The molecular
dynamics of a series of organometallic comple
xes covalently boun
d to amorphous silica surfaces is
determine
d experimentally using soli
d-state nuclear magnetic resonance (NMR) spectroscopy an
d density functional theory calculations (DFT). The
determination is carrie
d out for a series of alkyli
dene-base
d catalysts having the general formula [(
d1.gif">SiO)M(ER)(
db
d_2.gif">CH
tBu)(R′)] (M = Re, Ta, Mo or W; ER = C
tBu, NAr or CH
2tBu; R′ = CH
2tBu, NPh
2, NC
4H
4). Proton−carbon
dipolar coupling constants an
d carbon chemical shift anisotropies (CSA) are
determine
d experimentally by soli
d-state NMR. Room-temperature molecular
dynamics is quantifie
d through or
der parameters
determine
d from the experimental
data. For the chemical shift anisotropy
data, we vali
date an
d use a metho
d that integrates static values for the CSA obtaine
d computationally by DFT, obviating the nee
d for low-temperature measurements. Comparison of the room-temperature
data with the calculations shows that the wi
dths of the calculate
d static limit
dipolar couplings an
d CSAs are always greater than the experimentally
determine
d values, provi
ding a clear in
dication of motional averaging on the NMR time scale. Moreover, the
dynamics are foun
d to be significantly
different within the series of molecular comple
xes, with or
der parameters ranging from <
Sz> = 0.5 for [(
d1.gif">SiO)Ta(
db
d_2.gif">CH
tBu)(CH
2tBu)
2] an
d [(
d1.gif">SiO)Re(
d1.gif">C
tBu)(
db
d_2.gif">CH
tBu)(CH
2tBu)] to <
Sz> = 0.9 for [(
d1.gif">SiO)Mo(
d1.gif">NAr)(
db
d_2.gif">CH
tBu)(R′) with R′ = CH
2tBu, NPh
2, NC
4H
4. The
data also show that the motion is not isotropic an
d coul
d be either a jump between two sites or more likely restricte
d librational motion. The
dynamics are
discusse
d in terms of the molecular structure of the surface organometallic comple
xes, an
d the orientation of the CSAs tensor at the alkyli
dene carbon is shown to be
directly relate
d to the magnitu
de of the α-alkyli
dene CH agostic interation.