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Acceptor Ligands in Stabilizing and Assembling Pt Or Ir Carbonyl Clusters Simona El Afefey

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Acceptor Ligands in Stabilizing and Assembling Pt Or Ir Carbonyl Clusters Simona El Afefey UNIVERSITA’ DEGLI STUDI DI MILANO Scuola di Dottorato in Scienze Chimiche Dipartimento di Chimica PhD in Industrial Chemistry XXVCycle Electron-donor and -acceptor ligands in stabilizing and assembling Pt or Ir carbonyl clusters (Chim 03) Simona El Afefey Supervisor: Prof. ALESSANDRO CERIOTTI Coordinator: Prof. DOMINIQUE ROBERTO A.A. 2011/2012 Simona El Afefey Electron-donor and –acceptor ligands in stabilizing and assembling Pt or Ir carbonyl clusters ________________________________________________________________________________________________ Abstract ............................................................................................................................................... 7 Introduction ..................................................................................................................................... 21 1.1 Carbon Monoxide as ligand .................................................................................................... 21 1.2 General considerations on metal carbonyl clusters ............................................................. 25 1.2.1 Synthetic aspects of metal carbonyl clusters .............................................................. 26 1.2.2 Synthetic methods .......................................................................................................... 28 1.2.3 Direct reductive-carbonylation ................................................................................... 29 1.2.4 Thermal methods ........................................................................................................... 30 1.2.5 Redox methods .............................................................................................................. 32 1.2.6 Other chemically induced methods ............................................................................ 35 1.3 MCCs as nanocapacitors .......................................................................................................... 36 1.3.1 Electrochemistry of MCCs ........................................................................................... 39 1.3.2 Electron-sink behavior of MCCs ................................................................................. 41 1.3.3 Modulation of MCCs electronic properties and tuning of their electronic potential .................................................................................................................................... 43 1.3.4 Effectiveness of CO as insulating shielding .............................................................. 44 1.3.5 Size-induced insulator-to-metal transition of the metal core of MCCs................. 45 1.3.6 Size of MCCs .................................................................................................................. 46 1.4 Assembling MCCs ................................................................................................................... 49 1.4.1 Molecular 1D e 2D aggregates from self-assembly of MCCs .................................. 52 1.5 Magnetic properties of homo- and hetero-leptic metal clusters ........................................ 54 1.6 Analytical techniques ............................................................................................................... 57 1.6.1 Isolation ........................................................................................................................... 58 1.6.2 Infrared Spectroscopy.................................................................................................... 59 1.6.3 Nuclear Magnetic Resonance (NMR) .......................................................................... 60 1.6.3.1 Dynamic Varied Temperature NMR Spectroscopy ............................................... 61 1.6.3.2 13C NMR spectroscopy ............................................................................................... 61 1 Simona El Afefey Electron-donor and –acceptor ligands in stabilizing and assembling Pt or Ir carbonyl clusters ________________________________________________________________________________________________ 1.6.3.3 Multinuclear NMR spectroscopy .............................................................................. 62 1.6.4 X-ray crystallography .................................................................................................... 63 1.6.4.1 X-ray structure representation .................................................................................. 64 1.6.4.2 Disorder ........................................................................................................................ 65 1.7 Voltammetric techniques ......................................................................................................... 66 1.7.1 Cyclic voltammetry ........................................................................................................ 66 1.7.1.1 Reversible processes ................................................................................................... 67 1.7.1.2 Irreversible processes ................................................................................................. 71 1.7.1.3 Quasi-reversible processes ......................................................................................... 71 1.7.1.4 Chemical reaction coupled with a charge transfer ................................................. 72 1.7.2 Differential pulsed voltammetry .............................................................................. 73 1.7.3 Square wave voltammetry ........................................................................................... 75 1.7.4 Voltammetry with periodic renew of the electrodic diffusion layer ..................... 76 1.7.5 Controlled potential electrolysis .................................................................................. 77 Results and Discussion ................................................................................................................... 78 1 - Reaction between [Pt19(CO)22]4- and gold phosphane fragments ....................................... 79 3- 1.1 [Pt19(CO)22{Au(PPh3)}] ............................................................................................................ 79 1.1.1 Synthesis .......................................................................................................................... 79 - 1.2 [Pt19(CO)24{Au(PPh3)}3] (2) and [Pt19(CO)24{Au(PPh3)}4 ] (3)............................................. 81 1.2.1 Synthesis and reactivity ................................................................................................ 81 1.2.2 Solid state structures ...................................................................................................... 83 1.2.3 Electrochemical studies ................................................................................................. 85 1.3 [{Pt19Au(CO)22}4(180tetraphos)]12- .......................................................................................... 89 1.3.1 3,3-5,5’-tetrakis(diphenylphosphano)biphenyl(180tetraphos) and [{AuCl}4(180tetraphos)] .......................................................................................................... 89 1.3.2 Reactivity of [{AuCl}4(180tetraphos)] with [Pt19(CO)22]4- ......................................... 92 2- 2 - Reaction between [Ir6(CO)15] and gold phosphane fragments ......................................... 94 2 Simona El Afefey Electron-donor and –acceptor ligands in stabilizing and assembling Pt or Ir carbonyl clusters ________________________________________________________________________________________________ 2.1 [{Ir6Au(CO)15}4(180tetraphos)]4- .............................................................................................. 94 2.1.1 Reactivity of [{AuCl}4(180tetraphos)] with [Ir6(CO)15]2- ........................................... 94 2.1.2 Voltammetric study on [PPh4]4[{Ir6Au(CO)15}4(180tetraphos)] ............................... 97 2.2 [{Ir6Au(CO)15}6(120hexaphos)]6- ........................................................................................... 100 2.2.1 1,3,5-tris[3’-5’-bis(diphenylphosphano)phenyl]benzene (120hexaphos) and [{AuCl}6(120hexaphos)] ........................................................................................................ 100 2.2.2 Reactivity of [{AuCl}6(120hexaphos)] with [Ir6(CO)15]2- ......................................... 103 3 - Assembly of tetrairidium carbonyl clusters using multidentate phosphane ligands.... 105 3.1 Reactions of bis(diphenylphosphano)acetylene (dppa) and trans-1,2- bis(diphenylphosphano)ethane (t-dppethe) with [Ir4Br(CO)11]- ............................................ 107 3.1.1 Synthesis and characterization of [{Ir4(CO)11}2(dppa)] ........................................... 110 3.1.2 Solid state structure of [{Ir4(CO)11}2(dppa)] .............................................................. 111 3.1.3 Synthesis and characterization of [{Ir4(CO)11}2(t-dppethe)] ................................... 113 3.1.4 Solid state structure of [{Ir4(CO)11}2(t-dppethe)] ...................................................... 114 3.2 Reactivity of 1,4-bis(diphenylphosphano)butane (dppbut) and 1,6- bis(diphenylphosphano)hexane (dpphex) with [Ir4(CO)12] .................................................... 116 3.2.1 Synthesis and solid state characterization of [{Ir4(CO)9(-dppbut)}2(dppbut)] .. 116 3.2.2 Synthesis and solid state characterization of [{Ir4(CO)9}2(dpphex)3] ................
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