Palladium(II) macrocycles and lanterns

Polyhedron xxx (2015) xxx–xxx

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Palladium(II) macrocycles and lanterns Nancy L.S. Yue, Michael C. Jennings, Richard J. Puddephatt ⇑ Department of Chemistry, University of Western Ontario, London N6A 5B7, Canada

a r t i c l e

i n f o

Article history: Received 18 June 2015 Accepted 6 August 2015 Available online xxxx Keywords: Palladium Host-guest Lantern Pyridine Macrocycle

a b s t r a c t The coordination chemistry of palladium(II) with the bis(amidopyridine) ligands [LL = Ar(CONMe-4C5H4N)2, with Ar = 1,3-C6H4 (1), 5-t-Bu-1,3-C6H3 (2) and 2,5-C4H2S (3) has been investigated. The reaction of [PdCl2(NCPh)2] with the ligands in a 1:1 ratio gave the corresponding neutral binuclear macrocyclic complexes trans,trans-[Pd2Cl4(l-LL)2] in all cases. The cavity size and shape in these complexes is highly dependent on the ligand conformation and can change to accommodate guest molecules. The reaction of [PdCl2(NCPh)2] with the ligands in a 1:2 ratio gave the mononuclear bis(chelate) derivative [Pd(LL)2]2+, with LL = 3, but the binuclear ‘‘lantern” or ‘‘paddlewheel” complexes [Pd2(l-LL)4(l-Cl)]3+, with LL = 1 or 2. The selective encapsulation of a chloride ion in these complexes is favored by multiple secondary bonding interactions of the types Cl


Pd and Cl


HC. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction The self-assembly of palladium(II) complexes with bidentate ligands has yielded an impressive array of macrocycles, which have promise as molecular materials for applications in sensors or in catalysis, as outlined in recent reviews [1–4]. These macrocycles are often designed to contain two or more palladium atoms, with the preferred structure depending on both the palladium precursor complex and the bidentate ligand [1–10]. We have been interested in using amidopyridine ligands for synthesis of functional macrocycles [8–10]. For example, the bis(amidopyridine) ligand A has conformational flexibility and any of the three conformers A1–A3 can bridge between square planar palladium(II) centers to give complexes such as B and C (Chart 1) [8,9]. The macrocyclic (B) or lantern (C) complexes have been termed amphitopic receptors because the NH groups can bind anions and other nucleophiles through hydrogen bonding, while the carbonyl groups can bind cations and other electrophiles, and the ligands can switch conformations to adapt to a particular guest [8–10]. For example, the macrocyclic complex B has one ligand each in conformation A2 and A3 and it binds an N,N-dimethylformanide guest by forming a strong (host)NH


O@C(guest) hydrogen bond supported by three weaker (host)C@O


HC(guest) hydrogen bonds (Chart 1) [8,9]. The lantern complex C (Chart 1) has four NH and four C@O groups directed into the cavity and it can bind salts, with the anions binding to the NH groups (and also to the electrophilic

⇑ Corresponding author. E-mail address: [email protected] (R.J. Puddephatt).

Pd2+ centers) and with the cations binding to the carbonyl groups [8,9]. The amide units of the bis(amidopyridine) ligands in Chart 1 adopt the anti-NHC@O conformation and so the 3-pyridyl group in A is oriented to promote bridging coordination in complexes such as B or C. On the other hand, the ligands 1–3 (Chart 2) are expected to adopt the syn conformation of the MeNC@O units and so the ligand with 4-pyridyl groups is better oriented to promote bridging coordination [5,7,8,10]. The preferred orientation and bite distance of the 4-pyridyl donors can be modified by using either a six- or five-membered ring at the center (Chart 2) [10–14]. Of course, these ligands 1–3 have considerable flexibility by rotation of the central group or the terminal pyridyl groups with respect to the amide and also by twisting of the amide group, and they and similar ligands are capable of forming chelate, macrocyclic or ring-opened polymeric structures [5–17]. This article gives a detailed account of the palladium(II) complexes of 1–3 and their ability to act as hosts for chloride anions [10]. 2. Results and discussion The ligands 1–3 have been reported previously [12,18], but the structure of 1 was determined during the present work (Fig. 1). A surprising feature is that there is one anti and one syn MeNCO unit, with torsion angles C(8)N(7)C(9)O(10) = 6.5° and C(20)N(19)C (17A)O(18A) = 164°. Based on several precedents, the ligands are expected to exist in solution largely as the syn,syn conformers [12,18,19]. The 1H and 13C NMR spectra of 1 in CD2Cl2 solution indicate that the compound has effective C2v symmetry. For example, it gives a single methyl resonance at d(1H) = 3.41 and d(13C)

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N.L.S. Yue et al. / Polyhedron xxx (2015) xxx–xxx Table 1 Conformational parameters of the ligands and non-bonding N


N and Pd


Pd distances.

N N

N

O

O

H N N H

N H

R

R

Compound

O

1 4 5 6 7 8 9

R

H N

O

O

H N

O

H N

N

N

A1

N

A2

A3

Cl N O

Pd

N

Cl

N

O O

NH O

H O

Me

N 2+ N Pd N N H H

N N O

N H N H

N


Na/Å

Pd


Pda/Å

Amideb/° e

11.96 3.69 3.85 6.93 2.72 6.64 6.50

3.63 3.71 6.96 6.56 6.39

6, 168 9 11 13 3 10 18

Amide-arc/° 50, 68 44 54 26 11 48 41

Amide-pyd/°

e

46, 11e 43 44 48 72 36 31

a Mean distance between nitrogen donor atoms of terminal pyridyl groups or transannular Pd


Pd distance. b Mean torsion angle MeNCO. c Mean torsion angle between amide and central aryl or thiophen group. d Mean torsion angle between amide and pyridyl group. e For the syn and anti amide groups.

O

N H

Me

O

O

H N

N H

Cl Pd

N

H N H N

H H N N O N O N

O O N 2+ N Pd

N

Me

Me O

N

O

N

N

N (1)

Cl C

B

O Chart 1. A bis(amidopyridine) ligand and binuclear palladium(II) complexes.

N

N

O

N

Me 1, anti,syn

Me 1, syn,syn N

Me

Me O

N

N

O

N

N

N

N

S

R

O

N

Me 1, R = H; 2, R = t-Bu

N

O

Me 3

Chart 2. The bis(pyridine) ligands 1–3. The conformation is described as syn,syn with respect to the amide groups.

Fig. 1. The structure of the ligand 1, showing 30% probability ellipsoids.

= 37.7. Presumably the anti,syn conformer is less abundant but also less soluble than the syn,syn conformer and so crystallizes selectively from the equilibrating mixture of conformers (Eq. (1)). Some twisting of the pyridyl group out of the amide plane is necessary to reduce steric hindrance between the ortho-hydrogen and methyl substituents. Favorable intermolecular CH


N and CH


O@C hydrogen bonding may promote crystallization of the observed conformer. The conformational parameters of the compounds studied are summarized in Table 1. There is disorder of the carbonyl atoms of the anti-MeNCO unit and only one component is shown for clarity in Fig. 1. In the second form, the torsion angle C(20)N(19)C(17B)O(18B) = 172°.

The reaction of [PdCl2(NCPh)2] with the ligands LL = 1–3 in a 1:1 ratio gave the corresponding binuclear complexes [Pd2Cl4(l-LL)2], 4–6, with bridging bis(pyridine) ligands (Scheme 1). The 1H NMR spectra indicated that only one isomer was present in each case, thus precluding the presence of detectable amounts of the potential monomeric chelate complexes [PdCl2(LL)]. For example, the 1 H NMR spectrum of 4 contained only one MeN resonance at d 3.43. The structures of complexes 4 and 5 are shown in Fig. 2. Each complex has the stereochemistry trans,trans-[Pd2Cl4(l-LL)2] at the palladium(II) centers and the syn,syn-conformation of the amide groups. The transannular distances Pd


Pd are 3.63 and 3.71 Å in 4 and 5 respectively (Table 1). There is no space for solvent inclusion in the cavity of either complex, but there are weak transannular Pd


Cl interactions in 4, as shown in Fig. 3 [Pd(1)


Cl(4) 3.38(1); Pd(2)


Cl(2) 3.38(1) Å]. There is a major difference in conformation between complexes 4 and 5. In complex 4, the 1,3-C6H4 groups are mutually anti to give an extended chair conformation of the macrocycle but, in complex 5, the 1,3-C6H3-5-t-Bu groups are mutually syn to give an extended twist-boat conformation of the macrocycle. Neither macrocycle has crystallographically imposed symmetry, but complex 4 has an approximate inversion center while the highly twisted structure of 5 is unsymmetrical. It is also noteworthy that the syn,syn conformation at the N-methyl amide groups of the ligands in complex 4 is different from that established in the solid state for the free ligand 1 (Fig. 1). The structure of complex 6 is shown in Fig. 3. Like complexes 4 and 5 (Fig. 2), complex 6 has the trans,trans stereochemistry at the palladium(II) centers and the syn,syn-conformation of the amide

2 LL 2 [PdCl2(NCPh) 2] - 4 PhCN

Cl L Pd L Cl Cl L Pd L Cl

Scheme 1. Synthesis of complexes 4–6.

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4 , LL = 1 5, LL = 2 6 , LL = 3

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Fig. 2. Structures of the macrocyclic complexes 4 and 5, showing 30% probability ellipsoids. Selected bond parameters: Complex 4: Pd(1)–N(1) 2.03(1); Pd(1)–N(8) 2.04(1); Pd(1)–Cl(2) 2.306(4); Pd(1)–Cl(1) 2.321(4); Pd(2)–N(5) 2.00(1); Pd(2)–N(4) 2.02(1); Pd(2)–Cl(4) 2.314(4); Pd(2)–Cl(3) 2.315(4) Å; N(1)–Pd(1)–N(8) 178.0(4); Cl (2)–Pd(1)–Cl(1) 174.5(2)°. Secondary bonds: Pd(1)


Cl(4) 3.38(1); Pd(2)


Cl(2) 3.38(1) Å. Complex 5: Pd(1)–N(31) 2.023(4); Pd(1)–N(11) 2.025(4); Pd(1)–Cl(3) 2.297(1); Pd(1)–Cl(1) 2.312(1); Pd(2)–N(21) 2.012(4); Pd(2)–N(41) 2.022(4); Pd(2)– Cl(4) 2.289(1); Pd(2)–Cl(2) 2.309(1) Å; N(31)–Pd(1)–N(11) 177.9(1); Cl(3)–Pd(1)–Cl (1) 175.09(5)°.

solvent molecules, and one dichloromethane molecule is present within the macrocycle, as shown in Fig. 3. One of the chlorine atoms of this solvent molecule is roughly equidistant between the two palladium atoms, but the Pd


Cl distances are >3.5 Å which can represent only a very weak secondary interaction. There are weak hydrogen bonding interactions in which the dichloromethane acts as both an acceptor through a thiophen CH


Cl unit and donor through two CH


ClPd units. This combination of weak secondary bonding interactions appears to favor formation of the expanded macrocyclic structure needed to encapsulate the solvent molecule. Overall, the structures of the macrocyclic complexes 4–6 (Figs. 2 and 3) illustrate how conformational changes of the bis(amidopyridine) ligands allow the formation of cavities with different dimensions (Table 1). The ligand flexibility allows small cavities to be found in complexes 4 and 5 (Fig. 2), while complex 6 has a medium-sized cavity which can act as a host for a dichloromethane solvent molecule. If the reagent [PdCl2(NCPh)2] was first treated with silver trifluoroacetate to form the trifluoroacetate complex [Pd (O2CCF3)2(NCPh)2] in situ, and this mixture was then treated with the bis(pyridine) ligands 1–3 in a 1:2 ratio, it was possible to crystallize either the chelate complex [Pd(LL)2]2+, 7, as the trifluoroacetate salt with the ligand LL = 3, or the lantern complexes [Pd2(lCl)(l-LL)4]3+, 8 and 9, as mixed trifluoroacetate/chloride salts with the ligand LL = 1 or 2. The lantern complexes 8 and 9 both crystallized with an encapsulated chloride ion, and it has not been possible to isolate an ‘‘empty” lantern complex containing the 4+ cation [Pd2(l-LL)4]4+. It is possible that a chloride ion acts as a template in forming the lantern complexes [Pd2(l-Cl)(l -LL)4]3+. The complexes appear to exist as single isomers in solution. For example, the 1H NMR spectrum of complex 9 shows that all pyridyl groups and t-butyl groups are equivalent. These data are not consistent with the complex existing as a mixture of chelate and macrocyclic forms. The complexes are sparingly soluble so it was not possible to record low temperature NMR spectra (Scheme 2). The structure of complex 7 is shown in Fig. 4. There is a center of symmetry at the square planar palladium(II) atom. The bond angle N(1)–Pd–N(23) = 84.2(2)° does not indicate that there is a high degree of angle strain in forming the bis(chelate) complex. However, the pyridyl groups are twisted out of the plane of the amide groups by an average of 72° (Table 1) and this will cause a significant decrease in amide-pyridyl conjugation. Although the overall thiophen-amide twist angle for the chelate complex 7 (11°) and the bridged complex 6 (26°) appear similar, this is misleading because the thiophen conformation is opposite in the two complexes as shown in Chart 3. It is the conformational flexibility that gives the ligand 3 the versatility to chelate or bridge between metal atoms. The structures of the lantern complexes 8 and 9 are shown in Fig. 5. The complexes each have the primary coordination of the

Fig. 3. Structure of the macrocyclic complex 6, showing 30% probability ellipsoids. Selected bond parameters: Pd(1)–Cl(1) 2.311(2); Pd(1)–Cl(3) 2.299(2); Pd(1)–N(11) 2.017(6); Pd(1)–N(31) 2.006(7); Pd(2)–Cl(2) 2.308(2); Pd(2)–Cl(4) 2.300(2); Pd(2)– N(21) 2.020(6); Pd(2)–N(41) 2.026(6) Å; Cl(3)–Pd(1)–Cl(1) 177.32(9); N(31)–Pd(1)– N(11) 179.2(3); Cl(4)–Pd(2)–Cl(2) 176.51(9); N(21)–Pd(2)–N(41) 177.5(3)°.

groups. The thiophen groups are mutually anti to give an extended chair conformation of the macrocycle, analogous to the conformation of complex 4 (Fig. 2). However, the transannular distance Pd


Pd is much longer in 6 (6.96 Å) than in 4 (3.63 Å). The difference is partly attributable to the substitution of the 5-membered thiophen group in 6, compared to the 6-membered phenylene group in 4, but there are also minor conformational changes between 4 and 6 which allow the macrocycle to ‘‘breathe out” in forming 6. The lattice structure of complex 6 contains several

[PdCl2 (NCPh)2 ] + 2 AgO2 CCF3 + 2 LL LL = 3

L

L

Pd L L 7, LL = 3

LL = 1 or 2 3+

L

2+ L 0.5

Pd L Cl L

L

L Pd L 8, LL = 1 9 , LL = 2

Scheme 2. Synthesis of complexes 7–9.

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L

4

N.L.S. Yue et al. / Polyhedron xxx (2015) xxx–xxx

Fig. 4. Structure of the dicationic chelate complex 7, showing 30% probability ellipsoids. Selected bond parameters: Pd–N(1) 2.025(5); Pd–N(23) 2.026(4) Å; N (1)–Pd–N(23) 84.2(2); N(1A)–Pd–N(23) 95.7(2)°. Symmetry equivalent atoms: x + 1,y + 1,z + 1.

Me N

N

O

Me N

O

N S

S

N

O N

N

O

Me

N Me

Chart 3. Approximate conformations of the ligand 3 in the chelate complex 7 (left) and the bridged complex 6 (right).

form [Pd2(l-LL)4]4+, with the ligands LL = 1 or 2 (Chart 2) in 8 and 9 respectively. The cations have no crystallographically imposed symmetry but there is an approximate C4 axis in each case. The amide groups retain the syn conformation, and the central m-phenylene groups are oriented similarly (Fig. 5). The non-bonding separation Pd


Pd = 6.56 and 6.39 Å in 8 and 9, and there is an encapsulated chloride ion in each case, with secondary bonding interactions Pd


Cl = 3.28 Å in 8 and 3.20 Å in 9. There are also several weak NCH


Cl hydrogen bond interactions, involving inwardly directed pyridyl hydrogen atoms, in both 8 and 9, and the cavities in these complexes appear particularly well suited to act as a host for the chloride guest. The ESI mass spectrum of 8, obtained from a dilution solution in a mixture of dmf and methanol, contained envelopes of peaks at m/z = 1857, 1511 and 1165, corresponding to [Pd2Cl(LL)4(O2CCF3)2]+, [Pd2Cl(LL)3(O2CCF3)2]+, and [Pd2Cl(LL)2(O2CCF3)2]+, indicating that the chloride remains bound even while some of the bis(pyridine) ligands are lost.

Fig. 5. Structures of the lantern complexes 8 and 9, showing 30% probability ellipsoids. Selected bond parameters: above, 8; Pd(1)–N(21) 2.003(8); Pd(1)–N(41) 2.029(8); Pd(1)–N(11) 2.033(8); Pd(1)–N(31) 2.038(8); Pd(2)–N(61) 2.024(9); Pd (2)–N(71) 2.027(9); Pd(2)–N(81) 2.033(9); Pd(2)–N(51) 2.034(8) Å; N(21)–Pd(1)–N (41) 174.7(3); N(11)–Pd(1)–N(31) 179.1(3); N(61)–Pd(2)–N(81) 175.4(3); N(71)–Pd (2)–N(51) 179.3(3)°. Below, 9; Pd–N(41) 2.023(4); Pd–N(21) 2.033(4); Pd–N(11) 2.034(4); Pd–N(31) 2.036(4) Å; N(41)–Pd–N(21) 175.70(15); N(11)–Pd–N(31) 177.65(15)°.

3. Computations and conclusions DFT calculations were carried out for the complexes of ligands 1 and 3 (Chart 2) in order to gain some insight into the ligand preference for bridging versus chelation. The calculated structures for the unknown mononuclear complexes [PdCl2(LL)], D and E, and the known binuclear isomers [Pd2Cl4(LL)2], 4 and 6, with LL = 1 or 3, are shown in Fig. 6. The calculation reproduces the conformations of the complexes in the structurally characterized complexes 4 and 6, and gives a reasonable prediction of the Pd


Pd separation in complex 6 (7.17 Å, without the guest dichloromethane, versus the experimental value of 6.96 Å, with the dichloromethane, Fig. 3). For complex 4 the calculated structure (Fig. 6) has Pd


Pd = 3.77 Å compared to the experimental value of 3.63 Å (Table 1). However, the calculations predict another minimum with similar energy for a structure of 4 that is similar to 6, with Pd


Pd = 7.48 Å. In both cases, the dimer (4 or 6) is calculated to

be significantly more stable and so it is unlikely that D or E could be prepared. No doubt, the general preference for the trans stereochemistry for complexes [PdCl2L2], as well as differences in angle strain of the ligands when chelating or bridging, contribute to the greater stability of the dimer form. Similar calculations were carried out for the bis(chelate), [Pd (LL)2]2+, 7 and F, and lantern complexes [Pd2(l-Cl)(l-LL)4]3+, I and 8, (Fig. 7). In this case it is also possible to calculate structures of the unknown empty lantern complexes [Pd2(l-LL)4]4+, G and H. The calculated non-bonding Pd


Pd distances were 7.51 and 8.05 Å for G and H but 7.13 and 7.01 Å for I and 8. The experimental value for 8 was 6.56 Å. Evidently the encapsulated chloride ion provides an attractive force for the mutually repulsive Pd2+ centers. The charge on the chloride in I and 8 was calculated to be 0.82e in each case, so the Pd


Cl attraction appears to be mostly ionic in nature. The relative energies are not easily compared due to

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the bridged compounds can accommodate a range of transannular distances in either macrocyclic or lantern complexes. However they achieve this end in somewhat different ways. The thiophen derived ligand has a greater tendency to lie closer to coplanarity with the amide units and the bite distances is adjusted by rotation of the 5-membered thiophen group (Chart 3), whereas the phenylene group in 1 and 2 twists out of the plane of the amide groups to different degrees to achieve a similar outcome. The ability of the ligands 1–3 to change conformations to create cavities of different size and shape in the macrocyclic complexes is likely to be useful in host–guest chemistry, and the approach complements the use of more rigid bridging ligands to create cavities of fixed size and shape [1–7,20–25].

4. Experimental section

Fig. 6. Calculated structures of monomeric and dimeric isomers of complexes [{PdCl2(LL)}n], n = 1 or 2. Mean bond parameters: E, Pd–N 2.12, Pd–Cl 2.28 Å, N–Pd– N 85, Cl–Pd–Cl 85, C–N–C 124, NCC 120, C–C@C 122°; 6, Pd–N 2.11 (2.02), Pd–Cl 2.48 (2.30) Å, N–Pd–Cl 90 (91), (O)C–N–C 124 (124), (Me)NCC 118 (119), (O)C–C@C 129 (132)°. Values in parenthesis are mean experimental values.

Fig. 7. Calculated structures for known complexes 7 and 8 and unknown ones F–I. The complexes 7, G and I have LL = 3, while F, H and 8 have LL = 1. Only 7 and 8 are structurally characterized.

differences in charges, and hence differences in ionic attractions to anions. However, with this proviso, the calculated energies of conversion of the bis(chelate) complexes 7 and F to the empty lantern complexes G and H are +567 and +480 kJ mol1 and, with added chloride, to give I or 8 462 and 571 kJ mol1, respectively. The differences are modest and it is not obvious why the bis(chelate) 7 is preferred with ligand 3 but the lantern complex 8 with ligand 1. However, it can be predicted that the empty lantern complexes G and H are unfavourable, consistent with experiment. In conclusion, the ligands 1–3 can each adjust their bite distance to accommodate chelation or bridging coordination, and

The ligands 1–3 were prepared as described in the literature [12–14]. 1H NMR spectra were recorded using a Varian Mercury 400 spectrometer. Terminal pyridyl group protons are labeled normally, while other aromatic protons are labeled with an additional prime sign. ESI mass spectra were recorded using a Micromass LCT spectrometer and were calibrated with NaI at concentration 2 lg/ ll in 50:50 propan-2-ol: water. DFT calculations were carried out by using the Amsterdam Density Functional program based on the BP functional, with double-zeta basis set and first-order scalar relativistic corrections [26]. Calculations are gas phase, and energy minima were confirmed by vibrational analysis. [Pd2Cl4(l-1)2], 4. To a solution of [PdCl2(NCPh)2] (0.050 g, 0.130 mmol) in CH2Cl2 (10 mL) was added a solution of ligand 1 (0.045 g, 0.13 mmol) in CH2Cl2 (10 mL). The solution was stirred for 2 h., then pentane (40 mL) was added to precipitate the product as a yellow solid, which was collected by filtration, washed with diethyl ether and dried under vacuum. Yield: 58%. NMR in 0 0 CD2Cl2: d(1H) = 8.88 [m, 8H, H2,6]; 7.52 [m, 4H, H4 ,6 ]; 7.41 [m, 0 0 2H, H5 ]; 7.15 [m, 2H, H2 ]; 6.89 [m, 8H, H3,5]; 3.43 [s, 12H, Me]. Anal. Calc. for C40H36Cl4N8O4Pd2: C, 45.87; H, 3.46; N, 10.70. Found: C, 45.99; H, 3.86; N, 10.56%. ESI-MS: m/z = 1009, [MCl]+. An orange crystal of 4, as a CH2Cl2 solvate, was obtained from CH2Cl2/acetone. [Pd2Cl4(l-2)2], 5. To a solution of [PdCl2(NCPh)2] (0.040 g, 0.10 mmol) in CH2Cl2 (10 mL) was added a solution of the ligand 2 (0.042 g, 0.10 mmol) in CH2Cl2 (10 mL). The solution was stirred overnight, the volume was reduced to 10 mL and pentane (20 mL) was added to precipitate the product as a yellow solid, which was washed with hexane (10 mL) and dried under vacuum. Yield: 32%. 0 0 NMR in CD2Cl2: d(1H) = 8.87 [m, 8H, H2,6]; 7.32 [m, 4H, H4 ,6 ]; 7.15 20 3,5 [m, 2H, H ]; 6.71 [m, 8H, H ]; 3.46 [s, 12H, Me]; 1.10 [s, 18H, t-Bu]. Anal. Calc. for C48H52Cl4N8O4Pd2: C, 49.72; H, 4.52; N, 9.66. Found: C, 49.99; H, 4.82; N, 9.55%. ESI-MS: m/z = 1121, [MCl]+. Dark, yellow prisms of 5, as the CH2Cl2 solvate, were obtained from CH2Cl2/acetone. [Pd2Cl4(l-3)2], 6. To a solution of [PdCl2(NCPh)2] (0.054 g, 0.14 mmol) in CH2Cl2 (10 mL) was added a solution of the ligand 3 (0.050 g, 0.14 mmol) in CH2Cl2 (10 mL). The solution was stirred overnight and pentane (40 mL) was added to precipitate the product as a yellow solid, which was collected by filtration, washed with pentane and acetone, then dried under vacuum. Yield: 47%. NMR in dmf-d7: d(1H) = 8.94 [d, 8H, H2,6]; 7.38 [d, 8H, H3,5]; 7.04 0 0 [s, 4H, H3 ,4 ]; 3.49 [s, 12H, Me]. Anal. Calc. for C36H32Cl4N8O4Pd2S2: C, 40.81; H, 3.04; N, 10.58. Found: C, 40.55; H, 2.98; N, 10.27%. ESI-MS: m/z = 1021, [MCl]+. Yellow, needle crystals were grown from CH2Cl2/PhCN. [Pd(3)2](CF3CO2)2, 7. To a solution of [PdCl2(NCPh)2] (0.109 g, 0.28 mmol) in CH2Cl2 (5 mL) was added a solution of silver trifluoroacetate (0.125 g, 0.56 mmol) in acetone (5 mL). The mixture was

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stirred for 1 h., then filtered to remove AgCl, and the filtrate was added to a solution of the ligand 3 (0.20 g, 0.57 mmol) in CH2Cl2 (5 mL). The mixture was stirred overnight, then the volume of solvent was reduced and pentane (20 mL) was added to precipitate the product as a pale yellow solid, which was collected by filtration and washed with pentane. Yield: 62%. NMR in dmf-d7: d(1H) = 8.94 0 0 [d, 8H, H2,6]; 7.38 [d, 8H, H3,5]; 7.05 [s, 4H, H3 ,4 ]; 3.49 [s, 12H, Me]. Anal. Calc. for C40H32F6N8O8PdS2: C, 46.32; H, 3.11; N, 10.80. ESIMS: m/z = 923, [M-TFA]+. Found: C, 46.06; H, 2.62; N, 10.34%. Colourless plate crystals were grown from CH2Cl2/thf. [Pd2(l-1)4(l-Cl)]Cl0.5(CF3CO2)2.5, 8. To a solution of [PdCl2(NCPh)2] (0.050 g, 0.13 mmol) in PhCN (5 mL) was added a solution of silver trifluoroacetate (0.058 g, 0.26 mmol) in PhCN (5 mL). The mixture was stirred for 1 h., then filtered to remove AgCl, and the filtrate was added to a solution of ligand 1 (0.090 g, 0.261 mmol) in CH2Cl2 (5 mL). The solution was stirred for 2 h., then pentane/diethyl ether mixture (1:1, 30 mL) was added to precipitate the product as a pale yellow solid, which was collected by filtration, washed with ether and dried under vacuum. Yield: 48%. 0 0 NMR in CDCl3/CD3OD: d(1H) = 7.8 [br, m, 8H, H4 ,6 ]; 7.2–7.4 [br, m, 2,6 3,5 20 50 40H, H , H , H ,H ]; 3.3 [br, s, 24H, Me]. Anal. Calc. for C85H72Cl1.5F7.5N16O13Pd2: C, 52.79; H, 3.75; N, 11.59. Found: C, 52.33; H, 3.67; N, 11.09%. ESI-MS: m/z = 1857, [MCl0.5TFA0.5]+. Orange block crystals were grown from PhCN/dmf. [Pd2(l-2)4(l-Cl)]Cl(CF3CO2)2, 9. To a solution of [PdCl2(NCPh)2] (0.040 g, 0.10 mmol) in CH2Cl2 (10 mL) was added a solution of silver trifluoroacetate (0.046 g, 0.21 mmol) in PhCN (10 mL). The mixture was stirred for 2 h., filtered to remove AgCl, then added to a solution of the ligand 2 (0.084 g, 0.21 mmol) in CH2Cl2 (10 mL). The mixture was stirred overnight, the volume of solvent was reduced and hexane (20 mL) was added to precipitate the product as a yellow solid. Yield: 41%. NMR in CDCl3/CD3OD: d(1H) 0 0 = 7.77 [m, 8H, H4 ,6 ]; 7.55 [m, 16H, H2,6]; 7.39 [m, 16H, H3,5]; 20 7.36 [s, 4H, H ]; 3.32 [s, 24H, Me]; 1.32 [s, 36H, t-Bu]. Anal. Calc. for C100H104Cl2F6N16O12Pd2: C, 56.66; H, 4.95; N, 10.57. Found: C, 56.18; H, 4.87; N, 10.09%. ESI-MS: m/z = 2081, [MCl]+. Pale yellow plate crystals were obtained from CH2Cl2/PhCN/acetone.

crystallographically independent molecules of the complex present in the asymmetric unit. Soft geometric restraints were applied to the pyridyl rings. The solvent CH2Cl2 molecules exhibited disorder, and the C–Cl distances were fixed. One of the partial occupancy solvent molecules was disordered and modeled as a 25:25 isotropic mixture. Only the palladium and chlorine atoms of the two molecules of the complex and the chlorine atoms of the full occupancy solvent molecules were refined with anisotropic thermal parameters. A search for higher symmetry using PLATON suggested the orthorhombic space group Pnma, but attempts to refine the structure in either space group Pnma or Pna21 were unsuccessful, resulting in significantly higher R indices at convergence. Complex 5
2CH2Cl2. One of the solvent molecules was modeled as a 75:25 mixture of isotropic atoms, and the C–Cl distances were fixed. Complex 6
3CH2Cl2
1.5PhCN. One of the benzonitrile molecules was located near a symmetry element so it was modeled isotropically at half-occupancy. Complex 7
2H2O. The cation resided on a center of symmetry. The trifluoroacetate anion was very disordered and was modeled isotropically as a mixture of three parts (23:25:52) with fixed bond distances. The water of solvation was modeled complete with hydrogen atoms which were fixed at 0.84 Å. Complex 8
0.5dmf. The cation, chloride anions and one of the trifluoroacetate anions were well defined, but the other trifluoroacetate anions and dmf solvate molecule were disordered and were refined at ½ occupancy with fixed geometry. Only the palladium and chlorine atoms were refined with anisotropic thermal parameters. Complex 9
2CH2Cl2. The cation resided on a center of symmetry. One chloride anion, one trifluoroacetate anion and the CH2Cl2 solvate were well defined, but the other anions and some additional solvent were disordered and the associated electron density was accounted for by using SQUEEZE. Acknowledgments We thank the NSERC (Canada) for financial support.

5. X-ray structure determinations Data were collected using a Nonius Kappa-CCD area detector diffractometer with COLLECT (Nonius B.V., 1997–2002). The unit cell parameters were calculated and refined from the full data set. Crystal cell refinement and data reduction were carried out using HKL2000 DENZO-SMN (Otwinowski & Minor, 1997). The absorption corrections were applied using HKL2000 DENZO-SMN (SCALEPACK). The SHELXTL/PC V6.14 for Windows NT (Sheldrick, G.M., 2001) suite of programs was used to solve the structures by direct methods. The hydrogen atom positions were calculated geometrically and were included as riding on their respective carbon atoms. The non-hydrogen atoms, except as noted, were refined with anisotropic displacement parameters. The presence of large chelate or macrocyclic units led to formation of weakly diffracting crystals in many cases, with complications arising from the presence of large voids containing disordered solvent and/or anions. The essential connectivities are well-established but the precision is low in these examples. Details and unusual features are described below and in the cif files (CCDC 840460, 840463, 840464, 840467, 840468, 1407465, 1407466). Ligand 1. One of the methyl groups was disordered and was modeled as 0.5/0.5 occupancy. One of the carbonyl groups was disordered and was modeled at occupancies of 0.74/0.26. Complex (4)2
5.9CH2Cl2. The crystals of the complex formed as pseudo-orthorhombic merohedral twins. The twin law (1 0 0, 0–1 0, 0 0–1) was applied in the final refinement stages. There are two

Appendix A. Supplementary data CCDC 840460, 840463, 840464, 840467, 840468, 1407465, 1407466 contain the supplementary crystallographic data for the complexes. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

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