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Microwave-Assisted Synthesis of Modified Cyclopentadienyl Iridium and Rhodium Chloro- Bridged Dimers Loren Christopher Brown

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Microwave-Assisted Synthesis of Modified Cyclopentadienyl Iridium and Rhodium Chloro- Bridged Dimers Loren Christopher Brown Microwave-assisted Synthesis of Modified Cyclopentadienyl Iridium and Rhodium Chloro- bridged Dimers Loren Christopher Brown Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science In Chemistry Joseph S. Merola, Chair John R. Morris Gordon T. Yee Blacksburg, VA Keywords: iridium; rhodium; tetramethylcyclopentadiene; microwave; dimer; diene; crystal structure; diol; lactone I Microwave-assisted Synthesis of Modified Cyclopentadienyl Iridium and Rhodium Chloro- bridged Dimers Loren Christopher Brown Abstract The present work describes the design and synthesis of a series of dimers [(η5- 2 5 5 5 ring)MCl]2(μ -Cl)2, (where (η -ring)MCl = (η -Me4C5R)Rh(III)Cl or (η -Me4C5R)Ir(III)Cl). Iridium and rhodium dimeric complexes were synthesized via a microwave reaction and directly compared through single-crystal X-ray crystallography. Finally, the dimeric complexes were evaluated as potential oxidation catalysts. The modified HCp*R (R = isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, n- heptyl, n-octyl, phenyl, benzyl, phenethyl, cyclohexyl, and cyclopentyl) type ligands were synthesized by reaction of 2,3,4,5-tetramethylcyclopent-2-en-1-one with the respective Grignard reagent (RMgX), followed by elimination of water under acidic conditions to produce the tetramethyl(alkyl or aryl)cyclopentadienes in moderate to excellent yields (39 - 98%). Reaction of R 2 the HCp* ligands with [M(COD)](μ -Cl)2 (M = Rh, Ir; COD = 1,5-cyclooctadiene) gave the R 2 dimeric complexes [Cp* MCl]2(μ -Cl)2 in yields ranging from 16 - 96%. The dimers were characterized by nuclear magnetic resonance (NMR) spectroscopy, single-crystal X-ray diffraction (XRD) (supplemented by powder XRD), high-resolution mass spectrometry (HRMS), and elemental analysis. Complexes studied by XRD were analyzed to understand the bond lengths and bond angles throughout each complex. The dimeric complexes synthesized, will facilitate a complete study on how the R group influences catalytic activity. Acknowledgements I would like to thank Emily Ressegue who helped with the syntheses of these compounds. I would like to thank Chrissy DuChane for her assistance with biological testing, encouragement, and countless hours of proofreading. I would like to thank Dr. Paul Deck for his assistance with proofreading and support. I would like to thank Bryce Kidd and Chris Houser for their assistance in proofreading. I would like to thank Dr. Gordon Yee and Dr. John Morris for serving as my committee members. I would like to thank both Dr. Carla Slebodnick and Dr. Elinor Spencer for their guidance and assistance with crystallography. I would like to thank my advisor, Dr. Joseph Merola, for his guidance, encouragement, and resounding support. III Chapter 1 Introduction ............................................................................................................... 1 1.1 Importance of iridium and rhodium dimers ..................................................................... 1 1.2 Importance of half-sandwich complexes.......................................................................... 8 1.3 Background of microwave-assisted synthesis ................................................................ 12 1.4 Synthesis of iridium and rhodium dimers ...................................................................... 14 1.5 Project design ................................................................................................................. 15 Chapter 2 Experimental ........................................................................................................... 17 2.1 Materials and Instruments .............................................................................................. 17 2.1.1 Materials and Methods ............................................................................................ 17 2.1.2 High Resolution Mass Spectrometry ...................................................................... 17 2.1.3 Single X-ray Crystal Collection and Data Analysis: .............................................. 18 2.2 Synthesis......................................................................................................................... 18 R 2 2.2.1 General procedure for synthesis of [Cp* RhCl]2(μ -Cl)2 ....................................... 18 ethyl 2 2.2.1.1 Synthesis of [Cp* RhCl]2(μ -Cl)2 (1a) ........................................................ 18 n-propyl 2 2.2.1.2 Synthesis of [Cp* RhCl]2(μ -Cl)2 1b ...................................................... 19 isopropyl 2 2.2.1.3 Synthesis of [Cp* RhCl]2(μ -Cl)2 1c ...................................................... 19 n-butyl 2 2.2.1.4 Synthesis of [Cp* RhCl]2(μ -Cl)2 1d ........................................................ 19 isobutyl 2 2.2.1.5 Synthesis of [Cp* RhCl]2(μ -Cl)2 1e ....................................................... 20 sec-butyl 2 2.2.1.6 Synthesis of [Cp* RhCl]2(μ -Cl)2 1f ....................................................... 20 n-pentyl 2 2.2.1.7 Synthesis of [Cp* RhCl]2(μ -Cl)2 1g ....................................................... 21 n-hexyl 2 2.2.1.8 Synthesis of [Cp* RhCl]2(μ -Cl)2 1h ....................................................... 21 n-heptyl 2 2.2.1.9 Synthesis of [Cp* RhCl]2(μ -Cl)2 1i ........................................................ 21 n-octyl 2 2.2.1.10 Synthesis of [Cp* RhCl]2(μ -Cl)2 1j ......................................................... 22 phenyl 2 2.2.1.11 Synthesis of [Cp* RhCl]2(μ -Cl)2 1k ........................................................ 22 benzyl 2 2.2.1.12 Synthesis of [Cp* RhCl]2(μ -Cl)2 1l .......................................................... 22 phenethyl 2 2.2.1.13 Synthesis of [Cp* RhCl]2(μ -Cl)2 1m .................................................... 23 cyclohexyl 2 2.2.1.14 Synthesis of [Cp* RhCl]2(μ -Cl)2 1n .................................................... 23 cyclopentyl 2 2.2.1.15 Synthesis of [Cp* RhCl]2(μ -Cl)2 1o ................................................... 24 R 2 2.2.2 General procedure for synthesis of [Cp* IrCl]2(μ -Cl)2 ......................................... 24 ethyl 2 2.2.2.1 Synthesis of [Cp* IrCl]2(μ -Cl)2 2a............................................................. 24 n-propyl 2 2.2.2.2 Synthesis of [Cp* IrCl]2(μ -Cl)2 2b ......................................................... 25 isopropyl 2 2.2.2.3 Synthesis of [Cp* IrCl]2(μ -Cl)2 2c ........................................................ 25 IV n-butyl 2 2.2.2.4 Synthesis of [Cp* IrCl]2(μ -Cl)2 2d .......................................................... 25 isobutyl 2 2.2.2.5 Synthesis of [Cp* IrCl]2(μ -Cl)2 2e ......................................................... 26 sec-butyl 2 2.2.2.6 Synthesis of [Cp* IrCl]2(μ -Cl)2 2f ......................................................... 26 n-pentyl 2 2.2.2.7 Synthesis of [Cp* IrCl]2(μ -Cl)2 2g ......................................................... 26 n-hexyl 2 2.2.2.8 Synthesis of [Cp* IrCl]2(μ -Cl)2 2h .......................................................... 27 n-heptyl 2 2.2.2.9 Synthesis of [Cp* IrCl]2(μ -Cl)2 2i .......................................................... 27 n-octyl 2 2.2.2.10 Synthesis of [Cp* IrCl]2(μ -Cl)2 2j ........................................................... 27 phenyl 2 2.2.2.11 Synthesis of [Cp* IrCl]2(μ -Cl)2 2k ........................................................... 28 benzyl 2 2.2.2.12 Synthesis of [Cp* IrCl]2(μ -Cl)2 2l ............................................................ 28 phenethyl 2 2.2.2.13 Synthesis of [Cp* IrCl]2(μ -Cl)2 2m ...................................................... 29 cyclohexyl 2 2.2.2.14 Synthesis of [Cp* IrCl]2(μ -Cl)2 2n ...................................................... 29 cyclopentyl 2 2.2.2.15 Synthesis of [Cp* IrCl]2(μ -Cl)2 2o ...................................................... 29 R 2.2.3 Synthesis for HCp* ligands ................................................................................... 30 R 2.2.3.1 General procedure of HCp* ligands .............................................................. 30 2.2.3.2 Synthesis of 5-isopropyl-2,3,4,5-tetramethylcyclopenta-1,3-diene ................. 30 2.2.3.3 Synthesis of 5-butyl-1,2,3,4-tetramethylcyclopenta-1,3-diene ....................... 30 2.2.3.4 Synthesis of 5-isobutyl-1,2,3,4-tetramethylcyclopenta-1,3-diene ................... 30 2.2.3.5 Synthesis of 5-(sec-butyl)-1,2,3,4-tetramethylcyclopenta-1,3-diene .............. 30 2.2.3.6 Synthesis of 1,2,3,4-tetramethyl-5-pentylcyclopenta-1,3-diene ...................... 30 2.2.3.7 Synthesis of 5-hexyl-1,2,3,4-tetramethylcyclopenta-1,3-diene ....................... 31 2.2.3.8 Synthesis of 5-heptyl-1,2,3,4-tetramethylcyclopenta-1,3-diene ...................... 31 2.2.3.9 Synthesis of 1,2,3,4-tetramethyl-5-octylcyclopenta-1,3-diene ........................ 31 2.2.3.10 Synthesis of (2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)benzene ............... 31 2.2.3.11 Synthesis of ((2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)methyl)benzene . 31 2.2.3.12 Synthesis of (2-(2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)ethyl)benzene . 31 2.2.3.13 Synthesis of 2,3,4,5-tetramethyl[1,1’-bi(cyclopentane)]-2,4-diene ................ 31 2.2.3.14 Synthesis of (2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)cyclohexane ........ 31 2.2.4 Experimental Crystallography ................................................................................ 32 Chapter 3 Results
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