SYNTHESIS AND REACTIVITY OF RHENIUM AND TECHNETIUM POLYARYL COMPLEXES by CHRISTOPHER ALAN MORSE A.B., Chemistry, Dartmouth College (1993) SUBMITTED TO THE DEPARTMENT OF CHEMISTRY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY SEPTEMBER 1998 @ Massachusetts Institute of Technology, 1998 Signature of Author_ __ _ Department of Chemistry August 5, 1998 Certified by Alan Davison Thesis Supervisor Accepted by Dietmar Seyferth, Chairman Departmental Committee on Graduate Students MASSACHUSETTS INSTITUTE OF TECHNOLOGY SEP 3:0 1998 LIBRARIES This doctoral thesis has been examined by a committee of the Department of Chemistry as follows: Professor Daniel G. Nocera 7~ 2 ~7 N/ Chairman Professor Alan Davison Thesis Supervisor Professor Stephen J. Lippard I C rq- -- Department Chairman To my family for their unwavering support and love over the years Harry Chapin's "Flowers are Red" The little boy went first day of school; he got some crayons, and he started to draw. He put colors all over the paper for colors was what he saw. And the teacher said "What you doin', young man?" "I'm paintin' flowers," he said. She said "It's not the time for art young man, and anyway flowers are green and red. There's a time for everything young man, a way it should be done. You've got to show concern for everyone else for you're not the only one." And she said "Flowers are red, young man, green leaves are green. There's no need to see flowers any other way Than they way they always have been seen." But the little boy said "There are so many colors in the rainbow, So many colors in the morning sun, So many colors in the flower, and I see every one." Well, the teacher said "You're sassy. There's ways that things should be. And you'll paint flowers the way they are. So repeat after me..." And she said "Flowers are red, young man, green leaves are green. There's no need to see flowers any other way Than they way they always have been seen." But the little boy said again "There are so many colors in the rainbow, So many colors in the morning sun, So many colors in the flower, and I see every one." Well, the teacher put him in a corner. She said "It's for your own good. And you won't come out 'til you get it right and all responding like you should." Well, finally he got lonely, frightened thoughts filled his head, And he went up to the teacher, and this is what he said... And he said "Flowers are red, and green leaves 'er' green. There's no need to see flowers any other way Than they way they always have been seen." Of course time went by like it always does: they moved to another town. And the little boy went to another school, this is what he found: The teacher there was smiling. She said "Painting should be fun. And there are so many colors in a flower, so let's use every one." But that little boy painted flowers in neat rows of green and red, And when the teacher asked him why, this is what he said... And he said "Flowers are red, and green leaves 'er' green. There's no need to see flowers any other way Than they way they always have been seen." But there still must be a way to have our children say: "There are so many colors in the rainbow, so many colors in the morning sun, So many colors in the flower, and I see every one." SYNTHESIS AND REACTIVITY OF RHENIUM AND TECHNETIUM POLYARYL COMPLEXES by Christopher Alan Morse Submitted to the Department of Chemistry on August 5, 1998 in partial fulfillment of the requirements for the Degree of Doctor of Philosophy. Abstract Chapter 1. The organometallic chemistry of rhenium includes a variety of a-aryl complexes. The syntheses and structures for these complexes follow a pattern that relates predominantly to their oxidation states. The high oxidation state compounds all contain oxo or imido ligands. The low oxidation state complexes are mostly carbonyl and phosphine complexes, many of which result from orthometallation of a ligand. The middle oxidation state compounds bridge the motifs seen in the higher and lower oxidation states. A summary of rhenium-carbon bond lengths is presented. Chapter 2. Several complexes of the form Re(aryl)3(PMe2Ph)2 have been synthesized from ReCl 3 (PMe 2 Ph) 3, where aryl is m-tolyl, p-tolyl, phenyl, or p-methoxyphenyl. The complex Re(p-tolyl)3(THT)2 (THT = tetrahydrothiophene) was synthesized from ReBr3(THT) 3 and was structurally characterized by a single crystal X-ray diffraction study. It was found to have a nearly ideal trigonal bipyramidal structure with a propeller arrangment of aryl rings in the trigonal plane. The average Re-C bond length in Re(p-tolyl)3(THT)2 was 2.04 A. Treating in situ solutions of Re(p-tolyl)3(THT)2 with phosphines results in complexes of the form Re(p- tolyl) 3(PR3)2, where PR3 is PMe2Ph, PPh 3 or PMe3. Several polyaryl rhenium complexes with chelating phosphines are synthesized and examined. Chapter 3. The complex Re(p-tolyl)3(PMe2Ph) 2 is used as a probe to study the stability and reactivity of rhenium tris(aryl) complexes. The complexes are stable to temperature and substitution, but decompose in the presence of many oxidants by forming biphenyl as a reductive elimination product and unknown rhenium complexes without coordinated aryl groups. In the presence of carbon monoxide, Re(p-tolyl)3(PMe2Ph)2 reductively eliminates biphenyl and forms the rhenium(I) complex mer- Re(CO)3(PMe2Ph)2(p-tolyl). An X-ray structural analysis of mer- Re(CO)3(PMe2Ph)2(p-tolyl) shows a nearly ideal octahedral geometry with a long Re-C aryl bond length of 2.19 A. The complex Re(CO) 3 (PMe2Ph) 2 (p- tolyl) can be treated with iodine to form Re(CO) 3 (PMe 2Ph) 21. Chapter 4. Technetium has a limited number of known organometallic compounds. Most of these complexes have carbonyl or isonitrile ligands. A small number of technetium complexes have anionic or polyhapto organometallic ligands. These include a variety of cyclopentadienyl complexes and r 6 -arene complexes. Recently, the organometallic complexes of technetium have come to include ll-sigma donors as well as multiply bonded alkylidenes and alkylidynes. A summary of technetium- carbon bond lengths is presented. Chapter 5. The first technetium aryl complexes were synthesized from TcC13(PMe2Ph)3. They have the general formula Tc(aryl)3(PMe2Ph)2, where aryl is p-tolyl, m-tolyl, or phenyl. The complex Tc(p- tolyl) 3(PMe2Ph)2 was structurally characterized by a single crystal X-ray diffraction study which found the technetium in a trigonal bipyramidal arrangment with a Tc-C average bond length of 2.037 A. Both the m-tolyl and p-tolyl analogs of Tc(aryl)3(PMe2Ph)2 react with carbon monoxide to reductively eliminate biphenyl and benzophenone resulting in technetium(I) complexes of the form Tc(CO)3(PMe2Ph)2(aryl). An X-ray structural analysis of Tc(CO) 3(PMe 2Ph)2(m-tolyl) showed an octahedral coordination around the metal with a long Tc-C bond length of 2.242 A. The complex Tc(p-tolyl)3(PMe2Ph) 2 also reacts with tBuNC to form a technetium(I) organometallic oil formulated as Tc(tBuNC) 3 (PMe 2Ph) 2(p- tolyl). The complex TcC14(THT) 2 (THT = tetrahydrothiophene) was synthesized from TcC16 2- and was structurally characterized by an X-ray crystallographic analysis. The structure for TcC14 (THT) 2 showed a standard octahedral coordination around the technetium(IV) center. Thesis Supervisor: Alan Davison Title: Professor of Chemistry Table of Contents Abstract......................................................................................................................................5 Chapter 1. A Review of Rhenium Aryl Complexes Introduction................................................................................................................ 14 High Oxidation State Aryl Com plexes......................................... 15 M iddle Oxidation State Aryl Complexes........................................................21 Low Oxidation State Aryl Com plexes............................ ............. 27 Rhenium -Carbon Bonds in Aryl Complexes................................................. 32 Conclusion.............................................................. ................................................. 32 References............................................................... ......................................... 33 Chapter 2. The Synthesis of Rhenium Polyaryl Complexes Introduction.......................................................... ................................................ 39 Discussion.............................................................. ................................................. 40 Conclusion.............................................................. ................................................. 56 Experim ental ....... .................................................................................................. 57 References......... ..................................................................................................... 74 Chapter 3. The Reactivity of Rhenium Polyaryl Complexes Introduction................................................................................................................77 Discussion......... ...................................................................................................... 78 Conclusion................................... ............................................................................ 89 Experimental ..............................................................................................................