1,1,1,1 -Tetrakis[triorganylphosphineaurio(I)]ethanium(+) Tetrafluoroborates - Hypercoordinated Species Containing [H3C-C(AuL)4I+ Cations Oliver Steigeimann, Peter Bissinger, and Hubert Schmidbaur* Anorganisch-chemisches Institut der Technischen Universität München, Lichtenbergstraße 4, D-W-8046 Garching Z. Naturforsch. 48b, 72-78 (1993); received September 10, 1992 Auriophilicity, Gold(I) Phosphine Complexes, Ethane-tetraaurio(I) Compounds, X-Ray Hypercoordinate, tetraaurated carbon-complexes of the type [H 3C -C (A uP R 3)4]+BF4~, R = Ph (1), R = C6H u (2), (PR3)2 = l,2-C 6H4(CH 2CH 2PPh 2)2 (3) have been prepared by the reac­ tion of the appropriate (phosphane)gold(I) chlorides with l,l,l-tris(dimethoxyboryl)ethane H 3C -C [B(O M e)2]3 in the presence of CsF. The products have been characterized by standard analytical and spectroscopic methods, including single crystal X-ray analyses of 1 and 2. In each case the pentacoordinated carbon atoms have been located at the centre of a square pyr- amide built up by a methyl group at the apex and four gold atoms forming the base with short Au ••• Au distances of about 2.85 A, which strongly contribute to the formation and stability of these species. Introduction The special position of gold in the Periodic gation of complex units L -A u-X of phosphane Table is largely based on relativistic effects [1], gold compounds [3], but also to a clustering of which modify significantly the properties of the gold(I) atoms at or around a main group element valence electrons of Post-Lanthanide elements. like carbon, nitrogen, phosphorus, arsenic, oxy­ The relativistic contraction of the 6 s orbitals of the gen, sulfur, and selenium [4-10]. Apart from spe­ heavy elements reaches a pronounced local maxi­ cies with a more conventional stoichiometry mum for gold and leads to a break-up of the 5d 10 [(AuL)3E]+ (E = O [8], S [9a], Se [10a]), closed shell of electrons in the Au(I) oxidation [(AuL)4N]+ [5a-c,7], [(AuL)3NR]+ [5e-g], state. A wealth of evidence has been obtained from [(AuL)3PR ]+ [6], or C (A uL )4 [6c], novel cations structural and spectroscopic studies of both mono- [(AuL)4As]+ [7] with a nonclassical square-pyrami- and polynuclear gold(I) compounds for the exist­ dal structure and the unprecedented hypercoor­ ence of the resulting metal-metal bonding between dinated cations [(AuL) 5C]+ [4d], [(AuL)6C]2+ Au+ centers [2], Intra- and intermolecular metal- [4c, e-h], [(AuL) 5N]2+ [5d], and [(AuL) 5P]2+ [6 a] metal interactions give rise not only to the aggre­ have been discovered. r— — 2 + — _ n+ — L Au Au R 1 ..-A u L 1 ,,-A u L 1 LAu — X '' x LA u^ | "'^AuL | ^ * A u L LAu'"^ \^"'AuL Au Au LAu AuL L _ _ _ _ B: X = C, n = 1 E: X = C, n = 1 C: X = N, n = 2 F: X = P, n = 2 D: X = P, n = 2 * Reprint requests to Prof. Dr. H. Schmidbaur. While the number of homoleptic species A -D with the interstitial atom in the center of trigonal Verlag der Zeitschrift für Naturforschung, D-W-7400 Tübingen bipyramids or octahedra of gold atoms has been 0932-0776/93/0100-0072/$ 01.00/0 steadily increasing, only two examples are known Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung This work has been digitalized and published in 2013 by Verlag Zeitschrift in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der für Naturforschung in cooperation with the Max Planck Society for the Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Advancement of Science under a Creative Commons Attribution Creative Commons Namensnennung 4.0 Lizenz. 4.0 International License. O. Steigeimann et al. • Tetraaurio(I) Complexes 73 to date where the coordination sphere around the from the reaction of 1,1, 1-trichloromethane and hypercoordinate central atom contains also a non­ ClB(OM e)2 with lithium powder in tetrahydro- gold substituent (E,F): These two dications furan, as described by Matteson et al. [11], the [RP(AuL)4]2+ [6 b] (R = o-tolyl) and (dimeric) analogous reaction led to the title compounds. The [RC(AuL)4]+ [4 b] (R = oxazolinyl) feature square gold(I) chloride complexes of PPh3, P(C 6H ,,)3 and pyramidal structures with, respectively, phospho­ l,2-C6H 4(CH 2CH 2PPh 2)2 required, were readily rus or carbon at the center, the R substituent at the available via published methods [ 12, 13, 4 e]. apex, and the four gold atoms at the base of the Treatment of the individual (phosphine)gold(I) polyhedron, with short Au-- Au contacts, indica­ chloride with l,l,l-tris(dimethoxyboryl)ethane in tive of the origin of this unusual clustering of gold the presence of cesium fluoride in hexamethyl- in both cases. phosphoric triamide (HMPT) produced yellow We now report on simple compounds with solutions. After filtration and precipitation with five-coordinated carbon atoms in cationic pentane/benzene crystalline complexes CH 3-C [A u P R 3]4 units. [H3C -C (A u P P h 3)4]+BF4- (1), [H3C -C (A u P { C 6H u }3)4]+BF4- (2) and Results [H3C -C ({ A u P P h 2CH 2CH 2}2C 6H 4)2]+BF4- (3) In preceding work tetrakis(dimethoxyboryl)- were obtained. methane C[B(OMe )2]4 and bis(dimethoxyboryl)- The products 1, 2 (yellow) and 3 (colourless) are m ethane H 2C[B(OM e)2]2 were found to be excel­ airstable, hygroscopic substances, insoluble in lent starting materials for the synthesis of highly non-polar solvents like pentane, slightly soluble in aurated homoleptic carbon centered clusters [4 c, benzene and readily soluble in dichloromethane or d, e-h]. Thus, the reactions of C[B(OMe )2]4 with HMPT. The compounds decompose on melting. (triorganylphosphine)gold(I) chlorides LAuCl in Characterization is achieved by elemental analysis, the presence of CsF lead to the formation of hy­ mass spectrometry and NMR spectroscopy. The percoordinated hexakis(phosphineaurio(I))-meth- data are summarized in the Experimental Section. anium(2+) dications of the type [(AuL) 6C]2+. The The existence of the hypercoordinated species degree of auration could be reduced from six to [CH3-C(A uPR3)4]+ was first established by high- five and four by the use of gold chloride complexes resolution field desorption (FD) mass spectrosco­ with bulky phosphanes [6 c], py. In the mass spectral studies the parent peaks at When l,l,l-tris(dimethoxyboryl)ethane was m /z = 1864.7 (1), 1936.1 (2), and 1821.1 (3) can chosen as the precursor, which is readily obtained readily be assigned to the appropriate cations. CH + 4 RjPAuCI. + 4 CsF H3C -C[B (O M e)2]3 b f 4- - 4 CsCI, - 2 (MeO)jB R p ^ A u " - / \~ " A u . ‘ PR-i 3 Au Au / \ Ph2 RjP PR3 + 4 CsF PAuCI - 4 CsCI 1 : R = Ph - 2 (MeO)3B ocx.Ph, 2 : R = c—C6H„ b f 4~ 74 Q. Steigeimann et al. • Tetraaurio(I) Complexes Table I. {'H}3IP NMR chemical shifts 6 [ppm] for com­ are also in good agreement with that found for pounds R3PAuCl and [CH 3-C (A uP R 3)4]BF4. (H 3C)3C -A u P P h 3 (V HP = 6.5 Hz). In the {'H}13C NMR spectrum of p r 3 R3PAuC1 [CH3C(AuPR3)4]BF4 [H3C -C (A u P P h 3)4]BF4 the resonances of the PPh-, 33.4 32.1 phenyl carbon atoms show a pattern also common P(C6H n )3 54.9 49.5 for homoleptic carbon centered gold cluster '/2(Ph,PCH,CH,) 2C6H4 29.2 27.5 cations. The doublet for the ipso C atom is shifted downfield as compared to the corresponding reso­ nance in Ph 3PAuCl, whereas the other phenyl sig­ The {'H } 3IP-NMR spectra at room temperature nals are largely unchanged. The o- and w-carbon of compounds 1 -3 in dichloromethane-d 2 show atoms give rise to centered doublets caused by long one sharp singlet resonance in each case, which is range P-P ' coupling. The resonance of the termi­ not only indicative of a virtual fourfold symmetry nal H3C group appears as a singlet at Ö = 28.2 ppm. of the cations of 1 and 2, but also demonstrates the The signal of the interstitial carbon could not be equivalence of the ligand halves in the chelated detected, and partial enrichment with ,3C will cation of 3. When compared to the data of the cor­ probably be necessary for a direct observation of responding (phosphine)gold(I) chlorides, upfield the nucleus, a procedure already successfully ap­ shifts can be stated (Table I), as already reported plied for the [C(AuL)6]:+ species [4f], for the conversion of (phosphine)gold(I) com­ pounds to homoleptic hypercoordinated species Crystal Structure Determinations [(AuL)5C]+ [4d], [(AuL)6C]2+ [ 4 c , e-h]. The equi­ valence of the LAu units is further established by Because of strong crystal disorder in all samples the number and multiplicity of the signals in the ’H of 1 so far investigated, only the C -C (A u-P )4 NMR spectra. Besides the resonances of the (phos- skeleton could be determined for the cation in phine) ligands, symmetrical 1:4:6:4:1 quintets [H3C -C (A u P P h 3)4]BF4, which crystallizes in the could be observed for the methyl hydrogen atoms at triclinic space group P i with two stoichiometric ö = 3.55 (1), 3.22 (2) and 3.65 ppm (3) due to a VHP equivalents in the unit cell excluding any crystallo- coupling with the phosphorus atoms of the phos- graphical symmetry for the individual cation.