Theoretical Study of Oxidative Addition and Reductive Elimination of 14-Electron d¹⁰ML₂Complexes:  A ML₂+ CH₄(M = Pd, Pt; L = CO, PH₃, L₂= PH‘₂CH₂CH₂PH₂) Case Study

Abstract

We have chosen six ML 2 complexes, with a systematic variation in the ligands and metals, to investigate oxidative additions as well as reductive eliminations by using the MP2/LANL2DZ and the MP4SDTQ//MP2/LANL2DZ levels of theory. A qualitative model based on the theory of Pross and Shaik (Su, M.-D. Inorg. Chem. 1995, 34, 3829) has been used to develop an explanation for the barrier heights. Considering the geometrical effect, the substituent effect, and the nature of the metal center, the following conclusions emerge: for 14-electron ML 2 complexes, a smaller L-M-L angle and a better electron-donating ligand as well as a heavier transition metal center (such as Pt) should be a potential model for the oxidative addition of saturated C-H bonds. Conversely, a linear structure and a better electron-withdrawing ligand as well as a lighter transition metal center (such as Pd) would be a good candidate for reductive coupling of C-H bonds. The results obtained are in good agreement with the available experimental results and permit a number of predictions to be made. S0020-1669(97)00320-0 CCC: $15.00

d10-ML2 Complexes: Structure, Bonding, and Catalytic Activity

“…This destabilizing effect due to the need to decrease the ligand-metal-ligand angle (the bite angle) can be avoided by bending the catalyst in advance, as, for example, in chelate complexes Pd[PH 2 (CH 2 ) n PH 2 ] where the bite angle can be controlled by varying the length of the carbon-chain (CH 2 ) n . It is well known that the reactivity of a catalytic complex depends on its bite angle [21,[60][61][62][63][64]. By studying oxidative addition of several bonds to this series of model catalysts with n ¼ 2-6, bite angles from 98 to 156 can be achieved, and a clear relationship was found between the ligand-metal-ligand angles and the activation barriers.…”

Computational exploration of Pd‐catalyzed C–H bond activation reactions

“…The OA process can be either from Pd(0) to Pd(II) or from Pd(II) to Pd(IV) . The OA mechanism from Pd(0) to Pd(II) is the concerted breaking of C–H bond and formation of C–Pd and Pd–H bonds in the transition structure, with the formal increase by 2 units of the oxidation state of the Pd from 0 to 2, as shown in Figure . By contrast, the OA of C–H bond to Pd(II) center to produce Pd(IV) intermediate is normally very unfavorable.…”

“…Mota et al investigated the mechanism of cyclocarbopalladation‐Stille coupling tandem reaction of various γ‐bromopropargylic‐1,2 diols with alkenyls or alkynyl stannanes catalyzed by Pd(PPh 3 ) 4 . The computational results suggest that a pathway involving a Pd(IV) intermediate is not likely to occur …”

New Concepts for Designing d10‐M(L)n Catalysts: d Regime, s Regime and Intrinsic Bite‐Angle Flexibility

“…The effect of this phenomenon is that the resulting hybrid d orbital is pushed up in energy and oriented more towards the substrate s* CÀH . [6,29,37] Thus, as we proceed along the reaction coordinate for oxidative addition to the bisligated metal complexes, the interaction curve experiences an additional reinforcement, becomes steeper and pulls the TS "to the left", that is, to an earlier, reactant-like geometry.…”