Formation of cyclic (boryl)iminomethane derivatives by the insertion of isocyanides into a boron-carbon bond

Isocyanides are highly valuable reagents in organic synthesis and have been widely used in multicomponent reactions. Although η²-imidoyl metal complexes, which are important intermediates in isocyanide chemistry, have been extensively explored, their boron species analogues have remained elusive. Hererin, we reported the synthesis of cyclic (boryl)iminomethanes via direct isocyanide insertion into the B-C bond of amino alkenyl boranes in a facile synthetic procedure. A family of well-defined cyclic (boryl)iminomethanes are characterized. Furthermore, the intrinsic ring strain of cyclic (boryl)iminomethanes primes them to further react with isocyanides and selectively afford double insertion products. Our results provide new insights into novel isocyanide chemistry involving boron species.

Multiple and Highly Selective Alkyne-Isonitrile C-C and C-N Couplings at Group 4 Metallocenes

Reactions of the group 4 metallocene alkyne complexes [Cp'2 M(η(2) -Me3 SiC2 SiMe3 )] [Cp'2 =rac-(ebthi)=rac-1,2-ethylene-1,1'-bis(η(5) -tetrahydroindenyl): M=Ti, Zr, Hf; Cp'2 =Cp*2 (Cp*=η(5) -pentamethylcyclopentadienyl): M=Zr] with 2,6-dimethylphenyl isocyanide (2-xylyl isonitrile, XyNC) were investigated. Depending on the metal, the Cp' ligand, and/or the stoichiometry, as well as the reaction temperature and time, different products were obtained. The products included simple end-on coordination compounds of XyNC in addition to those of the coupling of Me3 SiC2 SiMe3 with two, three, or four isonitriles to form enimine complexes, aza-metallacycloallenes, and fused heterocyclic systems, respectively. One example of the latter tricyclic compounds was subject to demetalation by using HCl. Molecular structures of the heterometallacycles were determined by X-ray crystallography. The interconversion of the products was investigated by (1) H NMR spectroscopy.

Reactions of group 4 metallocenes with monosubstituted acetonitriles: keteniminate formation versus C-C coupling

The reactions of the Group 4 metallocene dichlorides [Cp'2 MCl2 ] (1 a: M=Ti, Cp'=Cp*=η(5) -pentamethylcyclopentadienyl, 1 b: M=Zr, Cp'=Cp=η(5) -cyclopentadienyl) with lithiated MesCH2-C≡N gave [Cp*2 TiCl(N=C=C(HMes))] (3; Mes=mesityl) in the case of 1 a. For compound 1 b, a nitrile-nitrile coupling resulted in a five-membered bridge in 4. The reaction of the metallocene alkyne complex [Cp*2 Zr(η(2) -Me3 SiC2 SiMe3 )] (2) with PhCH2 C≡N led in the first step to the unstable product [Cp*2 Zr(η(2) -Me3 SiC2 SiMe3 )(NC=CH2 Ph)] (5). After the elimination of the alkyne, a mixture of products was formed. By variation of the solvent and the reaction temperature, three compounds were isolated: a diazadiene complex 6, a bis(keteniminate) complex 7, and 8 with a keteniminate ligand and a five-membered metallacycle. Subsequent variation of the Cp ligand and the metal center by using [Cp2 Zr] and [Cp*2 Ti] with Me3 SiC2 SiMe3 in the reactions with PhCH2-C≡N gave complex mixtures.

Sulfur-containing stable five-membered “cycloallene” complexes: 1-thia-2-zircona- and 1-thia-2-titanacyclopenta-3,4-dienes

Stable five-membered sulfur-containing metallacyclic allenes, 1-thia-2-metallacyclopenta-3,4-diene, were synthesized from the reactions of low-valent zirconocene or titanocene with alkynylthioamides.

Unusual nitrile-nitrile and nitrile-alkyne coupling of Fc-C≡N and FC-C≡C-C≡N

The reactions of the Group 4 metallocene alkyne complexes, [Cp*2M(η2-Me3SiC2SiMe3)] (1 a: M=Ti, 1 b: M=Zr, Cp*=η5-pentamethylcyclopentadienyl), with the ferrocenyl nitriles, Fc-CN and Fc-C≡C-C≡N (Fc=Fe(η5-C5H5)(η5-C5H4)), is described. In case of Fc-C≡N an unusual nitrile–nitrile C-C homocoupling was observed and 1-metalla-2,5-diaza-cyclopenta-2,4-dienes (3 a, b) were obtained. As the first step of the reaction with 1 b, the nitrile was coordinated to give [Cp*2Zr(η2-Me3SiC2SiMe3)(N≡C-Fc)] (2 b). The reactions with the 3-ferrocenyl-2-propyne-nitrile FcC≡C-C≡N lead to an alkyne–nitrile C-C coupling of two substrates and the formation of 1-metalla-2-aza-cyclopenta-2,4-dienes (4 a, b). For M=Zr, the compound is stabilized by dimerization as evidenced by single-crystal X-ray structure analysis. The electrochemical behavior of 3 a, b and 4 a, b was investigated, showing decomposition after oxidation, leading to different redox-active products.

Nitrile-nitrile C-C coupling at group 4 metallocenes to form 1-metalla-2,5-diaza-cyclopenta-2,4-dienes: synthesis and reactivity

The CC coupling of aryl nitriles at Group 4 metallocenes leads to unusual ring-strained 1-metalla-2,5-diaza-cyclopenta-2,4-dienes. The structural, energetic, and chemical properties of these complexes are described. The reactions of these compounds towards CH3 CN, H2 , CO2 , and HCl usually lead to the release of one nitrile and its replacement by different co-substrates.