Masaaki Okazaki

Synthesis and reactivity of (phosphinoaklyl)silyl complexes

Abstract Silyl ancillary ligands are expected to generate the reactive unsaturated metal center due to their exceptionally strong trans -influence and -effect. Nevertheless, little has been known on the influence of silyl ligands on the reactivity of transition-metal complexes. This would be mainly due to the facile cleavage of the metal–silicon bond. (Phosphinoalkyl)silyl ligands have been developed to suppress the elimination of silyl groups from the metal center. This article reviews the synthesis and properties of the transition metal complexes having chelate-type (phosphinoalkyl)silyl ligands R 2 P(CH 2 ) n SiR 2 ( n =1, 2).

Synthesis and structures of bis(silylene)iron complexes containing new six-membered chelate rings

Reaction of Cp′Fe(CO)2SiMe2SiMe2Cl (1a: Cp′=η5-C5H5 (Cp), 1b: Cp′=η5-C5Me5 (Cp*)) with acetic acid in the presence of base (pyridine or Et3N) afforded Cp′Fe(CO)2SiMe2SiMe2OCOMe (2a: Cp′=Cp, 77%; 2b: Cp′=Cp*, 87%). Similarly, the reaction of 1b with 2-pyridone in the presence of Et3N gave Cp*Fe(CO)2SiMe2SiMe2O(2-C5H4N) (3, 43%). Photolysis of 2a, 2b, and 3 produced Cp′(CO)Fe{SiMe2⋯OC(Me)O⋯SiMe2} (4a: Cp′=Cp, 4b: Cp′=Cp*) and Cp*(CO)Fe{SiMe2⋯O(2-C5H4N)⋯SiMe2} (5) quantitatively, in which an acetoxy or 2-pyridyloxy group bridges two silylene ligands to form a six-membered chelate ring. 4a and 5 were structurally characterized by single-crystal X-ray diffraction experiments. All the FeSi bonds are significantly shorter than normal FeSi single bonds and are consistent with their unsaturated bond character. The six-membered chelate ring consists of two entirely different and delocalized unsaturated bond systems.

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.

Reactivity of silylene complexes

The metal–silicon bond in silylene complexes is highly polarized in a Mδ−–Siδ+ manner. Accordingly, silylene complexes show high reactivities toward nucleophiles, such as water, alcohols, ketones, isocyanates, and phosphorus ylides. The metal–silicon double bond can also activate aromatic carbon–hydrogen bonds. Among the various silylene complexes, silyl(silylene) complexes occupy a unique position; these complexes undergo intramolecular 1,3-migration, which is postulated as a key step in the metal-mediated redistribution of substituents on organosilicon compounds. Alkyl(silylene) complexes are not stable and undergo 1,2-alkyl migration to yield alkylsilyl complexes.

Cluster synthesis by the reactions of [Cp′2Fe2S4] with transition-metal complexes (Cp′=C5Me5, 1,3-C5H3(SiMe3)2)

Abstract Cluster synthesis was carried out by the reactions of [Cp′ 2 Fe 2 S 4 ] (Cp′=C 5 Me 5 , 1,3-C 5 H 3 (SiMe 3 ) 2 ) with some transition-metal complexes. The reaction of [Cp* 2 Fe 2 S 4 ] (Cp*=C 5 Me 5 ) with [M(CO) 3 (MeCN) 3 ] or [M(CO) 6 ] (M=Mo, W) resulted in the formation of tetranuclear tetrathiometalate clusters [{Cp*Fe(CO)} 2 {M(μ 3 -S) 2 (μ-S) 2 } {M(CO) 4 }]. In the reaction, redistribution of S and CO ligands took place between iron and tungsten atoms without losing them. The reaction of [Cp* 2 Fe 2 S 4 ] with [Cp*Ru(MeCN) 3 ](PF 6 ) gave a tetranuclear cluster [Cp* 4 Fe 2 Ru 2 S 4 ](PF 6 ) 2 . In contrast, when [Cp S2 2 Fe 2 S 4 ] containing a bulky Cp derivative (Cp S2 =1,3-C 5 H 3 (SiMe 3 ) 2 ) was used in place of [Cp* 2 Fe 2 S 4 ], a trinuclear cluster [(Cp S2 Fe) 2 (Cp*Ru)S 4 ](PF 6 ) was obtained. In the cluster, two disulfido ligands bridged over two iron atoms and one ruthenium atom in μ 3 –η 1 :η 2 :η 2 and μ 3 –η 1 :η 1 :η 2 fashion.

Cluster synthesis by the reactions of [Cp′2M2S4] with metal complexes (Cp′=Cp and substituted cyclopentadienyl ligands, M=Fe, Ru)

Abstract Dinuclear transition-metal sulfur complexes of the type [Cp′ 2 M 2 S 4 ] (Cp′=Cp and substituted cyclopentadienyl ligands) have been used as excellent starting materials for building up multinuclear transition-metal sulfur clusters. However, little is known about the versatility of the iron- and ruthenium-containing complexes. This urged us to examine the nature of Cp′ 2 M 2 S 4 (M=Fe, Ru). The present review describes the research on homo- and heteronuclear cluster synthesis by the reactions of Cp′ 2 M 2 S 4 (M=Fe, Ru) with various transition-metal complexes.

Insertion of pyridine into an iron–silicon bond: structure of the product Cp*(CO)Fe{η3(C,C,C)-C5H5NSiMe2NPh2}

Heating a toluene solution of Cp*(CO)(C5H5N)FeSiMe2NPh2 led to insertion of pyridine into the iron-silicon bond to form Cp*(CO)Fe[eta3(C,C,C)-C5H5NSiMe2NPh2].

Formation of Isomeric Tetrathiotungstate Clusters [{Cp*Ru(CO)}2(WS4){W(CO)4}] by the Reaction of [Cp*2Ru2S4] with [W(CO)3(MeCN)3]

Thermal and photochemical interconversion occurs between the isomeric pair of tetrathiotungstate [WS4 ]2- clusters 1 and 2, which were formed by thermolysis of [Cp*2 Ru2 S4 ] and [W(CO)3 (MeCN)3 ] [Eq. (1)] and then structurally characterized. During synthesis, a dramatic redistribution of ligands between the Ru and W atoms takes place without the loss of any CO and S ligands.

Redox-Responsive Recombination of Carbon-Carbon Bonds on Flexible Tetrairon Cores

When a brown powder of 2a was dissolved in acetonitrile, 2a was converted to 2b. Equilibrium was reached at a 74:26 molar ratio within 1 week at 303 K. The isomerization proceeds through a cubane-like transition state, in which recombination of a carbon-carbon bond occurs.

Recombination of an Fe−Si−P Linkage to an Fe−P−Si Linkage through an Isolable Intermediate Phosphasilaferracyclopropane

Phosphasilaferracycle [Cp*(CO)Fe{kappa(2)Si,P-SiMe(2)PPh(2)}], prepared upon irradiation of [Cp*(CO)(2)FeSiMe(2)PPh(2)], was converted to [Cp*(CO)(2)FeP(Ph)SiMe(2)Ph] under mild conditions. The unusual recombination of the iron, silicon, and phosphorus cores could be achieved through a sequence of 1,2- and 1,3-group migrations in an FeSiP system.