Cyclopentadienyls analogues

No photochemical rearrangements or transannular ring closure chemistry were observed with the corresponding cyclopentadienyl analogues (see Section VIII,A), illustrating the key role of the pentamethylcyclopentadienyl... 

The use of an indenyl complex as catalyst instead of the cyclopentadienyl analogue enhances the reactivity due to the opening of a coordination site by valence tautomerization. The reaction is highly chemoselective, and nonallylic alcohols and allyl ethers are not isomerized (Eq. 12.3). 

An interesting variant in the family of cyclopentadienlyirid-ium complexes are those containing )] -indenyl ligands. It had been shown by Mawby and coworkers that indenyl metal complexes are far more reactive with respect to ligand substitution chemistry than their cyclopentadienyl analogues.Basolo quantified this greatly accelerated reaction chemistry for a number of indenyl metal systems and dubbed this acceleration the indenyl effectThe indenyl effect also appears to play an important role in the chemistry of indenyl iridium complexes. Indenyliridium complexes may be prepared in much the same way as the cyclopentadienyl and pentamethyl-cyclopentadienyl iridium complexes. However, once formed, they are far more reactive in terms of substitution chemistry. 

It is remarkable that the compounds have been isolated as THF solvates, while their cyclopentadienyl analogues 9aLnCl were obtained solvent-free. The THF is bound fairly loosely and is partially given off in vacuo. An NMR spectroscopic investigation of the diamagnetic yttrium and lutetium complexes has revealed that the rac isomer equilibrates with the meso isomer in THF-cfe solution, the rac/meso equilibrium ratio being ca. 6 1 for these compounds. 

Indenydes of rare earth metals are isolated as tetrahydrofuranates, but the coordinated ligand can be removed by heating in vacuum. The complexes do not sublime. Other properties (colour, solubility, stability on air) are similar to those of cyclopentadienyl analogues (Table IV.L)... 

The unsubstituted cyclopentadienyl analogue of 1 Cp(CO)2lr similarly gave Cp(CO)Ir(CH3)H. The hydridomethyl compound 9 was not prepared directly from the dihydride 4 due to experimental difficulties. However, Bergman observed that primary alkyl complexes are thermodynamically more stable than secondary complexes [26]. For example, the reaction of 4 with n-propane (reaction 9) or n-pentane gave mixtures of primary and secondary insertion products (with preferential formation of primary compounds). Treating these mixtures at 110 °C converts the secondary complexes into the more stable primary derivatives this conversion takes place via reversible reductive elimination from the secondary hydrido alkyl isomers. This very interesting result allowed the preparation of selectively pure primary insertion products of linear alkanes and the achievement of methane activation (reaction 12). Thus, heating the secondary hydrido cyclohexyl compound 6 in cyclooctane under CH4 pressure caused the formation of the methyl product 9 which is the thermodynamic sink for the system. 

An unusual rearrangement which proceeds via a vinylihodiacyclopropane has been reported Scheme 5). 2 The cyclopentadienyl analogue is stable to 120 C while the indraiyl analogue rearranges to a cyclopentadiene without hydrogen transfer via the rhodium centre. 

Pauson and co-workers have prepared a variety of ir-pyrrole complexes which are isoelectronic with i-cyclopentadienyl analogues. 

The unsaturated, unsubstituted 71-pyrrole complexes are rather less stable than their 71-cyclopentadienyl analogues. Azaferrocene, 5.14, is isomorphous with ferrocene [100] and is oxidized to an unstable cation in... 

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