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Reactivity of [Rh(β-diketonato)(cod)] complexes: A DFT approach

“…Triphenyl phosphine can only substitute one CO in [Rh(b-diketonato)(CO) 2 ] [20] (Scheme 1 reaction 3) while triphenyl phosphite substitutes both CO groups [19,21] (Scheme 1 reaction 4). In contrast we observed that a series of derivatives of 1,10-phenanthroline (phen) or 2,2 0 -dipyridyl [22] reacts with the [Rh(b-diketonato)(cod)] with the replacement of the b-diketonato ligand (Scheme 1 reaction 5). This reaction makes it possible to study the effect of the electron donating or withdrawing properties of the R and R 0 side groups of b-diketonato (R 0 COCHCOR) À on the lability of the chelating ligand.…”

Synthesis, Substitution Kinetics, and Electrochemistry of the First Tetrathiafulvalene-Containing β-Diketonato Complexes of Rhodium(I)

“…Substitution is, however, dependent on p K a of the leaving β-diketonato ligand . It was concluded that Rh−N bond formation is not the rate-determining step but rather the Rh−O bond breakage is . Furthermore, the results from this earlier study were consistent with the Rh−O bond adjacent to the more electron-withdrawing terminal β-diketonato substituent breaking first .…”

“…It has been shown elsewhere that β-diketonato substitution in [Rh(cod)(β-diketonato)] complexes with phenanthroline derivatives having 3.03 < p K a < 6.31 are independent of the phen derivative p K a . p K a of phen is 4.86 . Substitution is, however, dependent on p K a of the leaving β-diketonato ligand .…”

“…Although the Δ S ⧧ values of both 3 and 4 are about half this, they still are substantially negative values and as such indicate that β-diketonato substitution predominantly must take place via an associative mechanism. It has been shown elsewhere that β-diketonato substitution in [Rh(cod)(β-diketonato)] complexes with phenanthroline derivatives having 3.03 < p K a < 6.31 are independent of the phen derivative p K a . p K a of phen is 4.86 .…”

“…Substitution of the β-diketonato group on [Rh(cod)(β-diketonato)] complexes by incoming NN ligands like phen usually takes place via an associative mechanism, which is characterized by a large negative entropy of activation (Δ S ⧧ ) and a negative volume of activation (Δ V ⧧ ). , A neutral five-coordinate 18-electron intermediate species of the type [Rh(β-diketonato)(cod)(NN)], where only one of the N atoms of the incoming NN ligand is coordinated, is first formed. The rate-determining step is thought to be bond breakage of the Rh−O bond closest to the more electronegative β-diketonato substituent …”