On the identification of ionic species of neutral halogen dimers, monomers and pincer type palladacycles in solution by electrospray mass and tandem mass spectrometry |
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| Authors: | Daniela M. Tomazela Gunter Ebeling Marcos N. Eberlin Jairton Dupont |
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| Affiliation: | a Thomson Spectrometry Laboratory, Institute of Chemistry, UNICAMP, Av. Bento Gonalves, 13083-970 Campinas, SP, Brazil
b Laboratory of Molecular Catalysis, Institute of Chemistry, UFRGS, 91501-970 Porto Alegre, RS, Brazil |
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| Abstract: | Electrospray (ESI) mass spectra analysis of acetonitrile solutions of a series of neutral chloro dimers, pincer type, and monomeric palladacycles has enabled the detection of several of their derived ionic species. The monometallic cationic complexes Pd[κ1-C,κ1-N,κ1-S-C(CH3S-2-C6H4)C(Cl)CH2N(CH3)2]+ (1a) and [Pd[κ1-C,κ1-N,κ1-S-C(CH3S-2-C6H4)C(Cl)CH2N(CH3)2](CH3CN)]+ (1b) and the bimetallic cationic complex [κ1-C,κ1-N,κ1-S-C(CH3S-2-C6H4)C(Cl)CH2N(CH3)2]Pd-Cl-Pd[κ1-C,κ1-N,κ1-S-C(CH3S-2-C6H4)C(Cl)CH2N(CH3)2]+ (1c) were detected from an acetonitrile solution of the pincer palladacycles Pd[κ1-C,κ1-N,κ1-S-C(CH3S-2-C6H4)C(Cl)CH2N(CH3)2](Cl) 1. For the dimeric compounds {Pd[κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2](μ-Cl)}2 (2, Y=H and 3, CF3), highly electronically unsaturated palladacycles [Pd[κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2]+ (2d, 3d) and their mono and di-acetonitrile adducts, namely, [Pd[κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2](CH3CN)]+ (2e, 3e) and [Pd[κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2](CH3CN)2]+ (2f and 3f) were detected together with the bimetallic complex [Pd[κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2]-Cl-Pd[κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N](CH3)2]+ (2a, 3a) and its acetonitrile adducts [κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2](CH3CN)Pd-Cl-Pd[ κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2]+ (2b, 3b) and [κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2](CH3CN)Pd-Cl-Pd[κ1-C, κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2(CH3CN)]+ (2c, 3c). The dimeric palladacycle {Pd[κ1-C,κ1-N-C(CH3O-2-C6H4)C(Cl)CH2N(CH3)2](μ-Cl)}2 (4) is unique as it behaves as a pincer type compound with the OCH3 substituent acting as an intramolecular coordinating group which prevents acetonitrile full coordination, thus forming the cationic complexes [(C6H4(o-CH3O)CC(Cl)CH2N(CH3)2-κO,κC,κN)Pd]+ (4b), [(C6H4(o-CH3O)CC(Cl)CH2N(CH3)2- κO,κC,κN)Pd(CH3CN)]+ (4c) and [(C6H4 (o-MeO)CC(Cl)CH2N(CH3)2-κO, κC,κN)Pd-Cl-Pd(C6H4(o-CH3O)CC(Cl)CH2N(CH3)2-κO,κC,κN)]+ (4a). ESI-MS spectra analysis of acetonitrile solutions of the monomeric palladacycles Pd[κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2](Cl)(Py) (5, Y=H and 6, Y=CF3) allows the detection of some of the same species observed in the spectra of the dimeric palladacycles, i.e., monometallic cationic 2d-3d, 2e-3e and {Pd[κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2](Py)}+ (5a, 6a) and {Pd[κ1-C,κ1-N-C(Y-2-C6H4)C(Cl)CH2N(CH3)2](CH3CN)(Py)}+ (5b, 6b) and the bimetallic 2a, 3a, 2b, 3b, 2c and 3c. In all cationic complexes detected by ESI-MS, the cyclometallated moiety was intact indicating the high stability of the four or six electron anionic chelate ligands. The anionic (chloride) or neutral (pyridine) ligands are, however, easily replaced by the acetonitrile solvent. |
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| Keywords: | Palladacycles Electrospray mass spectrometry DFT calculations Pincer complexes |
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