Tungsten Complexes Cp Research Articles

Reactions of (mesityl)n(methyl)2-nsilylene complexes with pyridine-N-oxide (n = 1 and 0): formation of silanone complexes and a disiloxanyloxy complex.

Silanones (OSiR2), a heavier congener of ketones (R2CO), are highly reactive species that are readily converted to oligomeric siloxane (O-SiR2)n. Coordination of silanones to the transition-metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Recently, our group reported the synthesis, structures, and reactivity of dimesityl-substituted silanone complexes Cp*(OC)2M{OSiMes2(L)}(SiMe3) (M = W, Mo, L: Lewis base, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2). Herein, to investigate the effect of substituents on the silicon atom during the formation of a silanone complex, we demonstrated the use of Mes and smaller Me groups. As a result, the formation of Mes(Me)-substituted silanone molybdenum complex Cp*(OC)2Mo{OSiMes(Me)(py)}(SiMe3) (5b, py: pyridine) was suggested, the silanone tungsten complex Cp*(OC)2W{OSiMes(Me)(DMAP)}(SiMe3) (4a, DMAP: 4-(dimethylamino)pyridine) was obtained, and a dimethyl-substituted disiloxanyloxy(dioxo) complex Cp*(O)2W(OSiMe2OSiMe3) (9) was formed. The reaction of 4a with PMe3 proceeded via the elimination of DMAP and migration of the SiMe3 group to the oxygen atom of the silanone ligand to afford Cp*(OC)2W(SiMes(Me)OSiMe3)(PMe3) (11a). The Mo complex Cp*(OC)2Mo(SiMes(Me)OSiMe3)(PMe3) (11b) was produced by the reaction of Cp*(OC)2Mo{SiMes(Me)}(SiMe3) (7b) with pyridine-N-oxide in the presence of PMe3.

Synthesis of Base-Stabilized Hydrido(hydroborylene)tungsten Complexes and Their Reactions with Terminal Alkynes To Give η3-Boraallyl Complexes

Reaction of the methyl(pyridine)tungsten complex Cp*(CO)2W(py)Me with borane–NHC (NHC = N-heterocyclic carbene; MeIMe, MeIiPr) (MeIMe = 1,3,4,5-tetramethylimidazol-2-ylidene, MeIiPr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) adducts gave the NHC-stabilized hydrido(hydroborylene)tungsten complexes Cp*(CO)2W(H)(BH·NHC) (1a: NHC = MeIMe, 1b: NHC = MeIiPr) as dark brown crystals in high yields accompanied by liberation of pyridine and methane. X-ray crystal structure analysis revealed that the W–B bond of 1b is bridged by a hydrido ligand. Reactions of 1a,b with phenylacetylene at room temperature afforded NHC-stabilized η3-boraallyl complexes 2a,b, respectively, through a new type of hydroboration of the alkyne triple bond: i.e., addition of a hydrogen and a borylene. Reaction of 1a with 3-butyn-2-one also led to hydroboration of the triple bond, not the C═O double bond, to give η3-boraallyl complex 3. In the reaction of 1a with (trimethylsilyl)acetylene, 1-oxo-4-borabutenyl complex 4 was formed as a ...

Synthesis of a Base-Stabilized Silanone-Coordinated Complex by Oxygenation of a (Silyl)(silylene)tungsten Complex

Base-stabilized silanone complex Cp*(OC)(2)W(SiMe(3)){O═SiMes(2)(DMAP)} (2) was synthesized by the reaction of (silyl)(silylene)tungsten complex Cp*(OC)(2)W(SiMe(3))(═SiMes(2)) (1) with 1 equiv of pyridine-N-oxide (PNO) in the presence of 4-(dimethylamino)pyridine (DMAP). Further oxygenation of 2 with 3 equiv of PNO at 80 °C resulted in the formation of a W-O-Si-O-Si framework to give disiloxanoxy complex Cp*(O)(2)W{OSiMes(2)(OSiMe(3))} (3). Complex 3 was also obtained by the direct reaction of complex 1 with 4 equiv of PNO at 80 °C.

Reactions of (Silyl)(silylene)tungsten and -molybdenum Complexes with Sulfur Reagents

Reaction of (silyl)(silylene)tungsten complex Cp*(OC)2W(SiMe3)(═SiMes2) (1) with sulfur reagents, S8 and ethylene sulfide 4, afforded cyclic carbene tungsten complex Cp*(S)W{═C(SiMe3)C(═O)OSi(Mes)2S} (3) via C═O bond fission of a carbonyl ligand and 1,2-migration of the SiMe3 group from W to the resulting carbene carbon. In contrast to the tungsten complex, reaction of (silyl)(silylene)molybdenum complex Cp*(OC)2Mo(SiMe3)(═SiMes2) (2) with 4 gave η2-thiocarbonyl complex Cp*(S)Mo[{η2-S═C(SiMe3)}C(═O)OSi(Mes)2S] (5), which would be formed by addition of a sulfur atom to the Mo═C bond of a molybdenum analogue of 3.

Facile 1,2-Migration of a Methyl Group on a {Dimethoxy(methyl)silyl}tungsten Complex: Formation of a Base-Stabilized (Dimethoxysilylene)(methyl) Complex

Reactions of Cp*(CO)2W(DMAP)Me [1, Cp* = η5-C5Me5, DMAP = 4-(dimethylamino)pyridine] with trialkylsilanes HSiR2Et (R = Me, Et) afforded (DMAP)(trialkylsilyl)tungsten complexes Cp*(CO)2W(DMAP)(SiR2Et) (2a, R = Me; 2b, R = Et). On the other hand, a reaction of 1 with dimethoxy(methyl)silane, HSi(OMe)2Me, gave a DMAP-stabilized (dimethoxysilylene)tungsten complex, cis-Cp*(CO)2W(Me){═Si(OMe)2·DMAP} (cis-3), through 1,2-migration of a methyl group from silicon to tungsten. Silylene complex cis-3 isomerized to its trans-isomer trans-3.

Reactions of a hydrido(hydrogermylene)tungsten complex with some heterocumulenes: hydrogermylation and thermal rearrangement

Reaction of a hydrido(hydrogermylene)tungsten complex Cp*(CO)2(H)WGe(H)[C(SiMe3)3] (1) with isocyanate PhNCO at room temperature resulted in stoichiometric hydrogermylation at the CO bond to give a W–Ge–O–C–N five-membered chelate complex. In contrast, the reactions of 1 with isothiocyanates RNCS (R = Ph, Me) led to hydrogermylation at the CN bond to yield W–Ge–N–C–S five-membered chelate complexes. In both cases, the most electronegative atom in the isocyanate or isothiocyanates attacks the germanium of 1. Gentle heating of the latter chelate complexes in hydrocarbon solvents caused rearrangement of the chelate ring to cleanly afford W–Ge–S–C–N chelate complexes. Molecular structures of these three different types of five-membered metallacycles have been determined by X-ray crystallography, and possible reaction mechanisms for the hydrogermylation and rearrangement reactions have been proposed.

A DFT Study on the Mechanism of Hydrosilylation of Unsaturated Compounds with Neutral Hydrido(hydrosilylene)tungsten Complex

Recently, Tobita et al. reported stoichiometric hydrosilylation reactions of acetone and acetonitrile with neutral hydrido(hydrosilylene)tungsten complexes Cp'(CO)2(H)W=Si(H)[C(SiMe(3))(3)] (Cp' = Cp*, C(5)Me(4)Et). The mechanisms of the hydrosilylation reactions of unsaturated compounds (ketone and nitrile) with the tungsten complexes have been investigated with the B(3)LYP density functional theory method. Four possible reaction mechanisms were studied. The results of the calculations indicate that the hydrosilylation of acetone proceeds via a metal hydride migration mechanism proposed by Tobita et al., while the hydrosilylation of nitrile occurs through a silyl migration mechanism, analogous to the modified Chalk-Harrod mechanism. The [2(sigma)+2(pi)] additions of various CX (CX = C=O or CN) multiple bonds with the Si-H bonds in the neutral complexes have very high barriers although similar additions were found feasible in other related cationic complexes. All the hydrosilylation reactions studied here give stable tungsten-silylene or tungsten-silyl products, which are not easily converted into the starting hydrido(hydrosilylene)tungsten complexes when reacting with a hydrosilane substrate molecule. Therefore, we predict that hydrosilylation of acetonitrile and acetone catalyzed by these tungsten complexes is difficult to achieve.

Three- and Five-Membered W/C/N Metallacycles Formed by Incorporation of Acetonitrile Molecules into Silyltungsten Intermediates

Treatment of Cp*(CO)2W(NCMe)Me (Cp* = η5-C5Me5) with HSiR3 (R = Et, p-Tol) afforded N-silylated η2-iminoacyl tungsten complexes Cp*(CO)2W{κ2(C,N)-C(Me)N(SiR3)} (1a, R = Et; 1b, R = p-Tol). Analogous reactions in the presence of excess acetonitrile for a prolonged reaction time led to the formation of five-membered metallacycles Cp*(CO)2W{κ2(C,N)-C(Me)N−C(Me)N(H)} (2) and Cp*(CO)2W{κ2(C,N)-C(CH2SiR3)N−C(Me)N(H)} (3, R = p-Tol) through a C−N coupling of nitrile molecules and migration of a silyl group.

Synthesis, Structure, and Fluxional Behavior of Base-Stabilized Silyl(silylene)tungsten Complexes

Donor-stabilized silyl(silylene)tungsten complexes Cp(OC)2W(SiMe3)(SiMe2·Base) (Cp = η-C5H5, Base = HMPA (1a) and THF (1b)) have been synthesized by photolysis of C6D6 solutions containing CpW(CO)3...

Sulfurization and Selenization of the Halfsandwich Nitrosylmetal Complexes Cp*M(CO)2NO (M = Cr, Mo) and Cp*M(NO)I2 (M = Mo, W)

The photo-induced decarbonylation of Cp*Cr(CO)2NO in acetonitrile solution in the presence of excess sulfur leads to the cyclo-pentasulfido complex Cp*Cr(NO)(S5) (1 a), while in the case of limited sulfur supply the binuclear bis(µ-disulfido) complex Cp*2Cr2(NO)2(µ-S2)2 (4a) is formed preferentially. The corresponding reaction with elemental selenium produces Cp*2Cr2(NO)2(µ-Se2)2 (4b), irrespective of the available amount of selenium. Photodecarbonylation of Cp*Mo(CO)2NO gives only the binuclear derivates Cp*2Mo2(NO)2(µ-E2) (E = S (5a), Se (5b)) which are also obtained by treating Cp*Mo(NO)I2 with H2S or H2Se, respectively. Nitrosyl loss predominates if the tungsten complex Cp*W(NO)I2 is reacted with H2S; in an argon atmosphere the products are Cp*W(S)(S2)(I) (7a) and Cp*2W2(S)2(µ-S)2 (8a), while in air some Cp*W(NO)(S5) (3a) and the oxo compounds Cp*W(O)(S2)I (7c), Cp*2W2(O)2(µ-S)2 (8c) and Cp*2W2(S)(O)(µ-S)2 (8d) are formed. The analogous reaction with H2Se leads to Cp*W(NO)(Se5) (3b), Cp*2W2(O)2(µ-Se)2 (9c) and Cp*2W2(Se)(O)(µ-Se)2 (9d), respectively. The binuclear tungsten complexes 8a,c,d and 9c,d contain a central W(µ-E)2W framework (E = S or Se) which is unaffected by air, while terminal sulfido and selenido ligands are quantitatively converted into the corresponding terminal oxo ligands in the presence of air in CH2C12 or THF solution. With the preparation of Cp*2W2(O)2(µ-E)2 (E = S (8c) and Se (9c)), the series of dioxo complexes containing a pair of monochalcogen bridges (E = O, S, Se, Te) has become complete. The new complexes have been characterized by their IR (v(NO)), 1H and 13C NMR (Cp*) spectra as well as by electron-impact mass spectrometry. According to the X-ray structure analyses, the binuclear compounds Cp*2Cr2(NO)2(µ-S2)2 (4a) and Cp*2Mo2(NO)2(µ-Se2)2 (5b) contain two 14-electron [Cp*M(NO)2] fragments which are connected by a pair of dichalcogen (η1,η2-E2) bridging ligands (M = Cr or Mo, E = S or Se). The central M2E2 four-membered ring is not planar, and the binuclear molecules are chiral.

New Ruthenium-Molybdenum and -Tungsten Heterodinuclear Complexes with trans-Styryl Ligand

Abstract New styryl ruthenium-molybdenum and -tungsten complexes Cp(CO)3M-Ru (trans-styryl)(CO)(PPh3)2 [M = Mo (2), W (3)] have been prepared by the metathetical reactions of Ru(trans-styryl)Cl(CO)(PPh3)2 with Na[MCp(CO)3]. The reactions of 2 with CO and with PMe3 give Cp(CO)3Mo-Ru(trans-styryl)(CO)2(PPh3)2 (4) and Cp(CO)3Mo-Ru(trans-styryl)(CO)(PMe3)2 (5), respectively. The complexes of 2, 3, 4, and 5 have been characterized by IR, 1H NMR, 31P{1H} NMR spectroscopy, and elemental analysis.

The spectroscopic characterization of tungsten(V) complexes of the type Cp 2W 2(μ-S) 2EE′. Crystal and molecular structure of Cp 2W 2(μ-S) 2(NSiMe 3) 2

The binuclear, sulfur-bridged tungsten complexes Cp 2W 2(μ-S) 2E 2 (ENSiMe 3 ( 1), O ( 2) and S ( 3)) and Cp 2W 2(μ-S) 2EE′ (ENSiMe 3, E′=O ( 4); E NSiMe 3, E′S ( 5); EO, E′S ( 6)) were obtained in low yields from the reactions of bis(trimethylsilyl)sulfur diimide, S(NSiMe 3) 2, with cyclopentadienyl tungsten compounds such as CpW(CO) 3Cl and [CpW(CO) 3] 2. The molecular stereochemistry of 1 was determined by a three-dimensional X-ray diffraction study. The centrosymmetric molecules of 1 contain a planar W 2(μ-S) 2 ring (W-W 2.903(3) Å, S···S 3.651(7) Å, angle WSW 77.0(1)°) and terminal 4-electron imido ligands N(SiMe 3) (angle WNSi 170.9(25)°). Complexes 1–6 were characterized by their IR, 1H and 13C NMR and mass spectra.