Transition Metal Complexes of Azulene and Related Ligands

Organotransition Metal Chemistry of Terpenes: Syntheses, Structures, Reactivity and Molecular Rearrangements

“…Guaiazulene (1,4-dimethyl-7-isopropylazulene) is a dark blue bicyclic sesquiterpene possessing five- and seven-membered rings, found as a constituent in oil of guaiac and in chamomile oil, and is widely used in skin care products. The synthesis and structure of the many metal complexes of azulene itself has been comprehensively reviewed [ 97 ]. Early work by Cotton established that guaiazulene forms bimetallic complexes in which the linked metals bind in a pentahapto fashion to the 5-membered ring and in a trihapto mode to the 7-membered ring ( Scheme 71 ) [ 98 ].…”

“…Guaiazulene (1,4-dimethyl-7-isopropylazulene) is a dark blue bicyclic sesquiterpene possessing five-and seven-membered rings, found as a constituent in oil of guaiac and in chamomile oil, and is widely used in skin care products. The synthesis and structure of the many metal complexes of azulene itself has been comprehensively reviewed [97]. Early work by Cotton established that guaiazulene forms bimetallic complexes in which the linked metals bind in a pentahapto fashion to the 5-membered ring and in a trihapto Attempts to attach organometallic fragments to humulene were generally unsuccessful, although there is a report of the formation of the π complex [(humulene)Fe(CO) 2 (C 5 H 5 )] + [BF 4 ] -; however, the combination of low yield and thermal instability precluded its unambiguous identification by NMR spectroscopy [96].…”

Poly(vinyl azulene)s: An Emerging Class of Poly(vinyl arene)s

“…Such an uneven distribution of electron density of azulene and its nonmirror-related frontier molecular orbitals also makes it exhibit a low oxidation potential of 0.9 V (vs SCE, the oxidation potential of the electron-rich thiophene is 1.6 V), 3 proton responsiveness, 4 anti-Kasha's emission, 5 and transition metal complexation capability. 6,7 Therefore, azulene has been employed as a useful building block of functional materials for selective electrodes, 8,9 (opto)electronic devices, 10−13 sensors, 14 energy applications, 15,16 and photothermal therapy. 17,18 However, these functional materials mainly focus on azulenebased small organic molecules and conjugated polymers.…”

“…The dipolar nature of azulene arises from an intramolecular charge transfer from the seven-membered ring to the five-membered ring owing to an aromatic stabilization according to Hückel’s rule. Such an uneven distribution of electron density of azulene and its nonmirror-related frontier molecular orbitals also makes it exhibit a low oxidation potential of 0.9 V (vs SCE, the oxidation potential of the electron-rich thiophene is 1.6 V), proton responsiveness, anti -Kasha’s emission, and transition metal complexation capability. , Therefore, azulene has been employed as a useful building block of functional materials for selective electrodes, , (opto)electronic devices, − sensors, energy applications, , and photothermal therapy. , However, these functional materials mainly focus on azulene-based small organic molecules and conjugated polymers . Insulating polymers with pendant azulene rings have rarely been synthesized, despite insulating polymers such as vinyl monomers containing benzenoid rings being widely used and having a longer history than organic conjugated polymers.…”

The 2-isocyanoazulene-gold(I) fragment as a versatile element for organometallic dyes and liquid crystals

“…There are many reports on the effects of introducing different types of organic substituents in the azulene core. However, the number of studies for inorganic substituents is lower [27][28][29][30][31][32][33][34][35]. The majority of them are metal complexes involving multi-hapto coordination of the azulenic framework to the metal [28][29][30][31], or azuliporphyrin derivatives [32][33][34][35].…”