0 Copyright 1995 American Chemical Society
Volume 14, Number 71, November 1995
Communications Hypercoordinate Carbon in Protonated Tetraauriomethane Molecules H. Schmidbaur," F. P. Gabbai, A. Schier, and J. Riede Anorganisch-chemischesInstitut der Technischen Universitat Miinchen, Lichtenbergstrasse 4, 0-85747 Garching, Germany Received September 1, 1995@ Summary: The reaction of ([(Ph3p)Aul3O}+BF4- with Me3SiCHN2 gives dinitrogen and three crystalline products, two of which have been identified as (PhPCH[Au(PPhdl2)+BF4- (1) and (HC[Au(PPhdl4>+BF4- (2). In crystals of 2.4CH2C12, the cation has a square pyramidal structure with an apical hydrogen atom a t a central pentacoordinate carbon atom. The cations are associated to centrosymmetrical dimers with auriophilic contacts. Hypercoordinate carbon with independent substituents is still a rare phenomenon in the structural chemistry of molecular species.' Protonated methane, CH5+, is an example: Although a plethora of data are available from quantum mechanical calculations, and detailed spectroscopic evidence has been accumulated, the structure is still ~ n k n o w n .The ~ same is true for protonated alkanes [CH,Rs-,]+ or pentaalkylated carbocations CR5+.3 For this reason the discovery of relatedpentaaurated carbocations C(AuL)5+, with L = PR3, has attracted considerable i n t e r e ~ t . ~ Salts of these cations were obtained in all attempts t o generate neutral tetraauriomethane complexes C(AuL)4, except for cases with very Abstract published in Advance ACS Abstracts, October 15, 1995. (1)Olah, G. A.; F'rakash, G. K S.;Williams, R. E.; Field, L. D.; Wade, K. Hypercarbon Chemistry; Wiley-Interscience: New York, 1987. (2)(a) Olah, G. A. Acc. Chem. Res. 1987,20, 422-428. (b) Raghavachari, K.; Whiteside, R. A,; Pople, J. A,; Schleyer, P. v. R. J.Am. Chem. SOC.1981,103, 5649-5657. (c) Schreiner, P. R.; Kim, S. J.; Schaeffer, H. F. J. Chem. Phys. 1993,99,3716-3720. (3)Crabtree, R. H. Chem. Reu. 1996,95,987-1008. (4)Scherbaum, F.; Grohmann, A.; Muller, G.; Schmidbaur, H. Angew. Chem., Int. Ed. Engl. 1989,28,463-465. @
bulky ligands L.5 The experimental results indicated that the closed-shell (octet electron-precise at carbon) C(AuL)d molecules (A) (Chart 1) exhibit surprisingly strong donor properties (!) toward LAu+ electrophiles. The cations were shown to have standard trigonalbipyramidal structures (B,fluxional in solution) with pentacoordinate central carbon atoms.4 A satisfactory picture of the bonding of these novel species is based on extensive quantum-chemical calculations using ab initio and density functional methods and including correlation and relativistic effect^.^,^ We now report the isolation and structural characterization of a mixed species of the type HC(AuL)4+,C, in which both the proton and the (isolobal)6 M u + cations are present simultaneously at a pentacoordinate carbon center. Formally, such species represent the products of a protonation of tetraauriomethane molecules (A),indicating beyond any doubt that species C(AuL)4 are indeed strong Lewis bases! The reaction of (trimethylsilyl)diazomethanegwith tris[(triphenylphosphine)gold(I)loxonium tetrafluorobo(5) Schmidbaur, H.; Steigelmann, 0. Z.Naturforsch. 1992, 47b, 1721-1724. (6)(a) Gorling, A.;Rosch, N.; Ellis, D. E.; Schmidbaur, H. Inorg. Chem. 1991,30, 3986-3994. (b) Hlberlen, 0.D.; Schmidbaur, H.; Rosch, N. J.Am. Chem. SOC.1994,116,0241-8248. (7) (a) Pyykkii, P.; Zhao, Y.-F. Chem. Phys. Lett. 1991, 177, 103106. (b) Li, J.;Pyykko, P. Inorg. Chem. 1993,32, 2630-2634. (c) Burdett, J. K.; Eisenstein, 0.;Schweizer, W. B. Inorg. Chem. 1994, 33,3261-3268.(d) Calhorda, M. J.; Veiros, L. F. J . Organomet. Chem. 1994,478,37-44. (8)Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982,21,711-720. (9)(a) Seyferth, D.;Dow, A. W.; Menzel, H.; Flood, T. C. J. Am. Chem. Soc. 1968,90,1080-1082. (b) Barton, T.J.; Hoekman, S. K. Synth. React. Inorg. Metalorg. Chem. 1979,9,297-300.
0276-733319512314-4969$09.00/00 1995 American Chemical Society
Communications
4970 Organometallics, Vol. 14, No. 11, 1995
Chart 1 B =
([(Ph3P)Au],0}+BF4L
l+
N2
+ Me,SiCHN2 -
+ {P~,P-CH[AU(PP~,)]~)+BF~+ 1 { HC[Au(PPh3)14}+BF4-(1)
-4
1.
I
. Au
Au
L
L
Pill
W
W
Figure 1. Molecular structure of the cation PhsPCH[Au(PPh3)I2+in crystals of 1.CH2C12 (ORTEP, 50% probalility ellipsoids, phenyl H atoms omitted for clarity).ll Selected bond distances (A)and angles (deg): P(l)-C 1.736(4), Au(l)-C 2.085(5),Au(~)-C 2.066(5),Au(l)-P(3) 2.269(1), Au(2)-P(2) 2.266(1),Au(l)*.*Au(2) 2.998(1);Au(l)-C-Au(2) 92.5(2), P(l)-C-AU(l) 109.3(2), P(l)-C-Au(2) 115.3(3), C-Au(l)-P(3) 179.3(1),C-AU(~)-P(~) 175.5(1). ratelo in a tetrahydrofuranhexane mixed solvent (starting at -78 "C and reaching ambient temperature after 30 min) gives dinitrogen and a mixture of three products (1-3), which have been isolated as colorless to yellow crystalline solids by fractional crystallization in low yield (110%). The compounds decompose slowly in air but can be handled in an inert atmosphere a t ambient temperature. Compound 1has been identified by its analytical and spectroscopic data as {bis[(triphenylphosphine)auriolmethy1)triphenylphosphonium tetrafluoroborate, and the structure of a solvate 1*CH2C12was determined by single-crystal X-ray diffraction methods.ll The result is shown in Figure 1. The cation has standard phosphonium geometry but features the expected small AuC-Au angle at the methyl carbon atom typical of auriophilic bonding.l2 Product 1 probably was generated via loss of N2 and desilylatiodauration of Me3SiCHN2, leaving a [CH(AuL)2]+ species, which was trapped by a triphenylphosphine ligand (eq 1). Compound 2 has been shown to be tetrakis[(triphenylphosphine)gold(I)1methanium tetrafluoroborate.11J3 Among the spectroscopic data, the 1:4:6:4:1 quintet = 4.0 Hz)and couplings of the methyne hydrogen (JP,H (lO)Nesmeyanov, A. N.; Grandberg, K. I.; Dyadchenko, V. I.; Lemenovskii, D. A.; Perevalova, E. G. Izv. Akad. Nauk SSSR, Ser. Khim. 1974, 740-750.
2 carbon atoms ( J p , c = 65.0 Hz) in the NMR spectra (CDCl3 solutions, 25 "C) are particularly diagnostic, as is the parent peak of the complete cation in the mass spectrum (FAB: mlz = 1849). In particular, these spectra are important direct proof of the presence of a methyne hydrogen atom, which naturally is difficult to locate unambiguously in the single-crystal diffraction study. The crystal structure of a tetrakis(dich1oromethane) solvate 2.4CHzC12 has been determined." The individual cationic units feature a distorted square-pyrumidal structure with a central carbon atom and with the hydrogen atom as the apical ligand and four gold atoms as the base ligands (Figure 2). The C-Au-P coordination at the gold atoms is close to linear. The Au-C-Au angles (for neighboring gold atoms) all are very small and virtually equal [82.2(2)-82.8(2)"1, associated with short Au-Au edge contacts [from 2.787(1) to 2.817(1) A]. In the crystal, two of these {HC[Au(PPh3)14}+units are loosely associated into dimers through two interca(11)Experimental details: To a slurry of [(Ph3P)Au]30CBF4-(500 mg, 0.34 mmol)1° in THF (8 mL) cooled to -78 "C was added a 2 M The resulting mixture solution of Me3SiCHN2 (0.25 mL, 0.5 was allowed to reach 25 "C over a period of 30 min (nitrogen evolution) and was stirred for another 3 h during which the solution turned brown in color. The THF solution was decanted, leaving a THF-insoluble precipitate. The solution was evaporated in a vacuum, and the residue was redissolved in dichloromethane (3 mL) and layered with hexane (3 mL) to give 24 mg (colorless, 4% yield) of 1, mp 145 "C (dec, turns opaque) (satisfactory elemental analysis) MS (FAB): m/z 1193 [PhsPCH(AuPPh3)21+, 931 [CH(AuPPh&l+. 31P{1H}NMR (CDCl3, 25 "C): 6 (ppm) 40.8 (d, J p , p = 4.4 Hz, PAu), 38.2 (t, PC). 13C{lH) NMR (CDC13): 6 ( J p , c ) 133.8 (13.81, 131.7, 129.2 (10.91, 129.9 (54.3) for PhPAu; 132.7(9.2),129.2, 129.0 (ll.O), 128.2 (50) for PhPC and m , p , 0 , and ipso, respectively; PCH not detected. lH NMR (CDC13): 7.157.90, m, Ph; CH not detected. X-ray structure determinations: Suitable crystals of 1 and 2 were mounted in glass capillaries and used for measurements of urecise cell constants and intensitv data collection. Diffraction intenskies were corrected for decay [l,-i.5%; 2, -15.0%1, Lp, and absorption effects [+scans, TmiJTmax= 0.8295/0.9994 (l), 0.6337/0.9995(211. Crystal data of 1.CH2C12 [2*4CHzC121:{(CsH&PCH[AUP(C~H~)~I~+BF~-.CH~C~Z [{ CH[AUP(C~H~)~I~}+BF~-.~CHZC~~I, Mr = 1365.57 [2276.60], triclinic, space group P1, a = 13.170(1)[14.337(1)1 A, b = 13.994(1)[16.438(2)1A, c = 16.438(1)[18.774(2)1A, a = 114.67(1) [66.24(1)1", j3 = 104.55(1) [78.75(1)]", y = 95.11(1) [87.59(1)1", V = 2599.2 [3968.3] AZ, 2 = 2. With use of 11248 [15 3681 measured reflections (10 359 [14 2141 unique, 8961 [12 2781 "observed" with F, 2 4u(F,)) collected at -62 [-681"C with Mo Ka radiation on an Enraf Nonius CAD4 diffractometer, the structures were solved by direct methods (SHELXTL-P1usl7)and refined by full-matrix least-squares techniques (SHELXTL-Plus17)with anisotropic temperature factors for all non-hydrogen atoms except for the B, F, and solvent C and C1 atoms of compound 2. All hydrogen atoms were placed in idealized calculated positions and allowed to ride on their corresponding carbon atom with fixed isotropic contributions (U,adh)= 0.08 and 0.05 Az, respectively), except for the Au-C-H in the cation of 2, which was located and included with tixed coordinates and isotropic contibutions. Final R (R,) values: 0.0256 (0.0289) f0.0396 (0.0429)l for 613 [7981 refined parameters. (12) (a)Schmidbaur, H. Gold Bull. 1990,23,11-21. (b) Scherbaum, F.; Grohmann, A,; Huber, B.; Kriiger, C.; Schmidbaur, H. Angew. Chem., Znt. Ed. Engl. 1988,27, 1544-1546. (13)Experimental details: The THF-insoluble precipitate" was dissolved in dichloromethane (4 mL) and the solution layered with hexane (3 mL) to give a 60 mg crop of yellow crystals (6.5%yield), mp 150 "C (dec, turns gray) (satisfactory elemental analysis). MS (FAB): m/z 1849 [HC(AuPPh3)4]+,1587 {[HC(AuPPh3)41- PPh}+, 721 [Au(PPh&]+, 459 [AuPPh3]+.31P{1H}NMR (CDCl3,25 "C): 6 (ppm) 34.2, s. 13C{lH} NMR (CDC13): d ( J p , c ) 134.0 (d, 13.2, m ) , 131.3 (d, 51.5, ipso), 131.2 ( 8 , p ) , 129 (br, 0);88.5 (quint, 65.0, AmCH). 'H NMR (CDCld: 7.0-7.5 (m, Ph); 4.85 (quint, JP,H4.0, Au4CZ-Z). Crystal structure: see ref 11.
Communications
Figure 2. Molecular structure of the cation HC[Au(PPh3)34+in crystals of 2-4CH2C12(ORTEP,50%probability ellipsoids, phenyl H atoms omitted for clarity).’ Selected bond distances (A)and angles (deg): Au(l)-Au(2) 2.817(1), Au(l)***Au(3) 2.812(1),Au(2)***Au(4) 2.796(l), Au(3)*-Au(4) 2.787(1), Au(l)-C 2.13(1), Au(2)-C 2.132(7), Au(3)-C 2.126(7), Au(41-C 2.112(8), AU(l)-P(l) 2.282(3), Au(2)P(2) 2.275(2), Au(3)-P(3) 2.268(2), Au(4)-P(4) 2.275(2); Au(l)-C-Au(B) 82.8(3),Au(~)-C-AU(~)82.8(3), Au(1)C-Au(4) 129.0(4), Au(~)-C-AU(~) 145.0(4), Au(2)-CAu(4) 82.4(3), Au(~)-C-AU(~)82.2(2), C-Au( 1)-P( 1) 165.4(2),C-AU(~)-P(~) 175.0(2),C-Au(3)-P(3) 173.8(2), C-AU(~)-P(~)175.2(3).
Organometallics, VoZ. 14,No. 11, 1995 4971
ment with a symmetrical species of 4-fold symmetry and thus suggest a dissociation of the dimers into their components in chloroform solution at ambient temperature. It is plausible to assume that product 2 was also formed from the silyldiazomethane by loss of N2 and desilylation but with the CH unit ending up quadruply aurated. Compound 3 has not yet been identified, but from preliminary analytical and spectroscopic evidence it is expected to represent yet another methyne trapping product. Compound 2 is a unique case in which a methyne unit is bridging four independent (closed-shell)metal atoms which are neither part of a metal-metal-bonded cluster system, tied together by polydentate ligands, nor fixed at the surface of a lattice. Most surprisingly, the system (C)is not a strong acid. Although the deprotonated species would be expected to be a stable molecule with tetracoordinate carbon (A),the cation remains intact even in the presence of a strong base like dimethylaniline.14 The new species (C)thus is another striking example in organogold chemistry of nonclassical structure and bonding which requires sophisticated new theoretical approaches. Structural parallels have previously been found with an analogous aZkyZated cation15of the type {MeC[Au(PPh3)]4}+ and with a tetraaurated arylphosphonium dication16 of the type {o-T0lP[Au(PPh3)]4}~+, but only a preliminary description of their bonding has been advanced. Complementary experimental and computational studies therefore are in progress.
Acknowledgment. This work was supported by the Deutsche Forschungsgemeinschaft, by the Fonds der Chemischen Industrie, and-through the donation of chemicals-by Degussa AG and Heraeus GmbH. F.P.G. is grateful to the A. v. Humboldt Foundation for a research fellowship. Figure 3. Association of the cations of compound 2 in
crystals 204CH2C12. The components of the dimer are symmetry-related via a center of inversion. Intercationic contacts Au(l)***Au(2)’/Au(l)’***Au(2) = 3.367(1) A. For other details see Figure 2. tionic Au-Au contacts [3.367(1)A,equal by symmetry]. The monomers are related by a center of inversion (Figure 3). The mutual approach of the monomers clearly is the main reason for the distortion of the square pyramids, the fundamental structure of which is retained, however. The NMR datal3 (above) are in agree-
Supporting Information Available: Tables of crystallographic data, positional and thermal parameters, and interatomic distances and angles and ORTEP diagrams for 1 and 2 (15 pages). Ordering information is given on any current masthead page.
OM950687+ (14)Brachthauser, B. Dissertation, Techn. Univ. Munich, 1992. Bissinger, P.; Schmidbaur, H. 2.Nuturforsch. (15)Steigelmann, 0.; 1993,48b, 72-78. ( 16)Schmidbaur, H.; Zeller, E.; Weidenhiller, G.; Steigelmann, 0.; Beruda, H. Inorg. Chem. 1992,31,2370-2376. (17)Sheldrick, G.M. SHELXTLPLUS,Release 4.0 for Siemens R3 Crystallographic Research System. Siemens Analytical Instruments, Inc., Madison, WI, 1989.
