Tolman s cone angle

Tmta — see Acetic acid, trimethylenediaminetetra-Tollen s reagent, 5, 780 Tolman s cone angle, 2, 1015 Toluene acetoxylation... 

For monodentate ligands, e.g., triphenylphosphane, Tolman s cone-angle 0 and the electronic parameter x have a significant influence on the activity and the selectivity of the resulting catalyst system [24,25]. As regards bidentate ligands, which provide two coordination centers for the transition metal, the so-called bite angle fi determines the selectivity of the formed aldehydes. 

As the size of R3P increases so does the value of k. A popular method of assessing the size of R3P is by using Tolman s cone angle. This is the apex angle of the cone centered on P which just encloses the van der Waals radii of the outermost atoms of R3P. The data are shown in Table 2.3 for (2.134) in CO-saturated C2CI4 at 70°C (Ref. 124)... 

Definitions of Cone Angle Based on Models or on X-Ray Data 14.3.6.1 Tolman s cone angle... 

Figure 6 Tolman s cone angle used in mononuclear complexes with the plane of coverage .

Several workers have pointed out that there is a large and growing body of X-ray structural data of transition metal phosphine complexes. Such data can provide real cone angles, which may then be compared to Tolman s cone angles derived from models. Of course this line only applies to crystalline solids. Since the main application of transition metal chemistry is homogeneous catalysis, crystal structure data, though useful, are of limited applicability. Inevitably, cone angles in complexes in solution will be more variable than in crystalline systems. 

C. The graph indicates that no reaction occurs for d > 141°. This is borne out very well, for no reaction is found for phosphines PPh3, PPr 3, PCy3 and PBu3, all for which 6 145°. Whatever the merits of Tolman s cone angle concept, his ideas have stimulated much research, particularly in the field of bulky ligands. 

The stereochemistry of ligands, especially that of tertiary phosphines is well described by Tolman s cone angle concept99. The cone angle describes the angle between the outer substituent atoms, determined by their van der Waals radii, and the metal atom in mononuclear complexes (see Fig. 15). 

The enthalpy trend can be examined in terms of electronic and steric contributions to the enthalpy of reaction, the relative importance of which can be quantified in terms of the respective Ai /A2 ratios obtained in a treatment first proposed by Tolman, where enthalpies of reaction are correlated with steric (6, cone angle, see Tolman s Cone Angle) and electronic (v, carbonyl stretching frequency in Ni(CO)3L, L = tertiary phosphine) factors. A correlation factor of 0.95 is obtained when enthalpic data are fitted to equation (3) and a value of 2.32 is calculated for the A1/A2 and quantitatively denotes the overwhelming influence of steric factors. Since the steric factors have such a profound influence on the enthalpy of reaction, a direct relationship between the enthalpy of reaction and the phosphine cone angle can be established as shown in Figure 1. 

Figures Tolman s cone angle (a) simple symmetrical tertiary phosphine and (b) chiral phosphine...

Figure 9 (a) Tolman s cone angle used in mononuclear complexes, indicating the plane of coverage and (b) a diagram showing the parameters of the cluster cone angle... 

Tolman s Cone Angle. The model Tolman used to define the cone angle is shown in Figure 5. In order to make the cone angles comparable, he chose an arbitrary value for d, the M-P bond length, of 2.28 A. The phosphine depicted in Figure 5(a), PR3, is a symmetrical model. In order to accommodate unsymmetrical ligands, the model was developed to include a measure of each substituent s... 

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