Journal article
Photothermally induced Bergman cyclization of metalloenediynes via near-infrared ligand-to-metal charge-transfer excitation
Inorganic chemistry, Vol.42(5), pp.1663-1672
03/10/2003
Handle:
https://hdl.handle.net/2376/113785
PMID: 12611537
Abstract
Reaction of 1,2-bis(tert-butyldimethylsilyloxy)-4,5-diiodobenzene with 2 equiv of phenylacetylene followed by deprotection with KF/HBr yields the catechol-enediyne ligand 4,5-bis(phenylethynyl)benzene-1,2-diol (CatED, 1). Metathesis of VO(SALIMH)ACAC.CH(3)OH (2) with 1 and subsequent air oxidation yields (4,5-bis(phenylethynyl)-1,2-dihydroxyphenyl)[4-(2-(salicylideneamino)ethyl)imidazolyl]oxovanadium(V).CH(3)OH [VO(SALIMH)CatED], (3), in 85%. The thermal Bergman cyclization temperature for 3 is very high (246 degrees C), which is expected for a rigid, benzannulated enediyne motif. The electronic spectrum of 3 exhibits two strong ligand-to-metal charge transfer (LMCT) transitions centered at 584 nm (epsilon = 6063 M(-)(1) cm(-)(1)) and 1028 nm (epsilon = 8098 M(-)(1) cm(-)(1)). These transitions derive from CatED-to-V(V) ligand-to-metal charge transfer, the assignment of which is verified by resonance enhancement of several CatED vibrational modes in the Raman spectra obtained with lambda = 785 vs lambda = 457.9 nm under low power and/or temperature conditions. At elevated temperatures (113-323 K) and powers (2-5 mW), excitation of 3 in the solid state with lambda = 785 nm leads to generation of a black, sparingly soluble, fluorescent product that exhibits weak vibrational features in the 580-600, 1200-1350, and 1450-1600 cm(-)(1) regions, indicative of V-O (CatED) and aromatic ring units. The C=C ring modes correspond well with the vibrational characteristics of poly(p-phenylene) and derivatives thereof. Additionally, materials generated in both the solid-state thermal and photothermal reactions of 3 demonstrate the formation of high molecular weight species ranging from 5000 to 274 000. On the basis of these data and the literature precedent for formation of poly(p-phenylene) via thermolysis of simple enediynes, the reaction poses a unique approach for photoinitiating Bergman cyclization with long-wavelength excitation, as well as the generation of polymeric products.
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Details
- Title
- Photothermally induced Bergman cyclization of metalloenediynes via near-infrared ligand-to-metal charge-transfer excitation
- Creators
- Brian J Kraft - Department of Chemistry and Biochemistry, Indiana University, Bloomington 47405, USANicole L CoalterMahendra NathAurora E ClarkAllen R SiedleJohn C HuffmanJeffrey M Zaleski
- Publication Details
- Inorganic chemistry, Vol.42(5), pp.1663-1672
- Academic Unit
- Chemistry, Department of
- Publisher
- United States
- Grant note
- R01 GM62541-01A1 / NIGMS NIH HHS
- Identifiers
- 99900547303201842
- Language
- English
- Resource Type
- Journal article