structurewhich is supported by the tendency of the cyclopentadienylidene residue to aromatizein fulvenoid phosphacyclohexadienes than is indicated in structure (2).
in Benzol oder CHCI3 in Gegenwart katalytischer Mengen Athyl-dicyclohexylamin rnit Cyanessigester und Malonsauredinitril zu (4) (R = CsH5, X = COOCzH5, Fp = 205-206 O C , = 277, 374 mp, Ausb. 54 x ; X = CN, Fp = 259 bis 260°C, Anlax = 285, 388 mp, Ausb. 31 x). Mit Malonsgure-
t h e AI, as has been shown for similar complexes 141. No noticeable exchange between R' on the Al and R on the Ti occurs before relatively slow reduction reactions take place.The methyl group is a weaker donor than the ethyl. This direrence may cause great changes in transition metal complexes[6? 7J. In (20) R' = CzH5 is more effective than R' = CH3 in (2b) against the delocalization of the unpaired electron of the Ti111: consequently there is a lower spin density at the A1 nucleus with R' = C~H S (lines in the spectra are closer together). The donor ligands on the A1 thus influence the electronic distribution in the whole complex; this influence is also to be expected for the TiIv species, and has in fact been detected. The higher the donor ability of R' the higher the electron density o n the Ti, and the higher the instability of the Ti-R bond. Such behavior is well illustrated by the reduction rate curves shown in Fig. 2, for the systems ( f a ) + (2n) (uppermost curve) and (fc) + (26) (middle curve). This result confirms the hypothesis [51 that the stability of a carbonmetal bond can be varied at will by varying the ligands. The 5 10 t ( h ) + Fig. 2. w : from the magnetic susceptibility. 0 @: from the ESR spectra (two series of experiments). Concentration of Ti(in) as a function of time.observed higher stability of the Ti-CH3 bond in the system ( l a ) + (2b) (Fig. 2, lowest curve) can be interpreted according to the Mulliken model of the CH3 group 181. This model considers the methyl as a triply bonded -C -H3 species, and "H3" as a heteroatom. The two bonding TC-MO's perpendicular to the axis of -C =H3 (and the corresponding antibonding MO's) have the right symmetry to match with the d-x-Ti orbitals (d,,, dyz). This convenient configuration is obviously not available in the case of other alkyls.The photochemical isomerization of cis-9,1O-dihydro-9,10naphthalenedicarboxylic anhydride (la) t o an anhydride with the bicyclo[4.2.2]deca-2,4,7,9-tetraene structure 111 disclosed a rearrangement that has since been demonstrated also for the parent hydrocarbon ( I b ) [21, the ester ( f c ) (31, and the compounds (Id) and ( I e ) 141. The isolation andlor detection ofthe tetracyclo[4.4.0.02~~o.O5,7]deca-3,8-diene intermediates (2d) 141, ( 2 e ) 141, and (2b) 151 suggested that the rearrangement took the course shown in Scheme 1. (b), R = H (C), R = CO2CHs If), R = CO2H Scheme 1.The bicyclo[4.2.2]deca-2,4,7,9-tetraene photoisomer obtained from (la) should then have structure (3~). in which the anhydride group is attached to one of the isolated double bonds. However, chemical degradation of the photoisomer showed that it has structure ( 5 2 ) with the anhydride group attached to the diene system. (a), R -R = -C -O -C -(c), R = C02CH3 (f), R = COzH II II 0 0 Scheme 2.On catalytic hydrogenation over platinum in glacial acetic acid the photoanhydride gives a hexahydro compound [m.p.from which cis-l,4-cyclohexanediacetic acid [61 (identified by means of the dimethyl ester prepared with diazomethane) is formed on ozonol...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.