Preparation and Structure of Poly(gold)telluronium Salts

Preparation and Structure of Poly(gold)telluronium Salts Klaus A ngerm aier, H u b ert Schm idbaur* Anorganisch-chemisches Institut der Technischen Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany Z. Naturforsch. 51b, 879-882 (1996), received December 22, 1995 Telluronium Complexes, Gold(I) Complexes, Tri- and Tetra(gold)telluronium Salts, Auriophilicity, Crystal Structure Tris[(triphenylphosphine)gold(I)]telluronium tetrafluoroborate (1) was prepared from the corresponding oxonium salt and bis(/-butyldimethylsilyl)tellurium in dichloromethane at -7 8 °C. The product forms yellow crystals, thermally stable to 125 °C. It was identified by standard analytical and spectroscopic techniques, including a single crystal X-ray diffraction study. In the crystal lattice, the cations form tellurium-capped triangles of gold, which are associated into dimers through short intermolecular A u -A u contacts, resembling those in the corresponding sulfur and selenium compounds. - The reaction of (r-BuMe2Si)2Te with four equivalents of [(Ph3P)Au]BF4 in tetrahydrofuran at -7 8 °C gives a tetranuclear com­ pound, {[(Ph3P)Au]4Te}2+ 2 BF4- (2) which differs from 1 in its analytical and spectroscopic data. Its structure could not be determined, but it is assumed that the dications have a square pyramidal geometry.

Introduction G old has a very special affinity to tellurium . In the w orld of m inerals, tellurium is the only m etal­ loid to form binary com pounds with gold [1], Bi­ nary anionic species have recently been p repared in a variety of stoichiom etries and structures, which show a unique relationship of the two ele­ m ents [2 -7 ]. G old o rganotellurides (RTeAu)„ and their com plexes w ere obtain ed only recently and ou r know ledge is lim ited to com pounds with very bulky substituents [8,9], The curren t in terest in the gold/tellurium system arises from a relevance of pertin en t research for sem iconductor technology, m aterial science, and pharm acology. This resem bles the situation with the analogous selenium / and sulfur/gold systems, for which extensive investigations w ere initiated at a m uch earlier stage. C om plex units L A u + (w ith L a stan d ard electron do n o r ligand) are know n to aggregate at sulfide or selen ide centers (E 2~) to give m ono-, di-, tri-, and finally tetran u clear coordination com pounds of the type ([L A u)„E ](,J_2)+ [10-12]. These units can be fu rth er aggregated into dim ers or polym ers through A u - A u con tacts (auriophilicity [13]). For E = Te only very few exam ples of this series have

* Reprint requests to Prof. Dr. H. Schmidbaur. 0932-0776/96/0600-0879 $06.00

been confirm ed [8,9], and we have th erefo re b e­ com e engaged in a study orien ted tow ards the syn­ thesis of the species with n - 3, 4 which are most prom inent for E = S, Se [10-12].

Results The preparative m ethods providing access to poly(gold)telluronium salts can be ad o p ted from previous studies with the corresponding sulfonium and selenonium salts. The key reaction for the trinuclear com pound is the trea tm e n t of the oxonium salt with a disilyl chalcogenide (R 3Si)2E in dichlo­ rom ethane at - 7 8 °C. W hile the trim eth yh i\y\ com pounds proved most useful in the sulfur and selenium series, the m ore stable t-b u tyld im eth yl silyl hom ologues offered dis­ tinct advantages in the tellurium case. For L = P h3P the isolated yield of p roduct 1 was 33% . W ith L = M e3P only decom position products w ere ob­ tained. {(Ph3P)Au]30}+ BF4- + (f-BuMe2Si)2Te — (r-BuMe2Si)20 + {[(Ph,P)Au],Te}+ BF4~

(1)

1 C om pound 1 form s yellow crystals, m.p. 125 — 127 °C with decom position, soluble in chloroform and dichlorom ethane. In the Fast A tom B o m bard­ m ent mass spectrum (nitrobenzyl alcohol m atrix) the mass of the cation is observed as the parent

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K. A ngerm aier-H . Schmidbaur • Preparation and Structure of Poly(gold)telluronium Salts

Table I. Crystal and structure solution data for com­ pound 1. Empirical formula Formula weight Crystal system Space group (No.) «[A] MA] c[A] a ß

y „

V [A3] 6> ca lc [gem 3] z F(000) [e] /((Mo-K„) [enr'] Cryst. dim. [ram] T[°C] Diffractometer Scan h k l Range Measured reflections Unique reflections Observed reflections F0 Refined parameters H-Atoms (found/calc.) Absorption corr.: Tx m in '/ Tx m a x R* R w„

Weighting scheme*** (?fin(max/min) [eA-3]

* R =

Cs4H4sAU',BF4 P,Tex0.5 C i H , „ 0 1629.18 triclinic Pi (No.2) 15.204(2) 17.877(2) 22.862(3) 89.23(1) 72.07(1) 69.91(1) 5522.7 1.960 4 3060 8 6 .0 0

0.25 / 0.40 / 0.45 -62 Enraf Nonius C A D 4 a>

+18/ ±2 2 / ±28 21512 19830 17006 4 cj(F0) 592 0 / 50 empirical 0.3781 / 0.9997 0.0441 0.0474 /= 1.0000 / k = 0.000619 + 1.80/ - 1.72

Z( I I F 0 I - I F CI I ) / Z I F 0 I;

** Rw = [2w( IF01—IFcI)2/ZwF02]1,2, *** w = l/a2(F0)+k(F0)2.

peak at m /z - 1508. The 31P{'H ) N M R spectrum of C D 2C12 solutions shows only one resonance at d = 37.9 ppm. T he 'H and 13C{1H} spectra contain the usual phenyl m ultiplet and the stan d ard set of four types of rings carbon atom s, respectively. Single crystals of com pound 1 o b tain ed from C H 2C12/(C 2H 5)20 contain half a m olecule of crys­

tal diethyl eth er per form ula unit. The crystals are triclinic, space group P i , with Z = 4 form ula units in the unit cell (Table I). The structure was refined from 19830 unique reflections m easured at -6 2 °C to R - 0.044 ( R w = 0.047). The asym etric unit con­ tains two independent cations with the gold atom s A u l- A u 3 at Tel and A u 4 -A u 6 at Te2, respec­ tively, with very similar dim ensions (Fig. 1, Table II). Each of these units is associated into centrosym m etrical dim ers through short intercationic contacts. The inversion centers are centroids of the gold rectangles generated in the dim erization process (Fig. 2). The anions and the diethyl eth e r molecules have no close contacts with the dications. The A u - T e - A u angles in the T eA u3 pyram ids are all much sm aller than 90°, with individual val­ ues betw een 72.6(1) and 84.7(1)°. A s a conse­ quence of these small angles, the A u - A u distances in the cation m onom ers are in the range from 3.074(1) to 3.515(1) Ä and can all be regarded as bonding contacts (auriophilicity, [13]). The intercationic distances ( A u l- A u 2 ' and A u 4 -A u 6 ') are also in the sam e range, indicating significant m etal-m etal interactions betw een th e two m ono­ m er com ponents. It should be no ted th at the intercationic A u -A u distances can be even sm aller than the intracationic distances: A u l- A u 2 ' is the shortest of all A u -A u contacts. The A u -T e distances in 1 are all close to 2.60 A , in good agreem ent with reference d ata (see ref­ erences in the Introduction). The geom etry of the rem ainder of the m olecules has no unusual fea­ tures. D etails have been deposited. T reatm ent of (f-BuM e2Si)2Te w ith fo u r equiva­ lents of [(Ph3P )A u]+ BF4~ in te trah y d ro fu ran at

Fig. 1. Molecular structure of the two crystallographically independent monomeric units (A. B) in the lattice of [(Ph3P)Au]3Te+ BF4~, 1, with atomic numbering. For distances and angles see Table II.

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K. A ng erm aier-H . Schmidbaur ■Preparation and Structure of Poly(gold)telluronium Salts Table II. Selected atomic distances [A] and bond angles [°] in the structure of com pound 1. (See Figures 1 and 2; standard deviations in parantheses). Aul - Au2 Au2 - Au3 Aul - Au3 A u l -Tel Au2-Tel Au3-Tel Aul - Au2'

3.515(1) 3.128(1) 3.115(1) 2.609(1) 2.610(1) 2.569(1) 3.040(1)

Au4-Au5 Au5 - A u 6 A u 6 - Au4 Au4-Te2 Au5-Te2 Au6-Te2 Au4-Au6 '

3.074(1) 3.3150(1) 3.304(1) 2.614(1) 2.259(1) 2.261(1) 3.308(1)

Aul -Tel - Au2 Au2-Tel - Au3 Au3-Tel - Aul

84.7(1) 74.3(1) 74.0(1)

Au4-Te2-Au5 A u 5 - Te2-Au 6 Au6-Te2-Au4

72.6(1) 74.9(1) 78.6(1)

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m ula (2), and th erefo re there is good reason to assum e th at the p roduct of reaction (2) is the tetraflu o ro b o rate salt of the tetran u clear telluronium dication (2). The analogous oxygen [14] and sulfur com ­ pounds [15,16] have recently been prepared. The form er has a standard te tra h ed ral structure, but the latter was found to have the dications in a nonclassical square pyram idal configuration. T here is an analogy for this non-conform al b e ­ haviour in the pnicogen series, w here the tetra(gold)am m onium cations are tetrah ed ral, while tetra(gold)phosphonium and -arsonium cations are square pyram idal [16,17]. Single crystals of com pound 2 could not be o b ­ tained, and experim ents with o th er phosphine li­ gands (L = PPh2Me, PM e3) did n o t give stable, crystalline products. H ence structural assignm ents for com pound 2 can only be tentative. From the analogies in the poly(gold) chalcogen and pnico­ gen series, it can be concluded, how ever, th at the tellurium com pound also has a square pyram idal structure, in which a tellurium atom is capping a square of gold atoms. E xperim ental

Fig. 2. Dimer of cation A (Figure 1) in the lattice of com­ pound 1. The two monomeric units are related by a cen­ ter of inversion. (The dimer of cation B is analogous.)

- 7 8 °C afforded a yellow crystalline product (2) in good yield (54% ): 4 [(Ph,P)Au]BF4 + (r-BuMe2Si)?Te+2 thf 2r-BuMe?SiF + 2 (thf)BF, + {[(Ph,P)Au]4Te}2+ (BF4~), (2) 2

The com pound decom poses at 1 0 3-104 °C and is soluble in di- and trichlorom ethane. The Field D esorption mass spectrum shows the cation with m /z = 1504 as the p a re n t peak, which can be as­ signed to the trin u clear cation as a stable frag­ m ent. In the 31P{1H} N M R spectrum of CDC13 so­ lutions only one sharp signal is observed, with a chem ical shift d = 39.2 ppm , distinctly different from th a t of com pound 1 (6 = 37.9 ppm ). The 'H N M R spectrum has a phenyl m ultiplet with a spe­ cific fine stru ctu re not identical with th at of 1. The elem ental analysis d ata are in good agreem ent with the values calculated for the p roposed fo r­

G en eral : All experim ents w ere carried out ro u ­ tinely u nder an atm osphere of dry nitrogen. Solvents were purified and satu rated with n itro ­ gen. G lassw are was oven-dried and filled with ni­ trogen. {[(Ph3P)A u]30 } + B F4- [18], [(Ph3P)A u]+ BF4"[19] and [r-BuM e2Si)2Te [20] w ere prep ared following literature m ethods. N M R spectra: Jeol X L 400. M ass spectra: V arian M A T 315. Tris[ (trip h en ylp h o sp h in e)g o ld (I) jtellu ro n iu m (+1) te tr a flu o r o b o r a te (-l) 1

To a solution of the oxonium salt (0.25 g, 0.17 m mol) in dichlorom ethane (20 m L) was added a solution of (r-BuM e2)2Te (0.12 g, 0.33 m m ol) in tetrahydrofuran (10 m L) at - 7 8 °C. A fter stirring for 60 min, the product was precipitated by careful addition of p entane (15 m L). The precipitate was recrystallized from dichlorom ethane/diethyl ether, yield 0.09 g (33% ), yellow crystals, dec. tem p. 125-127 °C. 'H N M R (CDC13, - 6 0 °C):