Bond disruption enthalpies

Bonds between many neutral ligands and transition metal atoms in low oxidation states, have mean bond disruption enthalpies in the range 80-200 kJ mol 1 (9). Bonds to charged ligands, e.g. 

In the previous exercise (whose outcome was not very successful), we used a new concept to assess the thermodynamic stability of chemical bonds the mean bond dissociation enthalpy (also known as mean bond disruption enthalpy). It is represented by DH° or by (DH°) (the symbol we adopt). As indicated, for... 

Marks et al. provided a valuable examination of the absolute bond-disruption enthalpies of various important organometallic ligands R in Cpf Sm-R [86], The data obtained by anionic iodinolytic and alcoholytic isoperibol titration calorimetry (performed in toluene) were calculated according to Scheme II. The knowledge of these absolute bond disruption enthalpies helps towards a better... 

Scheme II. Bond-disruption enthalpies of organosamarium(III) complexes...

As a consequence monomeric complexes are obtained much more easily. Also, the tendency to bridge lanthanide centers is less distinct and, for example, a small cluster chemistry as it exists for alkoxides, e.g. OiPr [13] and OtBu derivatives [14], is not yet known. However, the Ln-N(amide) bond is less strong than the Ln-O(alkoxide) bond, and even comparable to Ln-C(alkyl) bonds, which has an effect in synthetic chemistry. This has been confirmed by the determination of absolute bond disruption enthalpies D by means of calorimetric titrations for the representative systems Cp Sm X (X = OrBu, D = 82.4 kcalmol-1 NMe2, 48.2 CH(SiMe3)2, 47.0) [15]. 

The Cp3ThR complexes have been used to measure metal alkyl bond disruption enthalpies for a series of thorium alkyl complexes for both solution and gas phases. The thorium carbon bonds appear to be relatively strong when compared to other metal-carbon linkages, and solution bond disruption enthalpies range from ca. 75 to 90kcalmol . ... 

Actinide hydrides are rather hydridic and nndergo rapid reactions typical of snch systems for example, reactions with ketones and halocarbons provide actinide alkoxides and halides, respectively. Rapid qnantitative addition of terminal alkenes (the reverse of /S-hydride elimination) is consistent with the known bond disruption enthalpies (eqnation 66). ... 

Table 8 Relative average Ru-PRs bond disruption enthalpies (kcalmol" ) in the reaction ...

Figure 12 Relative bond disruption enthalpy (kcalmol ) vs steric parameter (%Vbut) in the Cp Ru(L)Cl system slope =...

Metal-silicon bond disruption enthalpies have been measured for a series of metallocene complexes including Gp3USi(SiMe3)3. This complex was synthesized by reaction of Cp3UCl with LiSi(SiMe3)3(THF)3 in diethyl ether. The thermodynamic data were obtained by titration calorimetry with I2 (Scheme 29).80... 

Bond disruption enthalpies have been determined for the complexes (C9H6SiMe3)3ThH, (G9H6SiMe3)3ThD, and (CsH4SiMe3)3ThH. The thermodynamic data were obtained by iodolysis batch-titration calorimetry.141... 

Marks and co-workers provided a most valuable examination of absolute bond disruption enthalpies of various relevant metalorganic ligands X in Cp 2Sm-X. The data were obtained by anionic titration calorimetry in toluene (Fig. 4) [41 ]. Although the Ln-X bonds seem to be thermodynamically very stable, they usually display kinetic lability due to high ligand exchange ability, chelating and solubility effects. 

Fig. 4. Bond disruption enthalpies of organolanthanide(III) complexes. The gray area indicates the bond disruption enthalpies of organolanthanide(O) arene species (TTB=q6-C6H3tBu3-1,3,5)...

Various types of solution reaction calorimetry have proven especially useful in thermochemical studies of organometallic molecules. Provided the reactions employed are clean, rapid, and quantitative, it is possible to employ processes as in Equation 16 to express relative M-R bond disruption enthalpies in terms of the meas-... 

Bond Disruption Enthalpy Data for Organolanthanide Complexes and the Corresponding Homoleptic Trihalides in Kcal/Mol ... 

Figure 1. Comparison of metal-iodine bond disruption enthalpies for several (Me5C5)2LnI complexes (Ln - lanthanide) with the published values for the corresponding lanthanide triiodides.

Enthaplles of Solution, Enthalpies of Reaction of Organolanthanide Compounds with Various Tltrants in Toluene, and Derived Bond Disruption Enthalpies ... 

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