Synthesis of Well-defined Solid Catalysts by Surface Organometallic Chemistry - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 13

d n 9 r 4 n g | 1

Scheme 1.6 Formation of group 4 hydrides by hydrogenolysis of the silica sup-
ported alkyl complexes.

5

.

10

15

20

25

12 10 8 6 4 2 ppm

Chemical shift (ppm)

2D double quanta 1 H MAS NMR spectrum of the reaction product of the
hydrogenolysis of Si-O-Zr[CH 2 -C(CH 3 ) 3 ] 3 on silica.

Figure 1.3

react with another siloxane bridge leading to the formation of a tri-grafted
metal hydride. This is the case for group 4 metal complexes which will lead
to the formation of a mixture of mono- and dihydrides on the surface
(Scheme 1.6). 65,66 The best characterization method for these species is two-
dimensional (2D) double quanta 1 H MAS NMR which allows the observation
of an autocorrelation peak for the dihydride (Figure 1.3). The formation of
these two species is probably related to the heterogeneity of the silanol
distribution on the solid as explained in the first part, the presence of nests
preventing the formation of the third metal-surface bond. Indeed, the