Open-Shell Organometallics as a Bridge between Werner-Type and Low-Valent Organometallic Complexes. The Effect of the Spin State on the Stability, Reactivity, and Structure.

A number of transition metal catalysts including early and late transition metals have been investigated for olefin polymerization and copolymerization. Progress of the field in this decade is reviewed, and important topics among them such as binary catalysts and polymerization of new monomers are described in detail. Our recent results on the polymerization of olefins having cycloalkenes and non-conjugated dienes using late transition metal complexes are also mentioned.

Recent progress in olefin polymerization catalyzed by transition metal complexes: new catalysts and new reactions

The eta(5)-to-eta(3) coordination shift of cyclopentadienyl (Cp=C(5)H(5)(-)) and indenyl (Ind=C(9)H(7)(-)) ligands in molybdenocene complexes, [(eta(5)-Cp')(eta(5)-Cp)Mo(CO)(2)](2+) (Cp'=Cp or Ind), driven by a two-electron reduction of those species, was studied and compared by means of molecular orbital calculations (B3LYP HF/DFT hybrid functional, DZP basis sets). The results obtained, in terms of optimized geometries, relative energies, and bond analysis parameters, compare well with the experimental data, and verify the well-known indenyl effect, that is, a significantly more facile eta(5)-to-eta(3) rearrangement for the indenyl ligand when compared to cyclopentadienyl. However, the study of the folding of free Cp and Ind, combined with the (eta(5/3)-Cp')-M bond analysis, shows that the observed difference is not the result of an intrinsic characteristic of the indenyl ligand, such as the traditionally accepted aromaticity gain in the benzene ring formed in eta(3)-Ind complexes. Instead, it is directly related to the Cp'-M bond strength. While the difference in the energy required to fold the two free ligands is negligible (< or =1 kcal mol(-1) for folding angles up to 20 degrees), the (eta(5)-Cp)-M bond is stronger than that of (eta(5)-Ind)-M; however, the opposite situation is found for the eta(3) coordination mode. The net result, for Cp'=Ind, is a destabilization of the eta(5) complexes and a stabilization of the eta(3) intermediates or transition states yielding smaller activation energies and faster reaction rates for processes in which that is the rate-determining step.

The nature of the indenyl effect

Synthesis and reactivity of functionalized cycloheptatrienyl–cyclopentadienyl sandwich complexes

Carbon-fluorine bond cleavage by zirconium metal hydride complexes

The new bimetallic complexes[(η5-C5H5)MCl2{(η5-C5H4)CMe2(η5-C9H6)}M*Cl2(η5-C5H5)](M = Zr, M*= Zr, Hf; M = Hf, M*= Zr, Hf), [(η5-C5H5)ZrCl2]{[(η5-C5H4)CM2(η5-C9H6)}ZrCl2(η5-C5Me5)], [(η5-C5H5)ZrCl2{(η5-C5H4)Cme2(η5-C9H6)}Rh(CO)2] and [(η5-C5H5)ZrCl2]{[(η5-C5H4)CMe2(η5-C9H6)}Mn(CO)3] have been prepared from the precursors [{Me2C(η5-C5H4)(η2-C9H6)}M(η5-C5H5)Cl](M = Zr 1, Hf 2); the X-ray crystal structure of 1 is reported.

Synthesis of homo- and hetero-bimetallic complexes incorporating the [(η5-C5H4)CMe2(η5-C9H6)] ligand

The new ansa-bridged compounds [{Me2C(η5-C5H4)(η2-C9H6)}M(η5-C5H5)Cl], [{(CH2)5C(η5-C5H4)(η2-C9H6)}M(η5-C5H5)Cl](M = Zr, Hf) and [{[Me2C(η5-C5H4)(η3-C13H8)}Zr(η5-C5H5)Cl] show unusual modes of coordination of the indenyl or fluorenyl groups.

New metallocene compounds of zirconium and hafnium showing unusual ansa-ligand coordination: X-ray crystal structures of [{(CH2)5C(η5-C5H4)(η2-C9H6)}Zr(η5-C5H5)Cl] and [{Me2C(η5-C5H4)(η3-C13H8)}Zr(η5-C5H5)Cl]

The diene compounds [Hf(η4-CH2CMeCMeCH2)(PMe3)2Cl2]1, [M(η4-C6H8)(PMe3)2Cl2](M = Zr 2 or Hf 3) and the divalent [Zr(η6-C6H5Me)(PMe3)2Cl2]5 have been prepared. The structure of compound 1 has been determined by low-temperature neutron diffraction (15 K) and the σ2, π nature of the bonding mode of the 2,3-dimethylbutadiene ligand demonstrated from the methylene hydrogen positions. Treatment of 1 with lithium indenide gave [Hf(η5-C9H7)2(η4-CH2CMeCMeCH2)]4. The crystal structure of 5 has been determined by X-ray diffraction.

Diene and arene compounds of zirconium and hafnium

The new ansa-bridged compounds [M{Me2C(η5-C5H4)2}(η5-C5H5)Cl](M = Zr or Hf) have been synthesised and their molecular structures determined by X-ray crystallography. The latter is the first example of a tris(η5-cyclopentadienyl) derivative of hafnium.

Dalton communications. ansa-Bridged tris(cyclopentadienyl) compounds of zirconium and hafnium: X-ray crystal structures of [M{Me2C(η5-C5H4)2}(η5-C5H5)Cl](M = Zr or Hf)

Treatment of [Zr(η6-C7H8)2]1 in tetrahydrofuran with iodine gives [Zr(η-C7H7)(thf)2I]2 which reacts with PMe3 forming [Zr(η-C7H7)(PMe3)2I]3. The latter reacts with iodotrimethylsilane to give the exo-trimethylsilylcycloheptatriene compound [Zr{exo-η6-C7H7(SiMe3)}(PMe3)2I2]4. Thermolysis of 4 gives [Zr(η6-C7H8)(PMe3)2I2]5. The compounds [M(η-C7H7)L2Cl][M = Ti, L2=(PMe3)26, Me2NCH2CH2NMe27 or Me2PCH2CH2PMe28; M = Zr, L2= Me2NCH2CH2NMe29] have been prepared in one-pot reactions.

Gary M. Diamond

Papers

Synthesis of homo- and hetero-bimetallic complexes incorporating the [(η5-C5H4)CMe2(η5-C9H6)] ligand

New metallocene compounds of zirconium and hafnium showing unusual ansa-ligand coordination: X-ray crystal structures of [{(CH2)5C(η5-C5H4)(η2-C9H6)}Zr(η5-C5H5)Cl] and [{Me2C(η5-C5H4)(η3-C13H8)}Zr(η5-C5H5)Cl]

Diene and arene compounds of zirconium and hafnium

Dalton communications. ansa-Bridged tris(cyclopentadienyl) compounds of zirconium and hafnium: X-ray crystal structures of [M{Me2C(η5-C5H4)2}(η5-C5H5)Cl](M = Zr or Hf)

Half-sandwich η-cycloheptatri-ene and -enyl derivatives of titanium and zirconium