Correlations Tolman cone angle

The Pt—P (and Pt—Cl) bond lengths correlate with the electron-donating ability of the phosphine (Tolman s Xi factor) rather than steric factors (the cone angle of the tertiary phosphine) [150b]. 

My question to Dr. J. Kochi is whether it is possible to correlate the steric factor in his equations describing the oxidation of alkylmetal compounds to some measure of the bulkiness of the alkyl groups such as cone angles similar to ones suggested by Dr. C.A. Tolman for tertiary phosphine ligands. 

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. 

Is there a direct correlation between these data and the original cone angles proposed by Tolman ... 

Phosphines and related P(III) compounds typically serve as ancillary ligands, but the dissociation of these ligands is crucial to the reactivity described in later chapters. Tolman correlated the ligand cone angle with the equilibrium for dissociation from NiL compounds.The extent of ligand dissociation in these nickel complexes and in related palladium complexes increases in the order PMej < PMe Ph < PMePlq < PEtj < PPhj < PPr j < PCyj < PPhBu, . 

Tolman correlated the position of the band in the infrared spectra of complexes NilCOl PR in dichloromethane with the electronic effect of the substituents R (Table 5.5). A reasonable correlation with Hammett (7-parameters was also found. The ligand behaviour of phosphorus donors are thus defined both by these electronic effects as well as by the steric effects measured by the cone angle (p. 169). 

Tolman introduced [27] electronic factors, xij, l or phosphine and phosphite ligands, based upon the totally symmetric CO stretching vibration in a phosphine nickel tricarbonyl derivative. More recently Bartik and co-workers have established this correlation more accurately [28]. These parameters, together with Tolman s cone angle data, have been of great utility in understanding the chemistry and dynamics of phosphine complexes. 

In recent years, numerous attempts have been made to correlate the geometry of catalyst/substrate intermediates with the l/b ratio of product aldehydes derived from the hydroformylation of 1-olefins [38]. Conclusions are mainly based on spectroscopic measurements or chemical calculations [39]. Especially, Tolman s cone angle (9) [40] and the natural bite angle ( ) [38], respectively, are used to estimate the space-filling properties of a ligand (see Chapter 2). These studies mainly refer to phosphorus-modified rhodium catalysts and 1-olefins as substrates, but they can also contribute to a better understanding of the isomerization - hydroformylation [41]... 

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