Cycloheptatrienyl-Pentadienyl Complexes of Zirconium (Half-Open Trozircenes): Syntheses, Structures, Bonding, and Chemistry

Abstract

The reactions of Zr(C 7 H 7 )(Cl)(tmeda) (tmeda = tetramethylethylenediamine) with pentadienyl anions lead to formally tetravalent Zr(C 7 H 7 )(Pdl) complexes, for Pdl = C 5 H 7 , 2,4-C 7 H 11 , 6,6-dmch, and c-C 7 H 9 (C 7 H 11 = dimethylpentadienyl, dmch = dimethylcyclohexadienyl, c-C 7 H 9 = cycloheptadienyl). Structural characterizations of the first three have been carried out, revealing much shorter Zr-C distances for the C 7 H 7 ligand and a pattern of Zr-C bond distances for the pentadienyl ligands that is consistent with a formally high (þ4) metal oxidation state, which is also supported by DFT calculations. As had been found for the analogous Cp complexes, these 16-electron species are susceptible to Lewis base coordination, and the 2,6-xylyl isocyanide adducts of the 2,4-C 7 H 11 and 6,6-dmch complexes have been isolated and characterized by IR spectroscopy and single-crystal X-ray diffraction studies. The IR spectroscopic studies indicate that the pentadienyl ligands are serving as better net electron donors than Cp ligands, opposite what is typically found for related but lower valent species. At high temperatures the 16-electron Zr(C 7 H 7 )(C 5 H 7 ) complex undergoes slow conversion to the corresponding Cp complex.

Twists and turns: Studies of the complexes and properties of bimetallic complexes featuring phenylene ethynylene and related bridging ligands

“…The explanation for these differences can be traced back to the differences in electronic structures, and in particular the different metalbased frontier orbitals offered.An examination of the frontier orbitals of the model system [Mo(CCC 6 H 5 )(dppe)(-C 7 H 7 )] reveals an important stabilisation of the d x 2 -y 2 and d xy orbitals by -interactions with the empty e 2 orbitals of the {C 7 H 7 } + ligand, whilst the d yz and d xz orbitals (filled in a d 6 Mo(I) electron counting system) are stabilised by -backbonding interactions from the e 1 ligand orbitals(Figure 9). These metal-ligand interactions with the e-type orbitals of the {C 7 H 7 } + ring are more important than in the case of the isoelectronic {C 5 H 5 }due to the lower energy of the ring orbitals as ring size increases, which especially favors the increased interactions of the metallic orbitals with the e 2 system in the case of the larger ring[200][201][202][203]. The net consequence is that the d z 2 remains relatively high in energy, being somewhat destabilised by the ring a-type orbital, and contributes substantially to the molecular HOMO.…”

Recent Advances of Imidazolin-2-iminato in Transition Metal Chemistry

“…The Imidazolin-2-iminato, being the ideal candidate for stabilizing high oxidation state metal so used as a spectator ligand for Zr(IV). [82] The Dipp substituted ligand (Im Dipp NH) was preferred for the study as the higher sterically encumbrance allowed to smooth incorporation of pentadienyl, [83][84][85] cyclopentadienyl, [86] and phospholyl ligands. [87][88][89] [90] The reaction followed the coordination insertion mechanism in which ε-caprolactone first coordinated to the metal.…”

How big is a Cp? Novel cycloheptatrienyl zirconium complexes with tri-, tetra- and pentasubstituted cyclopentadienyl ligands

“…The sodium salts NaCp chex , 32 Na 3 Cp, 27 Na 2 2 Cp, 26 Na 3 2 Cp 28 and NaCp Ph 31 as well as (C 7 H 7 )Zr(Cl)(tmeda) 33 were prepared according to literature procedures; a sample of NaCp BIGc was kindly provided by Professor S. Harder.…”