Cyclopalladated compounds derived from a [C,N,S] terdentate ligand: synthesis, characterization and reactivity. Crystal and molecular structures of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)] and [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe]}₂{μ-Ph₂P(CH₂)₄PPh₂}][CF₃SO₃]₂

Abstract

Treatment of the Schiff base 2-ClC₆H₄C(H)[double bond, length half m-dash]NCH₂CH₂SMe, 1, with palladium(II) acetate in dry toluene gave the mononuclear cyclometallated complex [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(O₂CMe)], 2. Reaction of 2 with aqueous sodium chloride gave [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)], 3, after a metathesis reaction. The X-ray crystal structure of 3 was determined and shows that the palladium atom is bonded to four different donor atoms: C, N, S and Cl. Treatment of 3 with triphenylphosphine in acetone gave the mononuclear cyclometallated complex [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)(PPh₃)] with cleavage of the Pd–S bond. However, treatment of 3 with silver triflate and triphenylphosphine gave [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(PPh₃)][CF₃SO₃], 10, in which the Pd–S bond is retained. Reaction of 3 with the diphosphines dppm, dppb or dppf in a 2 : 1 molar ratio gave the dinuclear cyclometallated complexes [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe](Cl)}₂{μ-Ph₂P(CH₂)_nPPh₂}], (n = 1, 5; n = 4, 6), and [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe](Cl)}₂(μ-Ph₂PC₅H₄FeC₅H₄PPh₂)], 7. Treatment of 3 with dppb in a 2 : 1 molar ratio and AgCF₃SO₃ gave the dinuclear cyclometallated complex [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe]}₂{μ-Ph₂P(CH₂)₄PPh₂}][CF₃SO₃]₂, 11, which was characterized by X-ray crystal structure analysis. Reaction of 3 with dppe in a 1 : 1 molar ratio and sodium perchlorate gave the mononuclear complex [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}{Ph₂P(CH₂)₂PPh₂-P,P}][ClO₄], 8. Treatment of 3 with bis(2-diphenylphosphinoethyl)phenylphosphine in a 1 : 1 molar ratio, followed by treatment with sodium perchlorate gave [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}{(Ph₂PCH₂CH₂)₂PPh-P,P,P}][ClO₄], 9, in which the triphosphine is bonded to the palladium atom through the three phosphorus atoms.

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Introduction

The study of cyclometallated compounds has attracted much attention over the last three decades.^1–5 They have numerous applications in organic and organometallic synthesis,⁶ insertion reactions,⁷ the synthesis of new metal mesogenic compounds⁸ and biologically active compounds^9,10 and as catalytic materials.¹¹ By far the most widely studied examples of cyclometallated complexes are five-membered palladacycles with nitrogen donor atoms. Among these, cyclometallated complexes derived from potentially terdentate [C,N,N] and [C,N,S] ligands have been described.^12–23 In previous work, we have shown that potentially terdentate ligands, such as Schiff bases I,^24–27 semicarbazones II^28,29 and thiosemicarbazones III,^30,31 undergo facile metallation with palladium(II), palladium(0) and platinum(II) to give compounds with two five-membered fused rings at the metal centre. The Schiff base and semicarbazone derivatives are monomeric species but the complexes derived from thiosemicarbazones present a tetranuclear structure.

As part of our studies on the synthesis and reactivity of cyclometallated complexes derived from multidentate ligands, we synthesized the potentially [C,N,S] Schiff base 2-ClC₆H₄C(H)[double bond, length half m-dash]NCH₂CH₂SMe, 1, where metallation may occur by activation of a C–H bond or by oxidative addition across the C–Cl bond, in order to study its reactivity and also the behavior of the subsequent metal compounds derived from 1. Therefore, in the present work, we report the reaction of 1 with the metallating reagents Pd(AcO)₂, [Pd₂(dba)₃] (dba = dibenzylideneacetone) and Li₂[PdCl₄]. In the resulting complexes, the ligand behaves as [C, N, S] terdentate yielding the monomeric species 2 and 3, in contrast with the tetrameric structure observed for the [C,N,S] thiosemicarbazone cyclometallated derivatives. Moreover, the reactivity of 3 with tertiary phosphines such as triphenylphosphine, bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,4-bis(diphenylphosphino)butane (dppb), 1,1′-bis(diphenylphosphino)ferrocene (dppf) and the triphosphine bis(2-diphenylphosphinoethyl)phenylphosphine (triphos), may be regulated to give compounds where the Pd–S bond may be retained or cleaved, which is achieved by the use of a chloride removing agent, usually a silver(I) salt, in the reaction media. In the former case, the coordination vacancy is occupied by the phosphine, and in the latter, opening of the coordination ring occurs. Such a reactivity pattern differs from that observed for the related thiosemicarbazones.

Results and discussion

For the convenience of the reader, the compounds and reactions are shown in Schemes 1 and 2. The compounds described in this paper were characterised by elemental analysis (C, H, N), IR spectroscopy (data in the Experimental section), ¹H, ³¹P-{¹H} (see Table 1) and, in part, ¹³C-{¹H} NMR spectroscopy, and FAB mass spectrometry (see Experimental section).

Scheme 1 (i) Pd(AcO)₂, (toluene); (ii) NaCl (acetone–water); (iii) PPh₃ (acetone); (iv) dppm, dppb or dppf (acetone, 2 : 1 molar ratio); (v) AgCF₃SO₃, PPh₃ (acetone); (vi) AgCF₃SO₃, dppb (acetone, 2 : 1 molar ratio); (vii) AgCF₃SO₃ (acetone).

Scheme 2 (i) dppe, NaClO₄ (acetone–water, 1 : 1 molar ratio); (ii) triphos, NaClO₄ (acetone, 1 : 1 molar ratio).

Table 1 ³¹P-{¹H}^a and ¹H NMR^bcd data

	^31P	Aromatic	Others
a In CDCl3. Measured at 80.9 MHz (ca.±20 °C); chemical shifts (δ) in ppm (±0.1) to high frequency of 85% H3PO4. b In CDCl3. Measured at 200 MHz (ca.±20 °C); chemical shifts (δ) in ppm (±0.01) to high frequency of SiMe4. c Coupling constants in Hz. d s, singlet; d, doublet; dd, doublet of doublets; t, triplet; dt, doublet of triplets; q, quadruplet; m, multiplet; br, broad. e ^4 J(HH). f ^3 J(HH). g HC = NCH2. h N values. i CH2SMe. j δ(PCH2P) = 4.70t. k J(PH). l δ(CH^Ferrocene) = 5.06 [br, 2H], 4.50 [br, 2H] m J(PP).
1		7.70 [m, 3H, H^3, H^4, H^5]	8.73 [t, 1H, Hi 1.5^e]
		8.02[dd, 1H, H^6 6.9^f, 2.3^e]	3.88 [2H, (CH2)^g 13.6^h]
			2.85 [2H, (CH2)^i]
			2.16 [s, 3H, Me]
2		7.25 [d, 1H, H^5 7.8^f]	8.34 [s, 1H, Hi]
		7.15 [t, 1H, H^4 7.8^f, 7.8^f]	3.94 [2H, (CH2)^g 12.2^h]
		7.00 [dd, 1H, H^3 7.8^f 1.0^e]	2.94 [2H, (CH2)^i]
			2.64 [s, 3H, Me]
			2.11 [s, 3H, OC(Me)O]
3		7.64 [dd, 1H, H^5 7.8^f, 1.0^e]	8.23 [t, 1H, Hi 1.7^e]
		7.11 [t, 1H, H^4 7.8^f]	4.02 [2H, (CH2)^g 12.2^h]
		6.96 [dd, 1H, H^3 7.8^f, 1.0^e]	3.11 [2H, (CH2)^i]
			2.57 [s, 3H, Me]
4	42.3s	6.87 [d, 1H, H^3 7.8^f]	8.64 [s, 1H, Hi]
		6.49 [t, 1H, H^4 7.8^f]	4.19 [2H, (CH2)^g 13.2^h]
		6.28 [d, 1H, H^5 7.8^f]	3.10 [2H, (CH2)^i]
			2.18 [s, 3H, Me]
5 ^i	30.1s	6.79 [d, 1H, H^3 7.6^f]	8.44 [s, 1H, Hi]
		6.43 [t, 1H, H^4 7.6^f]	4.05 [2H, (CH2)^g]
		5.90 [m, 1H, H^5]	3.04 [2H, (CH2)^i 11.2^h]
			2.19 [s, 3H, Me]
6	34.0s	6.83 [d, 1H, H^3 7.8^f]	8.49 [d, 1H, Hi 7.8^k]
		6.42 [t, 1H, H^4 7.8^f]	4.12 [2H, (CH2)^g]
		6.27 [dd, 1H, H^5 7.8^f, 5.4^k]	3.08 [2H, (CH2)^i 12.6^h]
			2.20 [s, 3H, Me]
7 ^j	31.1s	6.88 [d, 1H, H^3 7.3^f]	8.57 [br, 1H, Hi]
		6.51 [br, 1H, H^4]	4.16 [2H, (CH2)^g]
		6.21 [m, 1H, H^5]	3.07 [2H, (CH2)^i]
			2.17 [s, 3H, Me]
8	62.5 [d, 27.1^m]	6.99 [d, 1H, H^3 7.8^f]	8.69 [d, 1H, Hi 6.8^k]
	44.6d	6.73 [dt, 1H, H^4 7.8^f, 3.0^k]	3.51 [2H, (CH2)^g]
		6.55 [q, 1H, H^5 7.8^f, 7.8^k]	2.65 [2H, (CH2)^i]
			1.89 [s, 3H, Me]
9	90.1 [t, 26.3^m]	6.86 [d, 1H, H^3 7.8^f]	8.35 [s, 1H, Hi]
	45.4d	6.38 [dt, 1H, H^4 7.8^f, 2.3^k]	3.27 [2H, (CH2)^g 13.6^h]
		6.84 [t, 1H, H^5 7.8^f, 7.8^k]	2.69 [2H, (CH2)^i]
			1.85 [s, 3H, Me]
10	37.8s	6.95 [dd, 1H, H^3 7.8^f, 1.0^e]	8.76 [s, 1H, Hi]
		6.63 [t, 1H, H^4 7.8^f]	4.40 [2H, (CH2)^g 12.6^h]
		6.28 [dd, 1H, H^5 7.8^f, 1.0^e]	3.22 [2H, (CH2)^i]
			1.81 [s, 3H, Me]
11	32.5s	6.95 [d, 1H, H^3 7.8^f]	8.49 [d, 1H, Hi 7.8^k]
		6.74 [t, 1H, H^4 7.8^f]	4.24 [2H, (CH2)^g 12.6^h]
		6.40 [dd, 1H, H^5 7.8^f, 5.5^k]	3.23 [2H, (CH2)^i]
			1.98 [s, 3H, Me]

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Treatment of the Schiff base 2-ClC₆H₄C(H)[double bond, length half m-dash]NCH₂CH₂SMe, 1, with palladium(II) acetate in dry toluene gave the mononuclear cyclometallated complex [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(O₂CMe)], 2, in 21% yield, which was fully characterized. The ¹H NMR spectrum shows a singlet resonance at δ 7.93, assigned to the HC[double bond, length half m-dash]N proton, shifted to lower frequency due to coordination of the imine group to the palladium atom via the lone pair of the nitrogen atom.³² Coordination of the palladium atom to the C[double bond, length half m-dash]N moiety is confirmed by the shift to lower wavenumbers of the ν(C[double bond, length half m-dash]N) band in the IR spectrum (1635s, 1, 1613sh s cm⁻¹, 2).^33,34 The C[double bond, length half m-dash]N–CH₂CH₂–SMe resonances appear as well-defined virtual triplets at δ 3.94 and 2.94, respectively (N = 13.6 Hz). A singlet at δ 2.64 was assigned to the SMe protons. This signal is shifted to higher frequency from its value in the free ligand due to coordination of the sulfur atom. The ¹³C-{¹H} spectrum shows resonances at δ 172.4 (C[double bond, length half m-dash]N), 161.4 (C6) and 145.6 (C1) shifted to higher frequency from the free ligand values, thus confirming formation of the cyclometallated ring.^24,35 The signal at 18.1, assigned to the SMe group, is also shifted to higher frequency upon coordination of the sulfur atom. The FAB mass spectrum of the complex shows peaks assigned to [M − O₂CMe]⁺ and [2M+O₂CMe]⁺, both with chemically reasonable isotopic patterns. These data suggest the formulation [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe]}₂(μ-O₂CMe)]⁺[O₂CMe]⁻ for complex 2. However, the low conductivity shown by the complex in acetonitrile solution precludes an ionic formulation. Consequently, the signal assignable to [2M+O₂CMe] can be explained by the dimerization produced in the ionization chamber, as has been described for related cyclometallated complexes.²⁷ In order to improve the poor yield of the metallation reaction of 1 we attempted oxidative addition reactions with Pd(0) compounds, but with little or no success. For instance, treatment of 1 with [Pd₂(dba)₃] in dry toluene gave a large residue of metallic palladium as a black powder, and similarly, reaction of 1 with Li₂[PdCl₄] in methanol did not yield the expected cyclometallated complex.

Reaction of 2 with aqueous sodium chloride gave [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)], 3, as a pure air-stable solid which was fully characterized (see Table 1 and Experimental section). The ¹H NMR spectrum of the complex shows a singlet resonance at δ 2.57 assigned to the SMe protons (shifted to higher frequency by 0.41 ppm as compared with the free ligand) and the ¹³C-{¹H} spectrum shows a signal assigned to the SMe methyl carbon at δ 18.4 (also shifted to higher frequency), showing coordination of the sulfur atom to palladium. This was confirmed by the determination of the molecular structure of complex 3 by X-ray single crystal diffraction. Treatment of 3 with triphenylphosphine in acetone gave the mononuclear cyclometallated complex [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)(PPh₃)], 4, which was fully characterized (see Experimental section and Table 1). The low conductivity value observed for complex 4 precludes the alternative formulation as a 1 : 1 electrolyte [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(PPh₃)]Cl, after displacement of the chloride ligand rather than the thioether from the palladium coordination sphere. Furthermore, the SMe resonance in the ¹H NMR spectrum appears at δ 2.18 (2.16 for 1) and at 15.9 (16 for 1) in the ¹³C NMR spectrum, suggesting the SMe group is not coordinated to the palladium atom as in the complexes 10 and 11 (vide infra), in which cases δ values under 2 (¹H NMR) and 16 (¹³C NMR) would be expected for complex 4. Also, the IR spectrum of 4 shows a band assigned to the ν(Pd–Cl) stretch, at 306 m cm⁻¹, which was absent in the IR spectra of compounds 10 and 11. The ³¹P-{¹H} spectrum of 4 shows a singlet resonance at δ 42.3, in accordance with coordination of the phosphine ligand trans to the nitrogen atom.

Reaction of 3 with the diphosphines dppm, dppb and dppf in a 2 : 1 molar ratio the dinuclear gave the cyclometallated complexes [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe](Cl)}₂{μ-Ph₂P(CH₂)_nPPh₂}], (n = 1, 5; n = 4, 6) and [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe](Cl)}₂(μ-Ph₂PC₅H₄FeC₅H₄PPh₂)], 7, respectively (see Experimental section and Table 1). The ¹H (and ¹³C-{¹H} NMR in the case of compound 6) data are in agreement with Pd–S bond cleavage. The ³¹P-{¹H} NMR spectra show a singlet resonance, indicating the compounds to be centrosymmetric. Reaction of 3 with AgCF₃SO₃ followed by PPh₃ (1 : 1 molar ratio) or by Ph₂P(CH₂)₄PPh₂ (2 : 1 molar ratio), gave the mono- and dinuclear species [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(PPh₃)][CF₃SO₃], 10, and [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂-SMe]}₂{μ-Ph₂P(CH₂)₄PPh₂}][CF₃SO₃]₂, 11, respectively, after halide extraction. The IR spectra support the presence of the [CF₃SO₃]⁻ anion, showing the characteristic stretching bands of the free anion,³⁶ca. 1271, 1228, 1157 and 1028 cm⁻¹. The ¹H spectra of the complexes show singlet signals for the SMe protons at δ 1.81 and 1.98, we suggest these low values are due to shielding of the phosphine phenyl rings.²⁴ Nevertheless, the resonance at δ 22.7 in the ¹³C-{¹H} NMR spectrum of 11 is in agreement with coordination of the sulfur atom to palladium. Complexes 10 and 11 can also be prepared by treatment of 4 and 6, respectively, with silver triflate.

Treatment of 3 with dppe in a 1 : 1 molar ratio and sodium perchlorate gave the mononuclear cyclometallated complex [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}{Ph₂P(CH₂)₂PPh₂-,P,P}][ClO₄], 8 (see Experimental section and Table 1). The ³¹P-{¹H} NMR spectrum shows two doublets [J(PP) = 27.1 Hz], the resonance at lower frequency was assigned to the phosphorus nucleus trans to the phenyl carbon atom in accordance with the higher trans influence of the latter with respect to the C[double bond, length half m-dash]N nitrogen atom.³⁷ The HC[double bond, length half m-dash]N resonance in the ¹H NMR spectrum is only coupled to the ³¹P nucleus trans to nitrogen and the H5 resonance is coupled to both phosphorus nuclei. The SMe resonance is shifted to lower frequency as a consequence of Pd–S bond cleavage. Reaction of 3 with the tertiary triphosphine bis(2-diphenylphosphinoethyl)phenylphosphine in a 1 : 1 molar ratio, followed by treatment with sodium perchlorate gave [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}{(Ph₂PCH₂CH₂)₂PPh-P,P,P}][ClO₄], 9. The phosphorus resonances in the ³¹P-{¹H} NMR spectrum of the complex are downfield shifted from their values in the free phosphine, suggesting coordination of the three phosphorus atoms to the metal centre. A triplet resonance at δ 62.5 was assigned to the central ³¹P nucleus, trans to the phenyl carbon atom, and a doublet signal at δ 45.4 was assigned to the two equivalent mutually trans phosphorus nuclei. The latter signal appears at lower frequency, in accordance with the high trans influence of the phosphine ligand.³⁷ The resonance of the proton in the ortho position to the metallated carbon appears as a triplet showing coupling to the central ³¹P atom [J(PH) = 7.8 Hz]; no coupling was observed to the terminal phosphorus nuclei. The shift of the ν(C[double bond, length half m-dash]N) stretching vibration to lower wavenumbers,^33,34 as well as the upfield shift of the HC[double bond, length half m-dash]N proton resonance in the ¹H NMR spectrum,³² indicates the existence of palladium–nitrogen interaction in solution. In agreement with the results previously obtained by us for related species in solution and in the solid state,^26,38 these data strongly agree with a penta-coordinate palladium(II) compound in which the metallated ring is nearly perpendicular to the plane defined by the three phosphorus atoms, and point towards a square-pyramidal geometry in solution. These observations were confirmed by selective decoupling experiments (see Scheme 2). Recently, the chemistry of the related ligand C₆H₅C(H)[double bond, length half m-dash]NCH₂CH₂SEt, bearing no chlorine atom, has been reported and two compounds similar to 3 and 4 have been described. It should be noted that direct metallation of this Schiff base with Na₂[PdCl₄] and Na(CH₃COO) in methanol gave [Pd{C₆H₄C(H)[double bond, length half m-dash]NCH₂CH₂SEt}(Cl)] in good yield, as opposed to ligand 1 in the present paper, where metallation was achieved only by reaction with palladium(II) acetate.

Crystal structure of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂-CH₂SMe}(Cl)] (3)

Crystal data are given in Table 2 and selected bond distances and angles with estimated standard deviations are shown in Table 3. Suitable crystals of the title compound were grown by slowly evaporating a chloroform solution. The molecular structures, which are illustrated in Fig. 1 and 2, consist of discrete molecules separated by van der Waals distances.

Fig. 1 Molecular structure of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)] (3a), with labelling scheme. Hydrogen atoms have been omitted for clarity.

Fig. 2 Molecular structure of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)] (3b), with labelling scheme. Hydrogen atoms have been omitted for clarity.

Table 2 Crystal and structure refinement data for 3 and 11

	3	11
a R 1 = Σ‖Fo| − |Fc‖/Σ|Fo|, [F > 4σ(F)]. b wR 2 = [Σ[w(Fo^2 − Fc^2)^2/Σw(Fo^2)^2]^1/2, all data.
Formula	C10H11NCl2SPd2	C50H50N2O6F6Cl2P2S4Pd2
M r	354.56	1362.80
T/K	293(2)	173(2)
λ/Å	0.71073	0.71073
Crystal syst.	Monoclinic	Triclinic
Space group	P21/n	P1̄
a/Å	8.241(1)	10.350(1)
b/Å	15.229(1)	11.126(1)
c/Å	13.367(1)	12.780(2)
α/°		74.691(3)
β/°	90.207(1)	82.642(3)
γ/°		82.434(3)
U/Å^3	2430.6(1)	1400.7(4)
Z	4	1
μ/mm^−1	2.103	1.012
2θmax/°	56.6	56.6
Collected refl.	16 370	9629
Unique refl.	5963 (Rint = 0.04)	6726 (Rint = 0.04)
R ^a	0.0372	0.0515
wR ^b	0.0856	0.1513
max ρ/eÅ^3	0.946	0.832

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Table 3 Selected bond lengths [Å] and angles [°] for 3

3a		3b
Pd(1)–C(1)	1.999(4)	Pd(2)–C(11)	2.005(4)
Pd(1)–N(1)	1.989(3)	Pd(2)–N(2)	1.985(3)
Pd(1)–S(1)	2.413(1)	Pd(2)–S(2)	2.422(1)
Pd(1)–Cl(1)	2.314(1)	Pd(2)–Cl(3)	2.314(1)
C(1)–C(6)	1.420(5)	C(11)–C(16)	1.423(5)
C(6)–C(7)	1.447(5)	C(16)–C(17)	1.450(5)
C(7)–N(1)	1.276(5)	C(17)–N(2)	1.279(4)
Cl(2)–C(5)	1.750(4)	Cl(4)–C(15)	1.747(4)
C(1)–Pd(1)–N(1)	80.78(14)	C(11)–Pd(2)–N(2)	81.45(14)
C(1)–Pd(1)–Cl(1)	96.66(11)	C(11)–Pd(2)–Cl(3)	96.69(11)
C(1)–Pd(1)–S(1)	165.10(11)	C(11)–Pd(2)–S(2)	165.94(11)
N(1)–Pd(1)–Cl(1)	176.92(10)	N(2)–Pd(2)–Cl(3)	179.09(9)
N(1)–Pd(1)–S(1)	84.46(10)	N(2)–Pd(2)–S(2)	84.49(9)
Cl(1)–Pd(1)–S(1)	98.03(4)	Cl(3)–Pd(2)–S(2)	97.34(4)
Pd(1)–C(1)–C(6)	112.1(3)	Pd(2)–C(11)–C(16)	111.0(3)

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The structure of 3 comprises two molecules of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)(PPh₃)] per asymmetric unit (these are slightly different and will be labelled as 3a and 3b). In both cases, the palladium atom is bonded in a slightly distorted square-planar geometry to the carbon atom of the phenyl ring, the imine nitrogen atom, the sulfur atom and to a chlorine atom. The angles between adjacent atoms in the coordination sphere of palladium are close to the expected value of 90°, with the most noticeable distortions corresponding to the C(1)–Pd(1)–N(1) and C(11)–Pd(2)–N(2) angles of 80.78(14) and 81.45(14)° for 3a and 3b, respectively. The sum of the angles about palladium is approximately 360° in both cases. The Pd–N bond distances [1.989(3), 3a, and 1.985(3) Å, 3b], as well as the Pd–Cl bond distances [2.314(1) Å, 3a, 3b] are in accordance with previously reported values.^24,25,27,30 The Pd–C bond distances of 1.999(4), 3a, and 2.005(4) Å, 3b, are somewhat shorter than predicted from their covalent radii³⁹ but similar to values found earlier.^24,25,27 The Pd–S bond lengths of 2.413(1), 3a, and 2.422(1) Å, 3b, reflect the strong trans-influence of the metallated carbon atom.^13–16,30

The geometry around the palladium atom [Pd, C, N, S, Cl] is planar (r.m.s. = 0.0122 and 0.0371 Å for 3a and 3b, respectively; planes 1 and 2). The metallated rings [Pd(1), C(1), C(6), C(7), N(1) and Pd(2), C(11), C(16), C(17), N(2)] are also planar (r.m.s. = 0.0156 and 0.0256 Å for 3a and 3b, respectively; planes 3 and 4). Angles between planes are as follows: plane 1/plane 3 = 0.3 °; plane 2/plane 4 = 4.6 °. The two molecules of the asymmetric unit are nearly parallel (plane 1/plane 2 = 3.2 °; plane 3/plane 4 = 5.3 °). As expected, the coordination rings [Pd(1), N(1), C(8), C(9), S(1) and Pd(2), N(2), C(18), C(19), S(2)] show large deviations from planarity with C(8) [C(19) for 3b] lying above the least square plane and C(9) [C(18) for 3b] below. Recently, a structure similar to 3 has been reported⁴⁰ where the asymmetric unit consists of three molecules, in contrast to the two found in the structure of compound 3. The bond distances and bond angles show values very close to those observed in the present case.

Crystal structure of [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe]}₂(μ-Ph₂P(CH₂)₄PPh₂)][CF₃SO₃]₂  (11)

Crystal data are given in Table 2 and selected bond distances and angles with estimated standard deviations are shown in Table 4. The molecular structure is illustrated in Fig. 3. Suitable crystals of the title compound were grown by slowly evaporating a dichloromethane solution.

Fig. 3 Molecular structure of [{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe]}₂{μ-Ph₂P(CH₂)₄PPh₂}][CF₃SO₃]₂  (11), with labelling scheme. Hydrogen atoms have been omitted for clarity.

Table 4 Selected bond lengths [Å] and angles [°] for 11

Pd(1)–C(1)	2.030(6)	Pd(1)–N(1)	2.044(4)
Pd(1)–S(1)	2.399(2)	Pd(1)–P(1)	2.279(1)
C(1)–C(6)	1.424(7)	C(6)–C(7)	1.456(8)
C(7)–N(1)	1.283(7)	Cl(1)–C(5)	1.745(6)
C(1)–Pd(1)–N(1)	81.1(2)	C(1)–Pd(1)–P(1)	97.17(16)
C(1)–Pd(1)–S(1)	162.90(16)	N(1)–Pd(1)–P(1)	177.17(13)
N(1)–Pd(1)–S(1)	81.95(13)	P(1)–Pd(1)–S(1)	99.73(5)
Pd(1)–C(1)–C(6)	110.3(4)	C(1)–C(6)–C(7)	116.6(5)
C(7)–N(1)–Pd(1)	115.7(4)

---

The crystal structure comprises a centrosymmetric dinuclear cation (half the cation per asymmetric unit) and two triflate anions. Each four-coordinate palladium is bonded to the terdentate Schiff base ligand through the aryl C(1) carbon, the imine N(1) nitrogen and the sulfur atom, and to the phosphorus atom of the 1,4-bis(diphenylphosphine)butane, which bridges the two metal atoms.

The geometry around each metal atom is similar to that shown by complex 3, with each palladium atom coordinated in a slightly distorted square-planar environment [mean deviation from the Pd(1), C(1), N(1), S(1), P(1) least square plane of 0.014 Å]. The most noticeable distortions being the C(1)–Pd(1)–N(1) and N(1)–Pd(1)–S(1) angles of 81.1(2) and 81.95(13) °, respectively.

The Pd(1)–C(1) bond length [2.030(6) Å] is shorter than the expected value of 2.081.^24,25,27 The Pd(1)–N(1) bond distance [2.044(4) Å] is longer than the values found for complex 3 [1.989(3), 3a, and 1.985(3) Å, 3b], reflecting the trans influence of the P(1) phosphorus donor ligand.⁴¹ The Pd(1)–S(1) bond distance [2.399(2) Å] and the Pd(1)–P(1) length [2.279(1) Å] are within the expected range and similar to values reported for related complexes.^25,28,41 Thus, as for compound 3, the palladium atom in 11 is bonded to four different donor atoms: C, N, S and P.

The palladium coordination plane [Pd(1), C(1), N(1), S(1), P(1)] and the metallated ring [C(1), C(6), C(7), N(1), Pd(1)] are coplanar (angle between planes 5.3 °).

Experimental

General

Caution! . Perchlorate salts of metal complexes with organic ligands are potentially explosive. Only small amounts of these materials should be prepared and handled with great caution.

Solvents were purified by standard methods.⁴² Chemicals were reagent grade. The phosphines PPh₃, Ph₂PCH₂PPh₂ (dppm), Ph₂P(CH₂)₄PPh₂ (dppb), Ph₂PC₅H₄FeC₅H₄PPh₂ (dppf) and (Ph₂PCH₂CH₂)₂PPh (triphos), were purchased from Aldrich-Chemie. Microanalyses were carried out using a Carlo Erba Model 1108 elemental analyser. IR spectra were recorded from Nujol mulls or polythene discs on a Perkin-Elmer 1330 and a Mattson spectrophotometer. NMR spectra were obtained from CDCl₃ solutions, referenced to SiMe₄ (¹H, ¹³C-{¹H}) or 85% H₃PO₄ (³¹P-{¹H}) and were recorded on a Bruker AC-2005 spectrometer. All chemical shifts are reported downfield from the standards. The FAB mass spectra were recorded using a VG Quatro mass spectrometer with a Cs ion gun; 3-nitrobenzyl alcohol was used as the matrix.

Syntheses

Preparation of 2-ClC₆H₄C(H)[double bond, length half m-dash]NCH₂CH₂SMe (1). 2-chlorobenzaldehyde (1.166 g, 8.29 mmol) was added to a solution of 2-(methylthio)ethylamine (0.716 g, 7.85 mmol) in 50 cm³ of dry chloroform. The solution was heated under reflux in a Dean–Stark apparatus for 4 h. After cooling to room temperature (r.t.), the chloroform was removed to give a yellow oil. Yield 95%. IR: ν(C[double bond, length half m-dash]N) 1635s cm⁻¹. ¹³C-{¹H} NMR (50.28 MHz, CDCl₃): δ 158.6 (C[double bond, length half m-dash]N); 135.0, 133.0 (C1, C2); 131.5, 129.7, 128.3, 126.9 (C3–C6); 61.1 (N–CH₂), 34.9 (CH₂–S); 15.9 (SMe).

Preparation of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(O₂CMe)] (2). A pressure tube containing 2-ClC₆H₄C(H)[double bond, length half m-dash]NCH₂CH₂SMe (305 mg, 1.42 mmol), palladium(II) acetate (316 mg, 1.41 mmol) and 20 cm³ of dry toluene was sealed under argon. The resulting mixture was heated at 60 °C for 12 h. After cooling to r. t., the solution was filtered through Celite to remove the black palladium formed. The solvent was removed under vacuum to give a brown oil, which was chromatographed on a column packed with silica gel. Elution with dichloromethane–ethanol (7%) afforded an orange oil after solvent removal, which was recrystallized from dichloromethane–hexane to give the desired product as an orange solid. Yield 21%. Anal. found: C, 38.5; H, 3.4; N, 3.6; C₁₂H₁₄NO₂SClPd requires C, 38.1; H, 3.7; N, 3.7%. IR: ν(C[double bond, length half m-dash]N) 1613sh s; ν_as(COO) 1571s; ν_s(COO), 1328m cm⁻¹. ¹³C-{¹H} NMR (50.28 MHz, CDCl₃): δ 178.4 [OC(CH₃)O]; 172.4 (C[double bond, length half m-dash]N); 161.4 (C6); 145.6 (C1); 131.0 (C2), 132.3, 130.0, 125.5 (C3–C5); 56.5 (N–CH₂), 37.3 (CH₂–S); 23.4 (OC(CH₃)O); 18.1 (SMe). FAB-MS: m/z = 320 [M − AcO]⁺, 697 [2M+AcO]⁺.

Preparation of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)] (3). An aqueous solution of NaCl (ca. 10⁻² M) was added dropwise to a solution of 2 (218 mg, 0.29 mmol) in 15 cm³ of acetone. The resulting mixture was stirred for 24 h. The yellow precipitate formed was filtered off, washed with water, dried under vacuum and recrystallized from dichloromethane–hexane to give complex 3 as a yellow crystalline solid. Yield 98%. Anal. found: C, 38.7; H, 3.1; N, 4.0; C₁₀H₁₁NSCl₂Pd requires C, 38.9; H, 3.1; N, 3.9%) IR: ν(C[double bond, length half m-dash]N), 1612s cm⁻¹. ¹³C-{¹H} NMR (50.28 MHz, CDCl₃): δ 172.4 (C[double bond, length half m-dash]N); 162.1 (C6); 146.3 (C1); 131.1 (C2), 132.6, 132.5, 125.4 (C3–C5); 56.8 (N–CH₂), 38.6 (CH₂–S); 18.4 (SMe). FAB-MS: m/z = 355 [M]⁺; 320 [M − Cl]⁺.

Preparation of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(Cl)(PPh₃)] (4). PPh₃ (7.7 mg, 0.029 mmol) was added to a suspension of 3 (11 mg, 0.030 mmol) in acetone (15 cm³). The mixture was stirred for 12 h and the solvent removed to give a white solid which was recrystallized from dichloromethane–hexane. Yield 46%. Anal. found: C, 54.0; H, 3.9; N, 2.0; C₂₈H₂₆NPSCl₂Pd requires C, 54.5; H, 4.2; N, 2.3%. IR: ν(C[double bond, length half m-dash]N) 1617s, ν(Pd–Cl), 306m cm⁻¹. ¹³C-{¹H} NMR (50.28 MHz, CDCl₃): δ 174.6 (C[double bond, length half m-dash]N); 160.3 (C6); 145.0 (C1); 132.2 (C2), 136.6, 131.5, 125.1 (C3–C5); 59.0 (N–CH₂), 35.3 (CH₂–S); 16.0 (SMe); P–phenyl; 130.5 [d, C_i, J(PC) = 46.1 Hz], 135.3 [d, C_o, J(PC) = 12.0 Hz], 128.2 [d, C_m, J(PC) = 11.3 Hz], 131.0 [d, C_p, J(PC) = 2.2 Hz]. FAB-MS: m/z = 582 [M − Cl]⁺.

Compounds 5–7 were obtained following a similar procedure as white (5, 6) or orange (7) solids, but using a 2 : 1 complex 3 to diphosphine molar ratio.

[{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe](Cl)}₂(μ-Ph₂PCH₂PPh₂)] (5). Yield 65%. Anal. found: C, 47.3; H, 3.7; N, 2.3; C₄₅H₄₄N₂P₂S₂Cl₄Pd₂·CH₂Cl₂ requires C, 46.9; H, 3.9; N, 2.4%. IR: ν(C[double bond, length half m-dash]N) 1616s cm⁻¹. FAB-MS: m/z = 1058 [M − Cl]⁺; 1021 [M − 2Cl]⁺; 704 [(1 − H)Pd(dppm)]⁺.

[{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe](Cl)}₂{μ-Ph₂P(CH₂)₄PPh₂}] (6). Yield 76%. Anal. found: C, 50.7; H, 4.4; N, 2.3; C₄₈H₅₀N₂P₂S₂Cl₄Pd₂ requires C, 50.8; H, 4.4; N, 2.5%. IR: ν(C[double bond, length half m-dash]N), 1615s, ν(Pd–Cl), 308m cm⁻¹. ¹³C-{¹H} NMR (50.28 MHz, CDCl₃): δ 174.0 (C[double bond, length half m-dash]N); 160.0 (C6); 144.5 (C1); 132.1 (C2), 132.9, 131.5, 125.0 (C3–C5); 58.7 (N–CH₂), 34.9 (CH₂–S); 16.0 (SMe); P–phenyl: 129.9 [d,C_i, J(PC) = 46.1 Hz], 133.9 [d,C_o, J(PC) = 12.0 Hz], 128.6 [d, C_m, J(PC) = 10.6 Hz], 130.9(C_p) FAB-MS: m/z = 1101 [M−Cl]⁺; 1064 [M−2Cl]⁺; 746 [(1−H)Pd(dppb)]⁺.

[{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe](Cl)}₂(μ-Ph₂PC₅H₄FeC₅H₄PPh₂)] (7). Yield 97%. Anal. found: C, 51.2; H, 4.4; N, 2.3; C₅₄H₅₀N₂P₂S₂Cl₄FePd₂ requires C, 51.3; H, 4.0; N, 2.2%. IR: ν(C[double bond, length half m-dash]N) 1622s cm⁻¹. FAB-MS: m/z = 1192 [M−2Cl]⁺; 874 [(1−H)Pd(dppf)]⁺.

Preparation of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}{Ph₂P(CH₂)₂PPh₂-P,P}][ClO₄] (8). PPh₂(CH)₂PPh₂ (4.9 mg, 0.012 mmol) was added to a suspension of 3 (4.3 mg, 0.012 mmol) in acetone (20 cm³). The mixture was stirred for 1 h, after which an excess of sodium perchlorate was added. The complex was the precipitated out by addition of water, filtered off and dried in vacuo. Recrystallization from dichloromethane–hexane gave the final compound as a yellow solid. Yield 94%. Anal. found: C, 51.3; H, 4.4; N, 1.5; C₃₆H₃₅NO₄P₂SCl₂Pd·0.5CH₂Cl₂ requires C, 51.0; H, 4.2; N, 1.6%. IR: ν(C[double bond, length half m-dash]N), 1607s cm⁻¹. FAB-MS: m/z = 718 [M−ClO₄]⁺.

[Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}{(Ph₂PCH₂CH₂)₂PPh-P,P,P}][ClO₄] (9). Yield 72%. Anal. found: C, 52.3; H, 4.4; N, 1.5; C₄₄H₄₄NO₄P₃SCl₂Pd·CH₂Cl₂ requires C, 52.0; H, 4.5; N, 1.3%. IR: ν(C[double bond, length half m-dash]N) 1615s cm⁻¹. FAB-MS: m/z = 854 [M−ClO₄]⁺.

Preparation of [Pd{2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe}(PPh₃)][CF₃SO₃] (10). A solution of 3 (10.4 mg, 0.029 mmol) in acetone (15 cm³) was treated with silver trifluoromethanesulfonate (7.4 mg, 0.029 mmol) and stirred for 2 h. The resulting solution was filtered through Celite to remove the AgCl precipitate. PPh₃ (7.0 mg, 0.028 mmol) was added to the filtrate, the solution stirred for another 4 h and the solvent removed to give a yellow solid which was recrystallized from dichloromethane–hexane. Yield 89%. Anal. found: C, 48.5; H, 3.7; N, 1.7; C₂₉H₂₆NO₃F₃PS₂ClPd requires C, 47.7; H, 3.6; N, 1.9%. IR: ν(C[double bond, length half m-dash]N), 1628s cm⁻¹.

Compound 11 was obtained following a similar procedure as a white solid but using a 2 : 1 complex 3 to diphosphine molar ratio.

[{Pd[2-ClC₆H₃C(H)[double bond, length half m-dash]NCH₂CH₂SMe]}₂{μ-Ph₂P(CH₂)₄PPh₂}][CF₃SO₃]₂  (11). Yield 50%. Anal. found: C, 44.2; H, 3.7; N, 1.9; C₅₀H₅₀N₂O₆F₆P₂S₄Cl₂Pd₂ requires C, 44.1; H, 3.7; N, 2.1%. IR: ν(C[double bond, length half m-dash]N) 1626s cm⁻¹. ¹³C-{¹H} NMR (50.28 MHz, CDCl₃): δ 172.3 (C[double bond, length half m-dash]N); 157.6 (C6); 145.6 (C1); 132.4 (C2), 135.5, 129.3, 125.5 (C3–C5); 58.1 (N–CH₂), 36.1 (CH₂–S); 22.7 (SMe). P-phenyl: 129.8 [d, C_i, J(PC) = 46.8 Hz], 133.7 [d, C_o, J(PC) = 10.6 Hz], 128.8 [d, C_m, J(PC) = 9.2 Hz], 131.2(C_p) FAB-MS: m/z = 1213 [M−CF₃SO₃]⁺; 746 [(1−H)Pd(dppb)]⁺.

X-Ray crystallographic study

Three-dimensional, room temperature X-ray data were collected on a Siemens Smart CCD diffractometer by the ω scan method using graphite-monochromated Mo-Kα radiation. All the measured reflections were corrected for Lorentz and polarisation effects and for absorption by semi-empirical methods based on symmetry-equivalent and repeated reflections. The structures were solved by direct methods and refined by full matrix least squares on F². Hydrogen atoms were included in calculated positions and refined in riding mode. Refinement converged at a final R = 0.0372 and 0.515 (for complexes 3 and 11, respectively, observed data, F) and wR₂ = 0.0856 and 0.1513 (for complexes 3 and 11, respectively, unique data, F²), with allowance for thermal anisotropy of all non-hydrogen atoms. The structure solution and refinement were carried out using the program package SHELX-97.⁴³

CCDC reference numbers 157897 and 157898. See http://www.rsc.org/suppdata/nj/b1/b106511d/ for crystallographic data in CIF or other electronic format.

Acknowledgements

We thank the Ministerio de Educación y Cultura (Proyecto PB98-0638-C02-01/02), the Xunta de Galicia (Proyecto PGIDT99PXI20907B) and the Universidad de Coruña for financial support.

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