Zirconium sandwich complexes

Other homoleptic Lu(III) sandwich complexes 23, 25 (78), and 27 (34), have been prepared accordingly, as in Scheme 6. Zirconium sandwich complexes have been prepared by the method employed by Kim et al. (80) for the synthesis of zirconium porphyrin double deckers reaction of Zr(lV-Et2)4 with the pz ligands 24 (35%) and 26 (61%) produced the corresponding sandwich complexes (28 and 29) (Scheme 6). 

A heteroleptic zirconium sandwich complex in which Zr links octaethylporphyrazine (28) and the structurally analogous octa-ethylporphyrin has also been reported. To spectroscopically study the... 

Bis (indenyl) complexes, with Zr(IV), 4, 935 Bis(indenyl)dimethyl metallocenes, synthesis, 4, 884-885 Bis(indenyl)zirconium sandwich complexes, preparation and reactivity, 4, 728... 

Both alkane reductive elimination and alkali metal reduction reactions have been used to prepare a family of bis(indenyl)zirconium sandwich complexes.104 Crystallographic characterization of the Pr1 304 and the SiMe2But variants establishes an unprecedented 7y9-hapticity of the indenyl ligand where all nine carbons of the carbocycle are engaged in bonding with the zirconium center. Interestingly, this coordination mode was computationally predicted before structural confirmation.183... 

Reactivity studies reveal that the bis(indenyl)zirconium sandwich complexes serve as isolable, modular precursors to the rich chemistry of divalent zirconocene. Addition of 1 atm of carbon monoxide generates the bis(indenyl)-zirconocene dicarbonyl complex, 307, while treatment with N,N-dimethylaminopyridine results in C-H activation to form the zirconocene pyridyl hydride complex 308. Crystallographic characterization of both complexes as well as multinuclear NMR spectroscopy establishes that the more familiar 77s, 77s hapticity for the indenyl ligands has been restored. Alkyne coupling reactions are also observed as addition of 2-butyne to 302 allows observation of the alkyne complex, 208, and ultimately the zirconacyclopentadiene 309 (Scheme 50).104... 

Veiros, L. F. Substituent effects on haptotropic rearrangements of bis(indenyl) zirconium sandwich complexes. Organometallics, 25,2266-2273 (2006). 

All of the zirconium pz and porphyrin sandwich complexes have up to two reversible ring oxidations and three reversible ring reductions. The zirconium porphyrazines are harder to oxidize by -400 mV and easier to reduce by at least 400 mV than the analogous porphyrins, making them better oxidants and worse reductants. The heteroleptic pz-porphyrin sandwich complex has oxidation and reduction potentials between those measured for the porphyrin and the pz sandwiches, as expected (Table VII). 

Unbridged, bridged, substituted, and half-sandwich complexes have been used as metallocenes for ethylene polymerization (Figs. 1 and 2). To compare the activities and molecular masses, the polymerizations are carried out under the same conditions (30°C, 2 bar ethylene pressure, with toluene as a solvent) (105). Table IV shows the polymerization behavior of various met-allocene/alumoxane catalysts. Generally, zirconium-containing catalysts are... 

Access to polyolefins with a wider choice of properties has more recently been provided by various homogeneously soluble organometallic catalysts. Some of these catalysts, in particular those based on sandwich and half-sandwich complexes of zirconium and titanium and on nitrogen-containing complexes of group 4 and of some of the group 8-10 metals (see Section 7.4), are thus likely to be increasingly used for the production of polyolefins for special-purpose applications, which require properties not easily accessible otherwise. 

Treatment of 3-borolenes or 2-boraindans with bulky lithium amides yields the dihthiated aromatic borolide dianions, which are applicable as hgand precursors for transition-metal complexes. Many borole complexes including a number of unusual multidecker sandwich complexes and mixed-metal clusters have been described. 4 3,2i2 An unexpected new entry into the synthesis of borole complexes has been recently discovered. Bochmann found that attack of B(C6Fs)3 at a zirconium bound diene leads to a pentafluorophenylborole complex throngh snccessive C-H activation steps. ... 

Salt metathesis was employed to synthesize half-sandwich zirconium and hafnium dichloride complexes 331 incorporating the bidentate, mono-anionic benzamidinate ligand (Equation (26)). The corresponding zirconium dimethyl and dibenzyl complexes have also been prepared using appropriate alkylating reagents.260 The zirconium dichloride complex (R= H), upon activation with MAO, are active for both polymerizations of ethylene... 

The salt metathesis reaction of ZrCU and the lithium tetramethylcyclopentadienide bearing the 2-methoxyethyl or the 2-methylthioethyl donor sidearm produces half-sandwich zirconium trichloride complexes 445 (Equation (34)).314,315 As expected, these complexes show monomer-dimer dynamic behavior in solution and exist as doubly chloro-bridged dimers in the solid state. 

Ricciardi et al have investigated the heteroleptic tetrapyrrole sandwich complex formed with porphyrinato-porphyrazinato-zirconium(lV) using time-dependent density functional theory. They find that an accmate description of the UV/visible spectrum is obtained and the nature of the excitations is discussed and compared with previous work on bisporphyrins. A calculation of the /8-hyperpolarizabihty fads to reproduce the experimental result, which appears to predict a negative value for the SHG at all frequencies up to the experimental one. A pole is found in the calculated P function close to the laser frequency, which would lead to the possibhty of negative values at higher frequencies. 

Titanium, Zirconium and Hafnium A new type of macrocyclic sandwich complex (1) has been isolated from the reaction of the parent macrocyclic complex with NaCp. The same product has been characterised from the reaction when Ti(trataa)Cl2 or Ti(tmtaa)Cl is used as the substrate complex. The analagous vanadium complex CpV(tmtaa) has been prepared and demonstrated to contain 2 unpaired electrons compared with the single unpaired electron in the titanium complex.A more conventional complex CpTi(n -02C6H4)C1 is generated from the reaction of Ti(02C6H4)Cl2 with TlCp. ... 

Vanadium, Niobium, Tantalum and Zirconium Mixed sandwich complexes of vanadium containing arene rings have been described in two reports. The bisindenylbisvanadium complex (41) has been structurally characterised and contains a metal-metal bond length of 2.35A. The complex is formed in the reductive... 

While metallocene-derived complexes 103 deserve interest mainly because of their redox properties and applications resulting therefrom, half-sandwich complexes 104 and 105 show more diverse chemical reactions. Based on their synthesis of the fulvalene dianion 102, Smart et al. [99] prepared some molybdenum complexes such as 108 [62% yield based on Na(DME)Cp] by treatment of 102 with molybdenum hexacarbonyl followed by oxidation with bromine. Vollhardt reported the synthesis of a variety of homo- and heterodinuclear fulvalene complexes such as 109-112 by treatment of dihydrofulvalene and respective metal carbonyls. The dichromium complex 110 has some catalytic activity in the hydrogenation of conjugated dienes [110]. The authors report the reaction with iron carbonyls being unsuccessful, whereas the reaction with dicobaltoctacarbonyl resulted in the formation of fulvalene complex 112 lacking a metal-metal bond in 80% yield (Scheme 10.38) [100, 101]. Later, the diiron complex corresponding to 109 was reported [111]. Hermann et al. and Cuenca etal. prepared zirconium(IV) and zirconium(III) fulvalene complexes [112,113]. 

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