main group metal

Aug 1, 1987 - Reactivity of the Metallocarboxylates Cp(NO)(PPh3)ReCO2M toward Excess Carbon Dioxide: Degradation to a Bimetallic μ-[η-C(Re):η-O ...
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Volume 26 Number 17

Inorganic Chemistry

August 26, 1987

0 Copyright 1987 by the American Chemical Society

Communications Scheme I. Representative Syntheses and Reactions of Rhenium/Main-Group-Metal Bridging Carboxylate Complexes

Synthesis, Structure, and Reactivity of Transition-Metal/Main-Group-MetalBridging Carboxylate Complexes of the Formula (7I5-C5H5)Re(W(PPh3) (C02MLn) (M = Li, K, Ge, Sn, Pb)

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Metal-C02 complexes have attracted attention from both fundamental and applied viewpoints.' First, C 0 2 is an abundant C1 molecule that serves as nature's photosynthetic building block. Second, C02 exhibits a variety of binding modes to Third, the reactivity of metal-C02 complexes should provide insight regarding C 0 2activation and the design of new catalytic reactions.' We have previously described the synthesis of the

(a) Darensbourg, D. J.; Kudaroski, R. A. Adv. Organomet. Chem. 1983, 22, 129. (b) Palmer, D. A.; van Eldik, R. Chem. Reu. 1983,83, 651. (c) Sneeden, R. P. A. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: New York, 1982; Vol. 8, Chapter 50.4. (d) A reviewer has questioned whether the complexes in this paper are better described as "carboxylate" or T O z " complexes. We prefer the latter, since it clearly indicates that atomic grouping spanning the two metals. Additional nomenclature conventions are in (a) Lee, G. R.; Maher, J. M.; Cooper, N. J. J . Am. Chem. SOC.1987, 109, 2956. (b) Lee, G. R.; Cooper, N. J. Organometallics 1985,4, 794. (a) Forschner, T.; Menard, K.;Cutler, A. J. Chem. SOC.,Chem. Commun. 1984, 121. (b) Tso,C. T.; Cutler, A. R. J . Am. Chem. SOC.1986, 108, 6069. (c) The silylation of (g5-C5HS)Fe(C0)2((C(-O)=OLi) to (~5-C5H5)Fe(CO)z(C(=O)-OSiR(CH3)2) was reported after this paper had been submitted for publication: Giuseppetti, M. E.; Culter, A. R. Organometallics 1987, 6, 970. (a) Barrientos-Penna, C. F.; Gilchrist, A. B.; Klahn-Oliva, A. H.; Hanlan, A. J. L.; Sutton, D. Organometallics 1985, 4, 478. (b) Barrientos-Penna, C. F.; Einstein, F. W. B.; Jones, T.; Sutton, D. Inorg. Chem. 1985, 24, 632. See also: (a) Grice, N.; Kao, S. C.; Pettit, R. J . Am. Chem. SOC.1979, 101, 1627. (b) Sweet, J. R.; Graham, W. A. G. Organometallics 1982, I, 982. For C 0 2 complexes published since the review articles in ref 1, see: (a) Audett, J. D.; Collins, T. J.; Santarsiero, B. D.; Spies, G. H. J . Am. Chem. SOC.1982, 104, 7352. (b) Calabrese, J. C.; Herskovitz, T.; Kinney, J. B. Ibid. 1983, 105, 5914. (c) Bianchini, C.; Meli, A. Ibid. 1984, 106, 2698. (d) Alvarez, R.; Carmona, E.; Gutierrez-Puebla, E.; Marin, J. M.; Monge, A.; Poveda, M. L. J . Chem. SOC.,Chem. Commum 1984, 1326. (e) Karsch, H. H. Chem. Ber. 1984,117,3123. (f) DBhring, A.; Jolly, P. W.; Kriiger, C.; RomHo, M. J. 2.Naturforsch. B Anorg. Chem., Org. Chem. 1985, 408, 484. (g) Gambarotta, S.; Floriani, C.; Chiesi-Villa,A.; Guastini, C. J . Am. Chem. SOC.1985, 107, 2985. (h) Lundquist, E. G.; Huffman, J. C.; Caulton, K. G. Ibid. 1986, 108, 8309. (i) Alt, H. G.; Schwind, K.-H.; Rausch, M. D. J . Organomet. Chem. 1987, 321, C9. For representative examples of catalytic and stoichiometric C 0 2 reduction, see ref 3b and: (a) Gambarotta, s.;Strologo, s.;Floriani, C.; Chiesi-Villa, A.; Guastini, C. J . Am. Chem. SOC.1985, 107, 6278. (b) Darensbourg, D. J.; Ovalles, C. Inorg. Chem. 1986, 25, 1603. (c) Erdohelyi, A.; PBsztor, M.; Solymosi, F. J . Catal. 1986, 98, 166.


2 , Mi = Li'


3 , M+ = K+


- MBr




ONIF 'o/ P ' h, \\0

' 7I PPh,



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rhenium "carboxylic acid" ($-C,H,)Re(NO)(PPh,)(COOH)(1); in which a C 0 2 moiety spans a transition metal and a hydrogen atom. In this communication, we report the elaboration of 1 to rheniumlmain-group-metal bridging C 0 2 or carboxylate comAn plexes of the formula ($-C5H5)Re(NO)(PPh,)(C02MLn).'d added impetus for this study was the possibility that subsequent decarboxylation might provide a convenient entry to complexes with transition-metal-main-group-metal bonds. Reaction of ($-C,H,)Re(NO)(PPh,)(COOH) (1)8with LiH and K H (THF, 25 "C) gave, after workup, the rheniumlalkali-metal C 0 2 complexes ($-C,H,)Re(NO)(PPh,)(C(=O)=OLi) (2) and (a5-C,H,)Re(NO)(PPh3)(C(=O).-;OK) (3) as orange air-sensitive powders in 85-90% yields (Scheme I).9 Complexes 2 and 3 showed IR voco bands (cm-I, thin film) of 1435 and 1405 (vas,,) and 1248 and 1239 (vsym). The vasym and the AY (uaasymvSym) values are considerably lower than those found in 1 (vaSym 1551 cm-', vsym 11 17 cm-') or the "methyl ester" ($-C5H5)Re(NO)(PPh,)(C(=O)-OCH,) (vaSym 1584 cm-I, us ,1042 cm-1).8i10 In accord with extensive literature these



(8) Tam, W.; Lin, G.-Y.; Wong, W.-K.; Kid, W. A,; Wong;V. K.; Gladysz, J. A. J. Am. Chem. SOC.1982, 104, 141. (9) All new complexes have been characterized by IR and NMR ('H, "C, 3'P, 'I9&) spectroscopy; complexes 2,445, and 9 have given satisfactory microanalyses (supplementary material).

0 1987 American Chemical Society

2738 Inorganic Chemistry, Vol. 26, No. 17, 1987


data are used to assign the bidentate carboxylate (or w($C:s2-0,0')) binding mode. Similar transition-metal/alkali-metalor transition-metal/alkaline-earth-metal C 0 2 complexes have been previously isolated and studied by Cooper,2 C ~ t l e r and , ~ S ~ t t o n . ~However, .~ no structural data have been reported to date. We were unable to obtain crystals of 2 or 3 suitable for X-ray analysis, so derivatization with group 14 metals was attempted. We first turned our attention to tin because of the extensive interest in, and structural studies on, tin organocarboxylates.I2 Reaction of 3 with Ph3SnC1 (1.1 equiv, THF, -78 "C) and workup gave the air- and water-stable rhenium/triphenyltin C 0 2


complex (~5-CSHS)Re(NO)PPh3)(C(=O)=OSnPh,) (4) in 86% yield (Scheme I). The IR voce bands (1395, 1188 cm-I) indicated a bidentate carboxylate binding mode, and the NMR = 4.6 Hz) was upfield chemical shift (-167.1 ppm, d, from that normally found for tetracoordinate tin.12f Yellow prisms of 4 were obtained from CH2C12/hexanes,and X-ray data were collected as described in the supplementary material. The molecular structure of 4 is given in Figure l . The bonding to tin in 4 is unusual. As previously noted by Holmes, the structures of most monomeric triaryltin organocarboxylates can be derived by distorting the C=O oxygen of a hypothetical structure containing tetrahedral tin toward a tetraThe result can be hedral face opposite to one aryl considered a distorted trigonal bipyramid with the " C 4 " oxygen and unique aryl group in axial positions. However, the axial tin-oxygen bond typically remains 0.7-0.8 8, longer than the equatorial tin-oxygen bond.12c,eComplex 4 is unique in having nearly equal tin-oxygen bond lengths (2.257 (7), 2.175 (7) 8,). This small difference can likely be ascribed to the asymmetric steric environment about rhenium. Further, the sum of the equatorial bond angles in 4 is 351.2O (C11, C31,02), considerably closer to that of an idealized trigonal bipyramid (360") than in triaryltin organocarboxylates (333-341°).12b-eAlso, the tin is displaced only 0.364 A from the plane of the equatorial atoms, in contrast to 0.543-0.693 8, in triaryltin organocarboxylates. Finally, the 0 1 - 0 2 plane makes a 5 (1)" angle with the N-Re bond. This orientation is analogous to that of formyl and acyl ligands in complexes of the formula ($-C5H5)Re(NO)(PPh3)(COR)', and maximizes overlap of the rhenium fragment HOMO shown in I (Scheme I) with the acceptor orbital on C,. The reaction of 3 and Me3SnC1 (1.1 equiv, THF, -78 "C) gave the rhenium/trimethyltin C 0 2 complex ($-CjH5)Re(NO)(PPh,)(C(=O)=OSnMe,) (5, 95%). Complex 4 was also synthesized directly from 1 and (Ph,Sn),O (0.5 equiv, 'fHF, 25 "C; 95%). When 4 was heated, it cleanly decarboxylated (Scheme I; < l o min, 180 "C, solid; 20 h, 140 OC, xylenes) to the rheni(6, >98%). um-tin complex ($-C5H5)Re(NO)(PPh3)(SnPh3) The structure of 6 was confirmed by an independent, NMRmonitored synthesis from the uanionn14 Li+[(qS-C5H5)Re(NO)(PPh,)]- and Ph3SnC1 (1.0 equiv, THF, -78 "C). The synthesis of other rhenium/group 14 metal bridging C 0 2 complexes was attempted. First, reaction of 3 and Ph3GeBr (25

C,H,)Re(NO)(PPh,)(C(=O)-OGePh,) (7) in 52%yield after

(10) (a) Merrifield, J. H.; Strouse, C. E.; Gladysz, J. A. Organometallics 1982, 1, 1204. (b) The IR voce bands of 1 and (q5-C5Hs)Re(NO)(PPh,)(CO,CH,) were remeasured under the same conditions used to obtain those of 2-5, 7, and 8. (11) Deacon, G. B.; Phillips, R. J. Coord. Chem. Reu. 1980, 33, 227. (12) (a) Davies, A. G.;Smith, P. J. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: New York, 1982; Vol. 2, pp 564-572. (b) Swisher, R. G.; Vollano, J. F.; Chandrasekhar, V.; Day, R. 0.;Holmes, R. R. Inorg. Chem. 1984, 23, 3147. (c) Vollano, J. F.; Day, R. 0.;Rau, D. N.; Chandrasekhar, V.; Holmes, R. R. Ibid. 1984, 23, 3153. (d) Holmes, R. R.; Day, R. 0.;Chandrasekhar, V.; Vollano, J. F.; Holmes, J. M. Ibid. 1986.25, 2490. (e) Smith, P. J.; Day, R. 0.;Chandrasekhar, V.; Holmes, J. M.; Holmes, R. R. Ibid. 1986, 25, 2495. (f)HoleEek, J.; Nidvornik, M.; Handlii, K.; LyEka, A. J. Organomet. Chem. 1983,241, 177; 1983, 258, 147. (13) Bcdner, G. S.;Patton, A. T.; Smith, D. E.; Georgiou, S.; Tam, W.; Wong, W.-K.; Strouse, C. E.; Gladysz, J. A. Organometallics, in press. (14) Crocco, G. L.; Gladysz, J. A. J . Chem. Soc., Chem. Commun. 1985, 283.

CH2C12/hexanesrecrystallization. IR data (uw0 1545, 1048 cm-') indicated a monodentate carboxylate binding mode.12 An analogous reaction of 3 and Ph3PbC1 gave a (33 f 2):(67 f 2) mixture of the rhenium/lead C 0 2 complex ($-CjH5)Re(NO)(PPh3)(C(=O)=OPbPh3) (8; uoco 1425, 1184 cm-I) and the rhenium-lead complex ($2,H5)Re(NO)(PPh,)(PbPh3) (9). The latter compound crystallized as orange prisms from CH2C12/ hexanes. When the reaction of 3 and Ph,PbCI was conducted at -78 "C and worked up at 0 "C, pure 8 was isolated. Facile decarboxylation to 9 occurred in C6H6at room temperature (