Remarkably inert metal alkyl linkages in alkyl dioxo complexes of molybdenum and tungsten

Assignment of O–O and Mo=O Stretching Frequencies of Molybdenum/Tungsten Complexes Revisited

The assignment of peroxo stretching frequencies for Molybdenum and Tungsten complexes is studied by DFT and MP2 calculations. We found that M06 functional is unsuitable for assignment of Mo=O and O–O stretches in CpMo(η2-O2)OCH3and we found that MP2 and even the def2-TZVP do not give accurate order of asymmetric and symmetric Mo=O stretching. We recommend the M06L, which is a good compromise between speed and accuracy, for works involving these complexes. For a series of ten Molybdenum and Tungsten complexes studied we found that, for Mo/W=O stretching frequencies at M06L/def2-TZVP, after scaling, a small RMSD of 15 cm−1could be obtained. However peroxo stretching frequencies RMSD remains high at 40 cm−1after scaling. This could potentially point out the need for reassignment of experimental peroxo frequencies in some of the works cited in this report.

Reactions of d(0) tungsten alkylidyne complexes with O2 or H2O. Formation of an oxo siloxy complex through unusual silyl migrations

(Me3SiCH2)3(Me3SiC≡)W←O=PMe3 (1), an adduct between (Me3SiCH2)3W≡CSiMe3 (2) and O=PMe3, reacts with O2 to give O=W(OSiMe3)(CH2SiMe3)3 (3) and CO2. Reaction of 2 with H2O yields 3 and the trimer [(μ-O)W(CH2SiMe3)2(=O)(THF)]3 (4). In the reaction of D2O with 2, 3-d(n) and methane isotopologues CH2D2, CHD3 and CD4 have been observed.

Organorhenium(vii) and organomolybdenum(vi) oxides: syntheses and application in olefin epoxidation

The first members of the classes of the organorhenium(VII) oxides and organomolybdenum(VI) oxides were described during the 1960s and 1970s. However, despite the fact that methyltrioxorhenium(VII)(MTO) is probably the best examined organometallic oxide known, many of its derivatives as well as the Mo congeners were not tested for any application. Nevertheless, it is known that several organomolybdenum oxides, particularly those of formula eta5-(C5R5)MoO2Cl and eta5-(C5R5)MoO2R' are powerful epoxidation catalysts if applied together with tert-butylhydroperoxide (TBHP). MTO catalyzes a broad variety of organic reactions, among them being olefin epoxidation--in this case with the "green" oxidant H2O2- the most thoroughly examined. The heterogenization of the molybdenum compounds as well as of MTO both on carrier materials and in ionic liquids has already been achieved and it is to be expected that a suitable modification of the organic ligands will lead to applications in chiral catalysis in the near future.

Heterolytic cleavage of dihydrogen promoted by sulfido-bridged tungsten-ruthenium dinuclear complexes

A series of sulfido-bridged tungsten-ruthenium dinuclear complexes Cp*W(mu-S)(3)RuX(PPh(3))(2) (4a; X = Cl, 4b; X = H), Cp*W(O)(mu-S)(2)RuX(PPh(3))(2) (5a; X = Cl, 5b; X = H), and Cp*W(NPh)(mu-S)(2)RuX(PPh(3))(2) (6a; X = Cl, 6b; X = H) have been synthesized by the reactions of (PPh(4))[Cp*W(S)(3)] (1), (PPh(4))[Cp*W(O)(S)(2)] (2), and (PPh(4))[Cp*W(NPh)(S)(2)] (3), with RuClX(PPh(3))(3) (X = Cl, H). The heterolytic cleavage of H(2) was found to proceed at room temperature upon treating 5a and 6a with NaBAr(F)(4) (Ar(F) = 3, 5-C(6)H(3)(CF(3))(2)) under atmospheric pressure of H(2), which gave rise to [Cp*W(OH)(mu-S)(2)RuH(PPh(3))(2)](BAr(F)(4)) (7a) and [Cp*W(NHPh)(mu-S)(2)RuH(PPh(3))(2)](BAr(F)(4)) (8), respectively. When Cp*W(O)(mu-S)(2)Ru(PPh(3))(2)H (5b) was treated with a Brønstead acid, [H(OEt(2))(2)](BAr(F)(4)) or HOTf, protonation occurred exclusively at the terminal oxide to give [Cp*W(OH)(mu-S)(2)RuH(PPh(3))(2)](X) (7a; X = BAr(F)(4), 7b; X = OTf), while the hydride remained intact. The analogous reaction of Cp+W(mu-S)(3)Ru(PPh(3))(2)H (4b) led to immediate evolution of H(2). Selective deprotonation of the hydroxyl group of 7a or 7b was induced by NEt(3) and 4b, generating Cp*W(O)(mu-S)(2)Ru(PPh(3))(2)H (5b). Evolution of H(2) was also observed for the reactions of 7a or 7b with CH(3)CN to give [Cp*W(O)(mu-S)(2)Ru(CH(3)CN)(PPh(3))(2)](X) (11a; X = BAr(F)(4), 11b; X = OTf). We examined the H/D exchange reactions of 4b, 5b, and 7a with D(2) and CH(3)OD, and found that facile H/D scrambling over the W-OH and Ru-H sites occurred for 7a. Based on these experimental results, the mechanism of the heterolytic H(2) activation and the reverse H(2) evolution reactions are discussed.