Yasuro Kawano

Dehydrocoupling reactions of borane-secondary and -primary amine adducts catalyzed by group-6 carbonyl complexes: formation of aminoboranes and borazines.

Photoirradiation of a solution of BH(3).NHR(2) (1a: R = Me, 1b: R = 1/2C(4)H(8), 1c: R = 1/2C(5)H(10), 1f: R = Et) containing a catalytic amount of a group-6 metal carbonyl complex, [M(CO)(6)] (M = Cr, Mo, W), led to dehydrogenative B-N covalent bond formation to produce aminoborane dimers, [BH(2)NR(2)](2) (2a-c, f), in high yield. During these reactions a borane sigma complex, [M(CO)(5)(eta(1)-BH(3).NHR(2))] (3), was detected by NMR spectroscopy. Similar catalytic dehydrogenation of bulkier amineboranes, BH(3).NH(i)Pr(2) (1d) and BH(3).NHCy(2) (1e, Cy = cyclo-C(6)H(11)), afforded monomeric products BH(2) horizontal lineNR(2) (4d, e). The reaction mechanism of the dehydrocoupling was investigated by DFT calculations. On the basis of the computational study, we propose that the catalytic dehydrogenation reactions proceed via an intramolecular pathway and that the active catalyst is [Cr(CO)(4)]. The reaction follows a stepwise mechanism involving NH and BH activation. Dehydrocoupling of borane-primary amine adducts BH(3).NH(2)R (1g: R = Me, 1h: R = Et, 1i: R = (t)Bu) gave borazine derivatives [BHNR](3) (5g-i).

Photoreactions of silyliron(II) complexes Cp*Fe(CO)2SiMe3 (Cp*=η5-C5H5, η5-C5Me5) in the presence of trihydrosilanes

Abstract The photochemistry of silyliron(II) complexes Cp★Fe(CO)2SiMe3 (Cp★  η5-C5H5, η5-C5Me5) in the presence of trihydrosilanes is described. Three types of products were observed, depending on the bulkiness of the Cp★ ligands and the substituents on the trihydrosilanes: (η5-C5H5)Fe(CO)2SiMe3 reacts with tert-alkylsilanes RSiH3 (R  tBu, C(Me2)2H) upon irradiation to give silylene-bridged diiron complexes (η5-C5H5)2Fe2(CO)3(μ-SiHR) in good yields. In contrast, (η5-C5Me5)Fe(CO)2SiMe3 reacts with the tert-alkylsilanes photochemically to give silyl monoiron complexes (η5-C5Me5)Fe(CO)2SiH2R exclusively. Using p-TolSiH3 instead of tert-alkylsilane, the main photolysis product was the hydridobis(silyl)iron complex Cp★Fe(CO)SiMe3(H)SiH2-p-Tol. The X-ray crystal structure analysis of (η5-C5H5)2Fe2(CO)3(μ-SiHtBu) revealed that this complex adopts a geometry in which the two Cp rings and a SiH bond are located on the same side with respect to the SiFe2C four-membered ring. 29Si NMR spectra of the silylene-bridged diiron complexes showed signals at remarkably low field (δ 235.5–289.1 ppm). A mechanism for the formation of these silylene-bridged diiron complexes is proposed.

Thermal reactions of alkyl(hydrido)(hydrosilyl)iridium(III) complexes: generation of a hydrido(silylene)iridium(I) species via the reductive elimination of alkane and 1,2-H-shift from the silicon atom to the Ir(I) metal center

Abstract Heating of alkyl(hydrido)(hydrosilyl)iridium(III) complexes LnIr(R)(H) [Ln={η2-MesHSi(CH2)2PPh2}(PMe3)2, Mes=2,4,6-C6H2Me3, R=Me, Et] led to the reductive elimination of alkane. Subsequently, the resulting hydrosilyliridium(I) intermediate LnIr (A) activated the intramolecular carbon–hydrogen bond to give Ir(H){η3-CH2C6H2(CH3)2SiH(CH2)2PPh2}(PMe3)2. In the presence of MeOH, A was quickly trapped with MeOH to give a methoxysilyliridium(III) complex Ir(H)2{η2-Mes(MeO)Si(CH2)2PPh2}(PMe3)2. This reactivity of A with MeOH clearly supports the occurrence of a 1,2-H-shift from the silyl silicon atom to the iridium center to generate a hydrido(silylene)iridium(I) species Ir(H)[η2-{=SiMes(CH2)2PPh2}](PMe3)2.