Competitive Insertion of Isocyanide and Carbon Dioxide into Niobium− and Silicon−Amido Bonds

Abstract

Reaction of the amido-niobium complex [Nb{η 5 -C 5 H 4 SiMe 2 (NH t Bu)}(N t Bu)Cl(NH t Bu)] (2) with 1 equiv of CNAr (Ar ) 2,6-Me 2 C 6 H 3 ) in hexane gave the iminocarbamoyl compound [Nb{η 5 -C 5 H 4 SiMe 2 (NH t Bu)}(N t Bu)Cl{η 2 -C(NH t Bu)dNAr}] (5) in quantitative yield at room temperature, whereas heating to 120 °C was required when similar reactions were carried out with the bridged silyl amido compounds [Nb{η 5 -C 5 H 4 SiMe 2 (η 1 -N t Bu)}(N t Bu)Cl] (3) and 8), which rearranges to the silyl-η 1 -amido η 2 -iminoacyl derivative [Nb{η 5 -C 5 H 4 -SiMe 2 (η 1 -N t Bu)}(N t Bu){η 2 -C(CH 2 Ph)dNAr}] (9) on heating its C 6 D 6 solution to 145 °C. Reaction of compound 2 with CO 2 gave the dicarbamato complex [Nb{η 5 -C 5 H 4 SiMe 2 (η 1 -OOCNH t Bu)}(η 2 -OOCNH t Bu)(N t Bu)Cl] (10), whereas the same reaction with [Nb{η 5 -C 5 H 4 -SiMe 2 (NH t Bu)}(N t Bu)Cl 2 ] (1) gave an unidentified mixture of products, which were transformed after heating to 130-140 °C into the oxo derivative [{Nbwhich was further benzylated to give [{Nb(N t Bu)(CH 2 Ph) 2 } 2 -{η 5 -C 5 H 4 SiMe 2 -O-SiMe 2 -η 5 -C 5 H 4 }] (12). Similar reaction of 3 with CO 2 in toluene gave the oxo compounds [Nb(N t Bu)Cl-µ-(η 5 -C 5 H 4 SiMe 2 -η-O)] 2 (13) and [{Nb(N t Bu)Cl} 2 (µ-O){η 5 -C 5 H 4 -SiMe 2 -O-SiMe 2 -η 5 -C 5 H 4 }] (14). The molecular structure of 13 was determined by X-ray diffraction methods. Formation of the oxo complexes 11, 13, and 14 also resulted from hydrolysis of [Nb(η 5 -C 5 H 4 SiMe 2 Cl)(N t Bu)Cl 2 ] in the presence of NEt 3 .

Aspects of carbon dioxide utilization

“…For example, the catalyst of diethylzinc with resorcin forms many kinds of oligomers are formed as shown in Eq. (44). All these alternating copolymers formed with this catalyst have a resorcinol group at the terminal position.…”

Aryl-imido niobium complexes with chloro-silyl and aryl-η-amidosilyl cyclopentadienyl ligands: X-ray structure of the constrained-geometry compound [Nb(η5-C5H4SiMe2-η1-NAr)(NAr)Cl] (Ar=2,6-Me2C6H3)

“…It has been suggested that aryl-imido ligands provide more crystalline solids [26]. Consequently, we decided to extend our research on Si-Cl functionalized monocyclopentadienyl niobium complexes [11,27,28] to isolate new aryl-imido derivatives using the organomagnesium compounds [Mg(NAr)-(THF)] 6 (Ar = 2,6-Me 2 C 6 H 3 , 1a; Ph, 1b) as imido transfer reagents. This method was first published by Power and co-workers [29] to obtain titanium and zirconium imido compounds.…”

Synthesis and reactivity of imido niobium complexes containing the functionalized (dichloromethylsilyl)cyclopentadienyl ligand

“…Hydrolysis of these compounds also led to the isolation of dinuclear derivatives with Si-O-Si bridges for Nb [8,21,25], Mo and W [24] and Si-O-M bridges for Nb [25] and group 4 metals [2,26,27].…”