Selectivity of Allenylidene versus Butadienyl Protonation in an

Synopsis. Treatment of [Os{(E)-CH═CHC(CH3)═CH2}(═C═C═CPh2)(CH3CN)2(PiPr3)2]BF4 with HBF4 leads to the alkenylcarbene−allenylidene derivati...
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Organometallics 2009, 28, 2107–2111

2107

Selectivity of Allenylidene versus Butadienyl Protonation in an Osmium-Bisphosphine System Tamara Bolan˜o, Alba Collado, Miguel A. Esteruelas,* and Enrique On˜ate* Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n, UniVersidad de Zaragoza-CSIC, 50009 Zaragoza, Spain ReceiVed January 27, 2009

The complex [OsH(dCdCdCPh2)(CH3CN)2(PiPr3)2]BF4 (1) reacts with 2-methyl-1-buten-3-yne to give [Os{(E)-CHdCHC(CH3)dCH2}(dCdCdCPh2)(CH3CN)2(PiPr3)2]BF4 (2). Treatment of 2 with HBF4 leads to the alkenylcarbene-allenylidene derivative [Os{dCHCHdC(CH3)2}(dCdCdCPh2) (CH3CN)2(PiPr3)2][BF4]2 (3). In contrast to its reaction with HBF4, the reactions of 2 with acetic acid, acetylacetone,andacetoneoximeaffordthebutadienyl-alkenylcarbynespecies[Os{(E)-CHdCHC(CH3)dCH2}(κ2O 2 CCH 3 )(tCCHdCPh 2 )(P i Pr 3 ) 2 ]BF 4 (4), [Os{(E)-CHdCHC(CH 3 )dCH 2 }(κ 2 O,O′acac)(tCCHdCPh 2 )(P i Pr 3 ) 2 ]BF 4 (5), and [Os{(E)-CHdCHC(CH 3 )dCH 2 }{κ 2 N,O[ONdC(CH3)2]}(tCCHdCPh2)(PiPr3)2]BF4 (6), respectively. The X-ray structures of 4 and 6 are also reported. Introduction Ionic hydrogenation involves the sequential transfer of H+ and H- to an unsaturated organic substrate. Such hydrogenation mimics biological reductions, which heterolytically cleave the hydrogen molecule and H- and H+ are separately added to the substrate.1 A recent example of ionic hydrogenation is the selective reduction of the CR-Cβ double bond of the allenylidene ligand of the complex [OsH(dCdCdCPh2)(CH3CN)2(PiPr3)2]BF4 (1) by hydrogen transfer from alcohols (Scheme 1).2 In agreement with EHT-MO calculations indicating that the nucleophilic center in transition-metal allenylidene species is the Cβ atom of the unsaturated chain,3 in the presence of alcohols, the allenylidene ligand of 1 initially undergoes protonation at Cβ. The subsequent coordination of the resulting alkolates to the metal center affords alkoxy-hydride-carbyne species. Then, β-hydrogen elimination from the alkolates leads to a dihydridecarbyne intermediate, which is transformed into the hydridecarbene hydrogenation product by an intramolecular reduction.2,4 * To whom correspondence should be addressed. E-mail: maester@ unizar.es (M.A.E.); [email protected]. (1) (a) Clapham, S. E.; Hadzovic, A.; Morris, R. Coord. Chem. ReV. 2004, 248, 2201. (b) Bullock, R. M. Chem. Eur. J. 2004, 10, 2366. (c) Samec, J. S. M.; Ba¨ckvall, J. E.; Andersson, P. G.; Brandt, P. Chem. Soc. ReV. 2006, 35, 237. (d) Kubas, G. J. Chem. ReV. 2007, 107, 4152. (e) Vignais, P. M.; Billoud, B. Chem. ReV. 2007, 107, 4206. (f) FontecillaCamps, J. C.; Voldeba, A.; Cavazza, C.; Nicolet, Y. Chem. ReV. 2007, 107, 4273. (g) Esteruelas, M. A.; Garcı´a-Yebra, C.; On˜ate, E. Organometallics 2008, 27, 3029. (2) Bolan˜o, T.; Castarlenas, R.; Esteruelas, M. A.; On˜ate, E. J. Am. Chem. Soc. 2007, 129, 8850. (3) (a) Berke, H.; Huttner, G.; Vonseyerl, J Z. Naturforsch., B 1981, 36, 1277. (b) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Gonza´lez-Cueva, M.; Lastra, E.; Borge, J.; Garcı´a-Granda, S.; Pe´rez-Carren˜o, E. Organometallics 1996, 15, 2137. (c) Edwards, A. J.; Esteruelas, M. A.; Lahoz, F. J.; Modrego, J.; Oro, L. A.; Schrickel, J. Organometallics 1996, 15, 3556. (d) Esteruelas, M. A.; Go´mez, A. V.; Lo´pez, A. M.; Modrego, J.; On˜ate, E. Organometallics 1997, 16, 5826. (e) Esteruelas, M. A.; Go´mez, A. V.; Lo´pez, A. M.; Modrego, J.; On˜ate, E. Organometallics 1998, 17, 5434. (f) Baya, M.; Crochet, P.; Esteruelas, M. A.; Gutierrez-Puebla, E.; Lo´pez, A. M.; Modrego, J.; On˜ate, E.; Vela, N. Organometallics 2000, 19, 2585. (4) (a) Bolan˜o, T.; Castarlenas, R.; Esteruelas, M. A.; Modrego, J.; On˜ate, E. J. Am. Chem. Soc. 2005, 127, 11184. (b) Bolan˜o, T.; Castarlenas, R.; Esteruelas, M. A.; On˜ate, E. Organometallics 2007, 26, 2037.

Scheme 1

A selectivity problem arises from the presence in the same organometallic compound of different unsaturated C-donor ligands, with different nucleophilic centers and competing protonation sites. In order to develop selective processes of ionic hydrogenation, we have studied the selectivity of allenylidene versus butadienyl protonation. Transition-metal butadienyl complexes, like the allenylidene compounds, are a class of organometallic derivatives with two C-C double bonds. Reactivity studies indicate that in this case the nucleophilic center is the Cδ atom of the C-donor ligand. Thus, their reactions with electrophilic reagents, in particular with H+, afford R,β-unsaturated carbene complexes.5

Results and Discussion An effective method to prepare osmium- and rutheniumbutadienyl derivatives involves the selective insertion of the C-C triple bond of a conjugated enyne into the M-H bond of (5) (a) Esteruelas, M. A.; Oro, L. A. AdV. Organomet. Chem. 2001, 47, 1. (b) Cadierno, V.; Gamasa, M. P.; Gimeno, J. Coord. Chem. ReV. 2004, 248, 1627. (c) Esteruelas, M. A.; Lo´pez, A. M.; Oliva´n, M. Coord. Chem. ReV. 2007, 251, 795. (6) See for example: (a) Esteruelas, M. A.; Lahoz, F. J.; On˜ate, E.; Oro, L. A.; Valero, C.; Zeier, B. J. Am. Chem. Soc. 1995, 117, 7935. (b) Esteruelas, M. A.; Liu, F.; On˜ate, E.; Sola, E.; Zeier, B. Organometallics 1997, 16, 2919.

10.1021/om900059g CCC: $40.75  2009 American Chemical Society Publication on Web 03/20/2009

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Bolaño et al. Scheme 2

Figure 1. HOMO orbital of complex 2t.

a hydride compound.6 In agreement with this, in dichloromethane at room temperature, complex 1 reacts with 2-methyl1-buten-3-yne to afford [Os{(E)-CHdCHC(CH3)d CH2}(dCdCdCPh2)(CH3CN)2(PiPr3)2]BF4 (2), which contains two unsaturated groups: butadienyl and allenylidene. This compound is isolated as a brown solid in 86% yield (eq 1).

The 1H and 13C{1H} NMR spectra of 2 are consistent with the presence of a butadienyl ligand in the complex. In the 1H NMR spectrum, this ligand exhibits resonances at 9.89 (CRHR), 6.00 (CβHβ), 4.25 (CδH2), and 1.77 (CH3) ppm. The E stereochemistry at the CR-Cβ double bond is strongly supported by the HR-Hβ coupling constant of 16.8 Hz, which is a typical value for this arrangement. The C(sp2) resonances in the 13C{1H} NMR spectrum appear at 145.1 (Cγ), 142.1 (Cβ), 131.9 (CR), and 105.1 (Cδ) ppm, whereas those of the allenylidene group are observed at 273.7 (CR), 255.3 (Cβ), and 145.2 (Cγ) ppm. Figure 1 shows the HOMO orbital of the model cation [Os(CHdCHCHdCH)(dCdCdCH2)(CH3CN)2(PMe3)2]+ obtained by DFT/B3PW91 calculations.7 Among others, as expected, this orbital is located on the Cδ and Cβ atoms of the butadienyl and allenylidene ligands with molecular orbital py coefficients of 0.5445 and 0.0315, respectively. A natural bond orbital (NBO)8 analysis yields charges on these atoms of -0.44 (Cδ) and -0.21 (Cβ). These values reveal that the Cδ atom of the butadienyl ligand is not only a stronger nucleophilic center but also a harder Lewis base than the Cβ atom of the allenylidene. Therefore, one should expect that the protonation of the butadienyl ligand of 2 would be favored with regard to the protonation of the allenylidene group,9 at least from a kinetic point of view. Treatment of an acetonitrile solution of 2 at 243 K with 1.2 equiv of HBF4 · OEt2 leads to the instantaneous formation of [Os{dCHCHdC(CH3)2}(dCdCdCPh2)(CH3CN)2(PiPr3)2][BF4]2 (3), as a result of the selective addition of the proton of the (7) They were performed using Gaussian 03 software: Frisch, M. J. , Gaussian 03, revision C.02; Gaussian, Inc., Pittsburgh, PA, 2003 (see the Supporting Information for a complete citation). (8) NBO version 3. See: Weinhold, F.; Carpenter, J. E. In The Structure of Small Molecules; Naaman, R., Vager, Z. , Eds.; Plenum: New York, 1988; p 227. (9) Pearson, R. G. J. Am. Chem. Soc. 1963, 85, 3533.

acid at the Cδ atom of the butadienyl ligand10 (Scheme 2). This complex, which is isolated as a red solid in 70% yield, is a rare example in iron triad chemistry of a dication containing two M-C double bonds.11,12 In solution complex 3 exists as a mixture of the isomers 3a (77%) and 3b (23%). We have assigned the major isomer to 3a and the minor isomer to 3b, on the basis of the chemical shifts of the allenylidene resonances in the 13C{1H} NMR spectrum, assuming that the allenylidene ligand of 3a lies in the region of a negative shielding contribution due to the magnetic anisotropy of the C-C double bond of the alkenylcarbene, and therefore the chemical shifts of the C3 chain (279.6 (CR), 219.2 (Cβ), and 160.0 (Cγ) ppm) are found to lower field than those of 3b (278.0 (CR), 215.5 (Cβ), and 159.1 (Cγ) ppm).13 The most noticeable resonances of the alkenylcarbene ligand appear at 268.9 (CR), 163.1 and 161.2 (Cβ), and 152.0 and 150.4 (Cγ) ppm. Complex 3 appears to be favored with regard to its butadienylalkenylcarbyne isomer not only from a kinetic point of view but also from a thermodynamic perspective. DFT/B3PW91 calculations indicate that the optimized structure of the model dication [Os(dCHCHdCHCH3)(dCdCdCH2)(CH3CN)2(PMe3)2]2+ (3t in Chart 1) is 6.5 kcal mol-1 more stable than that of its hypothetic butadienyl-alkenylcarbyne isomer [Os(CHdCHCHdCH2)(t CCHdCH2)(CH3CN)2(PMe3)2]2+ (3t′). In contrast to HBF4, acetic acid affords a butadienylalkenylcarbyne derivative. Treatment at room temperature of an acetonitrile solution of 1 with 2.0 equiv of the carboxylic acid leads to [Os{(E)-CHdCHC(CH3)dCH2}(κ2O2CCH3)(tCCHdCPh2)(PiPr3)2]BF4 (4), which is isolated as a green solid in 79% yield. Figure 2 shows a view of the geometry of the cation of 4. The coordination around the osmium atom can be rationalized (10) Under the same conditions, in contrast to the case for 2, the styryl-allenylidene complex [Os{(E)-CHdCHPh}(dCdCd CPh2)(CH3CN)2(PiPr3)2]BF4 reacts by protonation at the allenylidene ligand. See: Bolan˜o, T.; Castarlenas, R.; Esteruelas, M. A.; On˜ate, E. Organometallics 2008, 27, 6367. (11) A dicationic osmacyclopentatriene (or osmacyclopentadienyl) derivate has been previously reported. See: (a) Pu, L.; Hasegawa, T.; Parkin, S.; Taube, H. J. Am. Chem. Soc. 1992, 114, 2712. (b) Pu, L.; Hasegawa, T.; Parkin, S.; Taube, H. J. Am. Chem. Soc. 1992, 114, 7609. (12) Examples of complexes with two Os-C double bonds are the bis(neopentylidene) derivatives Os(dCHtBu)2(CH2R)2 (R ) tBu, SiMe3). See: (a) LaPointe, A. M.; Schrock, R. R. Organometallics 1993, 12, 3379. (b) LaPointe, A. M.; Schrock, R. R.; Davis, W. M. J. Am. Chem. Soc. 1995, 117, 4802. (13) Crochet, P.; Esteruelas, M. A.; Lo´pez, A. M.; Martı´nez, M. P.; Oliva´n, M.; On˜ate, E.; Ruiz, N. Organometallics 1998, 17, 4500.

Allenylidene Versus Butadienyl Protonation

Organometallics, Vol. 28, No. 7, 2009 2109 Scheme 3

Figure 2. Molecular diagram of the cation of 4. Selected bond lengths (Å) and angles (deg): Os-C(6) ) 1.736(6), Os-C(1) ) 2.049(6), Os-O(1) ) 2.198(4), Os-O(2) ) 2.225(4), C(1)-C(2) ) 1.325(8), C(2)-C(3) ) 1.462(9), C(3)-C(4) ) 1.336(8); C(1)-Os-O(1) ) 153.5(2), C(6)-Os-O(2) ) 169.3(2), O(1)-Os-O(2) ) 58.77(16), P(1)-Os-P(2) ) 169.65(5), C(7)-C(6)-Os ) 179.7(5). Chart 1

butadienyl ligand displays resonances at 7.75 (CRHR), 5.62 (CβHβ), 4.48 and 4.47 (CH2), and 1.76 (CH3) ppm. In agreement with the E stereochemistry at the CR-Cβ double bond, the HR-Hβ coupling constant is 15.5 Hz. The most noticeable resonance of the alkenylcarbyne group is a singlet at 5.28 ppm, corresponding to the CβH proton. In the 13C{1H} NMR spectrum, the C(sp2) resonances of the butadienyl ligand appear at 142.9 (Cγ), 140.1 (Cβ), 135.1 (CR), and 111.1 (Cδ) ppm, whereas those of the alkenylcarbyne are observed at 274.6 (CR), 163.7 (Cγ), and 133.0 (Cβ) ppm. The butadienyl-alkenylcarbyne complex 4 is the product of thermodynamic control of the reaction of 1 with acetic acid. In fact, the treatment in acetonitrile of 3 with sodium acetate also affords 4. The replacement of the acetonitrile ligands by an acetate groupinvertstherelativestabilitiesofthealkenylcarbene-allenylidene and butadienyl-alkenylcarbyne forms. DFT/B3PW91 calculations (Chart 1) show that the optimized structure of the model cation [Os(CHdCHCHdCH2)(κ2-O2CCH3)(tCCHdCH2)(PMe3)2]+ (4t′) is 1.6 kcal mol-1 more stable than that of its isomer [Os(κ2O2CCH3)(dCHCHdCHCH3)(dCdCdCH2)(PMe3)2]+ (4t).

as a distorted octahedron with the phosphine ligands occupying trans positions (P(1)-Os-P(2) ) 169.65(5)°). The perpendicular plane is formed by the bidentate acetate (O(1)-Os-O(2) ) 58.77(16)°), the butadienyl ligand being disposed trans to O(1) (C(1)-Os-O(1) ) 153.5(2)°), and the carbyne disposed trans to O(2) (C(6)-Os-O(2) ) 169.3(2)°). The butadienyl ligand shows an E stereochemistry at the C(1)-C(2) double bond. The Os-C(1) bond length of 2.049(6) Å compares well with the Os-C(sp2) single-bond distances found in osmium-alkenyl complexes,14 whereas the C(1)-C(2) (1.325(8) Å), C(2)-C(3) (1.462(9) Å), and C(3)-C(4) (1.336(8) Å) distances agree well with the related parameters in other butadienyl derivatives.6b The Os-C(6) bond length of 1.736(6) Å is fully consistent with an Os-C triple-bond formulation.15 The 1H and 13C{1H} NMR spectra of 4 are consistent with the structure shown in Figure 2. In the 1H NMR spectrum, the (14) See for example: (a) Barrio, P.; Esteruelas, M. A.; On˜ate, E. J. Am. Chem. Soc. 2004, 126, 1946. (b) Bolan˜o, T.; Castarlenas, R.; Esteruelas, M. A.; On˜ate, E. J. Am. Chem. Soc. 2006, 128, 3965, and references therein. (15) Jia, G. Coord. Chem. ReV. 2007, 251, 2167.

Acetylacetone and acetone oxime react in a manner similar to that of acetic acid to afford butadienyl-alkenylcarbyne complexes (Scheme 3). At room temperature, the treatment of a dichloromethane solution of 2 with 2.0 equiv of the diketone leads to the acetylacetonate derivative [Os{(E)-CHdCHC(CH3)d CH2}(κ2O,O′-acac)(tCCHdCPh2)(PiPr3)2]BF4 (5), which is isolated as a brown solid in 74% yield. Under the same conditions, the addition of 1.2 equiv of acetone oxime to 2 gives [Os{(E)-CHdCHC(CH3)dCH2}{κ2N,O-[ONdC(CH3)2]}(tCCHd CPh2)(PiPr3)2]BF4 (6), which is isolated as a greenish brown solid in 91% yield. The IR and the 1H and 13C{1H} NMR spectra of 5 are consistent with the structure proposed for this compound in Scheme 3. The chelating coordination of the acac ligand is supported by the presence of two strong ν(CO) bands, at 1575 and 1523 cm-1 in the IR. The 1H NMR spectrum contains the CβH resonance of the alkenylcarbyne at 5.80 ppm. In the 13 C{1H} NMR spectrum, the CR resonance of this group appears at 278.8 ppm. The 1H and 13C{1H} NMR resonances of the butadienyl ligand (see the Experimental Section) agree well with those of 2 and 4. Figure 3 shows a view of the geometry of the cation of 6. If one considers that the oximate group occupies two sites in the coordination sphere of the metal,16 the geometry around the osmium atom could be described as a very distorted octahedron with trans phosphines. The perpendicular plane is formed by

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stabilities of the alkenylcarbene-allenylidene and butadienylalkenylcarbyne forms. As a consequence of this, butadienylalkenylcarbyne complexes are formed as products from a thermodynamic control of the reactions of [Os{(E)-CHdCHC(CH3)d CH2}(dCdCdCPh2)(CH3CN)2(PiPr3)2]+ with acetic acid, acetylacetone, and acetone oxime.

Experimental Section

Figure 3. Molecular diagram of the cation of 6. Selected bond lengths (Å) and angles (deg): Os-C(6) ) 1.721(6), Os-N ) 2.058(4), Os-C(1) ) 2.063(6), Os-O ) 2.187(4), C(1)-C(2) ) 1.347(8), C(2)-C(3) ) 1.472(8), C(3)-C(4) ) 1.355(9), C(6)-C(7) ) 1.432(8); N-Os-C(1) ) 136.4(2), C(6)-Os-O ) 162.95(19), N-Os-O ) 37.58(15), P(2)-Os-P(1) ) 169.57(5), C(7)-C(6)-Os ) 176.2(5).

the oximate (acting with a bite angle of 37.58(15)°),17 the butadienyl ligand disposed trans to the nitrogen atom (C(1)Os-N ) 136.4(2)°), and the alkenylcarbyne disposed trans to the oxygen atom18 (C(6)-Os-O ) 162.95(19)°). The Os-C(1) and Os-C(6) bond lengths of 2.063(6) and 1.721(6) Å compare well with those of 4 and support the butadienyl-alkenylcarbyne formulation. The 1H and 13C{1H} NMR spectra of 6 are consistent with the structure shown in Figure 3 and agree with those of 4 and 5. In the 1H NMR spectrum, the butadienyl ligand displays resonances at 8.45 (CRHR), 6.08 (CβHβ), 4.60 and 4.58 (CH2), and 1.85 (CH3) ppm, with a HR-Hβ coupling constant of 16.2 Hz. The CβH resonance of the alkenylcarbyne appears at 5.52 ppm. In the 13C{1H} NMR spectrum, the C(sp2) resonances of the butadienyl ligand are observed at 144.1 (Cγ), 141.4 (Cβ), 128.3 (CR), and 111.0 (Cδ) ppm, whereas those of the alkenylcarbyne appear at 272.9 (CR), 161.0 (Cγ), and 135.7 (Cβ) ppm.

Concluding Remarks In conclusion, the Cδ atom of the butadienyl ligand of the butadienyl-allenylidene cation [Os{(E)-CHdCHC(CH3)d CH2}(dCdCdCPh2)(CH3CN)2(PiPr3)2]+ is a stronger nucleophilic center and a harder Lewis base than the Cβ atom of the allenylidene. As a result of this, the protonation of the butadienyl ligand is kinetically favored with regard to the allenylidene. Thus, the reaction of this cation with HBF4 leads to the alkenylcarbeneallenylidene dication [Os{dCHCHdC(CH3)2}(dCdCd CPh2)(CH3CN)2(PiPr3)2]2+, which is also thermodynamically more stable than a butadienyl-alkenylcarbyne isomer. However, the replacement of the acetonitrile ligands by anionic chelating groups, such as acetate, acetylacetonate, and oximate, inverts the relative (16) If the oximate group is described as a monodentate three-electrondonor ligand, the structure can be rationalized as a distorted trigonal bipyramid with apical phosphines and inequivalent angles within the Y-shaped equatorial plane. (17) Similar values have been found in other oximate compounds. See: Kukushkin, V. Y.; Pombeiro, A. J. L Coord. Chem. ReV. 1999, 181, 147, and references therein. (18) This is also the disposition found in osmium-hydride-carbyne derivatives. See: (a) Barrio, P.; Esteruelas, M. A.; On˜ate, E Organometallics 2002, 21, 2491. (b) Barrio, P.; Esteruelas, M. A.; On˜ate, E. Organometallics 2003, 22, 2472.

All reactions were carried out with rigorous exclusion of air using Schlenk-tube techniques. Solvents were dried by standard procedures and distilled under argon prior to use. The starting material [OsH(dCdCdCPh2)(CH3CN)2(PiPr3)2]BF4 (1) was prepared by the published method.14b Preparation of [Os{(E)-CHdCHC(CH3)dCH2}(dCdCd CPh2)(CH3CN)2(PiPr3)2]BF4 (2). A solution of 1 (450 mg, 0.517 mmol) in 7 mL of dichloromethane was treated with 2-methyl-1buten-3-yne (97 µL, 1.034 mmol). After 30 min at room temperature, the mixture was concentrated and n-pentane was added to afford a brown solid. Yield: 445 mg (86%). Anal. Calcd for C42H65BF4N2OsP2: C, 53.84; H, 6.99; N, 2.99. Found: C, 53.89; H, 7.00; N, 3.14. IR (cm-1): ν(CtN) 2188 (w); ν(CdCdC) 1885 (s); ν(BF) 1053 (vs). MS: m/z 769 [M - 2 CH3CN]+, 609 [M 2CH3CN - PiPr3]+. 1H NMR (300 MHz, CD3CN, 293 K): δ 9.89 (dt, JH-H ) 16.8, JH-P ) 1.8, 1H, OsCH), 7.83 (d, JH-H ) 7.2, 4H, o-Ph), 7.80 (t, JH-H ) 7.5, 2H, p-Ph), 7.36 (dd, JH-H ) 7.5 and 7.2, 4H, m-Ph), 6.00 (dt, JH-H ) 16.8, JH-P ) 1.5, OsCHCH), 4.25 (s, 2H, CH2), 3.18, 2.87 (both s, 6H, CH3CN), 2.53 (m, 6H, PCH), 1.77 (s, 3H, CH3), 1.3-1.1 (36H, PCCH3). 31P{1H} NMR (121.4 MHz, CD3CN, 293 K): δ -10.3 (s). 13C{1H} APT NMR plus HMBC and HSQC (75.4 MHz, CD3CN, 293 K):19 δ 273.7 (t, JC-P ) 12.4, OsdC), 255.3 (t, JC-P ) 2.7, dCd), 155.2 (s, Cipso Ph), 145.2 (t, JC-P ) 2.0, CPh2), 145.1 (t, JC-P ) 2.0, CCH2), 142.1 (t, JC-P ) 3.0, OsCHCH), 131.9 (t, JC-P ) 10.1, OsCH), 130.1, 129.6, 127.9 (all s, Ph), 105.1 (s, CH2), 25.0 (vt, N ) 25.2, PC), 19.4, 19.3 (both s, PCCH3), 1.7 (s, CH3). Preparation of [Os(dCHCHdC(CH3)2)(dCdCd CPh2)(CH3CN)2(PiPr3)2][BF4]2 (3). A solution of 2 (205 mg, 0.219 mmol) in 7 mL of acetonitrile was treated with HBF4 · OEt2 (36 µL, 0.263 mmol). After 5 min at 243 K, the mixture was concentrated. The addition of diethyl ether gave a red solid. Yield: 170 mg (70%). Anal. Calcd for C42H66B2F8N2OsP2: C, 49.23; H, 6.49; N, 2.73. Found: C, 49.05; H, 6.01; N, 3.18. MS: m/z 769 [M - 2CH3CN - H], 701 [M - 2CH3CN - C5H8 - H]+, 609 [M 2CH3CN - H - PiPr3 ]+. IR (cm-1): ν(CtN) 2195 (w); ν(CdCdC) 1931 (s); ν(BF) 1052 (vs). Data for 3a are as follows. 1 H NMR (400 MHz, CD2Cl2, 243 K): δ 18.99 (d, JH-H ) 12.8, 1H, OsCH), 7.94 (d, JH-H ) 14.0, 1H, OsCCH), 7.9-7.1 (10H, Ph), 3.18, 2.92 (both s, 6H, CH3CN), 2.26 (m, 6H, PCH), 1.66, 1.48 (both s, 6H, CH3), 1.4-1.1 (36H, PCCH3). 31P{1H} NMR (161.9 MHz, CD2Cl2, 243 K): δ 14.4 (s). 13C{1H} APT NMR plus HMBC and HSQC (100.5 MHz, CD2Cl2, 243 K): δ 279.6 (t, JC-P ) 10.2, OsdC), 268.9 (t, JC-P ) 6.7, OsdCH), 219.2 (s, dCd), 163.1 (s, C(CH3)2), 160.0 (s, CPh2), 152.0 (s OsCCH), 149.0 (s, Cipso Ph), 139.0, 135.2 (both s, CN), 131.6, 129.5,129.3 (all s, Ph), 29.1, 22.0 (both s, CH3), 24.8 (br, PC), 18.0, 17.0 (both s, PCCH3), 4.3, 3.6 (both s, CH3CN). Data for 3b are as follows. 1H NMR (400 MHz, CD2Cl2, 243 K): δ 19.11 (d, JH-H ) 14.0, 1H, OsCH), 8.00 (d, JH-H ) 12.8, 1H, OsCCH), 7.9-7.1 (10H, Ph), 3.24, 2.95 (both s, 6H, CH3CN), 2.51 (m, 6H, PCH), 1.77, 1.57 (both s, 6H, CH3), 1.4-1.1 (36H, PCCH3). 31P{1H} NMR (161.9 MHz, CD2Cl2, 243 K): δ 15.2 (s). 13C{1H} APT NMR plus HMBC and HSQC (100.5 MHz, CD2Cl2, 243 K): δ 278.0 (t, JC-P ) 9.9, OsdC), 268.9 (t, JC-P ) 6.7, OsdCH), 215.5 (s, dCd), 161.2 (s, C(CH3)2), 159.1 (19) In dichloromethane-d2 the spectrum contains four acetonitrile resonances at δ 142.7 and 131.7 (both s, CN) and 4.8 and 4.0 (both s, CH3).

Allenylidene Versus Butadienyl Protonation (s, CPh2), 150.4 (s OsCCH), 147.7 (s, Cipso Ph), 139.8, 135.1 (both s, CN), 132.0, 130.2, 129.4 (all s, Ph), 28.6, 22.1 (both s, CH3), 24.8 (br, PC), 18.3, 17.9 (both s, PCCH3), 4.6, 3.7 (both s, CH3CN). Preparation of [Os{(E)-CHdCHC(CH3)dCH2}(K2-O2CCH3) (tCCHdCPh2)(PiPr3)2]BF4 (4). A solution of 2 (400 mg, 0.427 mmol) in 7 mL of acetonitrile was treated with acetic acid (27 µL, 0.868 mmol). After 30 min at room temperature, the solvent was removed in vacuo and n-pentane was added to afford a dark green solid. Yield: 310 mg (79%). Anal. Calcd for C40H63BF4O2OsP2: C, 52.51; H, 6.80. Found: C, 52.59; H, 6.80. MS: m/z 829 [M]+, 669 [M - PiPr3]+. IR (cm-1): νasym(OCO) 1527 (s); νsym(OCO) 1470 (s); ν(BF) 1051 (vs). 1H NMR (400 MHz, CD2Cl2, 293 K): δ 7.75 (d, JH-H ) 15.5, 1H, OsCH), 7.65-7.37 (10H, Ph), 5.62 (d, JH-H ) 15.5, 1H, OsCHCH), 5.28 (s, 1H, tCCH), 4.48, 4.47 (both s, 2H, CH2), 2.54 (m, 6H, PCH), 1.93 (s, 3H, CH3CO), 1.76 (s, 3H, CH3), 1.30 (dvt, N ) 13.6, JH-H ) 6.8, 36H, PCCH3). 31P{1H} NMR (161.9 MHz, CD2Cl2, 293 K): δ 18.7 (s). 13C{1H} APT NMR plus HMBC and HSQC (100.5 MHz, CD2Cl2, 293 K): δ 274.6 (t, JC-P ) 8.7, OstC), 186.7 (t, JC-P )1.8, CO), 163.7 (s, CPh2), 142.9 (t, JC-P )1.9, CCH2), 140.1 (t, JC-P ) 3.2, OsCHCH), 139.3, 138.2 (both s, Cipso Ph), 135.1 (t, JC-P ) 8.5, OsCH), 133.0 (s, tCC), 132.5, 132.4, 130.6, 129.8, 129.8, 129.2 (all s, Ph), 111.1 (s, CH2), 26.0 (s, CCH3), 25.7 (vt, N ) 24.5, PC), 19.5, 19.2 (both s, PCCH3), 19.0 (s, CH3CO). Preparation of [Os{(E)-CHdCHC(CH3)dCH2}(K2O,O′-acac) (tCCHdCPh2)(PiPr3)2]BF4 (5). A solution of 2 (140 mg, 0.149 mmol) in 7 mL of dichloromethane was treated with acetylacetone (30 µL, 0.300 mmol). After 2 h at room temperature the solvent was removed in vacuo and n-pentane was added to afford a brown solid. Yield: 105 mg (74%). Anal. Calcd for C43H67BF4O2OsP2: C, 54.08; H, 7.07. Found: C, 53.68; H, 7.32; MS: m/z 709 [M PiPr3]+. IR (cm-1): νasym(CO) 1575 (s); νsym(CO) 1523 (s); ν(BF) 1027 (vs). 1H NMR (300 MHz, CD2Cl2, 293 K): δ 8.56 (d, JH-H ) 16.5, 1H, OsCH), 7.71-7.29 (10H, Ph), 6.17 (d, JH-H ) 16.5, 1H, OsCHCH), 5.80 (s, 1H, tCCH), 5.69 (s, CHacac) 4.64, 4.50 (both s, 2H, CH2), 2.50 (m, 6H, PCH), 2.25, 2.01 (both s, 6H, CH3acac), 1.85 (s, 3H, CH3), 1.28 (dvt, N ) 13.5, JH-H ) 7.2, 36H, PCCH3). 31 P{1H} NMR (121.4 MHz, CD2Cl2, 293 K): δ 18.7 (s). 13C{1H} APT NMR plus HMBC and HSQC (75.4 MHz, CD2Cl2, 293 K): δ 278.8 (t, JC-P ) 10.8, OstC), 191.7, 189.4 (both s, CO), 163.7

Organometallics, Vol. 28, No. 7, 2009 2111 (s, CPh2), 145.1 (s, CCH2), 141.3 (s, OsCHCH), 140.3, 139.3 (both s, Cipso Ph), 136.9 (t, JC-P ) 8.8, OsCH), 134.5 (s, tCC), 132.6, 132.5, 131.7, 130.4, 130.3, 130.2 (all s, Ph), 109.9 (s, CH2), 102.9 (s, CHacac), 29.0, 27.8 (both s, CH3 acac), 26.5 (vt, N ) 23.1, PC), 19.2 (s, CCH3), 20.2, 19.8 (both s, PCCH3). Preparation of [Os{(E)-CHdCHC(CH3)dCH2}{K2N,O[ONdC(CH3)2]}(tCCHdCPh2)(PiPr3)2]BF4 (6). A solution of 2 (170 mg, 0.181 mmol) in 7 mL of dichloromethane was treated with (CH3)2CdNOH (16 mg, 0.219 mmol). After 20 min at room temperature, the solvent was removed in vacuo and n-pentane was added to afford a greenish brown solid. Yield: 153 mg (91%). Anal. Calcd for C41H66BF4NOOsP2: C, 53.07; H, 7.17; N, 1.51. Found: C, 52.70; H, 7.29; N, 1.35. MS: m/z 682 [M - PiPr3]+. IR (cm-1): ν(CN) 1537 (s); ν(BF) 1050 (vs). 1H NMR (300 MHz, CD2Cl2, 293 K): δ 8.45 (d, JH-H ) 16.2, 1H, OsCH), 7.63-7.31 (10H, Ph), 6.08 (d, JH-H ) 16.2, 1H, OsCHCH), 5.52 (s, 1H, tCCH), 4.60, 4.58 (both s, 2H, CH2), 2.43 (m, 6H, PCH), 2.26, 2.06 (both s, 6H, NC(CH3)2), 1.85 (s, 3H, CH3), 1.23 (dvt, N ) 14.1, JH-H ) 7.2, 36H, PCCH3). 31P{1H} NMR (121.4 MHz, CD2Cl2, 293 K): δ 15.2 (s). 13C{1H} APT NMR plus HMBC and HSQC (75.4 MHz, CD2Cl2, 293 K): δ 272.9 (t, JC-P ) 9.9, OstC), 161.0 (t, JC-P ) 1.0, CPh2), 144.1 (t, JC-P )1.9, CCH2), 141.4 (t, JC-P ) 3.0, OsCHCH), 140.1, 139.2 (both s, Cipso Ph), 135.7 (s, tCC), 128.3 (t, JC-P ) 9.3, OsCH), 132.1, 131.9, 130.7, 129.9, 129.8, 129.2 (all s, Ph), 111.0 (s, CH2), 24.9 (vt, N ) 24.4, PCH), 22.3, 20.6 (both s, NC(CH3)2), 19.7, 19.6 (both s, PCCH3), 19.2 (s, dCCH3).

Acknowledgment. Financial support from the Spanish MICINN (Projects CTQ2008-00810 and Consolider Ingenio 2010 CSD2007-00006) and the DGA (E35) is acknowledged. A.C. thanks the CSIC for her JAE grant. Supporting Information Available: Text, tables, and figures giving details of the X-ray analysis, computations, orthogonal coordinates of theoretical structures, and crystal structure determinations and a CIF file giving crystal data for compounds 4 and 6. This material is available free of charge via the Internet at http://pubs.acs.org. OM900059G