Metal–Cyclopentadienyl Bond Energies in Metallocene Cations Measured Using Threshold Collision-Induced Dissociation Mass Spectrometry

Abstract

Metal-cyclopentadienyl bond dissociation energies (BDEs) were measured for seven metallocene ions (Cp(2)M(+), Cp = η(5)-cyclopentadienyl = c-C(5)H(5), M = Ti, V, Cr, Mn, Fe, Co, Ni) using threshold collision-induced dissociation (TCID) performed in a guided ion beam tandem mass spectrometer. For all seven room temperature metallocene ions, the dominant dissociation pathway is simple Cp loss from the metal. Traces of other fragment ions were also detected, such as C(10)H(10)(+), C(10)H(8)(+), C(8)H(8)(+), C(3)H(3)(+), H(2)M(+), C(3)H(3)M(+), C(6)H(6)M(+), and C(7)H(6)M(+), depending on the metal center. Statistical modeling of the Cp-loss TCID experimental data, including consideration of energy distributions, multiple collisions, and kinetic shifts, allow the extraction of 0 K [CpM(+)- Cp] BDEs. These are found to be 4.85 ± 0.15, 4.02 ± 0.14, 4.22 ± 0.13, 3.51 ± 0.12, 4.26 ± 0.15, 4.57 ± 0.15, and 3.37 ± 0.12 eV for Cp(2)Ti(+), Cp(2)V(+), Cp(2)Cr(+), Cp(2)Mn(+), Cp(2)Fe(+), Cp(2)Co(+), and Cp(2)Ni(+), respectively. The measured BDE trend is largely in line with arguments based on a simple molecular orbital picture, with the exception of the anomalous case of titanocene, most likely attributable to its bent structure. The new results presented here are compared to previous literature values and are found to provide a more complete and accurate set of thermochemistry.

The bond energy of ReO+: Guided ion-beam and theoretical studies of the reaction of Re+ (7S) with O2

“…[62][63][64][65] The BP86 functional is chosen specifically because it was found to perform well for a variety of transition metal complexes 66 and has been found to yield reasonable upper limits on the thermochemistry of organometallic species in previous work, where B3LYP gives reasonable lower limits. 67 The def2-TZVPPD basis set was used for oxygen in most calculations and gives good results for the thermochemistry of O 2 with an O-O bond energy calculated using B3LYP as 5.25 eV, compared to the experimental value of 5.115 eV, Table I. 68 BP86 yields a high value (near 6.1 eV) and even the CCSD(T,full) approach is off somewhat with a bond energy of 4.88 eV.…”

Theoretical Study of the Dissociation Energy of First-Row Metallocenium Ions

“…TCID9 or TPEPICO,10,11 quite strongly disagree, the latter method systematically giving larger values. For the complexes TiCp 2 + , VCp 2 + , and CrCp 2 + , the CCSD(T) binding energies (considered more accurate than RASPT2, see previous section) closely correspond to the TCID result in case of VCp 2 + , whereas for the other two complexes the deviation between both sets of data is much larger and differs in sign: -6.4 kcal/mol for TiCp 2 + , +13 kcal/mol for CrCp 2 + .…”

“…Indeed, thermochemical data for the metal-cyclopentadienyl bond strength in metallocenium ions show variations of several eV, depending on the measurement method. [8][9][10] The first extensive study was performed by Müller and D'or 8 using electron ionization mass spectrometry (EIMS). The EIMS values are exceptionally high when compared to more recent values measured by threshold photoelectron photoion coincidence (TPEPICO) spectroscopy.…”

“…Most recently, a new set of experimental bond dissociation energies (BDEs) of all firstrow metallocenium ions was reported by Rowland et al 9 using threshold collision-induced dissociation (TCID). This report also points to some problems in previous studies as the cause of unreliable BDEs.…”

Chemical Vapor Deposition of Metallic Films Using Plasma Electrons as Reducing Agents

“…It does not follow the reported binding strength of cyclopentadienyl ligands to the metal centre, where the binding enthalpy increases as NiCp2 < FeCp2 < CoCp2. 21,22,23 3.3. Film structure SEM top-view images of Fe, Co and Ni films as-deposited on silver and silicon substrates (Fig.…”