Bis(amino)allenylidene complexes by displacement of the MeO group in methoxy allenylidene complexes of chromium and tungsten. Synthesis, DFT calculations and solid-state structures of new bis(amino)allenylidene complexes

Pentacarbonyl dimethylamino(methoxy)allenylidene tungsten, [(CO)5WCCC(OMe)NMe2] (1b), reacts with one equivalent of primary amines, H2NR, by selectively replacing the methoxy group to give dimethylamino(amino)allenylidene complexes, [(CO)5WCCC(NHR)NMe2]. When the amine is used in excess both terminal groups, OMe as well as NMe2, are replaced by the primary amino group giving [(CO)5WCCC(NHR)2 ]. The NHR substituent in these complexes may be modified by deprotonation with LDA followed by alkylation. The replacement of the methoxy group in 1b by a secondary amino group, NR2, can be achieved by a stepwise process. Addition of Li[NR2] to the Cγ atom of 1b affords an alkynyl tungstate. Subsequent OMe− elimination induced by TMS-Cl/SiO2 yields the allenylidene complexes [(CO)5WCCC(NR2)NMe2]. When bidentate diamines are used instead of monoamines both substituents, OMe and NMe2, are replaced and allenylidene complexes are formed in which Cγ constitutes part of a 5-, 6-, or 7-membered heterocycle. The reaction of [(CO)5CrCCC(OMe)NMe2] (1a) with diethylene triamine affords an allenylidene complex with a heterocyclic endgroup carrying a dangling CH2CH2NH2 substituent. All reactions follow a strict regioselective attack of the nucleophile at Cγ and proceed with good to excellent yields. The addition of N–H to the CαCβ bond is not observed. By applying either one of these routes nearly any substitution pattern in bis(amino)allenylidene complex can be realized.

The alkoxy substituent in pentacarbonyl dimethylamino(methoxy)allenylidene can easily be replaced by NH2, NHR, and NR2 thus offering a convenient access to nearly any substitution pattern of bisamino-substituted allenylidene complexes.Figure optionsDownload as PowerPoint slide