NMR STUDIES OF THE THERMAL AND PHOTOCHEMICAL REACTIONS OF CYCLOPENTADIENYL RUTHENIUM COMPLEXES By Johnathan Lee Clark A thesis submitted for the degree of Doctor of Philosophy University of York Department of Chemistry September 2011 ii Abstract The research reported in this thesis primarily focuses on the thermal and photochemical reactions of half-sandwich ruthenium complexes. The photochemical reactions employ the use of ex situ and in situ UV irradiation of the complexes. The latter of these techniques allows for samples to be irradiated within an NMR spectrometer, the principal method used to monitor reactions when highly unstable products result. The reactivity of [CpRu(PPh3)2Cl] towards a range of substrates is first described, where the thermal and photochemical (applying the ex situ method) reactions are contrasted. Replacement of PPh3 by a range of 2-electron donors, including CO, PEt3, ethene and t BuNC was achieved. Similar treatment is given to the complex, [CpRu(PPh3)2H]. However, this hydride complex proved to be slow to react and only minimal conversion to products was achieved, even using photochemical methods. The reactivity of CpRu(PPh3)2Me toward a range of 2 electron donors was considered in greater detail, particularly its ability to activate Si-H, H-H and C-H adducts under photochemical conditions. Low temperature photochemical techniques, using the in situ method, were employed to determine that both Si-H and C-H bond activation is undertaken 2 by the fragment [CpRu(κ -2-C6H4PPh2)]. This fragment was shown to activate the C-H bonds of solvent molecules, and form Ru(IV) complexes [CpRu(PPh3)(sol)(SiEt3)H], where sol = C-H activated solvent, e.g. THF) which were stable at room temperature. The substitution of PPh3 occurs in an analogous fashion to that of the chloride derivative. However, the rate of conversion was increased but no evidence for migration of either CO or ethene into the RuMe bond was observed. 3 3 3 The η -coordinated complexes, [CpRu(PPh3)(η -Si(Me2)-CH=CH2)], [CpRu(PPh3)(η - 3 3 CH2C2H3)], [CpRu(PPh3)(η -CH2C6H5)] and [CpRu(PPh3)(η -CH2C10H7)] were synthesised. 3 3 In the cases of [CpRu(PPh3)(η -CH2C2H3)] and [CpRu(PPh3)(η -CH2C6H5)], thermal and photochemical reaction was initiated with substrates to generate the corresponding η1 substituted derivatives. These products were characterised by NMR techniques. Finally, the ability of the fragment, [CpRh(NR3)], to C-H activate benzene was considered. NMR data were collected for the low stability products of the photochemical reaction which strongly indicated that this auxiliary is capable of C-H bond activation. Due to working at low temperatures (233 K) and the large amounts of amine required to generate [CpRh(NR3)], full characterisation by NMR of these species was not attained. iii Contents 1 Introduction 1 1.1 General Introduction 1 1.2 Activation of R-H bonds (where R = Si, H or C) 2 1.2.1 Si-H activation 2 1.2.1.1 Oxidative addition and metathesis reaction pathways 2 1.2.1.2 Classical and nonclassical products of oxidative addition 3 1.2.1.3 σ-CAM (σ-complex assisted metathesis) reaction 5 1.2.1.4 Hydrosilation 5 1.2.1.5 Polymerisation 10 1.2.2 H-H activation 12 1.2.2.1 Oxidative addition pathway 12 1.2.3 C-H activation 15 1.2.3.1 Oxidative addition pathway 16 1.2.3.2 Agostic interactions 18 1.3 Reactions of cyclopentadienyl ruthenium complexes 20 1.4 The role of phosphine ligands in organometallic complexes 26 1.5 Photochemically induced reactivity 29 1.5.1 Low temperature photochemistry 30 1.6 The role of NMR spectroscopy in organometallic chemistry 31 1.6.1 NOE 31 1.6.2 Dynamic NMR spectroscopy 33 1.7 Studies described in this thesis 35 2 Thermal and photochemical reactions of CpRu(PPh3)2Cl 37 2.1 Introduction 37 2.2 Overview 38 2.3 Synthesis and characterisation of CpRu(PPh3)2Cl 38 2.3.1 Synthesis of CpRu(PPh3)2Cl 38 2.3.2 NMR characterisation of CpRu(PPh3)2Cl 38 2.4 Thermal and photochemical reactions of CpRu(PPh3)2Cl with substrates 41 2.4.1 Reactions of CpRu(PPh3)2Cl with PEt3 41 2.4.1.1 Thermally initiated reaction of CpRu(PPh3)2Cl with PEt3 41 2.4.1.2 Photochemical reaction of CpRu(PPh3)2Cl with PEt3 46 iv 2.4.2 Reactions of CpRu(PPh3)2Cl with CO 47 2.4.2.1 Thermally initiated reactions of CpRu(PPh3)2Cl with CO 47 2.4.2.2 Photochemical reaction of CpRu(PPh3)2Cl with CO 48 t 2.4.3 Reactions of CpRu(PPh3)2Cl with BuNC 49 t 2.4.3.1 Thermally initiated reactions of CpRu(PPh3)2Cl with BuNC 49 t 2.4.3.2 Photochemical reaction of CpRu(PPh3)2Cl with BuNC 50 t 2.4.3.3 Synthesis of CpRu(PPh3)(CNBu )Cl 52 2.4.4 Reactions of CpRu(PPh3)2Cl with HSiEt3 52 2.4.4.1 Thermally initiated reactions of CpRu(PPh3)2Cl with HSiEt3 52 2.4.4.2 Photochemical reaction of CpRu(PPh3)2Cl with HSiEt3 53 2.4.5 Reactions of CpRu(PPh3)2Cl with H2 54 2.4.5.1 Thermally initiated reactions of CpRu(PPh3)2Cl with H2 54 2.4.5.2 Photochemical reaction of CpRu(PPh3)2Cl with H2 54 2.4.6 Reactions of CpRu(PPh3)2Cl with C2H4 55 2.4.6.1 Thermally initiated reactions of CpRu(PPh3)2Cl with C2H4 55 2.4.6.2 Photochemical reaction of CpRu(PPh3)2Cl with C2H4 55 2.4.7 Reactions of CpRu(PPh3)2Cl with C10H8 57 2.4.7.1 Thermally initiated reactions of CpRu(PPh3)2Cl with C10H8 57 2.4.7.2 Photochemical reaction of CpRu(PPh3)2Cl with C10H8 58 2.5 Conclusions 60 2.6 NMR Characterisation data 62 3 Thermal and low temperature reactions of CpRu(PPh3)2Me 71 3.1 Introduction 71 3.1.1 Context 73 3.2 Synthesis and characterisation of CpRu(PPh3)2Me 73 3.2.1 Synthesis of CpRu(PPh3)2Me 73 3.2.2 NMR characterisation of CpRu(PPh3)2Me 73 2 3.3 Synthesis and characterisation of CpRu(PPh3)(κ -2-C6H4PPh2) 75 2 3.3.1 Synthesis of CpRu(κ -2-C6H4PPh2)(PPh3) 75 2 3.3.2 NMR characterisation of CpRu(PPh3)(κ -2-C6H4PPh2) 75 2 3.3.3 The role of CpRu(PPh3)(κ -2-C6H4PPh2) 76 3.4 The thermal and photochemical reactions of CpRu(PPh3)2Me 77 3.4.1 Reactions with PEt3 77 3.4.1.1 Thermal reactions of CpRu(PPh3)2Me with PEt3 77 v 3.4.1.2 Photolysis of CpRu(PPh3)2Me with PEt3 78 3.4.1.3 Photolysis of CpRu(PPh3)2Me with PEt3 at 198 K 80 3.4.2 Photochemical reactivity of CpRu(PPh3)2Me with solvents 83 3.4.2.1 Low temperature photolysis with THF 83 3.4.2.2 Low temperature photolysis with acetone 90 3.4.2.3 Low temperature photolysis with methanol 90 3.4.3 Reactions with CO 90 3.4.3.1 Thermal reactions of CpRu(PPh3)2Me with CO 91 3.4.3.2 Photolysis of CpRu(PPh3)2Me with CO 93 3.4.4 Reactions with tBuNC 94 3.4.5 Photolysis with arenes 96 3.4.5.1 Reactions with naphthalene 97 3.4.5.2 Thermal reactions with naphthalene 98 3.4.5.3 Photochemical reaction with naphthalene 98 3.4.6 Reactions with ethene 102 3.4.6.1 Thermal reactions with ethene 102 3.4.6.2 Photochemical reaction with ethene 103 3.4.6.3 Determination of the rate of rotation for the η2-ethene moiety 106 3.4.7 Reactions with DMSO 109 3.4.7.1 Photochemical reaction with DMSO 109 3.4.8 Reactions with pyridine 112 3.4.8.1 Thermal reactions with pyridine 112 3.4.8.2 Photochemical reactions with pyridine 112 3.4.9 Reactions with H2 115 3.4.9.1 Thermal reaction with H2 116 3.4.9.2 Photochemical reaction with H2 117 3.4.10 Reactions with HSiEt3 120 3.4.10.1 Thermal reaction with HSiEt3 120 3.4.10.2 Photochemical reaction with HSiEt3 122 3.4.10.3 Photolysis of CpRu(PPh3)2Me with HSiEt3 at 298 K 123 3.4.10.4 Attempted synthesis of CpRu(PPh3)2SiEt3 128 3.4.10.5 Photolysis of CpRu(PPh3)2Me with HSiEt3 at low 129 temperature 3.4.10.6 Formation of CpRu(PPh3)2H 132 3.4.10.7 Formation of the metallated complex, Cp(SiEt2{CHCH3})2H 135 vi 3.4.10.8 Summary of the silane reactions 137 3.4.11 Attempts to selectively sequester PPh3 using sulfur and oxygen 138 3.4.11.1 Reactions involving sulfur and oxygen 139 3.4.12 Determination of the orthometallation pathway 141 3.5 Conclusions 144 3.6 NMR characterisation data 147 4 Thermal and photochemical reactions of CpRu(PPh3)2H 173 4.1 Introduction 173 4.2 Overview 175 4.3 Synthesis and characterisation of CpRu(PPh3)2H 176 4.4 Thermal and photochemical reactions of CpRu(PPh3)2H with substrates 177 4.4.1 Reactions of CpRu(PPh3)2H with PEt3 177 4.4.1.1 Thermally initiated reaction 177 4.4.1.2 Photochemical reaction 178 4.4.2 Reactions of CpRu(PPh3)2H with CO 179 4.4.2.1 Thermally initiated reaction 179 4.4.2.2 Photochemical reaction 179 t 4.4.3 Reactions of CpRu(PPh3)2H with BuNC 181 4.4.3.1 Thermal and photochemical reaction 181 4.4.4 Reactions of CpRu(PPh3)2H with HSiEt3 182 4.4.4.1 Thermally initiated reaction 182 4.4.4.2 Photochemical reaction 183 4.4.5 Reactions of CpRu(PPh3)2H with H2 183 4.4.6 Reactions of CpRu(PPh3)2H with ethene 183 4.4.7 Reactions of CpRu(PPh3)2H with naphthalene 184 4.5 Conclusions 185 4.6 NMR characterisation data 186 5 Synthesis, characterisation and photochemistry of ruthenium complexes 191 containing η1 and η3-ligands 5.1 Introduction 191 5.1.1 Context 194 vii 3 5.1.2 Synthetic routes to CpRu(PPh3)(η -Si(Me)2-CH=CH2), 196 3 3 CpRu(PPh3)(η -CH2C2H3), CpRu(PPh3)(η -CH2C6H5) and 3 CpRu(PPh3)(η -CH2C10H7) 3 5.2 Formation of CpRu(PPh3)(η -Si(Me)2-CH=CH2) 197 3 5.3 Synthesis and characterisation of CpRu(PPh3)(η -CH2C2H3) 203 3 5.3.1 Synthesis of CpRu(PPh3)(η -CH2C2H3) 204 3 5.3.2 NMR characterisation of CpRu(PPh3)(η -CH2C2H3) 204 5.3.2.1 NMR characterisation of CpRu(PPh3)2(CH2C2H3) 206 3 5.3.3 Thermal and photochemical reactions of CpRu(PPh3)(η -CH2C2H3) 206 3 5.3.3.1 Thermal reaction of CpRu(PPh3)(η -CH2C2H3) with CO 206 3 5.3.3.2 Photolysis of CpRu(PPh3)(η -CH2C2H3) with CO 208 3 5.3.3.3 Thermal reaction of CpRu(PPh3)(η -CH2C2H3) with H2 209 3 5.3.3.4 Photolysis of CpRu(PPh3)(η -CH2C2H3) with H2 209 3 5.3.3.5