Unexpected Coupling of Cp and Two RNC Ligands at a {Mo₂(μ-SMe)₃} Nucleus

Abstract

Reaction of the bis-isonitrile complex [Mo2Cp2(μ-SMe)3(t-BuNC)2](BF4) (1) with n-BuLi (in hexane) produced the dealkylated derivative [Mo2Cp2(μ-SMe)3(t-BuNC)(CN)] (2) in quantitative yield. However, upon treatment with either NaOH (suspension) or (Me4N)OH (in MeOH), 1 was converted into a mixture of 2 and the μ-alkylidyne species [Mo2Cp(μ-SMe)3{μ-(η5-C5H4)(t-BuN)CN(t-Bu)C}] (3), in which a deprotonated Cp and both isonitrile ligands of 1 are now linked by new carbon−carbon and carbon−nitrogen bonds.

Controlled nucleophilic activation of different sites in [Mo2Cp2L2(μ-SMe)2(μ-L′)]+ cations (L=ButNC, xylNC, CO; L′=SMe or PPh2)

“…Although the neutral derivatives 5 and 6 were difficult to separate, 6 was obtained in pure form, as shown below. Compound 5 was identified by comparing the 1 H NMR spectrum of a solution of the two products 5 and 6 of Reaction (3) with that of a pure sample of 5 obtained by the method described in Section 2.2. …”

“…When R is a good electron-donor, such as Bu t , no activation of the cyclopentadienyl carbon atoms occurs and thus no cyclopentadiene derivative is formed. However, when the anionic compound reacting with 1a is LiBu n , a dealkylation reaction, involving ejection of the Bu t group, is observed (Scheme 3) [3]; this requires that LiBu n should act as a base. On the other hand, when the anionic reagent is BH À 4 , hydride attack occurs at the isonitrile carbon in 1a (L = Bu t NC), affording the l-formimidoyl derivative 4.…”

“…These comments are prompted in part by our earlier study of the action of various nucleophiles on the cations [Mo 2 Cp 2 L 2 (l-SMe) 3 (2) or CO (3)). Thus, we have shown that 2 reacts with NaBH 4 to yield two products: substitution of both terminal MeCN ligands leads to the l-borohydride derivative [Mo 2 Cp 2 (l-BH 4 )(l-SMe) 3 ], whereas nucleophilic addition of hydride to one of the nitrile ligands gives the l-azavinylidene compound [Mo 2 Cp 2 (l-N@CHMe)-(l-SMe) 3 ] [2].…”

“…Thus, we have shown that 2 reacts with NaBH 4 to yield two products: substitution of both terminal MeCN ligands leads to the l-borohydride derivative [Mo 2 Cp 2 (l-BH 4 )(l-SMe) 3 ], whereas nucleophilic addition of hydride to one of the nitrile ligands gives the l-azavinylidene compound [Mo 2 Cp 2 (l-N@CHMe)-(l-SMe) 3 ] [2]. In addition, nucleophilic attack on 1a (R = Bu t ) by LiBu n is directed at an isocyanide ligand, subsequent dealkylation giving rise to the terminal cyanide ligand in the product complex [Mo 2 Cp 2 (CN)-(Bu t NC)(l-SMe) 3 ] [3].…”

“…Reactions of [Mo 2 Cp 2 L 2 (l-SMe) 3 ]Y (L = Bu t NC (1a) [3], xylNC (1b) or CO (3) [4]; Y = BF 4 ,Cl) with NaBH 4 , LiBu n , R 0 MgCl (R 0 = Me, Pr i , Bu n , Ph) are first described. Selectivity in these reactions is controlled by varying both the ligands L attached terminally to the Mo(III) centres and the strength of the nucleophile.…”