Sesquifulvalene complexes

In another approach, transition metals have been used to stabilize the chemically reactive sesquifulvalene [116, 122]. In an early report, the bimetallic (Fe-Cr) complex was reported to exhibit hyperpolarizabilities up to 570 x 10 ° esu. However, for some other ferrocene derivatives of the sesquifulvalene complexes multi-photon luminescence has been observed which prohibits the determination of the hyperpolarizability by HRS. However, replacement of Fe(II) by Ru(II) results in luminescence-free derivatives [122, 123[. Monometallic manganese(I) sesquifulvalene complexes, on the other hand, are reported to exhibit only modest hyperpolarizabilities [124]. 

Heck, J.. Dabek, S., Meyer-Friedrichsen, T., Wong, H. Mono- and dinuclear sesquifulvalene complexes, organometallic materials with large nonlinear optical properties. Coord. Chem. Rev. 190-192, 1217-1254(1999)... 

Wong, H., Meyer-Friedrichsen, T., Farrell, T., Meeker, C., Heck, J. Second harmonic generation and two-photon fluorescence as nonlinear optical properties of dipolar mononuclear sesquifulvalene complexes. Eur. J. Inorg. Chem 631-646 (20(X))... 

Theoretical studies predicted that sesquifulvalenes should have large nonlinearities, but these compounds are very reactive, and so experimental confirmation was not possible. However, coordination to transition metal(s) stabilizes the sesquifulvalenes experimental studies on the resultant sesquifulvalene complexes revealed large nonlinearities. 

The synthesis of heterobimetallic sesquifulvalene and hydrosesquifulvalene manganese(l)-chromium(0) complexes was reported by Tamm et al. [237] it involved the reaction between cycloheptatrienyltrimethyltin and (iodocyclopen-tadienyljtricarbonyhnanganese with subsequent chromium functionalization. Elaboration of (fluoroaryl)tricarbonylchromium complexes by reaction with vinyltributyltin has been described by Wilhelm and Widdowson [238]. 

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