Acyl complexes ligand effects

The linearity of the product of the Shell process is higher, 75-90% versus 60-70% for the non-ligand modified process. The reason for this is not entirely clear on steric grounds one might expect that the linear alkyl and acyl complexes are more stable leading to a higher linearity. Electronically the effects on rate and selectivity cannot be easily rationalised. 

The range of carbon nucleophiles that have been successfully employed for 1,4-addition to -a,/i-unsaturated iron-acyl complexes is limited to simple alkyl- and aryllithium species. Grignard reagents and the 1,3-propanedioate anion are reported to fail to react with. E-complexes36. The effect of varying the phosphane ligand has been examined little effect upon... 

The mechanism (Scheme 48) ° is expected to proceed through the acylpalladium species much as in the Rosenmund reduction. Indeed, the acyl complex 56 from oxidative addition of vinyl chloride with Pd(CO)(Ph3P)3 was isolated (Scheme 49). " The reaction of acid chlorides with the same catalyst provides aldehydes. However, aliphatic acid chlorides do not reduce effectively. The phosphine ligands present in the Heck acylpalladium intermediate are thought to be the cause, allowing decarbonylation and elimination to occur. Interestingly, the formylation will not occur with the Rosenmund catalyst. 

A most significant advance in the alkyne hydration area during the past decade has been the development of Ru(n) catalyst systems that have enabled the anti-Markovnikov hydration of terminal alkynes (entries 6 and 7). These reactions involve the addition of water to the a-carbon of a ruthenium vinylidene complex, followed by reductive elimination of the resulting hydridoruthenium acyl intermediate (path C).392-395 While the use of GpRuGl(dppm) in aqueous dioxane (entry 6)393-396 and an indenylruthenium catalyst in an aqueous medium including surfactants has proved to be effective (entry 7),397 an Ru(n)/P,N-ligand system (entry 8) has recently been reported that displays enzyme-like rate acceleration (>2.4 x 1011) (dppm = bis(diphenylphosphino)methane).398... 

The bare nitrogen analog of dihydroazaborine, where the R substituent on N is effectively replaced by an electron pair, is the azaboratabenzene anion H4C4BRN. The synthesis of this ligand and a ruthenium sandwich complex Cp Ru(H4C4BPhN) that is catalytically active in the acylation of benzyl alcohol have been reported.151... 

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