Reductive elimination of acetone

This species adds a ketone yielding the alkoxide complex (84) which, after reductive elimination of the corresponding alcohol, generates the 16-electron species (85). This intermediate undergoes oxidative addition of 2-propanol (species (86)) and subsequent reductive elimination of acetone, regenerating the hydride complex (83). 

This diagram illustrates many important points. First of all, it shows the mechanistic complexity that may be anticipated for even an apparently simple reaction, reductive elimination of acetone from 2.5. Second, it shows that RhCl(PPh3)3 is thermodynamically more stable than complex 2.5 by about 40 kJ/mol. However, complex 2.5 does not undergo spontaneous conversion to RhCl(PPh3)3 because it has sufficient kinetic stability (>92 kJ/mol). Third, the high free energy of activation is associated with a ligand dissociation step that precedes the reductive elimination step. The five-coordinated intermediate, once... 

Figure 2.12 A free energy diagram for the reductive elimination of acetone from a model complex. Note the high activation energies required for the forward and the backward reactions.

The stereochemistry was assigned from the H and P NMR spectra. Reductive elimination of acetone showed first-order kinetics, with A//J = 25.0kcalmol and AS% = 5.3 calK mol. ... 

Tetracarbonylalkyl derivatives of cobalt(I) have low stability. As early as 1964 it had been noted that ketones are formed in the thermal decomposition of CoR(CO)4 (R = Me, Et) presumably involving a binuclear intermediate or an intermolecular mechanism. The mechanism of acetone formation was studied for other cobalt systems that are more easily handled, namely, Co(>/ -C5H5)Me2(PMe3) and Co2(ti -CsH )2Me2(fi2-CO)2 . Upon carbonylation, in the former case, the transient carbonyl derivative Co()j -C5H5)Me2(CO) was observed spectroscopically, whereupon it underwent carbon monoxide insertion to give an acetyl-methyl complex, followed by reductive elimination of acetone ... 

Further reactions following insertion have been observed for a cationic l,2-bis(diisopropylphosphino)ethane complex (Scheme 2). Reaction of the precursor 1 with GO generates both the methyl-carbonyl 2 and acyl-carbonyl 3 complexes, which react together to give the neutral acyl-methyl complex 4 and the dicationic bis(carbonyl) 5. Reductive elimination of acetone then generates the Pd -monocarbonyl complex which forms an adduct with the Lewis-acidic methylpalladium complex to give dimer 6. 

AHylestrenol (37) is prepared from (32), an intermediate in the synthesis of norethindrone. Treatment of (32) with ethanedithiol and catalytic boron trifluoride provides a thioketal. Reduction with sodium in Hquid ammonia results in the desired reductive elimination of the thioketal along with reduction of the 17-keto group. Oxidation of this alcohol with chromic acid in acetone followed by addition of aHyl magnesium bromide, completes the synthesis... 

A formally -elimination reaction occurs when [Pt2Et3(jw-dppm)2]+ is thermolyzed to give [Pt2Et2( i-H)( i-dppm)2]+. This reaction across a biplatinum complex follows first-order kinetics, and is not retarded by added dppm. The -elimination step is not rate determining.56 Photolysis of [Pt2Me3(/r-dppm)2]+ in pyridine gives PtMe dppm) and [PtMe(py)dppm]+, but in MeCN, acetone or CH2C12 solvent, reductive elimination of ethane occurs.5 ... 

Another synthetic use of the M-P-V reaction has been exploited in the synthesis of new alkoxide derivatives.247,248 Hence, 2-hydroxybenzaldehyde (salicylaldehyde) will react with isoproxides of titanium and zirconium to initially displace isopropyl alcohol and give mixed derivatives which on heating undergo reduction of the aldehyde function with elimination of acetone. The stoichiometry of the overall reaction can be represented as shown in equation (66).248... 

Subsequent substitutions in these systems are often regiospecific (Scheme 44).459 460 461 Unlike the reductive elimination of cis hydrides in [Co(H)3(PPh3)3], ethane is not formed from cis Me groups in (120 Scheme 44), but for L = CO insertion into the Co—Me bond occurs with the release of acetone (Scheme 45) no intermediates have been observed.459 Using the diphosphomethamide anion as an analogue of allyl an interesting bonding isomerization has been observed (121 to 122 Scheme 46).462... 

We believe that the presence of free H in the acetone/water solvent system plays a role in the monocationic system. The rate determining step, once again, is the reductive elimination of aldehyde with a calculated barrier of 21.6 kcal (Fig. 14). Protonation of the monocationic dirhodium acyl is an alternate and likely pathway for eliminating aldehyde and forming the dicationic dirhodium catalyst Hr. Due to the very low activation barrier for the monocationic aUcyl-CO migratory insertion step, protonation of Rh-alkyl species to produce alkane is far less likely and consistent with the much lower alkane side reactions for 15r. 

---