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Organometallics 1996, 14, 1297-1301
Synthesis of Coinage Metal Cation Adducts of Nb(C5H4SiMe3)2H(CO). X-ray Crystal Structure of [{Nb(C5H4SiMe3)2(CO))2@-H)2CulPF6 Antonio Antiiiolo,t Fernando Carrillo,?Bruno Chaudret,*>$ Mariano Fajardo,$ Santiago Garcia-Yuste,t Fernando J. Lahoz,ll Maurizio Lanfranchi,lJose A. Lbpez,” Antonio Otero,*>?and Maria Angela Pellinghellil Departamento de Quimica Inorganica, Orgcinica y Bioquimica, Facultad de Quimicas, Campus Universitario, Universidad de Castilla-La Mancha, 13071-Ciudad Real, Spain, Laboratoire de Chimie de Coordination d u CNRS, 205, route de Narbonne, 31077 Toulouse Cedex, France, Departamento de Quimica Inorganica, Campus Universitario, Universidad de Alcalci, 28871 -Alcala de Henares, Spain, Departamento de Quimica Inorganica, Instituto de Ciencia de Materiales de Aragbn, Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain, and Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universita degli Studi di Parma, Centro di Studio per la Strutturistica Diffractometrica del CNR, Viale delle Scienze 78, I-43100 Parma, Italy Received September 27, 1994@ The reactions of Nb(CJi!LSiMe3)2H(CO)(2) with [Cu(MeCN)dBF4, CuPPhsCWlPFs, AgBF4, AgPPh3CYTlPF6, and Au(THT)CWlPF6 lead to the new adducts [{Nb(CsH4SiMe3)2(CO)}2@-H)zMI+(M = Cu (3),Ag (4, 5), Au (6)), in which the coinage metal cation is only linked to the hydride of each niobium center, whereas the reaction with [Au(PPh3)1+ leads to [{N~(C~H~S~M~~)~(CO)}@-H)AU(PP~~)IPF~ (7). The crystal structure of 3 has been determined by X-ray diffraction methods. The crystals are monoclinic, s ace group P21/c, with 2 = 4 in a unit cell of dimensions a = 13.048(5) b = 12.490(4) c = 30.131(9) p = 94.52(2)”. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by blocked full-matrix least squares on the basis of 3001 observed reflections to R and R, values of 0.0460 and 0.0608, respectively.
1,
A,
Introduction Bis(cyclopentadieny1)niobium hydride derivatives have long been of interest for both their high reactivity and their spectroscopic pr0perties.l Thus, the NMR properties of CpaNbH3 were k n o m to be anomalous for a long time2 until they were recognized as due t o exchange coupling^.^ By varying the electronic density on the metal using trimethylsilyl substituents on the cyclopentadienyl ring, we were able to produce new compounds displaying large, temperature-dependent exchange coupling^.^ In the course of our studies on the origin of these couplings, we reacted a series of bis(cyclopentadieny1)niobium trihydride derivatives with coinage element cations, namely “Cut”, “Ag+”,5and “AU+”,~ with the purpose of inhibiting the in-plane deformation mode of the central Nb-H bonds. This vibration was first assumed to be at the origin of the Universidad de Castilla-La Mancha. Laboratoire de Chimie de Coordination du CNRS. 5 Universidad de Alcala. II Universidad de Zaragoza. Universita degli Studi di Parma. Abstract published in Advance ACS Abstracts, February 1, 1995. (1)(a) Tebbe, F. N.; Parshall, G. W. J . A m . Chem. SOC.1971, 93, 3793. (b) Klabunde, U.; Parshall, G. W. J.A m . Chem. SOC.1972,94, 9081. (c) Tebbe, F. N. J . Am. Chem. SOC.1973,95, 5412. (2) (a) Labinger, J. A. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. X., Eds.; Pergamon Press: Oxford, U.K., 1983; Vol. 3, p 707. (b) Curtis, M. D.; Bell, L. G.; Butler, W. Organometallics 1985, 4, 701. (3)Heinekey, D. M. J . A m . Chem. SOC.1991, 113, 6074. (4) Antifiolo, A,; Chaudret, B.; Commenges, G.; Fajardo, M.; Jalon, F.; Morris, R. H.; Otero, A.; Schweitzer, C. T. J . Chem. SOC.,Chem. Commun. 1988, 211. (5) Antifiolo, A,; Carrillo, F.; Fernandez-Baeza, J.;Otero, A.; Fajardo, M.; Chaudret, B. Inorg. Chem. 1992,31, 5156. +
@
A,
tunneling phenomenon responsible for the appearance of the exchange coupling^.^^^ However, instead of the expected inhibition, a strong increase of the couplings was observed in the case of the reaction with “AU+”.~ An alternative model t o explain these couplings was t o involve rotational tunneling of dihydrogen in a thermally accessible dihydrogen state.g In the case of the coinage element adducts of niobium trihydrides, such a proposal would imply that only one hydride would remain firmly bound to the coinage cation while the two other would form a dihydrogen molecule. In order to test this hypothesis, we describe in this paper the substitution of two hydrides by a molecule of carbon monoxide and the synthesis of new coinage element adducts as well as the crystal structure of the new copper adduct [(Nb(CsH~SiMe3)2(CO)}2@-H)zCulPFs. Adducts involving copper, silver, and gold with transition metal polyhydrides are known,1° and several examples where only one hydride links a coinage element t o a transition metal have been reported, for example in the adducts [(PPh3)3H2Ir@-H)MPR31+ (M = Ag, Au; ~~
~~~~~
(6) Antifiolo. A,: Carrillo. F.: Chaudret. B.: Faiardo. M.: FernandezBaeza, J.; Lanfranchi, M.f Limbach, H.-H.I Miurer, M’.; Otero, A,; Pellinghelli, M. A. Inorg. Chem. 1994, 33, 5163. (7) (a) Zilm, K. W.; Heinekey, D. M.; Millar, J . M.; Payne, N. G.; Demou, P. J . A m . Chem. SOC.1989, 111, 3088. (b) Zilm, K. W.; Heinekey, D. M.; Millar, J . M.; Payne, N. G.; Neshyba, S. P.; Duchamp, J. C.; Szczyrba, J . J . A m . Chem. SOC.1990, 112,92. ( 8 )Jones, D.; Labinger, J. A.; Weitekamp, D. P. J . A m . Chem. SOC. 1989, I l l , 3087. (9) Limbach, H.-H.; Maurer, M.; Scherer, G.; Chaudret, B. Angew. Chem.. Int. Ed. Engl. 1992, 31, 1369. (10)See for example: (a) Venanzi, L. M. Coord. Chem. Reu. 1982, 43.251. (b) Rhodes, F. L.: Huffman, J. C.; Caulton, K. G. Inorg. Chim. Acta 1992, 198, C39.
0276-733319512314-1297$09.00/0 0 1995 American Chemical Society
1298 Organometallics, Vol. 14, No. 3, 1995
Antifiolo et al.
R = Et, Ph).ll Bimetallic complexes involving a carbonylniobium complex such as Cp2(CO)Nb@-H)M(CO)x (M = Fe, x = 4;12M = Ni, x = 313)have also been reported.
Results and Discussion Preparation of the Adducts. The reaction of Nb(C5H4SiMe3hH3 (1)with 1 atm of CO in THF at 65 “C for 3 h yields the carbonyl complex Nb(CsH4SiMe3hH(CO) @).I4 2 was isolated and was reacted in situ with a variety of salts of coinage elements, namely [Cu(MeCN)41BF4,I5“cu(pPh~)PF6”prepared in situ by reacting Cu(PPh3)C116with TlPF6 in THF, AgBF4, “Ag(PPh3)PFs” prepared in situ by reacting Ag(PPh3)C117 with TlPF6, and “Au(L)PF6”prepared in situ by reacting Au(L)Cl (L = PPh3,’8 THTl’) with TlPF6. The reactions with the copper salts are rapid in THF at 0 “C and yield orange solutions from which, after workup and recrystallization from THFEt20, red crystals of [ { N ~ ( C ~ H ~ S ~ M ~ ~ ) ~ ( C O ) ~ ~ (3) @ -were H)~CUIPF~ Cor) obtained in ca. 90% yield. Interestingly, 3 is air stable Figure 1. View of the structure of the cationic complex 3 for several days in the solid state but decomposes slowly with the atomic labeling scheme. in solution even in the absence of air. Similarly, both silver complexes react rapidly with 2 in THF at 0 “C t o The lH NMR spectra of 3-7 all show a singlet near give after a similar procedure red microcrystalline 0.24 ppm for the SiMes group and several signals compounds identified as [{N~(C~H~S~M~~)Z(CO))Z~L-H)~between 5 and 6 ppm for the cyclopentadienyl protons. AgIX (X= BF4, 4; X = PF6, 5). The behavior of 4 and In particular, complexes 3 and 4,5 show four signals, 5 with air and in solution is similar to that of 3. The respectively, at 5.91, 5.68, 5.47, and 5.38 ppm and at two gold reagents react differently with 2. Hence, the 5.88, 5.59, 5.42, and 5.35 ppm. The two downfield reaction with “Au(THT)PFs”produces at 0 “C in THF signals are attributed to the protons in positions 3 and the trinuclear species [(N~(C~H~S~M~~)~(CO)}Z@-H)~AUI4 on the Cp ring, whereas the two upfield ones are PF6 (61, whereas that with “Au(PPh3)PFs”under the attributed to protons 2 and 5. The observation of four same conditions yields [{Nb(CsH4SiMe3)dCO)}@-H)signals for each Cp ring indicates a lack of symmetry (AuPPhdlPFs (7). 6 and 7 are again air stable in the for the structure. In the gold complexes, protons 2 and solid state. 5 resonate at the same frequency, respectively 5.36 (6) Spectroscopic Characterization of Complexes and 5.46 (7) ppm. The bridging hydride is observed at 3-7. Complexes 3-7 show a YCO absorption near 1900 6 -7.67 in 3, -7.10 in 4 and 5, -3.75 in 6, and -5.62 in cm-l. Using PF6- as counteranion, the exact values are 7. In addition 4 and 5 show a coupling to silver (JH-A~ 1900 cm-l for 3,1917 cm-l for 5, 1932 cm-l for 6, and = 101 Hz: the signals are broad; therefore, the two 1936 cm-l for 7, whereas this band is found at 1910 different couplings to lo7Agand lo9Agare not resolved) cm-l for 2. This variation is at first sight surprising, and 7 shows a coupling to phosphorus (JH-P= 77.1 Hz). since the electrophilicity is expected to decrease from It is difficult to deduce any structural information from Cu+ to Au+, but using the CO stretching frequency as these chemical shift variations except perhaps that in a probe, the electron density on 3 seems similar to that 3-5 the hydride lies close to niobium, whereas in 6 it on 2 and higher than that on 6. However, this could is slightly further away in agreement with a stronger result both from the bonding interaction found in the coordination to gold. X-ray structure (vide infra) between the copper center These data all agree with a structure involving a and the two carbonyl ligands which behave as semibridgcoinage metal cation linked to the hydride of two ing and, on the other side, from the better overlap different niobium moieties in the case of 3-6, whereas between the niobium and the gold orbitals which could 7 would only contain one niobium moiety linked to a form a direct metal-metal bond. The effect of this “(AuPPh3)+”fragment. The nature of this bonding and bonding would be a decrease of the electron density on the geometry around the coinage cation are, however, niobium. It is interesting to note that this last effect not known, which led us to carry out an X-ray crystal would be in agreement with the observation that structure determination for 3. exchange couplings are much larger in the gold adduct.s Description of the X-ray Structure of [c34H54’ of niobiocene trihydrides than in the copper adducts. CuOzNb~SidPFd24HsO(3). In the crystals of 3, heterotrinuclear cationic complexes-formed by two (11)Albinati, A.; Eckert, J.; Hoffmann, P.; Ruegger, H.; Venanzi, ‘“b111(CsH4SiMe3)2(CO))) moieties linked to a Cu(1)atom I,. M. Inorg. Chem. 1993,32, 2377. through two bridging hydride ligands-PF6- anions, and (12)Wong, K. S.; Scheidt, W. R.; Labinger, J. A. Inorg. Chem. 1979, 18, 136. THF molecules of solvation are present. The structure (13)Skripkin, Y. V.; Paoyuskii, A. A,; Kaliunikov, V. T.; Poraiof the cation is depicted in Figure 1 together with the Koshits, M. A.; Minachova, L. K.; Autsyshkina, A. S.; Ostrikiva, V. N. J . Organomet. Chem. 1982,231,205. atomic numbering scheme; the most important bond (14)Antifiolo, A,; Fajardo, M.; Jalon, F.; Lopez-Mardomingo, C.; distances and angles are given in Table 1and the atomic Otero, A,; Sanz-Bernabe, C. J . Organomet. Chem. 1989,369, 187. coordinates for all non-hydrogen atoms appear in Table (15)Kubas, G.J. Inorg. Synth. 1989,19, 90. (16)Hall, K. P.;Mingos, D. M. P. Inorg. Chem. 1984,32, 237. 2. To the best of our knowledge, complex 3 represents (17)Hoffman, R.Angew. Chem., Int. E d . Engl. 1982,21,711. first structurally characterized compound containing the (18)Know, S. A. R.; Stone, F. G. A. J . Chem. SOC.A 1969,2559. (19) Uson, R.; Laguna, A.; Laguna, M. Inorg. Synth. 1989,26,86. niobium and copper simultaneously in a molecule.
Coinage Metal Cation Adducts of Nb(C&l&iMed2H(CO) Table 1. Selected Bond Distances (A) and Angles (deg) with Esd's in Parentheses for Compound 3" Nb( l)-CE(l) Nb( 1)-CE(2) Nb( 1)-Cu Wl)-C(1) Nb(2)-CE(3) Nb( 2) -CE(4) Nb(2)-Cu Nb(2)-C(18) CE(l)-Nb(l)-CE(2) CE(1)-Nb(1)-C(1) CE(2)-Nb(l)-C(l) CE(1)-Nb(1)-H(1) CE(2)-Nb(l)-H(1) C(1)-Nb(1)-H(1) CE(3)-Nb(2)-CE(4) CE(3)-Nb(2)-C(18) CE(4)-Nb(2)-C(18) CE(3)-Nb(2)-H(2) CE(4)-Nb(2)-H(2) C(18)-Nb(2)-H(2) Nb(l)-C~-Nb(2)
2.064(12) 2.061(11) 2.700(2) 2.072(15) 2.058(13) 2.070( 14) 2.732(2) 2.048( 14)
Cu-C(l) CU-C(18) C(1)-0(1) C( 18)-0(2) Nb(1)-H(1) Nb(2)-H(2) Cu-H(l) Cu-H(2)
137.3(4) 103.5(5) 107.7(5) lOl(3) lOl(4) lOl(4) 140.9(5) 102.2(6) 105.7(6) 104(3) lOl(3) 94(4) 167.1(1)
2.351(13) 2.510(13) 1.146(17) 1.146(17) 1.83(12) 1.9312) 1.86(11) 1.54(12)
C(l)-Cu-C(18) C(l)-Cu-H(l) C(l)-Cu-H(2) C(18)-Cu-H(1) C(18)-Cu-H(2) H(l)-Cu-H(2) CE(5)-Cu-H(1) CE(5)-Cu-H(2) Nb(1)-C(1)-O(1) Nb(2)-C(18)-0(2) Nb(1)-H(l)-Cu Nb(2)-H(2)-Cu
96.0(5) 90(4) 134(5) 133(3) 89(4) 119(6) 122(3) 119(4) 173.4(12) 172.2(12) 94(5) 102(6)
a CE(l), CE(2). CE(3), and CE(4) are the centroids of the C(2), ..., C(6), C(10). ..., C(14), C(19), ..., C(23), and C(27), ...,C(31) rings, respectively, and CE(5) is the midpoint of C(l)-C(l8).
The metal coordination description obviously requires positioning of the light hydride atoms. These two ligands were clearly in evidence in the final A F map and were refined as free isotropic atoms (an indirect location by means of a "potential energy" technique validated this assignment20). The resultant coordination sphere around the two independent niobium atoms may be described as distorted tetrahedral with very similar bond distances and angles about both metals. In each niobium center the two Cp' rings are almost eclipsed with the bulky SiMe3 groups pseudo-trans to each other. The intermetallic separations Nb-Cu, 2.700(2) and 2.732(2)A, are slightly longer than the sum of the atomic radii (-2.67 A) and are analogous to those reported in related Mo-Cu complexes also containing linear semibridging carbonyls (Mo-Cu x 2.721 A), where the existence of a direct metal-metal bond has been proposed.21 However, only the Nb-Cu distance should not be considered conclusive to assign the presence of the metal-metal bond (see below). The arrangement of the three metals is essentially linear (Nb(l)-Cu-Nb(B) = 167.1(1)'). The two p-hydride atoms form around the CUI atom an angle of 119(6)". The most intriguing geometrical features of the structure are the two short intramolecular distances observed between the copper atom and the two supposedly terminal carbonyls (Cu-C(l) = 2.351(13) A and Cu-C(18) = 2.510(13) A).22 These Cu-C distances clearly suggest the presence of a bonding interaction between the copper atom and the carbonyls, conferring to these ligands a semibridging character. Interestingly, however, this interaction does not modify the linearity of the carbonyl groups (Nb-C-0 angles 173.4(12) and 172.2(12)"),which places this complex among the rare group of compounds containing linear semibridging carbonyls.23 According to the geometrical parameters and electronic characteristics of the metals, 3 ~~~
~~~~~
~~
~~~~
~
(20) Orpen, A. G. J . Chem. Soc., Dalton Trans. 1980, 2509. (21) Sargent, A. L.; Hall, M. B. J . Am. Chem. SOC.1989,111,1563. (22),Typical values of direct Cu-CO bonds lie between 1.75 and 1.78 A: Itajima, N. K.; Fujisawa, K.; Fujimoto, C.; Moro-Oka, Y.; Hashimoto, S.;Kitagawa, T.; Toriumi, K.; Tatsumi, K.; Nakamura, A. J . Am. Chem. SOC.1992,114, 1277. (23) Crabtree, R. H.; Lavin, M. Inorg. Chem. 1986,25, 805.
Organometallics, Vol. 14,No. 3, 1995 1299 Table 2. Atomic Coordinates ( ~ 1 0 " and ) Isotropic Thermal Parameters (A2x lo4) with Esd's in Parentheses for the Non-Hydrogen Atoms of Compound 3 atom Nb( 1) Nb(2) cu Si(1) Si(2) Si(3) Si(4) O(1) O(2) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) (39) C(10) C(11) C(W ~(13) ~(14) ~(15) C(16) ~(17) C(18) C(19) C(20) C(21) C(22) ~(23) ~(24) C(25) C(26) ~(27) C(28) ~(29) ~(30) C(31) C(32) C(33) C(34)
P F(1) F(2) F(3) F(4) F(5) F(6) 0(3) C(35) C(36) C(37) C(38)
xla
Ylb
ZJC
U
2594(1) 2327(1) 2693( 1) 4023(3) 1170(3) 5270(3) -49 l(3) 3149(7) 915(7) 2931(9) 3957(8) 4393(8) 4249(9) 3752(9) 3573(8) 2767( 11) 4458( 12) 5005(12) 1196(8) 1359(8) 1128(9) 821(8) 885(8) llO(11) 2404( 11) 864(13) 1465(9) 3946(9) 3283( 10) 2449( 10) 2539( 11) 3468( 10) 6150( 10) 5487( 12) 5415(11) 745(8) 1021(10) 1916(12) 2247( 11) 1537(10) -237(12) -1157(11) -1267(12) 7893(3) 7188(9) 8539( 11) 8670( 10) 7 3 0 3 14) 7209(11) 8621( 13) 7 9 7 3 12) 8152( 16) 7192( 17) 6533( 15) 7226( 14)
1297(1) 3955( 1) 2595( 1) -541(3) 2738(3) 4321(3) 4328(3) 3790(8) 4285(8) 2915( 12) 153(9) 1166(10) 1338(13) 447( 12) -275(11) -1 152(12) 473(12) -1612(12) 1756(10) 632(10) 182(12) 962( 13) 1939(11) 2340( 15) 2755(13) 4060( 12) 4114(10) 4894( 10) 5261(10) 5800(10) 5722( 11) 5 174(10) 5470( 12) 3230( 11) 3843( 13) 3544(9) 2609( 10) 2183(11) 2791( 13) 3644( 11) 5769(12) 413 1(15) 3794( 16) 770(4) 74( 10) 1 0 9 312) 1410(11) 433( 15) 1708(12) - 199(15) 235 1(13) 225 1(18) 1816(19) 1538(17) 1615(16)
430( 1) 1828(1) 1149(1) 1273(1) -562(2) 1833(2) 2088(2) 335(3) 927(4) 395(4) 711(4) 616(5) 150(5) -43(5) 309(5) 1359(6) 1716(5) 1257(6) -92(5) -114(5) 296(5) 559(5) 342(4) -977(5) -833(6) -341(6) 1234(5) 1844(4) 1484(5) 1659(6) 2113(7) 224 l(5) 1971(6) 2236(6) 1269(5) 2137(4) 1897(5) 2096(6) 2455(5) 2478(4) 2 169(7) 1549(5) 2519(6) 1424(1) 1712(4) 1876(5) 1159(4) 1002(6) 1435(5) 1417(6) 476 l(6) 5228(7) 5382(7) 4956(7) 4630(7)
381(4)" 401(4)" 5 19(6)" 608(14)" 663(16)" 670( 16)a 669(16)" 768(42)" 85 l(45)" 529(50)" 443(43)" 535(49)" 670(58)0 617(54)" 528(48)" 935(73)" 9 12(71)" 1062(84)" 485(48)" 506(48)" 635(58)0 652(56)" 516(50)" 1054(8 1)" 936(74)" lOSO(85)" 556(50)" 497(47)" 65 1(59)" 681(63)" 807(73)" 677(58)" 944(76)" 980(79)0 1003(77)" 476(46)" 579(52)" 756(70)" 729(64)" 587(50)" 1137(90)" 1024(79)" 1357(98)" 810( 16)" 1589(41) 2029(55) 176l(47) 2581(75) 1994(55) 2484(72) 1726(56) 1633(83) 1722(89) 1394(70) 1302(65)
a Equivalent isotropic U, defined as one-third of the trace of the orthogonalized U, tensor.
should be included in type I11 of Crabtree's recent classification of semibridging linear carbonyls,23which are characterized by the presence of a metal not known to form stable carbonyls (Cu in 3). Considering these Cu-CO bonding interactions, the geometry around the Cu atom could be described as flattened distorted tetrahedral (t[H(l)CuH(2)I cpC(l)CuC(18)1= 123(4)"). The Cu, H(1), Nb(l), and C(1) atoms are coplanar (maximum deviation O.lO(11) A for H(l)),as are the Cu, H(2), Nb(21, and C(18) atoms (maximum deviation 0.32(11)A for H(2)). The dihedral angle between the two planes is 119.2(4)'. In summary, the most astonishing aspect of this structural determination is that copper is only bound to two hydrides, while the short intramolecular Cu-C
Antiiiolo et al.
1300 Organometallics, Vol. 14, No. 3, 1995
Figure 2. Representation of two MO bonding orbitals (see text). Cyclopentadienyl ligands have been omitted for clarity. distances, together with the pseudo-tetrahedral geometry around copper, suggest a weak interaction between copper and the carbon of the carbonyl groups linked t o niobium. Unfortunately, although we have attempted t o visualize the presence of such interactions by 13C NMR, with the exception of 7, all complexes decomposed at least partially in solution during the experiments. In an attempt to obtain a deeper understanding of the peculiar bridging bonding system in this complex, a theoretical analysis based on extended Huckel MO calculations has been carried out with the CACAO program.24 For this purpose we have used a model based on the crystallographic coordinates of the molecule but changed the C5H4Si(CH3)3ligands into ideal C5H5 rings for the sake of simplicity. Using the fragment molecular orbital analysis (FMO), we have built up the [(CpzNb(CO)H}2Cul+molecule with two “Cp2Nb(C0)H fragments plus a Cu(1) atom. Each of the Nb fragments present two filled orbitals revealed to be important in our study: the HOMO, formed by a Nb d-type orbital plus a n* carbonyl orbital in a bonding arrangement (nm,-co), and the bonding interaction between the niobium and the hydride ligand ( 0 ~ b - d . These two orbitals also have weak contributions from the Cp rings, but these we found to be insignificant in our analysis. In the whole molecule, we can observe the in-phase and out-of-phase combinations of these two orbitals (JCNb-CO and ONb-H) interacting with those of the copper atom. The stronger interactions are formed by the inphase and out-of-phase combinations of the O ~ - Horbitals of the Cp2Nb(CO)H fragments with the Cu atom, developing two clear intermetallic bridging hydrides. The in-phase bonding orbital is represented in Figure 2 (left side). These hydrides are linked to the metals in a slightly asymmetric manner, as indicated by the Mulliken population calculated for these four bonds: Nb-H = 0.514 and 0.483; Cu-H = 0.171 and 0.207, showing a stronger interaction with the Nb center. The two noticeable remaining interactions correspond t o the combinations of the two filled nm-co orbitals (inphase and out-of-phase) with the valence shell orbitals of the central Cu atom, forming two three-center-twoelectron interactions between the niobium, the carbonyl carbon, and the copper atom. Similar models have been proposed to explain the bonding situation in related linear semibridging carbonyls.25 Interestingly, the two HOMO’S of the whole molecule are the corresponding bonding orbitals of this interaction ( J G N ~ - C O - C ~orbitals), one of which is also depicted in Figure 2 (right side). The Mulliken populations calculated between the atoms involved in these interactions are Nb-C = 0.809 and (24) Mealli, C.; Proserpio, D. M. J . Chem. Educ. 1990, 67, 399. (25) Morris-Shenvood, B. J.; Powell, C. B.; Hall, M. B. J . Am. Chem. SOC.1984, 106, 5079.
0.832, Nb-Cu = 0.172 and 0.182, and Cu-C = 0.130 and 0.079. Due t o these facts, only a weak direct niobium-copper interaction could be suggested, in spite of the intermetallic separation observed, and consequently the stabilization of the trinuclear complex is fundamentally due to the bridging ligands: hydrides and the linear semibridging carbonyls. Referring to the controversy on the donorlacceptor nature of the linear semibridging carbonyl groups,26we can state that in 3 the niobium-carbonyl fragment-as a whole-is donating electron density to the highly acidic metal, as the charge on the Cu atom was observed to increase when the fragment is moved away from the proximity of the Cu atom by opening the angle Cu-HNb while the Cu-H distance is kept constant. Besides the d-type copper orbitals, the s and p orbitals also make significant contributions to the aforementioned interactions, but only for the s and, to a lesser extent one p orbital is this clear-cut. The electron populations in these four atomic orbitals, from the Mulliken analysis, are 0.637, 0.148, 0.055, and 0.040 for the s and p orbitals, respectively, with a total calculated charge for the Cu(1)atom of 0.267. Therefore, we can conclude that the copper atom is receiving electron density through four molecular orbitals, in a pseudo-tetrahedral environment, using up to, but not all, four initially empty atomic orbitals. This means that the copper is linked by four bonding interactions through the bridging ligands (hydrides and carbonyls) but clearly not by four bonds of bond order 1, which is also in good agreement with the geometrical data. Unfortunately, the lack of symmetry in this compound makes a more detailed explanation difficult. In conclusion, we describe in this paper the preparation of a new series of adducts of Ms(CsH4SiMe3)2H(CO) with coinage element cations. The most important result of this study is that the formation of the adducts essentially involves binding of the hydride of a niobium moiety to the Lewis acidic cation. In addition, a weak interaction between the Lewis acid and CO is present, at least in the copper case. A similar type of bonding was recently proposed to explain the NMR properties of adducts of CpzNbHs (Cp = C5H5, C5H4SiMe3, C5H3~ Ad)). This study (SiMe3)d with M+ (M = C U , Ag,5 shows that such a bonding can indeed exist, at least in the case of hydrido carbonyl derivatives.
Experimental Section General Procedures. All manipulations were performed under an inert atmosphere of dry nitrogen or argon using standard Schlenk-tubetechniques. Solvents were purified by distillation from appropriate drying agents and degassed before use.
The complexes Nb(CbH4SiMe3)2H3and N ~ ( C E , H ~ S ~ M ~ ~ ) ~ H (CO) were prepared as described earlier.’I2 [Cu(MeCN)41BF4, [CuPPh3C114,[AgPPh&l]*,AuPPh3C1, and Au(THT)Cl were prepared according to known procedure^.^^-'^ Other reagents were used as purchased. NMR spectra were obtained on a Varian Unity FT-300 instrument. IR spectra were recorded as Nujol mulls between CsI plates (in the region between 4000 and 200 cm-l) on a Perkin-ElmerPE883 IR spectrophotometer. Elemental analyses were performed on a Perkin-Elmer 2400
microanalyzer. [{Nb(CaH4SiMes)2(CO)OI-H))2MlX (M= Cu, X = PFe (3); M = Ag, X = BFd (4), PFe (5);M = Au, X = PFe (6)). A THF (26) Simpson, C. Q., 11; Hall, M. B. J . Am. Chem. SOC.1992, 114, 1641 and references therein.
Coinage Metal Cation Adducts of Nb(C&&SiMe&H(CO)
Organometallics, Vol. 14, No. 3, 1995 1301
solution of CuPPh3PF6 (0.40 mmol), prepared "in situ" by Table 3. Crystallographic Data for Compound 3 reaction of [CuPPh&114 (300 mg, 0.10 mmol) with TlPF6 (150 mol formula [C34H54C~02Nb2Si4]PF6~4H80 mg, 0.40 mmol) (the precipitate of TlCl was eliminated by mol wt 1073.573 filtration) was added to a THF solution (30 mL) of Nb(C5H4cryst syst monoclinic SiMe&H(CO) (0.81 mmol) at 0 "C. After the mixture was space group P21/c radiation graphite-mo_nochromated stirred for 15 min, an orange solution with a precipitate was Mo K a (1= 0.710 73 A) obtained, which was filtered, and the solvent was removed in a,A 13.048(5) vacuo. The solid was washed with diethyl ether and then b, 8, 12.490(4) extracted with a mixture of THF and Et20 (1:l). Complex 3 c, 8, 30.13 l(9) was isolated on cooling as red crystalline needles (92% yield). A deg 94.52(2) 3 was similarly prepared using [Cu(MeCN)4]BF4as precursor. v,A 3 4895(3) Complexes 4-6 were prepared using AgBF4, AgPPhsPFs, and Z 4 Au(THT)PF6, respectively, as red crystalline needles (61% Dcalcd, g 1.457 yield) for 4 and 5 and brown crystals (94% yield) for 6, by a F(000) 2200 cryst dimens, mm 0.16 x 0.18 x 0.20 procedure similar to that described for 3. In the reaction with 10.76 linear abs @), cm-l AuPPbPF6, the complex [{Nb(CsH4SiMe3)2(COXu-H)}(A~Pb)ldiffractometer Enraf-Nonius CAD4 PF6 (7)was obtained as deep orange crystalline needles (91% T, "C 22 yield). unique total no. of data 10 604 3: IR (Nujol) vco 1900 cm-I, Y P F ~840 cm-I; 'H NMR (CD3no. of unique obsd data ( I 2 2a(f)) 3001 COCD3, in ppm, referenced to TMS) 6 -7.67 (s, 2H, H), 0.26 Ra 0.0460 (s, 36H, SiMes),5.38 (4H),5.47 (4H),5.68 (4H), 5.91 (4H) (16H, RWb 0.0608 Ca4SiMe3). Anal. Calcd for C ~ ~ H ~ ~ O ~ S ~ ~ PC,N40.8; ~~CUFS: a R = 211Fol- l~clI/21~ol. RW = [Cw(lFol - I~cl)2/~w(Fo)211'2. H, 5.4. Found: C, 40.5; H, 5.3. 4: IR (Nujol) YCO 1920 cm-l, V B F ~1030 cm-'; 'H NMR (CD3were placed at their geometrically calculated positions (C-H COCD3, in ppm, referenced to TMS): 6 -7.10 (d, J H A=~101 = 0.96 A) and refined "riding" on the corresponding carbon Hz, 2H, p H ) , 0.27 (s, 36H, SiMes), 5.35 (4H), 5.41 (4H), 5.59 atoms. The positions of the hydride ligands were calculated (4H), 5.88 (4H) (16H, Ca4SiMe3). Anal. Calcd for C34H54also by minimization of the potential energy of the intramoOzSirBNbzAgF4: C, 41.3; H, 5.5. Found: C, 41.4; H, 5.5. lecular nonbonded interactions involving the two hydrides by 5: IR (Nujol) YCO 1917 cm-' Y P F ~840 cm-'; 'H NMR (CD3using the HYDEX program,20and they were in good agreement COCD3, in ppm, referenced to TMS): 6 -7.10 (d, J H A=~101 with those found in the final AF map. The final cycles of Hz, 2H, p-H), 0.26 (s, 36H, SiMea), 5.35 (4H), 5.41 (4H, 5.59 refinement were carried out on the basis of 451 variables; after (4H), 5.88 (4H) (16H, CpY4SiMe3). Anal. Calcd for C34Hs4the last cycles no parameters shifted by more than 0.62 esd. OzSi4PNbAgF6: C, 41.3; H, 5.5. Found: C, 41.2; H, 5.3. The biggest remaining peak in the final difference map was 6: IR (Nujol) vco 1932 cm-', Y P F ~840 cm-'; 'H NMR (CD3equivalent t o about 0.91 e/A3. In the final cycles of refinement a weighting scheme, w = k [ d F 0 ) gFo21-', was used; at COCD3, in ppm, referenced to TMS) 6 -3.75 (s, 2H, p H ) , 0.26 (s, 36H, SiMes), 5.36 (8H), 5.74 (4H), 5.84 (4H) (16H, C a 4 convergence the k and g values were 0.5929 and 0.0095, SiMe3). Anal. Calcd for C ~ ~ H ~ ~ O ~ S ~ ~ P N The analytical scattering factors, corrected for C,~35.5; ~ A H, U P F S respectively. : the real and imaginary parts of anomalous dispersions, were 4.6. Found: C, 35.4; H, 4.6. taken from ref 27. All calculations were carried out on the 7: IR (Nujol) YCO 1936 cm-l, Y P F ~840 cm-'; 'H NMR (CD3Gould Powernode 6040 and Encore 91 computers of the = 77.1 COCD3, in ppm, referenced to TMS) 6 -5.62 (d, JHP "Centro di Studio per la Strutturistica Diffrattometrica" del Hz, lH, p H ) , 0.25 (s, 18H, %Mea), 5.64 (4H), 5.99 (2H), 6.00 CNR, Parma, Italy, using the SHELX-86 and SHELX-76 (2H) (8H, Ca4SiMe3). Anal. Calcd for C25H42SizNbOAuPzsystems of crystallographic computer programs.2B The final F6: C, 41.9; H, 4.6. Found: C, 41.4; H, 4.6. atomic coordinates for the non-hydrogen atoms are given in X-ray Data Collection, Structure Determination, and the supplementary material. Refinement for [{N~(C~H~S~M~~)~(CO)}~~-H)~CUIPF~.C~HsO (3). A single crystal of 3 was sealed in a Lindemann capillary under dry nitrogen and used for data collection. The Acknowledgment. A.A., F.C., S.G.-Y., M.F., and crystallographic data are summarized in Table 3. Unit cell A.O. gratefully acknowledge financial support from the parameters were determined from the 8 values of 25 carefully DGICYT (Grant No. PB 89-0206)of Spain. M.L. and centered reflections, having 10 < 0 < 16". Data (3 < 8 < 27") M.A.P. gratefully acknowledge financial support from were collected at 22 "C on Enraf-Nonius CAD4 four-circle the Minister0 dell'Universit8 e della Ricerca Scientifica single-crystal diffractometer, using the graphite-monochroe Tecnologica (MURST) and the Consiglio Nazionale mated Mo Ka radiation and the w/28 scan type. The reflecdelle Ricerche (CNR) (Rome, Italy). tions were collected with a maximum scan speed of 3.3" min-' and a scan range of 0.80 0.35 tan 0 (the w scan area was Supplementary Material Available: Hydrogen atom extended a t each side of 25% for background determination). coordinates (Table SI), anisotropic and isotropic thermal Two standard reflections were monitored every 200 measureparameters for the non-hydrogen atoms (Table SII), complete ments; no significant decay was noticed over the time of data bond distances and angles (Table SIII), least-squares planes collection. Intensities were corrected for Lorentz and polariza(Table SIV),and complete crystallographic data (Table SV) (14 tion effects. Of 10 604 independent reflections, 3001 having1 pages). Ordering information is given on any current mastz 2dZ) were considered observed and used in the analysis. head page. The structure was solved by Patterson and Fourier methods. A THF molecule of solvation was found in the AF map. The OM940750F refinement was carried out first by full-matrix least squares with isotropic thermal parameters and then by blocked full(27) International Tables for X-Ray Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. IV. matrix least squares with anisotropic thermal parameters for (28) Sheldrick, G. M. SHELXS-86 Program for the Solution of all the non-hydrogen atoms of the cation and the P atom of Crystal Structures; University of Gbttingen, Gottingen, Germany, the anion. The two hydrides were well located on a final AF 1986. Sheldrick, G. M. SHELX-76 Program for Crystal Structure Determination; University of Cambridge, Cambridge, England, 1976. map and refined isotropically; all the other hydrogen atoms
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