(2-(Diphenylphosphino)ethyl)cyclopentadienyl - American Chemical

Sep 21, 2010 - Department of Chemistry, Macalester College, Saint Paul, Minnesota 55105-1899. Received July 12, 2010. The emerging utility of the brid...
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Organometallics 2010, 29, 4562–4568 DOI: 10.1021/om1006825

Allylnickel(II) and Allylpalladium(II) Derivatives of [(2-(Diphenylphosphino)ethyl)cyclopentadienyl]tricarbonylmetalates: Reactions with Free Radicals Paul J. Fischer,* Michelle C. Neary, Aaron P. Heerboth, and Kevin P. Sullivan Department of Chemistry, Macalester College, Saint Paul, Minnesota 55105-1899 Received July 12, 2010

The emerging utility of the bridging (2-(diphenylphosphino)ethyl)cyclopentadienyl (CpPPh) ligand to kinetically stabilize early-late metal-metal bonds to facilitate novel reactions in heterobimetallics is further established by the syntheses of four-legged piano stool M0 {M(η3-L)}(CO)3(μ-η5:η1-CpPPh) (M0 =Cr, Mo, W; M=Ni, Pd; L=allyl, 2-methylallyl, cyclohexenyl). Complexes 1-3 (M=Ni, L= allyl) and 4-6 (M = Ni, L = 2-methylallyl) are the first structurally characterized heterobimetallics with transition metal-Ni(η3-allyl) units, while 7-9 (M=Ni, L=cyclohexenyl) are the only structurally characterized transition metal-Ni(η3-cyclohexenyl) complexes. Like Pd(η3-allyl)Cl(PPh3), 1-3 and 10-12 (M=Pd, L=allyl) respectively provide 4,4,4-triphenyl-1-butene as the sole allyl ligand coupling product from competitive reactions of phenyl and trityl radicals. However, while phenyl radical attack at the Pd(II) of Pd(η3-allyl)Cl(PPh3) is proposed as the first step in the trityl radical-allyl ligand coupling reaction, direct trityl radical attack at η3-allyl is strongly suggested in 1-3 and 10-12, respectively. A modest heterobimetallic effect may render the chromium complexes 1 and 10 more reactive with trityl radical than the tungsten complexes 3 and 12.

Introduction The reaction of carbon nucleophiles with η3-π-ligands is a fundamental transformation in catalytic organometallic chemistry and is among the most important carbon-carbon bond formation strategies in organic synthesis. Pd(II) and Ni(II) allyl complexes are prominent reagents for these reactions; the development of methodology and ligand environments to tune the selectivity of allylic substitution at these metals is a vigorous research area. Recent advances in modulating η3-allylpalladium and η3-allylnickel reactivity via ancillary ligand modification include application of dinuclear allylpalladium complexes of pyrazolate-bridged bis(oxazoline) ligands1 and ferrocenylSchiff bases2 for asymmetric allylic alkylation, Pd(allyl)(NHC)Cl (NHC = N-heterocyclic carbene) complexes for Suzuki-Miyaura and Buchwald-Hartwig reactions,3 nickelcatalyzed hydroamination of 1,3-dienes by alkylamines,4 and nickel-catalyzed coupling of alkyne-tethered vinylcyclopropanes and allyl chloride.5 The activity of [Ni(allyl)(CH3CN)(NHC)]þ and [M(2-R-allyl)(arene)]þ (M = Pd, Ni; R = H, *To whom correspondence should be addressed. E-mail: fischer@ macalester.edu. (1) Ficks, A.; Sibbald, C.; John, M.; Dechert, S.; Meyer, F. Organometallics 2010, 29, 1117. (2) Perez, S.; L opez, C.; Bosque, R.; Solans, X.; Font-Bardı´ a, M.; Roig, A.; Molins, E.; van Leeuwen, P. W. N. M.; van Streijdonck, G. P. F.; Freixa, Z. Organometallics 2008, 27, 4288. (3) Marion, N.; Navarro, O.; Mei, J.; Stevens, E. D.; Scott, N. M.; Nolan, S. P. J. Am. Chem. Soc. 2006, 128, 4101. (4) Pawlas, J.; Nakao, Y.; Kawatsura, M.; Hartwig, J. F. J. Am. Chem. Soc. 2002, 124, 3669. (5) Ikeda, S.-I.; Obara, H.; Tsuchida, E.; Shirai, N.; Odashima, K. Organometallics 2008, 27, 1645. pubs.acs.org/Organometallics

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CH3, Cl; arene = mesitylene, hexamethylbenzene) as polymerization catalysts6 and olefin and alkyne coupling reagents,7 respectively, motivates further M(η3-allyl) complex research. Transition metal heterobimetallic hydrocarbyl ligand reactivity toward carbon-carbon bond formation has been extensively investigated.8 The potential of leveraging unique catalytic properties via exploitation of synergistic effects afforded by early late transition metal bonds inspires these studies.9 Despite broad exploration of M(η3-allyl) complexes, few studies describing carbon-element bond formation via heterobimetallics containing this fragment have been reported. Addition of [Pd(η3-C3H5)(μ-Cl)]2 to FeH(Si(OMe)3)(CO)3(η1-dppm) results in Fe{PdCl}(CO)3(μ-dppm)(μ-Si(OMe)3), presumably via propene reductive elimination from a FePd(allyl) intermediate.10 The η3-methylallyl ligand electrophilicity can be significantly enhanced by Ti-M00 (M00 = Ni, Pd, Pt) dative bonding enforced by a bridging titanium(IV) phosphinoamide ligand; the η3-methylallyl ligands of these heterobimetallics are much more reactive for C-N bond formation via Et2NH and aniline nucleophilic attack than [Pd(η3-methylallyl)(dppp)]þ.11 (6) (a) O’Connor, A. R.; Urbin, S. A.; Moorhouse, R. A.; White, P. S.; Brookhart, M. Organometallics 2009, 28, 2372. (b) Walter, M. D.; Moorhouse, R. A.; Urbin, S. A.; White, P. S.; Brookhart, M. J. Am. Chem. Soc. 2009, 131, 9055.  (7) Campora, J.; de la Tabla, L. O.; Palman, P.; Alvarez, E.; Lahoz, F.; Mereiter, K. Organometallics 2006, 25, 3314. (8) Ritleng, V.; Chetcuti, M. J. Chem. Rev. 2007, 107, 797. (9) Wheatley, N.; Kalck, P. Chem. Rev. 1999, 39, 3379. (10) (a) Braunstein, P.; Faure, T.; Knorr, M.; Balegroune, F.; Grandjean, D. J. Organomet. Chem. 1993, 462, 271. (b) dppm = 1,1-bis(diphenylphosphino)methane. r 2010 American Chemical Society

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Organometallics, Vol. 29, No. 20, 2010

Free radical addition to coordinated unsaturated organic ligands constitutes a relatively unexplored class of carboncarbon bond formation reactions.12 Insufficient fundamental knowledge of free radical reactions with ligands hinders their consideration in synthesis, even though free radicals are proposed intermediates in many transition metal mediated reactions including oxidative addition,13 chromium(II) complex reduction of organic halides,14 SmI2-induced coupling of organic halides with carbonyl compounds,15 and hydrogenation and hydrometalation of aromatic alkenes and conjugated dienes.16 Baird discovered unexpected allyl-derived product selectivity in competitive reactions of phenyl and trityl radicals with [Pd(η3-C3H5)(μ-Cl)]2, Pd(η3-C3H5)Cl(PPh3), and [Pd(η3-C3H5)(PPh3)2]Cl.17 While [Pd(η3-C3H5)(μ-Cl)]2 afforded exclusively kinetic product 3-phenylpropene, the phosphine derivatives provided 4,4,4-triphenyl-1-butene as sole allyl coupling product. Initial attack of phenyl radical at Pd followed by sterically directed coupling of trityl radical to form Ph3CCl ([Pd(η3-C3H5)(μ-Cl)]2) or 4,4,4-triphenyl-1butene (phosphine derivatives) was postulated. The (2-(diphenylphosphino)ethyl)cyclopentadienyl (CpPPh) ligand stabilizes heterobimetallics to permit novel reactivity at early late transition metal bonds. Salts of [M0 (CO)3(η5CpPPh)]- (M0 =Cr, Mo, W) react with CuCl to afford intermediates that permit phosphine installation at copper(I) in a rare instance of nucleophilic attack at heterobimetallic M-Cu bonds without concomitant heterolytic cleavage.18 The isolobal relationship between halides and [M0 (CO)3(η5-Cp)]suggested M0 {M(η3-allyl)}(CO)3(μ-η5:η1-CpPPh) (M = Ni, Pd) as Pd(η3-allyl)Cl(PPh3) analogues, ideal for inaugural free radical reactivity studies with heterobimetallic η3-allylpalladium and η3-allylnickel complexes. The allyl-derived coupling products from M0 {M(η3-allyl)}(CO)3(μ-η5:η1-CpPPh) would offer useful comparative data to Baird’s work and explore a possible early late heterobimetallic effect on allyl ligand reactivity.

Results and Discussion Synthesis of M0 {M(η3-L)}(CO)3(μ-η5:η1-CpPPh). Reactions of M0 (CO)3(RCN)3 (M0 = Cr, R = Me; M0 = Mo, W, (11) Tsutsumi, H; Sunada, Y.; Shiota, Y.; Yoshizawa, K.; Nagashima, H. Organometallics 2009, 28, 1988. dppp=1,3-bis(diphenylphosphino)propane. (12) (a) Torraca, K. E.; McElwee-White, L. Coord. Chem. Rev. 2000, 206-207, 469. (b) Baciocchi, E.; Floris, B.; Muraglia, E. J. Org. Chem. 1993, 58, 2013. (c) Schmalz, H.-G.; Siegel, S.; Bats, J. W. Angew. Chem., Int. Ed. Engl. 1995, 34, 2383. (d) Schmalz, H.-G.; Siegel, S.; Schwarz, A. Tetrahedron Lett. 1996, 17, 2947. (e) Carter, C. A. G.; McDonald, R.; Stryker, J. M. Organometallics 1999, 18, 820. (f ) Ogoshi, S.; Stryker, J. M. J. Am. Chem. Soc. 1998, 120, 3514. (g) Casty, G. L.; Stryker, J. M. J. Am. Chem. Soc. 1995, 117, 7814. (13) Rendina, L. M.; Puddephatt, R. Chem. Rev. 1997, 97, 1735. (14) (a) Kochi, J. K.; Powers, J. W. J. Am. Chem. Soc. 1970, 92, 137. (b) Sustmann, R.; Altevogt, R. Tetrahedron Lett. 1981, 22, 5167. (15) Krief, A.; Laval, A. M. Chem. Rev. 1999, 99, 745. (16) (a) Sweaney, R. L.; Comberrel, D. S.; Dombourain, M. F.; Peters, N. A. J. Organomet. Chem. 1981, 216, 57. (b) Ungvary, F.; Marko, L. Organometallics 1982, 1, 1120. (c) Bockman, T. M.; Garst, J. F.; King, R. B.; Mark o, L.; Ungvary, F. J. Organomet. Chem. 1985, 279, 165. (d) Bullock, R. M.; Samel, E. G. J. Am. Chem. Soc. 1990, 112, 6886. (e) Connolly, J. W. Organometallics 1984, 3, 1333. (f ) Ungvary, F.; Marko, L. Organometallics 1982, 3, 1466. (g) Wassink, B.; Thomas, M. J.; Wright, S. C.; Gillis, D. J.; Baird, M. C. J. Am. Chem. Soc. 1987, 109, 1995. (h) Shackleton, T. A.; Mackie, S. C.; Fergusson, S. B.; Johnston, L. J.; Baird, M. C. Organometallics 1990, 9, 2248. (17) (a) Reid, S. J.; Baird, M. C. Dalton Trans. 2003, 3975. (b) Reid, S. J.; Freeman, N. T.; Baird, M. C. Chem. Commun. 2000, 1777. (c) Reid, S. J.; Baird, M. C. J. Organomet. Chem. 2004, 689, 1257. (18) Fischer, P. J.; Heerboth, A. P.; Herm, Z. R.; Kucera, B. E. Organometallics 2007, 26, 6669.

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Scheme 1

R = Et) and NaCpPPh to afford (2-(diphenylphosphino)ethyl)cyclopentadienyltricarbonylmetalates,18 followed by salt elimination with [M(η3-L)(μ-X)]2 (M = Ni, L = allyl, 2-methylallyl, cyclohexenyl, X = Cl, Br; M = Pd, L = allyl, X=Cl), provided analytically pure 1-12 in moderate yields (Scheme 1). Bromide abstraction from [M(η3-L)(μ-Br)]2 by [M0 (CO)3(η5-CpPPh)]- (M0 =Mo, W) competes with M-M0 bond formation, resulting in kinetic products M0 Br(CO)3(η5CpPPh) that upon intramolecular pendant phosphine coordination afford M0 Br(CO)2(μ-η5:η1-CpPPh);19 these Mo-Br complexes can be removed from 2, 5, and 8 by diffusion of pentane into nearly saturated THF/pentane solutions of each compound, but application of [M(η3-L)(μ-Cl)]2 is necessary for the W syntheses. Limited L steric bulk can be accommodated; attempts to introduce Ni(η5-Cp*) and Ni(η3-C3H3(SiMe3)2)20 led to intractable products. The ν(CO) absorptions in THF solution suggest Ni(η3-allyl) is a slightly better donor than Pd(η3-allyl); the lowest energy ν(CO) bands of 10-12 are shifted to higher energies relative those of 1-3 by 21, 25, and 26 cm-1, respectively. The Ni(η3-L) electronic impact at M0 is modest on the basis of ν(CO) absorptions; the carbonyl stretching frequencies of 1-3 are nearly indistinguishable from those of 4-6, respectively, and η3-C6H9 is the best donor, with the lowest energy ν(CO) absorptions of 7-9 shifted lower by 10, 17, and 19 cm-1, respectively, relative to those of 1-3. Complexes 1-12 are not fluxional in solution on the basis of NMR spectroscopy; the carbon and hydrogen environments associated with the η5-cyclopentadienyl and η3-allyl units are unique. Structural Characterization of M0 {M(η3-L)}(CO)3(μ-η5:1 η -CpPPh). The four-legged piano stool structures of 1, 2-5, 6, 7, 8, 9, 10, 11, and 12 containing substituted η5-Cp ligands and chelated M(η3-L) fragments are displayed in Figures 1, S1-S4 (Supporting Information), 2, S5, 3, S6, S7, 4, and S8, respectively. The η3-C4H7 ligands are disordered over two positions in 5 (64:36) and 6 (61:39). In 10-12, the η3-allyl ligands are disordered over two positions (82:18). Complexes 1-6 are the first structurally characterized heterobimetallics with transition metal-Ni(η3-allyl) units. JimenezTenorio recently reported neutral allylnickel(II) complex structures containing Ni-metalloid bonds [Ni(η3-CH2C(R)CH2)BrL] (L = SbPh3, R = CH3; L = AsPh3, R = H).21 Heterobimetallics 7-9 are the only structurally characterized transition metal-Ni(η3-cyclohexenyl) complexes; Hartwig reported [bis(diphenylphosphino)ferrocene]nickel(II)(cyclohexenyl) trifluoroacetate, the first structurally characterized (19) This bromide abstraction pathway, monitored by solution ν(CO) IR spectroscopy, is related to the photochemical conversion of MoI(CO)3(η5-C5H4CH2CH2N(CH3)2) to MoI(CO)2(μ-η5:η1-C5H4CH2CH2N(CH3)2). See: Wang, T.-F.; Lee, T.-Y.; Chou, J.-W.; Ong, C.-W. J. Organomet. Chem. 1992, 423, 31. (20) Quisenberry, K. T.; Dominic Smith, J.; Voehler, M.; Stec, D. F.; Hanusa, T. P.; Brennessel, W. W. J. Am. Chem. Soc. 2005, 127, 4376. (21) Jimenez-Tenorio, M.; Carmen Puerta, M.; Salcedo, I.; Valerga, P.; de los Rı´ os, I.; Mereiter, K. Dalton Trans. 2009, 1842.

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Figure 1. Molecular structure of 1 (50% thermal ellipsoids). Selected bond lengths (A˚) and angles (deg): Cr-Ni = 2.6182(5), Cr-C(1) = 1.843(2), Cr-C(2) = 1.843(2), Cr-C(3) = 1.821(2), Cr-C(O) (av) = 1.84(1), Cr-C(4) = 2.244(2), Cr-C(5) = 2.210(2), Cr-C(6) = 2.183(2), Cr-C(7) = 2.189(2), Cr-C(8) = 2.206(2), Cr-C(dienyl) (av) = 2.21(2), O(1)-C(1) = 1.173(3), O(2)-C(2) = 1.177(3), O(3)-C(3) = 1.162(3), C-O (av) = 1.171(8), Ni-C(1) = 2.172(2), Ni-C(2) = 2.234(2), O(1)C(1)-Cr = 169.69(18), O(2)-C(2)-Cr = 170.10(18), O(3)-C(3)Cr = 178.1(2), Ni-P(1) = 2.1914(6), C(3)-Cr-C(1) = 89.31(10), C(3)-Cr-C(2) = 87.25(10), C(1)-Cr-C(2) = 108.59(9), C(3)-Cr-Ni = 103.66(7), C(1)-Cr-Ni = 55.02(6), C(2)-CrNi = 56.97(6), P(1)-Ni-Cr = 98.646(17), Ni-C(23) = 2.078(2), Ni-C(24) = 2.045(2), Ni-C(25) = 2.045(2).

Figure 2. Molecular structure of 6 (50% thermal ellipsoids). Selected bond lengths (A˚) and angles (deg): W-Ni = 2.7478(4), W-C(1) = 1.951(3), W-C(2) = 1.950(3), W-C(3) = 1.941(3), W-C(O) (av) = 1.947(6), W-C(4) = 2.388(3), W-C(5) = 2.357(3), W-C(6) = 2.337(3), W-C(7) = 2.341(3), W-C(8) = 2.361(3), W-C(dienyl) (av) = 2.36(2), O(1)-C(1) = 1.178(4), O(2)-C(2) = 1.170(4), O(3)-C(3) = 1.165(4), C-O (av) = 1.171(7), Ni-C(1) = 2.291(3), Ni-C(2) = 2.411(3), O(1)C(1)-W = 171.2(3), O(2)-C(2)-W = 171.2(3), O(3)-C(3)W = 178.1(3), Ni-P(1) = 2.1879(8), C(3)-W-C(1) = 82.22(13), C(3)-W-C(2) = 85.94(13), C(1)-W-C(2) = 104.50(14), C(3)W-Ni = 107.59(9), C(1)-W-Ni = 55.28(10), C(2)-WNi = 58.87(10), P-Ni-W = 99.21(3), Ni-C(23) = 2.072(5), Ni-C(24) = 2.015(6), Ni-C(25) = 2.100(8).

Ni(η3-cyclohexenyl) complex, but with no Fe-Ni interaction.4 Most crystallographically characterized bimetallics with Pd(η3-allyl) units contain two Pd atoms; 10-12 join Fe{Pd(η3-C3H5)}(CO)3{SiCH3(OSiMe3)2)}(μ-η1:η1-(2-Ph2PC6H4N)),22 Cr{Pd(η3-C3H5)}(CO)3(μ-η6:η1-RHC(C6H5)) (22) Braunstein, P.; Durand, J.; Morise, X.; Tiripiccho, A.; Ugozzoli, F. Organometallics 2000, 19, 444.

Fischer et al.

Figure 3. Molecular structure of 8 (50% thermal ellipsoids). Selected bond lengths (A˚) and angles (deg): Mo-Ni = 2.7212(4), Mo-C(1) = 1.950(2), Mo-C(2) = 1.969(2), Mo-C(3) = 1.958(2), Mo-C(O) (av) = 1.96(1), Mo-C(4) = 2.365(2), MoC(5) = 2.357(2), Mo-C(6) = 2.350(2), Mo-C(7) = 2.341(2), Mo-C(8) = 2.341(2), Cr-C(dienyl) (av) = 2.35(1), O(1)-C(1) = 1.178(2), O(2)-C(2) = 1.167(2), O(3)-C(3) = 1.157(3), C-O (av) = 1.17(1), Ni-C(1) = 2.2214(19), Ni-C(2) = 2.284(2), O(1)-C(1)-Mo = 167.85(16), O(2)-C(2)-Mo = 168.98(18), O(3)-C(3)-Mo = 178.82(19), Ni-P(1) = 2.2209(6), C(3)Mo-C(1) = 88.25(8), C(3)-Mo-C(2) = 88.20(8), C(1)-MoC(2) = 106.49(8), C(3)-Mo-Ni = 101.78(6), C(1)-Mo-Ni = 53.77(6), C(2)-Mo-Ni = 55.52(6), P(1)-Ni-Cr = 99.460(19), Ni-C(23) = 2.135(2), Ni-C(24) = 1.9970(19), Ni-C(25) = 2.058(2).

Figure 4. Molecular structure of 11 (50% thermal ellipsoids). Selected bond lengths (A˚) and angles (deg): Mo-Pd = 2.8402(4), Mo-C(1) = 1.931(4), Mo-C(2) = 1.953(4), MoC(3) = 1.961(4), Mo-C(O) (av) = 1.95(2), Mo-C(4) = 2.410(3), Mo-C(5) = 2.355(4), Mo-C(6) = 2.307(4), Mo-C(7) = 2.333(4), Mo-C(8) = 2.372(4), Mo-C(dienyl) (av) = 2.36(4), O(1)-C(1) = 1.175(5), O(2)-C(2) = 1.176(4), O(3)-C(3) = 1.177(5), C-O (av) = 1.176(1), Pd-C(2) = 2.458(4), Pd-C(3) = 2.413(4), O(1)-C(1)-Mo = 178.2(4), O(2)-C(2)-Mo = 171.3(3), O(3)-C(3)-Mo = 169.7(3), Pd-P(1) = 2.2800(9), C(3)Mo-C(1) = 84.99(18), C(3)-Mo-C(2) = 105.95(15), C(1)Mo-C(2) = 83.53(17), C(3)-Mo-Pd = 56.86(11), C(1)Mo-Pd = 107.43(17), C(2)-Mo-Pd = 58.24(11), P-PdMo = 97.03(2), Pd-C(23) = 2.224(8), Pd-C(24) = 2.162(4), Pd-C(25) = 2.188(5).

(R = H, Ph),23 [(Ph3P)2Pt(CCtBu)2{Pd(η3-allyl)}][ClO4],24 [NBu4][(C6F5)2Pt(CCSiMe3)2{Pd(η3-C3H5)}],25 and Fe{Pd(η3-C 3H5)}(CO)2(μ-CO)(μ-η3:η2-C7H7 )26 as structurally characterized Pd(η3-allyl) heterobimetallics.

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Table 1. Heterobimetallic Allyl Ligand Conversion to 4,4,4-Triphenyl-1-butenea Cr PAT

Mo TD

PAT

W TD

PAT

TD

Ni 1: 71(1) 1: 100 2: 37.2(5) 2: 72(2) 3: 54.8(3) 3: 87(3) Pd 10: 65.2(4) 10: 100 11: 42.0(1) 11: 73(1) 12: 50.6(9) 12: 89(1)

Figure 5. Related heterobimetallics kinetically stabilized by bridging ligands.

Diagnostic structural parameters that define the M0 {Ni(η -L)}(CO)3(μ-η5:η1-CpPPh) fragments of 1-6 are nearly identical to those of four-legged piano stool M0 {CuPMe3}(CO)3(μ-η5:η1-CpPPh) (M0 = Cr (13), Mo (14); Figure 5).18 While the phosphine and η3-L units render the Ni centers of 1-6 electronically unsaturated like Ni(η5-C5Me5), 1-6 and W{Ni(η5-C5Me5)}(CO)3(η5-C5H4Me) (15; Figure 5)27 feature dramatically different M0 -Ni binding modes. In paramagnetic 15 the W(CO)3(η5-C5H4Me) group interacts with the Ni(η5-C5Me5) unit via three semibridging CO ligands and a Ni-W bond with significant multiple-bond character; 15 is isolobal with nickelocene. In diamagnetic 1-6, the reduced steric bulk of η3-L, coupled with phosphine chelation, results in M0 -Ni single bonds and semibridging interactions to CO ligands defined by C(1) and C(2). The Cr-Ni bonds of 1 (2.6182(5) A˚), 4 (2.6110(8) A˚), and 7 (2.6283(3) A˚) are similar to that of Cr{Ni(η5-Cp)(CO)}(η5-Cp)(CO)3 (2.641(3) A˚).28 The M00 -Ni (M00 =Mo, W) bonds of 2, 3, 5, 6, 8, and 9 range from 2.7077(8) A˚ (2) to 2.7478(4) A˚ (6), unremarkable for M00 -Ni single bonds and longer than the W-Ni separation in 15 (2.457(2) A˚). The shortest Ni-C(1) separations in 1, 4, and 7 (av: 2.18(1) A˚) and corresponding O(1)-C(1)-Cr angles (av: 169(1)°) suggest more significant semibridging carbonyl interactions than in 13 (Cu-C(1): 2.3156(17) A˚, O(1)-C(1)-Cr: 172.67(16)°). The corresponding average parameters for 2, 3, 5, 6, 8, and 9 (Ni-C(1): 2.25(4) A˚, O(1)-C(1)-M00 : 170(1)°) indicate modestly increased semibridging interactions relative to those in 14 (Cu-C(1): 2.347(2) A˚, O(1)-C(1)-Mo: 173.5(2)°); the most important such interaction in 15 (Ni-C(O): 2.10(1) A˚) has a significantly greater impact on the carbonyl ligand (O-C-W: 159(1)°). The increased η3-L fragment steric impact relative to trimethylphosphine enforces more acute P-Ni-M0 chelating angles in 1-9 (av: 99(1)°) than the chelating P-CuM0 angles found in 13 (112.057(16)°) and 14 (111.156(19)°). The Ni-η3-allyl carbon distances are remarkably similar in 1-9 (av: 2.06(4) A˚); these distances are most irregular in 3

(23) (a) Kalinin, V. N.; Cherepanov, I. A.; Moiseev, S. K.; Dolgushin, F. M.; Yanovsky, A. I.; Struchkov, Y. T. Acta Crystallogr. 1993, C49, 805. (b) Kalinin, V. N.; Cherepanov, I. A.; Moiseev, S. K.; Batsanov, A. S.; Struchkov, Y. T. Mendeleev Commun. 1991, 1, 77. (24) Berenguer, J. R.; Fornies, J.; Lalinde, E.; Martinez, F. Organometallics 1996, 15, 4537. (25) Berenguer, J. R.; Fornies, J.; Lalinde, E.; Martinez, F. J. Organomet. Chem. 1994, 470, C15. (26) Fu, W.; McDonald, R.; Takats, J.; Bond, A. H.; Rogers, R. D. Inorg. Chim. Acta 1995, 229, 307. (27) (a) Chetcuti, M. J.; Grant, B. E.; Fanwick, P. E.; Geselbracht, M. J.; Stacy, A. M. Organometallics 1990, 9, 1343. (b) Clapham, S.; Braunstein, P.; Boag, N. M.; Welter, R.; Chetcuit, M. J. Organometallics 2008, 27, 1758. (28) Madach, T.; Fischer, K.; Vahrenkamp, H. Chem. Ber. 1980, 113, 3235.

a Conversions (average percentages with standard deviations) based on moles of heterobimetallic determined via GC/MS using an anthracene internal standard.

7-9, spanning average Ni(η3-cyclohexenyl) lengths of 1.9972(8) A˚ (Ni-C(24)) to 2.135(4) A˚ (Ni-C(23)), permitting closer approach of the less sterically hindered coordinated η3-cyclohexenyl central carbon. A similar range of distances was observed in [bis(diphenylphosphino)ferrocene]nickel(II)(η3-cyclohexenyl) trifluoroacetate4 (1.994(4)-2.081(3) A˚) and in Brookhart’s [Ni(η3-cyclohexenyl)(η6-mesitylene)][B((C6H3)(CF3)2)4] (1.934(5)-2.063(6) A˚).29 The Cr-Pd separation in 10 (2.7561(6) A˚) is statistically identical to analogous lengths in diastereomers of Cr{Pd(η3C3H5)}(CO)3(μ-η6:η1-PhHC(C6H5)) (16, Figure 5) (2.776(1), 2.770(1) A˚).23 While semibridging Pd-C(O) interactions appear more important in 10 than 16 on the basis of relevant Pd-C distances (10: Pd-C(2) = 2.398(3), Pd-C(3) = 2.341(3) A˚; 16: Pd-C(1) = 2.513(3), Pd-C(3) = 2.746(3) A˚), the modest O-C-Cr perturbation (10: O(2)-C(2)Cr(1)=170.0(2)°, O(3)-C(3)-Pd=168.5(2)°) suggests that these interactions are rather inconsequential toward quenching Pd electronic unsaturation. The M00 -Pd lengths in 11 (2.8402(4) A˚) and 12 (2.8525(5) A˚) are only slightly longer than the thiolate-enforced W-Pd separations in WS4{Pd(η3allyl)}2 (2.810(2), 2.800(2) A˚).30 The average P-Pd-M0 angle of 10-12 (av: 97.4(7)°) is statistically identical to the corresponding chelation angle in 1-9. The average Pd-η3allyl carbon length in 10-12 (2.17(7) A˚) is slightly longer, as expected, than the corresponding Ni-η3-allyl carbon average length in 1-9. Reactions with Free Radicals. Competitive reactions of 1-3 and 10-12 respectively with phenyl and trityl radicals derived from the thermal decomposition of phenylazoptriphenylmethane (PAT, 4 equiv) were carried out in boiling benzene. Conversions to 4,4,4-triphenyl-1-butene (17), the exclusive allyl ligand coupling product, are displayed in Table 1. The absence of phenylpropene isomers mirrors the selectivity reported by Baird for reactions of Pd(η3-allyl)Cl(PPh3) (18) with PAT, but this selectivity with 1-3 and 10-12 is almost certainly derived from an alternate mechanism than with 18.17a Initial phenyl radical attack at Pd(II) in 18 to afford a phenyl-palladium(III) intermediate followed by trityl radicalallyl ligand coupling was strongly supported by [Pd(C6H5)Cl(PPh3)]2 formation.17a Direct trityl radical attack at the 18 allyl ligand was inferred as slow on the basis of low yields of 17 from reactions of [Pd(η3-allyl)(PPh3)2]Cl and trityl dimer (TD); phenyl radical participation is necessary with 18 to obtain 17 in high yield.17a In contrast, direct trityl radical attack at the η3-allyl of 1-3 and 10-12 is strongly suggested on the basis of excellent conversions to 17 from reactions of these heterobimetallics with trityl dimer (Table 1, 2 equiv of (29) O’Connor, A. R.; White, P. S.; Brookhart, M. Organometallics 2010, ASAP, DOI: 10.1021/om100391v. (30) Howard, K. E.; Rauchfuss, T. B.; Wilson, S. R. Inorg. Chem. 1988, 27, 3561.

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TD) and determining the fate of phenyl radical in the PAT reactions. On the basis of GC/MS analysis, roughly 70% of phenyl radicals produced in reactions of 1-3 and 10-12, respectively, with PAT resulted in biphenyl (62(5)%) and tetraphenylmethane (6.5(4)%). GC/MS cannot account for 100% of PAT-derived phenyl radicals; biphenyl can form via phenyl radical coupling (accounting for two phenyl radicals), and benzene formed via phenyl radical hydrogen atom abstraction cannot be quantified. Biphenyl formation via phenyl radical attack at benzene to afford phenylcyclohexadienyl radical that donates a hydrogen atom to trityl or phenyl radical with restoration of aromaticity is a long-known outcome of PAT decomposition in benzene.31 Reactions of 1 and 10 with PAT (4 equiv) in boiling benzene-d6, as well as PAT independently in this solvent (equal initial PAT concentrations), afforded roughly 10 times more C6H5-C6D5 than C6H5C6H5 on the basis of molecular ion peak intensity comparisons (m/z 159 vs 154), assuming these isotopologues fragment at similar rates. These biphenyl isotopologues accounted for 93(3)% of phenyl radicals in reactions of 1 and 10 with benzene-d6. The consistency of the relative populations of C6H5-C6D6 and C6H5-C6H5 regardless of the presence of 1 or 10 suggests that PAT-derived phenyl radical reacts nearly exclusively with solvent under these conditions. Triphenylmethane, tetraphenylmethane, and 17 (83(4)% of trityl radicals accounted for via GC/MS) were the primary trityl radical derived products from the reactions of 1-3 and 10-12, respectively, with PAT (4 equiv) in boiling benzene. Scavenging of trityl radical by phenylcyclohexadienyl and phenyl radicals undoubtedly contributes to reduced conversions to 17 via reactions of 1-3 and 10-12, respectively, with PAT relative to those with trityl dimer. Conversions to 17 (Table 1) via both PAT and trityl dimer suggest a heterobimetallic effect, with allyl ligand reactivity toward trityl radical seemingly increasing based on group VI metal as Mo < W < Cr. The thermal instability of Mo complexes 2 and 11 in hot benzene contributes to the corresponding reduced conversions to 17. The 31P resonance peak areas of 2 and 11, respectively, decreased by ∼30% over 90 min in hot benzene-d6 (70 °C); the Mo-Ni and Mo-Pd bonds are not adequately stabilized by the chelating CpPPh ligand under the conditions necessary for efficient PAT decomposition. The corresponding 31P resonances of 1, 3, 10, and 12 are unchanged under these conditions; the Cr and W complexes are remarkably thermally robust.32 The differing conversions to 17 for reactions of 1, 3, 10, and 12, respectively, with PAT are likely governed by the relative rates of trityl radical attack at the η3-allyl ligand and trityl radical scavenging via phenyl and phenylcyclohexadienyl radicals. Consumption rates of 1, 3, 10, and 12, respectively (assumed as the rate of trityl radical-allyl ligand attack), were measured via 31P NMR spectroscopy in benzene-d6 (70 °C, 90 min trials, initial concentrations (mM): 1, 29.1(5); 3, 29.8(5); 10, 29.2(5); 12, 29.9(5)) with PAT (2.6-2.7 equiv). The corresponding 31P (31) (a) Hey, D. H.; Perkins, M. J.; Williams, G. H. J. Chem. Soc. 1965, 110. (b) Hey, D. H.; Perkins, M. J.; Williams, G. H. Tetrahedron Lett. 1963, 7, 445. (32) These 31P NMR spectroscopic observations suggest that the bridging CpPPh ligand significantly stabilizes 1, 3, 10, and 12, respectively, toward thermally induced metal-metal bond homolysis. The fate of 2 and 11 under these conditions is unclear. It is noteworthy that solutions of 1-3 and 10-12, respectively, can be stirred in benzene for at least 72 h at ambient temperature under fluorescent lighting without any evidence of decomposition by solution IR spectroscopy. Photochemical investigation of these complexes is underway in this laboratory.

Fischer et al.

singlet resonance (δ (ppm, ext. ref 80% H3PO4): 1, 18.9; 3, 22.0; 10, 21.4; 12, 22.0) decreased with the simultaneous appearance of a slightly upfield 31P singlet (δ: 1, 4.4; 3, 17.6; 10, 21.0; 12, 19.3). No phosphorus-containing intermediates were observed, consistent with the lack of phenyl radical attack at the group X metal proposed in 18. It is noteworthy that identical 31P NMR spectral changes were observed in similar experiments with 1, 3, 10, and 12, respectively, and trityl dimer, consistent with the same mechanism for 17 formation with both PAT and trityl dimer as trityl radical sources. The formulations of the phosphorus containing non-carbonyl products have not been established. The only carbonyl species in solution after 90 min was residual 1, 3, 10, and 12, respectively. The heterobimetallics 1, 3, 10, and 12 were consumed via initial rates ((mM/s, measured during the first 288 s of the 90 min experiments): 1, 0.0253(5); 3, 0.0109(5); 10, 0.0162(5); 12, 0.00827(5)) that rank as the corresponding conversions to 17 by 1, 3, 10, and 12, respectively. A 3-fold difference in reaction rates between 1 and 12 is modest, but does not rule out that higher rates of trityl radical attack at the η3allyl ligand of the heterobimetallic relative to the rate of trityl dimer scavenging by phenyl and phenylcyclohexadienyl radicals are at least partially responsible for the higher conversions to 17 by the Cr complexes 1 and 10 relative the W complexes 3 and 12. The lack of aforementioned trityl radical scavenging options contributes to the higher conversions to 17 with trityl dimer as the trityl radical source rather than PAT toward 1-3 and 10-12, respectively. Since a modest heterobimetallic effect cannot be ruled out on the basis of these data, these preliminary findings motivate current work to unambiguously elucidate the mechanism for formation of 17. If an interplay between the two metals manifests itself by subtlely altering the reactivity of 1-3 and 10-12 at the η3-allyl ligands, the origin of this effect will be challenging to establish spectroscopically. An electronic origin would be a reasonable working assumption; steric constraints on presumed trityl radical attack on the η3-allyl ligands of 1-3 and 10-12, respectively, seem similar. A resonance contributor to the electronic ground state of 1-12 features a dative interaction between a zerovalent group VI metal donor and a divalent group X metal acceptor. Enhanced group VI metal donation to the M(η3-allyl) fragment would be expected to render the η3-allyl ligand more electron rich and less reactive toward radical attack. However, while the Brønsted basicity of [W(CO)3(η5-Cp)]- is well established as stronger than [Cr(CO)3(η5-Cp)]-,33 ν(CO) infrared stretching frequencies do not distinguish chromium complexes 1 and 10 from tungsten complexes 3 and 12 in regard to group VI metal donor ability; the differences between the lowest energy ν(CO) absorptions of 1 and 3 (2 cm-1) and 10 and 12 (7 cm-1), respectively, in THF are very small. Comparison of the very similar 13C{1H} NMR η3-C3H5 chemical shifts of 1, 3, 10, and 12 does not offer a trend to rationalize a heterobimetallic effect on η3-allyl reactivity toward trityl radical. The modest 3-fold difference in reaction rate between 1 and 12, coupled with a lack of detailed mechanistic information, renders an explanation of the higher conversions of 17 from 1 and 10 relative 3 and 12 tenuous. Concluding Remarks. The emerging utility of the bridging CpPPh ligand to kinetically stabilize early late metal-metal bonds to facilitate novel reactions in heterobimetallics18 is (33) pKa (CH3CN, 298 K): W(η5-Cp)(CO)3H, 16.1(1); Cr(η5-Cp)(CO)3H, 13.3(1) from: Jordon, R. F.; Norton, J. R. J. Am. Chem. Soc. 1982, 104, 1255.

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further established by the syntheses of M0 {M(η3-L)}(CO)3(μ-η5:η1-CpPPh) (M0 =Cr, Mo, W; M=Ni, Pd; L=allyl (M= Ni, Pd), 2-methylallyl (M = Ni), cyclohexenyl (M = Ni)). Complexes 1-6 are the first structurally characterized heterobimetallics with transition metal-Ni(η3-allyl) units, while 7-9 are the only structurally characterized transition metal-Ni(η3cyclohexenyl) complexes. Like Pd(η3-allyl)Cl(PPh3), 1-3 and 10-12 respectively provide 4,4,4-triphenyl-1-butene as the sole allyl ligand coupling product from competitive reactions of phenyl and trityl radicals. However, while phenyl radical attack at the Pd(II) of Pd(η3-allyl)Cl(PPh3) is proposed as the first step in the trityl radical-allyl ligand coupling reaction,17a direct trityl radical attack at η3-allyl is strongly suggested in 1-3 and 10-12, respectively. A heterobimetallic effect may render the chromium complexes 1 and 10 more reactive with trityl radical than the tungsten complexes 3 and 12. Further studies designed to uncover more mechanistic details about these radical reactions and leverage heterobimetallic reaction chemistry with CpPPh and related ligands are underway in this laboratory.

Experimental Section Similar procedures were conducted to synthesize 1-6, 7-9, and 10-12, respectively. Representative procedures for 1, 9, and 10 are provided below. General procedures and complete experimental details for 2-8, 11, and 12 are given in the Supporting Information. Cr{Ni(η3-C3H5)}(CO)3(μ-η5:η1-CpPPh) (1). THF (60 mL) was added to Cr(CO)3(CH3CN)3 (0.601 g, 2.32 mmol) and NaCpPPh (0.696 g, 2.32 mmol). The yellow solution was refluxed for 1.5 h. A solution of Ni2Br2(η3-C3H5)2 (0.416 g, 1.16 mmol) in THF (15 mL) was added; the [Cr(CO)3(η5-CpPPh)]- was consumed within 10 min, resulting in a bright green solution. Filtration through alumina and removal of the solvent in vacuo revealed a green solid. The addition of pentane (50 mL) precipitated a deep green microcystalline solid. The product was isolated by filtration, washed with pentane (4  10 mL), dried in vacuo, and recrystallized from THF/pentane. Pentane diffusion into a nearly saturated pentane/THF solution provided dark purple, moderately air sensitive microcrystals (0.796 g, 67%). Anal. Calcd for C25H23NiO3PCr: C, 58.52; H, 4.52. Found: C, 58.58; H, 4.57. Mp: 184-185 °C (dec). IR (THF): ν(CO) 1897 (s), 1806 (m), 1781 (s, sh) cm-1; (Nujol): ν(CO) 1886 (s), 1787 (s), 1769 (s, sh) cm-1. 1H NMR (C4D8O, 300 MHz): δ 7.80-7.42 (m, 10H, Ph), 5.43 (app. septet, J=6.90 Hz, 1H, η3-C3H5), 4.85 (s, br, 1H, Cp), 4.74 (s, br, 1H, Cp), 4.62 (s, br, 1H, Cp), 4.42 (s, br, 1H, Cp), 3.53 (m, 1H, η3-C3H5), 3.13 (m, 1H, η3-C3H5), 2.64 (m, 1H, η3-C3H5), 2.49-2.37 (m, 4H, CH2CH2P), 2.13 (m, 1H, η3C3H5). 13C{1H} NMR (C4D8O, 75 MHz): δ 248.2 (s, br, CO), 136.1 (d, JPC =41.1 Hz, ipso, Ph), 134.7 (d, 2JPC =11.7, ortho, Ph), 132.4 (d, 2JPC =10.7, ortho, Ph), 131.9 (m, para, Ph), 130.7 (m, para, Ph), 129.9 (d, 3JPC =8.75, meta, Ph), 129.6 (d, 3JPC = 9.81 Hz, meta, Ph), 111.7 (s, C(2), η3-C3H5), 102.5 (s, quat, Cp), 91.3 (s, Cp), 89.8.9 (s, Cp), 82.7 (s, Cp), 81.7 (s, Cp), 76.4 (d, JPC =24.4, η3-C3H5), 63.6 (s, η3-C3H5), 33.3 (d, JPC =29.3 Hz, CH2P), 21.9 (s, CH2CH2P). 31P{1H} NMR (C4H8O, 121 MHz): δ 19.0 (s, PPh2). Deep green solutions prepared from green microcrystals and purple single crystals of 1, respectively, exhibited indistinguishable NMR spectra. Mo{Ni(η3-C3H5)}(CO)3(μ-η5:η1-CpPPh) (2). Yield: 60%. Anal. Calcd for C25H23NiO3PMo: C, 53.90; H, 4.16. Found: C, 54.29; H, 4.53. Mp: 135-137 °C (dec). IR (THF): ν(CO) 1904 (s), 1809 (m), 1788 (s, sh) cm-1; (Nujol): ν(CO) 1890 (s), 1788 (s), 1775 (s, sh) cm-1. 1H NMR (C4D8O, 300 MHz): δ 7.78-7.31 (m, 10H, Ph), 5.45 (m, 1H, Cp), 5.44 (app. septet, J= 6.90 Hz, 1H, η3-C3H5), 5.29 (m, 1H, Cp), 5.15 (m, 1H, Cp), 5.09 (m, 1H, Cp), 5.03 (m, 1H, η3-C3H5), 3.10 (m, 1H,

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η3-C3H5), 2.70 (m, 1H, η3-C3H5), 2.62-2.38 (4H, m, CH2CH2P), 2.11 (m, 1H, η3-C3H5). 13C{1H} NMR (C4D8O, 75 MHz): δ 238.5 (s, CO). 31P{1H} NMR (C4H8O, 121 MHz): δ 19.3 (s, PPh2). W{Ni(η3-C3H5)}(CO)3(μ-η5:η1-CpPPh) (3). Yield: 57%. Anal. Calcd for C25H23NiO3PW: C, 46.56; H, 3.59. Found: C, 46.83; H, 3.74. Mp: 149-150 °C (dec). IR (THF): ν(CO) 1899 (s), 1803 (m), 1783 (s, sh) cm-1; (Nujol): 1884 (s), 1771 (s, br) cm-1. 1H NMR (C4D8O, 300 MHz): δ 7.79-7.31 (m, 10H, Ph), 5.52 (m, 1H, Cp), 5.40 (m, 1H, η3-C3H5), 5.32 (m, 1H, Cp), 5.13 (m, 2H, Cp), 4.88 (m, 1H, η3-C5H5), 3.03 (m, 1H, η3-C3H5), 2.77 (m, 1H, η3-C3H5), 2.64-2.41 (m, 4H, CH2CH2P), 1.93 (m, 1H, η3-C3H5). 13C{1H} NMR (C4D8O, 75 MHz): δ 225.0 (s, br, CO). 31P{1H} NMR (C4H8O, 121 MHz): δ 22.0 (s, PPh2). Cr{Ni(η3-C4H7)}(CO)3(μ-η5:η1-CpPPh) (4). Yield: 68%). Anal. Calcd for C26H25NiO3PCr: C, 59.24; H, 4.78. Found: C, 59.30; H, 4.84. Mp: 150-151 °C (dec). IR (THF): ν(CO) 1897 (s), 1804 (m), 1779 (s, sh) cm-1; (Nujol): ν(CO) 1883 (s), 1795 (s), 1769 (s, sh) cm-1. 1H NMR (C4D8O, 300 MHz): δ 7.85-7.59 (m, 2H, Ph), 7.53-7.51 (m, 8H, Ph), 4.73 (m, 1H, Cp), 4.69 (m, 2H, Cp), 4.56 (m, 1H, Cp), 3.48 (m, 1H, η3-C4H7), 2.90 (m, 1H, η3-C4H7), 2.66 (m, 1H, η3-C4H7), 2.51 (m, 1H, η3-C4H7), 2.50 - 2.36 (m, 2H, CH2P), 2.17-2.00 (2H, m, CH2CH2P), 1.76 (s, 3H, CH3). 13 C{1H} NMR (C4D8O, 75 MHz): δ 249.3 (s, br, CO), 247.4 (s, br, CO), 244.5 (s, br, CO). 31P{1H} NMR (C4H8O, 121 MHz): δ 24.5 (s, PPh2). Mo{Ni(η3-C4H7)}(CO)3(μ-η5:η1-CpPPh) (5). Yield: 65%. Anal. Calcd for C26H25NiO3PMo: C, 54.68; H, 4.41. Found: C, 55.15; H, 4.54. Mp: 134-135 °C (dec). IR (THF): ν(CO) 1904 (s), 1807 (m), 1787 (s, sh) cm-1; (Et2O): ν(CO) 1911 (s), 1813 (m), 1789 (s, sh) cm-1; (Nujol): ν(CO) 1896 (s), 1802 (s), 1761 (s) cm-1. 1H NMR (C4D8O, 300 MHz): δ 7.81-7.62 (m, 2H, Ph), 7.55-7.26 (m, 8H, Ph), 5.28 (m, 1H, Cp), 5.19-5.13 (m, 3H, Cp), 3.51 (m, 1H, η3-C4H7), 2.81 (m, 1H, η3-C4H7), 2.68 (m, 1H, η3-C4H7), 2.58-2.45 (m, 2H, CH2P), 2.42 (m, 1H, η3-C4H7), 2.19-2.05 (2H, m, CH2CH2P), 1.76 (s, 3H, CH3). 13C{1H} NMR (C4D8O, 75 MHz): δ 236.2 (s, br, CO). 31P{1H} NMR (C4H8O, 121 MHz): δ 24.5 (s, PPh2). W{Ni(η3-C4H7)}(CO)3(μ-η5:η1-CpPPh) (6). Yield: 62%. Anal. Calcd for C26H25NiO3PW: C, 47.39; H, 3.82. Found: C, 47.62; H, 3.84. Mp: 146-147 °C (dec). IR (THF): ν(CO) 1899 (s), 1801 (m), 1781 (s, sh) cm-1; (Nujol): 1892 (s), 1801 (s), 1768 (s, sh) cm-1. 1H NMR (C4D8O, 300 MHz): δ 7.82-7.67 (m, 2H, Ph), 7.52-7.44 (m, 8H, Ph), 5.36 (m, 1H, Cp), 5.24 (m, 1H, Cp), 5.20 (m, 2H. Cp), 3.58 (m, 1H, η3-C4H7), 2.76 (m, 1H, η3-C4H7), 2.73 (m, 1H, η3-C4H7), 2.66-2.48 (m, 2H, CH2P), 2.31 (m, 1H, η3-C4H7), 2.14 (2H, dt, J = 20.1 Hz, 3JPH = 5.70 Hz, CH2CH2P), 1.77 (s, 3H, CH3). 13C{1H} NMR (C4D8O, 75 MHz): δ 225.5 (s, br, CO). 31 P{1H} NMR (C4H8O, 121 MHz): δ 31.1 (s, PPh2). Cr{Ni(η3-C6H9)}(CO)3(μ-η5:η1-CpPPh) (7). Yield: 65%. Anal. Calcd for C28H27O3CrNiP: C, 60.76; H, 4.92. Found: C, 61.16; H, 5.31. Mp: 114-115 °C (dec). IR (THF): ν(CO) 1894 (s), 1802 (m), 1767 (s) cm-1; (Nujol): 1880 (s), 1793 (w), 1755 (s, sh) cm-1. 1H NMR (C4H8O, 300 MHz): δ 7.91-7.84 (m, 2H, Ph), 7.58-7.37 (m, 8H, Ph), 5.87 (app. t, 1H, J=6.90 Hz, η3-C6H9), 4.89 (m, 1H, Cp), 4.77 (m, 1H, Cp), 4.54 (m, 1H, η3-C6H9), 4.45 (m, 1H, Cp), 4.43 (m, 1H, η3-C6H9), 4.23 (m, 1H, Cp), 2.72-2.38 (m, 4H, CH2CH2P), 1.59-1.30 (m, 4H, η3-C6H9), 0.89-0.60 (m, 2H, η3C6H9). 13C{1H} NMR (C4H8O, 75 MHz): δ 252.0 (s, CO), 249.8 (s, CO), 244.1 (s, CO). 31P{1H} NMR (C4D8O, 121 MHz): δ 24.1 (s, PPh2). Mo{Ni(η3-C6H9)}(CO)3(μ-η5:η1-CpPPh) (8). Yield: 65%. Anal. Calcd for C28H27O3MoNiP: C, 56.32; H, 4.56. Found: C, 56.33; H, 4.82. Mp: 134-135 °C (dec). IR (THF): ν(CO) 1902 (s), 1809 (m), 1771 (s) cm-1; (Nujol): 1891 (s), 1783 (m), 1757 (s, sh) cm-1. 1 H NMR (C4H8O, 300 MHz): δ 7.87-7.80 (m, 2H, Ph), 7.58-7.36 (m, 8H, Ph), 5.83 (app. t, 1H, J = 6.90 Hz, η3-C6H9), 5.46 (m, 1H, Cp), 5.36 (m, 1H, Cp), 4.88 (m, 1H, Cp), 4.84 (m, 1H, Cp), 4.60 (m, 1H, η3-C6H9), 4.36 (m, 1H, η3-C6H9), 2.72-2.48 (m, 4H, CH2CH2P), 1.56-1.29 (m, 4H, η3-C6H9), 0.80-0.44 (m, 2H,

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η3-C6H9). 13C{1H} NMR (C4H8O, 75 MHz): δ 239.0 (s, br, CO). 31 P{1H} NMR (C4D8O, 121 MHz): δ 24.1 (s, PPh2). W{Ni(η3-C6H9)}(CO)3(μ-η5:η1-CpPPh) (9). THF (70 mL) was added to W(CO)3(CH3CH2CN)3 (0.993 g, 2.29 mmol) and NaCpPPh (0.689 g, 2.29 mmol). The yellow solution was refluxed for 1.5 h. A solution of Ni2Cl2(η3-C6H9)2 (0.504 g, 0.869 mmol) in THF (15 mL) was added; the [W(CO)3(η5-CpPPh)]- was consumed within 15 min, resulting in a deep brown solution. Filtration through alumina and concentration of the filtrate in vacuo to ∼2 mL resulted in a saturated deep red solution. The addition of pentane (100 mL) precipitated a red-brown microcrystalline solid. The product was isolated by filtration, washed with pentane (3  10 mL), dried in vacuo, and recrystallized from THF/pentane. Pentane diffusion into a nearly saturated pentane/THF solution provided deep red, moderately air sensitive microcrystals (1.03 g, 66%). Anal. Calcd for C28H27O3NiPW: C, 49.09; H, 3.97. Found: C, 49.00; H, 4.26. Mp: 149-150 °C (dec). IR (THF): ν(CO) 1897 (s), 1802 (s), 1764 (s) cm-1; (Nujol): 1887 (s), 1774 (m), 1751 (s, sh) cm-1. 1H NMR (C4H8O, 300 MHz): δ 7.89-7.82 (m, 2H, Ph), 7.59-7.35 (m, 8H, Ph), 5.81 (app. t, 1H, J = 6.60 Hz, η3-C6H9), 5.52 (m, 1H, Cp), 5.38 (m, 1H, Cp), 4.94 (m, 1H, Cp), 4.91 (m, 1H, Cp), 4.65 (m, 1H, η3-C6H9), 4.28 (m, 1H, η3-C6H9), 2.72-2.58 (m, 4H, CH2CH2P), 1.61-1.31 (m, 4H, η3-C6H9), 0.83-0.53 (m, 2H, η3-C6H9). 13C{1H} NMR (C4H8O, 75 MHz): δ 231.3 (s, br, CO), 228.2 (s, br, CO), 224.7 (s, br, CO), 137.7 (d, JPC = 35.2 Hz, ipso, Ph), 136.0 (d, 2JPC = 12.7 Hz, ortho, Ph), 132.4 (s, para, Ph), 131.8 (d, 3JPC =8.83 Hz, meta, Ph), 131.0 (d, JPC =37.1 Hz, ipso, Ph), 130.1 (d, 2JPC =9.73, ortho, Ph), 130.0 (s, para, Ph), 129.5 (d, 3JPC = 7.85 Hz, meta, Ph), 108.0 (s, η3-C6H9), 106.6 (d, 3JPC=2.94 Hz, quat, Cp), 93.7 (s, Cp), 90.99 (s, Cp), 90.97 (d, JPC =27.4, η3-C6H9), 85.6 (s, η3-C6H9), 80.8 (s, Cp), 80.0 (s, Cp), 36.2 (d, JPC =28.3 Hz, CH2P), 29.1 (d, 2JPC = 3.93 Hz, CH2CH2P), 28.4 (s, η3-C6H9), 22.8 (s, η3-C6H9), 20.2 (s, η3-C6H9). 31P{1H} NMR (C4D8O, 121 MHz): δ 26.8 (s, PPh2). Cr{Pd(η3-C3H5)}(CO)3(μ-η5:η1-CpPPh) (10). THF (50 mL) was added to Cr(CO)3(CH3CN)3 (0.601 g, 2.32 mmol) and NaCpPPh (0.696 g, 2.32 mmol). The yellow solution was refluxed for 1.5 h. A solution of Pd2Cl2(η3-C3H5)2 (0.424 g, 1.16 mmol) in THF (20 mL) was added; the [Cr(CO)3(η5-CpPPh)]- was consumed within 15 min, resulting in a deep red solution. Filtration through alumina and in vacuo solvent removal provided a microcrystalline red solid. The product was suspended in pentane (75 mL), isolated by filtration, washed with pentane (3  10 mL), dried in vacuo, and recrystallized from THF/pentane. Pentane diffusion into a nearly saturated pentane/THF solution provided deep red, moderately air sensitive microcrystals (0.660 g, 51%). Anal. Calcd for C25H23O3CrPPd: C, 53.54; H, 4.13. Found: C, 53.37; H, 3.93. Mp: 182-183 °C (dec). IR (THF): ν(CO) 1902 (s), 1818 (m, sh), 1802 (s) cm-1; (Nujol): 1890 (s), 1787 (s), 1739 (m, sh), 1716 (m, sh) cm-1. 1H NMR (C4H8O, 300 MHz): δ 7.67-7.45 (m, 10H, Ph), 5.48 (app. septet, 1H, J= 7.2 Hz, η3-C3H5), 4.71 (m, 2H, Cp), 4.61 (m, 1H, Cp), 4.52 (m, 1H, Cp), 3.97 (m, 1H, η3-C3H5), 3.58 (m, 1H, η3-C3H5), 3.05 (m, 1H, η3-C3H5), 2.79 (m, 1H, η3-C3H5), 2.62-1.99 (m, 4H, CH2CH2P). 13C{1H} NMR (C4H8O, 75 MHz): δ 242.9 (s, br, CO), 136.3 (d, JPC = 39.1 Hz, ipso, Ph), 134.7 (d, JPC = 39.1, ipso, Ph), 134.3 (d, 2JPC =12.7 Hz, ortho, Ph), 133.0 (d, 2JPC = 11.7 Hz, ortho, Ph), 131.6 (s, para, Ph), 131.0 (s, para, Ph), 129.8 (d, 3JPC =9.8 Hz, meta, Ph), 129.7 (d, 3JPC =9.7 Hz, meta, Ph), 117.5 (d, JPC=6.8 Hz, η3-C3H5), 104.0 (s, quat, Cp), 90.0 (s, Cp), 89.2 (s, Cp), 82.5 (s, Cp), 81.5 (s, Cp), 78.5 (d, JPC = 36.2 Hz, η3-C3H5), 72.8 (d, JPC = 4.9 Hz, η3-C3H5), 32.5 (d, JPC = 27.3 Hz, CH2P), 22.7 (s, CH2CH2P). 31P{1H} NMR (C4D8O, 121 MHz): δ 27.0 (s, PPh2). Mo{Pd(η3-C3H5)}(CO)3(μ-η5:η1-CpPPh) (11). Yield: 52%. Anal. Calcd for C25H23O3MoPPd: C, 49.65; H, 3.83. Found: C, 50.05; H, 3.75. Mp: 158-159 °C (dec). IR (THF): ν(CO) 1913 (s), 1813 (s) cm-1; (Nujol): 1941 (w), 1900 (s), 1797 (s), 1720

Fischer et al. (m, sh) cm-1. 1H NMR (C4H8O, 300 MHz): δ 7.66-7.28 (m, 10H, Ph), 5.41 (app. septet, 1H, J= 6.9 Hz, η3-C3H5), 5.32 (m, 1H, Cp), 5.20 (m, 1H, Cp), 5.12 (m, 1H, Cp), 5.09 (m, 1H, Cp), 4.06 (m, 1H, η3-C3H5), 3.56 (m, 1H, η3-C3H5), 3.10 (m, 1H, η3-C3H5), 2.90-2.06 (m, 4H, CH2CH2P), 2.72 (m, 1H, η3-C3H5). 13 C{1H} NMR (C4H8O, 75 MHz): δ 233.3 (s, br, CO). 31P{1H} NMR (C4D8O, 121 MHz): δ 27.3 (s, PPh2). W{Pd(η3-C3H5)}(CO)3(μ-η5:η1-CpPPh) (12). Yield: 45%. Anal. Calcd for C25H23O3PPdW: C, 43.35; H, 3.35. Found: C, 43.09; H, 3.16. Mp: 167-168 °C (dec). IR (THF): ν(CO) 1910 (s), 1809 (s) cm-1; (Nujol): 1896 (s), 1789 (s), 1717 (m, sh) cm-1. 1H NMR (C4H8O, 300 MHz): δ 7.66-7.28 (m, 10H, Ph), 5.41 (m, 1H, Cp), 5.38 (app. septet, 1H, η3-C3H5), 5.22 (m, 2H, Cp), 5.12 (m, 1H, Cp), 4.16 (m, 1H, η3-C3H5), 3.58 (m, 1H, η3-C3H5), 3.2 (m, 1H, η3-C3H5), 2.90-2.13 (m, 4H, CH2CH2P), 2.69 (m, 1H, η3-C3H5). 13 C{1H} NMR (C4H8O, 75 MHz): δ 221.6 (s, br, CO). 31P{1H} NMR (C4D8O, 121 MHz): δ 23.4 (s, PPh2). X-ray Crystallographic Characterization of 1-12. X-ray quality crystals of 1-12 were obtained by diffusion of pentane into nearly saturated THF/pentane solutions of each compound. Crystals were selected from the mother liquor in a N2-filled glovebag. Crystallographic characterization details for 1-12, including data collection, solution, and refinement information, are in the Supporting Information. A summary of diagnostic X-ray crystallographic information for 1-4, 5-8, and 9-12 are provided in Tables S1, S2, and S3, respectively. General Protocol for Reactions of 1-3 and 10-12 with PAT. Benzene (30 mL) was added to three samples of 1-3 and 10-12 (0.178 mmol), respectively, and PAT (0.248 g, 0.712 mmol). The solution was refluxed (1.5 h). The resulting mixture and an aliquot (1 mL) were massed. An aliquot (150 μL) was diluted 10-fold in a vial containing an anthracene internal standard (0.00421 M final concentration). Samples were analyzed by GC/MS; concentrations of 4,4,4-triphenyl-1-butene, triphenylmethane, tetraphenylmethane, and biphenyl were determined via standard curves (Figures S10-13), and conversions were determined from reaction mixture volumes. General Protocol for Reactions of 1-3 and 10-12 with Trityl Dimer. Benzene (30 mL) was added in the dark to three samples of 1-3 and 10-12 (0.178 mmol), respectively, and trityl dimer (0.173 g, 0.355 mmol). Protective foil was removed and the solution was refluxed (1.5 h). The resulting mixture and an aliquot (1 mL) were massed. An aliquot (150 μL) was diluted 10-fold in a vial containing an anthracene internal standard (0.00421 M final concentration). Samples were analyzed by GC/MS; concentrations of 4,4,4-triphenyl-1-butene and triphenylmethane were determined via standard curves (Figures S10, S11), and conversions were determined from reaction mixture volumes.

Acknowledgment. The donors of the Petroleum Research Fund, administered by the American Chemical Society (ACS-PRF 46626-B), supported this research. P. J.F. thanks Letitia J. Yao (University of Minnesota) for facilitating NMR access, Victor G. Young, Jr. and Benjamin E. Kucera (University of Minnesota X-ray Crystallographic Laboratory), as well as Rebecca C. Hoye (Macalester College) and Timothy P. Hanusa (Vanderbilt University) for helpful discussions. Supporting Information Available: Text, figures, and tables giving additional experimental details, 13C NMR spectral data, GC/MS data, calibration curves and crystallographic data, as well as data collection, solution, and refinement information for 1-12; crystallographic data are also given as a CIF file. This material is available free of charge via the Internet at http:// pubs.acs.org.