Organometallics 1995, 14, 2422-2429
2422
Bis(2-pyridy1)phosphidesand -arsenidesof Group 13 Metals: Substituent-SeparatedContact Ion Pairs Alexander Steiner and Dietmar Stalke" Institut fur Anorganische Chemie der Universitat Giittingen, Tammannstrasse 4, 0-37077Gdttingen, Germany Received January 23, 1995@
Tris(2-pyridy1)phosphine reacts with lithium metal in THF with cleavage of a P-aryl bond and ligand coupling to give 2,2'-bipyridyl and lithium bis(2-pyridy1)phosphide. Hydrolysis of this solution leads to bis(2-pyridy1)phosphine 1. Deprotonation of 1 with n-butyllithium yields (THF)zLi@-Py)zP, 2, (Py = 2-pyridyl). Addition of trimethylaluminum to tris(2pyridy1)phosphine gives the Me&,u-Py)PPyz adduct complex 3,while deprotonation of 1 and elimination of methane forms MeAl@-Py)2P,4. 4 is also obtained by a transmetalation reaction of 2 with MeAC1. Lithium metal also cleaves one As-aryl bond in tris(2-pyridyllarsine to give lithium bis(2-pyridyl)arsenide, which is directly treated with MeAlC1 and MezGaC1, yielding MeAl@-Py)&, 5, and MezGa@-Py)As, 6, respectively. While in 1 the hydrogen atom is located at the phosphorus atom, as indicated by IR and NMR spectroscopy, X-ray structure analyses of 2-5 prove that there is no contact between the metal center and the central phosphorus or arsenic atoms of the ligand. The [PyzEI- ligands (E = P, As) chelate the metal centers exclusively by both pyridyl nitrogen atoms, leaving the central E atom two-coordinated. The negative charge in the monoanionic [PyzEI- ligands of 2-6 is largely delocalized from the central E atom t o both pyridyl ring systems. The correspondence in spectroscopic data of 5 and 6 suggests the same structure type in the gallium arsenide complex 6. Introduction N-Heteroaryl ring systems are well-known as bridging functions between transition metal centers, but related complexes in main group chemistry are hardly known up to n0w.l Recently we described the replacement of the central BH unit in the widely used tris(pyrazol-1yl)borates2 with tin(I1) or germanium(I1) atoms leading to monoanionic ligands of the composition [Pz3E]- (Pz = pyrazol-1-yl, E = Ge, Sn).3 We studied their coordination behavior toward s-block metal centers such as sodium and barium and also toward further Ge(I1) and Sn(I1)units. In all of these complexes pyrazol-1-yl acts almost exclusively in an exo-bidentate bridging manner via both N-donor functions. Surprisingly, one of the pyrazol-1-yl ligands in these substituents coordinates side on to a barium center. Recently we reported complexes in which group 13 and 15 elements are connected via two pyridyl ring system^.^ Low molecular aggregates containing group 13 and 15 elements are of great interest as precursors for I I W semiconductor^.^ Monomeric group 13/15 compounds are commonly obtained only with extremely @Abstractpublished in Advance ACS Abstracts, April 15, 1995. (1)(a)Steel, P. J. Coord. Chem. Reu. 1990,106,227.(b) Trofimenko, S.Prog. Inorg. Chem. 1986,34,115. (2)(a)Trofimenko, S.Chem. Reu. 1972,72,497;(b) 1993,93,943. (c) Byers, P. K.; Canty, A. J.; Honeyman, R. T. Adu. Organomet. Chem. 1992,34,1. (3)(a) Steiner, A.; Stalke, D. J. Chem. SOC.,Chem. Commun. 1993, 1702. (b) Steiner, A.; Stalke, D. Inorg. Chem. submitted for publication. (4)Steiner, A,; Stalke, D. J.Chem. SOC.,Chem. Commun. 1993,444. (5)(a) Cowley, A. H.;'Jones, R. A. Angew. Chem. 1989,101,1235; Angew. Chem., Int. Ed. Engl. 1989,28,1208.(b) Heaton, D.E.; Jones, R. A,; Kidd, K. B.; Cowley, A. H.; Nunn, C. M. Polyhedron 1988,7, 1901. (c) Cowley, A. H.; Jones, R. A. Polyhedron 1994,13,1149. (d) Buhro, W. E. Polyhedron 1994,13,1131.
bulky substituents, so the low valence metal centers are protected against nucleophilic attack.6 However, we showed that pyridyl substituents at the phosphorus atom inhibit oligomerization by donation to the group 13 metals exclusively by their nitrogen atoms, leaving the phosphorus atom two-coordinated. This paper is concerned with a more detailed discussion of the structural and electronic aspects of the [PyzPI- ligand and the investigation of analogous arsenic derivates.
Results and Discussion Preparations of 1-6 (Scheme 1). Tris(2-pyridy1)phosphine' and tris(2-pyridyl)arsine,8respectively, react with an equimolar amount of lithium metal in THF, yielding deep crimson solutions containing LiPyzE (Py = 2-pyridyl; E = P, As) and 2,2'-bipyridyl in a 2:l molar ratio (eq i). The cleavage of an E-aryl bond seems to be the initial step leading t o LiPyzE and 2-pyridyllithium. The latter product undergoes a ligand coupling reaction and a metal transfer t o excess Py3E to give LiPyzE and 2,2'bipyridyl. Uchida, Oae et al. describe ligand coupling reactions of heteroaryl-substituted phosphines with organolithium compoundsg assuming a hypervalent transition state [R4PLi], which is related to phosphoranideslO [PXJ. Decomposition yields the RzPLi spe(6) (a) Higa, K. T.; George, c. Organometallics 1990,9,275. (b) Byrne, E. K.; Parkanyi, L.; Theopold, K. H. Science 1988,241,332.(c) Petrie, M.A,; Power, P. P. J. Chem. SOC.,Dalton Trans. 1993,1737. (d) Petrie, M.A.; Ruhlandt-Senge, K.; Power, P. P. Inorg. Chem. 1992, 31,4038. (e) Wehmschulte, R. J.; Ruhlandt-Senge, K.; Power, P. P. Inorg. Chem. 1994,33,3205. (7) Keene, F. R.; Snow, M. R.; Stephenson, P. J.; Tiekink, E. R. T. Inorg. Chem. 1988,27,2040. (8)Plazek, E.;Tyka, R. Zesz. Nauk Politech. Wroclaw., Chem. 1967, 4,79.
Q276-7333/95/2314-2422$Q9.QQ/Q 0 1995 American Chemical Society
Bis(2-pyridy1)phosphides and -arsenides
Organometallics, Vol. 14, No. 5, 1995 2423
Scheme 1
I - , E =
P As As
M = AI AI
Ga
Figure 1. Molecular structure of 2 in the solid state, selected bond lengths (pm) and angles (deg);see also Table 1: P1-C1 179.4(4),Pl-C6 179.8(4),Lil-N1 196.9(8),LilN2 196.9(7),Lil-01 193.2(7),Lil-02 193.7(7);c1-P1C6 110.4(2),N1-Lil-N2 102.1(3),P1-C1-N1 127.0(3), Pl-C6-N2 127.1(3),C1-N1-Lil 126.4(3), C6-N2-Lil 126.3(3),01-Lil-02 99.9(3).
cies and biaryls. Although there are a lot of investigations concerning the biaryl coupling products, up to now only very little attention has been paid to the resulting phosphorus components. Hydrolysis of the reaction mixture from eq i leads to bis(2-pyridy1)phosphine 1 (eq ii). After filtration and extraction with diethyl ether, it can be separated from 2,2'-bipyridyl by distillation under reduced pressure. While 2,Y-bipyridyl boils at 73 "C/O.Ol Torr, 1 is obtained at 110 "C/O.Ol Torr as a dark crimson oil. Bis(2-pyridy1)arsineis not available via this route, probably because of thermal decomposition during distillation. In contrast to diacylphosphines, which are keto-enol tautomers in solution and crystallize exclusively in the enol form in the solid state without P-H contacts,ll the hydrogen atom in 1 is entirely bound to the phosphorus = 225 atom, indicated in the lH and 31PNMR (~JP-H Hz) and IR (vs(P-H) = 2312 cm-l) spectra. Addition of n-butyllithium to a solution of 1 in THF leads t o the pure corresponding lithium compound (eq iii). Slow evaporation of the solvent yields dark red crystals of the THF adduct 2. In contrast, the isolation of 2 by direct crystallization from the reaction mixture of tris(2-pyridy1)phosphine and lithium metal (eq i) is impossible because of the presence of 2,2'-bipyridyl. When tris(2-pyridy1)phosphine is treated directly with trimethylaluminum in diethyl ether, the adduct complex 3 is obtained (eq iv). Different from analogous reactions with organolithium compounds, the reaction stops with the adduct species rather than undergoing ligand coupling to the corresponding aluminum phosphide. The saturated coordination sphere of the aluminum atom in 3 and the strong Al-C bonds presumably prevent methyl transfer to the phosphorus atom. The dimethylaluminum derivative 4 can be obtained either by treating 1 with trimethylaluminum in nhexane (eq v) or by transmetalation reaction of 2 with
dimethylaluminum chloride in diethyl etherln-hexane (eq vi). 4 crystallizes from a diethyl etherln-hexane mixture a t 3 "C. The bis(2-pyridy1)arsenides MezAI(p-Py)&, 6, and MezGa@-Py)&, 6, are synthesized directly by using the reaction mixtures of tris(2-pyridy1)arsine and lithium metal (eq i). After the reaction is complete and THF replaced by toluene, MezMCl (M = Al, Ga) is added a t -40 "C (eq vi). Lithium chloride is filtered off and the resulting 2,2'-bipyridyl can be separated by washing with n-pentane. Spectroscopicdata show pure products. 6 crystallizes as dark violet needles from a diethyl ether/ n-hexane solution. Crystal Structure of 2. Figure 1 illustrates the tetrahedral environment of the central lithium atom, which is coordinated by both pyridyl nitrogen and two THF oxygen atoms. The Li-N distances are identical (196.9(8) and 196.9(7) pm). They are comparable to corresponding Li-N distances in lithium salts of 2-pyridyl-substituted carbanions.12 The molecule is almost planar with the exception of the THF ligands, which are arranged above and below the main plane (Figure 5). The bond angle at the phosphorus atom is 110.4(2)",and the P-C bond length is 179.6 pm on average. In contrast t o P-C single bonds, which are about 185 pm long, values for P-C double bonds in phosphaalkenes range from 161 to 171 pm.13 While in 2 the planes of the pyridyl rings intersect at an angle of 7", the correspondingvalue for both phenyl rings in the solventseparated ion pair of [Li(l2-crown-4)21[Ph~Plis 43".14 The negative charge of the sp2-hybridized phosphorus atom in 2 is highly delocalized throughout the whole ligand because of the good n-acceptor capacity of the 2-pyridyl substituents. The consequence is a partial P-C double bond character. Compounds containing a phosphorus atom in a delocalized carbon ring system
(9)(a) Uchida, Y.;Takaya, Y.; Oae, S. Heterocycles 1990,30,347. (b) Uchida, Y.;Kawai, M.; Masauji, H.; Oae, S. Heteroatom Chem. 1993, 4,421. ( c ) Oae, S.Croat. Chem. Acta 1986,59,129. (10)Dillon, K. B. Chem. Rev. 1994,94,1441. (11)(a)Becker, G.; Beck, H. P. 2. Anorg. Allg. Chem. 1977,430,77. (b) Becker, G.;Becker, W.; Schmidt, M.; Schwarz, W.; Westerhausen, M. 2. Anorg. Allg. Chem. 1991, 605, 7. (c) Becker, G.;Schmidt, M.; Schwarz, W.; Westerhausen, M. 2. Anorg. Allg. Chem. 1992,608,33.
(12)(a) Pieper, U.; Stalke, D. Organometallics 1993,12, 1201. (b) Engelhardt, L.M.; Jacobsen, G. E.; Junk, P. C.; Raston, C. L.; Skelton, B. W.; White, A. H. J. Chem. SOC.,Dalton Trans. 1988,1011. (13)(a)Appel, R.; Knoll, F.; Ruppert, I. Angew. Chem. 1981,93,771; Angew. Chem., Int. Ed. Engl. 1981,20, 731. (b) Appel, R.;Knoll, F. Adu. Inorg. Chem. 1989,33,259. (14)Hope, H.; Olmstead, M. M.; Power, P. P.; Xu, X. J. A m . Chem. SOC.1984,106,819.
Steiner and Stalke
2424 Organometallics, Vol. 14,No. 5, 1995 r?
C14
e1
PI
C’5
c4 5 L/
e11
C16 C17
Figure 2. Molecular structure of 3 in the solid state, selected bond lengths (pm)and angles (deg);see also Table 1: P1-C1 184.2(2), Pl-C6 184.2(2), P1-C11 183.2(2), All-N1 205.7(2), All-C16 197.8(3), All-C17 197.3(3), All-C18, 196.6(2); Cl-P1-C6 99.88(9), C1-P1-C11 100.08(9),C6-P1-C11 101.9(1),P1-C1-N1 116.2(1),C1N1-All 124.4(1),av N-Al-C 105.1, av C-Al-C 113.4.
Figure 3. Molecular structure of 4 in the solid state, selected bond lengths (pm)and angles (deg);see also Table 1: P1-C1 178.6(2), Pl-C6 178.2(2), All-N1 192.4(1), All-N2 191.9(1), All-C11 195.5(2),All-C12 195.2(2); C1-P1-C6 106.60(7),P1-C1-N1 127.1(1),Pl-C6-N2 126.9(1),C1-N1-All 123.2(2),C6-N2-All 123.2(1),N1All-N2 98.98(6),C11-All-C12 119.47(9).
atom prefers the “hard” nitrogen donor rather than the “soft”phosphine function. Three methyl groups and the are neutral pho~phabenzenesl~ (P-C 174 pm in 2,6single N-donor atom leave the central aluminum atom dimethyl-4-phenylphosphabenzene)16and ~,~~-coordinat- tetrahedrally-coordinated. The Al-N-donor bond length ed phospholides17 (P-C 179 pm in ( T , I ~ - C ~ * ) R U ( T , Iof~205.7(2) -~pm corresponds with bond lengths in related Bu2C4H2P)).18 The latter resembles the main structural donor-acceptorcomplexes. Three neutral pyridine molfeatures of 2 regarding the P-C bond length and 31P ecules donate to the central aluminum atom in the NMR spectroscopic shift. In both systems the phosphooctahedral complex (PyH)dCl3 with Al-N distances rus atom is part of a delocalized n-excess monoanion. between 206.7 and 209.6 pm.23 A slightly longer Two-coordinatedphosphorus atoms are also found in the distances is observed in the adduct of Med-NMe3 [(CN)2Pl- anion of the crown ether-solvated sodium (209.9 pm) in the gas phase.24 The Al-C distance in 3 saltlg and in the DME-saturated lithium dibenzoylphosis on average 197.2 pm long and comparable with that phide.20 This compound shows a structural pattern in Med-NMe3 (198.7 pm). The average C-Al-N related to 2. Both benzoyl substituents donate the angle is about 8” more acute than the average C-Allithium atom via their oxygen atoms. Lithium dipheC-angle, indicating the higher sterical demand of the nylphosphide is isoelectronic t o 2 and often used as a more covalent-bound methyl groups in the coordination transfer reagent for the diphenylphosphide group.21 sphere of the aluminum atom rather than the loosely With exception of the solvent-separated [Li(l2-crowndonating nitrogen atom.25 There is no significant dif4)2l[Ph~Plion pair, all known structures show Li-P ference in the P-C bond lengths of the single ring contacts. The P-C bond lengths in these systems are coordinated t o the aluminum atom and the two nonco185 pm on average and therefore about 5 pm longer ordinated pyridyl substituents, respectively. On averthan in 2. While the THF adduct gives a polymer in age, the C-P-C angle is 100.6” and comparable with the solid state, dimeric and monomeric complexes are Tranthose in noncomplexing tri~(2-pyridyl)phosphine.~~ formed in the presence of the chelating nitrogen donor sition metal complexes containing tris(2-pyridy1)phosbases TMEDA (Me2NCH2CH2NMe2)and PMDETA ((Me2phine as a neutral ligand are structurally well-known.27 NCH&H2)2NMe), respectively.22 The formal replaceToward zinc28and ruthenium’ it coordinates as a tripod ment of the o-phenyl-CH positions by N functions ligand via all three ring nitrogen atoms, while in the converts the monodentate diphenylphosphide into a linear gold complex Py3PAuC1, it coordinates the softer chelating system. As a consequence, the metal cation gold center exclusively with the phosphorus atom.29 is separated from the phosphorus ligand center and Crystal Structure of 4. In the monomeric complex oligomerization is prevented. 4 the aluminum and phosphorus atoms are p2-bridged Crystal Structure of 3. Just one of the three pyridyl by two pyridyl ring systems (Figure 3). The (THF)2Li substituents donates t o the aluminum atom via its unit in 2 is replaced by a M e d unit. As in 4, the nitrogen function (Figure 2). The (‘hard” aluminum (23) Pullmann, P.; Hensen, K.; Bats, J. W. 2. Naturforsch. 1982, (15)Ashe, A. J., 111. Top. Curr. Chem. 1982, 105, 125. (16) Fluck, E. Top. Phosphorus Chem. 1980, 10, 193. (17) Nixon, J. F. Chem. Reu. 1988, 88, 1327. (18)Carmichael, D.; Ricard, L.; Mathey, F. J . Chem. Soc., Chem. Commun. 1994, 1167. (19) Sheldrick, W. S.; Kroner, J.; Zwaschka, F.; Schmidpeter, A. Angew. Chem. 1979,91, 998; Angew. Chem., Int. Ed. Engl. 1979,18,
--
R 2 A-.
(20) Becker, G.; Birkhahn, M.; Massa, W.; Uhl, W. Angew. Chem. 1980,92, 756; Angew. Chem., Int. Ed. Engl. 1980,19, 741. (21) Issleib, K.; Wenschuh, E. Chem. Ber. 1964, 97, 715. (22) Mulvey, R. E.; Wade, K.; Armstrong, D. R.; Walker, G. T.; Snaith, R.; Clegg, W.; Reed, D. Polyhedron 1987, 6, 987.
B37. 1312. I
(24)Andersen, G. A,; Forgaard, F. R.; Haaland, A. Acta Chem. Scand. 1972,26, 1947. (25) (a) Gillespie, R. J.; Hargittai, I. The VSEPR Model ofMolecular Geometry; Allyn and Bacon: Boston, 1991. (b) Haaland, A. Angew. Chem. 1989,101, 1017;Angew. Chem., Int. Ed. Engl. 1989,28,992. (26) Keene, F. R.; Snow, M. R.; Tiekink, E. R. T. Acta Crystallogr. Sect. C 1988,44, 757. (27)Newkome, G. R. Chem. Reu. 1993,93, 2067. (28) Gregorzik, R.; Wirbser, J.; Vahrenkamp, H. Chem. Ber. 1992, 125, 1575. (29) Lock, C. L. J.; Turner, M. A. Acta Crystallogr. Sect. C 1987, 43, 2096.
Bis(2-pyridy1)phosphide.s and -arsenides
Figure 4. Molecular structure of 5 in the solid state, selected bond lengths (pm)and angles (deg);see also Table 1: Asl-C1 191.9(7),Asl-CG 189.3(8),All-N1 193.4(6), All-N2 192.3(6), All-C11 194.5(9), All-Cl2 194.0(8); Cl-Asl-CG 103.0(3),Asl-C1-N1 126.9(5),Asl-C6-N2 127.3(5),Cl-Nl-All 123.6(5),C6-N2-All 122.9(5),N1All-N2 101.2(3), C11-All-C12 119.4(4). phosphorus atom is two-coordinated and the two P-C bond lengths are very similar (Pl-C1 178.6(2)pm; P1C6 178.2(2) pm), indicating delocalization of the negative charge throughout the anion. A l l shows a distorted tetrahedral coordination sphere. Both Al-N bonds are of the same length (av 192.2 pm). While an Al-N single bond in the three-coordinated triamide Al[N(SiMe3)~13~~ is 14 pm shorter than in 4, the Al-N-donor bond in 3 is about 13 pm longer. Consequently, the Al-N bond order in 4 ranges between a single bond and a donor bond. A comparable Al-N bond distance is observed in the cationic bis[(2-pyridyl)bis(trimethylsilyl)methyllaluminum complex (av 192 pmh31 As in 4, the phosphorus atom in Meflh-NMes*)zP is only two-coordinated. The Al-N distance in the AlNzP ring system is 6 pm longer than in 4.32 The Al-C bond lengths (av 195.4 pm) are in accordance with those in related systems.33 Figure 5 illustrates the deviation from planarity in contrast to the lithium derivative 2. Both pyridyl ring planes intersect at an angle of 155”. Therefore, the methyl groups are chemically nonequivalent in the solid state. Nevertheless, lH and I3C NMR spectra from solution show only a single signal a t room temperature for both methyl groups. Not even cooling the solution to -80 “C reveals two different signals in the NMR spectrum. The C-P-C angle in 4 is 4” more acute than in 2. The intramolecular No * ONdistance (the “bite”)of the ligand differs in both compounds (2, 306.4 pm; 4, 292.2 pm). Hence, the ligand shows coordination flexibility toward different metal centers, while not giving up the full conjugation. Crystal Structure of 5. Replacement of the phosphorus atom by an arsenic atom does not change the basic structural features. 5 is isostructural with 4 in the solid state (Figure 4). Like the phosphorus atom in 4, the arsenic atom in 5 is two-coordinated. The As-C bonds (av 190.1 pm) are very short compared to (30) Sheldrick, G. M.; Sheldrick, W. S. J.Chem. SOC.A 1969,2279. (31)Engelhardt, L. M.; Kynast, U.; Raston, C. L.; White, A. H. Angew. Chem. 1987,99, 702; Angew. Chem., Int. Ed. Engl. 1987,26, 6Fll I”-.
(32) Hitchcock, P. B.; Jasim, H. A.; Lappert, M. F.; Williams, H. D.
J.Chem. SOC.,Chem. Commun. 1986, 1634.
(33) Kumar, R.; de Mel, S. J.; Oliver, J. P. Organometallics 1989,8, 2488.
Organometallics, Vol. 14,No.5,1995 2425
c12
P
7 c11
c_?2
Y Figure 5. View along the E-M axes of 2, 4, and 5 illustrating the deviation from planarity. the 8 pm longer As-C bonds in dioxane-solvated sodium diphenylar~enide.~~ Two-coordinated arsenic atoms in delocalized carbon ring systems are known from arsabenzenes35 (av As-C 185 pm) and the Cp-analogous arsolide anions36(av As-C 190 pm). The partial E-C double bond character in 5 corresponds t o that in the phosphorus derivative 4. In comparison to that, the As-C double bond distances in arsaalkenes on average are 182 pm.37 The aluminum atom in 5 shows the same coordination pattern as in 4 (av Al-N 192.8 pm; Al-C 194.3 pm). There is also a noticeable deviation from planarity of the ligand (Figure 5). Both planes of the pyridyl rings intersect at the same value as in 4 (155”). The N***Ndistance of the ligand is 298 pm. As in 4, the ligand shows coordination flexibility toward the metal center. Comparison of Structural and Spectroscopical Data. Average values of equivalent bond lengths in the (34) (a) Belforte, A,; Calderazzo, F.; Morvillo, A.; Pelizzi, G.; Vitali, D. Inorg. Chem. 1984, 23, 1504. (b) Doak, G. 0.;Freedman, D. Synthesis 1974, 328. (35) (a) Sanz, F.; Daly, J. J. J.Chem. SOC.,Dalton Trans. 1973,511. (b) Wong, T. C.; Bartell, L. S. J.Mol. S t r u t . 1978, 44, 169. (36) (a) Abel, E. W.; Nowell, I. W.; Modinos, G. J.; Towers, C. J. Chem. SOC.,Chem. Commun. 1973, 258. (b) Chiche, P. L.; Galy, J.; Thiollet, G.; Mathey, F. Acta Crystallogr. Sect. B 1980, 36, 1344. (37) (a) Weber, L.; Meine, G.; Boese, R. Angew. Chem. 1988,98,463; Angew. Chem., Int. Ed. Engl. 1986,25,469. (b) Driess, M.; Pritzkow, H.; Sander, M. Angew. Chem. 1993,105, 273; Angew. Chem., Int. Ed. Engl. 1993,32, 283.
2426 Organometallics, Vol. 14, No. 5, 1995
Steiner and Stalke
Table 1. Selected Bond Lengths (pm) of 2-5 [Chemically Equivalent Bonds Are Averaged (See Also Figure Captions)]
E=P,As M = Li, AI
3 (E = P, M = Al) 2 (E = P, M = Li) 179.6 135.7 141.2 136.5 138.8 136.9 135.7 196.9
bond E-CT21 N[1l1C[21 C[21-C[31 C[31-C[41 C[41-C[51 C[51-C[61 C[61-N[11 N[ll-M
P-PY 184.2 135.3 138.4 138.4 137.4 136.9 135.4 205.7
Scheme 2
J
a
b
'I
C
E = P, As
M = Li, AI, Ga ligands of 2, 4, and 5 and in the coordinating and noncoordinating substituents of 3 are listed in Table 1. The pyridyl rings of 2,4,and 5 exhibit alternating bond lengths. The C[3I-C[41 and C[51-C[61 bond distances are significantly shorter than the C[21-C[31 and C[41C[51 bond distances, indicating partial double bond localization in these positions. In contrast to this, the corresponding values in 3 are almost alike, even in the ring coordinated to aluminum, demonstrating full conjugation. The C-N bond lengths are marginally longer in the [Py2E]- anions than in the neutral donor molecule of 3, indicating charge accumulation a t the ring nitrogen atoms. As described above, the E-C bond lengths in the [PyzEI- anions are almost halfway between the value of the E-C single bonds (as in 3) and an E-C bond in heterobenzenes, with a formal bond order of 1.5. These observations permit a description of the bond situation in the [Py2Elligands as illustrated in Scheme 2. The partial negative charge at the central E atom (a) is partly delocalized from the p orbital of the sp2hybridized E atom onto both n-accepting pyridyl substituents (b, c). This delocalization is even more pronounced in the isoelectronic and isostructural com-
Py
4 (E = P, M = Al)
5 (E = As, M = Al)
183.7 133.4 138.5 138.6 136.5 136.3 134.0
178.4 136.8 141.5 136.2 139.8 135.8 136.2 192.1
190.1 135.5 142.0 135.0 140.0 134.9 138.2 192.8
plexes of MesM@-Py)zCH(M = Al, The central carbon atom is also regarded as sp2-hybridizedwithout any negative charge, whereas it is almost entirely located at both ring nitrogen atoms. Due to the even more striking delocalization in the [HCPyz] anion, it shows a quite rigid coordinational behavior toward different metals. Table 2 compares the 13CNMR shifts of 1,3,4,5and 6, and the corresponding n J ~ - pcoupling constants of 1, 3, and 4. It is worth noting the downfield shift of the C[21 nucleus in the monoanionic ligand of 4-6 relative to that in the neutral phosphine derivatives 1 and 3. The partially negatively charged E and N atoms shield the C[21 position, while the inductive effect of the phosphorus atom in the neutral molecules causes a high field shift. In addition, the n J ~ - pcoupling constants in 4 are much larger than in 1 and 3, demonstrating an extensive delocalization of the negative charge throughout the whole [PyzEI- unit and a partial double-bond character of the P-C bonds. We could not succeed in preparing crystals of 6 suitable for X-ray structure analysis. However, it can be assumed that 5 and 6 have similar structures because their spectroscopic properties are very similar. Compared to the starting material, the highest energetic pyridyl ring deformation vibration in the IR spectrum of 5 and 6 is shifted to lower frequencies by coordination toward the metal centers (Y = 1570 (Pyas), 1600 (51, 1595 (6)cm-1).28,39The metal coordination causes also a high field shift of the [61-H signal in the lH NMR spectrum of more than 1ppm (6 8.67 (PYAS),7.61 (51, 7.49 (6)).
Conclusion
The reaction of tris(2-pyridy1)phosphine and tris(2pyridyl)arsine, respectively, with lithium metal leads to (THF)aLi@-Py)zEvia cleavage of one E-aryl bond and ligand coupling yielding bipyridyl. Transmetalation reactions yield complexes of the composition MezM@(38) (a) Gornitzka, H.; Stalke, D. Organometallics 1994,13, 4398. (b) Gornitzka, H.; Stalke, D. Angew. Chem. 1994,106, 695; Angew. Chem., Int. Ed. Engl. 1994,33,693. (39)Anderegg, G.; Hubmann, E.; Wenk, F. Helu. Chim. Acta 1977, 60, 123.
Organometallics, Vol. 14, NO.5, 1995 2427
Bis(2-pyridy1)phosphide.s and -arsenides
Table 2. lSC NMR Spectroscopic Shifts of 1-6 and J c - p Coupling Constants (Hz)of 1,3,and 4
1
3 4
5 6
"Jc-P (Hz) 6 ("Jc-P) 6
YJC-P)
6 ("Jc-P) 6 6
C[21, n = 1 128.7 (18.5) 129.8 . (20.7) 179.0 (74.1) 186.5 185.7
C[31, n = 2 150.1 (10.3) 150.2 (11.3) 129.4 (53.0) 130.6 130.6
Py)zE (M = Al, Gal. The hard metal centers are exclusively chelated by the pyridyl N atoms, leaving the E atom two-coordinated. The negative charge is largely delocalized throughout the whole [PyzEI- anion. Nevertheless, this delocalization permits coordinational flexibility and deviation from planarity. It would be interesting to see what coordination properties these new [PyzPI- ligands and also the mixed group 13/15 complexes 2 and 4-6 have toward soft d-block metal centers. This might prevent a route to hard-soft bimetallic reagents due to coordination site selective behavior. Experimental Section All manipulations were performed under a n inert atmosphere of dry nitrogen gas with Schlenk techniques or in an argon drybox. Solvents were dried over Na/K alloy and distilled prior to use. NMR spectra were obtained with a Bruker MSL 400 or Ah4 250 instrument. All NMR spectra were recorded in benzened6 or CDC13 with SiMe4, Licl, and (85%)as external standards. E1 and FI mass spectra were measured on Finnigan MAT 8230 or Varian MAT CH 5 instruments. Elemental analyses were obtained from the Analytische Labor des Instituts fur Anorganische Chemie der Universitat Gattingen. 1 (Py2PH). Freshly rolled lithium wire (0.7 g, 100 mmol) is added to a solution of 12.8 g (50 mmol) of tris(2-pyridy1)phosphine in 100 mL of THF. The deep crimson reaction mixture is stirred for 3 h at room temperature and filtered from the unreacted lithium metal. The THF is removed under vacuum, and the precipitate is redissolved in 100 mL of ether. Under ice cooling the solution is hydrolyzed with 50 mL of degassed water. The organic layer is separated, and the water phase is extracted twice with 50 mL of ether. From the joint organic phases the ether is removed under vacuum. The product is purified by distillation at reduced pressure (lo-?Torr). After the first runnings a t 73 "C (2,2'-bipyridyl), the product is obtained a t 110 "C as a crimson oil: yield 6.2 g, 66%; IR(fi1m) Y (cm-l) 3041 st, 2988, m, 2930 m, 2854 m, 2312 st, 1572 vst, 1559 st, 1450 vst, 1419 vst, 1278 m, 1152 st, 1946 st, 988 s t , 883 m, 752 sst, 620 st, 519 st; 'H NMR (CDC13) 6 5.44 (d, l J ~ - p= 225 Hz, l H , P-H), 7.0-8.6 (m, 8H, Py);13C NMR (CDCl3) 6 122.3 (s,C[51), 128.7 (d, 'Jc-p = 18.5 Hz, C[21), 135.6 (d, Vc-p = 3.4 Hz, C[41), 150.1 (d, 'Jc-p = 10.3 Hz, C[31), 160.1 (d, Vc-p = 2.1 Hz, C[6]); 31PNMR (CDC13)6 -34.1; MS(EI) mlz 188 (M+, loo%), 109 (PyP,92%);MS(F1) mlz 188 (M+, 100%). Anal. Calcd (Found): C, 63.83 (64.42); H, 4.82 (4.60); N, 14.89 (14.41). 2 [(THF)2Li(p-Py)9]. A solution of 2.2 mL of 2.3 M (5 mmol) n-butyllithium in n-hexane is added dropwise t o 0.94 g
(341, n = 3 135.6 (3.4) 135.3 (4.1) 133.4 (18.3) 132.8 132.8
C[51, n = 4 122.3 (0)
122.5 (0)
115.6 (0)
116.4 116.7
C[61, n = 3 160.1 (2.1) 163.1 (0)
143.1 (4.5) 144.6 144.6
(5 mmol) of 1in 15 mL of THF. Slowly evaporating the solvent gives red crystals: yield 1.11g (66%); decomposition > 50 "C; 'H NMR (C&) 6 1.36 (8H, tho, 3.52 (8H, tho, 6.0-8.0 (m, 8H, h H ) ; 'Li NMR (C&) 6 2.5; 31P NMR (C6D6) 6 13.0. 3 (Me&l(p-Py)PPyZ).One gram (3.8 mmol) of tris(2pyridy1)phosphane is dissolved in 15 mL of ether. To this solution is added 1.9 mL of 2.0 M trimethylaluminum solution in n-hexane (3.8 mmol) at room temperature. The pink reaction mixture is stirred for 3 days and filtered subsequently through a glass frit. Light red single crystals are obtained after storage of the filtrate for 1day at -38 "C. The crystals are thermolabile and decompose instantaneously at ambient conditions. They were handled and transferred to the difiactometer at about -20 "C40 'H NMR (C&) 6 0.08 (s, 9H, Me), 6.52 (m, 3H, Py),6.94 (m, 3H, Py),7.46 (m, 3H, Py),8.48 (m, 3H, l3C NMR (C.5D6) 6 122.8 (9, c[5]),129.8 (d, 'Jc-p = 20.7 Hz, C[21), 135.3 (d, 3Jc-p = 4.1 Hz, C[41), 150.2 (d, 'Jc-P = 11.3 Hz, C[3]), 163.1 (9, C[6]); 31PNMR (C&) 6 -0.4. 4 (Me&l(p-Py)zP).(a) First Route. l ( 1 . 1 3 g, 6 mmol) is dissolved in 10 mL of diethyl ether. A solution of 2.6 mL of 2.3 M (6 mmol) n-butyllithium in n-hexane is added at room temperature over a period of 30 min. After stirring for 2 h, the dark red reaction solution is cooled to -40 "C, and a solution of 6 mL of 1 M (6 mmol) dimethylaluminum chloride in n-hexane is added over a period of 1h. The reaction solution is warmed to room temperature and stirred overnight. Lithium chloride is filtered off and 3 days of storage of the clear solution at 3 "C yielded dark red crystals. (b) Second Route. 1(3.76 g, 20 mmol) is suspended in 30 mL of n-hexane. After the mixture is cooled to -40 "C, a solution of 10 mL of 2 M trimethylaluminum in n-hexane (20 mmol) is added over a period of 30 min. The reaction solution is allowed to warm to room temperature and stirred overnight. After the organic solvent is evaporated, 3 is obtained as a crude product in a yield of 90%, which can be purified by recrystallization in a solution of n-hexanddiethyl ether at 3 "C: mp 105 "C; 'H NMR (C6D6) 6 -0.36 (s,6H, CHd, 5.94 (dddd, 3J5,4 = 7.0, 3J5,6 = 6.1, 4J5,3 = 1.3, 'J5,p = 0.5 Hz, 2H, 5-H), 6.37 (dddd, 3J4,3 = 8.6, 3 J 4 , 5 = 7.0, 4 J 4 , 6 = 1.6, 4J4,p = 1.0 Hz, 2H, 4-H), 7.30 (dddd, 3J3,p = 10.0, 3J3,4 = 8.6, 4J3,5 = 1.3, '53,s = 1.0 Hz, 2H, 3-H), 7.49 (dddd, 3J6,5 = 6.1, 4 J 6 , 4 = 1.6, 4 J ~ , =~ 1.0, 5J6,3 = 1.0 Hz, 2H, 6-H); 13CNMR (C&) 6 -12.1 (s,CHd, CC31), 133.4 (d, 3 J c - ~ 115.6 (s, C[51), 129.4 (d, 'Jc-p = 53.0 Hz, = 18.3Hz, C[4]), 143.1 (d, %Jc-p = 4.5 Hz, C[61), 179.0 (d, 'Jc-P = 74.1 Hz, C[2]); 31PNMR 6 25.7; MS(E1) mlz 244 (M', 85%). Anal. Calcd (Found): 59.02 (58.79); H, 5.78 (5.43); N, 11.47 (11.89). 5 (Med(p-Py)&). To a solution of 3.3 g (10.7 mmol) of AsPy3 in 100 mL of THF is added 0.15 g (21.4 mmol) of freshly rolled lithium wire. The deep purple reaction mixture is
e);
(40) Kottke, T.; Stalke, D.
J.Appl. Crystullogr. 1993,26,615.
2428 Organometallics, Vol. 14, No. 5, 1995
Steiner and Stalke
Table 3. Crystal Data of 2-5 formula fw cryst size (mm) space group a (pm) b (pm) c (pm) /3 (deg) V (nm3)
4
5
Ci2Hi=&lN2P 244.2 0.5 x 0.3 x 0.3
Pna2l
P211c
P2 1lC
1791.7(1) 935.69(7)
1282.3(3) 1877.6(5) 788.3(2) 102.26(3) 1.8547(8) 4 153(2) 1.208 0.198 712 8-55 5799 4276
1060.08(7) 864.42(6) 1414.91(9) 104.968(5) 1.2526(1) 4 153(2) 1.295 0.263 512 8-60 6370 3676
CizHidiUAsNz 288.2 0.5 x 0.5 x 0.2 P2 1lc 1065.7(5) 863.6(5) 1423.8(7) 104.56(4) 1.268(1) 4 153(2) 1.509 2.723 584 8-45 3241 1624
0
0
0
208 0.057 0.162 0.094; 0.833 0.41
201 0.040
147 0.061 0.177 0.112; 2.552 0.75
1085.0(1)
temp (K) (MP-~) I.L (mm-') ec
F(OO0) 28 range (deg) no. of reflns measd no. of unique reflns no. of restraints
a
3
CisHziAN3P 337.3 0.6 x 0.5 x 0.4
90 1.8191(1) 4 153(2) 1.235 0.162 720 8-45 2628 2386 70 259 0.045
z
refined param R1 [Z > 2o(Z)] wR2a (all data) g1; g z b highest diff peak
2
ClsH24LiN202P 338.3 0.4 x 0.3 x 0.2
0.100
e~ m - ~ )
0.022; 1.959 0.17
wR2 = {[Xw(C - F32Y[C~(F321}1'2. * w-' =
$(e)+
Table 4. Atomic Coordinates ( x 104) and Equivalent Isotropic Displacement Parameters (pm2 x 10-l) for 2 X Y z UeqP 34(1) 8400(1) 654(1) 8727(1) 33(4) 9446(4) -1788(7) 10640(7) 30(2) 8773(2) -2216(4) 9253(3) N(l) 9325(2) 30(2) N(2) 293(4) 10820(3) 29(2) 8421(2) -1249(4) 8526(4) -1734(5) 7491(4) 4U3) C(2) 8018(3) -3152(6) 7225(4) 45(3) C(3) 7953(3) C(4) 8308(3) -4140(5) 7984(5) 44(3) 8696(2) -3618(5) 8968(5) 36(3) C(6) c(5) 8906(2) 1156(4) 10090(4) 27(2) 8859(2) 2628(5) 10371(4) 34(3) c(7) 9224(3) 3203(5) 11338(4) 39(3) ('C(9) ) 9665(3) 2332(5) 12070(4) 39(3) C(10) 9691(3) 900(5) 11783(4) 36(3) -2319(3) 10441(3) 36(2) O(1) 10481(2) -1321(5) 10193(5) C(11) 11068(2) 42(3) -2187(9) 9728(16) 60(8) C(12) 11710(5) 10447(19) 11614(4) -3547(10) 66(8) C(13) -3734(5) 10413(6) 57(3) C(14) 10776(3) -2182(7) 10300(9) C(12') 11779(3) 60(4) -3626(3) 9856(8) C(13') 11534(3) 63(5) 9185(2) -2967(3) 12042(3) 38(2) C(15) o(2) 9633(3) -3048(5) 13134(4) 42(3) (316) 9174(3) -2442(6) 14162(4) 56(4) a U(eq) is defined as one-third of the trace of the orthogonalized U, tensor. P(1) Li(1)
+g 9 ;P
=
0.111
[e+ 2F:1/3.
0.059; 0.175 0.47
Table 5. Atomic Coordinates ( x lo4) and Equivalent Isotropic Displacement Parameters (pm2 x 10-l) for 3 X Y Z UeqP P(U Al(1)
NU) N(2) N(3) C(2) '(') C(3) C(4) C(5) C(6) c(7) c(8) C(9)
C(10) C(11) C(12) C(13) (314) C(15) C(16) C(17) C(18) C(17) C(18) a
6806(1) 7962(1) 8234(1) 5770(2) 8441(1) 7786(2) 8051(2) 8798(2) 9266(2) 8964(2) 5701(2) 4811(2) 3958(2) 4021(2) 4930(2) 7378(2) 6733(2) 7202(2) 8293(2) 8869(2) 8882(3) 6436(2) 8504(2) 8438(3) 8423(2)
9692(1) 11288(1) 10489(1) 8645(1) 8833(1) 9834(1) 9308(1) 9446(1) 10108(1)
10612(1) 9305(1) 9729(2) 9452(2) 8777(2) 8400(2) 8901( 1) 8450(1) 7902(1) 7826(1) 8296(1) 12068(2) 11548(2) 10886(1) -2021(5) -2866(6)
1738(1) 2187(1) 4014(2) 3224(4) 1340(2) 3784(3) 5030(3) 6538(3) 6762(3) 5499(3) 2593(3) 2543(3) 3160(4) 3780(4) 3812(5) 923(3) -244(3) -987(4) -553(4) 602(3) 3340(4) 1722(4) 238(3) 13585(5) 12418(4)
31(1) 36(1) 30(1) 54(1) 35(1) 29(1) 38(1) 42(1) 40(1) 37(1) 35(1) 44(1) 59(1) 64(1) 69(1) 31(1) 48(1) 57(1) 50(1)
42(1) 68(1) 58(1)
42(1) 55(3) 49(3)
Ueq) is defined as one-third of the trace of the orthogonalized
U, tensor. stirred for 3 h at room temperature and subsequently filtered from the not reacted lithium metal through a glass frit. THF is removed under vacuum and replaced by the equivalent amount of toluene. At -78 "C 10.7 mL of a 1 M solution of dimethylaluminum chloride in n-hexane (10.7 mmol) is added dropwise. The deep purple solution is warmed to room temperature overnight. The solution is filtered over Celite and separated from lithium chloride. Toluene is removed in vacuum, and the precipitate is washed twice with 10 mL of pentane. The product is recrystallized from an etherln-hexane solution. X-ray suitable single crystals were obtained as needles: mp 125 "C; yield 23.1 g (75%); IR(Nujo1)Y (cm-l) 1600 st, 1533 m, 1511 st, 1453 st, 1399 st, 1129 st, 1076 m, 1054 m, 1015 m, 972 st, 749 st, 697 st, 572 m; lH NMR (C&) 6 -0.32 (s, 6H, Me), 5.95 (ddd, 3&-[4]H = 7.0, 3JH-[6]H = 6.1, 4 & - [ 3 1 ~ = 1.3 Hz, 2H, [5lH), 6.28 (ddd, 3JH-[3]H = 8.5, 3&[5]H = 7.0, 4JH-[6]H = 1.7 Hz, 2H, [4lH), 7.39 (ddd, 3 J ~ - [ 4 1= ~ 8.5, 4JH-[5]H
= 1.3, 5 J ~ - r s l= ~ 1.0 Hz, 2H, [3lH), 7.61 (ddd, 3 J ~ - [ s l = ~ 6.1,
1.7, 6 J ~ - [ 3 1 ~= 1.0 Hz, 2H, [6lH); l3C NMR (CsD6) 6 -12.2 (s, Me), 116.4 (s, C[51), 130.6 (s, C[31), 132.8 (s, C[41), 144.6 (s, C[61), 186.5 (s, C[2]); MS(E1) mlz 288 (M+, 19%), 273 (M+ - Me, loo%), 258 (M+ - 2Me, 12%). Anal. Calcd (Found): C, 50.02 (49.28); H, 4.90 (4.76); N, 9.72 (10.04). 6 (MezGa@-Py)&). To a solution of 1.0 g (3.2 mmol) of AsPy3 in 100 mL of THF is added 50 mg (6.4 mmol) of freshly rolled lithium wire. The deep purple reaction mixture is stirred for 3 h a t room temperature and filtered from the remaining lithium metal. THF is removed under vacuum and replaced by the equivalent amount of toluene. At -78 "C a solution of 600 mg (3.2 mmol) of dimethylgallium chloride in 10 mL of n-hexane is added dropwise. The deep purple solution is warmed to room temperature overnight under stirring. Then the solution is filtered over Celite and separated 4 J ~ - [ 4 1 ~=
Organometallics, Vol. 14, No. 5, 1995 2429
Bis(2-pyridy1)phosphide.s and -arsenides Table 6. Atomic Coordinates ( x lo4) and Equivalent Isotropic Displacement Parameters (pm2 x 10-l)for 4 ~
X
P(1) NU) N(2) C(2) c(3) C(4) C(5) c(6) c(7) C(8) (C(10) ')'
C(11) C(12) a
2701(1) 2691(1) 2920(1) 1619(1) 3017(1) 3410(2) 3679(2) 3542(2) 3164(2) 1788(1) 1142(2) 294(2) 68(2) 751(2) 1642(2) 4389(2)
Y
2064(1) 4698(1) 5188(2) 2890(1) 4088(2) 4574(2) 6083(2) 7191(2) 6698(2) 1822(2) 387(2) 103(2) 1254(2) 2594(2) 6284(2) 4136(2)
2
9020(1) 7123(1) 8483(1) 7046(1) 9194(1) 10184(1) 10425(1) 9686(1) 8742(1) 7781(1) 7568(1) 6681(1) 5967(1) 6167(1) 6294(1) 6927(1)
UeqP 3U1) 24(1) 24(1) 26(U 331) 39(1) 37(1) 32(1) 25(U 30(1) 33(U 32(1) 29(1) 35(1) 35(1)
product is a black violet solid mp 65 "C; yield 0.70 g (66%); IR(Nujo1) Y (cm-') 1595 st, 1534 m, 1516 st, 1399 st, 1160 m, 1111st, 1071 m, 1053 m, 1010 m, 980 st, 749 st, 717 st, 690 m, 580 m; 'H NMR ( c a s ) 6 -0.03 (S,6H, Me), 5.98 (dd, 3 J ~ - r 4 1 ~ = 7.0, 3 J ~ - p 5 1 ~ = 5.5 Hz,2H, [5lH), 6.34 (dd, 3 J ~ - r 3 1=~ 8.3, 3 J ~ - [ 5 1= ~ 7.0 HZ, 2H, [4lH), 7.40 (d, 3J~-[41~ = 5.5 HZ, 2H, [6]H), 7.49 (d, 3 J ~ - r 5 1=~ 8.3 Hz, 2H, [3lH); 13C NMR (CsDs) 6 -10.1 (s, Me), 116.7 (s, C[51), 130.6 (s, C[31), 132.8 (s, C[41), 144.6 (s, C[6]), 185.7 (s, C[2]); MS(E1) mlz 330 (M+,26%), 315 (M+ - Me, loo%), 300 (M+ - 2Me, 25%). Anal. Calcd (Found): C, 43.56 (43.23); H, 4.26 (3.91); N, 8.47 (8.64). X-ray Measurements of 2-5. All data were collected a t low temperature using a n oil-coated shock-cooled crysta140on a Stoe-Siemens AED with MoKa (1 = 71.073 pm) radiation. The structures were solved by direct methods using SHELXS904' and refined with all data on F with a weighting scheme ( ~ I P ) g# ~ with P = (Ff+ e 1 1 3 using of w-l = u2 SHELXL-93.42 Refinement of the Flack x parametera3 [x = -0.09( 181, where x = 0 for the correct absolute structure and +1for the inverted structure] confirmed the absolute structure of 2. The twist disorder of the /%carbon atoms of the THF molecule around 01 was successfully defined to two positions using distance and ADP similarity restraints. The site occupation factor of the main component refined to 68%. Selected bond lengths and angles of 2-5 can be found in Table 1, relevant crystallographic data for 2-5 in Table 3, and fractional coordinates of 2-5 in Tables 4-7.
(e)+
U(eq)is defined as one-third of the trace of the orthogonalized
Ui tensor.
Table 7. Atomic Coordinates ( x 104) and Equivalent Isotropic Displacement Parameters (pm2 x 10-l) for 6 X .Y 2 U(euP 2264(1) 1924(1) 5952(1) 34U) Al(1) 2314(2) 4658(3) 7851(2) 27(1) 2076(6) 5178(7) 6496(4) 29(2) N(l) N(2) 3406(6) 2861(7) 7961(4) 2 4 1) C(1) 1981(7) 4113(8) 5789(5) 23(2) 1578(7) 4626(11) 4805(6) 38(2) c(2) 1301(7) 6121(11) 4580(6) 37(2) c(3) 1456(7) 7215(10) 5333(6) 35(2) c(4) 1835(7) 6725(9) 6258(6) 32(2) 7256(5) 22(2) 3246(7) 1759(8) c(6) 3929(7) 356(9) 7501(6) 33(2) c(7) 4761(7) 105(9) 8388(6) 32(2) 1304(9) C(9) c(8) 4967(7) 9069(5) 29(2) 2631(10) 8842(5) 30(2) C(10) 4285(8) 8665(6) 38(2) 3321(8) 6258(10) C(11) 4074(10) 8040(6) 36(2) C(12) 637(8) a U(eq) is defined as one-third of the trace of the orthogonalized UGtensor. ~~
As(1)
from lithium chloride. Toluene is removed in vacuum. The precipitate is washed twice with 5 mL of n-pentane. The
+
Acknowledgment. We thank the Deutsche Forschungsgemeinschafi and the Fonds der Chemischen Industrie for financial support. Supplementary Material Available: Tables of crystal data, fractional coordinates, and bond lengths and angles, fully labeled figures of 50% anisotropic displacement parameters of the structures 2-5, and tables of anisotropic displacement parameters and hydrogen atom coordinates of 2-5 (27 pages). Ordering information is given on any current masthead page. OM9500578 (41)Sheldrick, G. M. Acta Crystallogr. Sect. A 1990, 46, 467. (42)Sheldrick, G. M. SHELXL-93 program for crystal structure
refinement, 1993, Universitlt Gtittingen. (43)Flack, H. D. Acta Crystallogr. Sect. A 1983,39, 876.
