An Unprecedented Phosphinamidic Gold(III) Metallocycle: Synthesis

Organometallics 2009, 28, 1739–1747

1739

An Unprecedented Phosphinamidic Gold(III) Metallocycle: Synthesis via Tin(IV) Precursors, Structure, and Multicomponent Catalysis Pascual Onã-Burgos,† Ignacio Fernańdez,† Laura Roces,‡ Laura Torre Fernańdez,‡ Santiago Garcıá-Granda,‡ and Fernando Lo´pez Ortiz*,† A´rea de Quı´mica Orgańica, UniVersidad de Almerıá, Crta. Sacramento s/n, 04230, Almerıá, Spain, and Departamento de Quı´mica Fı´sica y Analı´tica, UniVersidad de OViedo, C/ Juliań ClaVerıá 8, 33006 OViedo, Spain ReceiVed NoVember 28, 2008

A straightforward method of synthesizing cycloaurated gold(III) phosphinamide-based molecules starting from their ortho-tin(IV) derivatives in excellent yields is described. The structure of the tin and gold complexes has been investigated by multinuclear magnetic resonance (1H, 13C, 15N,31P, 119Sn) and singlecrystal X-ray diffraction. In solution and in the solid state the ortho-functionalized phosphinamide moiety acts as a new C-C-P-O pincer ligand with formation of asymmetric five-membered ring metallocycles. Intramolecular PdO coordination to tin(IV) leads to a distorted trigonal-bipyramid configuration for the metal, while in the gold(III) metallocyclic complex the metal shows a square-planar geometry. The new Au(III) complex has been applied in multicomponent (A3) coupling processes, providing a variety of propargylamines in quantitative yields under very mild conditions without the use of any activator or additive. Diffusion NMR studies showed that the catalyst is present as a monomer in acetonitrile solution, while a slight charge-induced aggregation seems to take place in chloroform. Introduction

Chart 1. C,N-Cycloaurated Au(III) Complexes

Gold(III) complexes are currently the focus of great attention due to their applications as catalysts in organic synthesis1 and as chemotherapeutic agents for the treatment of a variety of diseases.2 The Au(III) can be stabilized by integrating the ion into a metallocycle. Cycloaurated d8 complexes are generally prepared through transmetalation from the corresponding organomercury(II) compounds.3 Direct cycloauration via C-H bond activation by gold(III) salts with4 or without3d,5 the assistance of silver(I) ions is also feasible in a number of cases. Most studies have concentrated on N,N-dimethylbenzylamine and phenyl- or benzylpyridines as C,N pincer ligands, leading to five- and six-membered chelate rings.6 Only four types of cycloaurated compounds in which chelation involves a polar * Corresponding author. Tel: +34 950 015478. Fax: +34 950 015481. E-mail: [email protected]. † Universidad de Almerıá. ‡ Universidad de Oviedo. (1) (a) Dyker, G. Angew. Chem., Int. Ed. 2000, 39, 4237. (b) Hashmi, A. S. K.; Hutchings, G. J. Angew. Chem., Int. Ed. 2006, 45, 7896. (c) Jimeńez-Nuń˜ez, E.; Echavarren, A. M. Chem. Commun. 2007, 333. (d) Hashmi, A. S. K. Chem. ReV. 2007, 107, 3180. (e) Fu¨rstner, A.; Davies, P. W. Angew. Chem., Int. Ed. 2007, 46, 3410. (f) Gorin, D. J.; Toste, F. D. Nature 2007, 446, 395. (g) Bongers, N.; Krause, N. Angew. Chem., Int. Ed. 2008, 47, 2178. (2) (a) Shaw, C. F. Chem. ReV. 1999, 99, 2589. (b) Sun, R. W.-Y.; Ma, D.-L.; Wong, E. L.-M.; Che, C.-M. Dalton Trans. 2007, 4884. (c) Barnard, P. J.; Berners-Price, S. J. Coord. Chem. ReV. 2007, 251, 1889. (d) Bruijnincx, P. C. A.; Sadler, P. J. Curr. Opin. Chem. Biol. 2008, 12, 197. (3) (a) Vicente, J.; Chicote, M. T. Inorg. Chim. Acta 1981, 54, L259. (b) Vicente, J.; Chicote, M. T.; Bermu´dez, M. D. Inorg. Chim. Acta 1982, 63, 35. (c) Vicente, J.; Chicote, M. T.; Bermu´dez, M. D. J. Organomet. Chem. 1984, 268, 191. (d) Constable, E. C.; Leese, T. A. J. Organomet. Chem. 1989, 369, 419. (e) Vicente, J.; Bermu´dez, M. D.; Carrillo, M. P.; Jones, P. G. J. Chem. Soc., Dalton Trans. 1992, 1975. (f) Vicente, J.; Bermu´dez, M. D.; Carrioń, F. J.; Martıńez-Nicola´s, G. J. Organomet. Chem. 1994, 480, 103. (4) (a) Fuchita, Y.; Ieda, H.; Tsunemune, Y.; Kinoshita-Nagaoka, J.; Kawano, H. J. Chem. Soc., Dalton Trans. 1998, 791. (b) Fuchita, Y.; Ieda, H.; Yasutake, M. J. Chem. Soc., Dalton Trans. 2000, 271. (c) Ieda, H.; Fujiwara, H.; Fuchita, Y. Inorg. Chim. Acta 2001, 319, 203.

π-system sidearm located at the ortho position of a phenyl ring have been reported (Chart 1). Complexes 1 (R ) Me),3e 2,7 3,8

(5) (a) Vicente, J.; Arcas, A.; Mora, M.; Solans, X.; Font-Altaba, M. J. Organomet. Chem. 1986, 309, 369. (b) Cinellu, M. A.; Zucca, A.; Stoccoro, S.; Minghetti, G.; Manassero, M.; Sansoni, M. J. Chem. Soc., Dalton Trans. 1995, 2865. (c) Fuchita, Y.; Ieda, H.; Kayama, A.; Nagaoka-Kinoshita, J.; Kawano, H.; Kameda, S.; Mikuriya, M. J. Chem. Soc., Dalton Trans. 1998, 4095. (d) Fuchita, Y.; Ieda, H.; Wada, S.; Kameda, S.; Mikuriya, M. J. Chem. Soc., Dalton Trans. 1999, 4431. (e) Nonoyama, M.; Nakajima, K.; Nonoyama, K. Polyhedron 2001, 20, 3019. (f) Zhu, Y.; Cameron, B. R.; Skerli, R. T. J. Organomet. Chem. 2003, 677, 57. (6) Henderson, W. AdV. Organomet. Chem. 2006, 54, 207. (7) Vicente, J.; Bermu´dez, M. D.; Carrioń, F. J.; Jones, P. G. Chem. Ber. 1996, 129, 1301. (8) Bonnardel, P. A.; Parish, R. V.; Pritchard, R. G. J. Chem. Soc., Dalton Trans. 1996, 3185.

10.1021/om801137y CCC: $40.75  2009 American Chemical Society Publication on Web 02/27/2009

1740 Organometallics, Vol. 28, No. 6, 2009 Chart 2. Bis-(C,N)-Chelated Gold(III) Complexesa

a

R1 ) H, OMe; R2 ) H, Me. Anion [AuCl4]- is omitted for clarity.

Chart 3. Complexes of Bidentate Phoshinamides

and 4,9 have a square-planar Au(III) center, attached to two Cl ligands, one nitrogen, and one C-ortho atom, establishing a fivemembered metallocycle, which is in all cases significantly puckered. Complexes containing two cycloaurating ligands containing a spirane gold as in 510a and 610b have also been reported. In 6, the difference between the N(sp3)-Au and N(sp2)-Au distances is scarcely significant and has been attributed to the more strained phenylazo chelate ring, which accounts for its greater lability. To the best of our knowledge, there are no examples of metallocycles of Au(III) containing C,O pincer ligands. Inspired by complex 4, we reasoned that C,O chelation of Au(III) salts could be achieved via ortho metalation of diphenylphosphinamides. Phosphinamide derivatives have been widely used as bidentate ligands for the synthesis of a large variety of metal complexes. Generally, metallocyclic formation takes place through metal binding to the oxygen of the PO group and to a heteroatom present in the nitrogen sidearm. Most complexes showing this coordination mode are based on the use of tetraorganodichalcogenoimidophosphorus acids11 7 or N-(diphenylphosphino)-P,P-diphenylphosphinic amides12 8 as ligands (Chart 3). Less common phosphinamide metallocylic complexes 913 and 1014 are also included in Chart 3.15 We have previously shown that diphenylphosphinamides can be readily functionalized at the ortho position of a P-phenyl ring in a one-pot reaction process involving ortho lithiation directed16 by the P(O)N linkage followed by electrophilic trapping.17 The directed ortho lithiation step produces the desymmetrization of the Ph2P(O) (Pop) moiety. Quenching the lithiated intermediate 12 with tin(IV) halides affords orthostannylated phosphinamides 13 in high yields (Scheme 1).17b The success of these lithium-tin transmetalation reactions suggests that the ortho-lithiated phosphinamide may become a (9) (a) Brown, S. D. J.; Henderson, W.; Kilpin, K. J.; Nicholson, B. K. Inorg. Chim. Acta 2007, 360, 1310. (b) Aguilar, D.; Contel, M.; Navarro, R.; Urriolabeitia, E. P. Organometallics 2007, 26, 4604.

Onã-Burgos et al.

valuable ligand in coordination chemistry with two favored binding modes: κ2-C,O- and κ2-C,N-chelation (see A and B in Scheme 1). The reaction of organolithium reagents with Au(III) halides generally promotes the reduction of the Au ion to metallic gold,18 which makes the synthesis of complexes A and B, with M ) Au(III), through lithium-gold(III) exchange reactions unfeasible. A more promising route for accessing gold(III) cycloaurated complexes of phosphinamides would be the use of stannylated derivatives 13 as starting materials. As far as we are aware, Sn(IV)-Au(III) transmetalation reactions have been applied with limited success only on three occasions.19 In this paper we present (1) a versatile method for preparing phosphinamidic gold(III) complexes by ligand transfer from tin(IV) to gold; (2) the solution and solid state structure of a tin(IV) phosphinamide derivative as key synthon in gold chemistry; (3) the crystal structure of the first metallocycle where a d8-gold metal is directly coordinated to a desymmetrized phosphinoyl group; (4) the use of this complex in the threecomponent coupling of aldehyde, alkyne, and amine free of any activator or additives; and (5) a diffusion NMR investigation of the mechanism of catalysis. Our catalyst represents a significant improvement relative to other Au sources in that the transformations proceed faster, in higher yields, and under milder reaction conditions. (10) (a) Vicente, J.; Chicote, M. T.; Bermudez, M. D. J. Chem. Soc., Dalton Trans. 1984, 557. (b) Vicente, J.; Chicote, M. T.; Bermudez, M. D.; Sanchez-Santano, M. J. J. Organomet. Chem. 1986, 310, 401. (11) (a) Review: Silvestru, C.; Drake, J. E. Coord. Chem. ReV. 2001, 223, 117. For some recent references see: (b) Morales-Juarez, J.; CeaOlivares, R.; Moya-Cabrera, M. M.; Jancik, V.; Garcia-Montalvo, V.; Toscano, R. A. Inorg. Chem. 2005, 44, 6924. (c) Rotar, A.; Silvestru, A.; Silvestru, C.; Drake, J. E.; Hursthouse, M. B.; Light, M. E.; Bunaciu, L.; Bunaciu, P. Appl. Organomet. Chem. 2005, 19, 555. (d) Cheung, W.-M.; Lai, C.-Y.; Zhang, Q.-F.; Wong, W.-Y.; Williams, I. D.; Leung, W.-H. Inorg. Chim. Acta 2006, 359, 2712. (e) Lemus-Santana, A. A.; Reyes-Lezama, M.; Zuniga-Villarreal, N.; Toscano, R. A.; Espinosa-Perez, G. E. Organometallics 2006, 25, 1857. (f) Cristurean, A.; Irisli, S.; Marginean, D.; Rat, C.; Silvestru, A. Polyhedron 2008, 27, 2143. (g) Cheung, W.-M.; Ng, H.Y.; Williams, I. D.; Leung, W.-H. Inorg. Chem. 2008, 47, 4383. (12) (a) Smith, M. B.; Slawin, A. M. Z. Inorg. Chim. Acta 2000, 299, 172. (b) Parr, J.; Smith, M. B.; Elsegood, M. R. J. J. Organomet. Chem. 2002, 664, 85. (c) Haid, R.; Gutmann, R.; Czermak, G.; Langes, C.; Oberhauser, W.; Kopacka, H.; Ongania, K.-H.; Bruggeller, P. Inorg. Chem. Commun. 2003, 6, 61. (d) Cole, M. L.; Deacon, G. B.; Junk, P. C.; Konstas, K.; Roesky, P. W. Eur. J. Inorg. Chem. 2005, 1090. (e) Chatziapostolou, K. A.; Vallianatou, K. A.; Grigoropoulos, Al.; Raptopoulou, C. P.; Terzis, A.; Kostas, I D.; Kyritsis, P.; Pneumatikakis, G. J. Organomet. Chem. 2007, 692, 4129. (13) Garcıá-Hernańdez, Z.; Flores-Parra, A.; Grevy, J. M.; RamosOrganillo, A.; Contreras, R. Polyhedron 2006, 25, 1662. (14) Henning, H. G.; Ladhoff, U. Zeit. Chem. 1973, 13, 16. (15) P,N-chelation leading to four-membered metallocylces is also well known. See, for instance: (a) Ruck, R. T.; Bergman, R. G. Organometallics 2004, 23, 2231. (b) Dolinsky, M. C. B.; Lin, W. O.; Dias, M. L. J. Mol. Catal. A: Chem. 2006, 258, 267. (c) Watson, D. A.; Chiu, M.; Bergman, R. G. Organometallics 2006, 25, 4731. (d) Platel, R. H.; White, A. J. P.; Williams, C. K. Inorg. Chem. 2008, 47, 6840. (16) (a) Fernańdez, I.; Gonza´lez, J.; Lo´pez-Ortiz, F. J. Am. Chem. Soc. 2004, 126, 12551. (b) Morań-Ramallal, A.; Lo´pez-Ortiz, F.; Gonza´lez, J. Org. Lett. 2004, 6, 2141. (c) Morań-Ramallal, A.; Fernańdez, I.; Lo´pezOrtiz, F.; Gonza´lez, J. Chem.-Eur. J. 2005, 11, 3022. (17) (a) Fernańdez, I.; Forceń-Acebal, A.; Lo´pez-Ortiz, F.; GarcıáGranda, S. J. Org. Chem. 2003, 68, 4472. (b) Fernańdez, I.; Onã-Burgos, P.; Ruiz-Gomez, G.; Bled, C.; Garcia-Granda, S.; Lo´pez-Ortiz, F. Synlett 2007, 611. (18) For some successful examples see: (a) Braye, E. H.; Hu¨bel, W.; Caplier, I. J. Am. Chem. Soc. 1961, 83, 4406. (b) Schmidbaur, H.; Franke, R. Inorg. Chim. Acta 1975, 13, 85. (c) Schmidbaur, H.; Hartmann, C.; Riede, J.; Huber, B.; Mu¨ller, G. Organometallics 1986, 5, 1652. (19) (a) Uson, R.; Vicente, J.; Chicote, M. T. Inorg. Chim. Acta 1979, 35, L305. (b) Uson, R.; Vicente, J.; Cirac, J. A.; Chicote, M. T. J. Organomet. Chem. 1980, 198, 105. (c) Paul, M.; Schmidbaur, H. Z. Naturforsch. B 1994, 49, 647.

Unprecedented Phosphinamidic Gold(III) Metallocycle

Organometallics, Vol. 28, No. 6, 2009 1741

Scheme 1. Directed ortho Functionalization of Phosphinamides and Possible Coordination Modes

Scheme 2. Synthesis of 17a

a Routes with trimethylstannane 15 or chlorodimethylstannane 16 as key intermediates.

Results and Discussion The gold(III) phosphinamidic complex 17 was synthesized according to Scheme 2. We have previously reported the ortho stannylation of 14 by treating the substrate with t-BuLi at -90 °C in THF solution and then trapping the anionic intermediate with trimethyltin chloride to afford 15.17b Chlorostannane 16 is obtained in the same manner in 89% yield by allowing the ortho-lithiated species to react with Cl2SnMe2 at -90 °C. Heating a CH3CN solution of compound 15 or 16 in the presence of 2 or 1 equiv of the gold salt K[AuCl4], respectively, provides the Au(III) complex 17 (Scheme 2). Stepwise recrystallization of the reaction crude in dichloromethane and then Et2O allowed us to isolate pure 17 in excellent yield (86%). Stannane 16 can be viewed as a synthetic intermediate in the transformation of 15 into 17. Indeed, substitution of a methyl group of 15 by a chlorine is achieved in less than 5 min at room temperature by mixing an equimolar CH3CN solution of 15 with K[AuCl4] (Scheme 2).20 Obviously, the synthesis of 17 from 16 is more efficient than the alternative pathway from 15. Besides the fact that only 1 equiv of the Au(III) salt is used, the byproduct formed, Me2SnCl2, can be recycled for the synthesis of the starting ortho stannane 16. Formally, the two-step reaction sequence toward 17 is equivalent to its direct preparation through auration of ortho-lithiated 14.18 The synthetic route shown here represents a versatile method of accessing cycloaureated compounds via almost unexplored tin(IV)-gold(III) transmetalation reactions,19 thus avoiding the use of organomercury(II) compounds. More(20) Substitution of a methyl group linked to tin and anti to a chelating group by halide is well known for hypervalent organostannanes. See for instance: (a) Podesta, J. C.; Chopa, A. B.; Ayala, A. D.; Koll, L. C. J. Organomet. Chem. 1987, 333, 25. (b) Davenport, A. J.; Davies, D. L.; Fawcett, J.; Russell, D. R. J. Chem. Soc., Dalton Trans. 2002, 3260.

over, ortho metalation of 14 produces the desymmetrization of the Ph2P(O) moiety, which represents an easy entry to chiral derivatives. Solution Structure of Complexes 16 and 17. The tin(IV) precursor 16 and the gold(III) complex 17 have been fully characterized through mass spectrometric, FT-IR, and multinuclear magnetic resonance spectroscopic methods (see Experimental Section). Simple inspection of the aromatic region of the 1H spectrum of 16 confirmed the replacement of an ortho proton of 14 by a Me2SnCl moiety. This assignment is evidenced by the two multiplets at δ 7.98 (2ArH) and 8.10 (1ArH) ppm, corresponding to the ortho protons of the unsubstituted and substituted P-phenyl rings, respectively, and the doublet at δ 8.59 (1ArH) ppm arising from the proton ortho to the metal, which shows 119Sn satellites [3J(119Sn1H) ) 35.0 Hz]. Desymmetrization of the Ph2P(O) moiety makes the methyl groups attached to tin(IV) diastereotopic, appearing at δ 0.72 and 0.91 ppm. The 31P signal of 16 at δ 37.1 ppm is shifted ca. 8 ppm to higher frequencies compared to the substrate 14 (δ 30.6 ppm) (Table 1).17 This shift is ascribed to intramolecular coordination of the phosphinamide group to the metal, an assignment supported by various heteronuclear couplings and chemical shifts. Thus, the 119Sn,31P coupling of 16.7 Hz [sum of 3 J(SnCCP) and 2J(SnOP)] is in the range found for analogous ortho-stannylated phosphine oxides21b,c and phosphonates.22 Tin pentacoordination in organotin compounds is characterized by an increase in 2J(119Sn1HMe) and 1J(119Sn13C), as well as a shift to higher frequencies of the 119Sn signal.23 The 119Sn satellites of the methyl protons provide couplings to the metal of 2 119 J( Sn1H) ) 75.8 and 76.8 Hz (Table 1), which are significantly larger than the 2J(119Sn1H) ) 58.5 Hz of PhMe2SnCl,21b but quite similar to the 76.0 Hz reported for 2J(119Sn1H) in the intramolecularly coordinated Ph2P(O)C6H4SnClMe2.21c The measured one-bond 119Sn,13C couplings in 16 are 685.1 and 577.2 Hz for the Cipso and methyl carbon, respectively, i.e., in the expected range for pentacoordinated tin.24 The 1H,119Sn gHMQC spectrum optimized for the detection of long-range couplings showed all possible correlations of protons separated by two, three, and four bonds with the 119Sn signal appearing at δ -84.1 ppm (Figure 1a). This value is shifted 132.4 ppm to higher frequencies with respect to PhMe2SnCl21b and is comparable to the δ(119Sn) measured for similar organotin (21) (a) Weichmann, H.; Mugge, C.; Grand, A.; Robert, J. B. J. Organomet. Chem. 1982, 238, 343. (b) Weichmann, H.; Schmoll, C. Z. Chem. 1984, 24, 390. (c) Hartung, H.; Petrick, D.; Schmoll, C.; Weichmann, H. Z. Anorg. Allg. Chem. 1987, 550, 140. (22) Mehring, M.; Schurmann, M.; Jurkschat, K. Organometallics 1998, 17, 1227. (23) (a) Wrackmeyer, B. In Annual Reports on NMR Spectroscopy; Webb, G. A., Ed.; Academic Press: London, 1985; Vol. 16, p 291. (b) Martins, J. C.; Biesemans, M.; Willem, R. Prog. NMR Spectrosc. 2000, 36, 271. (24) The range of 1J(119Sn13C) for typical four-coordinate trialkyltin compounds is 310-350 Hz. An increase larger than 100 Hz is expected upon pentacoordination. (a) Mitchell, T. N.; Godry, B. J. Organomet. Chem. 1995, 490, 45. (b) 1J(119Sn13C) in PhSnMe3 and Ph3SnCl are 347 and 614 Hz, respectively. (c) Schaeffer, C. D.; Ulrich, S. E.; Zuckerman, J. J. Inorg. Nucl. Chem. Lett. 1978, 14, 55. (d) Holecek, J.; Nadvornik, M.; Handlir, K. J. Organomet. Chem. 1983, 241, 177.

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Table 1. Selected Spectroscopic Data (δ in ppm, J in Hz, ν in cm-1) for Compounds 14, 16, and 17 compd

δ(Cipso-M) [1J(119Sn13CAr)]

δ(CMe-Sn) [1J(119Sn13CMe)]

14 16 17

151.67 [685.1] 144.16

3.32 [577.2] 4.35 [577.2]

δ(15N)

δ(31P) [1J(119Sn31P)]

-302.8 -304.4 -295.0

30.6 37.1 [16.7] 72.2

δ(119Sn)

-84.1

ν(PdO) 1182 1087 1027

One may assume that upon intramolecular oxygen binding to tin, the metal will tend to acquire a trigonal-bipyramide (tbp) geometry. In this configuration, apicophilicity rules predict that the most electronegative atoms will occupy the apical positions.27 For such positional preference, electron donation from oxygen will weaken the Sn-Cl bond trans to it.28 The electrospray mass spectrum (ES-MS) of 16 is in agreement with this assumption. For all potentials assayed a base peak at m/z

450 corresponding to the [M - Cl]+ fragment is obtained, as expected from the increased reactivity of the Sn-Cl in a tbp structure. Tin(IV)-gold(III) transmetalation caused a very large shift to higher frequencies of the 31P signal of 17 (δ 72.2 ppm) as compared with 16 (Table 1), a clear indication of the existence of NPO-metal binding. The 1H and 13C NMR spectra of 17 showed similar features to those discussed for the precursor 16 (see Experimental Section). The metalated carbon at δ 144.16 ppm fits within the range of other noncarbenoid gold(III)substituted phenyl rings.3 For instance, the C-Au carbon in 3, 4, and 6 resonates in the δ 147.7-151.0 ppm range.8,9,10b A strong oxygen-gold(III) interaction was ascertained by the large decrease of the PdO stretching vibration in the CH2Cl2 solution of 17 (ν 1027 cm-1) with respect to phosphinamide 14 and tin(IV) complex 16 (Table 1). Preferred O- vs N-metal coordination of the phosphinamide group was also supported by the small shift to lower frequencies of the 15N nucleus of 17 as compared with 14, ∆δ(15N)(17 - 14) ) 7.8 ppm (Figure 4). In contrast, 15N shieldings in the range from -78 to -85 ppm have been reported for N-coordination in Au(III) complexes29 and in other transition metals.30 Similar to 16, the ES-MS spectrum of 17 showed a single ion at m/z 532 arising from the highly favored fragmentation of chloride of the ionized molecule. Molecular Structure of Complexes 16 and 17. The solid state structure determination was carried out by single-crystal X-ray diffraction (Figure 2) and revealed intramolecular Sn-O coordination. The crystal structure of 16 consists of discrete monomeric units held together by normal van der Waals contacts. The geometry of the bonds around the tin atom shows a distorted trigonal bipyramid (tbp) with the phosphinoyl oxygen and the chlorine occupying apical positions. The axial Cl-Sn-O bond angle of 176.06(4)° and equatorial to axial C-Sn-Cl angles of 96.48(7)°, 94.4(1)°, and 92.7(1)° suggest distorted tbp. The degree to which the Sn atom deviates from the centroid of the plane created by the three equatorial atoms assist mapping the evolution from tbp to tetrahedral, the corresponding limiting values being 0 and 0.71 Å.28b In 16 the tin atom lies 0.177 Å away from the equatorial plane, confirming the tbp disposition and supporting the oxygen coordination encountered in solution. As a consequence, the P-O bond distance (1.506(2) Å) is slightly elongated with respect to uncomplexed systems.31a The Sn-C distances are in agreement with those observed for trimethyltin structures.21,26 The Sn-O bond distance (2.289(2) Å) corresponds to the values reported for pentacoordinated

(25) Chandrasekhar, V.; Nagendran, S.; Baskar, V. Coord. Chem. ReV. 2002, 235, 1. (26) (a) t-BuPhP(O)C6H4Sn(Cl)Me2 δ(119Sn). ) -59.2 ppm; see ref 21c. (b) Ph2P(O)C6H4CH2Sn(Cl)Me2 δ(119Sn) ) -57.7 ppm: Abicht, H.P.; Weichmann, H. Z. Chem. 1988, 28, 69. (27) (a) Trippett, S. Phosphorus, Sulfur Relat. Elem. 1976, 1, 89. (b) Nakamoto, M.; Kojima, S.; Matsukawa, S.; Yamamoto, Y.; Akiba, K.-Y. J. Organomet. Chem. 2002, 643-644, 441. (c) Matsukawa, S.; Kajiyama, K.; Kojima, S.; Furuta, S.-Y.; Yamamoto, Y.; Akiba, K.-Y. Angew. Chem., Int. Ed. 2002, 41, 4718. (28) (a) Jousseaume, B.; Villeneuve, P. J. Chem. Soc., Chem. Commun. 1987, 513. (b) Jastrzebski, J. T. B. H.; Boersma, J.; Esch, P.; van Koten, G. Organometallics 1991, 10, 930. (c) Davenport, A. J.; Davies, D. L.; Fawcett, J.; Russell, D. R. J. Chem. Soc., Dalton Trans. 2002, 3260.

(29) (a) Szlyk, E.; Pazderski, L.; Lakomska, I.; Kozerski, L.; Sitkowski, J. Magn. Reson. Chem. 2002, 40, 529. (b) Pazderski, L.; Tousek, J.; Sitkowski, J.; Kozerski, L.; Marek, R.; Szlyk, E. Magn. Reson. Chem. 2007, 45, 24. (c) Pazderski, L. Magn. Reson. Chem. 2008, 46, S3. (30) (a) Mason, J. Chem. ReV. 1981, 81, 205. (b) Szlyk, E.; Grodzicki, A.; Pazderski, L.; Wojtczak, A.; Chatlas, J.; Wrzeszcz, G.; Sitkowski, J.; Kamienski, B. J. Chem. Soc., Dalton Trans. 2000, 867. (c) Szlyk, E.; Pazderski, L.; Lakomska, I.; Surdykowski, A.; Glowiak, T.; Sitkowski, J.; Kozerski, L. Polyhedron 2002, 21, 343. (31) (a) Search of the Cambridge Structural Database for PhR(NR2)PO fragments: number of observations ) 64; mean P-O bond length ) 1.482 Å. (b) Search of the Cambridge Structural Database for C6H5Au-O fragments: number of observations ) 17; Au-O distance range ) 1.9712.108 Å.

Table 2. Crystal Data, Data Collection, and Structure Refinement for 16 and 17 16 empirical formula M cryst syst space group a /Å b/Å c/Å R/deg β/deg γ/deg V/Å3 µ /mm-1 Dcalcd/g cm-3 cryst dimens/mm Z T/K 2θmax/deg reflns measd reflns unique params/restraints R1 [I g 2σ(I)] wR2 (all data) max./min. res elec dens/e · Å -3

C20H29ClNOPSn 484.55 triclinic P1j (no. 2) 9.169(1) 9.787(4) 14.324(5) 96.620(3) 102.16(2) 115.10(2) 1107.1(6) 1.355 1.454 0.08 × 0.12 × 0.36 2 293 65.1 16 555 7246 (Rint ) 0.0294) 226/0 0.0408 0.0729 0.849/-0.387

17 C18H23Cl2NOPAu 568.21 monoclinic Cc (no. 9) 16.6228(3) 9.0976(1) 15.5802(3) 120.004(1) 2040.41(6) 16.736 1.85 0.09 × 0.04 × 0.02 4 293 74 7982 3164 (Rint ) 0.0247) 217/2 0.0202 0.0681 0.407/-0.851

compounds25 containing a pentacoordinate tin atom through binding to a PO sidearm.22,26 All these data indicate the pentacoordination at the tin atom. Intramolecular coordination of the PdO group was established by vibrational and 15N NMR spectroscopy. The decrease of ca. 100 cm-1 of the PdO stretching vibration measured in CH2Cl2 solution by introducing a Me2SnCl group at the ortho position of 14 (Table 1) strongly supports that the phosphinamide fragment of 16 is acting as a C,O bidentate ligand to the metal. In agreement with this result, the 15N chemical shift of complex 16 indirectly measured from the 1H,15N gHMQC spectrum scarcely differs from that of the precursor 14 (Table 1, Figure 1b).


Organometallics, Vol. 28, No. 6, 2009 1743

Figure 1. (a) 1H,119Sn gHMQC NMR and (b) 1H,15N gHMQC NMR (500.13 MHz) spectrum of 16. (b) Superposition of 1H,15N gHMQC NMR spectra of 14, 16, and 17 at ambient temperature in THF-d8 solution (S ) THF).

Figure 2. Structure of the ortho-chlorostannane 16. ORTEP representation, thermal ellipsoids are drawn at 50% probability. Bond lengths [Å] and angles [deg]: Sn(1)-C(17a) 2.106(3), Sn(1)-C(17b) 2.113(3), Sn(1)-C(8) 2.152(2), Sn(1)-Cl(1) 2.505(1), Sn(1)-O(1) 2.289(2), P(1)-O(1) 1.506(2), C(17a)-Sn(1)-C(17b) 123.6(2), C(17a)-Sn(1)-C(8) 115.1(1), C(8)-Sn(1)-C(17b) 119.6(1), O(1)-Sn(1)-Cl(1) 176.06(4), Cl(1)-Sn(1)-C(17b) 92.7(1), Cl(1)-Sn(1)-C(17a) 94.4(1), Cl(1)-Sn(1)-C(8) 96.48(7).

triorganotin halide complexes with axial ligands coordinated by PdO21,22 or CdO groups.32 The Sn-O interaction produces a slight lengthening of the Sn-Cl bond distance, Sn(1)-Cl(1) ) 2.505(1) Å, which falls in the range observed for related systems.21,22,32

Figure 3. Structure of the gold(III) complex 17. ORTEP representation, thermal ellipsoids are drawn at 50% probability. Bond lengths [Å] and angles [deg]: Au(1)-O(1) 2.009(4) Au(1)-C(2) 2.040(7), Au(1)-Cl(2) 2.357(2), Au(1)-Cl(1) 2.243(2), P(1)-O(1) 1.552(5), P(1)-N(1) 1.630(6), P(1)-C(1) 1.785(6), Cl(1)-Au(1)-Cl(2) 91.41(8), Cl(2)-Au(1)-O(1) 88.7(1), Cl(1)-Au(1)-O(1) 179.1(8), Cl(2)-Au(1)-C(2) 174.9(2), Cl(1)-Au(1)-C(2) 93.3(2), O(1)Au(1)-C(2) 86.6(3), Au(1)-O(1)-P(1) 117.0(2).

Cycloauration was demonstrated by single-crystal X-ray diffraction, as shown in Figure 3. The gold atom is in the center of a four-coordinated square plane surrounded by one oxygen atom, one ipso carbon, and two chlorines (cf. bond angles Cl(2)-Au(1)-C(2) 174.9(2)°, Cl(1)-Au(1)-O(1) 179.1(8)°). The bite angle of the cycloaurated ligand is 86.6(3)°, whose value is significantly higher than those found in 1 (80.13°), 2 (81.41°), 3 (81.73°), 4 (84.85°), and 6 (79.0°). The metallocyclic ring is slightly puckered (O(1)-P(1)-C(1)-C(2) 9.1(6)°) but


Onã-Burgos et al. Table 3. Three-Component Coupling Reaction Catalyzed by 17a

R1

R2

n (% mol)

t (h)

convn (%)b

Ph Ph Ph 4-ClC6H4 4-MeOC6H4 Ph CH2CH2Ph CH2CH2Ph CH2CH2Ph

Ph Ph Ph Ph Ph TMS Ph Ph TMS

3 1 1c 3 3 3 3 1 1

6 12 12 9 24 3 0.25 1.5 1.5

>99 81 89 >99 80 >99 >99 80 96d

Ph Ph CH2CH2Ph CH2CH2Ph

Ph TMS Ph Ph

3 3 3 1

9 1 0.25 1.5

>99 >99 >99 98

entry

Figure 4. Activity of 17 in the conversion of 19b in acetonitrile (red triangles) and chloroform (blue diamonds). Reaction conditions: room temperature, 3 mol % 17.

to a lesser extent than in 4 (17.63°). The Au-C bond distance [2.040(7) Å] is larger than that reported for azophenyl derivative 1 (R ) Me, 2.021 Å)3e but slightly shorter than the value found for the phosphazenyl complex 4 (2.035 Å).9a The Au-O distance observed of 2.009(4) Å is within bond literature values.31b As expected, the P-O bond length of 1.552(5) Å is significantly elongated due to gold complexation (mean P-O bond length in similar molecules 1.482 Å about the metal-oxygen).31a As in 16, the P(1)-N(1) and P(1)-C(1) distances are not noticeably altered. The longer Au-Cl(2) distance (2.357(2) Å) compared with the Au-Cl(1) bond length (2.243(2) Å) reflects the larger trans influence of carbon with respect to oxygen. Catalysis. With all these data in hand, we envisaged the use of 17 in catalysis. For that purpose, we chose the synthesis of propargylamines via three-component coupling (A3) of aldehydes, alkynes, and amines as a benchmark reaction. Propargylamines are valuable building blocks for the preparation of biologically active compounds.33 They are readily accessible through transition metal-catalyzed A3 coupling reactions.34 Generally, gold catalysts promote this one-pot multicomponent process very efficiently.35 However, the reactions catalyzed by AuX3 (X ) Cl, Br) proceed with low conversion in organic solvents.35c Low yields are also observed in the reactions of aliphatic aldehydes in refluxing water using AuBr3 as catalyst35c and in the Au(III) salen complex catalyzed synthesis of propargylamines employing electron-rich acetylenes.35e The three-component coupling of aromatic and aliphatic aldehydes (1 mmol), dialkylamines (1 mmol), and electron-rich (32) (a) Buckle, J.; Harrison, P. G.; King, T. J.; Richards, J. A. J. Chem. Soc., Dalton Trans. 1975, 1552. (b) Domazetis, G.; Magee, R. J.; James, B. D. J. Organomet. Chem. 1978, 148, 339. (c) Pelizzi, C.; Pelizzi, G. J. Organomet. Chem. 1980, 202, 411. (d) Holecek, J.; Handlir, K.; Nadvornik, M.; Lycka, A. J. Organomet. Chem. 1983, 258, 147. (e) Kolb, U.; Dra¨ger, M.; Jousseaume, B. Organometallics 1991, 10, 2737. (33) Zani, L.; Bolm, C. Chem. Commun 2006, 4263, and references therein. (34) (a) Review: Wei, C.; Li, Z.; Li, C.-J. Synlett 2004, 1472. (b) Akullian, L. C.; Snapper, M. L.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2003, 42, 4244. (c) Yan, W.; Wang, R.; Xu, Z.; Xu, J.; Lin, L.; Shena, Z.; Zhou, Y. J. Mol. Catal: A: Chem. 2006, 255, 81. (35) Au(0): (a) Kidwai, M.; Bansal, V.; Kumar, A.; Mozumdar, S. Green Chem. 2007, 9, 742. (b) Maggi, R.; Bello, A.; Oro, C.; Sartori, G.; Soldi, L. Tetrahedron 2008, 64, 1435. Au(I)/Au(III): (c) Wei, C.; Li, C.-J. J. Am. Chem. Soc 2003, 125, 9584. (d) Kantam, M. L.; Prakash, B. V.; Reddy, C. R. V.; Sreedhar, B. Synlett 2005, 2329. (e) Lo, V.K.-Y.; Liu, Y.; Wong, M.-K.; Che, C.-M. Org. Lett. 2006, 8, 1529. (f) Huang, B.; Yao, X.; Li, C.-J. AdV. Synth. Catal. 2006, 348, 1528. (g) Zhang, X.; Corma, A. Angew. Chem., Int. Ed. 2008, 47, 4358.

X ) CH2 1 (18a) 2 3 4 (18b) 5 (18c) 6 (18d) 7 (18e) 8 9 (18f) X)O 10 (18g) 11 (18h) 12 (18i) 13

a 17/aldehyde/amine/alkyne ) n:1:1:1.5. b Determined by 1H NMR analysis of the crude reaction mixture. c 1 mol % of AgOTf added. d Isolated yield 92%.

Table 4. Asymmetric Three-Component Coupling Reaction Catalyzed by 17a

entry R )H 1 (19a) 2 R3 ) CH2OH 3 (19b) 4 5 (19c) 6

R1

R2

t (h)

T (°C)

n

convn (%)

7 24

60 60

3 1

>99 85

1 1 1 1

25 60 25 60

3 3 3 3b

91b 97b 85b >99

3

Ph Ph

Ph Ph

Ph Ph Ph Ph

Ph Ph TMS TMS

a 17/aldehyde/amine/alkyne ) n:1:1:1.5. b Determined by 1H NMR analysis of the crude reaction mixture, dr 99:1.

and electron-deficient acetylenes (1.5 mmol) in the presence of gold(III) complex 17 (3 mol %) in acetonitrile under a nitrogen atmosphere for 0.25-12 h provides the corresponding propargylamine 18 and 19 quantitatively (Tables 3 and 4). Reducing the catalyst loading down to 1 mol % resulted in about a 20% decrease of conversion after 12 h of reaction (cf. entries 1 and 2, and 7 and 8, Table 3). In this case, high conversion is recovered by adding 1 mol % of AgOTf (entry 3, Table 3). With regard to amines, either piperidine (entries 1-9) or morpholine affords the desired propargylamines in excellent yields (entries 10-13). Aldehydes bearing electron-withdrawing substituents such as chlorine undergo coupling quantitatively in 9 h (entry 4); however, the electron-donating effect of the p-MeO decreased the reactivity. In the latter case the conversion reached 80% after 24 h of reaction (entry 5). It is worth mentioning that the aliphatic aldehyde 3-phenylpropanal showed the highest reactivity (entries 7-9, 12, and 13, Table 3). Complete conversions are observed in 15 and 90 min, when 3 and 1 mol % was employed, respectively. Moreover, the coupling reaction of the TMS-substituted alkyne proceeds with almost complete conversion even when only 1 mol % of 17 was used as catalyst (cf. entries 6, 9, and 11, Table 3).


Synthesis of 18f was performed in higher scale starting from 1.3 g of 3-phenylpropanal that after standard workup and flash chromatography afforded the propargylic derivative in an isolated yield of 92% (2.7 g), proving the success in scaling up the process.

Organometallics, Vol. 28, No. 6, 2009 1745 Table 5. D and rH Values for Species 14, 16, and 17 in Chloroform Solution at 295 Ka compd

conc (mM)

Dc

rH (Å)d

c

rH (Å)e

14

10

9.82

4.1

5.5

4.4

16

10

8.67

4.6

5.6

4.9

5.1

17

10

8.42

4.7

5.6

5.1

5.0

17

50

8.29

4.8

5.6

5.2

5.0

17

100

7.69

5.3

5.7

5.5

5.0

10

14.23

4.5

5.7

4.7

5.0

b

17

rX (Å)f

a

The reaction seems to be insensitive to the size of the cyclic amine employed, since quantitative conversion into the corresponding propargylic derivative was obtained when pyrrolidine was used as amine (entry 1, Table 4). At 1 mol % of catalyst the yield decreases ca. 15% (entry 2, Table 4). The A3 process with the enantiomerically pure prolinol as the amine component takes place with excellent diastereoselectivity (dr 99:1, entries 3-6, Table 4). Significantly, the reaction proceeds at room temperature in high yield in reasonably reduced times (entries 3 and 5). In order to examine the repeatability of the transformation, we performed four consecutive catalytic runs of the coupling of piperidine, 3-phenylpropanal, and trimethylsilylacetylene on a NMR tube (entry 9, Table 3) with only one loading of catalyst (3 mol %). No significant loss of catalytic activity is observed after the four reaction cycles (conversions for the successive cycles ) 99%, 99%, 99%, 98% determined by 1H NMR). Remarkably, the reaction crude in all the cycles remained clean without forming significant amounts of side products. Neutral dichloride gold(III) complexes are described to catalyze organic processes in the absence of any halide abstractor reagent.9b,35,36 It has been proposed that the catalytic cycle begins with the formation of a cationic species by dissociation of one chloride ligand.9b,37 In some instances, a qualitative correlation of the catalytic activity with the electronegativity of the halide and the strength of Au-X bonds (X ) Cl, Br or I) has been found.36c,37b In this dissociative mechanism, the intermediate cationic species might be stabilized by chargeinduced aggregation or through binding to the coordinative solvent frequently used. In order to shed light on these features, pulsed gradient spin-echo (pgse) NMR diffusion measurements were carried out.38 The results of the PGSE study for 10 mM solutions of 14, 16, and 17 in chloroform, a solvent that

(36) For very recent reviews see: (a) Skouta, R.; Li, C.-J. Tetrahedron 2008, 64, 4917. (b) Li, Z.; Brouwer, C.; He, C. Chem. ReV. 2008, 108, 3239. (c) Gorin, D. J.; Sherry, B. D.; Toste, F. D. Chem. ReV. 2008, 108, 3351. (d) Arcadi, A. Chem. ReV. 2008, 108, 3266, and references therein. (37) (a) Norman, R. O. C.; Parr, W. J. E.; Thomas, C. B. J. Chem. Soc., Perkin Trans. 1976, 1983. (b) Casado, R.; Contel, M.; Laguna, M.; Romero, P.; Sanz, S. J. Am. Chem. Soc. 2003, 125, 11925. (38) (a) Price, W. S. Concepts Magn. Reson. 1997, 9, 299. (b) Price, W. S. Concepts Magn. Reson. 1998, 10, 197. (c) Johnson, C. S. Prog. Nucl. Magn. Reson. Spectrosc. 1999, 34, 203. (d) Cohen, Y.; Avram, L.; Frish, L. Angew. Chem., Int. Ed. 2005, 44, 520. (e) Pregosin, P. S.; Kumar, P. G. A.; Fernández, I. Chem. ReV. 2005, 105, 2977. (f) Pregosin, P. S. Prog. Nucl. Magn. Reson. Spectrosc. 2006, 49, 261. (g) Macchioni, A.; Ciancaleoni, G.; Zuccaccia, C.; Zuccaccia, D. Chem. Soc. ReV. 2008, 37, 479.

All at 10 mM. Radii obtained from X-ray structures (rx) of 16 and 17 are given for comparison. b Measured in acetonitrile. c (2%, × 1010 m2 s-1. d η(CHCl3, 295 K) ) 0.54 × 10-3 kg s-1 m-1; η(CH3CN, 295 K) ) 0.34 × 10-3 kg s-1 m-1. Viscosities at room temperature were taken from ref 42. e These rH values have been calculated using constant c instead of 6. See ref 39. f Deduced from the X-ray structure by simply dividing the volume of the crystallographic cell by the number of contained molecules, assuming the latter have a spherical shape.

promotes strong ion pairing, and acetonitrile, a coordinating solvent, are given in Table 5 and Figures S6. The diffusion NMR methodology allowed us to estimate molecular volumes and ion pairing in solution.38e-g From the measured D value one can calculate the hydrodynamic radius, rH, via the Stokes-Einstein equation and compare these values with those based on X-ray data (rX), if available.39 Table 5 shows that the hydrodynamic radii in CHCl3 are very close to the rX obtained from the X-ray, as has been previously noticed in other systems.40,38e-g The D value of 16 (Table 5) provides a hydrodynamic radius of ca. 4.9 Å, which is, as expected, larger than the rH shown by the unfunctionalized phosphinamide 14. The calculated rH for complex 17 of ca. 5.1 Å matches also with the unimolecular structure found in the solid state (rX of 5.0 Å) and does not differ significantly from that of the tin derivative 16. Interestingly, in acetonitrile the rH of ca. 4.7 Å obtained for 17 is slightly shorter than in chloroform. This result strongly supports the existence of 17 as a monomer in acetonitrile, the solvent in which the catalysis is performed. The larger rH value found in chloroform solution could be due to some charge-induced aggregation, a known feature of neutral gold(III) compounds41 that has been correlated with poor conversions or no catalytic activity at all.37b To prove this (39) The hydrodynamic radii rH were calculated from the StokesEinstein equation: D ) (kBT)/(6πηr), in which D is the diffusion coefficient, kB is the Boltzman constant, T is the temperature, and η is the viscosity of the solvent. It has been suggested that the factor c ()6 in the equation) is only valid when the radius for the molecule is at least 5 times larger than that of the solvent; see ref 38g and references therein. This factor can be adjusted by using a semiempirical approach (see. (a) Chen, H.-C.; Chen, S.-H. J. Phys. Chem. 1984, 88, 5118. ) derived from the microfriction theory proposed by Wirtz and co-workers. [(b) Gierer, A.; Wirtz, K. Z. Naturforsch. A 1953, 8, 522; (c) Spernol, A.; Wirtz, K. Z. Naturforsch. A 1953, 8, 532] in which c is expressed as a function of the solute-to-solvent ratio of radii: c ) 6/[1 + {0.695(rsolv/rH) 2.234}]. (40) (a) Dinnebier, R. E.; Dollase, W. A.; Helluy, X.; Kummerlen, J.; Sebald, A.; Schmidt, M. U.; Pagola, S.; Stephens, P. W.; Smaalen, S. Acta Crystallogr. B 1999, B55, 1014. (b) Zuccaccia, D.; Bellachioma, G.; Cardaci, G.; Ciancaleoni, G.; Zuccaccia, C.; Clot, E.; Macchioni, A. Organometallics 2007, 26, 3930. (41) (a) Pope, W. J.; Gibson, C. S. Proc. Chem. Soc. 1907, 23, 245. (b) Burawoy, A.; Gibson, C. S.; Hampson, G. C.; Powell, H. M. J. Chem. Soc. 1937, 1690. (c) Komiya, S.; Huffman, J. C.; Kochi, J. K. Inorg. Chem. 1977, 16, 1253. (d) Usoń, R.; Laguna, A.; Laguna, M.; Abad, M. J. Organomet. Chem. 1983, 249, 437. (e) Contel, M.; Edwards, A. J.; Garrido, J.; Hursthouse, M. B.; Laguna, M.; Terroba, R. J. Organomet. Chem. 2000, 607, 129. (42) Kovacs, H.; Kowalewski, J.; Maliniak, A.; Stilbs, P. J. Phys. Chem. 1989, 93, 962.


hypothesis, we determined the diffusion coefficient for 17 at concentrations of 10, 50, and 100 mM in chloroform. The measurements showed clear concentration dependence (Figure S7), where the D values decrease (and thus the rH values increase) with increasing concentration (Table 5). Therefore, it seems that in chloroform the gold complex undergoes aggregation as a function of concentration.43 To evaluate the impact of catalyst aggregation on reactivity, we performed the multicomponent A3 process in chloroform solution. For comparison and due to the low boiling point of chloroform, we applied the experimental setup corresponding to entry 3 of Table 4 as the control catalytic run, since it could be achieved at room temperature. Under these conditions compound 19b was obtained in 81% of conversion in ca. 13 h of reaction time, i.e., 16 times slower than in acetonitrile solution (Figure 4). From these results one can establish a correlation between structure and catalytic activity, with mononuclear species observed in acetonitrile being the fastest in performing the A3 catalysis and the somehow aggregated complex found in chloroform slowing it down.

Conclusions In summary, we have developed a straightforward method of synthesizing in excellent yields cyclometalated gold(III) phosphinamide-based molecules starting from their tin(IV) derivatives. The synthetic strategy avoids the use of organomercury compounds and allows for recycling the organotin reagent used. The tin(IV) phosphinamidic precursor and the cycloaurated species have been structurally characterized, showing five-membered rings involving oxygen-tin or oxygen-gold coordination, respectively. Further, this new gold complex has been applied in A3 coupling processes, providing a variety of propargylamines in quantitative yields under very mild conditions without the use of any activator or additive. The performance of the organocatalyst proved to be superior to that of Au salts in analogous transformations. Diffusion NMR measurements indicated that the catalyst is monomeric in acetonitrile, whereas it tends to aggregate in chloroform solution. As a consequence, the catalytic activity decreases in the latter solvent. The results shown here demonstrate the usefulness of ortho-functionalized phosphinamides as new CCPO pincer ligands in coordination chemistry and catalysis. The application of enantiomerically pure phosphinamide-gold complexes in asymmetric catalysis is currently under investigation.

Experimental Section Glassware was dried overnight in a 110 °C oven to remove moisture. All procedures were carried out under nitrogen. Solvents were freshly distilled from potassium or sodium/benzophenone (THF, Et2O). The CD3CN was degassed prior to use in catalytic runs. K[AuCl4] was purchased from ABCR. The reactions involving organolithium reagents were performed under an inert atmosphere of nitrogen using Schlenk techniques. Anhydrous solvents were obtained via elution through a solvent column drying system.44 The CD3CN was degassed prior to use in catalytic runs. Commercial reagents t-BuLi, n-BuLi, Me3SnCl, Me2SnCl2, and K[AuCl4] were (43) Aggregation at higher concentrations is now well known. (a) Macchioni, A.; Romani, A.; Zuccaccia, C.; Guglielmetti, G.; Querci, C. Organometallics 2003, 22, 1526. (b) Song, F. Q.; Lancaster, S. J.; Cannon, R. D.; Schormann, M.; Humphrey, S. M.; Zuccaccia, C.; Macchioni, A.; Bochmann, M. Organometallics 2005, 24, 1315. (c) Zuccaccia, D.; Clot, E.; Macchioni, A. New J. Chem. 2005, 29, 430. (44) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics 1996, 15, 1518.

Onã-Burgos et al. used as obtained from commercial sources without further purification. Compounds 14 and 15 were prepared according to a literature method.17 Propargylamines18a,35c 18b,35c 18c,35c 18d,45 18e,35c 18g,35d 18h,46 18i,47 19a,35d and 19b35e have been characterized previously. TLC was performed on Merck plates with aluminum backing and silica gel 60 F254. IR data were acquired using an FTIR Mattson Genesis II spectrophotometer. Melting points were recorded on a Bu¨chi B-540 capillary melting point apparatus. Mass spectra were determined by atmospheric pressure chemical ionization (APCI) on a Hewlett-Packard 1100. 1H (300 MHz), 13C (75.47 MHz), and 31P (121.47 MHz) NMR spectra were recorded on a Bruker Avance DPX300 equipped with a QNP 1H/13C/19F/31P probe. Selective 1D NMR (gTOCSY, gNOESY) and 2D (gNOESY, gHMQC, and gHMBC) correlation spectra were measured on a Bruker Avance 500 spectrometer (1H, 500 MHz; 13C, 125.7 MHz; 15 N, 50.7 MHz, 31P, 202.4 MHz; 119Sn, 186.36 MHz) using an inverse TBI 1H/31P/BB. Chemical shifts are given relative to TMS for 1H and 13C, MeNO2 (+10% CDCl3) for 15N, 85% H3PO4 for 31 P, and Me4Sn for 119Sn. Unless otherwise stated the solvent used was CDCl3 and THF-d8. Standard Bruker software was used for acquisition and processing routines. Diffusion measurements were performed using the stimulated echo pulse sequence48 on the Bruker Avance DPX300 without spinning. The shape of the gradient pulse was rectangular, and its strength varied automatically in the course of the experiments. The D values were determined from the slope of the regression line ln(I/I0) versus G2, according to eq 1. I/I0 ) observed spin echo intensity/intensity without gradients, G ) gradient strength, ∆ ) delay between the midpoints of the gradients, D ) diffusion coefficient, and δ ) gradient length.

()

ln

I δ ) -(γδ)2 ∆ - DG2 I0 3

(

)

(1)

The calibration of the gradients was carried out via a diffusion measurement of HDO in D2O, which afforded a slope of 2.022 × 10-4.49 We estimate the experimental error in the D values to be (2%. All of the data leading to the reported D values afforded lines whose correlation coefficients were >0.999, and 8-12 points have been used for regression analysis. To check reproducibility, three different measurements with different diffusion parameters (δ and/or ∆) were always carried out. The gradient strength was incremented in 8% steps from 10% to 98%. A measurement of 1H and T1 was carried out before each diffusion experiment, and the recovery delay set to 5 times T1. In the diffusion experiments δ was set to 1.5 or 1.75 ms, and the number of scans were 8-64 per increment with a recovery delay of 10 to 60 s. Typical experimental times were 1-4 h. Synthesis of 16. To a solution of the phosphinamide 14 (1.66 mmol) in THF (5 mL) was added a solution of t-BuLi (1.1 mL of a 1.7 M solution in cyclohexane, 1.83 mmol) at -90 °C. After 2 h of metalation dichlorodimethyltin (1.83 mmol) was added. The reaction mixture was stirred at the same temperature for 30 min and then extracted following standard procedures. The reaction mixture was then purified by flash column chromatography (acetate/ hexane, 1:5), affording 16 in 89% of isolated yield. Mp: 196-197 °C. NMR data (THF-d8, 298 K, 500.13 MHz): 1H NMR δ 0.72 (s, 3H, CH3), 0.91 (s, 3H, CH3), 1.17 (d, 6H, J 6.9 Hz, CH3), 1.22 (d, 6H, J 6.9 Hz, CH3), 3.55 (dh, 2H, JPH 15.2 Hz, J 6.9 Hz, CH), 7.51 (m, 4H, ArH), 7.64 (m, 1H, ArH), 7.98 (m, 2H, ArH), 8.10 (45) Ramu, E.; Varala, R.; Sreelatha, N.; Adapa, S. R. Tetrahedron Lett. 2007, 48, 7184. (46) Shi, L.; Tu, Y.-Q.; Wang, M.; Zhang, F.-M.; Fan, C.-A. Org. Lett. 2004, 6, 1001. (47) Likhar, P. R.; Roy, S.; Roy, M.; Subhas, M. S.; Kantan, M. L.; De, R. L. Synlett 2007, 2301. (48) Stilbs, P. Prog. Nucl. Magn. Reson. Spectrosc. 1987, 23, 1. (49) Tyrrell, H. J. V.; Harris, K. R. Diffusion in Liquids; Butterworths: London, 1984.

Unprecedented Phosphinamidic Gold(III) Metallocycle (m, 1H, ArH), 8.59 (m, 1H, ArH); 13C NMR δ 3.32 (d, CH3, JPC 2.8, JSnC 577.2 Hz), 4.35 (d, CH3, JPC 2.3, JSnC 577.2 Hz), 23.15 (d, CH3, JPC 3.2 Hz), 23.42 (d, CH3, JPC 3.7 Hz), 48.12 (d, CH, JPC 3.7 Hz), 128.62 (d, CAr, JPC 12.6 Hz), 128.69 (d, CAr, JPC 12.1 Hz), 130.61 (d, JPC 12.6, JSnC 58.4 Hz), 131.40 (d, Cipso, JPC 130.5), 131.87 (d, JPC 3.3 Hz, JSnC 59.2), 132.24 (d, JPC 10.2 Hz), 132.47 (d, JPC 2.8 Hz), 135.78 (d, Cipso, JPC 130.3), 138.22 (d, CAr JPC 16, JSnC 46.4 Hz), 151.67 (d, Cipso, JPC 17.7, JSnC 685.1 Hz); 31P NMR δ 37.1; 119Sn NMR δ -84.1. Anal. Calcd for C20H29ClNOPSn: C 49.57, H 6.03, N 2.89. Found: C 49.20, H 6.10, N 2.99. ESI-MS: m/z 450 (100, M - Cl). Synthesis of 17. K[AuCl4] (159 mg, 0.41 mmol) was added to a solution of 16 (200 mg, 0.41 mmol) in CH3CN (5 mL). The reaction mixture was heated at 90 °C for 2 h, after which time the solution was cooled, filtered, and then slowly concentrated under vacuum. The resulting yellowish oil was dissolved in dichloromethane, filtered, and dried under vacuum, affording a yellow solid. This solid was washed with diethyl ether, filtered, and dried under vacuum. This sequence was repeated one more time. Isolated yield: 86% (201 mg). An acetonitrile solution of this solid was then layered with n-hexane and stored at room temperature, affording air-stable crystals of 17, suitable for X-ray diffraction. Mp: 165-166 °C (dec). NMR data (THF-d8, 298 K, 500.13 MHz): 1 H NMR δ 1.30 (d, 6H, J 6.8 Hz), 1.30 (d, 6H, J 6.8 Hz), 3.68 (dh, 2H, JPH 15.9, JPH 6.8 Hz), 7.45 (m, 2H, ArH), 7.68 (m, 4H, ArH), 8.00 (m, 1H, ArH), 8.10 (m, 2H, ArH); 13C NMR δ 22.56 (d, CH3, JPC 3.3 Hz), 22.76 (d, CH3, JPC 2.9 Hz), 49.38 (d, CH, JPC 3.3 Hz), 127.87 (d, Cipso, JPC 130.7 Hz), 128.28 (d, CAr, JPC 12.8 Hz), 129.21 (d, CAr, JPC 13.6 Hz), 131.22 (d, CAr, JPC 13.6 Hz), 131.32 (d, CAr, JPC 13.6 Hz), 132.57 (d, CAr, JPC 10.7 Hz), 133.66 (d, CAr, JPC 3.3 Hz), 133.79 (d, CAr, JPC 2.9 Hz), 135.62 (d, Cipso, JPC 140.2 Hz), 144.16 (d, Cipso, JPC 16.1 Hz); 31P NMR δ 72.2. Anal. Calcd for C18H23AuCl2NOP: C 38.05, H 4.08, N 2.46. Found: C 38.21, 3.88, N 2.58. ESI-MS: m/z m/z 532 (100, M - Cl). General Procedure for the Au(III)-Catalyzed Three-Component Coupling. Into an oven-dried J-Young 5 mm NMR tube loaded with acetonitrile (0.5 mL), benzaldehyde (20 µL, 0.197 mmol), piperidine (19.4 µL, 0.197 mmol), and the Au(III) catalyst (0.0059 mmol, 3% mol) was added phenylacetylene (32.4 µL, 0.295 mmol) at room temperature. After alkyne addition the tube was closed, shaken, and immediately transferred into the NMR probe head. The resulting mixture was monitored by 1H NMR spectroscopy at 25 or 60 °C. 1-[1-(2-Phenylethyl)-3-(trimethylsilil)prop-2-yn-1-yl]piperidine (18f). NMR data (CDCl3, 300 MHz): 1H NMR δ 0.27 (s, 9H), 1.51 (m, 2H), 1.67 (m, 4H), 2.00 (m, 2H), 2.45 (m, 2H), 2.65 (m,

Organometallics, Vol. 28, No. 6, 2009 1747 2H), 2.83 (m, 2H), 3.32 (dd, 1H, JHH 6.7, JHH 8.5), 7.23-7.36 (m, 5H, ArH); 13C NMR δ 0.36 (3CH3), 24.61 (CH2), 26.19 (2CH2), 32.75 (CH2), 34.92 (CH2), 50.31 (2CH2), 57.68 (CH), 89.88 (C′), 104.25 (C′), 125.79 (CAr), 128.29 (2CAr), 128.60 (2CAr), 141.84 (Cipso). Anal. Calcd for C19H29NSi: C 76.19, H 9.76, N 4.68. Found: C 76.02, 9.86, N 4.72. ESI-MS: m/z 300 (M + 1). {(2S)-1-[(1S)-1-Phenyl-3-(trimethylsilil)prop-2-yn-1]-pyrrolidi2-nyl}methanol (19c). NMR data (CDCl3, 300 MHz): 1H NMR δ 0.25 (s, 9H), 1.27 (m, 1H), 1.64 (m, 1H), 1.89 (m, 1H), 1.99 (m, 1H), 2.58 (m, 1H), 2.72 (m, 1H), 3.20 (m, 1H), 3.52 (m, 1H), 3.79 (m, 1H), 4.90 (s, 1H), 7.23-7.40 (m, 3H, ArH), 7.55 (m, 2H, ArH); 13 C NMR δ 0.13 (3CH3), 23.37 (CH2), 27.84 (CH2), 47.61 (CH2), 55.46 (CH), 61.50 (CH), 61.75 (CH), 92.37 (C′), 101.58 (C′), 127.61 (CAr), 127.87 (2CAr), 128.27 (2CAr), 138.40 (Cipso). Anal. Calcd for C19H29NSi: C 71.03, H 8.77, N 4.87. Found: C 71.18, 8.69, N 4.79. ESI-MS: m/z 288 (M + 1). Crystallography. Colorless and yellowish crystals of 16 and 17 suitable for X-ray diffraction were obtained by slow evaporation of a saturated chloroform solution and layering hexane on an acetonitrile solution, respectively. Both complexes are air stable. Data collection was performed on Oxford Diffraction Xcalibur single-crystal diffractometers, using a Gemini model with Mo KR (λ ) 0.71073 Å) for 16 and a Nova diffractometer with Cu KR (λ ) 1.54180 Å) for 17. Selected crystallographic and other relevant data are listed in Tables 1 and S1-S12 and in the Supporting Information. CCDC 710610 for 16 and 693265 for 17 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgment. Dedicated to Prof. Gregorio Asensio on the occasion of his 60th birthday. We thank Ministerio de Educacioń y Ciencia (project: CTQ2005-1792BQU, MAT2006-01997, and “Factorıá de Cristalizacioń” Consolider-Ingenio 2010) and Fondos FEDER for financial support. I.F. thanks the Ramoń y Cajal Program for a research contract. Supporting Information Available: Characterization data, crystallographic data for 16 and 17, and PGSE diffusion measurements. This material is available free of charge via the Internet at http://pubs.acs.org. OM801137Y

An Unprecedented Phosphinamidic Gold(III) Metallocycle: Synthesis

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