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Ruthenium and palladium halide complexes containing hemilabile ligands for luminescent chemosensing Matkovich, Kristin M. 2009

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Ruthenium and Palladium Halide Complexes Containing Hemilabile Ligands for Luminescent Chemosensing  by Kristin M Matkovich B. Sc. (Honours) University of Waterloo, 2003  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Chemistry)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  SEPTEMBER 2009  Kristin M Matkovich, 2009  Abstract The effect of the halide ligand on the fluorescence lifetime of a series of Ru(II) complexes, tcc-RuX2(POC4Pyr-P,O)2 (X = Cl (3), Br (4), I (5)) containing the hemilabile phosphine ether ligand 4-{2-(diphenylphosphino)phenoxy}butylpyrene (POC4Pyr (1)), is reported. The synthesis and characterization of both the ligand, POC4Pyr (1), and ligand oxide, P(=O)OC4Pyr (2), and the solid-state structure of 1 are also presented. New complexes based on a similar framework incorporating phosphine pyrenyl imine and phosphine pyrenyl amine ligands and a palladium metal center, PdCl2(PNPyrP,N) (14) (PNPyr = 2-diphenylphosphino-N-(1-pyrenyl)benzylidineimine (12)) and PdCl2(PNHPyr-P,N) (15) (PNHPyr = 2-diphenylphosphino-N-(1pyrenyl)benzylidineamine (13)), are presented . The UV-vis, steady-state fluorescence, and solid state structures of 14 and 15 are presented. The synthesis and characterization, as well as the solid state structures of both ligands, 12 and 13, are also presented. Preliminary steady-state fluorescence experiments provide promising results for a potential ―OFF-ON‖ or ―ON-OFF‖ chemosensor. However, initial reactivity of the palladium complexes with carbon monoxide and sulfur dioxide were unsuccessful; further experiments are needed to optimize the reactivity of these complexes.  ii  Table of Contents  Abstract ............................................................................................................................... ii Table of Contents ............................................................................................................... iii List of Tables .................................................................................................................... vii List of Figures .................................................................................................................. viii List of Schemes ................................................................................................................. xii List of Symbols and Abbreviations.................................................................................. xiii Acknowledgements ......................................................................................................... xvii Chapter 1 Introduction ......................................................................................................................... 1 1.1 Molecular sensors and the modular design approach ................................................... 1 1.2 A brief introduction to photoluminescence theory ....................................................... 5 1.2.1 Relaxation processes from the singlet excited states ...................................... 6 1.2.2 Relaxation processes from the triplet excited states ....................................... 7 1.3 Non-luminescent deactivation of the first excited singlet state .................................... 8 1.4 Fluorescence sensors based on photo-induced electron transfer (PET) ...................... 10 1.4.1 Basic design for simple PET sensors ............................................................ 10 1.4.2 PET sensors based on excimer formation ..................................................... 12 1.5 Pyrene as a fluorophore .............................................................................................. 14 1.5.1 Vibronic band structure of pyrene ................................................................ 15 1.5.2 Pyrene excimers ............................................................................................ 16 1.5.3 Spectroscopic detection of pyrene pre-association in the ground state ........ 18 1.5.3.1 Absorption spectrum ................................................................... 19 1.5.3.2 Excitation spectrum .................................................................... 19 1.5.3.3 Time dependent fluorescence spectrum ...................................... 20 1.5.4 PET sensors containing pyrene as the fluorophore ....................................... 21 1.6 Transition metal ion based chemosensors................................................................... 22 1.6.1 Utilization of hemilabile ligands in transition metal ion based sensors ....... 22 1.7 Ruthenium halide complexes containing a hemilabile phosphine pyrenyl ether ligand................................................................................................................................. 24 1.8 The scope of this thesis ............................................................................................... 26  iii  Chapter 2 The Phosphine Pyrenyl Ether (1) and Its Oxide (2) .......................................................... 28 2.1 Absorption and emission of 1 and 2 ........................................................................... 28 2.2 Excited state lifetimes of POC4Pyr (1) and P(=O)OC4Pyr (2) .................................. 31 2.3 Solid-state structure of POC4Pyr (1) .......................................................................... 31 2.4 Experimental ............................................................................................................... 34 2.4.1 General .......................................................................................................... 34 2.4.2 Materials ....................................................................................................... 36 2.4.3 Synthesis of P(=O)OC4Pyr (2) ..................................................................... 36 2.4.4 X-ray crystallographic analysis .................................................................... 37 Chapter 3 Ruthenium Halide Complexes Containing the Pyrenyl Ether Phosphine Ligand (POC4Pyr)......................................................................................................................... 38 3.1 Synthesis and characterization of tcc-RuX2(POC4Pyr-P,O)2 (X = Cl (3), Br (4), I (5)) ............................................................................................. 41 3.2 Characterization of ttt-RuX2(CO)2(POC4Pyr-P,O)2 (X = Cl (6), Br (7), I (8)) .......... 48 3.3 Characterization of cct-RuX2(CO)2(POC4Pyr-P,O)2 (X = Cl (9), Br (10), I (11))..... 53 3.4 Excited state lifetimes of RuX2(POC4Pyr-P,O)2 (X = Cl (3), Br (4), I (5)) before and after reaction with CO……………………………………………..…………….56 3.4.1 SPC results for tcc-RuX2(POC4Pyr-P,O)2 (X = Cl (3), Br (4), I (5)) and ttt-RuX2(CO)2(POC4Pyr-P,O)2 (X = Cl (6), Br (7), I (8)) ........................... 56 3.4.2 SPC results for analytically pure tcc-RuX2(POC4Pyr-P,O)2 (X = Cl (3), Br (4), I (5)).............................................................................. 61 3.5 Solid-state structure of RuCl2(POC19H17)2CHCl3...................................................... 62 3.6 Conclusions ................................................................................................................. 69  iv  3.7 Experimental ............................................................................................................... 70 3.7.1 General .......................................................................................................... 70 3.7.2 Materials ....................................................................................................... 72 3.7.3 Synthesis and characterization of tcc-RuBr2(POC4Pyr-P,O)2 (4) ................ 72 3.7.4 Synthesis and characterization of tcc-RuI2(POC4Pyr-P,O)2 (5) ................... 73 3.7.5 Preparation of samples for excited state lifetime measurements .................. 74 3.7.6 X-ray crystallographic analysis .................................................................... 74 Chapter 4 New Hemilabile Ligands Containing Phosphine Amine Functionalities with a Pendant Pyrenyl Moiety.................................................................................................................. 75 4.1 Motivation for the development of hemilabile ligands with phosphine amine functionalities .............................................................................................................. 75 4.2 Synthesis and characterization of PNPyr (12) and PNHPyr (13) ............................... 77 4.3 Absorption and emission properties of PNPyr (12) and PNHPyr (13) ....................... 80 4.4 Solid-state structure of PNPyr (12) and PNHPyr (13) ................................................ 87 4.4.1 Solid-state structure of PNPyr (12) ............................................................... 87 4.4.2 Solid-state structure of PNHPyr (13) ............................................................ 90 4.5 Experimental ............................................................................................................... 93 4.5.1 General .......................................................................................................... 93 4.5.2 Materials ....................................................................................................... 93 4.5.3 Synthesis and characterization of the phosphine pyrenyl imine ligand ........ 94 4.5.3.1 Synthesis of 1-nitropyrene .......................................................... 94 4.5.3.2 Synthesis of 1-aminopyrene ........................................................ 94 4.5.3.3 Synthesis and characterization of 12 (PNPyr) ............................ 95 4.5.4 Synthesis and characterization of 13 (PNHPyr) ........................................... 95 4.5.5 X-ray crystallographic analyses .................................................................... 96 4.5.5.1 X-ray crystallographic analysis of 12 ......................................... 96 4.5.5.2 X-ray crystallographic analysis of 13 ......................................... 97  v  Chapter 5 Palladium Halide Complexes Containing the Phosphine Pyrenyl Imine and Phosphine Pyrenyl Amine Ligands (PNPyr and PNHPyr) ............................................... 98 5.1 Motivation ................................................................................................................... 98 5.2 Synthesis and characterization of PdCl2(PNPyr-P,N) (14) ......................................... 99 5.2.1 Synthesis of PdCl2(PNPyr-P,N) (14) ............................................................ 99 5.2.2 Characterization of PdCl2(PNPyr-P,N) (14) ............................................... 100 5.3 Absorption and emission spectra of PdCl2(PNPyr-P,N) (14) ................................... 101 5.4 Solid-state structure of PdCl2(PNPyr-P,N) (14) ....................................................... 102 5.5 Reactivity of PdCl2(PNPyr-P,N) (14) towards sulfur dioxide .................................. 106 5.6 Synthesis and characterization of PdCl2(PNHPyr-P,N) (15) .................................... 111 5.6.1 Synthesis of PdCl2(PNHPyr-P,N) (15) ....................................................... 111 5.6.2 Characterization of PdCl2(PNHPyr-P,N) (15) ............................................ 112 5.7 Absorption and emission spectra of PdCl2(PNHPyr-P,N) (15) ................................ 113 5.8 Reactivity of PdCl2(PNHPyr-P,N) (15) towards sulfur dioxide ............................... 116 5.9 Conclusions ............................................................................................................... 118 5.10 Experimental ........................................................................................................... 119 5.10.1 General ...................................................................................................... 119 5.10.2 Materials ................................................................................................... 119 5.10.3 Synthesis and characterization of PdCl2(PNPyr-P,N) (14) ....................... 120 5.10.4 Synthesis and characterization of PdCl2(PNHPyr-P,N) (15) .................... 120 5.10.5 X-ray crystallographic analysis of 14 ....................................................... 121 References ...................................................................................................................... 122  vi  List of Tables Table 2.1  Crystallographic Data for 1 ....................................................................... 33  Table 2.2  Selected interatomic distances (Å) and angles (deg) for 1 ....................... 33  Table 3.1  Characterization data for 1-11 .................................................................. 47  Table 3.2  Lifetimes of decay components for 3-5 .................................................... 61  Table 3.3  Crystallographic data for RuCl2(POC19H17)2.CHCl3 .............................. 65  Table 3.4  Selected interatomic distances (Å) for RuCl2(POC19H17)2.CHCl3.......... 66  Table 3.5  Selected interatomic angles (deg) for RuCl2(POC19H17)2.CHCl3 ........... 67  Table 3.6  Selected Torsion angles (deg) for RuCl2(POC19H17)2.CHCl3 ................. 68  Table 4.1  Crystallographic data for 12...................................................................... 88  Table 4.2  Selected interatomic distances (Å) for 12 ................................................. 89  Table 4.3  Selected interatomic angles (deg) for 12 .................................................. 89  Table 4.4  Crystallographic data for 13...................................................................... 91  Table 4.5  Selected interatomic distances (Å) for 13 ................................................. 91  Table 4.6  Selected interatomic angles (deg) for 13 .................................................. 92  Table 5.1  Crystallographic data for 14.................................................................... 104  Table 5.2  Selected interatomic distances (Å) for 14 ............................................... 104  Table 5.3  Selected interatomic angles (deg) for 14 ................................................ 105  Table 5.4  Selected interatomic torsion angles (deg) for 14 .................................... 105  vii  List of Figures Figure 1.1  Schematic depiction of a modular design where the receptor, M, is linked to the reporter through the spacer ................................................. 2  Figure 1.2  Chemosensor in which the Rh metal center acts as the receptor; and the phosphine-ether ligand as well as the Rh metal center act as reporters.4 .................................................................................................... 3  Figure 1.3  Chemosensor in which the Co metal center acts a the receptor, the dansyl moieties as the reporters, and diamine acts as the spacer.5,6 ...................................................................................................... 3  Figure 1.4  Schematic representation of (a) an OFF-ON chemosensor and (b) an ON OFF chemosensor; M=metal, A=analyte, F=fluorophore ............................................................................................. 4  Figure 1.5  Photophysical processes that occur during and after electronic excitation. (Adapted from reference 20) ..................................................... 6  Figure 1.6  Schematic representation of an EET processes involving (a) a double electron exchange mechanism between an excited fluorophore, F, and a d9 metal, M, in an elongated Oh coordinate environment giving rise to (b) the ground state configuration of F and an excited M centre.23 .................................................................. 9  Figure 1.7  Schematic representation of PET processes – (a) electron transfer from F LUMO to M LUMO, (b) electron transfer from M HOMO to F HOMO, and (c) no electron transfer in presence of analyte.14 ...................................... 10  Figure 1.8  A PET sensor in which anthracene fluorescence is revived upon binding K+ in methanol.3.................................................................. 11  Figure 1.9  PET sensor in which fluorescence quenching of anthracene involves CuII/CuI couple.3,23...................................................................... 12  Figure 1.10  PET sensors involving excimer formation consisting of: (a) a diazacrown ether with two pendant pyrene moieties; (b) a diatopic receptor incorporating two anthracene units.3 .................... 13  Figure 1.11  PET sensor involving excimer formation where the excimer band decreases upon binding of Zn(II) and Cd(II).3,14 .............................. 14  viii  Figure 1.12  Schematic depiction of potential energy diagrams for pyrene excimer formation in (a) the absence of ground state association, and (b) the presence of ground state association. (Adapted from reference 24) ..................................................................... 18  Figure 1.13  An alkali metal sensor containing pyrene in which PET is most efficient when n  3.26 .................................................................. 21  Figure 1.14  Reactivity of RuCl2(PO)2 (PO = o-(diphenylphosphino)anisole) towards CO.36 ............................................................................................ 24  Figure 1.15  Reactivity of tcc-RuX2(POC4Pyr-P,O)2 toward CO.37............................. 25  Figure 2.1  UV-vis absorption spectra for (a) 1 and (b) 2; [1] and [2] 10-5 M in CH2Cl2. Excitation (---) and emission () spectra for (c) 1 and (d) 2; [1] and [2]  10-6 M in CH2Cl2. ex = 345 nm; em = 398 nm .................. 30  Figure 2.2  ORTEP view of 1. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability................................ 32  Figure 3.1  UV-vis absorption spectra of (a) 3, (b) 4, (c) 5; [tcc-RuX2(POC4Pyr-P,O)2]  10-5 M in CH2Cl2 ...................................... 43  Figure 3.2  Excitation (---) and emission () spectra of (a) 3, (b) 4, (c) 5; [tcc-RuX2(POC4Pyr-P,O)2]  10-6 M in CH2Cl2. ex = 345 nm; em = 398 nm...................................................................... 44  Figure 3.3  Emission spectra of 3 over a 48 hour period; [tcc-RuCl2(POC4Pyr-P,O)2]  10-6 M in CH2Cl2. ex = 345 nm; em = 398 nm...................................................................... 46  Figure 3.4  Visible d-d absorption bands of (a) 3 () and 6 (---), (b) 4 () and 7 (---), and (c) 5 () and 8 (---); [tcc-RuX2(POC4Pyr-P,O)2] and [ttt-Ru(CO)2X2(POC4Pyr-P)2]  2 10-3 M in CH2Cl2..................... 49  Figure 3.5  Schematic structure of (a) an intermolecular excimer and (b) an intramolecular excimer for ttt-RuCl2(CO)2(POC4Pyr-P)2........................ 51  Figure 3.6  Excitation (---) and emission () spectra for (a) 6, (b) 7 and (c) 8; [ttt-Ru(CO)2X2(POC4Pyr-P)2]  10-6 M in CH2Cl2. ex = 345 nm; em = 398 nm...................................................................... 52  Figure 3.7  Excitation (---) and emission () spectra for (a) 9, (b) 10 and (c) 11; [cct-Ru(CO)2X2(POC4Pyr-P)2]  10-6 M in CH2Cl2. ex = 345 nm; em = 398 nm...................................................................... 55  ix  Figure 3.8  SPC decay for (a) 3 [tcc-RuCl2(POC4Pyr-PO)2]  10-6 M and (b) 6 [ttt-Ru(CO)2Cl2(POC4Pyr-P)2]  10-6 M in benzene. ex = 345 nm ............................................................................................. 58  Figure 3.9  SPC decay for (a) 4 [tcc-RuBr2(POC4Pyr-PO)2]  10-6 M and (b) 7 [ttt-Ru(CO)2Br2(POC4Pyr-P)2]  10-6 M in benzene. ex = 345 nm ............................................................................................. 59  Figure 3.10  SPC decay for (a) 5 [tcc-RuI2(POC4Pyr-PO)2]  10-6 M and (b) 8 [ttt-Ru(CO)2I2(POC4Pyr-P)2]  10-6 M in benzene. ex = 345 nm ............................................................................................. 60  Figure 3.11  Views of [RuCl2(POC19H17)2.CHCl3]2. The hydrogen atoms are omitted for clarity, as well as the labels for the carbon atoms ............ 63  Figure 3.12  ORTEP view of RuCl2(POC19H17)2.CHCl3 (molecule 1). The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability .................................................................... 64  Figure 4.1  1  Figure 4.2  1  Figure 4.3  UV-Vis absorption spectrum of PNPyr (12); [12] ≈ 10-4 M in CHCl3 .................................................................................................... 81  Figure 4.4  UV-Vis absorption spectrum of PNHPyr (13); [13] ≈ 10-4 M in benzene ................................................................................................. 81  Figure 4.5  Excitation and emission spectra of 12; [12] ≈ 10-6 M in CH2Cl2.............. 83  Figure 4.6  Excitation (—) and emission (—) spectra of 1- aminopyrene compared to excitation and emission spectra of 12 (see Figure 4.5). [1-aminopyrene] ≈ 10-6 M in CH2Cl2; ex = 355 nm; em = 382 nm...................................................................... 84  Figure 4.7  Excitation (—) and emission (—) spectra of 13; [13] ≈ 10-6 M in benzene; ex = 373 nm; em = 426 nm .................................................. 85  Figure 4.8  Excitation and emission spectra of 13; [13] ≈ 10-4 M (—); [13] ≈ 10-5 M (—); [13] ≈ 10-6 M (—); in benzene; ex = 373 nm; em = 426 nm...................................................................... 86  Figure 4.9  ORTEP view of 12 (isomer 1). The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability ................... 88  H NMR spectrum of PNPyr (12) in CDCl3; T = 300 K; f = 300 MHz ............................................................................................. 79 H NMR spectrum of PNHPyr (13) in CDCl3; T = 300 K; f = 300 MHz ............................................................................................. 79  x  Figure 4.10  ORTEP view of 13. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability................................ 90  Figure 5.1  Reactivity of a palladium phosphine-imine pyridyl complex with CO.1................................................................................................... 98  Figure 5.2  1  Figure 5.3  UV-vis absorption spectrum of PdCl2(PNPyr-P,N) (14); [14] ≈ 10-6 M in CHCl3 ........................................................................... 101  Figure 5.4  ORTEP view of 14. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability.............................. 103  Figure 5.5  Emission spectra for 14 in CH3CN/H2O; at t = 0 (—) and t = 1 hr (—); [14] ≈ 10-6 M; ex = 362 nm; em = 428 nm ...................... 109  Figure 5.6  Excitation (—) and emission (—) spectra of 1-aminopyrene in CH3CN/H2O. Excitation (---) and emission (---) spectra of 1-aminopyrene in CH3CN/H2O sparged with SO2; [1-aminopyrene] ≈ 10-6 M; ex = 362 nm; em = 428 nm........................ 110  Figure 5.7  1  Figure 5.8  UV-Vis absorption spectrum of PdCl2(PNHPyr-P,N) (15); [15] ≈ 10-6 M (—) and [15] ≈ 10-5 M (—) in benzene ........................... 114  Figure 5.9  Excitation (—) and emission (—) spectra of 15; [15] ≈ 10-6 M; ex = 340 nm; em = 374 nm in benzene ................................................. 115  Figure 5.10  Excitation (—) and emission (—) spectra of pyrene; [pyrene] ≈ 10-6 M; ex = 339 nm; em = 373 nm in benzene ................... 116  H NMR spectrum of PdCl2(PNPyr-P,N) (14) in CDCl3; T = 300 K; f = 300 MHz ............................................................................................ 100  H NMR spectra of PdCl2(PNHPyr-P,N) (15) in CDCl3; T = 300 K; f = 300 MHz ......................................................................... 113  xi  List of Schemes Scheme 4.1  Syntheses of PNPyr (12) and PNHPyr (13) .............................................. 78  Scheme 5.1  Synthesis of PdCl2(PNPyr-P,N) (14) ........................................................ 99  Scheme 5.2  Proposed reactivity of 14 with SO2 (g) ................................................... 106  Scheme 5.3  Proposed reactivity of 14 with SO2 (g) in CH3CN/H2O upon hydrolysis of the phosphine pyrenyl imine ligand .................................. 111  Scheme 5.4  Synthesis of PdCl2(PNHPyr-P,N) (15) ................................................... 112  Scheme 5.5  Proposed reaction of 15 with HBF4 in CH3CN....................................... 117  xii  List of Symbols and Abbreviations Abbreviation  Description   a A A/A` Å A1g  unit cell parameter (X-ray crystallography) unit cell parameter (X-ray crystallography) analyte or absorbance arbitrary prefactor (see page 20) Ångstrom symmetry label (refers to totally symmetric irreducible representation) symmetrical vibronic energy level (CH2CH2CH2N)6, cyclic polyamine for solubilizing K+ unit cell parameter (X-ray crystallography) unit cell parameter (X-ray crystallography) non-symmetrical vibronic energy level non-symmetrical point group non-symmetrical point group unit cell parameter (X-ray crystallography) degrees Celsius cis, cis, trans – disposed centimeter cyclooctadiene (CH2CH2CH2O)6, cyclic polyether for solubilizing K+ chemical shift (ppm) doublet (NMR) degree excited dimer dihedral point group density (X-ray crystallography) dimethyl sulfoxide energy difference between the HOMO and LUMO enthalpy change extinction coefficient (M-1 cm-1) excimer (excited state dimmer) elemental analysis electronic energy transfer electron impact electrospray electrospray ionization ethyl acetate ethanol fluorescence or fluorophore excited fluorophore Fourier transform infrared spectroscopy  ag aza-18-crown-6  b b1g 1 B3u 1 B2u c o C cct cm COD 18-crown-6  d deg D* D2h Dcalc DMSO Dq H  E* EA EET EI ES ESI EtOAc EtOH F F* FTIR  xiii  g  h hr h HOMO HPLC in vacuo I IC IR J kcal  em ex  L 1 La LUMO  M s m M M+ MeOH min mg MHz mL mm mmol mM mol Mo-K m.p. MS m/z   n nm NMR ns  gram or gaseous unit cell parameter (X-ray crystallography) hour hour photon highest occupied molecular orbital high performance liquid chromatography under vacuum intensity internal conversion infrared spectroscopy coupling constant kilocalorie wavelength (nm) emission wavelength (nm) excitation wavelength (nm) change in wavelength (nm) ligand most intense absorption band lowest unoccupied molecular orbital linear absorption coefficient (X-ray crystallography) micromolar microsecond multiplet (NMR) molarity or transition metal ion molecular ion (obtained by the loss of an electron from the molecule) methanol minute milligram megahertz milliliter millimeter millimole millimolar mole monochromic radiation (X-ray crystallography) melting point mass spectroscopy or mass spectrometer mass-to-charge ratio IR stretching frequency (cm-1) refractive indices non-bonding orbital or spacer length nanometer nuclear magnetic resonance nanosecond xiv  OTf  * P PA PE PM Ph Py Py* PET PNPyr PNHPyr PO POC4Pyr P(=O)OC4Pyr POL ppm PR3 Oh m R R(Fo)a/Rw(Fo)b R(Fo2)a/Rw(Fo2)b RT    * s S0 S1 S2 SPC ST m t T T1 tcc TLC TMS TOF ttt UV V vis  trifluoromethane sulfonic acid (CF3SO3) p-type bonding orbital p-type anti-bonding orbital phosphorescence ratio of absorption intensity of most intense band to absorption intensity of adjacent minimum at shorter wavelength peak-to-valley ratio monitored at excimer emission peak-to-valley ratio monitored at monomer emission phenyl pyrene excited pyrene photo-induced electron transfer 2-diphenylphosphino-N-(1-pyrenyl)benzylidineimine 2-diphenylphosphino-N-(1-pyrenyl)benzylidineamine o-(diphenylphosphino)anisole 4-{2-(diphenylphosphino)phenoxy}butylpyrene 4-{2-(diphenylphosphino)phenoxy}butylpyrene oxide hemilabile phosphine ether ligand parts per million tri-alkyl phosphine octahedral coordinate environment quantum yield of monomer ratio or alkyl group residuals refined on F (X-ray crystallography) residuals refined on F2 (X-ray crystallography) room temperature s-type bonding orbital s-type anti-bonding orbital singlet (NMR) or seconds singlet ground electronic state singlet first excited electronic state singlet second excited electronic state single photon counting singlet-triplet intersystem crossing singlet lifetime of monomer triplet (NMR) or time temperature triplet first excited electronic state trans, cis, cis - disposed thin layer chromatography trimethylsilane time-of-flight trans, trans, trans - disposed ultraviolet unit cell volume visible  xv  VR  X z Z      vibrational relaxation measure of fit of series of data halogen or other element (O, P, N) intermolecular separation distance Z value (X-ray crystallography)  xvi  Acknowledgements I would like to thank my supervisor, Prof. Mike Wolf, for the opportunity to work on this project and for all of his guidance and support. I would also like to thank Prof. Mike Wolf, and Prof. Chris Orvig for providing me the opportunity to complete my master’s thesis after an extended leave of absence. In addition, I would like to thank all of the members of the Wolf group for all of their support and advice. In particular, I would like to thank Dr. Tracey Stott, Lisa Thorne, Carolyn Moorlag, and Dr. Agostino Pietrangelo for all of their assistance. A huge thank you to all of the departmental support staff, including Ms. Marietta Austria for their help with NMR, the Maclachlan group for the use of the UV-vis spectrometer; and Dr. Brian Patrick for solving the solid-state structures presented in this thesis. Lastly, I would like to thank the Microanalytical Services for running the EA and MS samples. I am also extremely grateful to my parents, Judy and Dennis Murphy, my sister, Shannon Matkovich, Owen Remers, and my brother, Trevor Matkovich, whose unwavering love and support allowed me to persevere in order to complete my master’s work.  xvii  Introduction 1.1  Molecular sensors and the modular design approach Chemosensors are molecule-based sensors that are able to bind selectively and  reversibly an analyte of interest with a concomitant change in one or more measurable properties.1 Electrochemical, magnetic, mass spectrometric, or optical (absorption or luminescence) changes may be measured.2  The development of chemosensors has  generated special interest due to their widespread applications in chemistry, biology, biochemistry, cell biology, materials science, and clinical and medicinal sciences.1 Fundamentally, a molecular sensor is derived from the coupling of a ligandreceptor reaction to a signal transducer.2 A signaling moiety acts as a signal transducer by converting the recognition event into an optical signal expressing a change in the photophysical properties in the fluorophore; the recognition moiety is responsible for the selectivity and efficiency of binding in the ligand receptor reaction.2 The modular design approach to chemosensors incorporates a receptor, at which the analyte binds; a reporter, where a measurable property change occurs in the presence and absence of analyte; and a spacer, which joins the receptor and the reporter together (Figure 1.1). A major advantage of this design approach is the ability to rationally adjust properties of the sensor by changing the molecular structure of any of the components.1  1  Spacer Receptor  +A M  M A -A  Reporter  Figure 1.1 Schematic depiction of a modular design where the receptor, M, is linked to the reporter through the spacer. M = metal, A = analyte. Two examples in which the modular design approach are demonstrated, are shown in Figures 1.2 and 1.3.5,6 Upon complexation of carbon monoxide to the rhodium metal center in the chemosensor shown in Figure 1.2 a change in the visible and IR spectra of the molecule occurs as well as a change in the reduction potential of the metal center.4 In the case of the chemosensor shown in Figure 1.3, complexation of nitrogen oxide to the cobalt metal center releases two of the nitrogen atoms from the metal center and increases the proximity of one dansyl unit to the metal center resulting in a significant increase in luminescence.5,6 A wealth of examples of luminescent and nonluminescent molecular chemosensors based on the modular design approach exist in the literature and are summarized in well-presented reviews on the topic.1,3,7-13  2  +  OCH3  +  H3CO OCH3  H3CO  Ar' P  Ar'  Rh  CO  Ar' + CO  O  Ar'  Rh  CO  H3CO  - CO H3C  P OC  P Ar'  Ar'  P  Ar'  Ar'  Ar' Ar'  Figure 1.2 Chemosensor in which the Rh metal center acts as the receptor; and the phosphine-ether ligand as well as the Rh metal center act as reporters.4 Me2N  Me2N  Me2N  SO2 N NO Co N NO  2 NO SO2  SO2  N  NMe2  N Co  N  N  N  strong luminescence  weak luminescence Figure 1.3  HN SO2  Chemosensor in which the Co metal center acts a the receptor, the dansyl  moieties as the reporters, and diamine acts as the spacer.5,6 Luminescence is an attractive reporter mechanism due to its high sensitivity (single molecule detection is possible), quick response time, and direct real-time detection with both spatial and temporal resolution.3 The properties of the fluorescent  3  lumophores may also be tuned to achieve a specific response. In order to maximize the response, fluorescence should be either ON-OFF or OFF-ON (Figure 1.4).  Figure 1.4  Schematic representation of (a) an OFF-ON chemosensor and (b) an ON  OFF chemosensor; M = metal, A = analyte, F = fluorophore. The quenching of the fluorescence of aromatic hydrocarbons by transition metal ions is a well-known phenomenon.14 Transition metal complexes have been designed and synthesized such that prior to analyte exposure, the fluorescence of the fluorophore is quenched by an open-shell transition metal via photo-induced electron transfer (PET) and/or electronic energy transfer (EET) or the heavy atom effect.14-18 Upon addition of the analyte the fluorophore is displaced from the metal center, and as a result, ligand fluorescence is revived.  4  1.2  A brief introduction to photoluminescence theory Photoluminescence can be defined as a phenomenon in which a molecule is  excited by electromagnetic radiation to a state in which it emits light.19 Figure 1.5 provides a summary of the photophysical processes that occur during and after electronic excitation.20 When a molecule absorbs electromagnetic radiation (A), its energy increases by an amount equal to the energy of the absorbed photon.19 Consequently, an electron is promoted from the ground state (S0), an occupied bonding or non-bonding orbital (, or n), to an unoccupied or antibonding orbital ( or ), referred to as the excited state (S1 or S2).20 Each electronic state has several vibrational levels associated with it. For simplicity it is assumed that the vibrational level occupied by the electron in the ground state is the lowest level; however, the electron may be promoted to one of several vibrational levels of the excited state.19  5  S2 VR IC  S1 VR ST  T1 VR  A  IC  F ST  P  S0 VR  Figure 1.5  Photophysical processes that occur during and after electronic excitation.  (Adapted from reference 20) Vibrational relaxation,VR, is the process by which an electron in a higher vibrational level of any given electronic state thermally descends to the lowest vibrational level of that electronic state.21 1.2.1 Relaxation processes from singlet excited states Internal conversion, IC, occurs when the higher vibrational levels of the lower electronic state overlap with the lower vibrational levels of the higher electronic state. In this case, the upper and lower electronic states are in a transient thermal equilibrium which permits IC to occur, populating the higher vibrational levels of the lower electronic  6  state.21 IC can occur between the first excited state and the ground state, the second excited state and the first excited state, etc. Fluorescence, F, offers another relaxation pathway from the first excited singlet state, S1, to the ground state, S0. It is of special interest in the development of luminescent chemosensors as it is a radiative electronic transition. The energy released from the relaxation of an electron from the lowest vibrational level of the first excited state to any of the vibrational levels of the ground state results in visible or UV light whose frequency is directly related to the energy gap between the two states.19 Fluorescence competes with the nonradiative decay mechanisms (IC and ST) and its occurrence is dependent on the energy difference between the upper and lower states as well as the number of vibrational levels associated with each electronic state.20 Examples of this are polyaromatic hydrocarbons, such as pyrene and anthracene, which are rigid molecules with relatively few vibrational degrees of freedom. As a result, there is less vibrational overlap between the first excited state and the ground state, IC is not as efficient, and these molecules are highly fluorescent.20 1.2.2 Relaxation processes from triplet excited states States having zero spin angular momentum are defined as singlet states.22 When an electron is promoted from an occupied orbital to a higher energy, previously unoccupied orbital, it usually retains its original spin; therefore, an electron from a singlet ground state (S0) is promoted to a singlet excited state (S1 or S2).20 Triplet states occur when there are two unpaired electrons, with three possible orientations for the spin angular momentum vector in an external magnetic field.22 There is less electronic repulsion in any given triplet state than in the singlet state of the same electron  7  configuration.20 Figure 1.5 shows the first excited triplet state, T1, at lower energy than the corresponding singlet state, S1. Singlet-triplet intersystem crossing, ST, occurs when there is overlap between the vibrational levels of the singlet and triplet excited states. The mechanism by which the triplet state may be populated by the excited singlet state is similar to IC.21 Although singlet-triplet intersystem crossing is a forbidden transition, efficient ST results from spin-orbit coupling which allows the transition to occur.20 This process is often referred to as the ―heavy atom effect‖, as spin-orbit coupling is more pronounced for heavy atoms.19 From the excited triplet state, the electron may relax to the ground state via two processes, non-radiative ST or the radiative process phosphorescence.21 Phosphorescence is longer-lived than fluorescence and is sometimes described as an afterglow after the exciting source is turned off.22 1.3  Non-luminescent deactivation of the first excited singlet state The two most prominent quenching pathways in a luminescent chemosensing  scheme are photoinduced electron transfer (PET), and electronic energy transfer (EET). 23 A metal can quench an excited fluorophore via EET if the metal possesses empty or partially-filled d-orbitals of appropriate energy. Deactivation occurs through a double electron exchange followed by rapid non-radiative relaxation of the excited metal ion to the ground state (Figure 1.6). Rare examples of chemosensors based on EET involve Cu(I) in an elongated octahedral environment.23  8  F* Figure 1.6  M  F  M*  Schematic representation of an EET processes involving (a) a double  electron exchange mechanism between an excited fluorophore, F, and a d9 metal, M, in an elongated Oh coordinate environment giving rise to (b) the ground state configuration of F and an excited M centre.23 PET is the most common quenching mechanism in molecular sensors. There are two ways in which electron transfer may occur to suppress radiative relaxation of the excited fluorophore (F*). If the metal (M) LUMO lies between the fluorophore (F) HOMO and LUMO electron transfer from the F LUMO to the M HOMO can occur (Figure 1.7a). In the case where the M HOMO lies between the F HOMO and LUMO, electron transfer from the M HOMO to the F HOMO (Figure 1.7b) is possible.14 Both processes are non-radiative such that the fluorescence from the fluorophore is quenched. When an analyte binds, the energies of the metal d-orbitals should change such that PET processes cannot occur and fluorescence is revived (Figure 1.7c). An important point to note is the dependence of quenching on the distance between the metal center and fluorophore. In order for PET to occur, the receptor and reporter must be close enough that orbital overlap occurs.  9  F* Figure 1.7  M  F*  M  F*  M  Schematic representation of PET processes – (a) electron transfer from F  LUMO to M LUMO, (b) electron transfer from M HOMO to F HOMO, and (c) no electron transfer in presence of analyte.14 1.4  Fluorescence sensors based on photo-induced electron transfer (PET)  1.4.1 Basic design for simple PET sensors The most common PET sensors involve cation receptors consisting of aliphatic or aromatic amines tethered to aromatic hydrocarbons.3 PET can take place from the amino groups to the aromatic hydrocarbons causing fluorescence quenching of the hydrocarbons. Upon cation binding the lone pairs on the amines are no longer available for PET and the hydrocarbon fluorescence is revived. Figure 1.8 shows an example of a simple PET sensor containing an aza-crown ether tethered to an anthracene moiety through a methyl spacer. Upon binding of K+ in methanol the fluorescence quantum yield increases from 0.003 to 0.14.3  10  O  O  O O N  O  Figure 1.8 A PET sensor in which anthracene fluorescence is revived upon binding K+ in methanol.3 Similar structures can bind transition metal ions, however, the PET mechanism differs from that described above for cations. Transition metal ions exhibit redox activity and electron transfer can occur from the fluorophore to the bound metal ion or vice versa.3 Figure 1.9 shows a PET sensor in which the crown contains four sulfur atoms tethered via an ester to anthracene. The thiacyclam has a strong affinity for Cu II.3,23 Upon CuII binding, fluorescence quenching arises from a PET from the anthracene moiety to the metal center involving the CuII/CuI couple.3,23 Examples of sensors containing polyamine chains tethered to anthracene have been shown to bind CuII and NiII and favour oxidation to the trivalent state. The PET mechanism in this case involves an electron transfer from the reducing divalent metal center to anthracene.3 Cryptand based receptors also bind cations favourably and have been exploited in PET sensor designs.3,14 Further examples of PET sensors involving transition metal ions are presented in the literature.1,3,14,23  11  S  S  S  S  O  O  Figure 1.9 PET sensor in which fluorescence quenching of anthracene involves CuII/CuI couple.3,23 1.4.2 PET sensors based on excimer formation Fluorophores like anthracene and pyrene can form excimers when an excited molecule closely approaches another molecule during the lifetime of the excited state. 3 An excimer is a dimer which is associated only in an electronic excited state but is dissociated in its ground state.24 Figure 1.10a shows a PET sensor consisting of a diazacrown ether with two pendant pyrene groups. This particular sensor preferentially binds K+ and Ba2+. Upon cation binding a large change in the monomer to excimer fluorescence intensity ratio occurs, with the excimer band decreasing in intensity. Overall, there is a concomitant increase in the overall fluorescence emission as a result of the reduction of PET from the nitrogen atoms to the pyrene moieties.3 Figure 1.10b shows a diatopic receptor that upon binding of ammonium ions in methanol the monomer-like emission increases 10-fold and the excimer emission band completely vanishes because the two anthracene rings are separated from each other.3 In the case of this sensor, the excimer band is due to intramolecular excimer formation  12  which is why the band completely vanishes when the anthracene moieties are no longer in close proximity. O  O  N  O O  N  O  N  N  O  O  O  O  O  N  a  O  N  O  Figure 1.10  O  O  O  O  b  PET sensors involving excimer formation consisting of: (a) a diazacrown  ether with two pendant pyrene moieties; (b) a diatopic receptor incorporating two anthracene units.3 Another example of a PET sensor in which excimer emission plays a role is shown in Figure 1.11. Binding of Zn2+ alters the spatial geometry of the pendant naphthalene groups affecting the ratio of monomer to excimer emission.14 This sensor is also known to bind Cd2+.3 In both cases the excimer band decreases in intensity upon complexation. The distinct advantage of PET sensors is the very large change in fluorescence emission. That is, the ability to design systems in which the fluorescence is completely quenched and then revived, ―OFF-ON‖ system, or vice versa, ―ON-OFF‖ system. In PET sensors the changes in fluorescence quantum yield are accompanied with proportional  13  changes in the excited state lifetime,3 providing another tool to investigate and determine the photophysical processes occurring when designing a chemosensor.  H N  H N N  N O  O O  O N  N  N H  N H  Figure 1.11 PET sensor involving excimer formation where the excimer band decreases upon binding of Zn(II) and Cd(II).3,14 1.5  Pyrene as a fluorophore Pyrene (Scheme 1) shows many properties that make it suitable as an effective  fluorescence probe. Mainly, the pyrene monomer has a long singlet lifetime (m = 450 ns, m = 0.60 in cyclohexane), and shows efficient formation of excimers.21 In addition, extensive studies on the photophysics of pyrene have been carried out on the electronic spectrum and state assignments, the kinetic details of excimer formation, the formation and kinetics of the excited states, photoionization, delayed luminescence, spectral pressure effects, and quasilinear spectra.21 The vibronic band structure of pyrene monomer emission also shows sensitivity to its environment.21,24,25 Pyrene monomer emission typically occurs between 380-400 nm and shows a characteristic colour indigoblue.  14  Scheme 1 - The structure of pyrene. 1.5.1 Vibronic band structure of pyrene Pyrene is one of the few condensed aromatic hydrocarbons that shows significant fine structure in its monomer fluorescence spectra in solution phase.25 The vibronic band structure characteristic of pyrene monomer emission in the absence of any solvent interactions is governed by the relative positions of the potential energy surfaces of the excited singlet states relative to the ground singlet state and by the Franck-Condon principle.25 The pyrene molecule belongs to the point group D2h such that its ground state electronic configuration is the totally symmetrical A1g state. The first (S1) and second (S2) electronic excited states have been assigned 1B3u and 1B2u and are polarized along the short and long axis of the molecule, respectively, making the first singlet absorption 1B3u  A1g.25 However, the S1 fluorescence of pyrene shows mixed polarization which has been interpreted as mixing of the first and second electronic excited states; that is, mixing of S1, the short-axis polarized state, S2, which is polarized along the long-axis. This gives rise to vibronic transitions that correspond to allowed b1g vibrations and forbidden ag vibrations, one of which is the 0-0 band.25  15  It should be noted here that forbidden vibronic bands shows significant intensity enhancement in polar solvents, while the allowed b1g transitions, specifically peak 3, show minimal intensity variation with changes in solvent polarity. The major contributions to vibronic band intensities is due to specific solute-solvent, dipole-dipole coupling arising from the strong dipole character of the excited singlet states of pyrene. Variations in ratio of the vibronic bands intensities of pyrene have been used to accurately determine critical micelle concentration and to investigate the extent of water penetration into micellar systems.25 1.5.2 Pyrene excimers The strong dipole character and long lifetime of the excited singlet states of pyrene facilitate the efficient formation of excimers. The steady-state fluorescence emission of pyrene excimers appears as a broad, structureless band, centered between 480-500 nm. Birks first demonstrated this by increasing the concentration of pyrene such that the quenching of pyrene monomer emission was accompanied by the appearance of a broad structureless band with blue-green emission.21 In this case, the structureless emission band is due to the fluorescence of excited dimers. The term excimer was introduced to describe an excited dimer which is associated in an electronic excited state and dissociated in the ground state. The formation of a pyrene excimer requires an excited molecule to come in contact with another molecule in its ground state within the excited state lifetime. In order for this to occur the pyrene molecules must be sufficiently far apart such that excitation is localized on one of the molecules, then diffusion of the molecules allows for an encounter between an excited pyrene and a ground state pyrene. Upon relaxation, the pyrene molecules are dissociated.  16  This traditional definition of an excimer is often referred to as a dynamic excimer. In contrast, the term static excimer refers to pre-associated pyrene molecules, that show no evidence that they are separated when light is absorbed, and relax to an associated ground state.24 A schematic representation of the potential energy processes that occur upon pyrene excimer (E*) formation in the absence of ground-state pre-association is shown in Figure 1.12(a). At large separations, i.e. z  10 Å in the ground state and in the excited state the pair is invariant to changes in separation distances. At small separation (i.e. 4 Å) the energy of the ground state pair rises rapidly because of molecular repulsion. A minimum on the excited state potential energy surface occurs as the ground state pyrene (Py) and the excited pyrene (Py*) approach and bonding between them occurs. Experimentally, the electronic stabilization of the pyrene excimer is substantial, H = 10 kcal/mol.24 Pyrene excimer emission is broad and structureless since the excimer dissociates upon deactivation of the excited state before it completes a vibrational cycle. Figure 1.12b illustrates the potential energy processes present when ground state association of pyrene molecules is present. Here, the ground state surface possesses a minimum at a separation distance intermediate between the electronically isolated pyrene molecules and the onset of -orbital repulsion (3 Å ≤ z ≤ 10 Å).24 The excited state surface presents a double minimum, with greatest stabilization occurring with the formation of E*, and a shallow minimum at greater separation distance corresponding to the excited dimer (D*). Emission from D* is structureless, but unlike E* it leads to an associative state as discussed above.  17  In terms of dynamic and static excimers, introduced above, the processes occurring in Figure 1.12a would describe those of ―dynamic‖ excimers (E*) and Figure 1.1.2b describes the processes of ―static‖ excimers (D*).  Figure 1.12  Schematic depiction of potential energy diagrams for pyrene excimer  formation in (a) the absence of ground state association, and (b) the presence of ground state association.(Adapted from reference 24) 1.5.3 Spectroscopic detection of pyrene pre-association in the ground state The steady-state fluorescence spectrum, of pyrene excimer emission gives very few clues to the actual mechanism of excimer formation. Pre-associated pyrene molecules cannot be excited separately without exciting electronically isolated pyrene molecules (or vice versa), as a result static and dynamic excimers are indistinguishable in a steady-state emission spectrum. However, the fluorescence intensity of excimer emission will vary with varying excitation wavelength, therefore, the emission intensity  18  monitored at the monomer excitation versus that monitored at the excimer excitation can provide insight to the presence of pre-associated chromophores. Alternatively, the absorption, excitation, and time-dependent fluorescence spectra provide key photophysical parameters in determining the presence of pyrene preassociation in the ground state. 1.5.3.1 Absorption spectrum The broadening of absorption bands is a clear indication of pyrene pre-association in the ground state. A good measure of this broadening is the ratio, PA, of the absorption intensity of the most intense band to the absorption intensity of the adjacent minimum at shorter wavelength. For 1-substituted pyrenyl compounds the PA value is usually greater than 3.0 for the 1La band in the absence of pre-association and decreases in relative proportion to extent of preassociation.24 The broadening of absorption bands is often accompanied by small red shifts in maxima positions and by the decrease of extinction coefficients. This is illustrated by Winnik in reference 24. 1.5.3.2 Excitation spectrum Excitation spectra can provide convincing evidence for pyrene pre-association in the ground state. Spectra monitored at monomer emission versus excimer emission show similar features but cannot be superimposed. The spectrum monitored at excimer emission is red-shifted (1-4 nm) compared to that monitored at monomer emission. In addition, the bands monitored at excimer emission are broadened.24 The peak-to-valley ratio PE/PM for the 0-0 transitions monitored at excimer emission and monomer emission respectively, will be less than one when pre-association  19  occurs. Also, the shift in wavelength, max(excimer) – max(monomer)  0 when preassociation occurs. These parameters can be correlated by normalizing each spectrum at their respective peak maxima and then plotting the intensity of the excimer scan versus that of the monomer scan.24 1.5.3.3 Time-dependent fluorescence spectrum In a time-dependent fluorescence measurement the emission intensity of the excited species is monitored as a function of time after an excitation pulse. Equation 1 gives the intensity of excimer emission as a function of time.24 IE(t) = Ae-t/ – A'e-t/'  (1)  If excimer formation is dynamic, that is, molecules are electronically isolated in the ground state, then the concentration of excimer in solution at the time of the pulse, t = 0, is equal to zero. Thus, the time-dependent fluorescence profile will show a rising component with a negative prefactor (-A), corresponding to excimer formation in solution, and a decaying component with a positive prefactor (A'), corresponding to excimer relaxation. In this case the ratio, R = A/A' = 1.0.24 For systems in which excimer is the result of pre-associated molecules (i.e. static excimers), time-dependent fluorescence measurements show no rising component in the excimer profile when the experiment is carried out on the typical nanosecond time scale, with 1-3 ns being the lower limit of detection.24 Where both types of excimers occur the time-dependent fluorescence profile will show a rising and decaying component as in the case of dynamic excimers, however, the ratio, R will vary from a value of 1.0.  20  1.5.4 PET sensors containing pyrene as the fluorophore Pyrene  derivatives  have  found  numerous  applications  in  luminescent  chemosenors.3,14,23 One example of a ratiometric sensor containing pyrene-based chromophores is given in Figure 1.10a, where in the presence of cation the excimer to monomer emission ratio changes drastically.3 Pyrene derivatives can interact both intermolecularly and intramolecularly. The example in Figure 1.10b shows a sensor in which intramolecular excimers are formed. In general, intermolecular excimer formation is negligible at concentrations less than 1  10-5 M.21 Thus, excimer emissions seen at low concentrations (1  10-5 M) is due to intramolecular excimer formation. Pyrenyl groups have also found use in ―ON-OFF‖ sensors. A notable example reported by Ji et al., involves an alkali metal sensor containing pyrene covalently bonded to an aza-18-crown-6 via vary hydrocarbon spacer lengths (Figure 1.13).26 It was shown that PET was most efficient when n ≤ 3.  O  (CH2)n  O  N  O  Figure 1.13  O  O  An alkali metal sensor containing pyrene in which PET is most efficient  when n  3.26  21  1.6 Transition metal ion based chemosensors Thus far PET sensors that incorporate alkali metal ions as well as transition metal ions have been discussed. However, examples of sensors have been reported that are based on transition metal ions where the metal center serves as the receptor for analyte binding.28-32 In most of these examples fluorescence quenching is achieved through spinorbit coupling (the heavy atom effect), or PET. The basic design principle utilizes the fact that transition metal ions do not exist in solution with empty coordination sites. One advantage of analyte coordination to the metal center is that metal-ligand interactions are generally significantly stronger than hydrogen bonding and other van der Waals interactions.27 In order for analyte coordination to occur, the metal center must have at least one ligand that is substitutionally labile and the analyte must have a greater affinity for the metal (i.e. a larger binding constant) than the labile ligand. In the case of the dirhodium tetracarboxylate complex [Rh2(-O2C(CH3))4(L)2] (L = dansyl-imidazole or dansyl-piperazine) the labile ligand (L) is also the fluorophore. In the absence of analyte these complexes are only weakly fluorescent due to quenching of the dansyl moieties via the heavy atom effect from the rhodium metal. Upon coordination of the analyte, NO, the fluorophores are released from the coordination sphere of the metal and fluorescence increases 15-fold.31 1.6.1 Utilization of hemilabile ligands in transition metal ion based sensors Polydentate ligands containing two or more chemical functionalities that can bind one or more metal centers have been of particular interest for the investigation of  22  reversible coordination, stoichiometric and catalytic activation, and in the transport of small molecules.33 Recently, incorporation of these types of ligands into the receptor moiety of molecular sensors has become increasingly interesting. The functionalities of the ligands are chosen to be different in order to promote differential binding to the metal center(s). Polydentate ligands of this nature containing one donor that is substitutionally labile and one or more donors that strongly bind to the metal center(s) are known as hemilabile ligands.33 The labile donor is easily substituted allowing for efficient analyte binding to the metal center. In addition, the ligand does not leave the coordination sphere of the metal center which allows for the promotion of reversible reactions in which the original complex is regenerated.33,34 Both the chemosensors shown in Figure 1.2 and Figure 1.3 incorporate hemilabile ligands for analyte sensing.4,5,6 The chemosensor developed by Lippard binds two equivalents of NO by displacement of one of the imine functionalities and one of the amine functionalities (Figure 1.3). The chemosensor investigated by Dunbar (Figure 1.2), which reversible reacts with CO, incorporates a phosphine ether ligand, where the ether moiety is labile while the phosphine donor is substitutionally inert. A wide variety of hemilabile phosphine ether ligands have been reported in the literature.34,35 One example of a colourimetric sensor that incorporates a phosphine ether ligand  involves  the  ruthenium(II)  complex,  RuCl2(PO)2  (PO  =  o-  (diphenylphosphino)anisole) that binds CO by displacement of the oxygen atoms from the ruthenium metal center (Figure 1.14).36  23  CH3 Ph2 Cl P  Ph2 P  O + 2 CO  OC  Ru O  Cl  CH3  Cl  PPh2  Ru O  Ph2P  CH3  Cl  CO  O H3C  Figure 1.14  Reactivity of RuCl2(PO)2 (PO = o-(diphenylphosphino)anisole) towards  CO.36 1.7 Ruthenium halide complexes containing a hemilabile phosphine pyrenyl ether ligand Based on the design principles presented throughout this chapter, a series of ruthenium (II) complexes incorporating a phosphine ether ligand with a pendant pyrenyl moiety,  tcc-[RuX2(POC4Pyr-P,O)2]  (X  =  Cl,  Br,  I;  POC4Pyr  =  4-{2-  (diphenylphosphino)phenoxy}butylpyrene) were previously developed by our group (Figure 1.15). The metal center acts as the receptor via the labile oxygen of the chelating phosphine pyrenyl ether ligand, and luminescent reporting is provided by the pyrene moiety. In  a  preliminary  communication  our  group  demonstrated  that  tcc-  RuCl2(POC4Pyr-P,O)2 (POC4Pyr = 4-{2-(diphenylphosphino)phenoxy}butylpyrene) (3) reacts with CO as shown in Figure 1.15.37 It was found that CO displaces both of the weakly coordinated ether ligands to form the complex ttt-RuCl2(CO)2(POC4Pyr-P)2 (6).37 The reaction with CO is accompanied by an immediate color change of the solution and the appearance of excimer emission.37 The initially formed trans-dicarbonyl complex  24  undergoes isomerization after excess CO is removed from solution to form cctRuCl2(CO)2(POC4Pyr-P)2 (7).37 Complex 3 was designed such that in the absence of CO the pyrene moiety would be in close proximity to the metal center and quenching of pyrene emission could occur via EET, PET, or the heavy atom effect.37 Upon complexation of CO the pyrene moiety should be displaced far enough from the metal center that its fluorescence would be revived.37 Unfortunately, pyrene monomer fluorescence was observed prior to exposure to CO for 3.  Ph2 X P Ru  Ph2 P  O  O  X  Pyr(H2C)  (CH2)4Pyr  3 X = Cl 4 X = Br 5X=I + 2 CO  O  X  (CH2)4Pyr  PPh2  OC  PPh2  X  Ru Ph2P Pyr(CH2)4  O  O  X Ru  CO  Ph2P  X Pyr(CH2)4  CO CO  O  Isomerization 6 X = Cl 7 X = Br 8X=I  9 X = Cl 10 X = Br 11 X = I  Figure 1.15 Reactivity of tcc-RuX2(POC4Pyr-P,O)2 toward CO.37  25  (CH2)4Pyr  One possible way of promoting fluorescence quenching is by altering the energies of the metal d-orbitals through substitution of the chloro ligands for other halides. The effect of changing the halide ligand in [tcc-RuX2(POC4pyr-P,O)2] (X = Cl (3), Br (4), I (5)) on the luminescence behavior with respect to reaction with CO was preliminarily investigated in our lab.38 The reactivity of 4 and 5 resembles that of 3 (Figure 1.15). Complexes 4 and 5 also display a visible colour change upon reaction with CO as seen with 3. Unfortunately, both complexes 4 and 5 also show pyrene monomer emission before reaction with CO. However, the amount of excimer emission observed after reaction of CO appears to vary depending on the halide ligand.38 Experiments to determine whether the excimer emission observed for complexes 6-8 and 9-11 was due to pre-associated pyrene molecules in solution, were also carried out. It was concluded that there was some pyrene pre-association in the ground state, however, further experiments, such as time dependent fluorescence, were recommended to determine definitively whether static or dynamic excimer processes were occurring.38 1.8  The scope of this thesis Complexes 3-5 all show pyrene monomer emission prior to CO exposure, and  therefore, do not act as ―OFF-ON‖ sensors. However, complexes 6-8 appear to show varying degrees of excimer emission, at similar concentrations, after reaction with CO. Absorption, steady-state fluorescence, and time-dependent fluorescence experiments were carried out under inert atmosphere in order to confirm whether pyrene preassociation was occurring in the ground state (Chapter 3). In addition, these experiments allowed us to infer whether the difference in intensity in the excimer emission observed for complexes 4-6 was due to quenching of excimer emission.  26  It was found that complexes 3-5 and 4-6 showed ligand dissociation in solution, thus quantitative results could not be obtained. Preparation and characterization of ligand oxide, P(=O)OC4pyr (2), by 1H NMR spectroscopy, 31P{1H} NMR spectroscopy, as well as the absorption, steady-state fluorescence, and time-dependent fluorescence spectra provided a tool for the observation of ligand dissociation of 3-5 and 4-6 in solution. The instability of these complexes in solution led to the investigation of possible new sensors based on a similar framework. A palladium complex with a phosphine imino pyridyl ligand that reacts with CO via replacement of the labile pyridine group has been reported by Vrieze and coworkers.39 They also reported that the imine was labile. Based on this chemistry, palladium complexes that incorporate phosphine pyrenyl imine and phosphine pyrenyl amine ligands were developed for use as chemosensors and are presented in this thesis.  27  Chapter 2 The Phosphine Pyrenyl Ether (1) and Its Oxide (2) P(=O)OC4Pyr 2 was prepared and characterized as this compound was a possible product of ligand dissociation (see Chapter 3). Although the absorption and emission properties of 1 and 2 are very similar and do not provide a tool to quantify the amount of dissociation occurring in the ruthenium complex solutions (see Chapter 3), the difference in the 31P{1H} NMR shifts of 1 and 2 does allow for detection of the presence of 2 and can be used to show that ligand dissociation does occur from the Ru complexes in solution. 2.1  Absorption and emission of 1 and 2 The synthesis of the phosphine pyrenyl ether (POC4Pyr) 1 was previously  reported by our group.37 The oxide (P(=O)OC4Pyr) 2 was synthesized by stirring 1 with H2O2 in a 1:1 mixture of dichloromethane/acetone. Both 1 and 2 (see Chart 2.1) were characterized by  1  H and  31  P{1H} NMR spectroscopies, elemental analysis, mass  spectrometry, UV-vis and fluorescence spectroscopies. Chart 2.1  P  P O  O  O  POC4Pyr 1  P(=O)OC4Pyr 2  28  The UV-vis absorption spectra of 1 and 2 are very similar (Figure 2.1a and 2.1b). The structured absorptions in the UV region arise predominantly from pyrene-based -* transitions.21 Weaker absorptions from electronic transitions localized on the non-pyrenyl portion of the molecule are buried beneath the strong pyrenyl -* bands.37 The PA values, defined as the ratio of the absorption intensity of the 1La band (345 nm) to that of the adjacent minimum at shorter wavelength (337 nm), for 1 and 2 are 2.8 ± 0.1 and 2.9 ± 0.1, respectively.24 PA values less than three indicate pyrene pre-association in the ground state, where the further the value deviates from three the larger the degree of preassociation.24 The PA values for 1 and 2 are slightly less than three, indicating a very small amount of possible pre-association of the pyrene moieties in the ground state. No pyrene excimer emission is observed for concentrations less than 10-4 M in the steadystate emission spectra of 1 or 2 (Figure 2c and 2d), indicating that the small degree of pre-association is not significant enough to influence excimer formation at low concentrations. Excitation of both compounds in dilute solution (10-6 M) with UV light leads to indigo-blue emission, as is typically observed for the pyrene monomer.21 The emission and excitation spectra are near mirror images of each other and a small Stokes shift typical of fluorescent aromatic molecules is observed.21 The excitation spectra contain the same features as the absorption spectra. Quantum yields for emission are 0.16 ( 0.1) and 0.19 ( 0.1) for 1 and 2, respectively.  29  60000  800000 30000  -1  -1  1200000  400000  15000 0  0  (b)  45000  (d)  1800000  30000  1200000  15000  600000  0  Emission Intensity (counts)  45000  Molar Absorptivity (M cm )  (c)  (a)  0 300  400  500  300  400  500  600  Wavelength (nm)  Figure 2.1 UV-vis absorption spectra for (a) 1 and (b) 2; [1] and [2] 10-5 M in CH2Cl2. Excitation (---) and emission () spectra for (c) 1 and (d) 2; [1] and [2]  10-6 M in CH2Cl2. ex = 345 nm; em = 398 nm.  30  2.2  Excited state lifetimes of POC4Pyr (1) and P(=O)OC4Pyr (2) Single photon counting (SPC) fluorescence experiments were carried out on 1 and  2 at the University of Victoria in collaboration with Professor Cornelia Bohne and Tamara Pace. Stock solutions of 1 and 2 were prepared by dissolving 0.54 mg and 0.55 mg in 100 mL dichloromethane, respectively. The stock solutions were diluted to prepare 1 M solutions of each complex, which were bubbled with N2 for at least 20 minutes prior to measurement. The SPC decay curves for 1 and 2 each showed one component, as observed for 1 M solutions of pyrene in benzene. The lifetimes for 1 and 2 in dichloromethane are 90 ± 5 ns and 101 ± 2 ns, respectively.40 As expected, they are slightly lower than the lifetime of molecular pyrene, 159 ns, as additional non-radiative relaxation pathways for pyrene fluorescence would be expected for 1 and 2, where the pyrene is linked to an aromatic phosphine. 2.3  Solid-state structure of POC4Pyr (1)  Crystals of 1 suitable for X-ray analysis were grown from hot ethyl acetate solution. The solid-state structure is shown in Figure 2.2. Intermolecular -stacking is observed in the unit cell between interpenetrating molecules of 1 with a pyrene-pyrene interplanar distance of 3.71 Å. The crystallographic data for 1 is presented in Table 2.1. The C-X (X = O, P) bond lengths and C-X-C (X = O, P) bond angles (Table 2.2) closely resemble those reported for (o-methoxyphenyl)diphenylphosphine.41  31  Figure 2.2 ORTEP view of 1. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability.  32  Table 2.1 Crystallographic data for 1. chemical formula  C38H31PO  formula weight  534.60  a/Å  24.212(3)  space group  P21/c (#14)  b/Å  15.116(1)  T/oC  -100.0 ± 0.1  c/Å  7.6453(7)  (Mo K)/ Å  0.71073  /º  90.0  Dcalc/g cm-3  1.282  /º  98.276(5)   (Mo K)/cm-1  1.30  /º  90.0  R(Fo)a (I > 0.00(I))  0.051  V/Å3  2769.0(5)  Rw(Fo)b (I > 0.00(I))  0.103  Z  4  R(Fo2)a (all data)  0.134  Rw(Fo2)b (all data)  0.129  a  R   Fo  Fc /  Fo  b  Rw  ( ( Fo2  Fc2 ) 2 /  w( Fo2 )2 )1 / 2  Table 2.2 Selected interatomic distances (Å) and angles (deg) for 1. Bond Length/Å  Bond Angle/deg  O(1)-C(21)  1.364(4)  C(20)-O(1)-C(21)  116.9(3)  O(1)-C(20)  1.450(4)  C(26)-P(1)-C(27)  100.64(18)  P(1)-C(26)  1.831(4)  C(26)-P(1)-C(33)  102.45(17)  P(1)-C(27)  1.825(4)  C(27)-P(1)-C(33)  102.06(18)  P(1)-C(33)  1.824(4)  Torsion angle/deg P(1)-C(26)-C(21)-O(1)  33  -6.4(4)  2.4  Experimental  2.4.1  General All reactions were carried out under a nitrogen atmosphere unless otherwise  stated. NMR spectra were acquired on Bruker Avance 300 or Avance 400 instruments. Residual protonated solvent peaks were used as internal 1H references (vs. TMS and  0). 31  P{1H} NMR spectra were referenced to 85% H3PO4 ( 0). Elemental analyses and  mass spectra were both performed by the UBC Department of Chemistry Microanalytical Services Laboratory. Electrospray (ES) mass spectra were obtained on a Micromass LCT time-of-flight (TOF) mass spectrometer equipped with an ES ion source. The samples were analyzed in MeOH: CH2Cl2 (1:1) at 100 M. UV-vis and fluorescence spectra were all carried out in HPLC grade dichloromethane. UV-vis spectra were obtained using a Cary 5000 UV-vis-near-IR spectrophotometer. A 1-cm quartz cell was used. Fluorescence spectra and quantum yield measurements were obtained on a Photon Technology International fluorimeter using a 1-cm quartz cell. Excitation and emission slit bandwidths were all 4 nm. The quantum yields were determined relative to anthracene. All solutions for quantum yield measurements were sparged with nitrogen gas for a minimum of 10 minutes. The relative quantum yields in solution were calculated based on the expression:42   I  ( )d   1  10  A  F    1  10  A S  I F ( )d  S 0 F   F  S       S       0  34    where  SF is the quantum yield of the standard, integrals   I F ( )d and 0    I  S F  ( )d are  0  the areas under the spectrum of the compound and the standard ( I F ( ) and I FS ( ) are the intensity of fluorescence of the compound and standard as function of wavenumber, respectively), A and AS are the absorptions of the compound and standard, and  and S are the refractive indices of the solvent used for the solutions of the compound and standard, respectively. Time-resolved fluorescence measurements were performed with an Edinburgh Instruments OB 920 single-photon counting system with a hydrogen flash lamp excitation source. The excitation and emission wavelengths were set to 345 and 375 nm, respectively, and the bandpass for the excitation and emission monochromators was ca. 16 nm (2 mm slits). An iris was employed to ensure that the frequency of the stop pulses was smaller than 2% of the start pulse frequency. The number of counts in the channel of maximum intensity was either 10000 or 2000. A Lauda RM6 bath was used to keep the sample at a constant temperature of 20oC. The instrument response function is very narrow for the measured timescale (1 μs) and deconvolution of the instrument response function from the decay was therefore not necessary. Data were fitted to monoexponential decays using the Edinburgh software. The value of 2 (0.9 to 1.1), and visual inspection of the residuals and the autocorrelation were used to determine the quality of the fit.43 Solutions were prepared in dichloromethane by preparing an appropriate 1 mM stock solution and diluting to 1 µM. Solutions were purged with N2 for at least 20 minutes prior to measurement.  35  2.4.2 Materials Chemicals were used as received from the supplier (Aldrich, Strem) unless otherwise specified. Deuterated solvents were used as received from Cambridge Isotope Labs. Spectroscopic grade CH2Cl2 used for UV-vis and fluorescence measurements gave negligible background luminescence at the excitation wavelengths used for the fluorescence measurements. 2.4.3 Synthesis of P(=O)OC4Pyr (2) POC4pyr (1) (0.096 g, 0.18 mmol) was dissolved in 20 mL of a 1:1 mixture of dichloromethane and acetone. 30% H2O2 (0.05 mL) was added and the solution was stirred open to air at room temperature for 15 minutes. The solution was washed with water (3  10 mL), and the organic layer was dried over Na2SO4 and concentrated by rotary evaporation to yield a clear, colorless oil. White analytically pure crystals were obtained by drying the oil in vacuo. Yield: 99 %. Elemental analysis calcd. for C38H31PO2 (%): C, 82.89; H, 5.67; found: C, 82.50; H, 6.02. ESI-MS: m/z = 551 (M + H)+.  31  P{1H}  NMR (300 MHz, 25 oC, CDCl3):  27.0 (s). 1H NMR (200 MHz, 25 oC, CDCl3):  8.22 – 7.90 (m, 9H, pyrene), 7.80 (m, 2H, Ph), 7.70 – 7.55 (m, 6H, Ph), 7.50 (m, 2H, Ph), 7.15 (m, 2H, Ph), 6.80 (m, 2H, Ph), 4.85 (t, 2H, pyrene-CH2(CH2)2CH2-O), 3.15 (m, 2H, pyrene-CH2(CH2)2CH2-O), 1.65 (t, 2H, pyrene-CH2CH2CH2CH2-O), 1.45 (t, 2H, pyreneCH2CH2CH2CH2-O); assignments based on previous experiments done for POC4Pyr.37  36  2.4.4 X-ray crystallographic analysis A colorless thin plate crystal of 1 was mounted on a glass fiber, and the data was collected at -100.0 ±0.1 oC. The structure was solved using direct methods44 and refined using SHELXTL.45 All measurements were made on a Bruker X8 APEX diffractometer with graphite monochromated Mo-K radiation. The data for 1 were collected to a maximum 2 value of 45.0°. Data were collected in a series of and  scans in 0.50° oscillations with 60.0 second exposures. The crystal to detector distance was 38.02 mm. Data were collected and integrated using the Bruker SAINT46 software package and were corrected for absorption effects using the multi-scan technique. (SADABS).47 The data were corrected for Lorentz and polarization effects. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were included in calculated positions but not refined.  37  Chapter 3 Ruthenium Halide Complexes Containing the Phosphine Pyrenyl Ether Ligand (POC4Pyr) A series of ruthenium complexes complexes containing a phosphine pyrenyl ether ligand, RuX2(POC4Pyr)2 (X = Cl (3), Br (4), I (5); POC4Pyr = 4-{2(diphenylphosphino)phenoxy}butylpyrene) were previously prepared in our group (Figure 1.15).37,38 Complexes 4 and 5 were synthesized to promote pyrene quenching by the metal center via PET.38 Substitution of the chloro ligands for bromo or iodo ligands changes the value of 10Dq, decreasing along the series Cl-  Br-  I-, such that if the pyrene LUMO moves above the metal eg orbitals in energy, PET can occur and an ―OFFON‖ sensor could be achieved. Although energies of the relevant orbitals can typically be estimated from cyclic voltammetry and UV-vis absorption spectroscopy, the orbital energies for 3 could not be determined due to decomposition of the complex during cyclic voltammetry experiments.37 The bromo (4) and iodo (5) analogues of 3 were previously synthesized in our lab and their spectroscopic characteristics investigated to determine if changing the halide had an effect on pyrene quenching. The bromo complex 4 was synthesized using an analogous procedure to that used to prepare 3,37 by reaction of ruthenium(III) bromide with 1 in a 5:1 ethanol-toluene mixture.38 The iodo complex 5 was synthesized via a halogen exchange reaction of 3 with NaI in acetone.38 All three complexes have been characterized by solution methods including 1H NMR,  31  P{1H} NMR, IR, UV-vis, and  steady-state fluorescence spectroscopy, as well as EA and ESI-MS.37,38  38  Substitution of the chloro ligands for bromo and iodo ligands in RuCl 2(POC4PyrP,O)2 did not result in significant quenching of pyrene monomer emission.38 It was concluded that either the changes in metal d-orbital energies with different halogen ligands were not significant enough to lead to quenching of pyrene monomer emission, or that the pyrene moieties were not close enough to the metal center for emission to be quenched. It has been reported that a tether length of four methylene groups is too long to observe significant quenching of pyrene emission via PET.26 Contrary to results for the free-ligand (1) at concentrations of ≥ 10-3 M, the steady-state fluorescence spectra of 3-5 did not show any excimer emission at any concentrations up to 10-2M.38 This led to the conclusion that conformational restraints imposed by ligand coordination prevented intra- or intermolecular -stacking in the excited state.38 However, complexes 6-8 (Figure 1.15) showed small amounts of excimer emission at 10-6 M. It is believed that the increase in conformational freedom of the pyrene moieties after reaction with CO allows for pyrene excimers to form.37,38 Experiments were carried out to determine whether the excimers were static or dynamic.38 Based on the PA values calculated from the absorption spectra as well as comparisons of the normalized steady-state spectra for 6-8 it was concluded that the excimers appear to originate from transient pyrene aggregates or loosely coupled molecular pairs in the ground state.38 It is important to note that the amount of excimer emission observed decreases (6  7  8) with almost no excimer emission observed for 8. This result was explained by inferring that the steric restraints of the ―larger‖ bromo- and iodo- complexes did not allow for intramolecular excimers to be formed.38  39  The thermodynamically favoured cis-dicarbonyl complexes, 9-11 (Figure 1.15), that form upon removal of excess CO from solution show an increase in excimer emission compared to 6-8 in their steady-state emission spectra, with the intensity of excimer emission increasing most drastically for 9, notably for 10, and very slightly for 11.37,38 The excimer emission observed for 9-11 at low concentrations (~ 10-6 M) is due to intramolecular excimer formation. The differences in the degree of excimer emission for 9-11 were explained by steric restraints due to the difference in size between the chloro, bromo, and iodo ligands.38 Based on the work presented above that was previously carried out in our laboratory, it was of interest to perform time-dependent fluorescence measurements on this series of ruthenium complexes, before and after exposure to CO. Determining excited state lifetimes for each of the complexes (3-5, 6-8, and 9-11) could provide insight into the electronic effects of changing the halide ligands, which may be useful in explaining the different degrees of pyrene excimer emission observed. In addition, these experiments could also be used in conjunction with previous absorption and steady-state fluorescence measurements to determine the true nature of the pyrene excimers observed.24 It should be noted that the UV-vis absorption and steady-state fluorescence spectra presented in this chapter show the same qualitative features as those previously observed by Lisa Thorne and Dr. Cerrie Rogers in the Wolf group, but are representative of the analytically pure samples that were synthesized and re-characterized for the purpose of single photon counting (SPC) experiments by this author. These spectra are included for completeness.  40  3.1  Synthesis and characterization of tcc-RuX2(POC4Pyr-P,O)2 (X = Cl (3) Br (4), I (5)) In order to perform time-dependent SPC fluorescence measurements it is  necessary to ensure the compounds are > 99% pure, due to the high sensitivity of the experiment to the presence of impurities. Complex 3 was synthesized according to the procedure previously reported.37 Complexes 4 and 5 were prepared with slight variations to the procedures previously used in our laboratory.38 1H NMR,  31  were carried out on 3-5 to ensure the complexes were pure. The  P{1H} NMR, and EA 31  P{1H} NMR shifts,  which are consistent with those previously observed in our group, are presented in Table 3.1 for comparison purposes with the  31  P{1H} NMR shifts observed for the free ligand,  POC4Pyr (1), and the ligand oxide, P(=O)OC4Pyr (2). In order to confirm the relative stereochemistry of the phosphines, a series of 13  C{1H} NMR experiments were previously carried out for 3.37 Complexes 4 and 5 were  presumed to have the same geometry with the two halide ligands trans-disposed to one another and the two P,O-coordinated phosphine ether ligands coordinated such that the phosphines are cis-disposed to one another and are chemically equivalent. The similarities in the 31P{1H} NMR data for 3-5 support this assignment (Table 3.1). UV-vis absorption and steady-state fluorescence measurements were also performed on pure samples of 3-5 in solutions that had been purged with N2 for minimum of 10 minutes. The UV-vis absorption spectra of 3-5 (Figure 3.1) are consistent with the spectra previously obtained in our group,37,38 with the exception of small variations in the peak-to-valley ratio of the most intense absorption to the adjacent minimum (PA). The PA values calculated for the analytically pure samples purged with N2 are slightly closer to 3  41  than those previously calculated for the air-saturated solutions (Table 3.1). Specifically, the PA ratios for 4 and 5 are 2.5 ± 0.2 (4) and 2.4 ± 0.1 (5), versus the previously calculated values of 2.14 (4) and 2.34 (5). Thus, pyrene pre-association in the ground state for 3-5 may not be as significant as previously suggested. However, the PA ratios of the analytically pure complexes, 3-5, are less than those of 1 and 2 indicating that there is more ground-state interaction between the pyrene moieties of 3-5 than in 1 and 2.24 The structured absorptions in the UV region of the spectra for 3-5 closely resemble those in the spectrum of 1 and 2. This result is consistent with the fact that these absorptions arise predominantly from pyrene-based -* transitions.21 Extinction coefficients were also calculated based on the most intense absorption band in the UV region (max = 345 nm). The molar absorptivities (max) for the low energy pyrenyl absorption band vary with halide (3 < 4 < 5). This is attributed to changes in the peak width which has previously been related to the degree of ground-state interaction between the pyrene groups.24 Each of the ruthenium complexes also has a weak, metal-based visible absorption band (d-d transition) that gives rise to the observed color (Table 3.1). The extinction coefficients calculated for the d-d transitions for 3-5 are the same as those previously caculated.38  42  120000  (a) -1  40000  -1  Molar Absorptivity (M cm )  80000  0  (b)  120000  60000  0  (c)  120000 60000 0  300  400  500  Wavelength (nm) Figure 3.1 UV-vis absorption spectra of (a) 3, (b) 4, (c) 5; [tcc-RuX2(POC4Pyr-P,O)2]  10-5 M in CH2Cl2.  43  The emission and excitation spectra for complexes 3-5 are shown in Figure 3.2. As with 1 and 2, excitation of each complex in dilute solution (10-6 M) with UV light gives indigo-blue emission, typical for the pyrene monomer.21 The emission and excitation spectra resemble those of 1 and 2, and the excitation spectra are identical to the absorption spectra.  (a)  Emission intensity (counts)  200 100 0 200  (b)  100 0 (c)  200 100 0  Figure 3.2  300 400 500 Wavelength (nm)  600  Excitation (---) and emission () spectra of (a) 3, (b) 4, (c) 5; [tcc-  RuX2(POC4Pyr-P,O)2]  10-6 M in CH2Cl2.ex = 345 nm; em = 398 nm. Quantum yield values for 3-5 were calculated relative to anthracene in the same fashion used to determine the quantum yields for 1 and 2. Unfortunately, repeated steady-  44  state fluorescence measurements on independently prepared solutions of the analytically pure complexes gave inconsistent results. The values calculated were not identical within experimental error. When the steady-state emission spectra of 3-5 were compared periodically over 48 hours, the intensities of the monomer emission increased with time. This suggests some decomposition may be occurring in solution leading to the formation of a more emissive species. The degree of monomer emission increased more quickly for samples stored in light versus those stored in the dark suggesting a photochemical process may be involved. However, both samples stored in the dark and light showed increases in monomer emission over time suggesting thermal decomposition may also be occurring. No shifts in the emission spectra were observed during these experiments. The species which formed was identified by 31P{1H} and 1H NMR spectroscopy as 2, suggesting that oxidation of some dissociated ligand occurs in solution. It is therefore impossible to exclude the possibility that steady state emission for 3-5 is partially due to dissociated ligand (1) or ligand oxide (2), therefore, reliable quantum yield values for 3-5 could not be obtained. Figure 3.3 shows the decomposition of 3 stored in the dark, over time.  45  4000000 chloro emission t = 0 chloro emission t = 2hr chloro emission t = 4hr chloro emission t = 6hr chloro emission t = 24 hr chloro emission t = 48hr  Intensity (a.u.)  3500000 3000000 2500000 2000000 1500000 1000000 500000  0 350  400  450  500  550  600  650  Wavelength (nm)  Figure 3.3  Emission spectra of 3 over a 48 hour period; [tcc-RuCl2(POC4Pyr-P,O)2]   10-6 M in CH2Cl2.ex = 345 nm; em = 398 nm.  46  Table 3.1 Characterization data for 1-11. 31  P{1H} NMR  CO Compound  (ppm)a (cm-1)b -14.2 1 2  27.0  -  3  63.7  -  4  64.7  -  5  66.0  -  6  27.1  2007  7  26.0  2001  8  22.5  2007  9  13.9  10  10.2  11  5.1  2059, 1998 2059, 2000 2055, 1989  a  max (max)c 345 (44700) 345 (45000) 345 (61400) 345 (71700)  PA ratiob  345 (89900) 345 (61400) 345 (72900) 345 (88300) 345 345 345  (d-d) (d-d )d 2.8  0.1 -  Color  2.9  0.1 -  colorless  2.5  0.1 517 (580) 2.5  0.2 542 (530)  red  2.4  0.1 577 (520) 2.5  0.1 440 (220) 2.3  0.1 455 (250) 2.3  0.1 502 (280) 2.5  0.1 none observed 2.0  0.1 none observed 2.2  0.1 shoulder at ~500  green  colorless  purple-red  yellow light orange red-orange white yellow light orange  CDCl3; bCH2Cl2, determined by averaging PA ratios from several samples; cmax (nm)  and max (M-1 cm-1) are respectively the maximum wavelength and the molar absorptivity of the lowest-energy vibronic band of the 1La electronic transition of the pyrene chromophore (CH2Cl2, 25 oC);  d    (d-d)  (nm) is the wavelength of the metal-based d-d  absorption. d-d (M-1 cm-1) is the molar absorptivity of the metal-based d-d transition (CH2Cl2, 25 oC).  47  3.2  Characterization of ttt-RuX2(CO)2(POC4Pyr-P)2 (X = Cl (6) Br (7), I (8)) It has been shown that complexes of the type RuX2(POL-P,O)2 (X = halogen;  POL = hemilabile phosphine ether ligand) react with CO to form RuX2(CO)2(POL-P)2 or RuX2(CO)(POL-P,O)(POL-P).14,36,49-51 Reaction of 3 with CO and accompanying changes in photophysical properties have been described.37 Complexes 4 and 5 were found to react similarly with CO (see Figure 1.15).38 Upon exposure to CO an immediate color change is observed for all three complexes in solution.37,38 A summary of the characterization data for 6-8 is shown in Table 3.1. Reaction of 3-5 with CO is accompanied by an immediate shift in the 31P{1H} NMR resonance. For all three complexes, the resonances shifted upfield relative to the resonances prior to reaction with CO. Previously, a series of using  13  13  C{1H} NMR experiments were conducted  C-labeled CO to assign the absolute stereochemistry of 6 as ttt.37 The  stereochemistry of 7 and 8 were assigned in the same way, supported by the similarities in the 31P {1H} NMR chemical shifts and IR bands for the three complexes (Table 3.1).38 The UV-vis absorption spectra of 6-8 are essentially identical, with no significant change in the molar absorptivities in the UV-region. The absorption bands in the UVregion are identical in structure to those of 3-5. The PA values calculated for the analytically pure, nitrogen-purged samples were essentially the same as those previously calculated.38 In addition, the PA values changed very little relative to those determined for the complexes 3-5 (Table 3.1), supporting a weak interaction between the pyrene moieties of 6-8 in the ground state.24 This is somewhat surprising as the pyrene ligands are disposed differently in 3-5 versus 6-8. For each trans-dicarbonyl complex, the weak metal-based transition is blue-shifted relative to its position before exposure to CO 48  (Figure 3.4). The molar absorptivities of the d-d bands for complexes 6-8 are similar to those for complexes 3-5 (Table 3.1), and are consistent with those previously determined.38  (a) 400  -1  -1  Molar Absorptivity (M cm )  800  800 0 (b) 400 800 0 (c) 400 0 400  500  600  700  Wavelength (nm) Figure 3.4 Visible d-d absorption bands of (a) 3 () and 6 (---), (b) 4 () and 7 (---), and (c) 5 () and 8 (---); [tcc-RuX2(POC4Pyr-P,O)2] and [ttt-Ru(CO)2X2(POC4Pyr-P)2]  2 10-3 M in CH2Cl2. At high concentrations of 3 (~10-2 M) reaction with CO under UV irradiation resulted in a change from the weak indigo-blue emission of 3, characteristic of pyrene  49  monomer emission, to the strong blue-green excimer emission of 6.37 This observation is consistent with the formation of intermolecular excimers (Figure 3.5a).21 In dilute solution (~10-6 M), a small amount of excimer emission was still observed. Since intermolecular excimer formation is insignificant at 10-6 M, this must be due to intramolecular excimers (Figure 3.5b).21 It was proposed that an increase in conformational freedom of the alkylpyrene moieties occurs after displacement of the ether from the metal center influencing the ability of the pyrene moieties to interact with one another.37 However, the displacement of the ether moieties from the metal center does not significantly affect the PA values, that is, it does not influence the ground-state interaction of the pyrene moieties at ~10-6 M.24 Thus, the formation of intramolecular excimers appears to be a dynamic process as a result of the increase in conformational freedom, and not the result of static excimers resulting from loosely coupled molecular pairs as previously postulated.38 The intensity of excimer emission at 10-6 M is lower for 7 and 8 than for 6; only a very small amount of intramolecular excimer is observed for 7 and almost no intramolecular excimer is observed for 8 (Figure 3.6). The differences in intensity of excimer emission for 6-8 were previously explained using steric arguments, that is the larger bromo, and iodo ligands prevented the ―folding-over‖ of the pyrene moieties to form intramolecular excimers as low concentrations (~ 10-6 M).38 The intensity of excimer emission is limited by the ability of an excimer to form within the lifetime of the excited state of the pyrene monomer.14,24 and by the stabilization of the excimer.24 Thus, if the lifetimes of the excited states for 7 and 8 are sufficiently shorter than for 6 such that a conformation suitable for excimer formation cannot be achieved, or that the  50  stabilization of the excimer cannot overcome the added steric repulsion resulting from the interaction of the alkylpyrene moieties ―folding over‖ the larger bromo and iodo ligands, excimer emission would be significantly reduced or eliminated completely. Another explanation of these results is that the d-d absorption for 7 and 8 is close enough in energy to the pyrene excimer emission, centered at 480 nm, for energy transfer to occur. Since EET is a non-radiative quenching pathway the extent of excimer emission observed would be expected to be less for 7 and 8 compared to 6.  OC  Cl Ru  OC Cl  O  (CH2)4  O  Ph2P  Cl  O  (CH2)4Pyr  PPh2 CO  (CH2)4  PPh2  Ru Ph2P Pyr(CH2)4  O  Cl  CO  (a)  O Ph2P  CO  Cl  Ru Cl CO  PPh2  O  (b)  Figure 3.5  Schematic structure of (a) an intermolecular excimer and (b) an  intramolecular excimer for ttt-RuCl2(CO)2(POC4Pyr-P)2 (6).  51  240  (a)  Emission Intensity (counts)  160 80 0 240  (b)  160 80 0 240  (c)  160 80 0 300  400  500  600  Wavelength (nm)  Figure 3.6  Excitation (---) and emission () spectra for (a) 6, (b) 7 and (c) 8; [ttt-  Ru(CO)2X2(POC4Pyr-P)2]  10-6 M in CH2Cl2. ex = 345 nm; em = 398 nm.  52  3.3  Characterization of cct-RuX2(CO)2(POC4Pyr-P,)2 (X = Cl (9), Br (10), I (11)) Complexes of the type ttt-RuX2(CO)2(PR3)2 are known to isomerize to the  thermodynamically more stable isomers cct-RuX2(CO)2(PR3)2.50,51 This isomerization typically occurs through a dissociative mechanism.48 This mechanism is consistent with the observation that isomerization does not occur until excess CO is removed from solutions of 6-8 by sparging the solutions with N2 or by degassing via repeated freezepump-thaw cycles. Preliminary kinetic studies using IR spectroscopy showed that the rate of isomerization decreased in the order Cl-> Br- > I-, supporting a dissociative mechanism for the geometric isomerization.38 A summary of the characterization data for 9-11 is given in Table 3.1. Like the ttt isomers, the cct isomers contain two equivalent phosphines, as indicated by the singlet resonance in the 31P{1H} NMR spectrum of each complex. The di-chloro complex 9 has previously been studied using  13  C{1H} NMR experiments with  13  C-labeled CO in order  to verify the stereochemical assignment as cct.37 Complexes 10 and 11 are presumed to have the same geometry. Complexes 9-11 were also characterized by IR spectroscopy.38 Two absorptions in the C-O stretching region are expected for cct-RuX2(CO)2(POC4PyrP)2, this was previously observed for all three complexes and is included in Table 3.1, supporting the assignment of these as cct.38 The UV-vis spectra for the cct isomers also show typical absorption from pyrenebased -* transitions in the UV-region.21 Originally it was reported that the metal based d-d absorption bands for the cis-dicarbonyl complexes, 9-11, did not change in energy compared to the trans-dicarbonyl complexes, 6-8.38 However, the metal-based d-d transition for 9 and 10 are not observed, they are presumably shifted to higher energy and 53  are obscured by the strong pyrene absorption band. Isomerization of other RuCl2(CO)2(phosphine)2 complexes from the ttt to the cct isomer results in a color change from yellow to white,50 consistent with the results observed for 9 and 10. Complex 11 does show an absorption band at ~500 nm which appears as a shoulder to the pyrene absorption band, slightly blue-shifted from the absorption of the ttt isomer 8. The molar absorptivities for the pyrene-based absorptions appear to decrease slightly. This is likely due to the small degree of dissociation occurring in solution over time. In addition, the PA values for each cct isomer are essentially the same as those obtained for the corresponding ttt isomer (Table 3.1), indicating a small degree of pyrene pre-association in the ground state.24 The steady-state fluorescence spectra of 9-11 are presented in Figure 3.7. Comparison of the fluorescence from the ttt isomers 6-8 with the cct isomers 9-11 is interesting. Previously it was reported that strong excimer emission was observed for 9, even in dilute solution.37 It was concluded that the pyrene moieties in 9 must be able to more easily interact to form an intramolecular excimer. At 10-6 M a small increase in the excimer intensity of 10 was observed with respect to 7 (Figure 3.7b). Almost no excimer emission is observed for 11 (Figure 3.7c), similar to the result for complex 8. These results support the conclusion that intramolecular energy transfer may be responsible for the changes in excimer intensity. The blue shift in the d-d band from the ttt isomers 6 and 7 to the cct isomers 9 and 10 results in poorer overlap between this band and the pyrene excimer emission, consistent with the increase in excimer intensity for the cct isomers of these two complexes. For both 8 and 11 the d-d band overlaps well with the expected emission band energy from excimer, and in these two complexes no excimer is observed.  54  It is still possible that the larger size of the bromo and iodo ligands impedes the formation of intramolecular excimers, implying that the formation of excimer in 9 is facilitated more easily by the cis disposed chloro ligands rather than the CO ligands.  400  Emission intensity (counts)  (a) 200 0 200  (b)  100 0 (c)  200 100 0  300  400  500  600  Wavelength (nm) Figure 3.7  Excitation (---) and emission () spectra for (a) 9, (b) 10 and (c) 11; [cct-  Ru(CO)2X2(POC4Pyr-P)2]  10-6 M in CH2Cl2. ex = 345 nm; em = 398 nm.  55  3.4  Excited state lifetimes of RuX2(POC4Pyr-P,O)2 (X = Cl (3) Br (4), I (5)) before and after reaction with CO Single photon counting (SPC) fluorescence experiments were carried out on 3-5  and 6-8, at the University of Victoria in collaboration with Professor Cornelia Bohne and Tamara Pace. Solutions were prepared by dissolving approx 0.2 mg of each complex in 100 mL benzene. Solutions of 3-5 were purged with N2 for at least 20 minutes prior to measurement.  Solutions of 6-8 were obtained by sparging the previously prepared  solutions of 3-5 with CO for at least 20 minutes prior to measurement. 3.4.1 SPC results for tcc-RuX2(POC4Pyr-P,O)2 (X = Cl (3) Br (4), I (5)) and tttRuX2(CO)2(POC4Pyr-P)2 (X = Cl (6), Br (7), I (8)) SPC experiments were initially performed on samples of 3-5 which were previously prepared in our laboratory. Results from these experiments showed one short lived component and one long lived component for 3 and 4 and one long lived component for 5. The short lived components for 3 and 4 had excited state lifetimes on the order of 1 ns. The long lived components for 3-5 all had lifetimes on the order of 102 ns. Solutions of 3-5 were then sparged with CO to obtain solutions of 6-8 for SPC measurements. Steady-state fluorescence spectra were run on the samples before and after bubbling through CO in order to ensure that reaction with CO had occurred. The data for complexes 6 and 7 showed two short lived components and one long lived component in their decay plots. Complex 8 showed one short lived component and one long lived component. The two short-lived components were on the order of 1 ns and 10 ns for 6 and 7, respectively, with the long lived components on the order of 102 ns. The short  56  lived component was on the order of 1 ns for 8, with the long lived component on the order of 102 ns. Figures 3.8-3.10 show the SPC spectra obtained for each of the complexes before and after reaction with CO, as well as the preliminary lifetimes fitted for the curves. It should be noted that the number of counts acquired for the SPC experiments described above are sufficient to determine lifetimes for qualitative purposes only (i.e. trends), and not for quantitative accuracy. The appearance of an additional short lived species in the SPC spectra of 6-8 was interesting as it may represent a component that could be attributed to excimer decay. However, the short lived components which originally were present in the SPC spectra of 3 and 4 could only be explained as due to the presence of an impurity in the samples. The long lived components for 3-8 all had lifetimes similar to the free ligand (1) and ligand oxide (2) and it was postulated that these decay components may be due to decomposition products. Therefore, new samples of 3-5 were synthesized and 1H NMR, 31  P{H} NMR, and EA were used to confirm the purity of the samples for SPC.  57  1 = 1.01 ns (3.17%) 1 = 0.61 ns (1.25%)  2 = 105.20 ns (94.65 %)  2 = 104.74 ns (98.75 %)  3 = 8.64 ns (2.17 %)  2 = 1.074  2 = 0.943  (b)  (a) Figure 3.8  SPC decay for (a) 3 [tcc-RuCl2(POC4Pyr-PO)2]  10-6 M and (b) 6 [ttt-  Ru(CO)2Cl2(POC4Pyr-P)2]  10-6 M in benzene. ex = 345 nm.  58  1 = 0.76 ns (3.45%) 1 = 0.28 ns (1.72%)  2 = 103.03 ns (90.92 %)  2 = 97.37 ns (98.28 %)  3 = 6.32 ns (5.62 %)  2 = 1.069  2 = 1.003  (b)  (a)  Figure 3.9  SPC decay for (a) 4 [tcc-RuBr2(POC4Pyr-PO)2]  10-6 M and (b) 7 [ttt-  Ru(CO)2Br2(POC4Pyr-P)2]  10-6 M in benzene. ex = 345 nm.  59  1 = 1.67 ns (1.10%)  1 = 99.94 ns (100%) 2  2 = 92.88 ns (98.90 %)  = 1.105  2 = 0.918  (a) Figure 3.10  (b)  SPC decay for (a) 5 [tcc-RuI2(POC4Pyr-PO)2]  10-6 M and (b) 8 [ttt-  Ru(CO)2I2(POC4Pyr-P)2]  10-6 M in benzene. ex = 345 nm.  60  3.4.2 SPC results for analytically pure tcc-RuX2(POC4Pyr-P,O)2 (X = Cl (3) Br (4), I (5)) Counts obtained for the SPC decays of 3-5 were low (400 – 650) due to the low fluorescence intensity and the need to replace the solution every 3 hours due to decomposition of the complexes over time. Longer collection times (12 to 13 hours) were not feasible since the degree of decomposition of 3-5 increases significantly after 3 hours. Each complex displayed both a long and a short decay component (Table 3.2). The major decay component for each of the complexes, 3-5, was the short-lived component. The contribution of this component was higher for 3 followed by 4 and was lowest for 5. The long-lived component was more prominent for the 4 and 5 than for 3. Table 3.2 Lifetimes of decay components for 3-5. Complex 3 4 5  (Short-lived Component) (ns) 0.1 0.3 0.5  (Long-lived Component) (ns) 12 8 7  The contribution of the long-lived component for 3 appeared to be less than in previous experiments prior to purification. This may be due to better purification of the complex, or to replacing the solution used for SPC every three hours, since the increase in intensity of the steady state fluorescence spectra is significant after three hours of SPC (the intensity after SPC is approximately 1.5 times greater than that of the freshly prepared solution). Although quantitative lifetimes for all of the complexes (3-11) could not be obtained due to low SPC counts, short measurement times, and decomposition of the  61  complexes in solution, the trends in decay, especially for the SPC experiments run on the analytically pure samples of 3-5, provide qualitative observations that allow insight into the effect of varying the halide ligand on the pyrene-based fluorescence of the molecules. The lifetimes decrease as 3 > 4 > 5 indicating a heavy atom effect. In addition the lifetimes increase for each of the complexes after reaction with CO; that is the lifetimes of 6-8 are greater than the corresponding lifetimes of 3-5, respectively, which indicates fewer non-radiative relaxation pathways, as would be expected since the pyrene moieties are farther from the metal center after displacement of the ether group upon binding of CO. Finally, the fact that the long lived component for 3-8 essentially remains the same supports the idea that it is due to dissociated ligand (1) and/or ligand oxide (2). 3.5  Solid-state structure of RuCl2(POC19H17)2.CHCl3 Attempts to grow crystals of 3 suitable for X-ray analysis were carried out by the  slow diffusion of dry, degassed hexanes into a solution of 3 in dry, degassed chloroform. The crystals collected that were suitable for X-ray analysis resulted in the solid state structure of RuCl2(POC19H17)2.CHCl3. It appears that in solution 3 reacted to give RuCl2(POC19H17)2 and H2C=CH-CH2-Pyr (Pyr = pyrene). This supports the conclusion presented earlier in this chapter that 3 releases a pyrenyl compound in solution over time. The material crystallizes with two Ru complexes and two molecules of CHCl3 in the asymmetric unit (Figure 3.11). The solid-state structure of RuCl2(POC19H17)2 (molecule  1)  is  shown  in  Figure  3.12.  The  crystallographic  data  for  RuCl2(POC19H17)2.CHCl3 is presented in Table 3.3. The C-X (X = O, P) bond lengths (Table 3.4) and C-X-C (X = O, P) bond angles (Table 3.5) closely resemble those reported for ruthenium dichloro-bis-(o-methoxyphenyl)diphenylphosphine.36 62  Figure 3.11  Views of [RuCl2(POC19H17)2.CHCl3]2. The hydrogen atoms are omitted  for clarity, as well as the labels for the carbon atoms.  63  Figure 3.12  ORTEP view of RuCl2(POC19H17)2.CHCl3 (molecule 1). The hydrogen  atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability.  64  Table 3.3 Crystallographic data for RuCl2(POC19H17)2.CHCl3 chemical formula  C39H35O2P2Cl5Ru formula weight  875.93  a/Å  12.6680(8)  space group  P – 1 (#2)  b/Å  17.924(1)  T/oC  -100.0 ± 0.1  c/Å  20.315(1)  (Mo K)/ Å  0.71073  /º  111.906(2)  Dcalc/g cm-3  1.519  /º  93.927(2)   (Mo K)/cm-1  8.76  /º  108.396(2)  R(Fo)a (I > 0.00(I))  0.032  V/Å3  3829.6(4)  Rw(Fo)b (I > 0.00(I))  0.075  Z  4  R(Fo2)a (all data)  0.049  Rw(Fo2)b (all data)  0.079  a  R   Fo  Fc /  Fo  b  Rw  ( ( Fo2  Fc2 ) 2 /  w( Fo2 )2 )1 / 2  65  Table 3.4 Selected interatomic distances (Å) for RuCl2(POC19H17)2.CHCl3 Bond Lengths /Å Molecule 1  Molecule 2  Ru(1)-O(1)  2.2747(13)  2.2660(13)  Ru(1)-O(2)  2.2659(14)  2.2535(13)  Ru(1)-P(1)  2.2187(5)  2.2348(5)  Ru(1)-P(2)  2.2268(5)  2.2193(5)  Ru(1)-Cl(1)  2.3967(5)  2.3909(5)  Ru(1)-Cl(2)  2.3964(5)  2.3854(5)  O(1)-C(6)  1.390(2)  1.387(2)  O(1)-C(7)  1.444(2)  1.462(2)  O(2)-C(25)  1.391(2)  1.388(2)  O(2)-C(26)  1.427(2)  1.442(2)  P(1)-C(1)  1.830(2)  1.8378(9)  P(1)-C(8)  1.8243(19)  1.837(2)  P(1)-C(14)  1.8306(19)  1.843(2)  P(2)-C(20)  1.833(2)  1.829(2)  P(2)-C(27)  1.829(2)  1.843(2)  P(2)-C(33)  1.842(2)  1.8296(19)  66  Table 3.5 Selected interatomic angles (deg) for RuCl2(POC19H17)2.CHCl3 Bond Angles /deg Molecule 1  Molecule 2  P(1)-Ru(1)-P(2)  104.087(19)  104.932(19)  P(1)-Ru(1)-O(1)  78.57(4)  80.05(4)  P(1)-Ru(1)-O(2)  176.40(4)  173.85(4)  P(1)-Ru(1)-Cl(1)  91.443(18)  91.270(19)  P(1)-Ru(1)-Cl(2)  97.652(19)  98.037(19)  P(2)-Ru(1)-O(1)  176.04(4)  173.64(4)  P(2)-Ru(1)-O(2)  78.59(4)  80.20(4)  P(2)-Ru(1)-Cl(1)  98.52(2)  97.014(19)  P(2)-Ru(1)-Cl(2)  91.89(2)  990.517(19)  O(1)-Ru(1)-Cl(1)  84.26(4)  86.72(4)  O(1)-Ru(1)-Cl(2)  84.81(4)  84.81(4)  O(2)-Ru(1)-Cl(1)  85.75(4)  84.67(4)  O(2)-Ru(1)-Cl(2)  84.59(4)  85.17(4)  Cl(1)-Ru(1)-Cl(2)  164.11(2)  166.139(18)  Ru(1)-P(1)-C(1)  102.80(6)  101.77(6)  Ru(1)-P(1)-C(8)  120.68(6)  121.67(6)  Ru(1)-P(1)-C(14)  120.83(6)  122.82(7)  Ru(1)-P(2)-C(20)  102.14(7)  103.24(6)  Ru(1)-P(2)-C(27)  121.12(7)  123.56(7)  Ru(1)-P(2)-C(33)  120.91(7)  118.43(6)  Ru(1)-O(1)-C(6)  116.75(11)  116.75(11)  Ru(1)-O(1)-C(7)  125.30(13)  124.61(12)  Ru(1)-O(2)-C(25)  117.53(12)  118.74(11)  Ru(1)-O(2)-C(26)  123.16(13)  122.87(12)  67  Table 3.6 Selected Torsion angles (deg) for RuCl2(POC19H17)2.CHCl3 Torsion Angles /deg Molecule 1  Molecule 2  C(7)-O(1)-Ru(1)-P(1)  -150.93(15)  -142.31(15)  C(7)-O(1)-Ru(1)-P(2)  -18.5(6)  -0.4(4)  C(26)-O(2)-Ru(1)-P(1)  -23.9(8)  -13.0(5)  C(26)-O(2)-Ru(1)-P(2)  -162.17(17)  -159.97(16)  68  3.6  Conclusions The fluorescence of 3-5 before exposure to CO is very similar due to monomer  emission from the pendant pyrenyl groups. After exposure to CO, monomer emission from the pendant pyrenyl groups is still observed for the trans-dicarbonyl products 6-8; however, excimer emission was also observed. The difference in excimer emission intensity is attributed to differences in the extent of non-radiative energy transfer between the excited state pyrene moieties and metal-based states in 6-8. Both non-radiative EET and the heavy atom effect may be contributing to the differences in excimer emission observed for 6-8. Steric constraints may also be attributed to favoring excimer formation for 6 over 7 and 8. There are no other examples known where tuning the electronics at a metal via ancillary ligands results in changes in the intensity of excimer emission from a second ligand. The luminescence properties of the ruthenium halide complexes presented in this chapter have been reported as a full paper in Inorganic Chemistry.40 Here, binding with CO triggers the formation of the excimer, however binding of other ligands in related complexes bearing such hemilabile pyrenyl ligands should also be possible. Fluorescence-based detection of non-fluorescent compounds is thus feasible. Alteration of the ligating end of the hemilabile ligand would allow increased control of binding selectivity and sensitivity. Here, the selected alkyl tether is four carbons in length. This length was selected largely on the basis of synthetic accessibility, however shorter lengths would clearly be of interest as pyrene emission quenching may be enhanced in these cases. Alternatively, it is of interest to investigate hemilabile ligands with different functionalities than phosphine-ether groups. Approaches to exploring  69  phosphine-amine and phosphine-imine ligands containing pendant pyrenyl groups with a palladium metal center will be presented in the next chapter. 3.7  Experimental  3.7.1 General All reactions were carried out under a nitrogen atmosphere unless otherwise stated. NMR spectra were acquired on Bruker Avance 300 or Avance 400 instruments. Residual protonated solvent peaks were used as internal 1H references (vs. TMS and  0). P{1H} NMR spectra were referenced to 85% H3PO4 ( 0). Elemental analyses and  31  mass spectra were both performed by the UBC Department of Chemistry Microanalytical Services Laboratory. Electrospray (ES) mass spectra were obtained on a Micromass LCT time-of-flight (TOF) mass spectrometer equipped with an ES ion source. The samples were analyzed in MeOH: CH2Cl2 (1:1) at 100 M. IR spectroscopic measurements were made using a BOMEM MB155S FTIR spectrometer and using solution samples. All spectra were corrected for solvent by subtracting the appropriate solvent spectrum. UVvis and fluorescence spectra were all carried out in HPLC grade dichloromethane. UVvis spectra were obtained using a Cary 5000 UV-vis-near-IR spectrophotometer. A 1-cm quartz cell was used. Fluorescence spectra for 3-11 were collected using a Varian Cary Eclipse spectrofluorometer. Measurements were made in a 1-cm quartz cell in nitrogen purged solutions. 5 nm excitation and emission slit widths were used. Fluorescence spectra for 1 and 2 and quantum yield measurements were obtained on a Photon Technology International fluorimeter using a 1-cm quartz cell. Excitation and emission slit bandwidths were all 4 nm.  70  Time-resolved fluorescence measurements were carried out using an Edinburgh Instruments OB 920 single-photon counting system with a hydrogen flash lamp excitation source. The excitation and emission wavelengths were set to 345 and 375 nm, respectively, and the bandpass for the excitation and emission monochromators was ca. 16 nm (2 mm slits). An iris was employed to ensure that the frequency of the stop pulses was smaller than 2% of the start pulse frequency. The number of counts in the channel of maximum intensity was either 10000 or 2000. A Lauda RM6 bath was used to keep the sample at a constant temperature of 20oC. The instrument response function is very narrow for the measured timescale (1 μs) and deconvolution of the instrument response function from the decay was therefore not necessary. Data were fitted to monoexponential decays using the Edinburgh software. The value of 2 (0.9 to 1.1), and visual inspection of the residuals and the autocorrelation were used to determine the quality of the fit.43 Solutions were prepared in dichloromethane by preparing an appropriate 1 mM stock solution and diluting to 1 µM. Solutions were purged with N2 for at least 20 minutes prior to measurement.  71  3.7.2 Materials Chemicals were used as received from the supplier (Aldrich, Strem) unless otherwise specified. Deuterated solvents were used as received from Cambridge Isotope Labs. Carbon monoxide was obtained from Praxair and was used as received. Spectroscopic grade CH2Cl2 used for UV-vis and fluorescence measurements gave negligible background luminescence at the excitation wavelengths used for the fluorescence measurements. The synthesis and characterization of tcc-RuCl2(POC4PyrP,O)2 (3), ttt-RuCl2(CO)2(POC4Pyr-P)2 (6), and cct-RuCl2(CO)2(POC4Pyr-P)2 (9) are reported elsewhere.37 The synthesis of ttt-RuBr2(CO)2(POC4Pyr-P)2 (7), and cctRuBr2(CO)2(POC4Pyr-P)2  (10)  and  ttt-RuI2(CO)2(POC4Pyr-P)2  (8),  and  cct-  RuI2(CO)2(POC4Pyr-P)2 (11) are reported elsewhere.38 3.7.3 Synthesis and characterization of tcc-RuBr2(POC4Pyr-P,O)2 (4) POC4Pyr (0.382 g, 0.710 mmol) was heated in ethanol (60 mL) to reflux. Toluene (17 mL) was then added to ensure that the ligand was completely dissolved. Distilled water (15 mL) was added to RuBr3xH2O (0.122 g, 0.360 mmol) and the solution was sonicated for 10 minutes followed by heating with a heat gun. This treatment was repeated two more times. The ruthenium (III) bromide solution was diluted with an equal volume of ethanol (15 mL) and was then added rapidly to the ligand solution. The reaction was heated at reflux for 72 h. Over the course of the reaction, the solution changed from opaque black to red-purple in color. The reaction mixture was hotfiltered and the residue was washed with 200 mL dichloromethane. The filtrate was concentrated to ~100 mL, by heating the solution to reflux, and then diluted with 200 mL hexanes. The solution was again heated to reflux, and as the dichloromethane evaporated 72  a purple-red powder precipitated. This was filtered from the hot solution and washed with hexanes. The red-purple solid was dried in vacuo. Yield: 39 %. Elemental analysis calcd. for C76H62Br2O2P2Ru (%): C, 68.63; H, 4.70; found: C, 68.41; H, 5.00. ESI-MS: m/z = 1249 (M – Br)+.  31  P{1H} NMR (300 MHz, 25 oC, CDCl3):  64.7 (s). 1H NMR (200  MHz, 25 oC, CDCl3):  8.22 – 7.85 (m, 16H, pyrene), 7.68 (d, 3JHH = 8.0 Hz, 2H, pyrene), 7.38 – 7.05 (m, 26H, Ph), 6.96 (m, 2H, Ph), 4.78 (m, 4H, pyrene-CH2(CH2)2CH2-O), 3.11 (m, 4H, pyrene-CH2(CH2)2CH2-O), 1.90 (m, 4H, pyrene-CH2CH2CH2CH2-O), 1.67 (m, 4H, pyrene-CH2CH2CH2CH2-O); assignments based on previous experiments done for tcc-RuCl2(POC4Pyr-P,O)2.37 3.7.4 Synthesis and characterization of tcc-RuI2(POC4Pyr-P,O)2 (5) Acetone (15 mL) was added to tcc-RuCl2(POC4Pyr-P,O)2 (0.096 g, 0.080 mmol) and NaI (0.054 g, 0.36 mmol). The reaction was heated at reflux for 2 h. During the reaction time, the solution changed in colour from red to green and a green precipitate formed. The reaction mixture was cooled and acetone was removed in vacuo to give a sticky green solid. The solid was re-dissolved in dichloromethane and passed through a Büchner funnel to remove NaCl and unreacted NaI. The filtrate was diluted with 100 mL of hexanes. The solution was heated to reflux, and as the dichloromethane was evaporated a green powder precipitated, which was filtered from the hot solution, and washed with hexanes. The green solid was dried in vacuo. Yield: 94%. Elemental analysis calcd. for C76H62I2O2P2Ru (%): C, 64.10; H, 4.39; found: C, 64.06; H, 4.79. ESI-MS: m/z = 1297 (M – I)+.  P{1H} NMR (400 MHz, 25 oC, CDCl3):  66.6 (s). 1H  31  NMR (400 MHz, 25 oC, CDCl3):  8.11 – 7.87 (m, 16H, pyrene), 7.69 (d, 2JHH = 7.3 Hz, 2H, pyrene), 7.34 – 7.07 (m, 26H, Ph), 6.96 (m, 2H, Ph), 4.82 (m, 4H, pyrene-  73  CH2(CH2)2CH2-O), 3.16 (m, 4H, pyrene-CH2(CH2)2CH2-O), 2.04 (m, 4H, pyreneCH2CH2CH2CH2-O), 1.71 (m, 4H, pyrene-CH2CH2CH2CH2-O); assignments based on previous experiments done for tcc-RuCl2(POC4Pyr-P,O)2.37 3.7.5 Preparation of samples for excited state lifetime measurements The purified complexes, 3-5, were dissolved in benzene to prepare 1 mM stock solutions. The stock solutions were diluted to 1M solutions and transferred into quartz cells. The samples were sparged with N2 as described above for SPC measurements. The samples were replaced every 3 hours to account for decomposition of the complexes that was described above; since changes in the intensity of the steady-state spectra for 3 were not significant up to 4 hours in solution. 3.7.6 X-ray crystallographic analysis A colorless thin plate crystal of RuCl2(POC19H17)2.CHCl3 was mounted on a glass fiber, and the data was collected at -100.0 ±0.1 oC. The structure was solved using direct methods44 and refined using SHELXTL.45 All measurements were made on a Bruker X8 APEX diffractometer with graphite monochromated Mo-K radiation. The data for RuCl2(POC19H17)2.CHCl3 were collected to a maximum 2 value of 56.0°. Data were collected in a series of and  scans in 0.50° oscillations with 5.0 second exposures. The crystal to detector distance was 38.00 mm. Data were collected and integrated using the Bruker SAINT46 software package and were corrected for absorption effects using the multi-scan technique. (SADABS).47 The data were corrected for Lorentz and polarization effects. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were included in calculated positions but not refined.  74  Chapter 4 New Hemilabile Ligands Containing Phosphine Amine Functionalities with a Pendant Pyrenyl Moiety 4.1  Motivation for the development of hemilabile ligands with phosphine amine functionalities The quenching of aromatic hydrocarbon fluorescence by transition metal ions is a  well known phenomenon.14 Sensors based on photoinduced electron transfer (PET) processes have been developed in which pyrene luminescence has been quenched in the presence of open-shelled metal ions such as Fe3+,16 Cu2+, and Ni2+.15 In particular, a Zn2+ sensor based on an alkyl pyrene group covalently bonded to an aza-18-crown-6 at nitrogen has been developed where the quenching of pyrene luminescence was dependent on the length of the tether between the receptor moiety of the sensor and pyrene.26 In the interest of shortening the tether between the receptor and the pyrene moiety relative to the tether in the phosphine pyrenyl ether ligand, POC4Pyr (1) presented in the previous chapters, a new hemilabile ligand containing a different functionality is presented in this chapter. A shorter tether length should promote ―OFF-ON‖ sensing via PET from the metal center. The nitrogen-based functional group may also provide an alternate nonradiative quenching pathway via PET from the nitrogen to the pyrene moiety, such that an ―ON-OFF‖ sensor may be established. Examples of this approach were presented in Chapter 1 for alkali metal sensors containing amine functionalities in the receptor. In addition, the amine would allow access to transition metal complexes containing different metals, which could provide selectivity toward different analytes. A palladium complex  75  containing a phosphine imino pyridyl ligand, that reacts with CO via replacement of the labile pyridine group has been reported.39 The imine was also found to be labile.39 Based on this work, it was proposed that functionalizing a simplified phosphine-imine ligand with pyrene may give access to metal complexes of this type for use in chemosensors. In order to prepare a phosphine imine ligand with a pendant pyrene it was desirable to synthesize an aminopyrene that could condensed with diphenylphosphine benzaldehyde to give a phosphine pyrenyl imine ligand. 1-Aminopyrene was chosen as a starting material since the pyrene moiety is directly bonded to the imine minimizing the tether length between the metal receptor and the fluorophore. In addition, 1-aminopyrene is synthetically accessible via the nitration of pyrene followed by subsequent reduction of the nitro group. A second ligand could also be prepared via hydrogenation of the phosphine pyrenyl imine, PNPyr (12) to give the corresponding phosphine pyrenyl amine, PNHPyr (13) (Chart 4.1). Chart 4.1  H  H  H  PPh2  N H PPh2  PNPyr 12  PNHPyr 13  N  76  4.2  Synthesis and characterization of PNPyr (12) and PNHPyr (13) PNPyr (12) was prepared via the nitration of pyrene to yield 1-nitropyrene, which  was then reduced to yield 1-aminopyrene. The subsequent condensation reaction of 2diphenylphosphine benzaldehyde and 1-aminopyrene was used to prepare 12. PNHPyr, 13, was then prepared by the reduction of 12 with lithium aluminum hydride (Scheme 4.1). Both 12 and 13 were characterized by 1H and  31  P{1H} NMR spectroscopies,  elemental analysis, mass spectrometry, UV-vis and fluorescence spectroscopies, as well as X-ray crystal analyses. The UV-vis, fluorescence and solid state properties of 12 and 13 will be discussed later in this chapter. The 31P{1H} NMR spectra of 12 and 13 each show one peak at  -11.5 ppm and  -15.2 ppm, respectively. The 1H NMR spectrum of 12 contains a doublet at  9.2 ppm corresponding to the imine proton. A doublet is observed as a result of coupling with the phosphine (Figure 4.1). In the 1H NMR spectrum of 13, the doublet at  9.2 ppm is absent and a singlet appears at  4.8 ppm, as well as a broad peak at  5.0 ppm (Figure 4.2). The singlet at  4.8 ppm is assigned to the pair of protons bound to the carbon adjacent to the amine, where the double bond is located in 12. The broad peak at  5.1 ppm corresponds to the amine proton. This peak is broad due to coupling with the phosphine. The EI-MS spectra for both 12 and 13 show parent peaks at m/z, 489 and 491, respectively.  77  HNO3 acetic anhydride  O2N  .  CuSO4 H2O/NaBH4  H 2N  EtOH + O H PPh2  Benzene  H H N H PPh2  LiAlH4  N  Ether, 0oC  PPh2  (13)  (12)  Scheme 4.1 Syntheses of PNPyr (12) and PNHPyr (13).  78  reflux, 2 hr, N2  10.0  10.0  9.8  9.8  9.6  9.4  9.6  Figure 4.1  9.4  1  9.2  9.2  9.0  8.8  9.0  8.6  8.8  8.4  8.6  8.4  8.2  8.2  8.0  8.0  7.8  7.8  7.6  7.6  7.4  7.2  7.4  7.0  7.2  6.8  7.0  6.8  6.6  6.6  6.4  6.4  6.2  6.2  H NMR spectrum of PNPyr (12) in CDCl3; T = 300 K; f = 300 MHz.  *  8.0  7.8  Figure 4.2  7.6  1  7.4  7.2  7.0  6.8  6.6  6.4  6.2  6.0  5.8  5.6  5.4  5.2  5.0  H NMR spectrum of PNHPyr (13) in CDCl3; T = 300 K; f = 300 MHz.  79  4.8  4.3  Absorption and emission properties of PNPyr (12) and PNHPyr (13) The UV-vis absorption spectra of 12 (Figure 4.3) and 13 (Figure 4.4) differ from  each other, and from the absorption spectra of 1 and 2 (chapter 2). The absorption bands for 12 and 13 are broad and structureless, suggesting that the pyrenyl based –* transitions that typically give rise to structured absorption bands in the UV region21 must be buried beneath absorption from the rest of the molecule. In the case of 1 and 2 these other absorptions were hidden beneath the strong pyrenyl –* transitions. In addition the 1  La bands for 12 and 13, at 385 nm and 411 nm respectively, are red shifted compared to  those of 1 and 2, both at 345 nm.  80  Molar Absorptivity  10-4 (M-1cm-1)  3.0  2.5  2.0  385  1.5  340 1.0  0.5  0.0 300  400  500  600  Wavelength (nm)  Molar Absorptivity  10-4 (M-1cm-1)  Figure 4.3 UV-Vis absorption spectrum of PNPyr (12); [12] ≈ 10-4 M in CHCl3.  3.0  290  2.5  411 384  2.0  1.5  1.0  0.5  0.0 300  400  500  600  Wavelength (nm)  Figure 4.4 UV-Vis absorption spectrum of PNHPyr (13); [13] ≈ 10-4 M in benzene. 81  The steady-state fluorescence spectrum of 12 in CHCl3 is shown in Figure 4.5. When the steady-state emission of 12 was observed over time a small red shift was observed, and the intensity of the emission increased significantly. After 3 days excimer emission was observed at ~ 540 nm. Hydrolysis of 12 in solution may explain the increase in emission intensity that is observed as a function of time as well as the appearance of the excimer emission. Hydrolysis of the imine could result in increased fluorescence from the pyrene group if non-radiative quenching occurs between the pyrene and the rest of the molecule in 12. The steady-state emission of 1-aminopyrene and 12 were compared (Figure 4.6). The emission of 1-aminopyrene is significantly more intense than that of 12. The emission bands of 12 at 412 nm and 436 nm coincide with the emission bands of 1-aminopyrene supporting the conclusion that hydrolysis of the imine functionality of 12 is occurring in solution. The difference in emission intensity between 1-aminopyrene and 12 indicates that non-radiative quenching may be occurring in 12 and that the emission observed for 12 may be due almost exclusively to the species generated upon hydrolysis of the compound in solution. Therefore, if upon complexation of 12 to a metal center, hydrolysis is prevented, then ―ON-OFF‖ fluorescence sensing may be possible.  82  450000 400000 PNPyr (immediately)- excitation (max= 358nm) PNPyr (immediately)- emission (max= 436nm) PNPyr (45 mins)- excitation (max= 361nm) PNPyr (45 mins)- emission (max= 435nm) PNPyr (1.5 hr)- excitation (max= 361nm) PNPyr (1.5 hr)- emission (max= 412nm) PNPyr (3 days)- excitation (max= 362nm) PNPyr (3 days)- emission (max= 412nm)  350000  Intensity (a.u.)  300000 250000 200000 150000 100000 50000 0 250  300  350  400  450  500  550  600  650  Wavelength (nm)  Figure 4.5 Excitation and emission spectra of 12; [12] ≈ 10-6 M in CH2Cl2.  83  3000000  Intensity (a.u.)  2500000  2000000  1500000  1000000  500000  0 250  300  350  400  450  500  550  600  650  Wavelength (nm)  Figure 4.6  Excitation (—) and emission (—) spectra of 1- aminopyrene compared to  excitation and emission spectra of 12 (see Figure 4.5). [1-aminopyrene] ≈ 10-6 M in CH2Cl2; ex = 355 nm; em = 382 nm.  84  The steady-state fluorescence spectrum of 13 (Figure 4.7) matches its absorption spectrum. The emission intensity observed for 13 at 10-6 M is notably less than that observed for 1 and 2 at 10-6 M, indicating that non-radiative quenching is occurring. Also, as in the case of 1 and 2, no excimer emission is observed for 13 when the concentration ≤ 10-4 M (Figure 4.8). At 10-4 M re-absorption effects are observed in the excitation spectra of 13. However, significant emission is still observed for 13 making it a potential ligand for an ―OFF-ON‖ sensor if complete quenching of its emission may be achieved via PET from a metal center.  300000  Intensity (a.u.)  250000  200000  150000  100000  50000  0 250  300  350  400  450  500  550  600  650  Wavelength (nm)  Figure 4.7 Excitation (—) and emission (—) spectra of 13; [13] ≈ 10-6 M in benzene; ex = 373 nm; em = 426 nm.  85  3500000  Intensity ( a.u .)  3000000 2500000 2000000 1500000 1000000 500000 0 250  300  350  400  450  500  550  600  650  Wavelength (nm)  Figure 4.8  Excitation and emission spectra of 13; [13] ≈ 10-4 M (—); [13] ≈ 10-5 M  (—); [13] ≈ 10-6 M (—); in benzene; ex = 373 nm; em = 426 nm.  86  4.4  Solid-state structure of PNPyr (12) and PNHPyr (13)  4.4.1 Solid-state structure of PNPyr (12) Crystals of 12 suitable for X-ray analysis were grown from a hot hexane solution. The solid-state structure of 12 (isomer 1) is shown in Figure 4.9. The molecule crystallizes with two independent molecules in the asymmetric unit; the crystal is a racemic twin. Final refinements indicate that there is roughly a 7:3 ratio between the two racemates. The crystallographic data for 12 are presented in Table 4.1. The C-X (X = N, P) bond lengths (Table 4.2) and C-X-C (X = N, P) bond angles (Table 4.3) closely resemble those reported for 1 (see Chapter 2, Table 2.2). In addition, the C-X (X = N, P) bond lengths and C-X-C (X = N, P) bond angles resemble those of similar phosphine imine ligands that have been reported in the literature.39,52 Intermolecular -stacking is not observed between interpenetrating molecules of 12. The closest pyrene-pyrene interplanar distance is 8.252 Å.  87  Figure 4.9 ORTEP view of 12 (isomer 1). The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability. Table 4.1 Crystallographic data for 12.  a  chemical formula C35H24PN  formula weight  489.52  a/Å  25.245(3)  space group  Pna21 (#33)  b/Å  8.2523(9)  T/oC  -100.0 ± 0.1  c/Å  24.778(4)  (Mo K)/ Å  0.71073  /º  90.0  Dcalc/g cm-3  1.2260  /º  90.0   (Mo K)/cm-1  1.31  /º  90.0  R(Fo)a (I > 0.00(I))  0.040  V/Å3  5162(1)  Rw(Fo)b (I > 0.00(I))  0.066  Z  8  R(Fo2)a (all data)  0.081  Rw(Fo2)b (all data)  0.075  R   Fo  Fc /  Fo  b  Rw  ( ( Fo2  Fc2 ) 2 /  w( Fo2 )2 )1 / 2  88  Table 4.2 Selected interatomic distances (Å) for 12. Bond Lengths /Å Isomer 1  Isomer 2  N(1)-C(1)  1.426(5)  1.408(5)  N(1)-C(17)  1.285(5)  1.287(5)  C(17)-C(18)  1.485(5)  1.475(5)  P(1)-C(23)  1.840(4)  1.840(4)  P(1)-C(24)  1.834(4)  1.827(4)  P(1)-C(30)  1.830(5)  1.831(4)  Table 4.3 Selected interatomic angles (deg) for 12. Bond Angles /deg Isomer 1  Isomer 2  C(1)-N(1)-C(17)  117.2(3)  117.3(4)  N(1)-C(17)-C(18)  121.1(4)  123.0(4)  C(2)-C(1)-N(1)  122.4(4)  123.4(4)  C(30)-P(1)-C(23)  101.17(18)  101.94(17)  C(23)-P(1)-C(24)  103.75(18)  103.3(17)  C(24)-P(1)-C(30)  101.75(18)  101.94(17)  Isomer 1  Isomer 2  N(1)-C(1)-C(2)-C(3)  -177.6(4)  178.7(4)  C(1)-N(1)-C(17)-C(18)  -175.9(3)  174.2(3)  N(1)-C(17)-C(18)-C(23)  -168.2(4)  -177.0(4)  P(1)-C(23)-C(18)-C(17)  -5.4(5)  0.7(5)  Torsion Angles/deg  89  4.4.2 Solid-state structure of PNHPyr (13) Crystals of 13 suitable for X-ray analysis were grown from a hot hexane solution. The solid-state structure of 13 is shown in Figure 4.10 and the crystallographic data for 13 are presented in Table 4.4. The C-X (X = N, P) bond lengths (Table 4.5) and C-X-C (X = N, P) bond angles (Table 4.6) are similar to those reported for 12 (above), with the exception of the torsion angle between the pyrenyl moiety (C1) and the diphenylphosphino moiety (C18). In the case of 12, the pyrenyl moiety lies almost planar to the rest of the molecule (Table 4.3); whereas, the pyrenyl moiety is almost perpendicular to the rest of the molecule in 13 (Table 4.6). As with 12, intermolecular stacking is not observed between interpenetrating molecules of 13. However, the pyrenepyrene interplanar distance of 4.64 Å for 13 is significantly smaller than the 8.252 Å observed in 12.  Figure 4.10 ORTEP view of 13. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability.  90  Table 4.4 Crystallographic data for 13.  a  chemical formula C35H26PN  formula weight  491.54  a/Å  9.7952(9)  space group  P – 1 (#2)  b/Å  10.697(1)  T/oC  -100.0 ± 0.1  c/Å  13.037(1)  (Mo K)/ Å  0.71073  /º  76.148(4)  Dcalc/g cm-3  1.289  /º  81.327(4)   (Mo K)/cm-1  1.34  /º  73.509(4)  R(Fo)a (I > 0.00(I))  0.041  V/Å3  1266.7(2)  Rw(Fo)b (I > 0.00(I))  0.096  Z  2  R(Fo2)a (all data)  0.067  Rw(Fo2)b (all data)  0.106  R   Fo  Fc /  Fo  b  Rw  ( ( Fo2  Fc2 ) 2 /  w( Fo2 )2 )1 / 2  Table 4.5 Selected interatomic distances (Å) for 13. Bond Lengths /Å N(1)-C(1)  1.396(2)  N(1)-C(17)  1.4618(19)  C(17)-C(18)  1.521(2)  P(1)-C(23)  1.8503(14)  P(1)-C(24)  1.8381(15)  P(1)-C(30)  1.8416(15)  91  Table 4.6 Selected interatomic angles (deg) for 13. Bond Angles /deg C(1)-N(1)-C(17)  121.97(14)  N(1)-C(17)-C(18)  116.03(13)  C(2)-C(1)-N(1)  120.81(14)  C(30)-P(1)-C(23)  102.67(6)  C(23)-P(1)-C(24)  103.03(6)  C(24)-P(1)-C(30)  101.85(7)  Torsion Angles/deg N(1)-C(1)-C(2)-C(3)  -174.05(15)  C(1)-N(1)-C(17)-C(18)  89.48(18)  N(1)-C(17)-C(18)-C(23)  178.18(14)  P(1)-C(23)-C(18)-C(17)  -9.71(19)  92  4.5  Experimental  4.5.1 General All reactions were carried out under a nitrogen atmosphere unless otherwise stated. NMR spectra were acquired on Bruker Avance 300 or Avance 400 instruments. Residual protonated solvent peaks were used as internal 1H references (vs. TMS and  0). P{1H} NMR spectra were referenced to 85% H3PO4 ( 0). Elemental analyses and mass  31  spectra were carried out by the UBC Department of Chemistry Microanalytical Services Laboratory. Electron impact (EI) mass spectra were obtained on a Kratos MS-50 mass spectrometer. IR spectroscopic measurements were carried out using a BOMEM MB155S FTIR spectrometer using solution samples. All FTIR spectra were corrected for solvent by subtracting the appropriate solvent spectrum. UV-vis and fluorescence spectra were all carried out in HPLC grade dichloromethane. UV-vis spectra were obtained using a Cary 5000 UV-vis-near-IR spectrophotometer. A 1-cm quartz cell was used. Fluorescence spectra for 3-11 were collected using a Varian Cary Eclipse spectrofluorometer (5 nm excitation and emission slit widths). Measurements were made in a 1-cm quartz cell in nitrogen purged solutions. 4.5.2 Materials Chemicals were used as received from the supplier (Aldrich, Strem) unless otherwise specified. Deuterated solvents were used as received from Cambridge Isotope Labs. Spectroscopic grade CH2Cl2 used for UV-vis and fluorescence measurements gave negligible background luminescence at the excitation wavelengths used for the fluorescence measurements.  93  4.5.3 Synthesis and characterization of the phosphine pyrenyl imine ligand 4.5.3.1 Synthesis of 1-nitropyrene Pyrene (98%) (10.0 g, 0.0490 mol) was dissolved in 250 mL of acetic anhydride. To the mixture, a solution of 95% HNO3 (3 mL) was added, and the solution was stirred for 16 hours. The reaction mixture was poured over ice containing 20 mL H2SO4. The reaction flask was rinsed with acetic anhydride (3  50 mL) and the washings added to the ice slurry. The mixture was stirred until all the ice had melted. The resulting brown precipitate was dissolved in methanol with heating, and hot filtered to remove insoluble material. The brown-yellow solid filtered from the cooled methanol solution was recrystallized in acetic acid to yield a orange-brown microcrystalline solid. m.p.= 155 oC. 4.5.3.2 Synthesis of 1-aminopyrene 1-Nitropyrene (5.17 g, 0.0209 mol) was added to 300 mL dry ethanol. The reaction flask was cooled in an ice bath and the mixture stirred for 10 min. To this mixture, CuSO4 (6.28 g, 0.0251 mol) was added and the reaction mixture stirred for 5 min. NaBH4 (1.98 g, 0.0523) was added slowly over 15 min. The ice bath was removed and the reaction was allowed to warm to room temperature. The reaction was followed by TLC (10% EtOAc in CH2Cl2). After 2 hours the reaction was complete and the mixture was filtered to remove insoluble material. To the filtrate, 400 mL H2O and 300 mL CH2Cl2 were added. The organic phase was separated and the aqueous phase extracted with CH2Cl2 (2  50 mL). The organic phase was dried over MgSO4 and concentrated via rotary evaporation to yield a yellow solid. The yellow solid was recrystallized from cyclohexanes to give yellow crystals. Yield: 74%. m.p. = 117 oC.  94  The physical properties, FT-IR and melting points of 1-nitropyrene and 1aminopyrene matched those available through the Aldrich website, such that both of the synthesized compounds were taken to be the desired products of acceptable purity for their subsequent syntheses. 4.5.3.3 Synthesis and characterization of 12 (PNPyr) 2-Diphenylphosphine benzaldehyde (534 mg, 1.84 mmol) was dissolved in 20 mL dry, degassed benzene. A solution of 1-aminopyrene (400 mg, 1.84 mmol) in 20 mL dry, degassed benzene was added via cannula transfer. The reaction mixture was heated to reflux for 2 hours and then allowed to cool to room temperature. The solution was dried over MgSO4. Benzene was removed in vacuo to give a dark yellow oil. The oil was crystallized from hot hexanes to yield dark yellow crystals. Yield: 54%.  31  P{1H} NMR  (300 MHz, CDCl3): δ -11.5. 1H NMR (300 MHz, CDCl3): δ 7.89- 8.46 (m, 9H, pyr), 7.30- 7.62 (m, 11H, Ph), 7.22-7.28 (m, 2H, Ph), 6.95- 7.08 (m,1H, Ph), 9.23- 9.27 (d, JP-H = 5.0 Hz, 1H, HC=N). MS (EI-MS), m/z 489. Anal. Calcd for C25H24NP: C, 85.87; N, 2.86; H 4.94. Found: C 86.00; N, 3.20; H 5.04. 4.5.4 Synthesis and characterization of 13 (PNHPyr) A reaction flask containing LiAlH4 (32.3 mg, 0.852 mmol) and dry, degassed ether (50 mL) was cooled in an ice bath. A solution of PNpyr (139 mg, 0.284 mmol) in 50 mL dry, degassed ether was added via cannula transfer. The ice bath was removed and the reaction mixture stirred at room temperature. The reaction was monitored by 31P{1H} NMR. After 18 hours the  31  P{1H} NMR spectrum no longer contained a peak  corresponding to the starting material, 12, and the reaction quenched by addition of ice to the reaction flask. The ether was removed in vacuo and the aqueous solution was 95  extracted with CH2Cl2 (5  50 mL). The organic phase was dried over MgSO4 and concentrated via rotary evaporation to yield a yellow-orange oil. The oil was crystallized from hot hexanes to give yellow-orange crystals. Yield: 94%. 31P{1H} NMR (300 MHz, CDCl3): δ -15.2. 1H NMR (300 MHz, CDCl3): δ 7.42- 7.97 (m, 9H, pyr), 7.19- 7.35 (m, 13H, Ph), 6.99- 7.01 (m,1H, Ph), 4.96 (broad, 1H, NH), 4.84 (s, 2H, CH2). MS (EI-MS), m/z 491. Anal. Calcd for C25H26NP: C, 85.52; N, 2.85; H 5.33. Found: C 85.42; N, 3.15; H 5.39. 4.5.5 X-ray crystallographic analyses 4.5.5.1 X-ray crystallographic analysis of 12 A yellow plate crystal of 12 was mounted on a glass fiber, and the data was collected at -100.0 ±0.1 oC. The structure was solved using direct methods44 and refined using SHELXTL.45 The crystal is a racemic twin, therefore, final refinements were carried out using the TWIN/BASF functions in SHELXL45, which determined roughly a 7:3 ratio between the two racemates. All measurements were made on a Bruker X8 APEX diffractometer with graphite monochromated Mo-K radiation. The data for 12 were collected to a maximum 2 value of 44.9°. Data were collected in a series of and  scans in 0.50° oscillations with 30.0 second exposures. The crystal to detector distance was 38.00 mm. Data were collected and integrated using the Bruker SAINT46 software package and were corrected for absorption effects using the multi-scan technique (SADABS).47 The data were corrected for Lorentz and polarization effects. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were included in calculated positions but not refined.  96  4.5.5.2 X-ray crystallographic analysis of 13 A yellow plate crystal of 13 was mounted on a glass fiber, and the data was collected at -100.0 ±0.1 oC. The structure was solved using direct methods44 and refined using SHELXTL.45 All measurements were made on a Bruker X8 APEX diffractometer with graphite monochromated Mo-K radiation. The data for 13 were collected to a maximum 2 value of 55.7°. Data were collected in a series of and  scans in 0.50° oscillations with 15.0 second exposures. The crystal to detector distance was 38.02 mm. Data were collected and integrated using the Bruker SAINT46 software package and were corrected for absorption effects using the multi-scan technique (SADABS).47 The data were corrected for Lorentz and polarization effects. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were included in calculated positions but not refined.  97  Chapter 5 Palladium Halide Complexes Containing the Phosphine Pyrenyl Imine and Phosphine Pyrenyl Amine Ligands (PNPyr and PNHPyr) 5.1  Motivation A palladium complex with a phosphine imino pyridyl ligand has been reported by  Vrieze and coworkers that reacts with CO via replacement of the labile pyridine group (Figure 5.1).39 They reported that the imine was also labile. Based on this chemistry, it was proposed that coordinating the phosphine pyrenyl imine and amine ligands reported in Chapter 4 to palladium, it may be possible to take advantage of the hemilability in chemosensors.  N Ph2P Pd N  + X-  + X-  N (CH2)2  CO  N Ph2P Pd CO  CH3  X = Cl, OTf  CH3 Figure 5.1 Reactivity of a palladium phosphine-imine pyridyl complex with CO.39 Reddy and coworkers have also reported palladium complexes with a variety of phosphine amine and phosphine imine ligands for use in the copolymerization of ethylene/carbon monoxide.52 These complexes have not been used for sensing applications, but they do provide precedence for the syntheses of palladium complexes of the type that are reported in this chapter (Chart 5.1).  98  Chart 5.1 H  H  Pyr N  P Ph2  Pyr  NH  Cl Pd Cl  Pd P Ph2  Cl Cl  Pyr =  PdCl2(PNHPyr-P,N) 15  PdCl2(PNPyr-P,N) 14  5.2  H  Synthesis and characterization of PdCl2(PNPyr-P,N) (14)  5.2.1 Synthesis of PdCl2(PNPyr-P,N) (14) To prepare complex 14, PdCl2(COD) was dissolved in a minimal amount of dry, degassed CH2Cl2 and then added rapidly to a solution of PNPyr, 12, in dry, degassed CH2Cl2 (Scheme 5.1). Upon addition of the PdCl2(COD) solution the reaction mixture immediately turned from bright yellow to orange-red. The reaction mixture was stirred under nitrogen at room temperature for 2 hours. The bright orange precipitate was filtered from the reaction mixture and washed with hexanes followed by hot CH2Cl2.  PdCl2(COD) +  N PPh2  N  CH2Cl2 RT, 2 hr, N2  Scheme 5.1 Synthesis of PdCl2(PNPyr-P,N) (14).  99  Pd P Ph2  Cl Cl  5.2.2 Characterization of PdCl2(PNPyr-P,N) (14) Complex 14 was characterized by  1  31  P{1H} NMR spectroscopies,  H and  elemental analysis, time of flight mass spectrometry, infrared spectroscopy, UV-vis and 31  P{1H} NMR  fluorescence spectroscopies, as well as by X-ray crystal analysis. The  spectrum of 14 contains one peak at  = 29.3 ppm. The 1H NMR spectrum of 14 contains a singlet at  = 8.42 ppm corresponding to the imine proton (Figure 5.2). In the case of the unbound ligand, 12, the peak due to the imine proton was split into a doublet (Figure 4.2), however, no splitting is observed for 14. Reddy and coworkers have reported similar phosphine imine palladium complexes,52 and the 1H NMR spectra of these complexes show similar features to those observed for 14.  HA N  Cl  Pd  P Ph2  Cl HA  1 0 .0  9 .8  9 .6  Figure 5.2  9 .4  9 .2  1  9 .0  8 .8  8 .6  8 .4  8 .2  8 .0  7 .8  7 .6  7 .4  7 .2  7 .0  6 .8  6 .6  6 .4  6 .2  H NMR spectrum of PdCl2(PNPyr-P,N) (14) in CDCl3; T = 300 K; f = 300  MHz.  100  5.3  Absorption and emission spectra of PdCl2(PNPyr-P,N) (14) The absorption spectrum of 14 is shown in Figure 5.3. Structured absorption  bands are observed for 14, and are assigned to pyrenyl based -* transitions.21 The 1La band observed for 14, at 370 nm, is slightly blue-shifted compared to that observed for 12, at 385 nm (see Figure 4.3). It should also be noted that the molar absorptivity of 14 is significantly larger that that for 12.  Molar Absorptivity (M-1cm-1)  700000 600000 273 500000 400000  334 300000 200000  370  100000 0 300  400  500  600  Wavelength (nm)  Figure 5.3  UV-vis absorption spectrum of PdCl2(PNPyr-P,N) (14); [14] ≈ 10-6 M in  CHCl3.  101  The steady-state fluorescence spectrum of 14 is very weak. When 14 is observed under hand held UV light, no fluorescence can be observed by the naked eye. It is possible that ligand fluorescence is quenched via PET by the metal center. No excimer emission was observed for samples of 14 ≤ 10-4 M. 5.4  Solid-state structure of PdCl2(PNPyr-P,N) (14) Crystals of 14 suitable for X-ray analysis were grown from hot CH2Cl2 solution.  The solid-state structure is shown in Figure 5.4. The crystallographic data for 14 are presented in table 5.1. The Pd-X (X = N, P, Cl) and C-X (X = N, P) bond lengths are shown in Table 5.2. The Pd-X bond lengths closely resemble those reported for similar palladium complexes by Reddy and coworkers.52 The C-X bond lengths for 14 remain almost the same as those reported for the free ligand, 12, with the exception of the C-P bond lengths with are slightly shorter for 14 than for 12 (Table 4.2). The X-Pd-X (X = N, P, Cl), Pd-X-C (X = N, P), and C-X-C (X = N, P) bond lengths are presented in Table 5.3. The X-Pd-X bond angles are similar to those reported by Vrieze and co-workers for their phosphino-imino-pyridyl palladium complexes.39 The C-X-C bond lengths remain almost the same as reported for the free ligand, 12, with the exception of the C-P-C bond angles which are slightly larger for 14 than for 12. Selected torsion angles for 14 are presented in Table 5.4. Intermolecular -stacking is not observed between interpenetrating molecules of 14. The closest pyrene-pyrene interplanar distance observed is 4.133 Å.  102  Figure 5.4 ORTEP view of 14. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability.  103  Table 5.1 Crystallographic data for 14. chemical formula  C35H24PNPdCl2 formula weight  666.82  a/Å  8.933(2)  space group  P – 1 (#2)  b/Å  10.221(2)  T/oC  -100.0 ± 0.1  c/Å  16.382(2)  (Mo K)/ Å  0.71073  /º  72.791(8)  Dcalc/g cm-3  1.558  /º  88.914(8)   (Mo K)/cm-1  9.23  /º  84.365(8)  R(Fo)a (I > 0.00(I))  0.049  V/Å3  1421.8(5)  Rw(Fo)b (I > 0.00(I))  0.110  Z  2  R(Fo2)a (all data)  0.093  Rw(Fo2)b (all data)  0.130  a  R   Fo  Fc /  Fo  b  Rw  ( ( Fo2  Fc2 ) 2 /  w( Fo2 )2 )1 / 2  Table 5.2 Selected interatomic distances (Å) for 14. Bond Lengths/ Å Pd(1)-N(1)  2.092(5)  N(1)-C(1)  1.443(8)  Pd(1)-P(1)  2.2297(16)  N(1)-C(17)  1.295(8)  Pd(1)-Cl(1)  2.2832(15)  C(17)-C(18)  1.470(9)  Pd(1)-Cl(2)  2.3764(17)  P(1)-C(23)  1.803(6)  P(1)-C(24)  1.806(6)  P(1)-C(30)  1.820(6)  104  Table 5.3 Selected interatomic angles (deg) for 14. Bond Angles/deg N(1)-Pd(1)-P(1)  89.51(15)  C(1)-N(1)-C(17)  117.0(5)  N(1)-Pd(1)-Cl(1)  177.87(14)  N(1)-C(17)-C(18)  128.9(6)  N(1)-Pd(1)-Cl(2)  90.53(15)  C(2)-C(1)-N(1)  120.1(7)  P(1)-Pd(1)-Cl(1)  89.43(6)  C(30)-P(1)-C(23)  105.1(3)  P(1)-Pd(1)-Cl(2)  175.30(7)  C(23)-P(1)-C(24)  106.4(3)  Cl(1)-Pd(1)-Cl(2)  90.68(6)  C(24)-P(1)-C(30)  106.4(3)  Pd(1)-N(1)-C(1)  116.6(4)  Pd(1)-N(1)-C(17)  125.9(4)  Pd(1)-P(1)-C(23)  106.7(2)  Pd(1)-P(1)-C(24)  112.1(2)  Pd(1)-P(1)-C(30)  119.27(19)  Table 5.4 Selected interatomic torsion angles (deg) for 14. Torsion Angles/deg C(1)-N(1)-Pd(1)-P(1)  -151.9(4)  N(1)-C(1)-C(2)-C(3)  173.9(7)  C(17)-N(1)-Pd(1)-P(1)  36.1(5)  C(1)-N(1)-C(17)-C(18)  -175.6(7)  C(23)-P(1)-Pd(1)-N(1)  -45.5(3)  N(1)-C(17)-C(18)-C(23)  -23.2(11)  C(24)-P(1)-Pd(1)-N(1)  70.6(3)  P(1)-C(23)-C(18)-C(17)  -1.0(9)  C(30)-P(1)-Pd(1)-N(1)  -164.1(3)  105  5.5  Reactivity of PdCl2(PNPyr-P,N) (14) towards sulfur dioxide Initially, complex 14 was reacted with carbon monoxide in order to compare its  reactivity with the reactivity of the ruthenium complexes 3-5 (Chapter 3). Unfortunately, attempts to displace the imine functionality from the palladium center of 14 in the same manner as for 3-5, by sparging their solutions with gaseous CO, were unsuccessful. The affinity of CO towards palladium appears lower than towards ruthenium. Pd is a softer transition metal, and reaction of CO with 14 may only occur under higher pressures. As other palladium complexes had been previously developed in our laboratory that coordinate thiophenes and oligothiophenes, it was proposed that 14 would likely show reactivity with an analyte such as sulfur dioxide (SO2), that would act as a ―soft‖ base. Scheme 5.2 outlines the proposed reactivity of 14 with SO2 (g). Pyr N Pd P Ph2  Cl  O2S  SO2 (g)  Pd Ph2P  Cl Pyr  Cl Pyr =  Cl  N  Scheme 5.2 Proposed reactivity of 14 with SO2 (g). Initial reaction of 14 with SO2(g) was carried out by sparging a 5 mM solution of 14 in CH2Cl2 with SO2 (g) for 10 minutes. After sparging the solution, the 31P{1H} NMR spectrum showed a single weak peak, at  = 36 ppm (cf  31  P{1H}  29.3 ppm for 14).  Although this result appeared promising, the absorption and excitation spectra of solutions of 14 in CH2Cl2 sparged with SO2 (g) did not match, indicating that some decomposition was occurring. Infrared spectroscopy (IR) was used to try to determine  106  whether SO2 was coordinating to the palladium. Solution IR spectra were first obtained for the ligand, 12 and complex 14 in CH3CN. The stretching frequency, C=N in CH3CN was 1615 cm-1 for 12, and 1608 cm-1 for 14. As expected, a decrease in the C=N stretching frequency is observed upon complexation of 12 to palladium, due to a slight weakening of the C=N bond. Solution IR spectra were then obtained for 14 in CH3CN that had been sparged with SO2(g), and then for the same samples that were further sparged with N2(g) to remove excess dissolved SO2(g) from the solution. If SO2 was not binding to the palladium center, the peaks attributed to sulfur-oxygen stretching and bending modes in the IR would be expected to disappear. Both spectra showed similar features with strong peaks at 2470 cm-1, peaks at 1356 cm-1, and weak peaks appearing around 1133 cm-1. Unfortunately, the IR spectra did not provide much insight into the reactivity of 14 with SO2, however it does appear a reaction was occurring as the SO2 IR modes present after sparging solutions of 14 with SO2 remained once excess SO2 was removed from the solution. It is known that SO2 and secondary or tertiary amines form stable 1:1 chargetransfer complexes.53-60 Recently, Leontiev and Rudkevich revisited non-covalent SO2amine chemistry for the colourometric detection of SO2.61 It is possible that the reaction of 14 with SO2 leads to the formation of a non-covalent SO2-amine interaction rather than coordination of SO2 to the palladium center. In the communication by Leontiev and Rudkevich the spectroscopic features of SO2amine complexes in apolar solution were revisited. They showed that upon addition of SO2 to a solution containing a Znporphyrin.amine complex, the complex dissociated forming an SO2amine adduct.61 They also reported that the stepwise addition of piperidine or pyrrolidine to a solution of SO2 in  107  CHCl3 at room temperature resulted in the disappearance of the free SO2 absorption at max ~ 288 nm.61 It was proposed that perhaps the addition of SO2 to a solution of 14 in CH3CN, would result in the displacement of the imine moiety from the palladium center. Subsequent hydrolysis (as observed for the free ligand), would release 1-aminopyrene which could then potentially form an SO2amine adduct. In order to determine if this was occurring here, 14 was first dissolved in CH3CN/H2O to cause hydrolysis of the phosphine pyrenyl ether ligand. The steady-state emission spectrum of 14 in CH3CN/H2O shows an increase in the emission intensity over a 1 hour period of time (Figure 5.5). This spectrum was compared to the excitation and emission spectrum of 1-aminopyrene in CH3CN/H2O (Figure 5.6). The emission spectra of 14 matches that observed for 1aminopyrene, indicating that hydrolysis of the ligand is likely occurring for 14 in CH3CN/H2O, and that the observed emission spectra may be attributed to the hydrolysis product. Upon addition of SO2 to the 1-aminopyrene solution a decrease in the excitation and emission intensity is observed (Figure 5.6). This is likely due to re-absorption effects caused by excess SO2 in solution.  108  14000  Intensity (a.u.)  12000  10000  8000  6000  4000  2000  0 400  450  500  550  600  650  700  Wavelength (nm)  Figure 5.5 Emission spectra for 14 in CH3CN/H2O; at t = 0 (—) and t = 1 hr (—); [14] ≈ 10-6 M; ex = 362 nm; em = 428 nm.  109  1600000 1400000  Intensity (a.u.)  1200000 1000000 800000 600000 400000 200000 0 -200000 250  300  350  400  450  500  550  600  650  700  750  Wavelength (nm)  Figure 5.6 Excitation (—) and emission (—) spectra of 1-aminopyrene in CH3CN/H2O. Excitation (---) and emission (---) spectra of 1-aminopyrene in CH3CN/H2O sparged with SO2; [1-aminopyrene] ≈ 10-6 M; ex = 362 nm; em = 428 nm.  110  In an attempt to mimic the experiments reported by Leontiev and Rudkevich,61 solutions of CHCl3 sparged with SO2 were titrated with 1-aminopyrene. However, the absorption due to SO2 observed at 285 nm appeared to increase upon addition of 1aminopyrene to the SO2 sparged CHCl3, and so this experiment was inconclusive. An alternate mechanism that could be occurring is shown in Scheme 5.3. However, further experiments would be necessary to fully understand the reactivity of 14 towards SO2.  N  Pyr  PPh2 Cl  SO2 CH3CN/H2O  Pd SO2 Cl  HSO3_  O PPh2 Cl  +  +  H3N  Pd SO2 Cl  Scheme 5.3 Proposed reactivity of 14 with SO2 (g) in CH3CN/H2O upon hydrolysis of the phosphine pyrenyl imine ligand. 5.6  Synthesis and characterization of PdCl2(PNHPyr-P,N) (15)  5.6.1 Synthesis of PdCl2(PNHPyr-P,N) (15) It was of interest to prepare the palladium complex analogous to 14 using the PNHPyr (13) ligand to investigate the differences in the steady-state fluorescence response with respect to potential analytes. In order to prepare 15, PdCl2(COD) was dissolved in a minimal amount of dry, degassed CH2Cl2 and then added rapidly to a solution of PNHPyr, 13, in dry, degassed CH2Cl2 (Scheme 5.4). Upon addition of the PdCl2(COD) solution the reaction mixture immediately turned from yellow to orange and then back to yellow. After 30 minutes a bright yellow precipitate started to form. The reaction mixture was stirred under nitrogen at room temperature for 2 hours. The bright  111  yellow precipitate was filtered from the reaction mixture and washed with hexanes to yield a yellow powder.  H PdCl2(COD) +  H N H PPh2  H CH2Cl2 RT, 2 hr, N2  H NH  Cl  Pd P Ph2  Cl  Scheme 5.4 Synthesis of PdCl2(PNHPyr-P,N) (15). 5.6.2 Characterization of PdCl2(PNHPyr-P,N) (15) Preliminary characterization of complex 15 included 1H and  31  P{1H} NMR  spectroscopy, as well as UV-vis and fluorescence spectroscopy. The  31  P{1H} NMR  spectrum of 15 shows one peak at  = 22.2 ppm. The 1H NMR spectrum of 15 contains a singlet at  = 4.17 ppm corresponding to the methyl protons adjacent to the nitrogen and a singlet at  = 9.14 ppm attributed to the amine proton (Figure 5.7). Reddy and coworkers reported a similar phosphine amine palladium complex that shows similar 1H NMR spectral characteristics.52  112  * HB  HB  Pyr N HA  Cl Pd Cl  P Ph2  HB  HA  9.0  Figure 5.7  8.5  1  8.0  7.5  7.0  6.5  6.0  5.5  5.0  4.5  H NMR spectra of PdCl2(PNHPyr-P,N) (15) in CDCl3; T = 300 K; f = 300  MHz. 5.7  Absorption and emission spectra of PdCl2(PNHPyr-P,N) (15) The UV-vis absorption spectrum of 15 is shown in Figure 5.8. The sharp-cut off  of the absorption spectrum at 282 nm is due to solvent absorption (benzene). Unlike the previous complexes reported in this thesis, 15 showed limited solubility in chlorinated and polar organic solvents. The 1La observed for 15 appears at 345 nm, the same as for the ruthenium complexes reported in Chapter 3. In addition, the 1La band for 15 is significantly blue-shifted compared to that observed for the free ligand, 13, at 411 nm (see Figure 4.4). As can be seen clearly from the absorption spectrum of a 10-5 M solution of 15, a shoulder appears at 332 nm. As in the case of 14, the structured absorptions observed for 15 are predominantly due to the strong pyrenyl -* transitions.  113  Molar Absorptivity (M-1cm-1)  400000  300000  345 200000  282 100000  0 300  400  500  600  Wavelength (nm) Figure 5.8 UV-Vis absorption spectrum of PdCl2(PNHPyr-P,N) (15); [15] ≈ 10-6 M (—) and [15] ≈ 10-5 M (—) in benzene. The steady-state fluorescence spectrum of 15 is shown in Figure 5.9. The emission intensity is significantly stronger than that observed for 14, however, it is notably weaker than that observed for the free ligand, 13. The excitation spectrum resembles the absorption spectrum; however, it is slightly red-shifted (~ 5 nm) compared to the absorption spectrum. No excimer emission was observed for concentrations of 15 ≤ 10-4 M. As observed for the ruthenium complexes reported in Chapter 3, the emission spectrum of 15 closely resembles that of molecular pyrene, with some variations in the intensity of the structured emission bands. The steady-state fluorescence spectrum of pyrene in benzene is shown in Figure 5.10 for comparison. The emission intensity of 15 114  is significantly less than that observed for pyrene as well as that for the ligand 13 (see Figure 4.8). Although the reduction in emission is not as pronounced as in the case of 14, it appears that PET could be occurring between the palladium center and the phosphine pyrenyl amine ligand of 15.  20000  Intensity (a.u.)  16000  12000  8000  4000  0 280  340  400  460  520  580  Wavelength (nm) Figure 5.9 Excitation (—) and emission (—) spectra of 15; [15] ≈ 10-6 M; ex = 340 nm; em = 374 nm in benzene.  115  400000  Intensity (a.u.)  300000  200000  100000  0 280  340  400  460  520  580  Wavelength (nm) Figure 5.10 Excitation (—) and emission (—) spectra of pyrene; [pyrene] ≈ 10-6 M; ex = 339 nm; em = 373 nm in benzene. 5.8  Reactivity of PdCl2(PNHPyr-P,N) (15) towards sulfur dioxide Attempts to displace the amine functionality of the phosphine pyrenyl amine  ligand from the palladium center of 15 with SO2 (g) were carried out by sparging solutions of 15 in both DMSO and CH2Cl2. No colour changes were observed.  31  P{1H}  NMR was used to monitor the reactions, however, no changes in the 31P{1H} NMR shift of 15 were observed, indicating that no reaction had taken place with SO2. The palladium-amine coordinate bond may be too strong to simply displace the amine by sparging the solution with SO2 (g) under atmospheric pressure. Ideally, promoting  116  reactivity under atmospheric pressure is desirable for sensing since gases such as SO2 would require sensitivity under ambient pressure and temperature. It was proposed that perhaps the amine functionality on the palladium center could be protonated in the reaction with SO2 (g) resulting in the displacement of RNH3+ from the metal center. Attempts to protonate the amine by stirring 15 in CH2Cl2 with concentrated HCl resulted in no reaction. No change was observed in the 31P{1H} NMR spectrum of 15. However, a shift in the 31P{1H} NMR spectrum of 15 from  = 22.2 ppm to  = 28.7 ppm was observed after stirring a mixture of 15 in CH3CN with HBF4 at room temperature. Scheme 5.5 outlines the proposed reaction, however more experiments must be carried out to verify the species formed upon protonation of the amine.  H  H  H  Pyr Cl  NH Pd P Ph2  Cl  H  HBF4  N H2  CH3CN  BF4 Pyr  PPh2 Cl  Pd  NCCH3  Cl  Scheme 5.5 Proposed reaction of 15 with HBF4 in CH3CN.  117  Pyr =  5.9  Conclusions Weak fluorescence was observed for both complexes 14 and 15, implying that  PET may be occurring between the palladium metal center and the phosphine pyrenyl imine and phosphine pyrenyl amine ligands. As has been shown in a Zn2+ sensor based on an alkyl pyrene group covalently bonded to an aza-18-crown-6 at the amino nitrogen the quenching of pyrene luminescence is dependent on the length of the tether between the receptor moiety of the sensor and pyrene.26 The short tether length between the pyrene moieties of 14 and 15 and the palladium center most likely facilitates PET. Further experiments must be performed in order to investigate the reactivity of 14 and 15 with potential analytes other than CO (g) and SO2 (g). However, the differences in the ligand fluorescence for 12 and 13 compared to that for their palladium complexes are promising for the development of ―OFF-ON‖ chemosensors. It is also of interest to investigate similar complexes incorporating the phosphine pyrenyl imine and phosphine pyrenyl amine ligands with different metal centers that may promote the lability of the nitrogen functionalities.  118  5.10  Experimental  5.10.1 General All reactions were carried out under a nitrogen atmosphere unless otherwise stated. NMR spectra were acquired on Bruker Avance 300 or Avance 400 instruments. Residual protonated solvent peaks were used as internal 1H references (vs. TMS and  0). P{1H} NMR spectra were referenced to 85% H3PO4 ( 0). Elemental analyses and mass  31  spectra were both performed by the UBC Department of Chemistry Microanalytical Services Laboratory. Electrospray (ES) mass spectra were obtained on a Micromass LCT time-of-flight (TOF) mass spectrometer equipped with an ES ion source. The samples were analyzed in MeOH: CH2Cl2 (1:1) at 100 M. IR spectroscopic measurements were made using a BOMEM MB155S FTIR spectrometer and using solution samples. All spectra were corrected for solvent by subtracting the appropriate solvent spectrum. UVvis and fluorescence spectra were all carried out in HPLC grade dichloromethane. UV-vis spectra were obtained using a Cary 5000 UV-vis-near-IR spectrophotometer. A 1-cm quartz cell was used. Fluorescence spectra for 3-11 were collected using a Varian Cary Eclipse spectrofluorometer. Measurements were made in a 1-cm quartz cell in nitrogen purged solutions. 5 nm excitation and emission slit widths were used. 5.10.2 Materials Chemicals were used as received from the supplier (Aldrich, Strem) unless otherwise specified. Deuterated solvents were used as received from Cambridge Isotope Labs. Sulfur dioxide was obtained from Praxair and was used as received. Spectroscopic grade CH2Cl2 used for UV-vis and fluorescence measurements gave negligible  119  background luminescence at the excitation wavelengths used for the fluorescence measurements. 5.10.3 Synthesis and characterization of PdCl2(PNPyr - P,N) (14) PNPyr (206 mg, 0.421 mmol) was dissolved in 5 mL dry, degassed CH2Cl2. PdCl2(COD) was dissolved in 5 mL dry, degassed CH2Cl2 in a small flask and then added rapidly to the ligand solution. The flask was rinsed with 5 mL dry, degassed CH2Cl2 and the wash was added to the reaction mixture. The colour of solution immediately changed from bright yellow to orange upon addition of PdCl2(COD). The reaction mixture was stirred at room temperature for 2 hours. The bright orange precipitate was filtered from the reaction mixture and washed first with hexanes, and then with hot CH2Cl2. Yield: 66%. IR (KBR): C=N = 1612.17 cm-1.  31  P{1H} NMR (300 MHz, CDCl3): δ 29.3. 1H  NMR (300 MHz, CDCl3): δ 8.42 (s, 1H, HC=N), 6.98- 8.36 (m, 23H). TOF MS ESI, m/z = 632.3 (M+- Cl- + 1), m/z = 630.4 (M+- Cl- - 1). Anal. Calcd for PdCl2C25H24NP: C, 60.92; N, 2.03; H 3.50. Found: C 60.99; N, 2.20; H 3.86. 5.10.4 Synthesis and characterization of PdCl2(PNHPyr - P,N) (15) PNHPyr (309 mg, 0.628 mmol) was dissolved in 5 mL dry, degassed CH2Cl2. PdCl2(COD) was dissolved in 7 mL dry, degassed CH2Cl2 in a small flask and then added rapidly to the ligand solution. The flask was rinsed with 5 mL dry, degassed CH 2Cl2 and the wash was added to the reaction mixture. The colour of the solution immediately changed from yellow to orange, then back to yellow upon addition of PdCl2(COD). After stirring for 30 min. a bright yellow precipitate started to appear. The reaction mixture was stirred for 2 hours. The bright yellow precipitate was filtered from the solution and washed with hexanes to yield a yellow powder. Yield: 71%.  120  31  P{1H} NMR (300 MHz,  CDCl3): δ 22.2. 1H NMR (300 MHz, CDCl3): δ 9.14 (s, 1H, NH), 7.30- 8.81 (m, 23H), 4.17 (s, 2H, CH2) 5.10.5 X-ray crystallographic analysis of 14 An orange needle crystal of 14 was mounted on a glass fiber, and the data was collected at -100.0 ±0.1 oC. The structure was solved using direct methods44 and refined using SHELXTL.45 All measurements were made on a Bruker X8 APEX diffractometer with graphite monochromated Mo-K radiation. The data for 14 were collected to a maximum 2 value of 48.3°. Data were collected in a series of and  scans in 0.50° oscillations with 40.0 second exposures. The crystal to detector distance was 38.01 mm. Data were collected and integrated using the Bruker SAINT46 software package and were corrected for absorption effects using the multi-scan technique (SADABS).47 The data were corrected for Lorentz and polarization effects. All non-hydrogen atoms were refined anisotropically. 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