(2-(Dimethylammonium)ethyl)cyclopentadienyltricarbonyl-metalates: Group VI metal zwitterions. Attenuation of the brønsted basicity and nucleophilicity of formally anionic metal centers

Paul J. Fischer, Kristina M Krohn, Edward T. Mwenda, Victor G Young

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

Protonation of (2-(dimethylamino)ethyl)cyclopentadienyl (Cp N) group VI metal carbonyl anions with acetic acid proceeds at the amine to provide zwitterionic (2-(dimethylammonium)- ethyl)cyclopentadienyltricarbonylmetalates, M(CO) 35-Cp NH) (M = Cr (1), Mo (2), W (3)). Few zwitterionic organometalates with anionic metal centers and positive charges that cannot be delocalized have been reported to date. The impact of the intramolecular charge separation on the structures and reactivity of zwitterionic organometalates is of current interest. The M(CO) 3 units of structurally characterized 1-3 are significantly perturbed in solution and the solid state due to ion-pairing between the pendant ammonium cation and anionic metal center. The concentration and solvent dependence of the 1H NMR ammonium hydrogen chemical shifts of 1-3 and the intramolecular N⋯M separations of these zwitterions in the solid state are consistent with three-center-four-electron N - H⋯M hydrogen bonding. One other hydrogen bond with a zerovalent group VI metal acceptor has been characterized to date. The intramolecular charge separation attenuates the reactivity of the anionic metal centers of 1-3 relative to that of [M(CO) 35-Cp)] -. Structurally characterized [WH(CO) 3- (η 5-Cp NH)]Cl (4) was the only isolable salt obtained from protonation of 1-3; the Cr and Mo analogues are unstable relative to 1 and 2, respectively. Structurally characterized [M(AuPPh 3)(CO) 35-Cp NH)]Cl (M = Mo (5), W(6)) were synthesized via reactions of 2 and 3, respectively, with Ph 3PAuCl and protonation of M(AuPPh 3)(CO) 35-Cp N) (M = Mo (8), W (9)) with HCl. Pure samples of the analogous chromium salt were inaccessible from either 1 or structurally characterized Cr(AuPPh 3)(CO) 35-Cp N) (7).

Original languageEnglish (US)
Pages (from-to)5116-5126
Number of pages11
JournalOrganometallics
Volume24
Issue number21
DOIs
StatePublished - Oct 10 2005

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