Ring opening complexes

The mesoionic tetrazole dehydrodithizone is transformed by iron penta-carbonyl into 4-phenyl-2-phenylazo-A2-l,3,4-thiadiazolin-5-one, presumably by a mechanism of ring opening, complexation, carbonyl insertion and subsequent ring closure (Scheme 128).193 Unfortunately, analogous processes do not occur on other mesoionic compounds in the 1,2,3-oxadiazole, s-triazole or tetrazole series, and the scope of this unusual carbonylation is probably limited. 

Scheme III shows Liberman s associative ring closure mechanism 19). The participation of surface hydrogen atoms (26) in the cyclization-ring-opening complex is noteworthy. The other atoms of the C5 ring are claimed as lying on the metal linked to it by physisorption forces.

Wu and Brodbelt have studied the gas-phase fragmentation reactions of HOMg(L) complexes of crown ethers and glymes . A common loss involves units of C2H4O, which can either directly occur from the precursor ion, or can be triggered by an initial interligand reaction between HO and L. This latter reaction is illustrated in Scheme 11 for the complex of 12-Crown-4. Thus loss of H2O from the initial adduct 56 yields the ring-opened complex 57, which contains a coordinated alkoxide moiety, which can then lose an epoxide to form the related complex 58. 

Fig. 12. The 2D [1H,15N] HSQC-NMR spectrum of the HPLC-isolated dien ring-opened complex at pH 4.0. Only the NH2 group of L-MetH was 15N-labelled, and the four sets of crosspeaks (peaks a, a to d, d ) can be assigned to the non-equivalent Pt-NH2 groups in the four diastereomers of [Pt(dienH-A,AO(15N-L-Met-YA012+- All peaks have 2J(NHa, NHb) of ca. 12 Hz, while only peaks a and b have an additional V( a-CH.NHj of ca. 13 Hz. (Adapted...

The synthesis and chemistry of an 7] -selenophene osmium complex 50 has been studied <19990M1559>. Protonation and electrophilic substitution with acetaldehyde diethyl acetal occurred at C-2. Methylation of complex 50 with methyl triflate gave 51 which upon treatment with tetrabutylammonium borohydride (TBAB) led to the selenophene ring-opened complex 52 (Scheme 5). 

Bis-3,4-(trifluoromethyl)-l,2-diselenete 651 is prepared by refluxing selenium with hexafluoro-2-butyne. It reacts with triphenylphosphine and triphenyl-arsine. Triphenylphosphine selenide was isolated, but no other compounds were identified.Ring-opened complexes with nickel, copper, vanadium, molybdenum (652), tungsten, iron, and cobalt are analogous to complexes of the 1,2-dithiete (527) (Section XXXV.2.C.). 

The preparation of nylon resins from lactam precursors involves ring opening, which is facihtated by a controlled amount of water in the reaction mixture. The salt complex condenses internally to produce the polyamide (57). The synthesis of nylon-6 [25038-54-4] from S-caprolactam is as follows ... 

Removal of AT-oxide groups by PCI3 follows normal behaviour (63JCS6073), but with acetic anhydride the AAoxides (332) underwent a complex ring-opening reaction leading to (333), and an isomeric 8-alkoxy-6-oxide behaved similarly (75H(3)38l). 

Results of studies of the electrocyclic ring opening of 3 fluoro-, 3,3-difluoro-, and 3-tnfluoromethylcyclobutene are consistent with the theoretical predictions of the effect of fluonne on this reaction [142] Surpnsingly, fluonnated analogues of hexa tnene-cyclohexadiene systems undergo complex rearrangements mainly via free radical mechanisms and not by electrocyclic nng operung as expected [143] (equation 35)... 

In principle, complex hydrides (NaBHj, LiAlH ) ought to react similarly with 4-pyrones and lead after treatment with Bronsted or Lewis acids to 4-unsubstituted pyrylium salts. This reaction has not been reported the reduction of 2-pyrones with LiAlH4 results in ring opening. " ... 

OKO-l,3,7-triazanaphthalene (450) forms acyloxy derivatives in situ with phosphorus oxychloride and pentasulfide which undergo nucleophilic displacement with chloride ion and with a complex sulfide ion, respectively, to form the 4-chloro and 4-thioxo derivatives. The 4-carboxymethylthio compoimd failed to undergo the ring-opening reaction (see below) characteristic of more activated azino- and diazino-pyrimidines, but it did yield about 10% of the 4-0X0 displacement product. 

Ring-opening is not a mandatory direction of the complexation reaction. Thus, the ring-closed form of the benzothiazoline 395 ligand was found to be preserved in its complex 396 with BuSnCla, whose structure was determined with X-rays (Scheme 146) [93JOM(454)67]. 

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