No abstract

The unsaturated compound [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] (1, Cp = η5-C5H5) reacts with trace amounts of water in the presence of [FeCp2]BF4 to give a mixture of the hydroxycarbyne complex [Mo2Cp2(μ-COH)(μ-CPh)(μ-PCy2)]BF4 (minor) and the hydroxo complex [Mo2Cp2(μ-CPh)(OH)(μ-PCy2)(CO)]BF4 (major product), with the latter rapidly rearranging to give the carbene isomer cis-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-PCy2)(CO)]BF4 (Mo–Mo = 2.9435(3) Å). An analogous reaction takes place with phenol, to give selectively the related phenoxo complex [Mo2Cp2(μ-CPh)(OPh)(μ-PCy2)(CO)]BF4. In contrast, the reactions of 1 with H2SiPh2 or H3BNH2 t Bu in the presence of [FeCp2]BF4 result in the selective H transfer to the O atom of the carbonyl ligand, to give the mentioned hydroxycarbyne complex. All the above reactions can be rationalized by assuming the initial formation of the radical cation [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)]+ (2), a molecule displaying a somewhat weakened intermetallic bonding (Mo–Mo = 2.537 Å vs 2.493 Å in 1) and a linear semibridging carbonyl, with both the LUMO and most of the unpaired electron density being located at a single molybdenum atom, with a much smaller distribution over the oxygen atom of the carbonyl ligand, according to density functional theory calculations. As expected, the radical 2 adds rapidly a molecule of nitric oxide to give a diamagnetic product, but spontaneous decarbonylation also takes place to eventually give the 30-electron nitrosyl complex [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-NO)]BF4. Deprotonation of cis-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-PCy2)(CO)]BF4 gives the neutral carbyne complex cis-[Mo2Cp2(μ-CPh)(O)(μ-PCy2)(CO)] (Mo–Mo = 2.8024(5) Å), which upon protonation reverts to its carbene precursor, via the corresponding hydroxo complex. Related trans isomers can be prepared through protonation reactions of trans-[Mo2Cp2(μ-CPh)(O)(μ-PCy2)(CO)] (Mo–Mo = 2.8206(6) Å), a complex easily prepared by reacting the dicarbonyl [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] with air.

The title complex was formed instantaneously by reacting [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] with [FeCp2]BF4 in the presence of diphenyl disulfide, but it could not be isolated as a pure material. It most likely displays bridging phosphide and thiolate ligands and essentially terminal carbonyl (Mo–C = 1.987 Å) and carbyne (Mo–C = 1.820 Å) ligands, according to density functional theory calculations. In solution this complex released CO spontaneously to yield the 30-electron complex [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)]BF4 (Mo–Mo = 2.4772(6) Å), and attempts to crystallize it at low temperature yielded instead the electron-precise aquo derivative [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)(CO)(OH2)]BF4 (Mo–Mo = 2.7820(4) Å). The addition of CO induced the coupling between the carbyne and phosphide ligands, to yield the tricarbonyl phosphinocarbene complex [Mo2Cp2(μ-η1:η1,κ1-CPhPCy2)(μ-SPh)(CO)3]BF4 (Mo–Mo = 2.928(1) Å). This coupling process was reversible, since the latter complex could be decarbonylated stepwise by thermal methods, to give first the 32-electron phosphinocarbene derivative [Mo2Cp2(μ-η1:η1,κ1-CPhPCy2)(μ-SPh)(CO)2]BF4 (Mo–Mo = 2.7863(4) Å) and eventually yielding [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)]BF4 via the title complex. In contrast to this behavior, the reaction of the title complex with CN t Bu did not induce a P–C coupling process, but eventually led to the displacement of the thiolate ligand to give the dication trans-[Mo2Cp2(μ-CPh)(μ-PCy2)(CN t Bu)4]2+ via the bis(isocyanide) complex cis-[Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)(CN t Bu)2]BF4, with these differences being probably steric in origin.

The title compound reacted with HBF4·OEt2 at room temperature to give a mixture of the agostic-like, phosphine-bridged complex [Mo2Cp2(μ-CPh)(μ-κ1:η2-PHCy2)(CO)2]BF4 (major) and the carbene-bridged complex [Mo2Cp2(μ-η1:η2-CHPh)(μ-PCy2)(CO)2]BF4 (minor). It readily added a molecule of HCCCO2Me or a single Se atom at its Mo2C(carbyne) center to give with high yield the corresponding propenylylidene- or selenoacyl-bridged derivatives [Mo2Cp2{μ-η2:η3-CPhCHC(CO2Me)}(μ-PCy2)(CO)2] and [Mo2Cp2{μ-η,κ:η,κ-C(Ph)Se}(μ-PCy2)(CO)2], respectively. In contrast, the addition of a neat donor at the metal site can induce a reversible carbyne–carbonyl coupling, as observed in the reaction with N2CPh2 to give the ketenyl derivative [Mo2Cp2{μ-η1:η2-C(Ph)CO}(μ-PCy2)(CO)(κ1-N2CPh2)].

The unsaturated methoxycarbyne complex [Mo 2 Cp 2 (μ-COMe)(μ-CPh)(μ-PCy 2 )](CF 3 SO 3 ) (Cp = η 5 -C 5 H 5 ; Mo−Mo = 2.4707(3) Å) reacted with CO (293 K, 40 bar) or CNR (233 K, R = t Bu, Xyl) to give the corresponding methoxyalkynebridged derivatives [Mo 2 Cp 2 {μ-η 2 :η 2 -C(OMe)CPh}(μ-PCy 2 )L 2 ]-(CF 3 SO 3 ) following from a reductive C−C coupling between methoxycarbyne and benzylidyne ligands (L = CO, CNR). This coupling could be fully reversed for the dicarbonyl product upon photolysis in tetrahydrofuran solution. The related hydroxycarbyne complex [Mo 2 Cp 2 (μ-COH)(μ-CPh)(μ-PCy 2 )]BF 4 reacted analogously with CO (293 K, 4 bar) to give the hydroxyalkyne-bridged derivative [Mo 2 Cp 2 {μ-η 2 :η 2 -C(OH)CPh}(μ-PCy 2 )(CO) 2 ]BF 4 (Mo−Mo = 2.6572(5) Å) as a result of C−C coupling between hydroxycarbyne and benzylidyne ligands, but this process could not be reversed photochemically. The latter complex could be prepared more efficiently via protonation of the ketenyl precursor [Mo 2 Cp 2 {μ-C(Ph)CO}(μ-PCy 2 )(CO) 2 ] with HBF 4 •OEt 2 in dichloromethane solution. The hydroxycarbyne complex also reacted with CN t Bu and CNXyl to give C−C coupled products, but different than anticipated: in both cases this reaction yielded selectively the corresponding aminoalkyne-bridged derivatives [Mo 2 Cp 2 {μ-η 2 :η 2 -C(NHR)CPh}(μ-PCy 2 )-(CNR) 2 ]BF 4 (Mo−Mo = 2.6525(5) Å when R = t Bu), as a result of H-transfer from hydroxycarbyne to isocyanide ligands and subsequent C−C coupling between aminocarbyne and benzylidyne ligands.

No abstract

Considering the results obtained, supplementation with iron salts in excess of Lf appears to be the best way of iron supplementation of formula milk.

The development of methods assessing the nutritional value and metabolism of selenium are of growing interest. In this work, the integrated used of a methodology based on HPLC-isotope pattern deconvolution (IPD)-ICP-MS and a molecular tandem mass spectrometric technique, such as HPLC-APCI-MS/MS, in the selected reaction monitoring (SRM) mode, was applied to quantify and identify the selenosugar SeGalNAc in liver and kidney tissues of lactating rats fed with formula milk supplemented with 77 selenite. The SeGalNAc levels found in liver and kidney of maternal feeding rats (kidney 23 AE 3 ng g À1 ; liver 26 AE 3 ng g À1 ) were much higher than those found in supplemented (kidney 9.9 AE 0.3 ng ng À1 ; liver 10 AE 4 ng g À1 ) and non-supplemented rats (kidney 3.4 AE 0.5 ng g À1 ; liver 4 AE 1 ng g À1 ). The percentage of exogenous SeGalNAc for the supplemented group in kidney and liver reached 32 AE 1% and 30 AE 10%, respectively. Conversely, the percentage of exogenous selenium in high molecular weight selenospecies reached values higher than 58%. Thereby, most exogenous selenium seems to be incorporated into the synthesis of selenoproteins, indicating that the turnover rates are different for the different species and their synthesis might occur in different tissue compartments. Finally, the identification of SeGalNAc was confirmed in liver and, for the first time to our knowledge, in the kidney cytosol of maternal feeding and supplemented rats. Overall, we expect that the judicious use of elemental and molecular mass spectrometry tools to obtain integrated quantitative Se speciation information might help to expand our knowledge of selenium metabolism.