Acyl ligand

Note that the a designation, when applied to carbons of an acyl ligand, follows the usual organic convention and refers to the carbon adjacent to the carbonyl carbon. The organometal-lic convention, which is not used here for acyl ligands, is referenced to the metal atom and would refer to the acyl carbon (which is bound to the metal) as a and the next adjacent carbon as / . 

Another route to complexes with a,/i-unsaturated acyl ligands involves reaction of the dicar-bonyl(r/5-cyclopentadienyl)iron anion of 12 with a,/ -unsaturated acyl halides38. 

Jacobson, A.E. and O Donohue, T.L. A specific acylating ligand for phencyclidine (PCP) receptors antagonizes PCP behavioral effects. ur J Pharmacol 111 405-406, 1985. 

The term metalla-/3-diketonate refers to an anionic diacyl complex, such as L M(RCO)(R CO) , in which the two acyl ligands occupy adjacent coordination sites of the metal atom. Resonance stabilization of the negative charge by 7r-delocalization onto the two acyl ligands gives Lewis structures 1 and 2. The two acyl ligands acquire an acyl/carbene... 

Neutral b/.v(acyl)Fe(CO)4 complexes have been reported by Stewart et al. (23). The acyl ligands have perfluoroalkyl substituents. These complexes are isoelectronic to the anionic diacyltetracarbonylmanganate species mentioned above. 

The second important structural feature in concerns the orientation of the n -acyl ligand. The C-0 vector in the present case points in the direction away from the Cl ligand, while in the aforementioned titanium and zirconium compounds, the C-0 vector is oriented toward the non-acyl monohapto ligand (E vs F). 

We converted the alkoxyacetyl complexes 9 to the ethyl complex 8, by employing the aforementioned acyl ligand activation and BH reduction procedures, as outlined in Scheme 2. The a, -dialkoxyethylidene salts 9a, b resulted from alkylation of 6a,b with EtsO+PFg" in CH2CI2 recrystallization from CH2CI2-ether provided 9 in 72% yields as air-stable yellow PFg" salts. 

Towards Catalytic Relevance Bimetallic Activation of Acyl Ligands and Transition Organometallic Hydrides as Reducing Agents... 

Bimetallic activation of acetyl and alkoxyacetyl ligands — through formation of cationic P2 acyl complexes — to reaction with nucleophilic hydride donors was established. Cationic transition metal compounds possessing an accessible coordination site bind a neutral T -acyl ligand on another complex as a cationic P2 acyl system. These i2 3icyl systems activate the acyl ligand to reduction analogous to carbocation activation. Several examples of i2-acyl complexation have been reported previously. 

The compounds used allow the steric and electronic effects of the acyl ligand to be studied relatively independently of each other. From the data in Table 1, Heck22 reached the following conclusions ... 

Scheme 7.20 summarises the results of these two experiments. Upon p-H transfer from the acyl ligand, an unstable Pd"-H complex is formed, which decomposes to give Pd and free ligand in the absence of co-monomers. The free ligand reacts with residual Pd" species forming various compounds, including the bis-chelate [Pd(dppe)2] + [5ej. 

Iron acyl complexes bearing an a,/ -unsaturated acyl ligand possess multiple sites of electrophilic reactivity. Strong bases may be induced to react with the acyl ligand, and in Section 1.1.1.3.4.1.1. the chemoselective y-deprotonation of Z-a,/i-unsaturated acyl ligands to generate enolate species was addressed. The profoundly different reactivity of the unsubstituted complex 1 and E-a,/ -unsaturated acyl complexes, such as 2, is discussed here. 

Reaction of the ambidentate complex 1 with carbon nucleophiles results in exclusive 1,4-addition (Michael addition) to the enone-like acyl ligand no products of 1,2-addition of the nucleophile are observed (see also Houben-Weyl, Volume 13/9 a, p 416)38 39. 

Rhenium-acyl complexes, such as 1, are isoelectronic with the iron-acyl complexes discussed above and many reactivity patterns are common to the two groups of compounds. Treatment of complex 1 with strong bases, such as butyllithium or lithium diisopropylamide, results in abstraction of a cyclopentadienyl proton which is followed by rapid migration of the acyl ligand to the cyclopentadienyl ring to produce the metal-centered anion 384. Alkylation of 3generates a metal-alkyl species, such as 4. 

The molybdenum-acyl enolate 4 has been characterized spectroscopically by NMR and has been reported to exist as a single (observable) isomer88. Extended Hiickel calculations on model complexes suggest that a conformation similar to A is most favorable for enolates such as 488. The deprotonated di-hapto acyl ligand may also be described as a 2-(C,0)-ketene ligand both the ketene and enolate terminology appear in the literature. 

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