Synthesis of Gold Complexes From Diphosphine Ligands and Screening Reactions of Heterocyclic Acetylacetonato (ACAC) Ligands with Transitional Metal Complexes Page: 12
This thesis is part of the collection entitled: UNT Theses and Dissertations and was provided to UNT Digital Library by the UNT Libraries.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
1.3.3 Tolman's Cone Angle
Phosphorous' ability to compete for coordination positions on Ni (0) can only be
explained by the ligand cone angle. The ligand cone angle is used to measure the size of the
ligand, and it is defined as an angle formed at center vertex of the metal and hydrogen atoms
around the perimeter of the cone.
The ligand cone angle concept has been applied in organic synthesis, particularly in
homogenous catalysis. This is due to the fact that the size of the ligand tends to affect metal
reactivity. Studies were conducted by Uttley'7 and his group on the reaction between H3IrCI6 and
phosphine ligands. When very bulky ligands PPh(tBu)2 and P(tBu)3 react with H3IrCI6, the
product is dihydride H2IrCIL2. One hydride and five chloride atoms are replaced by two ligand
molecules, but when less bulky ligands PMe(tBu)2 and PEt(tBu)2 are used, the product is
monohydride HIrCI2L2. This implies that bulky ligands prefer hydrogen over chloride because
the hydride ligand causes less steric strain.
In general, one can control the reactivity of a metal complex by controlling the size of the
ligand; for example, bulky phosphine ligands tend to dissociate faster than small size ligands;
this allows reactions to happen faster when bulky ligands are used. Conversely, if dissociation is
to be done slow, small size ligands are preferred, and in this way one can lower the reaction rate.
It is possible change electronic effects without changing steric effects or to change steric effects
without changing electronic effects. Table 1.3 provides information on the relation between cone
angle and ligand size; note that there is a direct correlation between the two: as the ligand gets
bigger so does the cone angle.12
Upcoming Pages
Here’s what’s next.
Search Inside
This thesis can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Thesis.
Nyamwihura, Rogers. Synthesis of Gold Complexes From Diphosphine Ligands and Screening Reactions of Heterocyclic Acetylacetonato (ACAC) Ligands with Transitional Metal Complexes, thesis, August 2015; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc804890/m1/25/?rotate=270: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .