Synthesis, Reactivity, Structural Aspects, and Solution Dynamics of

572

Organometallics 2011, 30, 572–583 DOI: 10.1021/om1009445

Synthesis, Reactivity, Structural Aspects, and Solution Dynamics of Cyclopalladated Compounds of N,N0 ,N00 -Tris(2-anisyl)guanidine Kanniyappan Gopi and Natesan Thirupathi* Department of Chemistry, University of Delhi, Delhi 110 007, India

Munirathinam Nethaji Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Received September 30, 2010

N,N0 ,N00 -Tris(2-anisyl)guanidine, (ArNH)2CdNAr (Ar = 2-(MeO)C6H4), was cyclopalladated with Pd(OC(O)R)2 (R = Me, CF3) in toluene at 70 °C to afford palladacycles [Pd{κ2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))-2}(μ-OC(O)R)]2 (R=Me (1a) and CF3 (1b)) in 87% and 95% yield, respectively. Palladacycle 1a was subjected to a metathetical reaction with LiBr in aqueous ethanol at 78 °C to afford palladacycle [Pd{κ2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))-2}(μ-Br)]2 (2) in 90% yield. Palladacycle 2 was subjected to a bridge-splitting reaction with Lewis bases in CH2Cl2 to afford the monomeric palladacycles [Pd{κ2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))-2}Br(L)] (L = 2,6-Me2C5H3N (3a), 2,4-Me2C5H3N (3b), 3,5-Me2C5H3N (3c), XyNC (Xy = 2,6-Me2C6H3; 4a), tBuNC (4b), and PPh3 (5)) in 87-95% yield. Palladacycle 2 upon reaction with 2 equiv of XyNC in CH2Cl2 afforded an unanticipated palladacycle, [Pd{κ2(C,N)-C(dNXy)(C6H3(OMe)-4)-2(NdC(NHAr)2)-3}Br(CNXy)] (6) in 93% yield, and the driving force for the formation of 6 was ascribed to a ring contraction followed by amine-imine tautomerization. Palladacycles 1a,b revealed a dimeric transoid in-in conformation with “open book” framework in the solid state. In solution, 1a exhibited a fluxional behavior ascribed to the six-membered “(C,N)Pd” ring inversion and partly dissociates to the pincer type and κ2-O,O0 -OAc monomeric palladacycles by an anchimerically assisted acetate cleavage process as studied by variable-temperature 1H NMR data. Palladacycles 3a,b revealed a unique trans configuration around the palladium with lutidine being placed trans to the Pd-C bond, whereas cis stereochemistry was observed between the Pd-C bond and the Lewis base in 4a (as determined by X-ray diffraction data) and 5 (as determined by 31P and 13C NMR data). The aforementioned stereochemical difference was explained by invoking relative hardness/softness of the donor atoms around the palladium center. In solution, palladacycles 3a-c exist as a mixture of two interconverting boat conformers via a planar intermediate without any bond breaking due to the six-membered “(C,N)Pd” ring inversion, whereas palladacycles 4a,b and 5 exist as a single isomer, as deduced from detailed 1H NMR studies.

Introduction [C,N ] Palladacycles are one of the popular classes of organometallic compounds discovered as early as 1965,1 and

their widespread use as stoichiometric reagents in organic synthesis, precatalysts in C-C and C-heteroatom bondforming reactions, metallomessogens, resolving agents, and anticancer agents is well known.2-7 The labile Pd-C bond in

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various nitrogen heterocycles and carbocycles.2,3b,c,j,8 [C,N] Palladacycles with ring size from four to 11 are known, and among these, the five-membered [C,N] palladacycles are by far the most thoroughly studied system. Six-membered [C,N] palladacycles are less well studied than their five-membered counterparts, and the scarcity of the former was believed to be due to their lesser stability as compared with the latter.9 Examples of six-membered [C,N] palladacycles have become more common recently,8c,9c,10-13 but still remain relatively rare. Some six-membered [C,N] palladacycles were proven as excellent precatalysts for C-C and C-heteroatom bond-forming reactions.10f,j,m,q,r,11b,e,j,13 Moreover, the six-membered [C,N] palladacycle skeleton was often encountered as intermediate species in stoichiometric3b,j,14 and catalytic15 organic transformations mediated by palladium. Recently, we reported a one-pot synthesis for a series of N,N0 ,N00 -triarylguanidines and studied their conformational features by NMR and X-ray diffraction data.16 We set out to study the cyclopalladation reactions of N,N0 ,N00 -tris(2-anisyl)guanidine, (ArNH)2CdNAr (Ar = 2-(MeO)C6H4; LH22-anisyl) with Pd(OC(O)R)2 (R = Me, CF3) to investigate how the intrinsic basic and 2-anisyl substituent in the guanidine influence the solid-state and solution structures and the reactivity pattern of the resulting guanidine palladacycles. From such an endeavor, guanidine palladacycles [Pd{κ2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))-2}(μ-X)]2 (Ar = 2-(MeO)C6H4; X = OC(O)R (R = Me (1a), CF3 (1b), and Br (2)), [Pd{κ2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))-2}Br(L)] (L = 2,6-Me2C5H3N (3a), 2,4-Me2C5H3N (3b), 3,5Me2C5H3N (3c), XyNC (4a), tBuNC (4b), and PPh3 (5)), and [Pd{κ2(C,N)-C(dNXy)(C6H3(OMe)-4)-2(NdC(NHAr)2)3}Br(CNXy)] (Xy = 2,6-Me2C6H3; 6) shown in Chart 1 were isolated, and the structures and solution dynamics of representative palladacycles were studied by X-ray diffraction data and variable-temperature (VT) 1H NMR data. The molecular structure of the partly cyclopalladated complex of N,N0 ,N00 (12) (a) Albert, J.; G omez, M.; Granell, J.; Sales, J.; Solans, X. Organometallics 1990, 9, 1405–1413. (b) Dupont, J.; Pfeffer, M.; Daran, J.-C.; Gouteron, J. J. Chem. Soc., Dalton Trans. 1988, 2421–2429. (c) Dorokhov, V. A.; Cherkasova, K. L.; Lutsenko, A. I. Bull. Acad. Sci. USSR Div. Chem. Sci. (Engl. Transl.) 1987, 36, 2179–2181. (d) Ceder, R. M.; Granell, J.; Sales, J. J. Organomet. Chem. 1986, 307, C44–C46. (e) Canty, A. J.; Minchin, N. J.; Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1986, 2205–2210. (f) Albert, J.; Granell, J.; Sales, J.; Solans, X.; Font-Altaba, M. Organometallics 1986, 5, 2567–2568. (g) Polyakov, V. A.; Ryabov, A. D. J. Chem. Soc., Dalton Trans. 1986, 589–593. (h) Fuchita, Y.; Hiraki, K.; Uchiyama, T. J. Chem. Soc., Dalton Trans. 1983, 897–899. (i) Fuchita, Y.; Hiraki, K.; Kage, Y. Bull. Chem. Soc. Jpn. 1982, 55, 955–956. (j) Nonoyama, M. Trans. Met. Chem. 1982, 281–284. (k) Hiraki, K.; Fuchita, Y.; Takechi, K. Inorg. Chem. 1981, 20, 4316–4320. (l) Cameron, N. D.; Kilner, M. J. Chem. Soc., Chem. Commun. 1975, 687– 688. (13) (a) Marion, N.; Nolan, S. P. Acc. Chem. Res. 2008, 41, 1440– 1449. (b) Broggi, J.; Clavier, H.; Nolan, S. P. Organometallics 2008, 27, 5525–5531, and references therein. (14) (a) Barker, J.; Cameron, N. D.; Kilner, M.; Mohmoud, M. M.; Wallwork, S. C. J. Chem. Soc., Dalton Trans. 1991, 3435–3445. (b) Chao, C. H.; Hart, D. W.; Bau, R.; Heck, R. F. J. Organomet. Chem. 1979, 179, 301–309. (c) Thompson, J. M.; Heck, R. F. J. Org. Chem. 1975, 40, 2667– 2674. (15) (a) Neumann, J. J.; Rakshit, S.; Dr€ oge, T.; Glorius, F. Angew. Chem., Int. Ed. 2009, 48, 6892–6895. (b) Tan, Y.; Harwig, J. F. J. Am. Chem. Soc. 2010, 132, 3676–3677. (c) Orito, K.; Miyazawa, M.; Nakamura, T.; Horibata, A.; Ushito, H.; Nagasaki, H.; Yuguchi, M.; Yamashita, S.; Yamazaki, T.; Tokuda, M. J. Org. Chem. 2006, 71, 5951–5958. (d) Orito, K.; Horibata, A.; Nakamura, T.; Ushito, H.; Nagasaki, H.; Yuguchi, M.; Yamashita, S.; Tokuda, M. J. Am. Chem. Soc. 2004, 126, 14342–14343. (16) Gopi, K.; Rathi, B.; Thirupathi, N. J. Chem. Sci. 2010, 122, 157–167.

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Chart 1

triphenylguanidine, (PhNH)2CdNPh, is reported,17 but no other data are presently available. The results presented in this paper were communicated in a national conference.18

Results and Discussion Carboxylato-Bridged Six-Membered Guanidine Palladacycles (1a,b). Metallacycles are usually prepared by a C-H activation process.2,19 Therefore, LH22-anisyl was cyclopalladated with Pd(OC(O)R)2 (R=Me, CF3) in toluene at 70 °C for 8 h to afford 1a,b in 87% and 95% yield, respectively. The 1 H NMR data of 1a,b appeared complicated, and hence these palladacycles were structurally characterized by X-ray diffraction data. The molecular structure of 1a is depicted in Figure 1. Palladacycle 1a exists as a dimer wherein two palladium atoms are bridged by a pair of syn-syn bidentate bridging acetate moieties. Palladacycle 1a revealed a pseudo C2 symmetry that passes across the center of the Pd 3 3 3 Pd vector to afford a transoid in-in conformation with “open book” framework. The palladium atom is surrounded by two oxygen atoms of the acetate, imine nitrogen, and palladated carbon and displayed a distorted square-planar geometry. The six-membered “(C,N)Pd” rings exhibited a pseudo boat conformation. The Pd-N distances, 2.010(3) and 2.017(2) A˚, in 1a are comparable with the predicted value of 2.01 A˚ (based upon r(Pd(II))=1.31 A˚ and r(N)=0.70 A˚)20 and that reported for the N,N0 -diphenylbenzamidine-derived six-membered [C,N] palladacycle (2.013(3) A˚).17 The Pd-C distances, 1.956(4) and 1.967(3) A˚, in 1a are comparable with that reported for the N,N0 -diphenylbenzamidine-derived six-membered [C,N] palladacycle (1.960(3) A˚)17 but are shorter than the predicted value of 2.05 A˚,21 indicating some multiple-bond character in the Pd-C(aryl) linkages. The Pd-O distances, 2.153(3) and 2.144(3) A˚, trans to the palladated carbon are longer than those that are trans to the imine nitrogen (2.054(2) and (17) Berry, J. F.; Cotton, F. A.; Ibragimov, S. A.; Murillo, C. A.; Wang, X. Inorg. Chem. 2005, 44, 6129–6137. (18) Presented at the 12th Biennial Symposium on Modern Trends in Inorganic Chemistry (MTIC-XII), Dec 06-08, 2007 (p P-D1-019 of the book of Abstracts), Indian Institute of Technology Madras, Chennai 600 036, India. (19) (a) Albrecht, M. Chem. Rev. 2010, 110, 576–623. (b) Ryabov, A. D. Chem. Rev. 1990, 90, 403–424. (20) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell University Press: Ithaca, NY, 1960; Table 7-2, p 224. (21) Churchill, M. R.; Wasserman, H. J.; Young, G. J. Inorg. Chem. 1980, 19, 762–770. (22) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev. 1973, 10, 335–422.

Figure 1. ORTEP representation of 1a at the 40% probability level. Only the NH hydrogens are shown for clarity. Selected bond distances (A˚) and angles (deg): N1-Pd1, 2.010(3); C21Pd1, 1.956(4); O1-Pd1, 2.153(3); O3-Pd1, 2.054(2); C12-N1, 1.307(4); C12-N2, 1.382(4); C12-N3, 1.350(4); C20-N3, 1.408(3); N4-Pd2, 2.017(2); C43-Pd2, 1.967(3); O4-Pd2, 2.144(3); O2-Pd2, 2.040(2); C34-N4, 1.300(4); C34-N5, 1.372(4); C34-N6, 1.361(3); C42-N6, 1.393(5); Pd1 3 3 3 Pd2, 3.005(2); C21-Pd1-N1, 89.2(1) C21-Pd1-O3, 91.1(2); N1-Pd1-O1, 92.3(1); O3-Pd1-O1, 87.1(2); N1-Pd1-O3, 177.9(9); C21-Pd1-O1, 172.0(1); N1C12-N3, 122.3(2); N1-C12-N2, 123.0(3); N3-C12-N2, 114.7(3); C12-N3-C20, 124.3(3); C43-Pd2-N4, 89.9(2); C43-Pd2-O2, 90.0(3); N4-Pd2-O4, 94.3(2); O2-Pd2-O4, 85.8(2); N4-Pd2O2, 179.2(9); C43-Pd2-O4, 174.1(1); N4-C34-N6, 122.6(3); N4-C34-N5, 122.7(3); N6-C34-N5, 114.6(3); C34-N6C42,126.2(3). Chart 2

2.040(2) A˚) due to higher trans influence of the palladated carbon than that of the imine nitrogen.22 The Pd 3 3 3 Pd distance, 3.005(2) A˚, in 1a is shorter than the sum of the van der Waals radii (3.26 A˚)23 but longer than the sum of the covalent radii (2.62 A˚)24 of two palladium atoms, and hence the Pd 3 3 3 Pd interaction is considered as weak. The structure and bonding of the CN3 core in 1a can be understood from the values of ΔCN, ΔCN0 , and the degree of pyramidalization (DP%) defined in Chart 2. The ΔCN value is the difference between the endocyclic C-N single and CdN double bond distances, whereas the ΔCN0 value is the difference between the exocyclic C-N single and CdN double bond distances, and these values are used as a measure of the delocalization of π-electron density across (23) Bondi, A. J. Phys. Chem. 1964, 68, 441–451. (24) Churchill, M. R. Perspect. Struct. Chem. 1970, 3, 91–164 (see, particularly, Section X-A on pp 153-155).

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Figure 2. VT 1H NMR (400 MHz, CD2Cl2) spectrum of 1a shown for OC(O)CH3 protons. For structures of A-E see Scheme 1. b: adventitious moisture in CD2Cl2.

the -N-CdN- component of amidines.25a The DP% value estimates the deviation of the bond angles in a three-coordinate amino nitrogen center from the full angle (normalized to 90°) and is expressed as a percentage.25b The ΔCN 0.032(6) A˚ value for the CN3 unit around Pd1 is significantly shorter than the ΔCN0 0.075(6) A˚ value, and the difference between ΔCN and ΔCN0 around Pd2 is comparable within the experimental uncertainties [ΔCN =0.061(5) A˚; ΔCN0 =0.072(6) A˚]. The smaller ΔCN value compared with ΔCN0 around Pd1 may be ascribed to a better alignment of the lone pair on the endocyclic amino nitrogen with the CdN π* orbital than that on the exocyclic amino nitrogen for a maximum n-π conjugation. Further, ΔCN and ΔCN0 values in 1a are considerably smaller than that observed in LH22-anisyl (ΔCN =0.100(6) A˚ and ΔCN0 =0.111(6) A˚),16 indicating a better n-π conjugation in the former. The amino nitrogens in 1a and LH22-anisyl are planar (DP%: 0.0). Palladacycle 1b is isostructural with 1a except for a crystallographic C2 symmetry that passess across the center of the Pd 3 3 3 Pd vector (see Figure S1 in the SI). The ΔCN 0.038(4) A˚ value in 1b is slightly shorter than the ΔCN0 0.059(4) A˚ value, and the amino nitrogens are planar (DP%: 0.0). The IR spectrum of 1a revealed a band at 3384 cm-1, and that of 1b revealed two bands at 3408 and 3314 cm-1 assignable to the NH stretch. Palladacycles 1a,b revealed a band at 1636 and 1624 cm-1, respectively, assignable to the CdN stretch. The Δν=ν(CdN)complex - ν(CdN)LH22-anisyl =-19 and -31 cm-1 values for 1a,b, respectively, indicate (25) (a) H€ afelinger, G.; Kuske, F. K. H. In The Chemistry of Amidines and Imidates; Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, 1991; Vol. 2. (b) Maksic, Z. B.; Kovacevic, B. J. Chem. Soc., Perkin Trans. 2 1999, 2623–2629. (26) Garcı´ a-Ruano, J. L.; L opez-Solera, I.; Masaguer, J. R.; Monge, M. A.; Navarro-Ranninger, C.; Rodrı´ guez, J. H. J. Organomet. Chem. 1994, 476, 111–120.

coordination of the guanidine moiety through the imine nitrogen.10m,n,12a,26-28 Two signature bands were observed at 1579 and 1412 cm-1 for 1a and at 1676 and 1536 cm-1 for 1b, assignable to νas(OCO) and νs(OCO), respectively. The Δν=νas(OCO) - νs(OCO)=167 and 140 cm-1 values for 1a, b, respectively, indicate a syn-syn bidentate bridging carboxylate coordination mode.29 Palladacycle 1a was subjected to a VT 1H NMR study from 303 to 213 at 10 K intervals, and the stack plot obtained for OC(O)CH3 protons is shown in Figure 2. At 293 K, six signals were observed at δH =1.26, 1.32, 1.42, 1.48, 1.54, and 1.58 ppm, assignable to the OC(O)CH3 protons. However, only three signals were observed, at δH =1.25, 1.42, and 1.50 ppm, at 213 K, while three remaining signals almost merged with the baseline. This observation can be explained by invoking a dynamic equilibria involving transoid in-in (A), transoid in-out (B), and transoid out-out (C) conformers by a process involving “(C,N)Pd” ring inversion, and such ring inversion was previously invoked to explain the fluxional behavior of the related acetato-bridged six-membered [C,N] palladacycle12k (see Scheme 1). Conformers A and C were anticipated to reveal one singlet, whereas conformer B was anticipated to reveal two singlets for OC(O)CH3 protons, as two former conformers possess a C2 symmetry whereas the latter lacks it. Cisoid in-in, cisoid in-out, and cisoid (27) Garcı´ a-Ruano, J. L.; L opez-Solera, I.; Masaguer, J. R.; NavarroRanninger, C.; Rodrı´ guez, J. H.; Martinez-Carrera, S. Organometallics 1992, 11, 3013–3018. (28) Navarro-Ranninger, C.; L opez-Solera, I.; Alvarez-Valdes, A.; Rodrı´ guez-Ramos, J. H.; Masaguer, J. R.; Garcı´ a-Ruano, J. L.; Solans, X. Organometallics 1993, 12, 4104–4111. (29) Nakammoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed.; Wiley: New York, 1997.

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Gopi et al.

Scheme 1

Chart 3

out-out conformations are less likely for 1a, as there will be an unfavorable steric repulsion between two o-anisyl moieties attached to the imino nitrogen, although such conformers were invoked to explain the 1H NMR spectral data of some six-membered [C,N] palladacycles.10m,11u,y,12h The o-OMe substituent on the aryl moiety of the imine nitrogen in 1a could have cleaved the acetate bridge intramolecularly by anchimeric assistance30 to afford a pincer-type monomer (D) and κ2-O,O0 -OAc monomer (E). We, therefore, conclude that palladacycle 1a exists as conformer A in the solid state but as a mixture of conformers A-C and monomers D and E in solution at 293 K and as a mixture of conformers A and B at 213 K. Intermediates of Cyclopalladation. Pd(OAc)2 was treated with LH22-anisyl in 1:1 mol ratio in CH2Cl2 at 10 °C to afford [(LH22-anisyl)Pd(μ-OAc)(OAc)]2 (1c) as a brown solid in 90% yield. The IR data of 1c indicated both monodentate (Δν = 290 cm-1) and bridging bidentate (Δν=161 cm-1) coordination modes for the OAc moiety.29 The 1H NMR spectrum of 1c revealed seven signals at δH = 1.37, 1.46, 1.54, 1.60, 1.86 (br), 1.98 (br), and 2.10 ppm assignable to the OC(O)CH3 protons of trans/cis-[(LH22-anisyl)Pd(μ-OAc)(OAc)]2 (F and G) and a monomer [(LH22-anisyl)Pd(κ2-O,O0 -OAc)(OAc)] (H) (see Chart 3). Further, four singlets were observed at δH = 3.14, 3.20, 3.25, and 3.39 ppm in 1.00:0.57:0.57:0.47 ratios for OCH3 protons of the o-anisyl moiety bound to the imine (30) Zanini, M. L.; Meneghetti, M. R.; Ebeling, G.; Livotto, P. R.; Rominger, F.; Dupont, J. Inorg. Chim. Acta 2003, 350, 527–536.

Figure 3. ORTEP representation of 2 at the 40% probability level. Hydrogen atoms except the NH hydrogens and acetone are omitted for clarity. Selected bond distances (A˚) and angles (deg): N1-Pd1, 2.038(3); C17-Pd1, 1.985(4); Br1-Pd1, 2.465(8); Br1-Pd1, 2.590(8); C8-N1, 1.310(5); C8-N3, 1.348(5); C8-N2, 1.362(5); C16-N3, 1.417(5); Pd1 3 3 3 Pd1, 3.696(4); C17-Pd1N1, 86.6(1); C17-Pd1-Br1, 94.1(1); N1-Pd1-Br1, 94.6(9); Br1-Pd1-Br1, 84.8(3); N1-Pd1-Br1, 179.3(9); C17-Pd1-Br1, 175.5(1); Pd1-Br1-Pd1, 95.2(3); N1-C8-N3, 119.9(3); N1C8-N2, 121.8(4); N3-C8-N2, 118.3(3); C8-N1-Pd1, 122.6(3); C8-N3-C16, 123.2(3).

nitrogen of F (first signal), G (middle two signals), and H (last signal), respectively. Thus, the adduct 1c exists as trans F in the solid state (IR evidence) and as a mixture of trans F, cis G, and monomeric H (1H NMR evidence) in solution. The dimer of the type F was previously identified as an intermediate in the formation of six-membered [C,N] palladacycles.11g,s Bromo-Bridged Six-Membered Guanidine Palladacycle (2). Palladacycle 1a was subjected to a metathetical reaction with LiBr in aqueous ethanol at 78 °C to afford 2 in 90% yield. The molecular structure of 2 is depicted in Figure 3. Palladacycle 2 exists as a dimer in transoid conformation. The palladium atom is surrounded by two bromine, an imine nitrogen, and palladated carbon and revealed a slightly distorted square-planar geometry. Two halves of the molecule are related by an inversion symmetry. The six-membered “(C,N)Pd” ring revealed a pseudo boat conformation, and the “[Pd(μ-Br)2Pd]” unit revealed a planar rhomboid conformation (Pd-Br-Pd: 95.2(3)°; Br-Pd-Br: 84.8(3)°). The Pd-C(aryl) distance, 1.985(4) A˚, in 2 is slightly shorter than that known for the related six-membered [C,N] palladacycle (Pd-CH2 = 2.021(7) A˚)11x perhaps owing to better back-donation in the former. The 1H NMR spectrum of 2 revealed three signals at δH =3.73 (s), 3.85 (s), and 4.17 (br) ppm assignable to OCH3 protons and a typical28,31 upfield shifted doublet at δH =6.56 ppm (JHH =8.10 MHz) assignable to the aryl CH proton adjacent to the palladated carbon. Monomeric Six-Membered Guanidine Palladacycles (3a-c, 4a,b, and 5). A suspension of 2 in CH2Cl2 was treated with Lewis bases at ambient temperature to afford 3a-c, 4a,b, and 5 in 87-95% yield. The 1H NMR spectra of 3a,b appeared quite complex, and hence these palladacycles were subjected to X-ray diffraction analyses. The molecular structures of 3a,b are depicted in Figures 4 and 5, respectively. The palladium atom in (31) (a) Bednarski, P. J.; Ehrensperger, E.; Sch€ onenberger, H.; Burgemeister, T. Inorg. Chem. 1991, 30, 3015–3025. (b) Selbin, J.; Gutierrez, M. A. J. Organomet. Chem. 1981, 214, 253–259. (c) Gutierrez, M. A.; Newkome, G. R.; Selbin, J. J. Organomet. Chem. 1980, 202, 341–350.

Article

Figure 4. ORTEP representation of molecule 1 of 3a at the 40% probability level. Two molecules were obtained in an asymmetric unit, but only molecule 1 is shown. Only the NH hydrogens are shown for clarity. Selected bond distances (A˚) and angles (deg): N1-Pd1, 2.060(4); C17-Pd1, 1.983(4); N4-Pd1, 2.173(4); Br1-Pd1, 2.441(6); C8-N1, 1.298(6); C8-N3, 1.365(6); C8-N2: 1.375(6); C16-N3, 1.410(6); C17-Pd1-N1, 90.0(2); N1-Pd1-N4, 89.9(1); C17-Pd1-Br1, 92.1(1); N4Pd1-Br1, 87.9(1); C17-Pd1-N4, 178.1(2); N1-Pd1-Br1, 176.1(1); N1-C8-N3, 121.7(4); N1-C8-N2, 123.7(5); N3-C8N2, 114.6(4); C8-N1-Pd1, 123.2(3); C8-N3-C16, 125.8(4).

3a,b is surrounded by an imine nitrogen, a palladated carbon, a bromine, and the nitrogen atom of the lutidine and revealed a slightly distorted square-planar geometry. Remarkably, lutidine is coordinated to the palladium in trans relation with respect to the Pd-C bond in both palladacycles. The six-membered “(C,N)Pd” ring in 3a,b revealed a pseudo boat conformation. The lutidine plane in 3a,b is rotated by 79.2(1)° (molecule 1), 76.9(1)° (molecule 2), and 86.9(9)°, respectively, along the Pd-Nlutidine bond with respect to the palladium coordination plane to avoid the unfavorable steric repulsion with the o-anisyl ring bound to the imine nitrogen. The molecular structure of 4a is depicted in Figure 6. The XyNC is coordinated to the palladium atom in cis relation with respect to the Pd-C bond as anticipated (see later). The six-membered “(C,N)Pd” ring in 4a revealed a pseudo boat conformation. The ΔCN value (0.026(1) A˚) is smaller than the ΔCN0 value (0.038(1) A˚), and the amino nitrogens are planar (DP%: 0.0). Usually, Lewis bases such as 2,4,6-collidine and 2,6-lutidine lie cis to the Pd-C bond in five-membered [C,N] palladacycles,32 although five five-membered [C,N] palladacycles26,28,33,34 and two five-membered [C,N] platinacycles35 are known to contain Lewis bases trans to the M-C bond. It was shown that preferences of cis or trans isomers in squareplanar palladium and platinum complexes depend upon a (32) (a) Calmuschi, B.; Alesi, M.; Englert, U. Dalton Trans. 2004, 1852–1857. (b) Ryabov, A. D.; Kazankov, G. M.; Yatsimirsky, A. K.; Kuz'mina, L. G.; Burtseva, O. Y.; Dvortsova, N. V.; Polyakov, V. A. Inorg. Chem. 1992, 31, 3083–3090. (33) Xu, C.; Gong, J.-F.; Zhang, Y.-H.; Zhu, Y.; Wu, Y.-J. Aust. J. Chem. 2007, 60, 190–195. (34) (a) Calmuschi-Cula, B.; Kalf, I.; Wang, R.; Englert, U. Organometallics 2005, 24, 5491–5493. (b) Pfeffer, M.; Sutter-Beydoun, N.; De Cian, A.; Fischer, J. J. Organomet. Chem. 1993, 453, 139–146. (35) (a) Ryabov, A. D.; Kuz’lmina, L. G.; Polyakov, V. A.; Kazankov, G. M.; Ryabova, E. S.; Pfeffer, M.; van Eldik, R. J. Chem. Soc., Dalton Trans. 1995, 999–1006. (b) Yen, S. K.; Young, D. J.; Huynh, H. V.; Koh, L. L.; Andy Hor, T. S. Chem. Commun. 2009, 6831–6833.


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Figure 5. ORTEP representation of 3b at the 40% probability level. Only the NH hydrogens are shown for clarity. Selected bond distances (A˚) and angles (deg): N1-Pd1, 2.049(3); C17Pd1, 1.977(3); N4-Pd1, 2.160(3); Br1-Pd1, 2.446(5); C8-N1, 1.297(4); C8-N3, 1.361(4); C8-N2, 1.362(4); C16-N3, 1.413(4); C17-Pd1-N1, 88.2(1); N1-Pd1-N4, 91.4(1); C17-Pd1-Br1, 92.9(1); N4-Pd1-Br1, 87.6(8); C17-Pd1-N4, 178.2(1); N1Pd1-Br1, 177.2(8); N1-C8-N3, 121.3(3); N1-C8-N2, 122.6(3); N3-C8-N2, 116.0(3); C8-N1-Pd1, 123.0(2).

Figure 6. ORTEP representation of 4a at the 40% probability level. Hydrogen atoms except the NH hydrogens and CH2Cl2 are omitted for clarity. Selected bond distances (A˚) and angles (deg): N1-Pd1, 2.037(6); C17-Pd1, 1.986(1); Br1-Pd1, 2.496(2); C23-Pd1, 1.901(9); C8-N1, 1.299(1); C8-N3, 1.325(1); C16-N3, 1.397(1); C23-N4, 1.132(1); C24-N4, 1.395(1); C17-Pd1-N1, 86.8(3); C23-Pd1-Br1, 86.5(3); N1-Pd1-Br1, 94.7(2); C23-Pd1C17, 91.9(4); C23-Pd1-N1, 178.3(4); C17-Pd1-Br1, 175.7(3); N1-C8-N3, 120.6(7); N1-C8-N2, 122.4(8); N3-C8-N2, 116.9(7); N4-C23-Pd1, 177.4(9); C8-N1-Pd1, 121.6(6); C8-N3-C16, 123.3(7); C23-N4-C24, 173.9(1).

combination of factors such as steric, antisymbiosis, π-backbonding, electrostatics, packing forces, and solvation.36 The absence or presence of noncovalent interactions in conjunction with steric effects34a,35a and relative hardness/softness of the substituents around the palladium and its antisymbiotic behavior37 were invoked to explain the trans configuration of neutral and a cationic five-membered [C,N] metallacycles, respectively. The trans configuration around the palladium atom in two neutral five-membered [C,N] palladacycles26,28 and a (36) Harvey, J. N.; Heslop, K. M.; Orpen, A. G.; Pringle, P. G. Chem. Commun. 2003, 278–279.

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cationic six-membered [C,N] palladacycle38 may be explained by considering relative hardness/softness of the donor atoms around the palladium center. The guanidine moiety in 3a,b is basic by virtue of a planar CN3 unit, and the imine nitrogen in these palladacycles is harder than the palladated carbon. Hence, harder lutidine (with respect to Br) lies trans to the softer Pd-C (with respect to the imine nitrogen) due to antisymbiosis.39 A hypothetical cis analogue of 3a,b would be unstable according to antisymbiosis, as soft Br is placed trans to the soft palladated carbon. In 4a and 5, XyNC and PPh3 are placed cis to the Pd-C bond, as these Lewis bases are softer than Br (see later). Further, PPh3 is bulkier than 2,6-lutidine, 2,4-lutidine, and XyNC. We, therefore, believe that relative hardness/ softness of the substituents around the palladium atom dictates the trans configuration in 3a,b and the cis configuration in 4a and 5. The IR spectra of palladacycles 3a-c, 4a,b, and 5 revealed signature band(s) for the NH and CdN moieties. Palladacycles 4a,b revealed additional bands at 2187 and 2206 cm-1, respectively, assignable to ν(CtN) stretch, and these values are comparable with that reported for the related six-membered [C,N] palladacycles10i,12b but higher than that known for uncoordinated XyNC (2131 and 2109 cm-1) and tBuNC (2125 and 2134 cm-1).40 The 1H NMR spectrum of 3a at 194.1 μM concentration in CDCl3 revealed three isomers in ca. 1.75:1.00:0.17 ratios. Two isomers revealed an identical 1H NMR pattern and somewhat close resonances: two signals at δH = 2.86 (br), 3.42 (br) (isomer 1); 2.83 (s), 3.24 (s) (isomer 2) ppm for the CH3 protons of 2,6-lutidine; three singlets at δH =3.76, 3.87, 4.08 (isomer 1); 3.54, 3.78, 3.82 (isomer 2) ppm for the OCH3 protons of the guanidine moiety. The third isomer revealed a singlet at δH =2.52 ppm for the CH3 protons of 2,6-lutidine and three singlets at δH = 3.74, 3.83, and 4.16 ppm for the OCH3 protons of the guanidine moiety. The anisochronicity of o-CH3 protons and chemical shift separation of these protons in isomer 1 (Δδ=0.56 ppm) and isomer 2 (Δδ=0.41 ppm) clearly indicated a pseudo boat conformation for the six-membered “(C,N)Pd” ring in solution, as observed in the solid state. The anisochronicity of the o-CH3 protons of 2,6lutidine- and 2,4,6-collidine-coordinated six-membered [C,N] palladacycles at ambient temperature11u and at -50 °C,12g respectively, was considered an indication of a boat conformation for the six-membered “(C,N)Pd” ring. Hence, we assign R and β notations for isomers 1 and 2, respectively. The o-OMe substituent on the aryl moiety bound to the imine nitrogen is pointing upward in the R isomer as observed in the solid state but pointing downward in the β isomer. The isochronicity of the o-CH3 protons of 2,6-lutidine of the third isomer indicated a planar conformation for the six-membered “(C,N)Pd” ring. Thus, the 1 H NMR pattern of 3a suggests two boat conformers (R and β) interconverting via a planar conformer by six-membered “(C, N)Pd” ring inversion without any bond breaking, as illustrated in Scheme 2. (37) Falvello, L. R.; Fernandez, S.; Navarro, R.; Pascual, I.; Urriolabeitia, E. P. Dalton Trans. 1997, 763–771. (38) Bosque, R.; Granell, J.; Sales, J.; Font-Bardı´ a, M.; Solans, X. J. Organomet. Chem. 1993, 453, 147–154. (39) Pearson, R. G. Inorg. Chem. 1973, 12, 712–713. (40) (a) Fornies, J.; Sicilia, V.; Larraz, C.; Camerano, J. A.; Martı´ n, A.; Casas, J. M.; Tsipis, A. C. Organometallics 2010, 29, 1396–1405. (b) Vicente, J.; Arcas, A.; Julia-Hernandez, F.; Bautista, D.; Jones, P. G. Organometallics 2010, 29, 3066–3076.

Gopi et al. Scheme 2

Table 1. Population of r, β, and Planar Conformers of 3a As a Function of Concentration Measured by 1H NMR Dataa conc (μM)

population (R:β:planar)

7.5

14.9

22.4

29.8

37.3

44.8

52.2

0.08:

0.13:

0.19:

0.25:

0.27:

0.27:

0.38:

1.00: 0.42

1.00: 0.26

1.00: 0.25

1.00: 0.18

1.00: 0.17

1.00: 0.19

1.00: 0.15

a The signals of OCH3 protons at δH = 3.55 (β), 4.09 (R), and 4.18 (planar) ppm at 7.5 μM concentation were used to calculate the population of conformers. The values of δH may vary slightly depending on the sample concentration.

Palladacycle 3a revealed concentration-dependent ratios of R, β, and planar conformers, as investigated by 1H NMR data (see Table 1). The population of the R conformer increases and that of the planar conformer decreases, although not smoothly relative to the β conformer upon increasing the sample concentration (see also Figure S2 in the SI). The environment around the molecule in solution at higher concentration perhaps resembles that present in the solid state, explaining the observed trend. VT 1H NMR data of a freshly prepared solution of 3a (500 MHz, CD2Cl2) indicate three conformers at 303 K, but the population of the R conformer increases, the planar conformer decreases relative to the β conformer upon decreasing the temperature, and this trend suggests that the “(C,N)Pd” ring inversion is quenched in the low-temperature limit (see Figure S3 in the SI). The room-temperature 1H NMR data of 3b and VT 1H NMR data (500 MHz, CD2Cl2; see Figure S4 in the SI) of 3c clearly indicated the presence of three isomers in solution, as identified from the signals of the CH3 and o-OCH3 protons of the former and the o-OCH3 protons of the latter. It is to be noted that 3b exists as an R conformer in the solid state (see above). The CH3 protons of 3,5-lutidine in all three conformers of 3c are located far away from the center of the boat and are thus isochronous even at 213 K. In solution, pyridine-coordinated six-membered [C,N] palladacycles exhibited fluxional behavior due to an equilibrium between two boat conformers through inversion of the six-membered “(C,N)Pd” ring.12g,h,k The 1H NMR spectral identification of the three conformers of 3a-c in solution is unprecedented, although the planar intermediate was invoked to explain the fluxional behavior of the related six-membered [C,N] palladacycle.12g

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579

Scheme 3

The 1H NMR spectrum of 4a,b and 5 indicated incorporation of one XyNC, tBuNC, and PPh3, respectively per “(C,N)Pd” unit and further revealed the presence of only one conformer in solution in each case. Palladacycle 4b is believed to possess a cis configuration as analogously observed in 4a. The 31P NMR spectrum of 5 revealed a singlet at δP=36.00 ppm, and this value falls within the 32-41 ppm range reported for the known cis-configured six-membered [C,N] palladacycles.8c,10d,e,h,n,u,w,11a,b,g-i,k,l,o,q,s,t,z,12a Further, the 13C NMR spectral pattern for the carbon nuclei of PPh3 and Pd-C(aryl) in 5 matched well with the known cis-configured sixmembered [C,N] palladacycles.8c,10e,n,11b,g,i,s Insertion Reaction. The insertion reaction of [C,N] palladacycles with isocyanides was shown to afford ring-expanded [C,N] palladacycles.10i,41 Therefore, palladacycle 2 was treated with XyNC in 1:2 ratio with a view to probe the lability of the Pd-C bond, and this reaction afforded palladacycle 6 in 93% yield instead of the anticipated seven-membered [C,N] palladacycle [Pd{κ2(C,N)-C(dNXy)(C6H3(OMe)-4)-2(NHC(NHAr)(dNAr))-3}Br(CNXy)] (Ar= 2-(MeO)C6H4, Xy = 2,6-Me2C6H3) (I). The palladacycle I is envisaged as one of the intermediates in the formation of 6 and possibly undergoes ring contraction to afford another intermediate (J) that subsequently undergoes amineimine tautomerization to afford 6 as depicted in Scheme 3. Amine-imine tautomerization was invoked to explain the formation of a few organopalladium12b,42 and organolanthanide43 complexes. A species such as J was proposed as one of the intermediates in the insertion of CO into an aryl carbon-palladium bond of the amidine-derived six-membered [C,N] palladacycle.14a The molecular structure of 6 is depicted in Figure 7. The XyNC is coordinated to the palladium atom in cis orientation with respect to the Pd-C bond. The palladium atom is (41) (a) Vicente, J.; Saura-Llamas, I.; Gr€ unwald, C.; Alcaraz, C.; Jones, P. G.; Bautista, D. Organometallics 2002, 21, 3587–3595. (b) Yamamoto, Y.; Yamazaki, H. Inorg. Chim. Acta 1980, 41, 229–232. (c) Ma, J.-F.; Kojima, Y.; Yamamoto, Y. J. Organomet. Chem. 2000, 616, 149–156. (d) O'Sullivan, R. D.; Parkins, A. W. J. Chem. Soc., Chem. Commun. 1984, 1165–1166. (e) Zografidis, A.; Polborn, K.; Beck, W.; Markies, B. A.; van Koten, G. Z. Naturforsch., B: Chem. Sci. 1994, 49, 1494–1498. (42) Wu, K.-M.; Huang, C.-A.; Peng, K.-F.; Chen, C.-T. Tetrahedron 2005, 61, 9679–9687. (43) Zhang, J.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2004, 23, 3303–3308.

Figure 7. ORTEP representation of 6 at the 40% probability level. Only NH hydrogens are shown for clarity. Selected bond distances (A˚) and angles (deg): N1-Pd1, 2.112(2); C23-Pd1, 2.009(3); Br1-Pd1, 2.585(4) C32-Pd1, 1.939(3); C1-N1, 1.336(4); C1-N2, 1.346(4); C1-N3, 1.355(4); C16-N1, 1.418(4); C23N4, 1.268(4); C32-N5, 1.152(4); C23-Pd1-N1, 80.7(1); C32Pd1-Br1, 84.8(1); C32-Pd1-C23, 95.1(1); N1-Pd1-Br1, 99.3(7); C32-Pd1-N1, 175.6(1); C23-Pd1-Br1, 178.3(9); N1C1-N2, 117.5(3); N1-C1-N3, 126.0(3); N2-C1-N3, 116.5(3); N5-C32-Pd1, 171.1(3); C16-N1-Pd1, 108.5(2); C23-N4C24, 127.3(3); C32-N5-C33, 172.9(4).

surrounded by an imine nitrogen, a ring carbon, a carbon atom of XyNC, and Br and exhibited a slightly distorted squareplanar environment. The N4-C23 distance, 1.268(4) A˚, is shorter than the N1-C1 distance, 1.336(4) A˚, and the greater length of the latter may be ascribed to n-π conjugation involving the lone pair of electrons on the amino nitrogen with the CdN π* orbital of the guanidine unit. The fivemembered “(C,N)Pd” ring revealed an envelope conformation with N1, C16, C17, and C23 atoms forming a plane and the palladium atom lying above the mean plane at 0.7334(2) A˚. The five-membered “(C,N)Pd” ring in palladacycle 7 revealed a planar conformation (see Chart 444), and the conformational difference between 6 and 7 may be ascribed to the unfavorable steric repulsion between the C(NHAr)2 and OMe moieties on the palladated ring in the former. The IR spectrum of 6 revealed two bands at 3284 and 3184 cm-1 assignable to the ν(NH) stretch. In addition, three signature bands were observed at 2180, 1629, and 1609 cm-1 assignable to ν(CtN), ν(CdNXy), and ν(CdN) stretches, respectively. The 1H NMR spectrum of 6 revealed incorporation of two XyNC per palladium. The 13C NMR spectrum of 6 revealed two signals at δC =18.7 and 19.5 ppm assignable to the CH3 carbon of the XyNC moiety and two signals at δC=55.3 and 55.6 ppm assignable to the OCH3 carbon of the guanidine moiety. Further, two characteristic signals were observed at δC = 151.7 and 178.2 ppm assignable to PdCtN and Pd-CdN carbon nuclei, respectively, and these δC values are comparable with those reported for 7 [δC 152.2 (CtN); 175.0 (CdN)].44

Concluding Remarks LH22-anisyl was cyclopalladated with Pd(OC(O)R)2 (R = Me, CF3) under facile reaction conditions to afford dimeric palladacycles 1a,b in high yield. The solid-state structures of (44) Vicente, J.; Abad, J.-A.; Frankland, A. D.; L opez-Serrano, J.; Ramirez de Arellano, M. C.; Jones, P. G. Organometallics 2002, 21, 272–282.

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Organometallics, Vol. 30, No. 3, 2011 Chart 4

1a,b and solution dynamics of 1a were studied by X-ray diffraction data and VT 1H NMR studies, respectively. The salt metathesis reaction of 1a with LiBr in aqueous ethanol afforded dimeric palladacycle 2 in high yield. Palladacycle 2 was subjected to a bridge-splitting reaction with various Lewis bases in CH2Cl2 to afford monomeric, rare transconfigured palladacycles 3a,b or cis-configured palladacycles 4a and 5 depending on the relative hardness/softness of the Lewis bases. The stereochemical outcome of the bridge-splitting reaction indicates that 3a,b are kinetic products, whereas 4a and 5 are thermodynamic products. The six-membered “(C,N)Pd” ring in guanidine palladacycles revealed a pseudo boat conformation with a significant n-π conjugation involving the lone pair on the amino nitrogen with the CdN π* orbital of the guanidine unit. Palladacycle 2 upon insertion reaction with 2 equiv of XyNC afforded a novel ring-contracted five-membered [C,N] palladacycle (6) in high yield, and the driving force for the formation of 6 was ascribed to the ring contraction followed by amine-imine tautomerization.

Experimental Section All manipulations were performed using standard Schlenk line technique under a nitrogen atmosphere unless stated otherwise. All reagents were purchased from commercial vendors and weighed and handled in air. LH22-anisyl was prepared following the reported procedure.16 Solvents were purified by standard methods.45 Melting points for 1a,b and 4a were determined on a PerkinElmer Thermal Analysis DSC instrument. The IR spectral data were obtained using KBr pellets on a Shimadzu IR435 spectrometer. 1H, 13C, 31P, and 19F NMR spectra were recorded on a Bruker Avance 300 NMR spectrometer operating at field strengths of 300, 75.5, 121.5, and 282.4 MHz, respectively. Chemical shifts were referenced to tetramethylsilane (TMS) or residual solvent signal (1H and 13C), 85% H3PO4 (external standard, 31P), and CFCl3 (external standard, 19F). The 13C, 31P, and 19F NMR spectra are proton decoupled. VT 1H NMR spectra of 1a was obtained on a Bruker AMX-400 spectrometer operating at a field strength of 400 MHz. The solid-state CP-MAS 13C NMR spectra of 1a and 3a were recorded on a Bruker DSX-300 spectrometer operating at a field strength of 75.5 MHz, and the chemical shifts were referenced with respect to TMS. The electrospray ionization mass spectra (ESI-MS) were obtained from a Thermo Finnigan LCQ 6000 advantage max ion trap mass spectrometer using CH2Cl2 as carrier solvent. Time of flight mass (TOF-MS) spectra were obtained on a JEOL MS Route using electrospray positive ion mode. Elemental analyses were carried out on an Elementar Analysen Systeme GmbH VarioEL V3.00. Synthesis of [Pd{K2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))2}(μ-OC(O)R)]2 (Ar = 2-(MeO)C6H4; R = Me (1a), CF3 (1b)). 1a: Pd(OAc)2 (100 mg, 0.445 mmol) and LH22-anisyl (166 mg, 0.445 mmol) were dispersed in toluene (15 mL) in a 25 mL Schlenk flask, and the starting materials dissolved upon heating to 70 °C. The reaction mixture was stirred at the same temperature (45) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory Chemicals, 5th ed.; Butterworth-Heinemann; Elsevier Science: USA, 2002.

Gopi et al. for 8 h and then cooled. During the course of the reaction, palladacycle 1a deposited as a yellow residue. The residue was filtered, washed with toluene (10 mL), and dried under vacuum. Crystals suitable for X-ray diffraction data were grown from a toluene/CH2Cl2 mixture over a period of several hours. Yield: 210 mg, 0.194 mmol, 87%. Dec pt (DSC): 226.9 °C. Anal. Calcd for C48H50N6O10Pd2 (1083.80): C, 53.20; H, 4.65; N, 7.75. Found: C, 53.21; H, 4.69; N, 7.74. IR (KBr, cm-1): ν(NH) 3384; ν(CdN) 1636; νas(OCO) 1579, νs(OCO) 1412. 1H NMR (300 MHz, CDCl3): δ 1.26, 1.37, 1.46, 1.53, 1.59, 1.61 (s, 6 H, CH3), 3.14, 3.21, 3.27, 3.41, 3.66, 3.74, 3.76, 3.80, 3.82, 3.91, 3.92, 3.94 (s, 18 H, OCH3), 5.94, 6.06, 6.17 (t, JHH=8.81 Hz), 6.26 (d, JHH=7.66 Hz), 6.39 (br m), 6.62 (d, JHH =8.01 Hz), 6.72-7.22 (m), 7.36, 7.42, 7.59 (t, JHH=7.85 Hz), 7.78, 8.06 (ArH and NH protons). Solidstate CP-MAS 13C NMR (75.5 MHz): δ 22.06, 25.55 (CH3), 52.76, 53.65, 55.08, 56.59, 56.93 (OCH3), 102.36, 104.75, 108.33, 110.59, 112.56, 114.65, 118.59, 119.97, 122.10, 123.56, 124.24, 125.84, 127.34, 128.97, 129.96, 130.25, 131.32, 132.50, 133.23, 135.14, 142.91, 143.97, 146.49 (br), 153.46, 154.21, 155.07, 156.05 (ArC and CdN), 177.01, 177.55 (OCO). Note: only 5 and 27 carbon resonances were observed for OCH3 and ArC carbons, respectively, rather than the expected 6 and 36 resonances, presumably due to overlapping peaks. TOF-MS ESþ, m/z (relative intensity %), [ion]: 1026 (100), [M - OAc]þ; 523 (81), [(C,N)Pd þ K]þ; 482 (45), [(C,N)Pd]þ; 376 (77), [LH22-anisyl - H]þ. 1b: Palladacycle 1b was synthesized from Pd(TFA)2 (50 mg, 0.15 mmol) and LH22-anisyl (57 mg, 0.15 mmol) in tolu ene (12 mL) following the procedure previously described for 1a. Crystals suitable for X-ray diffraction data were grown from CHCl3 at ambient temperature over a period of two days. Yield: 85 mg, 0.07 mmol, 95%. Mp (DSC): 239.58 °C. Anal. Calcd for Pd2C48H44N6O10F6 (1191.74): C, 48.38; H, 3.72; N, 7.05. Found: C, 48.38; H, 3.60; N, 6.93. IR (KBr, cm-1): ν(NH) 3408, 3314; ν(CdN) 1624; νas(OCO) 1676, νs(OCO) 1536; ν(CF3) 1146, 1201. 1 H NMR (300 MHz, CDCl3): δ 3.13, 3.23, 3.30, 3.49, 3.64, 3.76, 3.80, 3.88, 3.92, 4.04 (br m, 18 H, OCH3), 6.22 (d, JHH=6.71 Hz, 2 H), 6.37, 6.60 (br, 2 H), 6.73-6.93 (br m, 9 H), 7.05-7.09 (br m, 8 H), 7.48, 7.50, 7.55 (br m, 3 H), 7.89, 8.04 (br, 2 H) (ArH and NH). 19 F NMR (282.4 MHz, CDCl3): δ -74.33, -74.39, -74.56, -74.62. MS ESIþ, m/z (relative intensity %) [ion]: 1220 (11) [M þ Na]þ; 1079 (75) [M - TFA]þ; 992 (14) [M - 2TFA]þ; 523 (40) [(C, N)Pd þ K]þ; 376 (100) [LH22-anisyl - H]þ. Synthesis of [(LH22-anisyl)Pd(μ-OAc)(OAc)]2 (1c). LH22-anisyl (83 mg, 0.22 mmol) and Pd(OAc)2 (50 mg, 0.22 mmol) were dissolved in CH2Cl2 (15 mL) in a 25 mL RB flask in air. The brown solution was stirred at 10 °C for two days, and the reaction mixture was set aside at the same temperature for 2 days to afford 1c as a brown residue. Yield: 121 mg, 0.100 mmol, 90%. Anal. Calcd for C52H58N6O14Pd2 (1203.90): C, 51.88; H, 4.86; N, 6.98. Found: C, 51.98; H, 4.79; N, 7.36. IR (KBr, cm-1): ν(NH) 3398; ν(CdN) 1628; νas(μ-OAc) 1572; νas(OAc) 1540; νs(μ-OAc) 1411; νs(OAc) 1250. 1H NMR (300 MHz, CDCl3): δ 1.37, 1.46, 1.54, 1.60, 1.86 (br), 1.98 (br), 2.10 (10 3H, CH3), 3.14, 3.20, 3.25, 3.39 (each s, 5 3H, OCH3), 3.67, 3.74, 3.75, 3.77, 3.82, 3.91, 3.92, 3.95 (each s, 5 6H, OCH3), 5.95, 6.08, 6.16 (t, JHH =7.80 Hz), 6.26 (d, JHH =7.80 Hz), 6.40 (br), 6.63 (d, JHH=6.90 Hz), 6.72-7.24 (m), 7.29, 7.35, 7.43, 7.58 (t, JHH= 6.90 Hz), 7.78, 8.05 (ArH and NH). The aforementioned reaction carried out at 35 °C afforded an inseparable mixture of cyclopalladated 1a and 1c as identified by 1H NMR data. Synthesis of [Pd{K2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))2}(μ-Br)]2 (Ar = 2-(MeO)C6H4) (2). Palladacycle 1a (500 mg, 0.461 mmol) was dispersed in dry ethanol (180 mL) in a 250 mL RB flask. To the aforementioned heterogeneous mixture was slowly added 20 mL of aqueous LiBr solution (200 mg, 2.306 mmol), and the contents in the RB flask were stirred at 78 °C for 8 h and cooled. The volatiles from the reaction mixture were removed under vacuum to leave a yellow residue and water. The residue was extracted with CH2Cl2 (3 150 mL) and washed with distilled water (3 20 mL). The extract was dried over

Article anhydrous MgSO4 and concentrated under vacuum to afford a yellow residue. The residue was further purified by crystallization from CH2Cl2 at ambient temperature over a period of several hours to afford 2 as colorless crystals. Crystals suitable for X-ray diffraction study were grown from acetone at ambient temperature over a period of several hours. Yield: 540 mg, 0.417 mmol, 90%. Anal. Calcd for C44H44N6O6Pd2Br2 3 2CH2Cl2 (1295.40): C, 42.65; H, 3.73; N, 6.49. Found: C, 42.69; H, 3.77; N, 6.38. IR (KBr, cm-1): ν(NH) 3392, 3318; ν(CdN) 1619. 1H NMR (300 MHz, CDCl3): δ 3.73, 3.85 (each s, 2 6 H, OCH3), 4.17 (br, 6 H, OCH3), 6.56 (d, JHH = 8.10 Hz, 2 H, ArH), 6.67 (br, 2 H, NH), 6.73 (t, JHH=7.95 Hz, 2 H, ArH), 6.93 (t, JHH=8.25 Hz, 2 H, ArH), 7.00-7.11 (br, 8 H, ArH), 7.28 (br, 2 H, ArH), 7.35-7.53 (br, 6 H, ArH), 7.91 (br, 2 H, NH). The 13 C NMR spectrum for 2 was not recorded owing to its poor solubility in common deuterated solvents. MS ESIþ, m/z (relative intensity %), [ion]: 1045 (44), [M - Br]þ; 992.20 (14), [M - 2Br]þ; 523 (32), [(C,N)Pd þ K]þ; 376 (100), [LH22-anisyl - H]þ. Synthesis of [Pd{K2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))2}Br(L)] (Ar=2-(MeO)C6H4; L=2,6-Me2C5H3N (3a), 2,4-Me2C5H3N (3b), 3,5-Me2C5H3N (3c)). 3a: Palladacycle 2 (300 mg, 0.266 mmol) was dispersed in CH2Cl2 (10 mL) in a 25 mL RB flask in air and set to stir. To the aforementioned heterogeneous solution was slowly added 2,6-lutidine (60 mg, 0.56 mmol) that was previously dissolved in CH2Cl2 (5 mL), and the resulting heterogeneous mixture was stirred for 24 h at ambient temperature. During the course of the reaction, the residue gradually dissolved and led to the formation of a transparent pale yellow solution. The reaction mixture was concentrated under vacuum to ca. 5 mL and layered with toluene to afford 3a as colorless crystals. Yield: 340 mg, 0.508 mmol, 95%. Anal. Calcd for C29H31N4O3PdBr (669.91): C, 52.00; H, 4.66; N, 8.36. Found: C, 52.03; H, 4.70; N, 8.20. IR (KBr, cm-1): ν(NH) 3401, 3378, 3316; ν(CdN) 1622. The 1H NMR spectrum of 3a recorded at 7.50 μM was not conclusive, as no 1H NMR signals were apparent for CH3 protons of 2,6-lutidine of the R conformer. Hence, the 1H NMR spectrum was recorded at 194.1 μM concentration. The intensities of OCH3 protons were considered for the calculation of ratio of conformers. 1H NMR (300 MHz, 194.1 μM, CDCl3): R:β:planar conformers = ca. 1.75:1.00:0.17; δ 2.52 (s, 6 H, CH3; planar conformer), 2.83 (s, 3 H, CH3; β conformer), 2.86 (br, 3 H, CH3; R conformer), 3.24 (s, 3 H, CH3; β conformer), 3.42 (br, 3 H, CH3; R conformer), 3.54 (s, 3 H, OCH3; β conformer), 3.74 (s, 3 H, OCH3; planar conformer), 3.76 (s, 3 H, OCH3; R conformer), 3.78 (s, 3 H, OCH3; β conformer), 3.82 (s, 3 H, OCH3, β conformer), 3.83 (s, 3 H, OCH3; planar conformer), 3.87 (s, 3 H, OCH3; R conformer), 4.08 (s, 3 H, OCH3; R conformer), 4.16 (s, 3 H, OCH3; planar conformer), 5.57 (dd, JHH =6.90; 2.10 Hz, 2 H), 6.32 (dd, JHH =8.10 Hz, 1 H), 6.50-6.61 (m, 6 H), 6.70-7.30 (m, 29 H), 7.42-7.52 (m, 4 H), 7.74 (s, 2 H), 7.78 (dd, JHH =7.20 Hz, 1 H), 7.93 (s, 2 H), 8.00 (s, 1 H) (ArH and NH). Solid-state CP-MAS 13C NMR (75.5 MHz): δ 24.80, 26.00, 27.44 (CH3), 53.07, 55.21, 56.79 (OCH3), 105.17, 109.11, 110.42, 112.27, 118.89, 120.62, 124.81, 126.30, 127.45, 128.77, 133.12, 136.20, 139.75, 145.55, 149.00, 150.78, 157.63, 161.32 (ArC and CdN). MS ESIþ, m/z (relative intensity %), [ion]: 523 (37), [(C, N)Pd]þ; 376 (100), [LH22-anisyl]þ. Palladacycles 3b,c were prepared from 2 and the corresponding lutidine in CH2Cl2 by a procedure analogous to that described for 3a. 3b: Yield: 318 mg, 0.475 mmol, 89%. Anal. Calcd for PdC29H31N4O3Br (669.91): C, 52.00; H, 4.66; N, 8.36. Found: C, 51.97/51.93; H, 4.69/4.80; N, 8.31/8.25. IR (KBr, cm-1): ν(NH) 3381; ν(CdN) 1621. 1H NMR (300 MHz, CDCl3): R:β:planar conformers=ca. 0.57:1.00:0.38; δ 2.19, 2.30 (each s, 6 H, CH3, β conformer), 2.51, 2.68 (each br, 6 H, CH3, planar conformer), 3.05, 3.28 (each br, 6 H, CH3, R conformer), 3.54, 3.62 (each br, 6 H, OCH3, planar conformer), 3.78 (s, 6 H, OCH3, R conformer), 3.84 (s, 3 H, OCH3, β conformer), 3.86 (s, 6 H, OCH3, R and β conformers), 4.10 (s, 3 H, OCH3, β conformer), 4.18 (br, 3 H, OCH3, planar conformer), 5.75 (br, 2 H), 6.31, 6.44 (br, 3 H), 6.56, 6.58, 6.62 (m, 6 H), 6.82-7.00 (br m, 15 H), 7.08 (t, JHH = 7.20 Hz, 6 H), 7.16 (d, JHH =7.50 Hz, 4 H), 7.38 (br, 1 H), 7.45


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(d, JHH =6.90 Hz, 2 H), 7.72 (br, 2 H), 7.82 (d, JHH =7.50 Hz, 2 H), 7.92 (s, 2 H), 8.01 (s, 1 H), 8.39, 8.52 (each br, 2 H) (ArH and NH). MS ESIþ, m/z (relative intensity %), [ion]: 589 (14), [M Br-]þ; 523 (47), [(C,N)Pd]þ; 376 (100) [LH22-anisyl - H]þ. The sample was crystallized from a CH2Cl2/toluene mixture at ambient temperature to afford 3b as colorless crystals. 3c: Yield: 310 mg, 0.463 mmol, 87%. Anal. Calcd for C29H31N4O3PdBr (669.91): C, 52.00; H, 4.66; N, 8.36. Found: C, 51.69; H, 4.69; N, 8.04. IR (KBr, cm-1): ν(NH) 3397; ν(CdN) 1618. 1H NMR (300 MHz, CDCl3): R:β conformers=ca. 1:1; δ 2.10 (br, 6 H, CH3), 2.20 (s, 6 H, CH3), 3.55 (br, 3 H, OCH3), 3.77, 3.79, 3.84, 3.86, 4.10 (each s, 5 3 H, OCH3), 5.91 (d, JHH=6.60 Hz, 1 H), 6.35 (br, 1 H), 6.58-6.68 (br m, 3 H), 6.82 (t, JHH =7.80 Hz, 2 H), 6.89-6.99 (m, 9 H), 7.08 (t, JHH = 7.05 Hz, 3 H), 7.17 (t, JHH =7.65 Hz, 3 H), 7.36-7.44 (br m, 2 H), 7.58-8.00 (br m, 6 H), 8.42 (s, 2 H) (ArH and NH). MS ESIþ, m/z (relative intensity %), [ion]: 591 (12), [M - Br-]þ; 523 (45), [(C,N)Pd]þ; 376 (100), [LH22-anisyl - H]þ. Synthesis of [Pd{K2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))2}Br(CNR)] (Ar=2-(MeO)C6H4; R=Xy (4a), tBu (4b)). 4a: Palladacycle 2 (300 mg, 0.266 mmol) and XyNC (73 mg, 0.56 mmol) were charged into a 25 mL Schlenk flask. To the aforementioned flask was added CH2Cl2 (15 mL) to afford a brown solution. The solution was stirred for 12 h, concentrated under vacuum to 8 mL, and subsequently layered with toluene (2 mL) to afford 4a as colorless crystals after two days. Yield: 390 mg, 0.501 mmol, 94%. Dec pt (DSC): 137.36 °C. Anal. Calcd for C31H31N4O3PdBr 3 CH2Cl2 (778.87): C, 49.35; H, 4.27; N, 7.19. Found: C, 49.16; H, 4.42; N, 7.17. IR (KBr, cm-1): ν(NH) 3393; ν(CtN) 2187; ν(CdN) 1621. 1H NMR (300 MHz, CDCl3): δ 2.44 (s, 6 H, CH3), 3.80, 3.86, 4.09 (each s, 3 3 H, OCH3), 6.69 (d, JHH=7.80 Hz, 1 H, ArH), 6.86 (t, JHH=7.80 Hz, 1 H, ArH), 6.91-7.25 (m, 12 H, ArH), 7.56, 7.92 (each s, 2 H, NH). 13 C NMR (75.5 MHz, CDCl3): δ 19.0 (CH3), 55.2, 55.7, 55.9 (OCH3), 106.5, 111.2, 111.3, 120.5, 121.0, 122.0, 122.3, 125.3, 126.1, 126.5, 126.8, 127.7, 128.9, 129.1, 130.0, 133.3, 135.6, 135.8 (ArC), 144.3 (br, XyNtC), 146.0, 147.5, 150.9 (ArC), 153.8 (CdN). Note: only 21 carbon resonances were observed for ArC carbons rather than the expected 22 resonances, presumably due to overlapping peaks. MS ESIþ, m/z (relative intensity %), [ion]: 613 (100), [M - Br-]þ; 376 (45), [LH22-anisyl - H]þ. 4b: Palladacycle 4b was prepared from 2 (300 mg, 0.266 mmol) and tBuNC (49 mg, 0.59 mmol) in CH2Cl2 by a procedure analogous to that described for 4a. Yield: 285 mg, 0.477 mmol, 90%. Anal. Calcd for C27H31N4O3PdBr (645.89): C, 50.21; H, 4.84; N, 8.67. Found: C, 50.43; H, 4.71; N, 8.64. IR (KBr, cm-1): ν(NH) 3382; ν(CtN) 2206; ν(CdN) 1623. 1H NMR (300 MHz, CDCl3): δ 1.48 (s, 9 H, CH3), 3.78, 3.85, 4.06 (each s, 3 3 H, OCH3), 6.67 (d, JHH =8.10 Hz, 1 H, ArH), 6.85 (t, JHH =7.80 Hz, 1 H, ArH), 6.92 (t, JHH = 7.65 Hz, 2 H, ArH), 6.97, 7.00 (each s, 2 H, ArH), 7.08 (t, JHH=7.65 Hz, 2 H, ArH), 7.13-7.21 (m, 3 H, ArH), 7.52, 7.86 (each s, 2 H, NH). 13C NMR (75.5 MHz, CDCl3): δ 28.7 (CH3), 54.1, 54.6, 54.8 (OCH3), 56.3 (Me3CNC), 105.2, 110.1, 110.2, 119.3, 119.8, 120.8, 121.1, 124.0, 125.0, 125.4, 125.6, 127.7, 128.8 (ArC), 130.4 (br, tBuNtC), 131.4, 134.6, 144.7, 146.2, 149.7 (ArC), 152.6 (CdN). MS ESIþ, m/z (relative intensity %), [ion]: 565 (100), [M - Br-]þ; 509 (14), [(C,N)Pd]þ; 376 (34), [LH22-anisyl - H]þ. Synthesis of [Pd{K2(C,N)-C6H3(OMe)-3(NHC(NHAr)(dNAr))2}Br(PPh3)] (Ar=2-(MeO)C6H4 (5)). Palladacycle 5 was prepared from 2 (300 mg, 0.266 mmol) and PPh3 (154 mg, 0.586 mmol) in CH2Cl2 (15 mL) by a procedure analogous to that described for 4a. Yield: 400 mg, 0.485 mmol, 91%. Anal. Calcd for C40H37N3O3PPdBr (823.03): C, 58.23; H, 4.52; N, 5.09. Found: C, 58.27; H, 4.48; N, 4.95. IR (KBr, cm-1): ν(NH) 3382; ν(CdN) 1617. 1H NMR (300 MHz, CDCl3): δ 3.78, 3.88, 4.06 (each s, 3 3 H, OCH3), 6.15 (t, JHH =7.80 Hz, 1 H, ArH), 6.30 (t, JHH =7.05, 1 H, ArH), 6.36 (d, JHH=7.80 Hz, 1 H, ArH), 6.94 (t, JHH=8.10 Hz, 4 H, ArH), 7.11 (t, JHH=7.65 Hz, 2 H, ArH), 7.17-7.34 (m, 11 H, ArH and NH), 7.61 (t, JHH =9.15 Hz, 6 H, ArH), 7.83 (d, JHH =6.00 Hz, 2 H, ArH). 13 C NMR (75.5 MHz, CDCl3): δ 55.2, 55.7, 56.2 (OCH3), 105.2,

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Gopi et al.

Table 2. Crystal Data and Structure Refinement for Complexes 1a, 1b, 2, and 3a

formula fw temp (K) cryst syst space group wavelength (λ) a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) volume (A˚3) Z Fcalcd (g cm-3) F(000) μ(Mo KR) (mm-1) θ range (deg) no. of reflns coll no. of reflns used parameters R1 [I > 2σ(I)] wR2 (all reflns) goodness of fit on F2 largest diff peak/hole (e 3 A˚-3)

1a

1b 3 CHCl3

2 3 Me2CdO

3a

Pd2C48H50N6O10 1083.74 293(2) monoclinic P21/n 0.71073 15.769(2) 15. 769(2) 19.401(2) 90.00 90.00(3) 90.00 4824.0(9) 4 1.492 2208 0.808 1.66-33.00 87 566 18 490 603 0.0453 0.1693 0.768 1.189/-1.838

PdC25H23N3O5Cl3F3 715.21 293(2) monoclinic C2/c 0.71073 20.559(2) 13.884(1) 21.528(2) 90.00 108.011(1) 90.00 5844.2(8) 8 1.626 2864 0.968 1.80-27.50 31 794 6689 365 0.0396 0.1254 0.700 1.019/-1.058

Pd2C50H56N6O8Br2 1241.63 293(2) monoclinic P21/c 0.71073 10.432(5) 10.795(5) 22.836(10) 90.00 96.078(7) 90.00 2557.2(19) 2 1.613 1248 2.323 1.79-27.75 21 643 6026 312 0.0445 0.1224 0.932 0.801/-0.669

PdC29H31N4O3Br 669.89 293(2) monoclinic P21/c 0.71073 17.836(1) 15.092(1) 21.160(2) 90.00 90.654(2) 90.00 5695.3(7) 8 1.563 2704 2.091 1.66-27.50 48 676 13 305 695 0.0616 0.1091 1.118 0.578/-0.547

Table 3. Crystal Data and Structure Refinement for Complexes 3b, 4a, and 6

formula fw temp (K) cryst syst space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z Fcalcd (g cm-3) F(000) μ (mm-1) θ range (deg) no. of reflns coll no. of reflns used parameters R1 [I > 2σ(I)] wR2 (all reflns) goodness of fit on F2 largest diff peak/hole (e 3 A˚-3)

3b

4a 3 CH2Cl2

6

PdC29H31N4O3Br 669.89 293(2) monoclinic P21/n 10.4074(7) 15.092(1) 18.066(1) 90.00 95.409(1) 90.00 2824.9(3) 4 1.575 1352 2.108 1.76-28.02 23 960 6628 348 0.0471 0.1103 1.111 0.605/-0.438

PdC32H33N4O3Cl2Br 778.83 293(2) monoclinic P21/n 10.268(4) 14.844(7) 21.449(9) 90.00 94.897(12) 90.00 3257(2) 4 1.588 1568 1.999 2.66-30.00 22 611 9439 393 0.0746 0.2727 0.784 1.081/-1.535

PdC40H40N5O3Br 825.08 293(2) monoclinic P21/n 11.0241(3) 22.6339(7) 16.1571(5) 90.00 108.578(1) 90.00 3821.4(2) 4 1.434 1680 1.574 1.61-29.33 49 232 10 490 458 0.0393 0.1380 1.072 0.712/-0.872

111.2, 111.8, 120.5, 121.1, 122.2, 122.3, 125.0, 126.1, 126.7, 127.4, 127.5 (d, 2JPC =10.57 Hz, o-CH, PPh3), 128.7, 129.7 (d, 4JPC =2.26 Hz, p-CH, PPh3), 132.0, 132.1, 132.5 (d, 1JPC=49.10 Hz, i-C, PPh3), 135.2 (d, 3JPC =11.32 Hz, m-CH, PPh3), 136.7 (d, 2JPC =14.34 Hz, Pd-C), 147.1, 147.8, 151.0 (ArC), 153.9 (CdN). 31P NMR (121.5 MHz, CDCl3): δ 36.00 ppm. MS ESIþ, m/z (relative intensity %), [ion]: 744 (100), [M - Br]þ, 376 (48) [LH22-anisyl - H]þ. Synthesis of [Pd{K2(C,N)-C(dNXy)(C6H3(OMe)-4)-2(NdC(NHAr)2)-3}(Br)(CNXy)] (Ar = 2-(MeO)C6H4 (6)). Palladacycle 2 (300 mg, 0.266 mmol) and XyNC (147 mg, 1.119 mmol) were charged into a 25 mL Schlenk flask. To the aforementioned flask was added CH2Cl2 (15 mL) under nitrogen atmosphere, and the contents of the flask were stirred at room temperature for 12 h to obtain a brown solution. The solution was concentrated to ca. 8 mL and allowed to stand at ambient temperature for several hours to afford 6 as colorless crystals. Yield: 410 mg, 0.497 mmol, 93%. Anal. Calcd for

C40H40N5O3PdBr (825.11): C, 58.23; H, 4.89; N, 8.49. Found: C, 58.04; H, 5.04; N, 8.44. IR (KBr, cm-1): ν(NH) 3284, 3184; ν(CtN) 2180, ν(CdNXy) 1629; ν(CdN) 1609. 1H NMR (300 MHz, CDCl3): δ 2.16 (s, 2 3 H, CH3), 2.40 (br, 2 3 H, CH3), 3.55 (s, 3 H, OCH3), 3.80 (s, 2 3 H, OCH3), 6.51 (t, JHH =7.44 Hz, 1 H, ArH), 6.58 (d, JHH=7.91 Hz, 1 H, ArH), 6.63-6.71 (m, 7 H, ArH and NH), 6.84 (t, JHH =7.83 Hz, 4 H, ArH), 6.94 (d, JHH = 7.54 Hz, 2 H, ArH), 7.04-7.12 (m, 3 H, ArH and NH), 7.38 (d, JHH = 7.12 Hz, 1 H, ArH). 13C NMR (75.5 MHz, CDCl3): δ 18.7, 19.5 (CH3), 55.3, 55.6 (OCH3), 110.5 (br), 112.7, 116.6, 120.2, 122.3 (br), 123.2, 124.5 (br), 126.5, 126.8, 127.2, 127.6, 128.6, 134.5, 140.7, 141.0, 143.7, 150.0 (ArC), 151.7 (Pd-CtN), 152.9 (Pd-NdC), 178.2 (Pd-CdN). Note: only 2 and 17 carbon resonances were observed for OCH3 and ArC carbons, respectively, rather than the expected 3 and 26 resonances, presumably due to overlapping peaks. MS ESIþ, m/z (relative intensity %), [ion]: 744 (63), [M - Br-]þ; 654 (18),

Article [(C,N)Pd þ K]þ; 613 (100), [(C,N)Pd]þ; 548 (18), [{(C,N)Pd þ K} - Xy]þ; 507 (20), [(C,N)Pd - Xy]þ; 401 (24), [LH22-anisyl þ Na]þ. Crystal Structure Determinations. Suitable crystals of 1a,b, 2, 3a,b, 4a, and 6 for X-ray diffraction study were carefully selected after examination under an optical microscope and mounted on the goniometer head with paraffin oil coating. The unit cell parameters and intensity data were collected at room temperature using a Bruker SMART APEX CCD diffractometer equipped with a fine-focus Mo KR X-ray source (50 kV, 40 mA). The data acquisition was done using SMART software, and SAINT software was used for data reduction.46 The empirical absorption corrections were made using the SADABS program47 and empirical method.48 The (46) SMART and SAINT, Version 6.22a; Bruker AXS: Madison, WI, 1999. (47) Sheldrick, G. M. SADABS, version 2, Multiscan Absorption Correction Program; University of G€ottingen: G€ottingen, Germany, 2001. (48) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33–38. (49) Sheldrick, G. M. SHELX-97, Program for the Solution of Crystal Structures; University of G€ottingen: G€ottingen, Germany, 1997.


583

structure was solved and refined using the SHELXL-97 program.49 The palladium atom position was observed by the Patterson method, and the non-hydrogen atoms were located by successive difference Fourier maps and refined anisotropically. Hydrogen atoms were fixed in idealized positions and refined in a riding model. The relevant crystallographic data and details of the refinement for the structures of 1a,b, 2, 3a,b, 4a, and 6 are listed in Tables 2 and 3.

Acknowledgment. We thank the Department of Science and Technology, New Delhi, for financial support (SR/S1/ IC-22/2004) and for a fellowship (K.G.). We also thank NMR Research Centre, Indian Institute of Science, Bangalore 560 012, for VT 1H NMR measurements. Supporting Information Available: Molecular structure of 1b, VT 1H NMR stack plots for 3a and 3c, VC 1H NMR stack plot for 3a, CIF files for 1a,b, 2, 3a,b, 4a, and 6. This material is available free of charge via the Internet at http://pubs.acs.org.

Synthesis, Reactivity, Structural Aspects, and Solution Dynamics of

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