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] ................