Unsymmetrical Zirconacyclopentadienes from Isolated

(37, 41, 42) The 1H NMR spectra for zirconacyclopropenes 1 and 2 contain ..... The substitution of Ph2PC≡CPh with tolan in zirconacyclopentadiene 9 ...
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Organometallics 2009, 28, 1252–1262

Unsymmetrical Zirconacyclopentadienes from Isolated Zirconacyclopropenes with 1-Alkynylphosphine Ligands Adam D. Miller, Samuel A. Johnson, Karl A. Tupper, Jennifer L. McBee, and T. Don Tilley* Department of Chemistry, UniVersity of California, Berkeley, Berkeley, California 94720-1460 ReceiVed October 29, 2008

The reaction of one equiv of 1-alkynylphosphines, R2PCtCR′ (R ) Et, iPr, or Ph and R′ ) Ph or Mes), with Cp2Zr(pyr)(η2-Me3SiCtCSiMe3) resulted in formation of monoalkyne complexes. In the case where R ) Et, iPr, or Ph and R′ ) Ph, a “ligand free” zirconacyclopropene complex is produced. These complexes are stabilized by intermolecular donation of the phosphorus lone-pair in the dimeric complexes [Cp2Zr(η2-R2PCtCPh)]2 (R ) Et, iPr, or Ph). However, with R ) Ph and R′ ) Mes, the zirconocyclopropene-pyridine complex Cp2Zr(pyr)(η2-Ph2PCtCMes) is formed. Homocoupling of the 1-alkynylphosphines was demonstrated by reaction of a second equiv of Ph2PCtCPh with [Cp2Zr(η2-Ph2PCtCPh)]2 to give the diphosphinozirconacyclopentadiene Cp2Zr[2,5-(Ph2P)2-3,4-Ph2C4] with high regioselectivity (77%). The zirconacyclopropene complexes also react with one equiv of PhCtCPh or EtCtCEt to give zirconacyclopentadienes in which the phosphino substituent preferentially adopts the 2-position (R) of the zirconacyclopentadiene ring. These unsymmetrical zirconacyclopentadienes undergo substitution of the R2PCCR′ moiety with the less bulky alkynes PhCtCPh or EtCtCEt. The substituents on the 1-alkynylphosphines significantly influence the rates of alkyne substitution such that sterically more demanding substituents in either the R- (-PiPr2) or β- (-Mes) position of the zirconacycle lead to faster exchange. The R-phosphinozirconacyclopentadienes were readily converted to 1-phosphinobutadienes via reaction with benzoic acid. The zirconacyclopentadiene Cp2Zr[2-Ph2P-3,4,5-Ph3C4] was converted to the corresponding thiophene oxide by the oxo-transfer reaction with sulfur dioxide. In the case of ((1Z,3E)3-ethyl-2-phenylhexa-1,3-dienyl)diphenylphosphine and (3,4,5-triphenylthiophen-2-yl oxide)diphenylphosphine, the molecules were isolated as their phosphine oxides. Reactions of the zirconacyclopropene complexes [Cp2Zr(η2-Ph2PCtCPh)]2 and Cp2Zr(pyr)(η2-Ph2PCtCMes) with the diyne (F5C6)CtC-1,4C6H4-CtC(C6F5) gave bis(zirconacycle)s terminated with phosphino groups. These bis(zirconacycle)s were converted to the corresponding phosphino-terminated oligomers by protonolysis with hydrochloric acid. In addition, the Ph2PCCMes moiety of Cp2Zr[2-Ph2P-3-Mes-4-(C6F5)C4]-1,4-C6H4-Cp2Zr[2-Ph2P3-Mes-4-(C6F5)C4] was exchanged with PhCtCPh to give the phenylene(zirconacyclopentadiene) Cp2Zr[2,3-Ph2-4-(C6F5)C4]-1,4-C6H4-Cp2Zr[2,3-Ph2-4-(C6F5)C4]. Introduction The reductive coupling of alkynes by zirconocene is an important carbon-carbon bond forming reaction.1-3 The resulting zirconacyclopentadienes are useful precursors to a wide range of organic molecules including (for example) dienes,4 arenes,5-9 cyclopentadienes,10-12 thiophenes,13,14 phospholes,15 thiophene oxides,16 and bicyclic compounds.17 An important * To whom correspondence should be addressed. E-mail: [email protected]. (1) Negishi, E.; Takahashi, T. Bull. Chem. Soc. Jpn. 1998, 71, 755– 769. (2) Broene, R. D.; Buchwald, S. L. Science 1993, 261, 1696–1701. (3) Buchwald, S. L.; Nielsen, R. B. Chem. ReV. 1988, 88, 1047–1058. (4) Lucht, B. L.; Tilley, T. D. Chem. Commun. 1998, 1645–1646. (5) Takahashi, T.; Hara, R.; Nishihara, Y.; Kotora, M. J. Am. Chem. Soc. 1996, 118, 5154–5155. (6) Takahashi, T.; Ishikawa, M.; Huo, S. Q. J. Am. Chem. Soc. 2002, 124, 388–389. (7) Takahashi, T.; Kotora, M.; Xi, Z. F. J. Chem. Soc., Chem. Commun. 1995, 361–362. (8) Takahashi, T.; Tsai, F. Y.; Li, Y. Z.; Nakajima, K.; Kotora, M. J. Am. Chem. Soc. 1999, 121, 11093–11100. (9) Takahashi, T.; Xi, Z. F.; Yamazaki, A.; Liu, Y. H.; Nakajima, K.; Kotora, M. J. Am. Chem. Soc. 1998, 120, 1672–1680. (10) Takahashi, T.; Sun, W. H.; Xi, C. J.; Kotora, M. Chem. Commun. 1997, 2069–2070.

factor that determines the structure of the products in these conversions is the regiochemistry of the alkyne coupling at zirconium, which is known to be sensitive to both steric and electronic factors. For example, sterically demanding groups such as -SiMe3 and -CMe3 direct alkyne couplings such that they adopt the less-crowded R-positions (-2 and -5) of the zirconacyclopentadiene ring.17-19 On the other hand, electron poor substituents (e.g., pentafluorophenyl groups) prefer the (11) Kotora, M.; Xi, C. J.; Takahashi, T. Tetrahedron Lett. 1998, 39, 4321–4324. (12) Xi, Z.; Li, P. Angew. Chem., Int. Ed. 2000, 39, 2950–2952. (13) Fagan, P. J.; Nugent, W. A.; Calabrese, J. C. J. Am. Chem. Soc. 1994, 116, 1880–1889. (14) Fagan, P. J.; Nugent, W. A. J. Am. Chem. Soc. 1988, 110, 2310– 2312. (15) Hay, C.; Hissler, M.; Fischmeister, C.; Rault-Berthelot, J.; Toupet, L.; Nyulaszi, L.; Reau, R. Chem.-Eur. J. 2001, 7, 4222–4236. (16) Jiang, B. W.; Tilley, T. D. J. Am. Chem. Soc. 1999, 121, 9744– 9745. (17) Nugent, W. A.; Thorn, D. L.; Harlow, R. L. J. Am. Chem. Soc. 1987, 109, 2788–2796. (18) Erker, G.; Zwettler, R.; Kruger, C.; Hylakryspin, I.; Gleiter, R. Organometallics 1990, 9, 524–530. (19) Hara, R.; Xi, Z. F.; Kotora, M.; Xi, C. J.; Takahashi, T. Chem. Lett. 1996, 1003–1004.

10.1021/om801040t CCC: $40.75  2009 American Chemical Society Publication on Web 01/29/2009

Unsymmetrical Zirconacyclopentadienes

β-positions (-3 and -4) of the zirconacyclopentadiene ring.20 The ability to control the coupling of unsymmetrical alkynes in a regioselective manner is not only useful for the preparation of small molecules but also for the synthesis of macrocycles21-27 and polymers20,28 via the coupling of diynes of the type RCtC-R′-CtCR. For the synthesis of macrocycles by this method, another important requirement is that the alkyne substituents promote reversibility for zirconacyclopentadiene formation.21 Due to the inherently high reactivity of zirconocene (Cp2Zr), the regioselective cross-coupling of two alkynes, to form unsymmetrical zirconacyclopentadienes, has proven difficult to control. Generally, two alkynes may be added sequentially if the first addition gives a relatively stable zirconacyclopropene intermediate (A), and several different methods for the stabilization of this monoalkyne adduct (or an analogous synthon) have been investigated (eq 1).29-33 One approach involves the synthesis of a zirconacyclopropene that is stabilized by coordination of a Lewis base (L ) PMe3, DMAP, etc.; B).29-31 A second equiv of alkyne may then be added to displace the Lewis base. Another approach involves intermediate zirconacyclopentenes, formed by the relatively efficient cross-coupling of an alkyne with ethylene (C). The ethylene may then be replaced by heating the zirconacycle in the presence of a second alkyne, to form the desired cross-coupled product.33 An approach that has yet to be examined is the use of an isolable, base-free zirconacyclopropene. This approach will require use of cyclopentadienyl or alkyne substituents that stabilize the inherently reactive zirconacyclopropene.34,35

Organometallics, Vol. 28, No. 4, 2009 1253

via donation of the phosphorus lone pair to zirconium. In related work by Majoral and co-workers, Ph2PCtCR alkynes were observed to couple with the transient benzyne complex Cp2Zr(η2C6H4) to produce the corresponding zirconaindene complexes.36,37 In the latter compounds, the diphenylphosphino group adopts the R-position of the metallocyclic zirconaindene ring, presumably due to interaction of the lone pair on the phosphorus with the metal center.36 It has also been proposed that 1-alkynylphosphines and 1-alkynylphosphonates form zirconacyclopropenes as intermediates in zirconocene-mediated cross-couplings with other alkynes.37,38 Takahashi and co-workers have reported that Ph2PCtCR reacts with diethylzirconocene to form the corresponding zirconacyclopentene. These species then react with a second alkyne with displacement of ethylene and formation of unsymmetrical zirconacyclopentadienes.39 In an attempt to further develop methodologies for the control of regioselectivity in the cross-couplings of alkynes by zirconocene, 1-alkynylphosphine substrates have been examined. To the best of our knowledge zirconacyclopropenes derived from 1-alkynylphosphines have not been isolated and fully characterized. This report describes such zirconacyclopropenes, and the characterization of their structures and reactivities toward alkynes. This chemistry has been utilized in the synthesis of phosphino-terminated oligomers, from diynes of the type RCtC-R′-CtCR containing a rigid spacer R′ group. In addition, conditions are described that allow facile substitution of the 1-alkynylphosphine by other alkynes in a zirconacyclopentadiene.

Results and Discussion Synthesis and Structural Characterizations of Zirconacyclopropene Complexes. The zirconacyclopropenes used in this study were synthesized by reaction of one equiv of R2PCtCR′ (R ) Et, iPr, or Ph; R′ ) Ph or Mes) with Rosenthal’s complex Cp2Zr(pyr)(η2-Me3SiCtCSiMe3)40 in toluene at ambient temperature. Alkyne-alkyne homocoupling was prevented by careful control of the ratio of alkyne to Cp2Zr. In the case where R ) iPr, Et, or Ph and R′ ) Ph, both the pyridine and Me3SiCtCSiMe3 were displaced from the metal center and a “ligand-free” zirconacyclopropene was formed (1-3, eq 2). On the other hand, when R ) Ph and R′ ) Mes, the pyridine is retained to stabilize the resulting zirconacyclopropene (4, eq 3). Alkynes that incorporate a Lewis base, such as a phosphino group, may be useful coupling partners in reactions of this type, given their potential ability to form stable monoalkyne adducts (20) Johnson, S. A.; Liu, F. Q.; Suh, M. C.; Zurcher, S.; Haufe, M.; Mao, S. S. H.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 4199–4211. (21) Mao, S. S. H.; Tilley, T. D. J. Am. Chem. Soc. 1995, 117, 5365– 5366. (22) Mao, S. S. H.; Liu, F. Q.; Tilley, T. D. J. Am. Chem. Soc. 1998, 120, 1193–1206. (23) Nitschke, J. R.; Zurcher, S.; Tilley, T. D. J. Am. Chem. Soc. 2000, 122, 10345–10352. (24) Nitschke, J. R.; Tilley, T. D. Angew. Chem., Int. Ed. 2001, 40, 2142–2145. (25) Nitschke, J. R.; Tilley, T. D. J. Am. Chem. Soc. 2001, 123, 10183– 10190. (26) Schafer, L. L.; Tilley, T. D. J. Am. Chem. Soc. 2001, 123, 2683– 2684. (27) Schafer, L. L.; Nitschke, J. R.; Mao, S. S. H.; Liu, F. Q.; Harder, G.; Haufe, M.; Tilley, T. D. Chem.-Eur. J. 2002, 8, 74–83. (28) Mao, S. S. H.; Tilley, T. D. Macromolecules 1997, 30, 5566–5569. (29) Buchwald, S. L.; Watson, B. T.; Huffman, J. C. J. Am. Chem. Soc. 1987, 109, 2544–2546. (30) Takahashi, T.; Swanson, D. R.; Negishi, E. Chem. Lett. 1987, 623– 626.

Zirconacyclopropenes 1-3 are probably stabilized by bridging interactions involving donation of the lone-pair on the phosphorus to the open coordination site of a zirconium center, to give dimeric structures with a central, six-membered ring.37,41,42 (31) Vanwagenen, B. C.; Livinghouse, T. Tetrahedron Lett. 1989, 30, 3495–3498.

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The 1H NMR spectra for zirconacyclopropenes 1 and 2 contain resonances for inequivalent Cp ligands, and inequivalent alkyl groups on the phosphino groups suggest a dimeric or higherorder, rigid ring structure. Zirconacyclopropene 3 has a room temperature 1H NMR spectrum that is consistent with a monomeric structure (single Cp resonance at 5.45 ppm and equivalent Ph groups by 13C{1H} NMR spectroscopy). However, this simplified spectrum could result (for example) from a dynamic process in a dimeric structure, which would interconvert axial and equatorial Cp and Ph groups of a six-membered ring in a chair conformation. To investigate this possibility, a variable-temperature NMR study was undertaken. By monitoring the Cp resonance of compound 3, a coalescence temperature of -50 °C was observed. At lower temperatures, inequivalent Cp resonances were observed at 5.34 and 5.29 ppm. This corresponds to a Gibb’s free energy of activation at the coalescence temperature of 11.2(2) kcal/mol. It has been proposed that 31P{1H} NMR chemical shifts might be used to characterize the presence of phosphorus-zirconium interactions in alkynylphosphine complexes of zirconocene.37 The diisopropylphosphino group of zirconacyclopropene 1 has a 31P{1H} chemical shift of 37.0 ppm. The chemical shifts of zirconacyclopropenes 2 and 3 are 14.6 and 18.5 ppm, respectively. For all three complexes, coordination of the alkynylphosphine therefore results in a downfield 31P NMR shift of 50-54 ppm with respect to that of the free alkyne. The base-stabilized zirconacyclopropene 4, which should possess little bonding interaction between phosphorus and zirconium, exhibits a 31 P{1H} chemical shift of 10.6 ppm. This corresponds to a downfield shift of 43 ppm relative to the free alkyne. Thus, while donation of the lone pair to the metal center may have an affect on the chemical shift of the phosphorus, this effect is rather subtle. In the 13C NMR spectra, the most downfield signals are generally associated with a zirconium-bound sp2 carbon atom.43,44 For complexes 1-3, the most downfield resonances are in the range of 197.9-200.9 ppm and correspond to the zirconium-bound carbon with a phenyl group substituent. Resonances for the zirconium-bound carbon with the phosphino group substituent appear in the range of 144.1-154.9 ppm for these three complexes. Thus, sp2 carbon atoms with zirconium and phenyl substituents are observed to resonate 50 ppm downfield of sp2 carbon atoms with zirconium and phosphino group substituents. In contrast, the base-stabilized complex 4 (32) Takahashi, T.; Kageyama, M.; Denisov, V.; Hara, R.; Negishi, E. Tetrahedron Lett. 1993, 34, 687–690. (33) Xi, Z. F.; Hara, R.; Takahashi, T. J. Org. Chem. 1995, 60, 4444– 4448. (34) Hiller, J.; Thewalt, U.; Polasek, M.; Petrusova, L.; Varga, V.; Sedmera, P.; Mach, K. Organometallics 1996, 15, 3752–3759. (35) List, A. K.; Koo, K.; Rheingold, A. L.; Hillhouse, G. L. Inorg. Chim. Acta 1998, 270, 399–404. (36) Miquel, Y.; Igau, A.; Donnadieu, B.; Majoral, J. P.; Dupuis, L.; Pirio, N.; Meunier, P. Chem. Commun. 1997, 279–280. (37) El Harouch, Y.; Cadierno, V.; Igau, A.; Donnadieu, B.; Majoral, J. P. J. Organomet. Chem. 2004, 689, 953–964. (38) Quntar, A. A.; Srebnik, M. Org. Lett. 2001, 3, 1379–1381. (39) Xi, Z. F.; Zhang, W. X.; Takahashi, T. Tetrahedron Lett. 2004, 45, 2427–2429. (40) Rosenthal, U.; Ohff, A.; Baumann, W.; Tillack, A.; Gorls, H.; Burlakov, V. V.; Shur, V. B. Z. Anorg. Allg. Chem. 1995, 621, 77–83. (41) Karsch, H. H.; Grauvogl, G.; Kawecki, M.; Bissinger, P. Organometallics 1993, 12, 2757–2766. (42) Rosa, P.; LeFloch, P.; Ricard, L.; Mathey, F. J. Am. Chem. Soc. 1997, 119, 9417–9423. (43) Mattia, J.; Sikora, D. J.; Macomber, D. W.; Rausch, M. D.; Hickey, J. P.; Friesen, G. D.; Todd, L. J. J. Organomet. Chem. 1981, 213, 441– 450. (44) Sabade, M. B.; Farona, M. F. J. Organomet. Chem. 1986, 310, 311–316.

Miller et al.

Figure 1. ORTEP depiction of the solid-state molecular structure of 1. Hydrogen atoms are omitted for clarity. Ellipsoids are drawn with 50% probabilities. Selected bond lengths (Å), bond angles (deg): Zr-P′, 2.80; Zr-C1, 2.298(3); Zr-C2, 2.219(3); P-C1, 1.806(3); C1-C2, 1.306(4); C2-C3, 1.470(4); Cpcent-Zr-Cpcent, 125.1; C1-Zr-C2, 33.6(1); C1-Zr-P′, 78.9; C1-C2-C3, 141.9(3); P-C1-C2, 133.4(2).

exhibits its most downfield 13C NMR resonance at 184.4 ppm, but this corresponds to the zirconium-bound carbon with the phosphino group substituent. The zirconium-bound carbon with the phenyl group substituent has a similar resonance of 184.0 ppm for compound 4. Therefore, while the 31P NMR shifts provides little diagnostic information, it appears that the resonance of the carbon attached to phosphorus gives some indication that the phosphorus lone-pair is coordinated to the metal center for zirconacyclopropenes 1-3 (Vide infra). The solid state structures of zirconacyclopropenes 1 and 4 were determined by single-crystal X-ray crystallography, and the ORTEP diagrams45 are shown in Figures 1 and 2. As predicted for zirconacyclopropene 1, two Cp2Zr fragments are bridged by two iPr2PCCPh groups to form a central sixmembered ring flanked by two fused, three-membered rings. The structure is centrosymmetric and folded along the P-P′ axis by 53.4° (angle between Zr-C1-P plane and Zr′-C1′-P′ plane). The presence of a rigid, bent ring is also consistent with the NMR data of zirconacyclopropenes 1-3. At 2.80 Å, the Zr-P′ distance of 1 is considerably longer than that for other phosphine-stabilized zirconacyclopropenes such as Cp2Zr(η2(2.70 Å) and Cp 2 Zr(η 2 PhCtCPh)(PMe 3 ) 29,30 HCtC(CH2)3CH3)(PMe3) (2.66 Å). This is likely due to the smaller steric demand and greater electron-donating ability of the PMe3 ligand. The Zr-P′ distance compares well with a similar dimeric diphosphinomethanide zirconocene complex in which the Zr-P distance associated with the bridging Me2PCPMe2 group is 2.75 Å.41 The structure of zirconacyclopropene 4 is very similar to that of the related complex, Cp2Zr(pyr)(η2-Me3SiCtCSiMe3).40 These compounds are best described as pyridine-stabilized zirconacyclopropenes. All bond distances and angles in the two compounds compare well, including the bond distances and angles around the metal center (Zr-Cpcent distance of 2.275 Å (45) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.

Unsymmetrical Zirconacyclopentadienes

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coupled diphosphinozirconacyclopentadienes. For example, reaction of zirconacyclopropene 3 with diphenyl(phenylethynyl)phosphine in toluene at 85 °C for 16 h gives zirconacyclopentadiene 5 with both phosphino groups in the R-positions, as the major product (77%, by 1H NMR spectroscopy of the crude reaction mixture). A minor product, presumably the R,β regiosomer (6) on the basis of its solution NMR spectra, is formed in 23% yield (eq 4). The R,β regiosomer is characterized by a 1H NMR Cp resonance at 5.71 ppm (JH-P ) 1.2 Hz) and 31 P{1H} NMR resonances of -8.5 and -50.0 ppm (4JP-P ) 5 Hz).

Figure 2. ORTEP depiction of the solid-state molecular structure of 4. Hydrogen atoms are omitted for clarity. Ellipsoids are drawn with 50% probabilities. Selected bond lengths (Å), bond angles (deg): Zr-N, 2.449(2); Zr-C1, 2.208(2); Zr-C2, 2.243(2); P-C1, 1.781(2); C1-C2, 1.314(3); C2-C3, 1.482(3); Cpcent-Zr-Cpcent, 128.66(1); C1-Zr-C2, 34.34(8); C2-Zr-N, 103.12(8); C1-C2-C3, 134.7(2); P-C1-C2, 141.7(2).

and Cpcent-Zr-Cpcent bond angle of 128.7°). The C1/C2/N plane is perpendicular to the Cpcent/Zr/Cpcent plane and bisects the Cpcent-Zr-Cpcent angle, as is expected for an 18 electron zirconocene complex. The most notable feature is the regiochemistry of the Ph2PCCMes coordination, which places the mesityl substituent near the pyridine ligand. In addition, the phosphino group is positioned symmetrically within the “wedge” formed by the Cp ligands. It is possible that the greater steric bulk of the mesityl group prevents it from approaching the Cp ligands. Further evidence for the dimeric structures of zirconacyclopropenes 1-3 in solution was obtained by DOSY NMR studies. It was reasoned that the diffusion coefficients of the dimeric complexes would be smaller than those for the monomeric complex 4. The following diffusion coefficients were measured by these investigations: 1, 1.00(3) × 10-9 m2/s; 2, 1.01(3) × 10-9 m2/s; 3, 1.04(1) × 10-9 m2/s; 4, 1.16(5) × 10-9 m2/s. From this it is apparent that zirconacyclopropenes 1-3 have similar diffusion coefficients that are smaller than that measured for monomeric complex 4. The diffusion coefficient is inversely proportional to the hydrodynamic radius, according to the Stokes-Einstein equation.46 To examine whether the difference between diffusion coefficients of the dimeric and monomeric complexes was consistent with the differences in the hydrodynamic radii, the average molecular radii of zirconocene complexes 1 and 4 were computed with Gaussian0347 at the B3LYP48-51/LanL2DZ52 level of theory using the atomic coordinates from the crystal structure data.53 Accordingly, the radius of 1 is 6.07 Å and the radius of 4 is 5.35 Å. The ratio of the diffusion coefficients of 1 to 4 is 0.86 and the ratio of the radii of 4 to 1 is 0.88. Thus, the diffusion coefficients are consistent with dimeric complexes in solution based on comparison of the radii of the two structurally characterized complexes. Reactivity of Zirconacyclopropene Complexes with Alkynes. Zirconacyclopropene complexes 1-4 react with a second equivalent of 1-alkynylphosphine to form the homo(46) Bird, R. B.; Stewart, W. E.; Lightfoot, E. N. Transport Phenomena; John Wiley & Sons, Inc.: New York, 1960.

The solid-state structure of zirconacyclopentadiene 5, determined by single crystal X-ray crystallography, confirmed the expected R,R regiochemistry (Figure 3). The most notable feature of this structure is the donation of the lone-pair of one of the phosphorus atoms to zirconium. This results in a highly acute Zr-C4-P2 bond angle of 89.4(1)°, which is significantly less than the Zr-C1-P1 bond angle of 135.4(1)°. The Zr-P2 dative bond distance of 2.8219(7) Å is somewhat longer than might be expected for complexes of the type Cp2Zr(X)(Y)(PR3) (2.62-2.75 Å).29,30,41,54-56 A similar Zr-P interaction was observed by Majoral and co-workers for a zirconaindene complex with a diphenylphosphino group in the R-position relative to zirconium.37 In contrast to this zirconaindene (47) Frisch, M. J. T. G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; AlLaham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.; Gaussian, revision A.01; Gaussian, Inc.: Wallingford, CT, 2004. (48) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (49) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys 1980, 58, 1200– 1211. (50) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. ReV. B 1988, 37, 785– 789. (51) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980, 72, 650–654. (52) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299–310. (53) Tight convergence criteria were used for the SCF and volume calculations. (54) Kreutzer, K. A.; Fisher, R. A.; Davis, W. M.; Spaltenstein, E.; Buchwald, S. L. Organometallics 1991, 10, 4031–4035. (55) Buchwald, S. L.; Watson, B. T.; Huffman, J. C. J. Am. Chem. Soc. 1986, 108, 7411–7413. (56) Karsch, H. H.; Grauvogl, G.; Deubelly, B.; Muller, G. Organometallics 1992, 11, 4238–4245.

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Figure 3. ORTEP depiction of the solid-state molecular structure of 5. Hydrogen atoms are omitted for clarity. Ellipsoids are drawn with 50% probabilities. Selected bond lengths (Å), bond angles (°): Zr-P1, 3.88; Zr-P2, 2.82; Zr-C1, 2.350(2); Zr-C4, 2.235(2); P1-C1, 1.838(2); P2-C4, 1.744(2); C1-C2, 1.368(3); C2-C3, 1.493(3); C3-C4, 1.349(3); Cpcent-Zr-Cpcent, 132.4; C1-Zr-C4, 71.28(8); Zr-C1-P1, 135.4; Zr-C4-P2, 89.4.

complex, compound 5 exhibits a bending of the zirconacyclopentadiene framework which presumably enhances the interaction of the phosphorus with the metal center. The resulting envelope structure exhibits a fold angle of 28.7° along the C1-C4 axis. This is also accompanied by an elongation of Zr-C1 (vs Zr-C4) by 0.115(2) Å. The room temperature NMR spectra of zirconacyclopentadiene 5 are consistent with a symmetrical structure, indicating a fast dynamic process which exchanges the two phosphorus environments. The 1H NMR Cp resonance appears as one singlet at 5.83 ppm and there is a single 31P{1H} NMR resonance at -16.8 ppm which is upfield from the phosphorus resonance of zirconacyclopropene 3 by 35.3 ppm. A variable temperature 31 P{1H} NMR study was undertaken to measure the activation energy of phosphorus exchange, but decoalesence was not observed down to -90 °C. Cross-couplings of alkynes were investigated by reactions of zirconacyclopropenes 1-4 with tolan and/or 3-hexyne to form unsymmetrical zirconacyclopentadienes. Cross-couplings with zirconacycle 1 were generally performed at 80 °C for 16 h, and those with zirconacycle 3 were carried out at 50 °C for 16 h, to give zirconacyclopentadienes 7-10 (eq 5). In all cases, analysis of the crude reaction mixtures (by 1H NMR spectroscopy) indicates that one product formed in high yield. Reaction of zirconacyclopropene 2 with tolan was not observed until the reaction mixture was heated to 160 °C or higher. At this elevated temperature, control of regioselectivity was not maintained and two products were formed in a nearly statistical ratio (11 and 12, eq 6). Analysis by 1H and 31P{1H} NMR spectroscopy indicates that the major species is β-phosphinozirconacyclopentadiene (12), with a 1H NMR Cp resonance at 6.00 ppm and a 31P{1H} NMR resonance at -51.0 ppm. In this case, the minor product is R-phosphinozirconacyclopentadiene (11), with a 1H NMR Cp resonance at 5.63 ppm (JH-P ) 1.2 Hz) and a 31 P{1H} NMR resonance at -39.5 ppm. The Lewis basestabilized zirconacyclopropene 4 was found to readily react with tolan at room temperature within 16 h to give 13 (eq 7). The only observed regioisomer contains the phosphino group in the

Miller et al.

Figure 4. ORTEP depiction of the solid-state molecular structure of 8. Hydrogen atoms are omitted for clarity. Ellipsoids are drawn with 50% probabilities. Selected bond lengths (Å), bond angles (deg): Zr-P1, 2.78; Zr-C1, 2.366(3); Zr-C4, 2.248(3); P1-C4, 1.738(3); C1-C2, 1.344(4); C2-C3, 1.489(4); C3-C4, 1.351(4); Cpcent-Zr-Cpcent, 129.4; C1-Zr-C4, 69.7; Zr-C4-P1, 87.4.

R-position, as determined by 1D and 2D (NOESY, HMQC, HMBC) NMR experiments. Thus, while dimeric zirconacyclopropenes 1-3 required elevated temperatures to react with 3-hexyne or tolan, the reaction of tolan with complex 4 occurred at room temperature on the same time scale. Presumably, this difference reflects the slower rate by which the dimeric species dissociate to give the required reaction intermediate, a monomeric zirconacyclopropene complex.

The solid-state structures of the unsymmetrical zirconacyclopentadienes 8 and 10 (eq 5), determined by single crystal X-ray crystallography, confirm that for each complex the phosphino group is in the R-position (Figures 4 and 5). The significant difference between the two structures is that 8, which is substituted with a diisopropylphosphino group, exhibits a Zr-P bonding interaction while for zirconacyclopentadiene 10, containing a diphenylphosphino group, there is no interaction of the lone-pair on phosphorus with the metal center. This

Unsymmetrical Zirconacyclopentadienes

Organometallics, Vol. 28, No. 4, 2009 1257 Table 1. Substitution of 1-Alkynylphosphines in Zirconacyclopentadienes 7, 9, and 13 by Tolan to Form Cp2Zr[2,3,4,5-Ph4C4]

Figure 5. ORTEP depiction of the solid-state molecular structure of 10. Hydrogen atoms are omitted for clarity. Ellipsoids are drawn with 50% probabilities. Selected bond lengths (Å), bond angles (deg): Zr-P1, 3.75; Zr-C1, 2.239(7); Zr-C4, 2.278(7); P1-C4, 1.819(7); C1-C2, 1.341(9); C2-C3, 1.509(9); C3-C4, 1.375(8); Cpcent-Zr-Cpcent, 135.7; C1-Zr-C4, 79.4(3); Zr-C4-P1, 132.4(4).

difference is consistent with a very weak Zr-P bonding interaction for the diphenylphosphino substituent of compound 5, as observed in the VT NMR study (Vide supra). This difference may be largely ascribed to the greater electrondonating ability of the diisopropylphosphino group. Zirconacyclopentadiene 8 is structurally similar to compound 5, with a Zr-P bond which is slightly shorter (2.7774(9) Å) than that in the latter complex (2.8219(7) Å). The zirconacyclopentadiene framework of 8 is folded along the C1-C4 axis by 13.6°, and this appears to be associated with a contraction of the Zr-C bond for the carbon attached to the phosphino group, relative to the carbon attached to the ethyl group, of 0.118(3) Å. This distortion allows for a stronger Zr-P interaction, as reflected in the acute Zr-C4-P1 bond angle of 87.4(1)°. Zirconacyclopentadiene 10, which has no Zr-P bonding interaction in the solid state, has a Zr-P1 distance of 3.773(2) Å and a Zr-C4-P1 bond angle of 132.4(4)°. The structure of complex 10 is noteworthy because of the distorted zirconacyclopentadiene framework. Unlike most zirconacyclopentadienes which have a nearly planar framework, no four atoms of the zirconacyclopentadiene ring of 10 are in the same plane. The deviations from planarity vary from 0.1 - 0.55 Å. The structure of zirconacycle 10 is also in contrast to the structures of 5 and 8, which have an envelope framework with the four carbons of the butadiene backbone in the same plane and the Zr out of the plane by 0.89 and 0.44 Å for 5 and 8, respectively. Selective Alkyne-Alkyne Exchange in Zirconacyclopentadienes. It has previously been observed that sterically demanding substituents, such as -SiMe3 and -CMe3, promote reversible fragmentations of a zirconacyclopentadiene ring.19,57-59 In principle, this reactivity should allow selective transformations of unsymmetrical zirconacyclopentadienes, as illustrated in eq (57) Erker, G.; Zwettler, R. J. Organomet. Chem. 1991, 409, 179–188. (58) Takahashi, T.; Kotora, M.; Hara, R.; Xi, Z. F. Bull. Chem. Soc. Jpn. 1999, 72, 2591–2602. (59) Miller, A. D.; McBee, J. L.; Tilley, T. D. J. Am. Chem. Soc. 2008, 130, 4992–4999.

8. Consistent with this, zirconacycle 13 was transformed to Cp2Zr[2,3-Ph2-4,5-Et2C4] by selective substitution of the Ph2PCCMes group with 3-hexyne. This reaction was observed to occur in the presence of a slight excess of 3-hexyne (1.1 equiv) at 80 °C in benzene-d6, to give free Ph2PCtCMes and the unsymmetrical zirconacyclopentadiene Cp2Zr[2,3-Ph2-4,5Et2C4] (1H NMR: 5.98 ppm, Cp). Complete substitution was observed to occur in less than 10 h, and was accompanied by a small amount (5%) of the symmetrical tetraphenylzirconacyclopentadiene.

To examine the influence of the substituents on the rates of alkynylphosphine substitution in zirconacyclopentadienes, reactions of 7, 9, and 13 with a slight excess of tolan were monitored (100 °C, benzene-d6). These reactions cleanly form tetraphenylzirconacyclopentadiene, and substituents on the 1-alkynylphosphine were found to have a significant influence on the rates of alkyne substitution (Table 1). The substitution of Ph2PCtCPh with tolan in zirconacyclopentadiene 9 was significantly slower than the corresponding substitution reactions of iPr2PCtCPh and Ph2PCtCMes for zirconacycles 7 and 13, respectively, which were observed to proceed at similar rates. Alkyne substitutions of zirconacyclopentadienes have been shown both experimentally59 and theoretically20,60 to proceed dissociatively through a zirconacyclopropene intermediate. Therefore, it might seem reasonable that sterically hindered substituents on the leaving alkyne would lead to a faster rate of dissociation (and therefore alkyne exchange). However, it is worth noting that steric hindrance associated with the bis(cyclopentadienyl) ligand set retards such reactions.59 As shown in Table 1, the least sterically demanding set of alkyne (60) Imabayashi, T.; Fujiwara, Y.; Nakao, Y.; Sato, H.; Sakaki, S. Organometallics 2005, 24, 2129–2140.

1258 Organometallics, Vol. 28, No. 4, 2009

substituents (-PPh2 and -Ph of zirconacycle 9) corresponds to the slowest exchange reaction. Zirconacycles with larger substituents in the R- (-PiPr2, 7) and β- (-Mes, 13) position undergo faster exchange reactions. Thus, for these exchange reactions, bulky substituents on the zirconacyclopentadiene ring appear to lower the barrier for “alkyne decoupling” at the metal center. Functionalized Phosphines and Phosphine Oxides from r-Phosphinozirconacyclopentadienes. Zirconacyclopentadienes have been transformed, via metathesis reactions at the metal-center, to a wide array of organic compounds.4-17 To evaluate the utility of these alkyne couplings for the synthesis of functionalized phosphorus compounds, zirconium-transfer reactions of zirconacyclopentadienes 9 and 10 were examined. Two types of transformations were examined: protonolysis to form a substituted butadiene,4 and reaction of sulfur dioxide with zirconacyclopentadienes to form substituted thiophene oxides.16 Zirconacyclopentadiene 9 was treated with 10 equiv of benzoic acid at room temperature to give butadienylphosphine 14 in 88% yield after purification by flash column chromatography (eq 9). Solid 14 is stable for long periods (several months) in air, but it significantly oxidizes within hours in solution to the corresponding phosphine oxide as indicated by a characteristic downfield shift of the phosphorus resonance in the 31 P{1H} NMR spectrum (-23.6 ppm vs 18.4 ppm). However, solutions of 14 may be handled briefly in air. This compound was previously synthesized by Takahashi and co-workers from the in situ generated zirconacycle 14 and was shown to have the desired regiochemistry by single-crystal X-ray analysis.39 The butadienylphosphine oxide 15 was synthesized in a similar manner. Zirconacyclopentadiene 10 was treated with 10 equiv of benzoic acid and then 2 equiv of H2O2 to ensure complete oxidation of the phosphorus (eq 10). The resulting butadienylphosphine oxide was purified by flash column chromatography to give the product in 82% yield. The resulting 31P{1H} NMR spectrum contains a chemical shift of 17.4 ppm and the IR spectrum has an absorption at 1168 cm-1 assigned to the phosphine oxide (PdO).

The synthesis of thiophene oxide 16 was accomplished by exposure of a THF solution of zirconacyclopentadiene 9 to an atmosphere of sulfur dioxide for 20 min. After aqueous workup and column chromatography 16 was obtained as a bright yellow solid in 75% yield (eq 11). In this case, oxidation of the phosphorus moiety was a result of exposure to the ambient atmosphere during workup. To rule out oxidation of the phosphorus by the sulfur dioxide, an NMR scale experiment was conducted in a sealed tube. This investigation revealed that the reaction of 9 with SO2 cleanly gave a new compound that exhibits a 31P{1H} NMR shift of -18.3 ppm, attributed to (3,4,5triphenylthiophen-2-yl oxide)diphenylphosphine. Thiophene oxide 16, with the oxidized phosphorus moiety, exhibits a downfield chemical shift of 17.3 ppm. The IR spectrum is also consistent with the assigned structure for 16, as it contains

Miller et al.

absorptions assigned to phosphine oxide (1199 cm-1) and sulfoxide (1049 cm-1) groups but no absorption was observed for the asymmetric SdO stretch of a sulfone (1300-1335 cm-1).61

Extended π-Systems from Reactions of Diynes with Zirconacyclopropenes. The zirconocene-coupling of diynes has proven to be an efficient and versatile pathway to a variety of conjugated polymers and oligomers.4,16,20-22,28,62-66 Thus, it was of interest to study the possible use of zirconocenephosphinoalkyne complexes in the construction of phosphinoterminated, conjugated oligomers. In addition, it was thought that oligomers derived from such zirconocene reagents might allow a degree of “end-group control” for the synthesis of functionalized oligomers, via alkyne-exchange reactions. Preliminary results from such studies are described below. For synthesis of a linear, conjugated system, a starting diyne must possess a rigid, conjugated spacer group as well as terminal, β-directing groups. It has previously been shown that 1,4-bis(pentafluorophenylethynyl)benzene is useful in this regard.20 This diyne was found to react with 2 equiv of zirconacyclopropene 3 at 50 °C, to give the bis(zirconacycle) 17. Similarly, 4 reacted with the diyne at room temperature to produce 18 (eq 12). These compounds were purified by washing with pentane, and were isolated in 44-67% yield. Compounds 17 and 18 are slightly soluble in aromatic solvents such as benzene and toluene and were characterized by 1H, 31P{1H}, and 19F NMR spectroscopy and elemental analysis. The 31P{1H} NMR chemical shifts of -27.4 ppm and -25.8 ppm for bis(zirconacycles) 17 and 18, respectively, are indicative of a phosphino group in the R-position of a zirconacyclopentadiene (Vide supra).37

Bis(zirconacycles) 17 and 18 contain two zirconocene fragments that may function as useful reaction centers, and terminal phosphino groups that offer intriguing binding and/or linking sites. Bis(zirconacycle) 17 (generated in situ) was converted to the corresponding bis(butadienyl)benzene 19 by hydrolysis with a degassed, aqueous HCl solution to avoid oxidation of the phosphino group (eq 13). The product was purified by an aqueous workup with a saturated NaHCO3 solution to remove (61) Coates, J. Interpretation of Infrared Spectra: A Practical Approach; Meyers, R. A., Ed.; John Wiley & Sons Ltd: Chichester, 2000. (62) Lucht, B. L.; Buretea, M. A.; Tilley, T. D. Organometallics 2000, 19, 3469–3475. (63) Lucht, B. L.; Mao, S. S. H.; Tilley, T. D. J. Am. Chem. Soc. 1998, 120, 4354–4365. (64) Mao, S. S. H.; Tilley, T. D. J. Organomet. Chem. 1996, 521, 425– 428. (65) Mao, S. S. H.; Tilley, T. D. Macromolecules 1996, 29, 6362–6364. (66) Suh, M. C.; Jiang, B. W.; Tilley, T. D. Angew. Chem., Int. Ed. 2000, 39, 2870–2873.

Unsymmetrical Zirconacyclopentadienes

the excess acid, and subsequent washing of the resulting organic solid with MeOH gave the analytically pure compound in 56% yield. The 31P{1H} NMR spectrum of 19 has a single resonance at -22.4 ppm which is consistent with an unoxidized phosphino group.

As observed for zirconacycles 7, 9, and 13, the R2PCCR′ group of the zirconacyclopentadienes may be selectively substituted in the presence of a smaller alkyne. To demonstrate the exchange of end groups in a conjugated bis(zirconacycle), a solution of 18 was heated in the presence of 3 equiv of tolan to give the slightly soluble bis(zirconacycle) 20 (eq 14). The solid product was washed with pentane to give the analytically pure compound in 25% yield. In general, this approach should prove useful for the introduction of various end groups onto oligomers obtained by zirconocene-coupling methods.

Organometallics, Vol. 28, No. 4, 2009 1259 oxygen-free solvents were used. Olefin impurities were removed from pentane by treatment with concentrated H2SO4, 0.5 N KMnO4 in 3 M H2SO4, and saturated NaHCO3. Pentane was then dried over MgSO4, stored over activated 4 Å molecular sieves, and distilled from potassium benzophenone ketyl under a nitrogen atmosphere. Toluene was purified by stirring with concentrated H2SO4, washing with saturated NaHCO3, then drying over CaCl2 and distillation from sodium under a nitrogen atmosphere. Spectrophotometric grade diethyl ether and reagent grade THF were distilled from sodium benzophenone ketyl under a nitrogen atmosphere. Acetonitrile was refluxed over P2O5 and distilled under a nitrogen atmosphere. Benzene-d6 was vacuum distilled from sodium/ potassium alloy and benzophenone. NMR spectra were recorded on a Bruker AVB-400 instrument operating at 400.1 MHz (1H), 100.7 MHz (13C), 376.5 MHz (19F), and 162 MHz (31P), with a Bruker AV-300 instrument operating at 300.1 MHz (1H), or with a Bruker DRX-500 instrument operating at 500.1 MHz (1H) and 125.8 MHz (13C). Chemical shifts are reported in ppm relative to SiMe4 and are referenced internally to residual solvent resonances (1H, 13C) or externally to 85% H3PO4 (31P). 19F NMR spectra were referenced internally by a C6F6 standard relative to CFCl3 at 0 ppm. Splitting patterns are designated as s, singlet; d, doublet; t, triplet; q, quartet; sept, septet; m, multiplet; v, virtual. Infrared spectra were recorded as thin films on NaCl plates or as KBr pellets using a Mattson FTIR spectrometer at a resolution of 4 cm-1. Elemental analyses were performed by the Microanalytical Laboratory in the College of Chemistry at the University of California, Berkeley.

Experimental Section

The compounds Cp2Zr(pyr)(η2-Me3SiCtCSiMe3)23 and 1,4bis(pentafluorophenylethynyl)benzene20 were synthesized according to published procedures. All other chemicals were obtained from commercial suppliers and used as received. The n-butyl lithium reagent was used as a 1.6 M solution in hexanes. Diisopropyl(phenylethynyl)phosphine. To a cold (0 °C) solution of phenylacetylene (0.69 mL, 6.3 mmol) in diethyl ether (60 mL) was added n-BuLi (3.9 mL, 6.3 mmol) dropwise via syringe. The solution was stirred for 10 min before the ice bath was removed, and it was then stirred for an additional 1.5 h. The reaction mixture was then cooled with a dry ice/isopropanol bath and chlorodiisopropylphosphine (1.0 mL, 6.3 mmol) was added dropwise via syringe. The reaction mixture was slowly warmed to ambient temperature and was stirred for 16 h. The yellow solution with a white precipitate was concentrated under reduced pressure and then pentane (60 mL) was added and the lithium chloride precipitate was removed by cannula filtration. The solution was concentrated under vacuum and the resulting yellow oil was purified by short path vacuum transfer at 0.05 mTorr and 70 °C giving a 59% yield (0.81 g, 3.7 mmol) of the desired compound, which was spectroscopically identified.671H NMR (400 MHz, C6D6): δ 7.47 (m, 2H), 7.01 (m, 3H), 1.93 (sept, 3JH-H ) 7.0 Hz, 2H), 1.34 (dd, 3JH-H ) 7.0 Hz, 3JH-P ) 11.0 Hz, 6H), 1.17 (dd, 3JH-H ) 7.0 Hz, 3JH-P ) 16.8 Hz, 6H). 31P{1H} NMR (162 MHz, C6D6): δ -12.5. Diethyl(phenylethynyl)phosphine. See the preparation of diisopropyl(phenylethynyl)phosphine for the synthetic protocol. The amounts of reagents used were phenylacetylene (0.49 mL, 4.5 mmol), n-BuLi (2.8 mL, 4.5 mmol), and chlorodiethylphosphine (0.50 mL, 4.1 mmol). Purification by short path vacuum transfer at 0.05 mTorr and 45 °C resulted in a light-yellow oil, identified spectroscopically,67 in 52% yield (0.41 g, 2.1 mmol). 1H NMR (400 MHz, C6D6): δ 7.41 (m, 2H), 6.92 (m, 3H), 1.61 (qt, 4JH-H ) 3JH-H ) 7.6 Hz, 2H), 1.46 (qt, 4JH-H ) 3JH-H ) 7.6 Hz, 2H), 1.13 (m, 6H). 31P{1H} NMR (162 MHz, C6D6): δ -39.3.

General Procedures. Unless otherwise noted, all manipulations were performed under a dry, nitrogen atmosphere using either standard Schlenk techniques or a nitrogen-filled glovebox. Dry,

(67) Aguiar, A. M.; Irelan, J. R. S.; Morrow, C. J.; John, J. P.; Prejean, G. W. J. Org. Chem. 1969, 34, 2684–2686.

Conclusions Zirconacyclopropenes derived from 1-alkynylphosphines are useful reagents for the synthesis of unsymmetrical zirconacyclopentadienes. For either dimeric zirconacyclopropenes or related Lewis base-stabilized adducts, efficient cross-couplings with an additional equiv of alkyne occur regioselectively to give a zirconacyclopentadiene containing a phosphino group in the R-position. This regiocontrol is observed for diisopropylphosphino and diphenylphosphino groups, and is presumed to be due to interaction of the phosphino group with zirconium, possibly through a stabilizing Zr-P interaction in the transition state. Clearly, this type of Zr-P bonding is characteristic of several zirconacyclopentadienes with R-phosphino substituents. However, it should be noted that it is difficult at this time to rule out a purely steric factor, which may also direct the phosphino groups into the R-position. Zirconacyclopentadienes containing the R2PCCR′ group are labile, such that the 1-alkynylphosphines are readily substituted for a less bulky alkyne. The observed coupling reactions also represent a potentially useful approach for the synthesis of well-defined oligomers with functional end groups. For example, an oligomer terminated with an alkynyl group may be functionalized with a phosphino group in a “click”-type reaction with a phosphine-containing zirconacyclopropene. Such phosphino groups may be of use in the organization of conjugated oligomers into hybrid, metalcontaining materials.

1260 Organometallics, Vol. 28, No. 4, 2009 Diphenyl(phenylethynyl)phosphine. This procedure is a modification of a procedure described in the literature.68 To a cold (0 °C) solution of phenylacetylene (5.0 mL, 46 mmol) in 250 mL of diethyl ether was added 28 mL of a 1.6 M solution of n-BuLi in hexane while the mixture was efficiently stirred. The reaction mixture was allowed to warm to room temperature over 2.5 h and was then cooled to -78 °C in a dry ice/acetone bath. Diphenylchlorophosphine (8.2 mL, 46 mmol) was then slowly added to this solution. The dry ice/acetone bath was removed and the solution was allowed to stir at room temperature for 3 h. The reaction mixture was exposed to the atmosphere and the solvent was removed under vacuum and the residue was extracted with pentane (200 mL). The solution was filtered and the solvent was removed under vacuum. The resulting solid was dissolved in ethanol (75 mL) and the resulting solution was then cooled to -30 °C overnight. The white crystals that formed were collected and dried under vacuum. Yield: 72% (9.4 g). mp: 40-41 °C (lit. 43 °C).681H NMR (400 MHz, CDCl3): δ 7.69 (m, 4H), 7.55 (m, 2H), 7.35 (m, 9H). 31 P{1H} NMR (162 MHz, CDCl3): δ -33.5. IR (cm-1): 3054 (w), 2919 (w), 2161 (w, CtC), 1488 (m), 1434 (s), 1095 (w), 1025 (w), 838 (w), 751 (s), 691 (s), 507 (m), 451 (w). Diphenyl(mesitylethynyl)phosphine. The mesitylethyne (1.89 g, 13.1 mmol) was dissolved in ether (250 mL) and then this solution was cooled with an ice bath. A solution of n-BuLi (8.2 mL, 13.1 mmol) in hexanes was then added dropwise, the ice bath was removed, and the reaction mixture was allowed to stir at ambient temperature for an hour. The reaction mixture was then cooled with a dry ice/isopropanol bath and chlorodiphenylphosphine (2.35 mL, 13.1 mmol) was slowly added. The reaction mixture was allowed to slowly warm to ambient temperature while stirring over the next 16 h. The reaction mixture was exposed to the atmosphere and then filtered through silica gel and concentrated under vacuum. The resulting solid was crystallized from a pentane solution at -30 °C resulting in white crystals in 62% yield (2.68 g, 8.2 mmol). mp: 72-73.5 °C. 1H NMR (400 MHz, C6D6): δ 7.81 (m, 4H), 7.10 (m, 4H), 7.03 (m, 2H), 6.64 (s, 2H), 2.40 (s, 6H), 2.03 (s, 3H). 13 C{1H} NMR (100.7 MHz, C6D6): δ 141.4 (d,3JC-P ) 1 Hz), 138.9, 138.1 (d, 1JC-P ) 8 Hz), 133.5, 133.3, 129.5, 129.3 (d, 2JC-P ) 7 Hz), 128.5, 120.6, 107.0 (d, 2JC-P ) 4 Hz), 94.2 (d, 1JC-P ) 6 Hz), 21.7, 21.6. 31P{1H} NMR (162 MHz, C6D6): δ -32.5. IR (cm-1): 3054 (m), 2915 (m), 2853 (w), 2148 (m, CtC), 1609 (w), 1478 (m), 1435 (m), 1376 (w), 1227 (w), 1094 (w), 1026 (w), 853 (m), 811 (w), 740 (m), 695 (s), 579 (w), 510 (m). Anal. calcd for C23H21P: C, 84.12; H, 6.45. Found: C, 83.97; H, 6.46. [Cp2Zr(η2-iPr2PCCPh)]2 (1). A solution of diisopropyl(phenylethynyl)phosphine (0.40 g, 1.8 mmol) in toluene (20 mL) was cannula-transferred to a flask containing Cp2Zr(pyr)(η2Me3SiCtCSiMe3) (0.86 g, 1.8 mmol). The reaction mixture was then stirred at ambient temperature for 16 h. The toluene was removed under vacuum and the resulting solid was washed with diethyl ether (2 × 20 mL) and dried under vacuum to give a yellow solid in 58% yield (0.46 g, 0.50 mmol). X-ray quality crystals were grown by layering a solution of diisopropyl(phenylethynyl)phosphine in toluene over a toluene solution of Cp2Zr(pyr)(η2Me3SiCtCSiMe3) and allowing reaction to occur over 2 days. mp: 192 °C, dec 1H NMR (400 MHz, C6D6): δ 7.25 (m, 4H), 6.98 (m, 1H), 5.63 (s, 5H), 5.46 (s, 5H), 2.87 (m, 1H), 2.41 (m, 1H), 1.34 (m, 6 H), 1.16 (dd, 3JH-H ) 7.5 Hz, 3JH-P ) 14.0 Hz, 3H), 1.05 (dd, 3JH-H ) 3JH-P ) 6.5 Hz, 3H). 13C{1H} NMR (125.8 MHz, C6D6): δ 199.2 (Cp2Zr(η2-iPr2PCtCPh)), 172.8 (Ph), 154.9 (Cp2Zr(η2i Pr2PCtCPh)), 127.9 (Ph), 123.4 (Ph), 122.4 (Ph), 106.1 (Cp), 105.1 (Cp), 31.5 (iPr), 30.9 (iPr), 23.2 (iPr), 22.2 (iPr), 20.7 (iPr), 1.8 (iPr). 31 P{1H} NMR (162 MHz, C6D6): δ 37.0. Anal. calcd for C24H29PZr: C, 65.56; H, 6.65. Found: C, 65.51; H, 6.36. (68) Samb, A.; Demerseman, B.; Dixneuf, P. H.; Mealli, C. Organometallics 1988, 7, 26–33.

Miller et al. [Cp2Zr(η2-Et2PCCPh)]2 (2). See the preparation of zirconacyclopropene 1 for the synthetic protocol. The amounts of reagents used were diethyl(phenylethynyl)phosphine (0.10 g, 0.5 mmol) and Cp2Zr(pyr)(η2-Me3SiCtCSiMe3) (0.25 g, 0.5 mmol). A yellow solid was obtained in a 65% yield (0.14 g, 0.17 mmol). 1H NMR (400 MHz, C6D6): δ 7.30 (t, 3JH-H ) 7.6 Hz, 2H), 7.16 (overlap with residual solvent, 2H), 7.04 (m, 1H), 5.37 (s, 5H), 5.35 (s, 5H), 2.00 (m, 2H), 1.65 (qd, 2JH-H ) 3JH-H ) 7.4 Hz, 1H), 1.29 (qd, 2JH-H ) 3JH-H ) 7.6 Hz, 1H), 0.93 (m, 3H), 0.63 (m, 3H). 13C{1H} NMR (125.8 MHz, C6D6): δ 200.9 (vt, 2JC-P ) 21 Hz, Cp2Zr(η2Et2PCtCPh), 156.4 (i-Ph), 144.3 (vt, 1JC-P ) 30 Hz, Cp2Zr(η2Et2PCtCPh), 128.9 (m-Ph), 123.3 (p-Ph), 121.7 (o-Ph), 105.3 (Cp), 104.0 (Cp), 19.3 (Et), 18.2 (vdd, 1JC-P ) 24 Hz, 1JC-P ) 10 Hz, Et), 9.2 (Et), 8.2 (vt, 2JC-P ) 4 Hz, Et). 31P{1H} NMR (162 MHz, C6D6): δ 14.6. Anal. calcd for C24H29PZr: C, 64.19; H, 6.12. Found: C, 64.40; H, 5.95. [Cp2Zr(η2-Ph2PCCPh)]2 (3). A mixture of diphenyl(phenylethynyl)phosphine (0.30 g, 1.1 mmol) and Cp2Zr(pyr)(η2Me3SiCtCSiMe3) (0.50 g, 1.1 mmol) was cooled to -78 °C and toluene (50 mL) was added via cannula. The dry ice/acetone bath was removed and the solution was then stirred for 16 h at ambient temperature. The solvent was removed under vacuum and then pentane (50 mL) was added via cannula. The solution was sonicated for 1 h and then the solvent was removed via cannula filtration, to give a yellow solid that was then dried under vacuum. Yield: 67% (0.36 g, 0.35 mmol). mp: 151-153 °C, dec 1H NMR (400 MHz, C6D6): δ 7.48 (m, 4H), 7.22 (m, 4H), 6.89 (m, 7H), 5.45 (s, 10H). 13 C{1H} NMR (125.8 MHz, C6D6): δ 197.9 (d, JC-P ) 46 Hz, Cp2Zr(η2-Ph2PCtCPh)), 152.7 (Ph), 144.1 (d, JC-P ) 80 Hz, Cp2Zr(η2-Ph2PCtCPh)), 141.1 (Ph), 134.5 (Ph), 128.8 (Ph), 128.1 (m, Ph), 124.3 (Ph), 124.0 (Ph), 105.8 (Cp). 31P{1H} NMR (162 MHz, C6D6): δ 18.5. IR (cm-1): 3050 (m), 3017 (w), 2958 (w), 1681 (m), 1630 (w), 1585 (m), 1478 (m), 1434 (m), 1364 (w), 1260 (w), 1166 (w), 1089 (w), 1024 (m), 794 (s), 696 (s), 543 (w), 499 (m). Anal. calcd for C47H41PZr: C, 77.54; H, 5.68. Found: C, 77.44; H, 5.57. Cp2Zr(η2-Ph2PCtCMes)(pyr) (4). Diphenyl(mesitylethynyl)phosphine (0.469 g, 1.4 mmol) and Cp2Zr(pyr)(η2-Me3SiCtCSiMe3) (0.706 g, 1.5 mmol) were cooled in a dry ice/isopropanol bath and then toluene (20 mL) was added. The reaction mixture was stirred for 0.5 h at this temperature and then the bath was removed and the reaction mixture was stirred at ambient temperature for 16 h. The solvent was removed under vacuum and the resulting solid was washed with ether (30 mL) to produce an orange solid in 82% yield (0.73 g, 1.2 mmol). mp: 160 °C, dec 1H NMR (400 MHz, C6D6): δ 8.49 (m, 2H), 7.70 (m, 4H), 7.13 (m, 4H), 7.06 (m, 2H), 6.73 (s, 2H), 6.59 (m, 1H), 6.22 (m, 2H), 5.64 (s, 10H), 2.22 (s, 3H), 2.17 (s, 6H). 13C{1H} NMR (125.8 MHz, C6D6): δ 184.4 (d, 1 JC-P ) 52 Hz, Cp2Zr(η2-Ph2PCtCMes)), 184.0 (Cp2Zr(η2Ph2PCtCMes)), 154.72 (o-pyr), 144.4 (d, 3JC-P ) 4 Hz, i-Mes), 141.1 (d, 1JC-P ) 11 Hz, i-Ph), 137.2 (p-pyr), 134.6 (d, 2JC-P ) 20 Hz, o-Ph), 132.4 (d, 4JC-P ) 1 Hz, o-Mes), 131.8 (p-Mes), 128.7 (m-Mes), 128.4 (m-Ph), 128.1, (p-Ph), 124.0 (m-pyr), 107.9 (Cp), 21.9, (d, 5JC-P ) 6 Hz, o-Me), 21.4 (p-Me). 31P{1H} NMR (162 MHz, C6D6): δ 10.6. Anal. calcd for C38H36NPZr: C, 72.57; H, 5.77; N, 2.23. Found: C, 72.25; H, 5.58; N, 2.18. Cp2Zr[2,5-(Ph2P)2-3,4,-Ph2C4] (5). A solution of zirconacylopropene 3 (0.14 g, 0.14 mmol) and diphenyl(phenylethynyl)phosphine (0.08 g, 0.28 mmol) in toluene (7 mL) was heated at 85 °C for 16 h. The solvent was removed under vacuum and the resulting solid was washed with pentane (3 × 15 mL) to produce a redorange solid in 73% yield (0.16 g, 0.20 mmol). 1H NMR (500 MHz, C6D6): δ 7.56 (m, 8H), 7.20 (m, 4H), 6.97 (m, 12H), 6.75 (t, 3JH-H ) 7.8 Hz, 4H), 6.65 (m, 2H), 5.83 (s, 10H). 13C{1H} NMR (125.8 MHz, C6D6): δ 185.7 (dd, 1JC-P ) 57 Hz, 3JC-P ) 3 Hz, -ZrC(Ph2Ph)dC(Ph)-), 162.6 (dd, 2JC-P ) 20 Hz, 3JC-P ) 9 Hz, -ZrC(Ph2P)dC(Ph)-), 143.6 (m, Ph), 139.1 (d, JC-P ) 8 Hz, Ph),

Unsymmetrical Zirconacyclopentadienes 134.9 (d, JC-P ) 17 Hz, Ph), 130.3 (Ph), 128.6 (Ph), 128.4 (Ph), 127.5 (Ph), 126.1 (Ph), 108.9 (Cp).31P{1H} NMR (162 MHz, C6D6): δ -16.8. Anal. calcd for C50H40P2Zr: C, 75.63; H, 5.08. Found: C, 75.25; H, 5.00. Cp2Zr[2-iPr2P-3,4,5-Ph3C4] (7). A solution of zirconacyclopropene 1 (0.25 g, 0.3 mmol) and tolan (0.10 g, 0.6 mmol) in toluene (10 mL) was heated at 80 °C for 16 h. The resulting solution was concentrated to 5 mL and then pentane was added until a small amount of precipitate formed. The solution was then cooled to -80 °C for 18 h, and then the solvent was removed via cannula filtration. The resulting solid was dried under vacuum to give an orange solid in 58% yield (0.20 g, 0.3 mmol). 1H NMR (300 MHz, C6D6): δ 7.37 (m, 2H), 7.16 (m, overlaps with residual solvent peak), 6.95 (m, 7H), 6.74 (tt, 3 JH-H ) 7.2 Hz, 1H), 5.78 (d, 4JH-P ) 1.2 Hz, 10H), 1.98 (sept, 3JH-H ) 7.5 Hz, 2H), 1.20 (dd, 3JH-H ) 7.5 Hz, 3JH-P ) 12.9 Hz, 6H), 0.79 (dd, 3JH-H ) 7.5 Hz, 3JH-P ) 15.9 Hz, 6H). 13C{1H} NMR (125.8 MHz, C6D6): δ 210.9 (d, 3JC-P ) 10 Hz, -ZrC(Ph)dC(Ph)-), 170.7 (d, 1JC-P ) 68 Hz, -ZrC(iPr2P)dC(Ph)-), 165.1 (d, 2JC-P ) 15 Hz, -ZrC(iPr2P)dC(Ph)-), 155.9 (Ph), 154.7 (d, 3JC-P ) 29 Hz, -ZrC(Ph)) C(Ph)-), 145.4 (d, 3JC-P ) 8 Hz, Ph), 142.6 (d, 4JC-P ) 5 Hz, Ph), 132.0 (Ph), 129.1 (Ph), 128.39 (Ph), 128.2 (Ph), 127.7 (Ph), 127.4 (Ph), 127.0 (Ph), 125.2 (Ph), 123.4 (Ph), 105.5 (Cp), 27.8 (d, 1JC-P ) 6 Hz, iPr), 22.2 (iPr), 21.3 (d, 2JC-P ) 8 Hz, iPr).31P{1H} NMR (162 MHz, C6D6): δ -33.3. Anal. calcd for C38H39PZr: C, 73.86; H, 6.36. Found: C, 73.80; H, 6.30. Cp2Zr[2-iPr2P-3-Ph-4,5-Et2C4] (8). To a solution of zirconacylopropene 1 (0.21 g, 0.24 mmol) in toluene (10 mL) was added 3-hexyne (60 µL, 0.53 mmol). The solution was placed in an oil bath and was heated at 80 °C for 16 h. The solvent was removed under vacuum and to the resulting crude solid was added pentane (15 mL). The insoluble solids were removed by cannula filtration and the resulting solution was then cooled to -30 °C for 18 h. The solvent was removed via cannula filtration and the solid was dried under vacuum resulting in a red-orange solid in 72% yield (0.18 g, 0.35 mmol). 1H NMR (400 MHz, C6D6): δ 7.32 (m, 2H), 7.16 (m, 2H), 7.08 (m, 1H), 5.72 (d, 3JC-P ) 1.2 Hz, 10H), 2.75 (q, 3JH-H ) 3.6 Hz, 2H), 2.43 (q, 3JH-H ) 3.2 Hz, 2H), 1.68 (dqq, 3JH-H ) 2 JH-P ) 7.2 Hz, 2H), 1.44 (t, 3JH-H ) 7.6 Hz, 3H), 1.02 (m, 9H), 0.91 (dd, 3JH-H ) 7.2 Hz, 3JH-P ) 15.6 Hz, 6H). 13C{1H} NMR (125.8 MHz, C6D6): δ 207.1 (d, 3JC-P ) 9 Hz, -ZrC(Et)dC(Et)-), 169.4 (d, 2JC-P ) 15 Hz, -ZrC(iPr2P))C(Ph)-), 163.6 (d, 1JC-P ) 68 Hz, -ZrC(iPr2P)dC(Ph)-), 157.9 (d, 3JC-P ) 30 Hz, -ZrC(Et)) C(Et)-), 147.2 (d, 3JC-P ) 9 Hz, i-Ph), 128.4 (Ph), 128.3 (Ph), 126.7 (p-Ph), 104.6 (Cp), 33.3 (d, 4JC-P ) 1 Hz, Et), 127.6 (d, 1JC-P ) 10 Hz, iPr), 24.0 (d, 4JC-P ) 4 Hz, Et), 22.2 (d, 5JC-P ) 2 Hz, Et), 21.6 (d, 2JC-P ) 8 Hz, iPr), 16.9 (Et), 15.5 (iPr).31P{1H} NMR (162 MHz, C6D6): δ -45.1. Anal. calcd for C30H39PZr: C, 69.05; H, 7.53. Found: C, 69.11; H, 7.60. Cp2Zr[2-Ph2P-3,4,5-Ph3C4] (9). A solution of zirconacylopropene 3 (0.50 g, 0.50 mmol) and tolan (0.18 g, 1.0 mmol) in toluene (10 mL) was heated at 50 °C for 16 h. The solution was concentrated until the solid persisted in solution (4 mL). This mixture was then cooled to -30 °C for 5 days, and then the solvent was removed via cannula filtration. The resulting solid was dried under vacuum to give an orange solid in 66% yield (0.45 g, 0.66 mmol). mp: 229-231 °C. 1H NMR (400 MHz, C6D6): δ 7.40 (m, 4H), 7.25 (m, 4H), 7.12 (m, 4H), 6.94 (m, 9H), 6.75 (m, 4H), 5.75 (d, 4JH-P ) 0.8 Hz, 10H). 13C{1H} NMR (125.8 MHz, C6D6): δ 212.1 (d, 3JC-P ) 10 Hz, -ZrC(Ph)dC(Ph)-), 166.4 (d, 2JC-P ) 9 Hz, -ZrC(Ph2P)dC(Ph)-), 165.5 (d, 1JC-P ) 68 Hz, -ZrC(Ph2P)d C(Ph)-), 154.6 (Ph), 153.3 (d, 3JC-P ) 31 Hz, -ZrC(Ph)dC(Ph)-), 142.2 (Ph), 142.1 (d, JC-P ) 5 Hz, Ph), 135.9 (d, JC-P ) 9 Hz, Ph), 133.8 (d, JC-P ) 13 Hz, Ph), 131.9 (Ph), 129.4 (d, JC-P ) 2 Hz, Ph), 129.2 (Ph), 129.0 (Ph), 128.9 (Ph), 127.9 (Ph), 127.8 (Ph), 127.3 (Ph), 127.0 (Ph), 125.5 (Ph), 123.6 (Ph), 107.5 (Cp).31P{1H} NMR (162 MHz, C6D6): δ -43.6. Anal. calcd for C44H35PZr: C, 77.04; H, 5.14. Found: C, 76.79; H, 5.05.

Organometallics, Vol. 28, No. 4, 2009 1261 Cp2Zr[2-Ph2P-3-Ph-4,5-Et2C4] (10). To a solution of zirconacylopropene 3 (0.40 g, 0.39 mmol) in toluene (10 mL) was added 3-hexyne (94 µL, 0.83 mmol). The resulting solution was placed in an oil bath and was heated at 50 °C for 16 h. The solvent was removed under vacuum and to the resulting crude solid was added pentane (2 × 20 mL). The insoluble solids were removed by cannula filtration and the resulting solution was concentrated to 6 mL. The solution was then cooled to -30 °C for 3 days, and then the solvent was removed via cannula filtration. The resulting solid was dried under vacuum to give a red-orange solid in 60% yield (0.28 g, 0.47 mmol). 1H NMR (400 MHz, C6D6): δ 7.47 (m, 4H), 7.25 (d, 3 JH-H ) 7.0 Hz, 2H), 6.98 (m, 9H), 5.82 (s, 10H), 2.31 (q, 3JH-H ) 7.5 Hz, 2H), 2.23 (q, 3JH-H ) 7.5 Hz, 2H), 1.12 (t, 3JH-H ) 7.5 Hz, 3H), 0.98 (t, 3JH-H ) 7.5 Hz, 3H). 13C{1H} NMR (125.8 MHz, C6D6): δ 202.4 (d, 3JC-P ) 4 Hz, -ZrC(Et)dC(Et)-), 174.2 (d, 1JC-P ) 44 Hz, -ZrC(Ph2P)dC(Ph)-), 160.8 (d, 2JC-P ) 10 Hz, -ZrC(Ph2P))C(Ph)-), 145.1 (d, 3JC-P ) 18 Hz, -ZrC(Et)dC(Et)-), 144.8 (d, JC-P ) 13 Hz, Ph), 140.7 (d, JC-P ) 9 Hz, Ph), 134.7 (d, JC-P ) 18 Hz, Ph), 129.0 (d, JC-P ) 1 Hz, Ph), 128.6 (Ph), 128.5 (Ph), 128.0 (Ph), 126.4 (Ph), 109.6 (Cp), 30.9 (Et), 23.8 (d, JC-P ) 5 Hz, Et), 16.1 (Et), 15.1 (Et).31P{1H} NMR (162 MHz, C6D6): δ -18.9. Anal. calcd for C36H35PZr: C, 73.30; H, 5.98. Found: C, 72.91; H, 5.82. Cp2Zr[2-Ph2P-3-Mes-4,5-Ph2C4] (13). Zirconacyclopropene 4 (0.30 g, 0.48 mmol) and tolan (0.085 g, 0.48 mmol) were loaded into a Schlenk flask and then cooled in a dry ice/isopropanol bath. Toluene (10 mL) was added dropwise and the reaction mixture was allowed to slowly reach ambient temperature. The reaction mixture was stirred for 16 h and then the toluene was removed under vacuum. The resulting solid was dissolved in ether (10 mL) and this solution was cannula-filtered to remove the insoluble impurities. The solution was then concentrated to 5 mL and cooled to -30 °C for 72 h to give the product, isolated by filtration, as orange crystals in 60% yield (0.21 g, 0.29 mmol). 1H NMR (500 MHz, C6D6): δ 7.52 (m, 4H), 7.04 (m, 2H), 6.97 (m, 10H), 6.60 (m, 3H), 6.66 (m, 1H), 6.48 (s, 2H), 5.92 (s, 10H), 2.39 (s, 6H), 1.94 (s, 3H). 13C{1H} NMR (125.8 MHz, THF-d8): δ 205.1 (d, 3 JC-P ) 4 Hz, -ZrC(Ph)dC(Ph)-), 175.9 (d, 1JC-P ) 53 Hz, -ZrC(Ph2P)dC(Mes)-), 164.9 (d, 2JC-P ) 5 Hz, -ZrC(Ph2P)d C(Ph)-), 152.8 (Ph), 149.8 (d, 3JC-P ) 23 Hz, -ZrC(Ph)dC(Ph)-), 142.9 (d, JC-P ) 4 Hz, Ph), 142.4 (d, JC-P ) 9 Hz, Ph), 139.4 (d, JC-P ) 13 Hz, Mes), 135.3 (d, JC-P ) 18 Hz, Ph), 135.2 (Mes), 134.2 (d, JC-P ) 20 Hz, Ph), 131.1 (Ph), 129.3 (d, JC-P ) 1 Hz, Mes), 128.8 (d, JC-P ) 8 Hz, Ph), 128.6 (Ph), 128.0 (Ph), 127.3 (Ph), 126.6 (Mes), 125.1 (Ph), 123.1 (Ph), 110.2 (Cp), 22.0 (d, 5JC-P ) 3 Hz, Mes), 21.2 (Mes). 31P{1H} NMR (162 MHz, C6D6): δ -27.0. Anal. calcd. for C47H41PZr: C, 77.54; H, 5.68. Found: C, 77.44; H, 5.57. Reaction of Zirconacyclopentadienes with Tolan. Zirconacyclopentadienes 7, 9, or 13 (ca. 20 mg, 31 µmol) and tolan (6.0 mg, 34 µmol) were dissolved in benzene-d6 (ca. 500 mg) and loaded into a Teflon-sealed NMR tube. The tubes were placed in a 100 °C oil bath and were monitored by 1H NMR spectroscopy at regular intervals. The conversion of starting material to Cp2Zr[2,3,4,5Ph4C4] was calculated by comparison of the integrals of the Cp resonances for these two species. ((1E,3E)-2,3,4-Triphenylbuta-1,3-dienyl)diphenylphosphine (14). Zirconacycle 9 (0.10 g, 0.15 mmol) was loaded into a Schlenk flask and benzoic acid (0.18 g, 1.5 mmol) was added under a flow of nitrogen. To this flask was added THF (12 mL) and the resulting solution was stirred for 4 h. The reaction mixture was exposed to the atmosphere, the solvent was removed, and the resulting crude solid was purified by column chromatography (10% EtOAc in hexanes) to give a white solid in 88% yield (0.060 g, 0.13 mmol), which was spectroscopically identified.391H NMR (500 MHz, CD2Cl2): δ 7.30 (m, 20H), 7.07 (m, 3H), 6.82 (m, 2H), 6.42 (s, 1H), 6.29 (d, 2JH-P ) 1.8 Hz, 1H). 13C{1H} NMR (125.8 MHz,

1262 Organometallics, Vol. 28, No. 4, 2009 CD2Cl2): δ 159.8 (d, JC-P ) 27 Hz), 145.3 (d, JC-P ) 7 Hz), 140.8 (d, JC-P ) 11 Hz), 140.4 (d, JC-P ) 7 Hz), 139.9, 137.3, 133.8 (d, JC-P ) 2 Hz), 133.1, 132.9, 131.5 (d, JC-P ) 9 Hz), 130.72, 130.70, 130.1, 129.3, 128.9 (d, JC-P ) 6 Hz), 128.7, 128.3, 128.1, 128.0, 127.6. 31P{1H} NMR (162 MHz, C6D6): δ -23.6. ((1Z,3E)-3-Ethyl-2-phenylhexa-1,3-dienyl)diphenylphosphine oxide (15). Zirconacycle 10(0.15 g, 0.25 mmol) was loaded into a Schlenk flask and dissolved in THF (10 mL). To the resulting solution was added benzoic acid (0.31 g, 2.5 mmol) under a flow of nitrogen and the reaction mixture was stirred for 4 h. The reaction mixture was quenched with water (20 mL) and the resulting solution was extracted with diethyl ether (20 mL). The organic layer was collected and washed with 2N NaOH (2 × 20 mL), a saturated, aqueous solution of NaHCO3 (20 mL), water (20 mL), and brine (20 mL). The organic layer was then transferred to a flask and a 30 wt% hydrogen peroxide solution (52 µL, 0.51 mmol) was added via syringe and the solution was stirred for 16 h. The solvent was removed and the resulting crude solid was purified by column chromatography (10% EtOAc in hexanes) to give a yellow oil in 82% yield (0.080 g, 0.21 mmol). 1H NMR (400 MHz, CDCl3): δ 7.57 (m, 4H), 7.35 (m, 2H), 7.28 (m, 4H), 7.03 (m, 5H), 6.43 (d, 2JH-P ) 19.6 Hz, 1H), 5.39 (t, 3 JH-H ) 7.4 Hz, 1H), 2.33 (q, 3JH-H ) 7.6 Hz, 2H), 2.12 (dq, 3JH-H ) 7.5 Hz, 2H), 1.06 (t, 3JH-H ) 7.5 Hz, 3H), 0.92 (t, 3JH-H ) 7.4 Hz, 3H). 13C{1H} NMR (125.8 MHz, CD2Cl2): δ 163.3 (d, JC-P ) 2 Hz), 143.2 (d, JC-P ) 16 Hz), 138.4, 137.7, (d, JC-P ) 7 Hz), 135.5, 134.7, 130.7, 130.6 (d, JC-P ) 9 Hz), 129.9 (d, JC-P ) 11 Hz), 128.1 (d, JC-P ) 12 Hz), 127.7, 127.0, 21.9, 21.1, 13.6, 13.3. 31P{1H} NMR (202 MHz, CDCl3): δ 17.4. IR (cm-1): 3058 (m), 2924 (s), 2876 (m), 2851 (m), 1717 (s), 1593 (w), 1457 (s), 1438 (s), 1379 (w), 1168 (PdO, s), 1118 (s), 1101 (m), 1072 (w), 751 (m), 724 (m), 696 (s), 527 (s). FAB-MS: m/z ) 387 (M + H+). HRMS calcd for C26H28OP, 387.1878; Found, 387.1865. (3,4,5-Triphenylthiophen-2-yloxide)diphenylphosphine oxide (16). Zirconacycle 9 (0.10 g, 0.15 mmol) was loaded into a Schlenk flask and then dissolved in THF (15 mL). This solution was then exposed to an atm of SO2 for 20 min. The reaction mixture was quenched with water (15 mL) and the resulting solution was extracted with diethyl ether (50 mL). The organic layer was collected and washed with water (50 mL) and brine (50 mL) and then dried over MgSO4. The solvent was removed and the resulting crude solid was purified by column chromatography (50% EtOAc in DCM) to give a bright yellow solid in 75% yield (0.060 g, 0.11 mmol). Analytically pure samples were obtained by crystallization from methylene chloride/ether at -30 °C. 1H NMR (500 MHz, CD2Cl2): δ 7.90 (dd, JH-P ) 12.7 Hz,3JH-H ) 7.3 Hz, 2H), 7.75 (dd, JH-P ) 12.6 Hz,3JH-H ) 7.3 Hz, 2H), 7.61 (t, 3JH-H ) 7.4 Hz, 1H), 7.55 (m, 3H), 7.46 (m, 2H), 7.29 (m, 3H), 7.25 (m, 3H), 7.14 (m, 3H), 7.01 (t, 3JH-H ) 7.6 Hz, 2H), 6.86 (m, 4H).13C{1H} NMR (125.8 MHz, CD2Cl2): δ 159.2 (d, JC-P ) 6 Hz), 155.7 (d, JC-P ) 4 Hz), 140.9, 140.1, 139.3 (d, JC-P ) 10 Hz), 133.3 (d, JC-P ) 3 Hz), 132.1, 132.0, 131.8 (d, JC-P ) 4 Hz), 131.7, 129.9 (d, JC-P ) 15 Hz), 129.7, 129.2, 128.8, 128.6, 128.5, 128.4 (d, JC-P ) 9 Hz), 128.3 (d, JC-P ) 8 Hz), 128.2, 127.3. 31P{1H} NMR (162 MHz, CD2Cl2): δ 17.3. IR (cm-1): 3057 (m), 3026 (w), 2961 (m), 2923 (s), 2852 (m), 1734 (m), 1474 (m), 1438 (s), 1261 (m), 1199 (P ) O, s), 1117 (s), 1101 (s), 1072 (s), 1049 (SdO, s), 1029 (s), 914 (w), 791 (m), 725 (s), 688 (s), 530 (m). FAB-MS: m/z ) 529 (M + H+). Anal. calcd for C34H25O2PS: C, 77.25; H, 4.77; S, 6.07. Found: C, 76.91; H, 4.78; S, 6.16. Bis(zirconacycle) (17). The zirconacyclopropene 3 (0.20 g, 0.40 mmol) and 1,4-bis(pentafluorophenylethynyl)benzene (0.090 g, 0.20 mmol) were loaded into a Schlenk flask and then dissolved in toluene (6 mL). The flask was placed in a 50 °C oil bath and the reaction solution was stirred for 16 h. The reaction mixture was then allowed to cool to ambient temperature and the solvent was removed under vacuum. The resulting solid was washed with pentane (3 × 5 mL) to give a yellow-gold solid in 44% yield (0.13

Miller et al. g, 0.086 mmol). 1H NMR (400 MHz, C6D6): δ 7.44 (m, 8H), 7.30 (d,3J ) 8.0 Hz, 4H), 6.96 (m, 18H), 6.87 (s, 4H), 5.77 (s, 20H). 19 F NMR (376.5 MHz, CDCl3): δ -138.3 (m, 4F), -157.2 (t, 3JF-F ) 22.6 Hz, 2F), -163.6 (m, 4F).31P{1H} NMR (162 MHz, C6D6): δ -27.4. IR (cm-1): 3066 (w), 3021 (w), 1511 (s), 1485 (s), 1434 (m), 1070 (m), 1015 (m), 980 (s), 880 (m), 794 (s), 736 (m), 699 (m), 500 (w). Anal. calcd for C82H54F10P2Zr2: C, 66.83; H, 3.69. Found: C, 66.50; H, 3.75. Bis(zirconacycle) (18). The zirconacyclopropene 4 (0.32 g, 0.50 mmol) and 1,4-bis(pentafluorophenylethynyl)benzene (0.12 g, 0.25 mmol) were loaded into a Schlenk flask and then dissolved in toluene (8 mL). The resulting solution was then stirred at ambient temperature for 16 h. The volatile components were then removed and the resulting solid was washed with pentane (3 × 5 mL) to give an orange solid in 67% yield (0.26 g, 0.17 mmol). 1H NMR (400 MHz, C6D6): δ 7.48 (m, 8H), 6.96 (m, 12H), 6.74 (s, 4H), 6.58 (s, 4H), 5.86 (s, 20H), 2.45 (s, 12H), 1.95 (s, 6H). 19F NMR (376.5 MHz, C6D6): δ -134.3 (d, 3JF-F ) 22.6 Hz, 4F), -157.4 (t, 3JF-F ) 21.3 Hz, 2F), -164.3 (m, 4F).31P{1H} NMR (162 MHz, C6D6): δ -25.8. Anal. calcd for C88H66F10P2Zr2: C, 67.85; H, 4.27. Found: C, 66.56; H, 4.11. 1,4-Bis(1E,3E-4-diphenylphosphino-2-pentafluorophenyl-3phenylbuta-1,3-dienyl)benzene (19). The zirconacyclopropene 3 (0.25 g, 0.49 mmol) and 1,4-bis(pentafluorophenylethynyl)benzene (0.11 g, 0.25 mmol) were loaded into a Schlenk flask and then dissolved in toluene (10 mL). The flask was placed in a 90 °C oil bath and the reaction mixture was stirred for 40 min. The reaction mixture was then allowed to cool to ambient temperature and the solvent was removed under vacuum. The solid was suspended in THF (10 mL) and a degassed, 1.1 M solution of HCl (5 mL) was added. The resulting solution was stirred for 2.5 h and then quenched with a saturated solution of NaHCO3 (20 mL). This solution was extracted with dichloromethane (2 × 20 mL) and the organic layers were collected, dried with MgSO4, filtered, and concentrated to give a crude yield of 95%. Analytically pure samples were obtained by washing with MeOH to give a yellow solid in 56% yield (0.14 g, 0.14 mmol). 1H NMR (400 MHz, C6D6): δ 7.40 (m, 8H), 7.33 (m, 4H), 7.03 (m, 18H), 6.76 (s, 2H), 6.59 (d, 2 JH-P ) 1.4 Hz, 2H), 6.39 (s, 4H). 19F NMR (376.5 MHz, C6D6): δ -139.8 (m, 4F), -152.9 (t, 3JF-F ) 21.3 Hz, 2F), -161.3 (m, 4F).31P{1H} NMR (162 MHz, C6D6): δ -22.4. Anal. calcd for C62H38F10P2: C, 71.96; H, 3.70. Found: C, 71.61; H, 3.59. Bis(zirconacycle) (20). The bis(zirconacycle) 18 (0.10 g, 0.064 mmol) and tolan (0.034 g, 0.19 mmol) were loaded into a Schlenk flask and suspended in toluene (4 mL). The flask was placed in a 85 °C oil bath and heated for 4 days. The reaction mixture was allowed to cool to ambient temperature and the solvent was removed under vacuum. The resulting solid was washed with pentane (3 × 7 mL) to give a yellow solid in 25% yield (0.020 g, 0.016 mmol). 1 H NMR (400 MHz, C6D6): δ 7.78 (m, 8H), 7.35 (m, 4H), 7.08 (m, 8H), 6.65 (s, 4H), 5.99 (s, 20H). 19F NMR (376.5 MHz, C6D6): δ -138.0 (m, 4F), -157.4 (t, 3JF-F ) 20.7 Hz, 2F), -164.0 (m, 4F). Anal. calcd for C70H44F10Zr2: C, 66.86; H, 3.53. Found: C, 66.96; H, 3.87.

Acknowledgment. Jamin L. Krinsky of the Molecular Graphics and Computation Facility in the College of Chemistry for calculation of the average molecular radii of complexes 1 and 4. This work was supported by the National Science Foundation research grant CHE0314709. Supporting Information Available: Tables of bond lengths and angles, computational results, and the X-ray crystallographic data for compounds 1, 4, 5, 8, and 10 in the form of CIF files. This material is available free of charge via the Internet at http://pubs.acs.org. OM801040T