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In the case of diphosphines, the θ i / 2 of the backbone is approximated as half the chelate bite angle, assuming a bite angle of 74°, 85°, and 90° for diphosphines with methylene, ethylene, and propylene backbones, respectively. The Manz cone angle is often easier to compute than the Tolman cone angle: [4] [clarification needed]
The Tolman electronic parameter (TEP) is a measure of the electron donating or withdrawing ability of a ligand. It is determined by measuring the frequency of the A 1 C-O vibrational mode (ν(CO)) of a (pseudo)-C 3v symmetric complex, [LNi(CO) 3 ] by infrared spectroscopy , where L is the ligand of interest.
The steric properties of phosphine ligands can be ranked by their Tolman cone angle [7] or percent buried volume. [12] Spectroscopy.
Trimethylphosphine is a highly basic ligand that forms complexes with most metals. As a ligand, trimethylphosphine's Tolman cone angle is 118°. [7] This angle is an indication of the amount of steric protection that this ligand provides to the metal that to which it is bound.
The Tolman cone angle and Tolman electronic parameter [3] are named after him. In 1972, he proposed the 16 and 18 electron rule , extending Irving Langmuir 's 18-Electron rule to include the many examples of stable 16 electron square planar d 8 complexes. [ 4 ]
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In terms of steric bulk, PPh 3 has a Tolman cone angle of 145°, [19] which is intermediate between those of P(C 6 H 11) 3 (170°) and P(CH 3) 3 (115°). In an early application in homogeneous catalysis, NiBr 2 (PPh 3) 2 was used by Walter Reppe for the synthesis of acrylate esters from alkynes, carbon monoxide, and alcohols. [20]
Sterimol parameters are built upon the Corey-Pauling-Koltun atomic models, which take into consideration the Van der Waals radii of each atom in the molecule. Unlike most other steric parameters such as A-value, Taft parameters and Tolman cone angle, which group all the spatial information into a single cumulative value, Sterimol parameters consist of three sub-parameters: one length parameter ...