Effect of Ligand Variation on the Site of Protonation in the Metal Carbynes CpL₂Mo⋮CBu and TpL₂Mo⋮CBu [L = CO, P(OR)₃]

Abstract

The site of thermodynamic protonation of the Fischer carbynes CpL2Mo⋮CBu and TpL2Mo⋮CBu [L = CO, P(OR)3] with HBF4 depends on the number of π-acid CO ligands. As the number of carbonyls increases from zero to two and the electron density at the metal center is decreased by back-bonding, the protonation site shifts from the metal to the carbyne carbon. Parallel behavior in the Tp and Cp series of complexes allows the change in protonation site to be attributed to electronic effects in the ancillary ligands.

Alkynylcarbyne complexes containing various tri- and bidentate ligands such as cyclopentadienide, tris(pyrazolyl)borate, bis(pyrazolyl)acetate and tmeda: synthesis and spectroscopic properties

“…The same order has been reported before by Stone and coworkers [5] for tbutylethinylcarbyne complexes of molybdenum. A higher electron-donating potential of Tp compared to Cp has also been observed by McElwee-White and coworkers [21] with some molybdenum carbyne complexes.…”

Protonation and Methylation of Zerovalent Molybdenum Complexes of the Types trans-[Mo(CNR)(L)(Ph2PCH2CH2PPh2)2] (R = Ph or Bun; L = N2, CO, or Nitrile) and trans-[Mo(CO)(L‘)(Ph2PCH2CH2PPh2)2] (L‘ = N2 or Nitrile) To Give Carbyne or Hydrido Complexes1

“…The other peak at -7.25 ppm, at a glance, seems to be attributable to the hydride (MoH) rather than the carbene proton (ModCH-), since the carbene proton is expected to resonate generally in a much lower field, e.g., 10-18 ppm. 25 However, the observed peak is correlated to the NH proton with the coupling constant of as large as 7.8 Hz, and furthermore the coupling of this resonance with the P atoms by J P-H ) 10.7 Hz seems to be too small to be assigned as that of the hydride bound to the Mo center (vide supra). In addition, the 13 C NMR spectrum showed the R-C resonance at 203.2 ppm, which split into a doublet with J C-H ) 61 Hz in the coupled spectrum.…”

Activation of propargylic alcohols by dimolybdenum tris(μ-thiolate) complexes: Influence of the substituents R in HCCCR2(OH)-vinylidene/allenylidene transformation. Reactivity of allenylidene complexes

“…Thus, the 1 H NMR spectrum displayed the resonances expected for the phenyl groups, the {Mo 2 Cp 2 (l-SMe) 3 } core and the methylene group (at 4.20 ppm), as well as a broad (unresolved triplet) high-field resonance at À4.78 ppm ascribed to a single hydrogen atom. This high-field shift strongly suggests the presence of a {Ph 2 CH 2 C(l-H)Mo} backbone featuring an a-agostic interaction [33,34]. Comparison of the 1 H and 13 C NMR data of 15 (see Section 4) with those of the closely related compounds [Mo 2 Cp 2 (l-SMe) 3 (l-g 1 :g 2 -CHCH 2 R)](BF 4 ) (R = Tol, n-Pr) [28] supports this suggestion.…”

“…of tetrafluoroboric acid in diethyl ether at room temperature, obtaining good yields of the desired l-alkylidene derivative 15 [Reaction (h) in Scheme 5 and Section 4]. Analytical data and NMR spectroscopy clearly indicated that 15 arose from a face-addition [33] of a proton to a Mo-C bond in 14. Thus, the 1 H NMR spectrum displayed the resonances expected for the phenyl groups, the {Mo 2 Cp 2 (l-SMe) 3 } core and the methylene group (at 4.20 ppm), as well as a broad (unresolved triplet) high-field resonance at À4.78 ppm ascribed to a single hydrogen atom.…”

“…Full 13 C NMR assignments of compounds 5 and 7 were based on 1 H-13 C HMQC and HMBC experiments. 33.0 (C(OH)Me 2 ), 18.6,10.5 and 6.7 (SCH 3 (1 equiv. ) …”