Compared Reductive Chemistry of Molybdenocene and Indenyl-Substituted Complexes

Abstract

Reduction of [IndCpMo(L)Br]Br (L = 1a, CO; 2, NCMe) with under the same conditions. With the aim of continuing the comparative study of the

The Nature of the Indenyl Effect

“…[33,34] A twoelectron reduction of those complexes yields the corresponding neutral molecules with a slipped coordination of one ring (h 3 -Cp'), therefore keeping the 18-electron count by the cleavage of two MÀC(Cp') bonds.…”

“…The larger folding of the h 3 -Cp ligand found for the W complex (W 208), relative to that calculated for the Mo species (W 128) is expected for a 5d metal [67] and compares well with the value optimized for the same complex by a different approach (W 148). [33] Some points emerge from the structural analysis of the optimized complexes, discussed above. The complexes are forced to undergo geometrical rearrangements to accommodate the increase of electronic density on the metal, resulting from the reduction.…”

“…[72] In all the theoretical work, the nature of the indenyl effect was always assumed to be based on the increased stability of h 3 -Ind complexes owing to the benzene aromaticity, as initially proposed by Mawby and Hart-Davies in 1969. [3] However, experimental data based on calorimetric studies of Mo and W complexes with Cp and Ind, [73] as well as theoretical studies focused on the indenyl effect, [33,69] hinted that the more facile h 5 -to-h 3 ring slippage showed by indenyl, when compared to cyclopentadienyl, might be related to the Cp' À M bond strength, specially in the h 5 -coordination mode.…”

Structural preferences of cyclopentadienyl and indenyl rings in iridium(I) carbene complexes

“…When both rings are Cp, the same reaction only takes place with strong p-acceptor carbonyls as L coligands [6]. The d 4 electron count appears to favour this haptotropic shift, being the source of many of the known examples [1b,7].…”

“…On the other hand, g 5 ! g 3 shifts seldom result in stable species in the case of d 6 complexes. Here, the strong drive to form octahedral (or pseudo octahedral) structures prevents ligand addition.…”