Abstract
The reaction of the Tc(I) complex [Tc(NO)Cl2(HOMe)(PPh3)2] with stoichiometric amounts of 2-mercatopyridine and a proton scavenger yields [Tc(NO)Cl(Spy)(PPh3)2] or [Tc(NO)(Spy)2(PPh3)], depending upon quantities of ligands employed. These two complexes have been structurally characterized. The small bite angles of the bidentate mercaptopyridine ligands cause significant deviation from octahedral coordination geometry.
Keywords: Technetium, Nitrosyl, X-ray crystal structure, Bidentate, Thiolate
1. Introduction
The infrared spectra of nitrosyl complexes display strong, sharp absorptions in the 1550–1900 cm−1 region, and these absorptions are significantly influenced by the character of the ligands trans-to them [1]. This was displayed recently when comparing the IR spectra of the structurally characterized mer- and fac- isomers of [TcCl2(NO)(PNPpr)] [2].
The reaction of the Tc(II) nitrosyl complex (Bu4N)[TcNOCl4] [3] with stoichiometric amounts of 2-mercaptopyridine (HSpy) and a proton scavenger gives a mixture of products as determined by multiple absorptions in this region in the infrared spectroscopy of the crude product. However, the reaction of [TcCl2(NO)(HOMe)(PPh3)2] with a stoichiometric amounts of 2-mercaptopyridine and a proton scavenger gives a single product, [Tc(NO)CI(PPh3)2(Spy)]. The reaction with an excess of 2-mercaptopyridine and proton scavenger gives [Tc(NO)(PPh3)(Spy)2].
2. Experimental
Caution! Technetium-99 is a weak β− -emitter (E = 0.292 MeV, t1/2 = 2.12 × 105 years). All work has been done in laboratories approved for the use of low levels of radioactive materials. Precautions have been detailed elsewhere [4]. Reagents and solvents were used as received unless otherwise stated. Routine infrared spectra were obtained on a Perkin-Elmer Spectrum One FT-IR Spectrometer. Mass spectra were recorded on a Bruker Daltonics APEXII 3 Tesla Fourier Transform Mass Spectrometer (Ion Cyclotron Resonance Mass Spectrometer). See Table 1 for summation of X-ray crystallographic data set collection and refinement.
Table 1.
Instrument employed – 'Siemens three-circle diffractometer, Bruker APEX CCD.
| [TcCl(NO)(Spy)(PPh3)2] | [Tc(NO)(Spy)2(PPh3)] | |
|---|---|---|
| Symmetry | monoclinic | monoclinic |
| Space group | P2(1)/m | C2/c |
| Cell length a | 9.5620(14) | 34.217(3) |
| Cell length b | 24.715(4) | 9.4819(8) |
| Cell length c | 15.456(2) | 16.3980(15) |
| Cell angle α | 90.00 | 90.00 |
| Cell angle β | 90.006(2) | 92.052(2) |
| Cell angle γ | 90.00 | 90.00 |
| Cell volume | 3652.6(9) | 5316.9(8) |
| Cell formula units Z | 4 | 8 |
| Temperature | 100(2) | 100.2 |
| Reflections used | 9851 | 9567 |
| Theta minimum | 2.47 | 2.38 |
| Theta maximum | 30.43 | 30.54 |
| Crystal description | needle | plate |
| Crystal color | purple | red |
| Crystal size | 0.30 × 0.12 × 0.07 | 0.45 × 0.30 × 0.05 |
| Density calc | 1.451 | 1.526 |
| Absorption coefficient μ | 0.648 | 0.768 |
| Tmax/Tmin | 0.9561/0.8294 | 0.9618/0.7188 |
| SADABS (Sheldrick, 2009), total reflections collected | 93,802 | 68,710 |
| Theta maximum/minimum | 29.57/1.32 | 29.57/1.19 |
| R, Rw | 0.0530/0.0863 | 0.0263/0.0619 |
| Goodness-of-fit (GOF) | 1.048 | 1.078 |
3. Synthesis
3.1. [Tc(NO)Cl(Spy)(PPh3)2], complex (1)
To an orange solution of [Tc(NO)Cl2(HOCH3)(PPh3)2] (79 mg, 0.104 mmol) and 2-mercaptopyridine (14 mg, 0.108 mmol) in dichloromethane was added diisopropylethylamine (27 mg, 0.209 mmol). This addition caused the solution to darken immediately to a wine red color. The sample was refluxed overnight, and no further color change was observed. The solution was concentrated to 1 ml under reduced pressure and then refrigerated overnight to yield a lilac-purple precipitate. The solid was collected on a fritted glass funnel, and dried in vacuo. Large, block shaped crystals of complex (1) formed overnight from dichloromethane layered with methanol and diethylether. Yield: 41 mg (50%).
Anal. Calc. for C41H34ClN2OP2STc: C, 61.65; H, 4.26; Cl, 4.39; S, 4.01. Found: C, 61.42; H, 4.30; CI, 4.52; S, 4.11%.
FAB-MS(+): 798 [Tc(NO)CI(PPh3)2(Spy)]+, 763 [Tc(NO)(PPh3)2(Spy)]+, 688 [Tc(NO)Cl(PPh3)2]+, 536 [Tc(NO)Cl(PPh3)(Spy)]+, 501 [Tc(NO)(PPh3)(Spy)+. IR (KBr) (cm−1): v(NO) 1696 (vs, br).
1H NMR (CD2Cl2): 7.59 (m, 12H), 7.29 (m, 18H), 6.73 (m, 2H), 6.03 (d of d, 1H), 5.65 (t of d, 1H).
3.2. [Tc(NO)(Spy)2(PPh3)], complex (2)
A mixture of 2-mercatopyridine (10 mg, 0.09 mmol) and diisopropylethylamine (15 mg, 0.116 mmol) was added to a solution of [Tc(NO)Cl(Spy)(PPh3)2] (38 mg, 0.062 mmol) in dichloromethane. The orange solution rapidly darkened to a ruby red color within minutes. The ruby solution was refluxed for 24 h, after which time it was concentrated under reduced pressure. Slow evaporation at room temperature resulted in the formation of a deep orange microcrystalline solid. The product was collected on a fritted glass funnel and dried in vacuo and recrystallized from dichloromethane layered with methanol and ether. Yield: 12 mg (40%).
Anal. Calc. for C28H28N3OPS2Tc: C, 54.99; H, 3.76; N, 6.87; S, 10.47. Found: C, 54.88; H, 3.74; N, 6.82; S, 10.55%.
FAB-MS(+) (m/z): 611 [Tc(NO)(PPh3)(Spy)2]+, 581 [Tc(PPh3)(Spy)2]+, 501 [Tc(NO)(PPh3)(Spy)]+, 349 [Tc(NO(Spy)2]+, 319 [Tc(Spy)2]+.
IR (KBr) (cm−1): v(NO) 1677 (vs).
1H NMR ((CD3)2CO): t ~ 8.30 (d of d, 1H), 7.56 (m, 7H), 7.37 (m, 10H), 7.11 (t of d, 1H), 6.93 (d of d, 1H), 6.86 (m, 1H), 6.51 (d of d, 1H), 6.22 (t of d, 1H).
4. Discussion
In exploring the coordination chemistry of technetium nitrosyl complexes with polydentate ligands, we have recently concluded that the Tc(II) precursor (Bu4N)[TcNOCl4] is too reactive to allow selective incorporation of polydentate ligands and formation of a single product. Reactions invariably lead to the formation of multiple products, which is easily observed in the infrared spectra of the crude products. Multiple absorptions in the 1550–1900 cm−1 region, where few other functional groups display absorption bands, is an easy and accurate method for monitoring how many products are present in a crude product. We recently reported multiple structural isomers of the Tc(I) complex [TcCl2NO(PNP)], isolated and structurally characterized from the reaction of [TcNOCl4]− and the neutral, tridentate ligand [2]. The redox active Tc(II) complex [TcNOCl4]− can be easily reduced to Tc(I), which can lead to redox chemistry competing with the substitution reaction. Additionally, the labile chloride ligands, along with the coordinative unsaturation of this square pyramidal synthon, contribute to the lack of stereo selectivity in reactions with polydentate ligands. This has led us to explore alternative nitrosyl precursors, which are inherently less reactive and which allow a more selective incorporation of the polydentate ligands. The precursor we utilized in this study is [TcCl2(NO)(HOMe)(PPh3)2], a Tc(I) species [6]. This complex appears ideal for this application in that it contains a combination of easily replaced hard and soft ligands allowing a more selective introduction of these polydentate ligands.
In the reactions with 2-mercaptopyridine and a proton scavenger, depending on the stoichiometries employed, the monosubstituted product [TcClNO(Spy)(PPh3)2] or the disubstituted product [TcNO(Spy)2(PPh3)] can be formed [7]. Both complexes have been previously reported synthesised from [TcCl2NO(NCMe)(PPh3)2] [5].
The X-ray crystal structure of [TcClNO(Spy)(PPh3)2] displays the bulky triphenylphosphine ligands in mutually trans- coordination sites and the nitrosyl nitrogen trans- to the mercaptopyrindine nitrogen. An ORTEP diagram of [TcClNO(Spy)(PPh3)2] is shown in Fig. 1, with selected bond lengths and angles in Table 2. The nitrosyl ligand is in linear form, with Tc–N–O bond angle at 177.7(3)° and short bond lengths of Tc–N 1.748(4) Å and N–O 1.196(5) Å, reflecting the multiple bonding throughout the unit. The small bite angle of the mercaptopyridine, N1–Tc–S1 is 65.82(10)°, results in significant distortion from octahedral around the equatorial band.
Fig. 1.
ORTEP diagram of complex 2, [Tc(NO)Cl(Spy)2(PPh3)].
Table 2.
Selected bond lengths (Å) and angles (°) for [TcCl(NO)-(Spy)(PPh3)2].
| Tc-Cl1 | 2.4410(11) |
| Tc-N2 | 1.748(4) |
| Tc-S1 | 2.4979(11) |
| Tc-N1 | 2.173(4) |
| Tc-P1 | 2.4338(8) |
| Tc-P2 | 2.4312(8) |
| N2-O1 | 1.196(5) |
| O1 N2 Tc1 | 177.7(3) |
| N2 Tc1 N1 | 167.63(15) |
| N2 Tc1 P1 | 90.36(2) |
| N1 Tc1 P1 | 89.995(19) |
| N2 Tc1 P1 | 90.36(2) |
| N1 Tc1 P1 | 89.995(19) |
| P1 Tc1 P1 | 176.70(4) |
| N2 Tc1 Cl1 | 103.86(11) |
| N1 Tc1 Cl1 | 88.52(10) |
| P1 Tc1 Cl1 | 88.348(19) |
| P1 Tc1 Cl1 | 88.348(19) |
| N2 Tc1 S1 | 101.81(11) |
| N1 Tc1 S1 | 65.82(10) |
| P1 Tc1 S1 | 91.505(18) |
| P1 Tc1 S1 | 91.505(18) |
| Cl1 Tc1 S1 | 154.33(4) |
The X-ray crystal structure of [TcNO(Spy)2(PPh3)] also displays the nitrosyl ligand in linear coordination mode with Tc–N–O bond angle of 173.35(12)° and short Tc–N and N–O bond lengths of 1.7497(12) Å and 1.1941(17) Å. The distortion in this bis-chelate complex from ideal octahedral coordination geometry is significant. A pyridine nitrogen is coordinated trans- to the phosphine with the P–Tc–N bond angle of 166.25(4)°. The two sulfur atoms are trans- to each other with the S–Tc–S bond angle of 151.528(13)°. Selected bond lengths and angle can be seen in Table 3. An ORTEP diagram of [TcNO(Spy)2(PPh3)] is shown in Fig. 2.
Table 3.
Selected bond lengths (Å) and angles (°) for [Tc(NO)-(Spy)(PPh3)].
| Tc-N2 | 2.1771(12) |
| Tc-N3 | 1.7497(12) |
| Tc-N1 | 2.1527(13) |
| Tc-S1 | 2.4445(4) |
| Tc-S2 | 2.4676(4) |
| Tc-P1 | 2.3777(4) |
| N3-O1 | 1.1941(17) |
| O1 N3 Tc1 | 173.35(12) |
| N3 Tc1 N1 | 97.91(5) |
| N3 Tc1 N2 | 163.59(5) |
| N1 Tc1 N2 | 84.00(5) |
| N3 Tc1 P1 | 89.22(4) |
| N1 Tc1 P1 | 166.25(4) |
| N2 Tc1 P1 | 92.48(3) |
| N3 Tc1 S1 | 105.27(4) |
| N1 Tc1 S1 | 67.00(4) |
| N2 Tc1 S1 | 90.52(3) |
| P1 Tc1 S1 | 99.832(13) |
| N3 Tc1 S2 | 97.33(4) |
| N1 Tc1 S2 | 93.21(3) |
| N2 Tc1 S2 | 66.27(3) |
| P1 Tc1 S2 | 97.537(13) |
| S1 Tc1 S2 | 151.528(13) |
Fig. 2.
ORTEP diagram of complex 1, [Tc(NO)Cl(Spy)(PPh3)2]
5. Summary
By employing the less reactive, octahedral, Tc(I) nitrosyl precursor [TcCl2(NO)(HOMe)(PPh3)2] we were able to synthesize and easily isolate the mono-mercaptopyridine [Tc(NO)CI(Spy)(PPh3)2] and the bis-mercaptopyridine complex [Tc(NO)(Spy)2(PPh3)] cleanly, and report the X-ray crystal structures of both. For a comprehensive discussion of the spectroscopy of these complexes see [5].
Supplementary Material
Footnotes
Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2010.09.025.
References
- [1].Miki E, Mizumachi K, Ishimori T, Okuno H. Bull. Chem. Soc. Jpn. 1973;46:3779. [Google Scholar]
- [2].Nicholson TL, Mahmood A, Refosco F, Tisato F, Müller P, Jones AG. Inorg. Chim. Acta. 2009;362:3637. doi: 10.1016/j.ica.2009.04.017. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [3].Brown DS, Newman JL, Thornback JR, Davison A. Acta Crystallogr., Sect. C. 1987;43:1692. [Google Scholar]
- [4].Davison A, Orvig C, Trop HS, Sohn M, DePamphilis BV, Jones AG. Inorg. Chem. 1980;19:1988. [Google Scholar]
- [5].Blanchard SS, Nicholson T, Davison A, Jones AG. Inorg. Chim. Acta. 1996;241:95. [Google Scholar]
- [6].Blanchard SS, Nicholson T, Davison A, Davis W, Jones AG. Inorg. Chim. Acta. 1996;244:121. [Google Scholar]
- [7].Blanchard SS. PhD Thesis. MIT; 1994. p. 183. [Google Scholar]
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