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Poly[(tri-'butyl-phosphine)gold(I)]ammonhim Tetrafluoroborates and Bis(tri-'butyI-phosphine)gold(I) Tetrafluoroborate Alexander Sladek, H ubert Schmidbaur* Anorganisch-Chemisches Institut der Technischen Universität München, Lichtenbergstraße 4, D-85747 Garching Z. Naturforsch. 50b, 859-863 (1995); received November 11, 1994 (Phosphine)gold(I) Complexes, [(Phosphine)gold(I)]ammonium Cations, Auriophilicity, G o ld -G o ld Contacts The reaction of tris[(tri-'butyl-phosphine)gold(I)]oxonium tetrafluoroborate with close to stoichiometric quantities of ammonia in dichloromethane at -7 8 °C affords tetrakis[(tri'butyl-phosphine)gold(I)]ammonium tetrafluoroborate, the structure of which has been determined by single crystal X-ray diffraction. The cation features a strongly distorted NAu4 tetrahedron with four short and two longer A u -A u edges. - With a large excess of ammonia, only partially aurated ammonium salts are formed, as suggested by detailed NMR spectro scopic and mass spectrometric studies. These partially aurated intermediates have not been isolated. Slow decomposition processes in these solutions lead to the precipitation of bis(tri'butyl-phosphine)gold(I) tetrafluoroborate. The structure of the bis(chloroform) solvate has also been determined. The crystals contain two independent C3-symmetrical cations with similar structures. Gold clusters with interstitial atoms of the main group metalloids have attracted considerable in terest in recent years owing to their unusual struc ture and bonding situation [1-3]. Surprisingly, the non-classical structures appear to be caused by significant A u -A u interactions between the seem ingly closed-shell metal centers. Pertinent phe nomena are particularly striking in clusters with hypercoordinate interstitial atoms [4-8], but even species which feature standard coordination num bers for the metalloid atoms often show struc tural anomalies. A n example in case is the stereochemistry of tetrakis[(phosphine)gold(I)]<7mA770/m/m cations of the general formula [(R3P)Au]4N+. The first rep resentative of this series has been discovered by Nesmeyanov et al. for R = Ph [9], For the BF4 salt a crystal structure determ ination [10] has shown a highly irregular structure with strong deviations of the param eters from the tetrahedral standard. Later work by Strähle et al. on the PF^ salt has also confirmed a distorted structure, but with dif ferent details in the param eters [11], Finally, for the fluoride salt an interesting C3-symmetrical trigonal pyramidal structure of the cation was * Reprint requests to Prof. Dr. H. Schmidbaur. 0932-0776/95/0600-0859 $06.00 found, with three gold atoms at the corners of a small base triangle and the fourth gold atom set apart in the axial position [12]. In the corresponding phosphonium system no salt with a cation of the stoichiometry [(Ph3P)Au]4P+ has been isolated, and only hyper coordinate species with more than four gold atoms at the central phosphorus atom have been ob served for R = Ph [13]. It was only with the bulky phosphine 'Bu3P that a salt [(fBu3P)Au]4P+BF4 became available, and for this a strongly distorted tetrahedral structure was again detected [14]. This finding was at variance with the results of theoreti cal studies [13-16], which have predicted cations of this type to be square pyramidal. Such a non-classical square-pyramidal structure had indeed been confirmed [17] for the corre sponding arsonium salt with the cation [(Ph3P)Au]4As+. These experimental data were the starting point - and an im portant backing for the theoretical calculations. No analogous anti mony or bismuth compounds are known, but an isoelectronic dication of the type [(R3P)Au]4S2+ has meanwhile been obtained and fully charac terized [3, 18], At this state of affairs it was felt that the struc ture and properties of the ammonium system with the bulky (rBu3P) ligand should also be investi- © 1995 Verlag der Zeitschrift für Naturforschung. All rights reserved. Unauthenticated Download Date | 6/18/17 2:20 AM 860 A. S ladek-H . Schmidbaur • Poly[(tri-'butyl-phosphine)gold(I)]ammonium Tetrafluoroborates gated in order to further delineate the structural preferences of tetra(aurated) nitrogen. In this paper we report the results on metallo complexes of ammonia with ('Bu3P)Au+ ligands. Results and Discussion Tris[(phosphine)gold(I)]oxonium salts are ex cellent aurating agents for ammonia and amines [9-12, 19-21]. The recently prepared fully 'butylsubstituted compound has now been chosen for the treatm ent of ammonia in varying stoichiomet ric ratios. With a large excess of ammonia present (100:1), solutions in dichloromethane are ob tained, which exhibit a pro m in en t31P NMR singlet signal at (3 = 86.7 ppm, accompanied by a minor one at d = 87.7 ppm. Mass spectrometric studies (FAB) of the residue remaining after evaporation of the solvent give a parent peak at m/z = 814.5, which can be assigned to the [('Bu3P)Au]2NH 2 cation. The compound could not be purified by crystallization. With a reduced excess of ammonia (70:1), the solutions showed new 31P NM R signals at d = 85.4 and d = 84.1 ppm, the latter appearing as a 1:1:1 triplet with /(P N ) = 12.0 Hz. A signal at <3 = 86.7 ppm is present in low intensity. The mass spectrum (FAB) of this mixture of products has m/z = 1214 as the parent peak corresponding to the cation [('Bu3P)Au]3N H +, accompanied still by m/z = 814.5 (above). With near-stoichiometric quantities of ammonia and at very low tem perature (-7 8 °C) in dichloro m ethane the fully aurated ammonium cation is generated. The tetrafluoroborate salt can be pre cipitated with pentane and recrystallized from dichlorom ethane/diethylether at -3 0 °C. The prod uct is obtained as a colorless, polycrystalline material in 60% yield. The vacuum-dried samples gave satisfactory elemental analyses. Single crys tals of the bissolvate can be grown from chloro form, decomp. temp. 115 °C. Solutions of this com pound in dichlorom ethane show the 31P{1H} NMR singlet signal at d = 89.9 ppm, a ‘H doublet signal at (3 = 1.52 ppm [./(PH) = 13.2 Hz], and two 13C doublet signals at d = 32.4 and 39.7 ppm with J 2.7 and 22.1 Hz, respectively ('H -decoupled). In the mass spectrum only the tris- and bis-aurated cations have been detected (m/z = 1212.4 and 814.9, respectively). Crystals of the bis-chloroform solvate are orthorhombic, space group Pbca (No. 61), with Z = 8 formula units in the unit cell. The lattice is com posed of independent tetrakis[(phosphine)gold]ammonium cations, tetrafluoroborate anions, and solvent molecules. The cation has no crystallographically imposed symmetry. Its core is an irreg ular pyramid of four gold atoms with an interstitial nitrogen atom and four peripheral phosphorus atoms. All four N - A u - P axes are close to linear [176.8(6)-178.7(5)°], and the four phosphine “umbrellas” have standard dimensions (Fig. 1). The most intriguing feature of the cation struc ture is the distortion of the NAu4 core which devi ates very strongly from the structure of a centered regular tetrahedron. The A u - N - A u angles range from the significantly subtetrahedral value of 104.2(9)° for A u l - N - A u 2 to a value of as much as 125(1)° for A u 3 -N -A u 4 . Three other of the six angles are found at 105.1(8), 105.7(7) and 105.8(9)°, and only one is 109.5(7)°. These angles are associated with A u -A u distances ranging be tween 3.268(2) and 3.658(2) A for the six edges of the “tetrahedron” . This virtually random struc tural irregularity is not caused by crystal packing, since the approach of neither the counter ions, nor of the solvent molecules is sufficiently close. It should also be noted that intram olecular repulsion Fig. 1. Structure of the cation in the crystal of [ ('B u 3P ) A u ] 4N +B F j - 2 C H C 13 with atomic numbering (SCHAKAL). The cation has no crystallographic symmetry. Unauthenticated Download Date | 6/18/17 2:20 AM 861 A. S lad ek -H . Schmidbaur • Poly[(tri-'butyl-phosphine)gold(I)]ammonium Tetrafluoroborates of the bulky phosphines should rather favour a symmetrical ligand positioning at the surface of the cation. It therefore appears that the energy profile of the distortion of the NAu4 tetrahedron is rather flat owing to the efficient compensation of the en ergy loss associated with the bending of N -A u bonds away from vertices of an ideal tetrahedron by the gain in energy originating from peripheral A u -A u approach. It has been pointed out pre viously [14, 17] that for the sum of standard cova lent radii for N and Au, the edges of a regular NA u4 tetrahedron are obtained too long for effi cient A u -A u interactions as observed in non strained (unsupported) systems (3.01 ± 0.15 A). In order to gain A u -A u bond energy the polyhe dron has to undergo al least some distortion which allows intram olecular A u -A u approaches. This idea is supported by a comparison of the new data with literature values for hom olo gous compounds of the type [(R3P)Au]4N+X “, and analogous organoammonium compounds [(R3P)A u]3N R +X - [22]: While in the latter small A u -N -A u angles and concomitantly short A u -A u distances have been observed for the NA u3 pyramids in all cases, the NAu4 tetrahedra of the former are always distorted with both small and large A u - N - A u angles and short and long A u -A u distances. This distortion is even more drastic in the phosphonium case with 'Bu3P ligands [14], where the longer A u -P distances allow for more space of the peripheral 'Bu groups to move together following the A u -A u attraction. On the basis of the new data we predict an even more severe distortion of [(R3P)Au]4N + cations for small groups R. Unfortunately, the structure of the R = Me case has not yet been determined. The species has been detected by mass spectrometry and other spectroscopic and analytical techniques [22], but no salts could be crystallized. 97.4 ppm (in CDC13). Its crystallization is not nec essarily accompanied by formation of elem ental gold, which suggests that high-nuclearity gold clus ters containing interstitial nitrogen atoms are also formed in the early stages of decomposition. The 31P NMR spectra of the solutions show several peaks other than at d = 97.4 ppm, which have not yet been assigned. The salt in question can also be obtained in a metathesis reaction of the chloride salt [23] with AgBF4 in ethanol (Exp. Part). The product is identical with the decomposition prod uct of the poly(gold)ammonium salts. Single crystals of a bis-chloroform solvate are obtained from chloroform/diethylether-mixed sol vents. These crystals are trigonal, space group R3, with six stoichiometric units in the unit cell. The lattice is composed of two crystallographically in dependent cations (each with a crystallographic threefold axis), two tetrafluoroborate anions and two chloroform molecules (all with threefold sym metry), none of which shows subnormal intermolecular contacts. The two independent cations have very similar dimensions and conformations, which furtherm ore are in excellent agreem ent with the data for the same cation in the (solvent-free) chloride salt [23]. This result is suggesting that the structure shown in Fig. 2 is representing a configuration which is largely insensitive to the external field of anions or solvent molecules in the crystal. The conform a tion as viewed down the P - A u - P axis is shown in Fig. 3. C H a ^ C21b Au1 /ÄC21 P2 Bis(tri-'butyl-phosphine)gold(I) tetrafluoroborate If any of the poly[(phosphine)gold]ammonium salts are left in solution for a prolonged time at ambient tem perature, colorless crystals of ['Bu3P]2Au+BF4 are formed, which appear to be the primary product of decomposition. The com pound gives satisfactory elemental analyses and is identified also by its 31P NM R singlet signal at d = C21a Fig. 2. Structure of the cation in the crystal of [(fBu3P)2Au]+BF 4 -2CHC13 with atomic numbering (ORTEP). The cation has a crystallographic threefold axis. Unauthenticated Download Date | 6/18/17 2:20 AM 862 A. S ladek-H . Schmidbaur • Poly[(tri-fbutyl-phosphine)gold(I)]ammonium Tetrafluoroborates Glassware was oven-dried and filled with nitrogen. [('Bu3P)Au]30 +BF4 and ('Bu3P)2Au+Cl~ were pre pared according to literature m ethods [23, 24], NMR: Jeol GX 400. - MS: MAT 311 (FAB). Tetrakisf (tri-'butylphosphine)gold (I) ] ammonium tetrafluoroborate 1 Fig. 3. View down the threefold axis in the cation shown in Fig. 2 (SCHAKAL). Experim ental Part All experiments were carried out under dry, puri fied nitrogen. Samples and solutions were pro tected against direct incandescent light. Solvents were dried, distilled and saturated with nitrogen. Empirical formula Formula weight [g/mol] Crystal system Space group (No.) «[A] MA] c[A] a[°] [g Cm 3] Z F(000) [e] /<(M o-K „) [ c m '1] T [°C] h k l Range Measured reflections Unique reflections Observed reflections S e a le d F> Refined param eters Weighting param eters 1/k Weighting param eters a/b H Atoms (found/calcd) R/Rw wR2/Rbased o n f (O M IT4) {?fjn (max/min) [eA -3] A solution of [('Bu3P)Au]30 +BF4 (0.50 g. 0.38 mmol) in C H 2C12 is cooled to -7 0 °C and NH 3 (g) is very slowly condensed into this solution with vigorous stirring. The reaction mixture is con centrated in a vacuum and pentane (50 ml) is added. The white precipitate is crystallized from CH2C12/E t20 at -3 0 °C, yield 0.29 g, 60%. 3IP{'H} NMR (CDC13, 20 °C): d = 89.9 [s, PPh3], 'H NMR (CDC13, 20 °C): (3 = 1.52 [d, 3/ Hp = 13.2 Hz, CH3], - 13C{1H} NM R (CDC13, 20 °C): (3 = 32.4 [d, 2JCP = 2.8 Hz, C H 3]; Ö = 39.7 [d, 7 CP = 22.1 Hz, CP]. - MS (FAB pos.): m/z (% ) = 1213.4 (15.80) [(M -'B u 3PAu)+ + 1]; 814.9 (77.95) [(M -2 rBu3PAu)+ + 1]. C48H W8A u4BF4NP4 (1697.97) Calcd Found C 33.95 C 33.42 1 2 C4gHiosAu4BF4NP4 •2 CHC13 1936.64 orthorhom bic Pbca (61) 19.120(2) 20.067(3) 38.361(6) 90 90 90 1.748 C24H S4AuBF4P2 •2 CHCI3 927.13 trigonal R3 (146) 11.308(1) 11.308(1) 52.560(1) 90 90 120 1.587 8 7488 82.90 -6 2 + 23/+20/+46 14832 10004 5422 0.1040 4cr(F) 311 1.00/0.001088 0/110 0.0913/0.0994 + 2.103/-2.236 H 6.41% , H 6.28% . Table I. Crystallographic data for the compounds 1 and 2. 6 2784 43.23 -6 2 -1 4 /+ 1 4 /1 6 9 6656 6205 6205 0.0161 4cr(F) 223 0.0660/17.7190 0/56 0.1096 (0.1080)/ 0.0348 (0.0352)* + 1.980/-1.780 * Refinement of the in verse model gave no sig nificant changes in the values of w R 2/R hased on 1 (OM IT 4). Unauthenticated Download Date | 6/18/17 2:20 AM A. S lad ek -H . Schmidbaur • Poly[(tri-'butyl-phosphine)gold(I)]ammonium Tetrafluoroborates Bis(tri-'butylphosphine)gold(I) tetrafluoroborate 2 A solution of ('Bu 3 P) 2 A u+Cl~ (3.00 g, 4.71 mmol) in ethanol ( 2 0 ml) is treated at room tem perature with one equivalent of AgBF 4 (0.92 g, 4.71 mmol) in ethanol (5 ml). A fter 30 min of stirring undis solved m aterial (AgCl) is filtered off. The solvent is removed in vacuo and the residue crystallized from C H 2 Cl2/ether at -3 0 °C, yield 3.24 g, 100%. - 3 1 P{rH} NM R (CDC13, 20 °C): Ö = 97.4 [s, PPh3], C24H54A uBF4P2 (688.43) Calcd Found D 41.87 C 41.22 H 7.91 H 7.75 Au 28.61%, Au 29.20%. Crystal structure determination Colorless crystals of compound 1 were obtained from CDCI 3 at room tem perature, and colorless crystals of com pound 2 by carefully adding E t20 to a CDC13 solution at -3 0 °C. The samples were m ounted in glass capillaries. Graphite-monochrom ated M o -K a radiation was used. The structures were solved by D irect M ethods (SHELXTLPLUS [25]). Only gold and phosphorus atoms of 1 were refined with anisotropic displacement param eters (SHELXTL-PLUS [25]), but all heavy [1] H. Schmidbaur, Gold Bull. 23, 11-20 (1990). [2] K. Angermaier, H. Schmidbaur, Inorg. Chem. 33, 2069-2070 (1994). [3] K. Angermaier, H. Schmidbaur, Chem. Ber. 127, 2387-2391 (1994). [4] F. Scherbaum, A. Grohm ann, B. Huber, C. Krüger, H. Schmidbaur, Angew. Chem. 100, 1602-1604 (1988); Angew. Chem., Ind. Ed. Engl. 27, 15441546 (1988). [5] F. Scherbaum, A. Grohm ann, G. Müller, H. Schmid baur, Angew. Chem. 101, 464-466 (1989); Angew. Chem., Int. Ed. Engl. 28, 463-465 (1989). [6] A. G rohm ann, J. Riede, H. Schmidbaur, Nature 345, 140-142 (1990). [7] H. Schmidbaur, G. Weidenhiller, O. Steigelmann, Angew. Chem. 103, 442-444 (1991); Angew. Chem., Int. Ed. Engl. 30, 433-435 (1991). [8] E. Zeller, H. Schmidbaur, J. Chem. Soc. Chem. Commun. 1992, 69-70. [9] E. G. Perevalova, E. I. Smyslova, V. P. Dyadchenko, K. I. Grandberg, A. N. Nesmeyanov, Izv. Akad. Nauk SSSR, Ser. Khim. 1980, 1455. [10] Yu. L. Slovokhotov, Yu. T. Struchkov, J. Organomet. Chem. 277, 143-146 (1984). [11] A. Brodbeck, J. Strähle, Acta Crystallogr. A 46, C232 (1990). [12] E. Zeller, H. Beruda, A. Kolb. P. Bissinger, J. Riede, H. Schmidbaur, N ature 352, 141-143 (1991). [13] H. Beruda, E. Zeller, H. Schmidbaur, Chem. Ber. 126, 2037-2040 (1993). [14] E. Zeller, H. Beruda, H. Schmidbaur, Chem. Ber. 126, 2033-2036 (1993). 863 atoms of 2 (SHELXTL-93 [26]). The solution of structure of 1 was complicated by disorder of the BF 4 group. Its position could be accounted for by using a split model of rigid groups with SOF = 0.5/ 0.5. Rigid group refinem ent was also used for three 'Bu groups at the structure of 1 and the BF 4 groups of 2. Hydrogen atoms, which could not be refined isotropically, were placed in calculated positions. A theoretical absorption correction was carried out for both structures (DIFABS [27]). The final cell param eters and specific data collec tion param eters are summarized in Table I. Details of the X-ray structure determ inations have been deposited at the Fachinformationszentrum Karls ruhe GmbH, D-76344 Eggenstein-Leopoldshafen, Germany, and may be obtained on quoting the names of the authors, the journal citation, and the CSD num ber 58911. Acknowledgements This work was supported by the Deutsche For schungsgemeinschaft, Fonds der Chemischen In dustrie, and - through the donation of chemi cals - by Degussa AG and H eraeus GmbH. The authors are grateful to Mr. J. Riede for carefully establishing the X-ray data sets. [15] J. Li. P. Pyykkö, Inorg. Chem. 32, 2630-2634 (1993). [16] J. K. Burdett, O. Eisenstein, W. B. Schweizer, Inorg. Chem. 33, 3261 -3268 (1994). [17] E. Zeller, H. Beruda, A. Kolb. P. Bissinger, J. Riede, H. Schmidbaur, N ature 352, 141-143 (1991). [18] F. Canales, M. C. Gimeno, P. G. Jones, A. Laguna, Angew. Chem. 106, 811-812 (1994); Angew. Chem., Int. Ed. Engl. 33, 769-770 (1994). [19] a) A. G rohm ann, J. Riede, H. Schmidbaur, J. Chem. Soc. Dalton Trans. 1991, 783-788; b) Yi Yang, V. Ramamoorthy, P. R. Sharp, Inorg. Chem. 32, 1946-1950 (1993). [20] H. Schmidbaur, A. Kolb, P. Bissinger, Inorg. Chem. 31, 4370-4375 (1992). [21] P. Lange, H. Beruda, W. Hiller, H. Schmidbaur, Z. Naturforsch. 49b, 781-787 (1994). [22] K. Angermaier, H. Schmidbaur, J. Chem. Soc. Dalton Trans. 1995, 559-564. [23] E. Zeller, A. Schier, H. Schmidbaur, Z. Naturforsch. 49b, 1243-1246 (1994). [24] A. N. Nesmeyanov, E. G. Perevalova, Y. T. Struch kov, M. Y. Antipin, K. I. Grandberg, V. P. Dyad chenko, J. Organomet. Chem. 201, 343-349 (1980). [25] SHELXTL-PLUS, Release 4.1, Siemens Analytical X-Ray Instruments, Inc., Madison (Wisconsin) (1990). [26] G. M. Sheldrick, Program for the Refinement of Structures, University of G öttingen (1993). [27] a) N. Walker, D. Stuart, A cta Crystallogr. A 39, 158 (1983); b) N. Walker, Program DIFABS, Version 9.0, BASF AG (1993). Unauthenticated Download Date | 6/18/17 2:20 AM