"Front Matter". In: Organosilanes in Radical Chemistry - Index of

Ion Thermochemistry 27
Table 2.5 Electron affinities of silyl radicals together with gas-phase acidities and bond
dissociation enthalpies of silanes a
Silane (R3SiH) EA(R3Si:)
(eV)
DHacid(R3Si w H) b
(kJ=mol)
DH(R3Si w H) b
(kJ=mol)
H3Si w H 1:41 0:03 1560 8 383 8
MeSiH2 w H 1:19 0:03 1583 8 386 12
Me2SiH w H 1:07 0:02 1601 392 c
Me3Si w H 0:97 0:03 1616 397.4 c
PhSiH2 w H 1:44 0:01 1551 8 377 8
PhMeSiH w H 1:33 0:04 1566 8 382 12
Me2Si(H)SiMe2 w H 1:40 0:03 1555 378 d,e
(Me3Si) 2SiH w H 1:94 0:08
(Me3Si) 3Si w H 2:03 0:09 1468 351.5 d
a Taken from References [25,26], unless otherwise mentioned.
b Experimental data in roman and calculated values from Equation (2.13) in italic.
c From Table 2.1.
d From Table 2.2.
e For Me3SiSiMe2 w H.
that EA(Me3SiH) EA(Me4Si) ¼ 3:8 eV [29], a bond strength of 670 kJ/mol is
calculated.
Me3SiH : !Me3Si þ H: (2:14)
DH(Me3SiH : ) ¼ DHacid(Me3SiH) IP(H:) þ EA(Me3SiH) (2:15)
2.3.2 HYDRIDE-AFFINITY CYCLES
Thermodynamic properties related to R3SiH can also be obtained from the
hydride-affinities of R3Siþ . The following thermochemical cycle (cf. Scheme
2.1):
R3Si H !R3Si: þ H: DH(R3Si H) (2:1)
w w
R3Si: !R3Si þ þ e IP(R3Si:) (2:16)
H: þ e !H EA(H:) (2:17)
R3Si w H !R3Si þ þ H DHbase ¼ DH(R3Si w H) þ IP(R3Si:) EA(H:) (2:18)
links the gas-phase basicity of silane (DHbase) to the bond dissociation enthalpy
of Si w H, the ionization potential of the silyl radical and the electron affinity of
a hydrogen atom. Equation (2.18) can be used to obtain different parameters
depending on what information is already known [22,23].