li2(C[PPh2NSiMe3]2)}2] as a ligand transfer reagent resulted in the formation of the 2:1 complex [{La(μ-I)3Li(THF)2}2{μ-C(PPh2NSiMe3)2}] (5), and contamination with unreacted and cocrystallized [{Li2(C[PPh2NSiMe3]2)}2] prevented any development of this method. However, the potassium methanide complex [K{CH(PPh2NMes)2}] was found to react with [La(I)3(THF)4] to give the methanide complex [La{CH(PPh2NMes)2}(I)2(THF)2] (6), and 6 was found to react with 1 equiv of [K(Bn)] to afford the methanediide complex [La{C(PPh2NMes)2}(I)(THF)3] (7). A DFT study of 6 and 7 revealed an increased accumulation of charge at the endocyclic carbon following deprotonation and conversion of 6 to 7, and although the La-C bond indices increase substantially upon a second deprotonation, the bonding remains highly ionic and is dominated by carbon 2p contributions with little orbital contribution from lanthanum. Our studies to expand the range of f-element N-aryl bis(iminophosphorano)methanediides are ongoing and will be reported in forthcoming publications.

Experimental Section

In summary, attempts to prepare “[Dy(Bn)2(I)(THF)3]” (“2”) led to a product that is ill-defined. This indicates that although erbium and yttrium are small enough to be kinetically stable with respect to Schlenk-type equilibria, the larger dysprosium is apparently too large to be stable with the iodide-dibenzyl ligand combination. This is underscored by the isolation of [Dy{CH(PPh2NSiMe3)2}(I)2(THF)] (3) and

General Considerations. All manipulations were carried out using standard Schlenk techniques or an MBraun UniLab glovebox under an atmosphere of dry nitrogen. Solvents were dried by passage through activated alumina towers and degassed before use. All solvents were stored over potassium mirrors (with the exception of THF, which was stored over activated 4 A˚ molecular sieves). Deuterated solvents were distilled from potassium, degassed by three freeze-pump-thaw cycles, and stored under nitrogen. The compounds H2C(PPh2NSiMe3)2,27 H2C(PPh2NMes)2,26 [K{CH(PPh2NSiMe3)2}(THF)n ], 2 1 , 2 2 [{Li 2 (C[PPh 2 NSiMe 3 ]2 )}2 ], 4 0 [K{CH(PPh 2 NMes)2}],36 [LnI3(THF)n],23 and [K(Bn)],24 were prepared according to published procedures. 1 H, 13C, 31P, and 29Si NMR spectra were recorded on a Bruker 400 spectrometer operating at 400.2, 100.6, 162.0, and 79.5 MHz, respectively; chemical shifts are quoted in ppm and are relative to TMS (1H, 13C, and 29Si) and external 85% H3PO4 (31P). FTIR spectra were recorded on a Bruker Tensor 27 spectrometer. Calculations were carried out on a Parallel Quantum Solutions 32-Quad Core Quantum Cube. Elemental microanalyses were carried out by Mr Stephen Boyer at the Microanalysis Service, London Metropolitan University, U.K. Attempted Synthesis of “[Dy(Bn)2(I)(THF)3]” (“2”). THF (20 mL) was added to a precooled (0 °C) mixture of [K(Bn)] (1.04 g, 8.00 mmol) and [Dy(I)3(THF)3.5] (3.18 g, 4.00 mmol), and the resultant yellow-orange mixture was stirred at this temperature for 4 h. The mixture was filtered and volatiles were removed in vacuo, yielding a yellow oil presumed to be “2”. Yield: 2.65 g, 96% (based on a formulation of [Dy(Bn)2(I)(THF)3]). This compound was used without analysis, which was precluded by its oily and paramagnetic nature. Synthesis of [Dy{CH(PPh2NSiMe3)2}(I)2(THF)] (3). A solution of H2C(PPh2NSiMe3)2 (1.68 g. 3.00 mmol) in toluene (20 mL) was added dropwise to a suspension of “[Dy(Bn)2(I)(THF)3]” (2.06 g, 3.00 mmol) in toluene (20 mL) at -78 °C. The mixture was slowly warmed to room temperature with

(39) Michalak, A.; DeKock, R. L.; Ziegler, T. J. Phys. Chem. A 2008, 112, 7256.

(40) Hull, K. L.; Carmichael, I.; Noll, B. C.; Henderson, K. W. Chem. Eur. J. 2008, 14, 3939.

Summary and Conclusions

Article stirring over 20 h. Volatiles were removed in vacuo, and the resulting solid was washed with hexane and recrystallized from THF (5 mL) layered with hexane (5 mL) at -30 °C to afford 3 as yellow crystals. Yield: 0.40 g, 11.9%. Anal. Calcd for C39H55DyI2N2O2P2Si2: C, 41.89; H, 4.96; N, 2.51. Found: C, 41.83; H, 4.82; N, 2.52. IR ν/cm-1 (Nujol): 2284 (m), 1258 (m), 1097 (m), 1022 (br, s), 839 (m), 773 (w), 660 (w), 531 (w). Magnetic moment (Evans method, 300 K, THF): μeff = 9.09 μB. Synthesis of [{Dy(CH[PPh2NSiMe3]2)(I)}2(μ-O)] (4). A solution of H2C(PPh2NSiMe3)2 (1.12 g. 2.00 mmol) in toluene (20 mL) was added dropwise to a suspension of “[Dy(Bn)2(I)(THF)3]” (1.38 g, 2.00 mmol) in toluene (20 mL) at -78 °C. The mixture was slowly warmed to room temperature with stirring over 24 h. Volatiles were removed in vacuo, and the resulting solid was washed with hexane and recrystallized from toluene (2 mL) at -30 °C to afford 4 as colorless crystals. Yield: 0.16 g, 8.5%. IR ν/cm-1 (Nujol): 1959 (w), 1261 (s), 1092 (s, br), 1019 (s, br), 815 (w), 799 (s), 693 (w). Magnetic moment (Evans method, 300 K, THF): μeff = 8.67 μB. Synthesis of [{La(μ-I)3Li(THF)2}2{μ-C(PPh2NSiMe3)2}] (5). Toluene (20 mL) and diethyl ether (20 mL) were added to a mixture of [La(I)3(THF)4] (1.62 g, 2.00 mmol) and [{Li2(C[PPh2NSiMe3]2)}2] (1.14 g, 2.00 mmol), and the resultant colorless mixture was stirred for 5 days. Volatiles were removed in vacuo, and the resulting white solid was extracted into toluene (30 mL). Volatiles were removed in vacuo, and the resulting white powder was recrystallized from toluene (4 mL) at -30 °C to afford colorless crystals of 5 with concomitant crystallization of [{Li2(C[PPh2NSiMe3]2)}2]. Yield: 0.38 g, 15%. Anal. Calcd for C78H109I6La2Li3N4O4P4Si4: C, 37.94; H, 4.41; N, 2.27. Found: C, 37.97; H, 4.41; N, 2.24. 1H NMR (d8-THF, 298 K): δ 0.06 (18 H, s, SiMe3), 1.83 (16 H, m, CH2), 3.68 (16 H, m, OCH2), 7.02-7.25 (12 H, m, phenyl CH), 7.95 (8 H, m, phenyl CH). 13 C{1H} NMR (d8-THF, 298 K): δ 3.85 (SiMe3), 25.43 (CH2), 67.38 (OCH2), 74.21 (t, JPC = 189.20 Hz, La2CP2). 31P{1H} NMR (d8-THF, 298 K): δ 1.50. IR ν/cm-1 (Nujol): 1588 (w), 1435 (m), 1307 (w), 1259 (m), 1247 (m), 1228 (m), 1181 (w), 1107 (s), 1059 (br, s), 835 (s), 760 (m), 715 (m), 694 (s), 659 (w), 606 (w), 561 (w), 521 (w, br), 469 (w). Synthesis of [La{CH(PPh2NMes)2}(I)2(THF)2] (6). THF (25 mL) was added to a mixture of [La(I)3(THF)4] (2.42 g, 3.00 mmol) and [K{CH(PPh2NMes)2}] (2.10 g, 3.00 mmol), and the resultant yellow mixture was stirred for 20 h. The resulting colorless suspension was filtered, volatiles were removed in vacuo, and the resulting white solid was recrystallized from toluene (12 mL) at -30 °C to afford 6 as colorless crystals. Yield: 3.25 g, 77%. Anal. Calcd for C68.50H79I2LaN2O2P2: C, 58.06; H, 5.62; N, 1.98. Found: C, 57.87; H, 5.52; N, 1.93. 1H NMR (d8-THF, 298 K): δ 1.90 (8 H, m, CH2), 2.29 (6 H, s, p-CH3), 2.42 (12 H, s, o-CH3), 3.36 (1 H, t, 2JHP = 14.5 Hz, HCP2), 3.73 (8 H, m, OCH2), 6.80 (4 H, s, br, m-CH), 7.18-7.32 (12 H, m, br, phenyl CH), 7.71 (8 H, m, br, phenyl CH). 13C{1H} NMR (d8THF, 298 K): δ 5.73 (t, JPC = 136.8 Hz, La(H)CP2), 17.86 (o-CH3), 18.66 (p-CH3), 23.54 (CH2), 65.41 (OCH2), 123.20, 126.82, 128.45, 129.30, 130.32, 133.27, 135.59, 141.10. 31P{1H} NMR (d8-THF, 298 K): δ 11.46. IR ν/cm-1 (Nujol): 1434 (m), 1301 (w), 1260 (m), 1218 (s), 1158 (m), 1105 (s), 1020 (br, m), 984 (m), 853 (w), 800 (m), 735 (s), 695 (m), 662 (m), 560 (m), 466 (w). Synthesis of [La{C(PPh2NMes)2}(I)(THF)3] (7). THF (25 mL) was added to a precooled (-78 °C) mixture of 6 (3.14 g, 2.22 mmol) and [K(Bn)] (0.29 g, 2.22 mmol). The resulting orange-brown suspension was slowly warmed to room temperature with stirring over 24 h. The suspension was filtered, and volatiles were removed in vacuo to afford a brown solid. Recrystallization from toluene (12 mL) afforded 7 as colorless crystals. Yield: 1.33 g, 53%. Anal. Calcd for C55H66ILaN2O3P2: C, 58.41; H, 5.88; N, 2.48. Found: C, 58.42; H, 5.81; N, 2.51. 1H NMR (d8-THF, 298 K): δ 1.87 (12 H, m, CH2), 2.15 (12 H, s, o-CH3), 22.5 ()6 H, s, p-CH3), 6.70 (4 H, s, m-CH), 7.05 (8 H, t, 3 JHH = 7.20 Hz, o-CH), 7.17 (4 H, t, 3JHH = 7.20 Hz, p-CH),

Organometallics, Vol. 29, No. 10, 2010

2321

7.62 (8 H, m, m-CH). 13C{1H} NMR (d8-THF, 298 K): δ 17.90 (p-CH3), 19.48 (o-CH3), 23.53 (CH2), 58.76 (t, JPC = 148.4 Hz, LaCP2), 65.41 (OCH2), 124.25, 125.94, 126.38, 126.82, 130.27, 133.13, 137.94 (virtual t, JPC = 42.3 Hz, PC), 145.33. 31P{1H} NMR (d8-THF, 298 K): δ 4.81. IR ν/cm-1 (Nujol): 1959 (w), 1290 (m), 1261 (m), 1248 (m), 1217 (s), 1156 (m), 1098 (m, br), 1021 (s), 968 (w), 936 (w), 800 (br, m), 726 (m), 702 (m), 586 (m), 532 (s). X-ray Crystallography. Crystal data for compounds 3-7 and further details of the structure determinations are given in the Supporting Information. Bond lengths and angles are given in Table 1. Crystals were examined variously on Bruker AXS SMART 1000 and APEX CCD area detector diffractometers using graphitemonochromated Mo KR radiation (λ = 0.710 73 A˚). Intensities were integrated from a sphere of data recorded on narrow (0.3°) frames by ω rotation. Cell parameters were refined from the observed positions of all strong reflections in each data set. Semiempirical absorption corrections based on symmetryequivalent and repeat reflections were applied. The structures were solved variously by direct and heavy atom methods and were refined by full-matrix least squares on all unique F2 values, with anisotropic displacement parameters for all non-hydrogen atoms and with constrained riding hydrogen geometries; Uiso(H) was set at 1.2 (1.5 for methyl groups) times the Ueq value of the parent atom. The largest features in final difference syntheses were close to heavy atoms and were of no chemical significance. Highly disordered solvent molecules of crystallization in 4 and 6 could not be modeled and were treated with the Platon SQUEEZE procedure.41 Programs were Bruker AXS SMART (control) and SAINT (integration),42 and SHELXTL was employed for structure solution and refinement and for molecular graphics.43 Computational Details. Restricted geometry optimizations were performed for models of 6 and 7 using coordinates derived from the respective X-ray crystal structures. No constraints were imposed on the structures during the geometry optimizations. The calculations were performed using the Amsterdam Density Functional (ADF) suite, version 2009.01.37,38 The DFT geometry optimizations employed Slater type orbital (STO) triple-ζ plus polarization basis sets (from the ZORA/TZP database of the ADF suite). The cores for C, N, P, and La were frozen up to 1s for C and N, 2p for P, and 5p for La. Scalar relativistic approaches were used within the ZORA Hamiltonian for the inclusion of relativistic effects, and the local density approximation (LDA) with the correlation potential due to Vosko et al.44 was used in all of the calculations. Gradient corrections were performed using the functionals of Becke45 and Perdew.46 The program MOLEKEL47 was used to prepare the three-dimensional plot of the electron density.

Acknowledgment. We thank the Royal Society for a University Research Fellowship (S.T.L.) and the EPSRC and the University of Nottingham for generously supporting this work. Supporting Information Available: Tables giving calculated coordinates and energies of 6 and 7 and a table and CIF files giving X-ray crystallographic data for 3-7. This material is available free of charge via the Internet at http://pubs.acs.org. Observed and calculated structure factor details are available from the authors upon request. (41) 2000. (42) (43) 112. (44) (45) (46) (47)

Spek, A. L. Platon; University of Utrecht, Utrecht, The Netherlands, SMART and SAINT; Bruker AXS Inc., Madison, WI, 2001. Sheldrick, G. M. SHELXTL. Acta Crystallogr., Sect. A 2008, 64, Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200. Becke, D. Phys. Rev. A 1988, 38, 3098. Perdew, J. P. Phys. Rev. B 1986, 33, 8822. Portmann, S.; Luthi, H. P. Chimia 2000, 54, 766.