Heterometallic assemblies from ruthenium 4 ethynylpyridyl precursors

Chapter Two describes the syntheses, characterization and general properties of RuII 4-ethynylpyridine based mononuclear and heteronuclear complexes.. 81Optical Properties of RuII 4-Eth

HETEROMETALLIC ASSEMBLIES FROM RUTHENIUM 4-ETHYNYLPYRIDYL

PRECURSORS

GE QINGCHUN

NATIONAL UNIVERSITY OF SINGAPORE

2010

HETEROMETALLIC ASSEMBLIES FROM RUTHENIUM 4-ETHYNYLPYRIDYL

PRECURSORS

BY

GE QINGCHUN

(M.Sc Nankai University, P R China)

A THESIS SUBMITTED FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

DEPARTMENT OF CHEMISTRY

NATIONAL UNIVERSITY OF SINGAPORE

2010

CONTENTS

ACKNOWLEDGEMENTS………i

SUMMARY………iii

CHAPTER LIST………vi

LIST OF SCHEMES………xii

LIST OF TABLES………xiv

LIST OF FIGURES……….xvi

LIST OF ABBREVIATIONS AND SYMBOLS………xxi

LIDY OF NUMBERED COMPLEXES……… xxiv

LIST OF CONFERENCE PAPERS AND PUBLICATIONS……… xxvi

APPENDIX: CIF FILES OF SINGLE-CRYSTAL X-RAY CRYSTALLOGRAPHY,

ESI-MS AND NMR SPECTRA CD-ROM

ACKNOWLEDGEMENTS

First of all, I am heartily thankful to my supervisor, Professor Hor Tzi Sum, Andy,

whose guidance, encouragement and patience throughout the course of this project enabled me to develop an overall understanding of this subject Without his support, this thesis would not have been possible Saying that “the day as a teacher for life is the father”, Prof Hor’s spirit of hard working, his interest in chemistry and profound philosophy of life will have a lasting impact on my attitude towards life and career

Secondly, I would like to express my gratitude to Professor Mark Humphrey at Australian National University I appreciate his kind help on the nonlinear optical studies of this work, his helpful discussion and constructive suggestions Thanks are extended to the staff of CMMAC (X-ray, Microananlytical, NMR and Mass spectrometry Laboratories) for their technical support and assistance

Thirdly, I am indebted to many of my labmates in Prof Hor’s group Specifically I would like to thank Sheau Wei for her kind help and patience in my research and daily life; Dr Weng Zhiqiang, Parag, Swee Kuan, Kian Eang, Jing Qiu, Hsiao Wei,

Dr Guo Yanhe, Dr Li Fuwei, Dr Zhang Jun, Dr Bai Shiqiang, Dr Zhao Jin, Ni Ni, Wen Hua, Gabriel, Xiao Yan, Shen Yu and Wang Jing for their help in one way or another They make the research life in laboratory colorful and full of fun

I would also like to thank National University of Singapore for granting me the research scholarship which provided me the opportunity to carry out the research for

SUMMARY

The aim of this project is to synthesize and investigate the reactivity of a series

of mononuclear Ru(II) 4-ethynylpyridine complexes: trans-[Ru(L)(C≡Cpy-4)(P-P)2]

or [Ru(η5

-C5H5)(C≡Cpy-4)(P-P)] (L = Cl or H; P-P = 2PPh3, dppm, dppe, dppf), which are used as “building blocks” to construct high nuclearity complexes with precisely controlled lengths

A range of metal fragments, from square planar Pd(II)/Pt(II) chloride, paddlewheel geometrical dirhodium tetracetate to octahedral Re(I) diimine carbonyls, have been combined with mononuclear Ru(II) acetylides to yield a diverse range of architectures and properties This project will address some of the deficiency in our knowledge of acetylide heterometallic assemblies

Chapter One gives a general introduction of Ru(II) acetylide based

mononuclear, oligo- and poly-nuclear complexes Their synthetic methods, chemical

reactivity, properties and applications are described

Chapter Two describes the syntheses, characterization and general properties of

Ru(II) 4-ethynylpyridine based mononuclear and heteronuclear complexes

In this work, the mononuclear Ru(II) acetylides are obtained by incorporation of 4-ethynylpyridine into Ru(II) fragments 4-Ethynylpyridine is the spacer of choice because it is chemically stable, conjugative, stereochemically active, geometrically directive, and able to support variety of metals in different redox states It has been

shown to serve as versatile and powerful building blocks in the construction of heterometallic complexes As a bridging ligand, 4-ethynylpyridine moiety plays an important role since it connects the donor and acceptor and is directly responsible for the degree of electronic communication between the metal centers

Systematic studies on the spectroscopic properties of both mononuclear and heteronuclear systems have been conducted They show the similarities and differences of these related complexes Individual parameters from different spectroscopies reflect the subtle changes in the bonding, induced by the electronic properties of the electron-withdrawing metal fragments introduced X-ray structural studies have been performed on most of the complexes under investigation, and could lead to their further development as molecular wires

Nonlinearity can be enhanced by either increasing the conjugation length or increasing the strength of donor or acceptor groups In this project, a series of transition metals of different nature, coordination geometry, coordination number, and oxidation states have been incorporated into Ru(II) 4-ethynylpyridine moieties and a change in the optical properties was anticipated Linear and nonlinear optical properties of the mononuclear and heteronuclear complexes will be described in

Chapter Three

Chapter Four reports the electrochemical behavior of the complexes presented

in Chapter Two Incorporation of the redox center(s), mononuclear Ru(II)

4-ethynylpyridine complexes, into one-dimensional delocalized metal fragments

increases the electron delocalization, and enhances their electronic communication Hence the heterometallic acetylide systems in this project exhibit more significant electrochemical properties Electrochemical behavior of the mononuclear Ru(II) 4-ethynylpyridine complexes and their corresponding high nuclear (di-, tri- and tetra-nuclear) assemblies have been examined by cyclic voltammetry

The experimental section is in Chapter Five The collection and refinement details of X-ray diffraction studies are listed in Tables 5.1 to 5.8 The

crystallographic analysis data (CIF files) of the structures presence in the thesis and spectra (ESI-MS and NMR) of all compounds are included in a companion CDROM placed at the back of the thesis

CHAPTER LIST

Chapter One 1

General Information of Ru(II) Acetylide Based Mononuclear, Oligo- and Poly-Nuclear Complexes 1

1.1 Introduction 1

1.2 Synthetic Methods 3

1.2.1 Mononuclear Ru(II) Acetylide Systems 3

1.2.2 Oligonuclear and Polynuclear Systems 4

1.2.2.1 Mononuclear Ru(II) Acetylides with Group 6 Metal Fragments 5

1.2.2.2 Mononuclear Ru(II) Acetylides with Group 7 Metal Fragments 6

1.2.2.3 Mononuclear Ru(II) Acetylides with Group 8 Metal Fragments 6

1.2.2.4 Mononuclear Ru(II) Acetylides with Group 9 Metal Fragments 8

1.2.2.5 Mononuclear Ru(II) Acetylides with Group 10 Metal Fragments 9

1.2.2.6 Mononuclear Ru(II) Acetylides with Group 11 Metal Fragments 10

1.2.2.7 Mononuclear Ru(II) Acetylides With Group 12 Metal Fragments 11

1.3 Chemical Reactivity 12

1.3.1 Reaction on Ru(II) Metal Center 13

1.3.1.1 Oxidation Reactions 13

1.3.1.2 Ligand Exchange 14

1.3.2 Reaction on the Spacer R 14

1.3.3 Reaction on the C≡C Moiety 15

1.3.3.1 Reactions with Electrophiles 15

1.3.3.2 Reactions with Nucleophiles 17

1.3.3.3 Fabrication of Binuclear or Cluster Systems 17

1.4 Properties and Applications 18

1.4.1 Electrochemical Properties 19

1.4.1.1 Mononuclear Ru(II) Acetylides 19

1.4.1.2 Ru(II) Acetylide Based Oligo- and Poly-Nuclear Complexes 21

1.4.2 Electronic Absorption and Photoluminescent Properties 23

1.4.2.1 Electronic Absorption Properties 23

1.4.2.2 Photoluminescent Properties 25

1.4.3 Nonlinear Optical (NLO) Properties 27

1.4.3.1 Ru(II) Mononuclear Acetylides 27

1.4.3.2 Ru(II) Acetylide Based Oligo- and Poly-Nuclear Complexes 29

1.5 Conclusions & Objectives 33

1.5.1 Ru(II) Acetylide Based Mononuclear and Heteronuclear Complexes 34

1.5.2 Diphosphine as Auxiliary Ligands 35

Chapter Two 37

Syntheses, Characterization and General Properties of Ru(II) 4-Ethynylpyridine

Based Monometallic and Heterometallic Complexes 37

2.1 Introduction 37

2.2 Results and Discussion 38

2.2.1 Monometallic Ru(II) Acetylide and Vinylidene Complexes 38

2.2.1.1 Preparation 38

2.2.1.2 Characterization and General Properties 40

2.2.1.3 Structural and Reactivity Characteristics 43

2.2.2 Heterobimetallic Complexes of d5 - d6 Series 49

2.2.2.1 Preparation 49

2.2.2.2 Characterization and General Properties 51

2.2.2.3 Structural and Reactivity Characteristics 53

2.2.3 Heterotrimetallic Complexes of d6 - d8 - d6 Series 60

2.2.3.1 Preparation 60

2.2.3.2 Characterization and General Properties 61

2.2.3.3 Structural and Reactivity Characteristics 64

2.2.4 Heterotetrametallic Complexes of d6 - d7 - d7 - d6 Series 71

2.2.4.1 Preparation 71

2.2.4.2 Characterization and General Properties 72

2.2.4.3 Structural Analysis 74

2.3 Conclusions 78

Chapter Three 81

Optical Properties of Ru(II) 4-Ethynylpyridine Based Monometallic and Heterometallic Complexes 81

3.1 Linear Optical Properties (UV-vis) 81

3.1.1 Introduction 81

3.1.2 Results and Discussion 81

3.1.2.1 Monometallic Ru(II) 4-Ethynylpyridine Complexes 81

3.1.2.2 Heterometallic Assemblies 85

3.1.3 Conclusions 92

3.2 Nonlinear Optical Properties 93

3.2.1 Introduction 93

3.2.1.1 Theory for Nonlinear Optics 94

3.2.1.2 Experimental Technique 95

3.2.2 Results and Discussion 96

3.2.2.1 Features of Real Components (γ real ) of the Nonlinearities 97

3.2.2.2 Features of Imaginary Components (γ imag ) of the Nonlinearities 98

3.2.2.3 Two-Photon Absorption (TPA) Cross-Section ζ 2 101

3.2.2.4 Comparison of Third-Order Nonlinearities between Complexes in the Present Studies and Related Complexes Reported 102

3.2.3 Conclusions 104

3.2.4 Experimental Section 105

Chapter Four 108

Electrochemical Behavior of Ru(II) 4-Ethynylpyridine Based Monometallic and Heterometallic Complexes 108

4.1 Introduction 108

4.2 Results and Discussion 109

4.2.1 Mono- and Tri- metallic Systems 110

4.2.2 Bi- and Tetra- Metallic Systems 114

4.2.2.1 Bimetallic System (RuII-ReI) 114

4.2.2.2 Tetrametallic Sytem (RuII-RhII-RhII-RuII) 117

4.3 Conclusions 120

4.4 Experimental Section 121

Chapter Five 123

Experimental Section 123

5.1 General Techniques 123

5.1.1 Reagents and Solvents 123

5.1.2 Nuclear Magnetic Resonance Spectroscopy 123

5.1.3 Electrospray Mass Spectra 124

5.1.4 Infra-red Spectroscopy 124

5.1.5 Elemental Analyses 124

5.2 X-Ray Crystal Structure Determination and Refinement 125

5.3 Syntheses and Reactions 135

5.3.1 Syntheses of Monometallic Ru(II) Acetylide or Vinylidene Complexes 135

5.3.1.1 Material Information 135

5.3.1.2 Syntheses 135

5.3.2 Syntheses of d5 – d6 Heterobimetallic Complexes 141

5.3.2.1 Material Information 141

5.3.2.2 Syntheses 141

5.3.3 Syntheses of d6 - d8 - d6 Heterotrimetallic Complexes 147

5.3.3.1 Material information 147

5.3.3.2 Syntheses 147

5.3.4 Syntheses of d6 - d7 - d7 - d6 Heterotetrametallic Complexes 151

5.3.4.1 Material information 151

5.3.4.2 Syntheses 152

References 158

LIST OF SCHEMES

Scheme 1.1 Synthesis of Ru-W binuclear complex 2 by the replacement of labile

ligand 5

Scheme 1.2 Formation of air and thermally stable trimetallic complex 4 6

Scheme 1.3 Synthesis of Fe-Ru diyndiyl complex 6 possessing three stepwise one-electron oxidation property 7

Scheme 1.4 Formation of bimetallic complexes 8 & 9 from the metallocynoacetylide ligand 7 8

Scheme 1.5 Synthesis of bimetallic cluster 11 by nucleophilic addition reation of complex 10 9

Scheme 1.6 Formation of the first Ru-Pd polymetallayne 13 and its oligomer analogue 15 9

Scheme 1.7 Synthesis of the Ru 6 Pt 3 dentrimer 18 with interesting NLO properties 10

Scheme 1.8 Synthesis of complex 20 which shows interation between Ru and Fe centers upon oxidation 11

Scheme 1.9 Nucleophilic reaction of C≡C in complex 21 11

Scheme 1.10 Synthesis of unusually bent bimetallic acetylide complex 24 12

Scheme 1.11 Oxidation reactions of complex 25 13

Scheme 1.12 Oxidation reaction of dentrimer 28 14

Scheme 1.13 Ligand exchange reactions of complexes 29 & 31 14

Scheme 1.14 Ligand alkylation of complex 33 15

Scheme 1.15 Electrophilic reaction of complex 35 16

Scheme 1.16 Nucleophilic reaction of complex 37 17

Scheme 2.1 (i) CH2 Cl 2 /MeOH/NaPF 6 , overnight at r.t.; (ii) Al 2 O 3 ; (iii) CH 2 Cl 2 /MeOH/NaPF 6 , 5h at r.t.; (iv) NaOH, 2h at r.t 39

Scheme 2.2 (i) CH2 Cl 2 /MeOH/NaPF 6 , 20h at r.t.; (ii) NaOH, 2h at r.t 39

Scheme 2.3 Formation of 5.2 from 5.1: CH2 Cl 2 , 12h at r.t 40

Scheme 2.4 (i) toluene, 4h reflux; (ii) AgPF6 , CH 3 CN, 12h reflux 50

Scheme 2.5 Formation of complexes 5.11-5.16: THF, 12h, reflux 51

Scheme 2.6 Formation of 5.17-5.21: CH2 Cl 2 , 12h at r.t 61

Scheme 2.7 Formation of 5.22-5.23: CH2 Cl 2 , 12h at r.t 61

Scheme 2.8 Formation of 5.24-5.27: THF, 12h, reflux 71

Scheme 2.9 Formation of 5.28-5.34: THF, 12h, reflux 72

Scheme 3.1 Structural changes of 5.1 upon addition of p-toluenesulfonic acid 85

Scheme 3.2 Structural changes of 5.22 upon addion of p-toluenesulfonic acid 90

Scheme 3.3 Structural changes of 5.15 upon addion of p-toluenesulfonic acid 91

Scheme 4.1 Electrochemical processes of 5.11 115

LIST OF TABLES

Table 1.1 Cyclic voltammetric data of some Ru(II) acetylide complexes 20

Table 1.2 NLO data of some Ru(II) acetylides 27

Table 1.3 Comparison of second-order NLO between precursors and mixed metal complexes 30

Table 1.4 NLO data of compounds with octupolar and dentrimer structures 32

Table 2.1 Selected bond lengths (Å) and angles (°) of 5.1, 5.2 and 5.7 47

Table 2.2 Selected bond lengths (Å) and angles (°) of 5.3, 5.4 and 5.6 47

Table 2.3 Selected bond lengths (Å) and angles (°) of 5.9, 5.11 and 5.12 56

Table 2.4 Selected bond lengths (Å) and angles (°) of 5.13 - 5.15 57

Table 2.5 Selected bond lengths (Å) and angles (°) of 5.17, 5.18, 5.22 and 5.23 67

Table 2.6 Selected bond lengths (Å) and angles (°) of 5.19 – 5.21 68

Table 2.7 Selected bond lengths (Å) and angles (°) of 5.24, 5.27, 5.31 and 5.34 75

Table 3.1 Linear and third-order nonlinear optical data 103

Table 4.1 Cyclic voltammetric data for complexes 5.1, 5.3, 5.7, 5.17 – 5.19, 5.22 and 5.23 111

Table 4.2 Cyclic voltammetric data for complexes 5.7, 5.8 and 5.11 – 5.16 115

Table 4.3 Cyclic voltammetric data for complexes 5.24, 5.26 – 5.29 and 5.34 118

Table 5.1 Crystal data and structure refinement of 5.1, 5.2 and 5.7 126

Table 5.2 Crystal data and structure refinement of 5.3, 5.4 and 5.6 127

Table 5.3 Crystal data and structure refinement of 5.9, 5.14 and 5.15 128

Table 5.4 Crystal data and structure refinement of 5.11 – 5.13 129

Table 5.5 Crystal data and structure refinement of 5.19 – 5.21 130

Table 5.6 Crystal data and structure refinement of 5.17, 5.18 and 5.22 131

Table 5.7 Crystal data and structure refinement of 5.23, 5.24 and 5.27 132

Table 5.8 Crystal data and structure refinement of 5.31 and 5.34 133

Table 5.9 Complexes crystallized as solvated molecules 134

LIST OF FIGURES

Fig 1.1 A dimetallic alkynyl complex as model for studying electron transfer

properties 22

Fig 1.2 Mixed Ru-Fe complex 47 as an electrochemical switch for NLO 23

Fig 1.3 A series of organometallic wires with numbering of the presented

Fig 2.1 Positive-ion ESI mass spectrum of 5.1 43

Fig 2.2 Crystal structure of trans-[RuCl(C Cpy-4)(dppm) 2] (5.1) with hydrogen

atoms and solvent molecules omitted for clarity 44

Fig 2.3 Crystal structure of trans-[Ru(C Cpy-4)(CH 3 CN)(dppm) 2 ](PF 6 ) (5.2)

with hydrogen atoms, anion and solvent molecules omitted for clarity 44

Fig 2.4 Crystal structure of trans-[RuCl(C Cpy-4)(dppe) 2] (5.3) with hydrogen

atoms and solvent molecules omitted for clarity 45

Fig 2.5 Crystal structure of trans-[RuH(C Cpy-4)(dppe) 2] (5.4) with hydrogen

atoms and solvent molecules omitted for clarity 45

Fig 2.6 Crystal structure of trans-[RuCl(HC=CHpy-4)(dppe)2] (5.6) with

hydrogen atoms, anion and solvent molecules omitted for clarity 46

Fig 2.7 Crystal structure of [RuCp(C Cpy-4)(dppf)] (5.7) with hydrogen atoms

and solvent molecules omitted for clarity 46

Fig 2.8 Positive-ion ESI mass spectrum of 5.10 53

Fig 2.9 Crystal structure of [ReBr(CO) 3(tpy)] (5.9) with hydrogen atoms and

solvent molecules omitted for clarity 54

Fig 2.10 Crystal structure of [RuCp(C  Cpy-4)(dppf)][Re(CO) 3 (bpy)](PF 6) (5.11)

with hydrogen atoms, anion and solvent molecules omitted for clarity 54

Fig 2.11 Crystal structure of [RuCp(C  Cpy-4)(dppf)][Re(CO) 3 (Me 2 bpy)](PF 6 )

(5.12) with hydrogen atoms, anion and solvent molecules omitted for

clarity 55

Fig 2.12 Crystal structure of [RuCp(C  Cpy-4)(dppf)][Re(CO) 3 (tBu 2 bpy)](PF 6 )

(5.13) with hydrogen atoms, anion and solvent molecules omitted for

clarity 55

Fig 2.13 Crystal structure of [RuCp(C  Cpy-4)(dppf)][Re(CO) 3 (phen)](PF 6) (5.14)

with hydrogen atoms, anion and solvent molecules omitted for clarity 56

Fig 2.14 Crystal structure of [RuCp(C  Cpy-4)(dppf)][Re(CO) 3 (tpy)](PF 6) (5.15)

with hydrogen atoms, anion and solvent molecules omitted for clarity 56

Fig 2.15 Positive-ion ESI mass spectrum of 5.19 64

Fig 2.16 Crystal structure of [trans-RuCl(C Cpy-4)(dppm) 2 ] 2 [PdCl 2] (5.17) with

hydrogen atoms and solvent molecules omitted for clarity 65

Fig 2.17 Crystal structure of [trans-RuCl(C Cpy-4)(dppm) 2 ] 2 [PtCl 2] (5.18) with

hydrogen atoms and solvent molecules omitted for clarity 65

Fig 2.18 Crystal structure of [trans-RuCl(C Cpy-4)(dppe) 2 ] 2 [PdCl 2] (5.19) with

hydrogen atoms and solvent molecules omitted for clarity 66

Fig 2.19 Crystal structure of [trans-RuCl(C Cpy-4)(dppe) 2 ] 2 [PtCl 2] (5.20) with

hydrogen atoms and solvent molecules omitted for clarity 66

Fig 2.20 Crystal structure of [trans-RuH(C Cpy-4)(dppe) 2 ] 2 [PdCl 2] (5.21) with

hydrogen atoms and solvent molecules omitted for clarity 66

Fig 2.21 Crystal structure of [RuCp(C  Cpy-4)(dppf)] 2 [PdCl 2] (5.22) with

hydrogen atoms and solvent molecules omitted for clarity 67

Fig 2.22 Crystal structure of [RuCp(C Cpy-4)(dppf)] 2 [PtCl 2] (5.23) with hydrogen

atoms and solvent molecules omitted for clarity 67

Fig 2.23 Crystal structure of [RuCp(C  Cpy-4)(dppf)] 2 [Rh 2 (O 2 CCH 3 ) 4] (5.24) with

hydrogen atoms and solvent molecules omitted for clarity 74

Fig 2.24 Crystal structure of [RuCp(C  Cpy-4)(dppf)] 2 [Rh 2 (O 2 C(CH 3 ) 3 ) 4] (5.27)

with hydrogen atoms and solvent molecules omitted for clarity 74

Fig 2.25 Crystal structure of [trans-RuCl(C Cpy-4)(dppm) 2 ] 2 [Rh 2 (O 2 CC(CH 3 ) 3 ) 4 ]

(5.31) with hydrogen atoms and solvent molecules omitted for clarity 75

Fig 2.26 Crystal structure of [trans-RuH(C Cpy-4)(dppe) 2 ] 2 [Rh 2 (O 2 CC(CH 3 ) 3 ) 4 ]

(5.34) with hydrogen atoms and solvent molecules omitted for clarity 75

Fig 3.1 UV-vis absorption spectra of 5.1- 5.3 and 5.7 in CH2 Cl 2 at 298K (inset:

in air at 298K) 83

Fig 3.2 UV-vis absorption changes of 5.1 (concentration = 4.0 x 10-5 M) in

M) (inset: Plots of absorbance at 336, 377 and 424 nm against the total

concentration of p-toluenesulfonic acid) 85

Fig 3.3 UV-vis absorption spectra of 5.7, 5.11, 5.23 and 5.25 in CH2 Cl 2 at 298K

Fig 3.4 UV-vis absorption changes of 5.22 (concentration = 8.0 x 10-6 M) in

5.22-1 to 5.22-10, representing 10 samples): 0, 0.20, 0.40, 0.60, 0.80,

and 388 nm against the total concentration of p-toluenesulfonic acid) 89

Fig 3.5 UV-vis absorption changes of 5.15 (concentration = 2.0 x 10-5 M) in

5.15-1 to 5.15-10, representing 10 samples): 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0,

against the total concentration of p-toluenesulfonic acid) 91

Fig 3.6 Selected mononuclear complexes with different acetylide ligands 103

Fig 4.1 Cyclic voltammograms of 5.1, 5.18 and 5.22 in CH2 Cl 2 (0.1 M Bu 4 NPF 6 )

at r t 111

Fig 4.2 Cyclic voltammogram of 5.12 in CH2 Cl 2 (0.1 M nBu 4 NPF 6 ) at r t 116

Fig 4.3 Cyclic voltammogram of 5.24 in CH2 Cl 2 (0.1 M nBu 4 NPF 6 ) at r t 119

LIST OF ABBREVIATIONS AND SYMBOLS

NLO nonlinear optical

NMR nuclear magnetic resonance

V voltage

v/v volume/volume

vs versus

LIST OF NUMBERED COMPLEXES

P P = dppm

P P = dppe

5.1 5.3

5.9

5.10

Cl Cl Cl

C(CH3)3

P P R

dppe

dppm dppm dppm dppm

L Cl Cl Cl Cl

C(CH3)3

dppe dppe

H H H

5.32 5.33 5.34

CH3

CH2CH3 (CH2)3CH3

CH2CH3 (CH2)3CH3

LIST OF CONFERENCE PAPERS AND PUBLICATIONS

Publications from this research work:

Journal Papers

1 Q Ge, T C Corkery, M G Humphrey, M Samoc and T S A Hor,

“Organobimetallic RuII–ReI

4-ethynylpyridyl complexes: structures and non-linear

optical properties”, Dalton Trans., 2009, 6192–6200

2 Q Ge, G T Dalton, M G Humphrey, M Samoc and T S A Hor, “Structural

and Nonlinear Optical Properties of Aligned Heterotrinuclear [RuII-(Spacer)-MII-(Spacer)-RuII] Complexes (M=Pd, Pt; spacer=4-ethynylpyridine)”,

Chem Asian J 2009, 4, 998 – 1005

3 Q Ge and T S A Hor, “Stepwise assembly of linearly-aligned Ru–M–Ru (M =

Pd, Pt) heterotrimetallic complexes with ζ-4-ethynylpyridine spacer”, Dalton Trans.,

2008, 2929–2936

4 Q Ge, G T Dalton, M G Humphrey, M Samoc and T S A Hor, “Structural,

electrochemical, linear and nonlinear optical studies of RuII -acetylide complexes and their heterometallic assembly with -4-ethynylpyridine-type spacers”, manuscript in preparation

5 Q Ge, T C Corkery, M G Humphrey, M Samoc and T S A Hor, “Linear

Heterotetranuclear RuII-RhII-RhII-RuII Assembly: A Comprehensive Study of Their

Preparation, Structure, Electrochemistry, Optical Absorption and Nonlinear Optical Properties”, submission in preparation

Conference Papers

6 Q Ge and T S A Hor, “Use of Directional Bifunctional Spacers to Construct

μ,2

-Alkynyl-Bridged Multinuclear Systems”, 6th International Symposium by

Chinese Inorganic Chemists (ISCIC-6) & 9th International Symposium by Chinese Organic Chemists (ISCOC-9) (17 - 20 Dec 2006, Grand Copthorne Waterfront Hotel,

-blank-, Singapore) Publication No 0328723, (Poster Presentation)

7 Q Ge and T S A Hor, “Multimetallic assembly of Ru(II) complexes with sigma-4-ethynylpyridine-type spacers”, in XXXVIth International Conference on

Coordination Chemistry (13 - 18 Aug 2006, Cape Town International Convention

Centre, Cape Town, South Africa), Publication No 0309662, (Poster Presentation)

8 Q Ge and T S A Hor, “RuII-based Heterometallic Assembly with

-Pyridylacetylide Spacer”, in Singapore-China Collaborative and Cooperative

Chemistry Symposium (S=C=C=C=C=S) (5 - 6 Jan 2006, National University of

Singapore, Singapore), Publication No 0226165, (Poster Presentation)

9 Q Ge and T S A Hor, “RuII-based Heterometallic Assembly with

-4-Ethynylpyridine-type Spacers”, in Pacifichem 2005 (15 - 20 Dec 2005, Honolulu,

Hawaii, United States) 168 Publication No 0211723, (Poster Presentation)

10 Q Ge and T S A Hor, “RuII-based Heterometallic Assembly with

-Ethynylpyridine Spacer”, in Singapore International Chemical Conference 4 (8 -

10 Dec 2005, Shangri-La Hotel, Singapore) Publication No 0300186, (Poster Presentation)

11 Q Ge and T S A Hor, “Nitrito-bridged heterodinuclear complexes” In The 8th

International Symposium for Chinese Organic Chemists (ISCOC-8); The 5th International Symposium for Chinese Inorganic Chemists (ISCIC-5) (19 - 22 Dec

2004, The Chinese University of Hong Kong, Hong Kong, China) Publication No

0202954, (Poster Presentation)

One possible strategy for altering and manipulating the properties of these materials is by incorporation of metal center units, MLn, into the conjugated carbon-rich organic systems This will introduce a range of properties, such as redox,6-8 luminescence,9-12 optical5,13,14 and electronic properties,15-17 since the electronic properties are modified by the incorporation of metal fragments due to the interplay among the metal ion, auxiliary ligands, and π-conjugated groups.18,19 This

effect cannot be matched by the conventional π-conjugated organic systems Moreover, compared to their organic molecules, the corresponding metal complexes, such as metal alkynyl complexes, have the advantage of much greater design flexibility, i.e by variation in metal, oxidation state, ligand environment and geometry.20-22

Metal alkynyl complexes were first reported in 1960,23 and the study of transition metal alkynyl complexes has been an intense area of research since the mid-1980’s.24 There are now over 20,000 papers focusing on metal alkynyl species and many carbon-rich organometallic systems are well documented.5,18,25-29 The scope of the research not only covers traditional organometallic areas, but also reflects the interest in utilizing these species in materials science.18,30,31 The chemistry of metal alkynyl complexes is a very topical and diverse area of interest and it is necessary to be selective in the coverage by concentrating on Ru(II) related acetylide complexes

Ru(II) acetylide complexes have been playing a key role in the development of electrochemistry14,32,33 and nonlinear optics.4,5 These complexes have also highly contributed to the development of multimetallic electrochemistry8,32,34 and nonlinearities,5 and in particular to aspects related to photoinduced electron and energy transfer processes within multicomponent assemblies, including light-active dendrimers.35-37 The chemistry of Ru(II) acetylide based mononuclear, oligonuclear and polynuclear assemblies is described in the following sections of this chapter

1.2 Synthetic Methods

1.2.1 Mononuclear Ru(II) Acetylide Systems

Mononuclear Ru(II) complexes containing C≡C groups occupy a very important position in the development of oligo- and poly-nuclear organometallic chemistry Efficient synthetic procedures to mononuclear Ru(II) acetylide complexes are

therefore crucial The synthetic scheme developed by Dixneuf et al.,38,39 in which the reaction between a dichlororuthenium phosphine complex with a terminal alkyne in the presence of NaPF6 and a base represents a significant breakthrough Up to now, a number of synthetic strategies have been developed.40-45

Mononuclear Ru(II) acetylide complexes can be obtained from reactions of terminal alkynes or anionic alkynylating agents such as alkali-metal with a 16-electron Ru(II) metal species The intermediate vinylidene metal complexes undergo deprotonation to yield the desirable metal acetylide analogues The formation of these coordinatively unsaturated species from a suitable precursor complex is achieved by the following ways: (a) the dissociation of a halide ligand driven by the precipitation of an insoluble salt of the cationic vinylidene complex.40,41 Some Ru(II) complexes have been proven to easily yield vinylidene species Ru+=C=CHR by the displacement of a halide in the presence of both a non-coordinating anion and a terminal alkyne;42 (b) the dissociation of a monodentate phosphine ligand;43 (c) the dissociation of a solvent molecule coordinated to the metal center;44,46 (d) the partial dissociation of hemilabile ligands,

which produces a vacant coordination site.45 Some preparations used more than one

of the above methods.18

1.2.2 Oligonuclear and Polynuclear Systems

There are a variety of methods to construct oligonuclear and polynuclear metal acetylide systems One of the most attractive and convenient synthetic approaches is employing “metalloligands”, i.e “metal complexes as ligands”47, as building blocks Metal complexes with a basic pendant donor can serve as metalloligands

The use of metalloligands as building blocks is very appealing for several reasons: (a) tremendous versatility due to the potentially large and diverse number of suitable transition metal complexes which can provide various spatial and electronic structures in accordance with their coordination numbers, geometries, and oxidation states; (b) the properties of each metal-containing subunit may undergo perturbation upon incorporation into the multicomponent system, and (c) a number of new processes involving different metal-containing units (intercomponent processes) may take place in the multinuclear complexes

The design of metalloligands is important for the construction of multinuclear assemblies A suitable choice of metalloligands leads to the possibility of controlling the overall structure and allows the occurrence of interesting and useful properties, such as electrochemical behavior, luminescence, optical characteristics, and function

as catalysts In order to produce defined architectures in a controlled fashion from

multiple subunits, special care must be devoted to the choice of metals, auxiliary ligands and bridging ligands There are many known metalloligands.48-51 However species containing both carbon-rich rigid bridging ligand and Ru(II) metal fragments are relatively sparse.52-55 The donor group on mononuclear Ru(II) acetylides [Ru-C≡C-R] can help the Ru(II) acetylide complexes to serve as metalloligands to prepare high-nuclearity assemblies Ru(II) acetylides containing terminal C≡C, C≡N, pyridyl, etc are widely used as building blocks in the construction of high-nuclear complexes Examples of mononuclear Ru(II) acetylides as metalloligands in the formation of oligo- or poly-nuclear assemblies are introduced based on different groups of the metals below

1.2.2.1 Mononuclear Ru(II) Acetylides with Group 6 Metal Fragments

Ruthenium and Group 6 mixed metal acetylide complexes are usually prepared from Ru(II) acetylides containing uncoordinated CN or pyridyl moieties with Cr/Mo/W bound by carbonyl and labile ligands.52,56 Reaction of complex 1 with

[W(THF)(CO)5] resulted in the displacement of the labile THF ligand and formation

of the Ru-W binuclear complex 2 in moderate yield (Scheme 1.1).57

Treatment of octahedral cluster [n-Bu4N]2[Mo6Br8(OTf)6] (OTf = triflate) with metalloligand [RuCp(C≡Cpy-4)(PPh3)2] afforded the metal-cluster-cored complex [Mo6Br8][RuCp(C≡Cpy-4)(PPh3)2]6(OTf)4.53 The apical triflate ligands in the Mo-cluster undergo hexa-substitution by the ruthenium metalloligand

1.2.2.2 Mononuclear Ru(II) Acetylides with Group 7 Metal Fragments

Only a few complexes formed from Ru(II) acetylides and metal fragments of Group 7 have been reported in the literature.58,59 Most of them are constructed

through 4-ethynylpyridine as the linker, as shown in Scheme 1.2 Treatment of Ru(II) biacetylide 3 with two equivalents of [Re(tBu2bipy)(CO)3(MeCN)](OTf) under

reflux in THF afforded the trimetallic complex 4.58

1.2.2.3 Mononuclear Ru(II) Acetylides with Group 8 Metal Fragments

There are a variety of homo- and hetero-metallic acetylide systems of Group 8

metals Most of these complexes are obtained by the reaction of Ru(II) acetylides with terminal alkynes and metal fragments from the same group.41,60 Ruthenium diynyl 5

was coupled with iron precursor [FeCp*Cl(dppe)] in NEt3 in the presence of NaBPh4

and 1,8-diazabicyclo[5.4.0] undec-7-ene (dbu) to give the Fe-Ru heterobimetallic

complex 6 in high yield (Scheme 1.3).54 This mixed Fe/Ru complex has been demonstrated to undergo three stepwise one-electron oxidations, allowing the investigation of the relative contributions of the metal and auxiliary ligands to the properties of the [{M}-CC-CC-{M}]n+ assemblies.54

oxidation property

Due to its strong coordinating ability, the CN ligand can bond strongly with late transition metal ions compared to ζ-only donor ligands or ζ- and π-donor ligands, e.g halide ions Ru(II) acetylides carrying CN group are good building blocks for the

fabrication of high nuclearity assemblies The reactions shown in Scheme 1.4 illustrate this reactivity Reaction of compound 7 with [RuCpCl(PPh 3)2] and NH4PF6

in MeOH resulted in a conversion to the homobinuclear species 8 A similar

procedure with [FeCpCl(dppe)] led to the formation of the heterobimetallic species

9.61

Ru(II) acetylide complexes can also react with osmium carbonyl complexes through C≡C unit,62

but this type of reaction is not as common as that of the Group 9 series

1.2.2.4 Mononuclear Ru(II) Acetylides with Group 9 Metal Fragments

The reaction of Ru(II) acetylide complexes with metal fragments of Group 9 is

depicted in Scheme 1.5, in which triyne 10 reacts with cobalt carbonyl complex

Co2(CO)8 and mixed metal complex 11 was obtained.62

Scheme 1.5 Synthesis of bimetallic cluster 11 by nucleophilic addition reation of complex 10

The C≡C unit in Ru(II) acetylide complexes can react with other cobalt carbonyl complexes and metal carbonyls.51,62,63

1.2.2.5 Mononuclear Ru(II) Acetylides with Group 10 Metal Fragments

A d6/d8 Ru-Pd mixed-metal polymer 13 was prepared from Ru(II) tetrayne

complex trans-[Ru(C≡C-p-C6H4-C≡CH)2(dppe)2] (12) and trans-[PdCl2(PBu3)2] through a Cu-catalyzed dehydrohalogenation process.64 Compound 13 represents the

first Ru-Pd polymetallayne to be isolated in the literature and its trimetallic model

compound 15 was also prepared from Ru(II) acetylide complex 14 and

trans-[PdCl2(PBu3)2] (Scheme 1.6).65