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

Abstract

Pentacarbonyl dimethylamino(methoxy)allenylidene tungsten, [(CO)5Wdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(OMe)NMe2] (1b), reacts with one equivalent of primary amines, H2NR, by selectively replacing the methoxy group to give dimethylamino(amino)allenylidene complexes, [(CO)5Wdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(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)5Wdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(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)5Wdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(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)5Crdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(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 Cαdouble bond; length as m-dashCβ bond is not observed. By applying either one of these routes nearly any substitution pattern in bis(amino)allenylidene complex can be realized.