Facile η5–η3 hapticity interconversion in pentamethylcyclopentadienyl ruthenium(ii) complexes containing a phenylmethallyl (“open indenyl”) ligand

Abstract

The indenyl effect has been introduced to pentadienyl ("open cyclopentadienyl") chemistry by preparation of the phenylmethallyl ("open indenyl") ligand oInd(Me). The reaction of its potassium salt K(oInd(Me)) with [(η(5)-C(5)Me(5))RuCl](4) afforded the sandwich complex [(η(5)-C(5)Me(5))Ru(η(5)-oInd(Me))] (1), which, upon treatment with PMe(3), CO, and 2,6-dimethylphenyl isocyanide (CN-o-Xy), easily underwent η(5)-η(3) hapticity interconversion and formed the complexes [(η(5)-C(5)Me(5))Ru(η(3)-oInd(Me))(L)] (2, L = PMe(3); 3, L = CO; 4, L = CN-o-Xy). In these complexes, the η(3)-bound phenylmethallyl ligand adopts an anti-conformation with regard to the relative positions of the phenyl and methyl substituents. For the PMe(3) complex anti-2, slow conversion to the syn-isomer was observed, and this equilibrium reaction was monitored by NMR spectroscopy at 50 °C to determine a first order rate constant of k(323 K) = 6.57 × 10(-6) (± 0.02 × 10(-6)) s(-1) and an activation barrier of ΔG° = 26.8 kcal mol(-1). DFT calculations afforded a stabilization of syn-2 and syn-3 by ΔG(298) = -1.54 and -1.74 kcal mol(-1) over the respective anti-isomer.

Flexibility of an Open Indenyl Ligand in Iron(II) Complexes

“…NMR spectroscopy suggests the presence of oInd Me in 1 as an η 5 -pentadienyl ligand, but there are striking differences relative to the ruthenium analogue, for which we did not observe dynamic behavior on the NMR time scale at ambient temperature . The 1 H NMR spectrum of 1 in THF- d 8 shows two individual sharp signals for the protons of the CH 2 group, showing that the rotation about the C1–C2 axis is slow (see Scheme for the numbering of 1 ).…”

“…Similarly, we have recently introduced the indenyl effect to the pentadienyl (“open Cp”) chemistry with the preparation and coordination of a phenylmethallyl ligand, oInd Me (Figure ), which can be classified as an open indenyl ligand . Although conventional pentadienyl ligands are already known to coordinate to transition metals in various bonding modes, the relatively weak C–X π-bond in heteropentadienyl systems usually results in even more facile η 5 –η 3 haptotropic shifts .…”

“…However, as a result of the indenyl effect, the complex [(η 5 -C 5 Me 5 )Ru(η 5 -oInd Me )] undergoes a hapticity shift significantly faster than its oxapentadienyl congener upon addition of a ligand L (L = CO, PMe 3 , CN- o -xylyl), resulting within minutes at room temperature in anti -[(η 5 -C 5 Me 5 )Ru(η 3 -oInd Me )(L)] complexes. For the PMe 3 complex, slow isomerization to the syn isomer takes place, which suggests that η 1 -oInd Me intermediates are also accessible . As part of our continuing interest in metal–pentadienyl and metal–allyl chemistry, we wished to seek a deeper insight into the characteristic features of the open indenyl ligand, oInd Me , including detailed studies on the anti -to- syn isomerization and the isolation of an η 1 -complex.…”

Efficient Norbornene (NBE) Incorporation in Ethylene/NBE Copolymerization by Half-Titanocene Catalysts Containing Chlorinated Aryloxo Ligands

“…Since the Ti–C bond distances [carbon attached to phenyl, 2.397(4)–2.435(4) Å] are longer than those of ordinary half-titanocenes containing a cyclopentadienyl fragment (with aryloxo ligand etc. ), ,,,− the results suggest that the indenyl ligand coordinates to Ti in η 3 mode (favorably) rather than η 5 fashion, although these should be present as an equilibrium in solution …”

The organometallic chemistry of cycloheptatrienyl zirconium complexes

“…The corresponding ligand was synthesized from K(6,6dmch) and ClPPh 2 , which resulted in selective nucleophilic attack of the central carbon atom, followed by deprotonation. 31 Finally, it was not possible to attach the recently introduced novel open indenyl ligand, oInd Me , 33 to the (C 7 H 7 )Zr fragment; attempts to synthesize [(Z 7 -C 7 H 7 )Zr(Z 5 -oInd Me )] failed several times.…”