Zirconium complexes with 7/6-arenes

Bis(arene)zirconium complexes, characteristics, 4, 697 Bis(arylamido)pyridines, with Hf(IV), 4, 792 Bis(aryl) bridges, in complexes with chromium(VI), 5, 346... 

Similar behavior is observed for calix[4]arene (5ee Calixarenes) complexes of the type (89). " Moreover, the oxygen donor atoms are particularly appropriate for the oxophilic early transition metals. A rich chemistry has been developed with complexes containing zirconium- carbon bonds. In this area, aryne zirconocene compounds can be thermally generated and isolated without trimethylphosphane additional coordination. Zirconium-butadiene chemistry has been explored as well and constitutes a source of zirconium complexes. 

Wolczanski and Bergman concurrently showed that the addition of hydrocarbon C-H bonds occurs to zirconium(rV) imido complexes, as shown in Equations 6.55 and 6.56. - The shylamidozircononium-imido complex reacted with both alkanes and arenes, whereas the zirconocene-imido complex reacted with arenes. Kinetic studies showed that the generation of the unsaturated zirconium-imido complex is rate limiting and that the unsaturated zirconocene compoimd is generated reversibly by dissociation of THE prior to the C-H bond cleavage process. Most likely, this reaction occurs by formation of an alkane or arene complex and subsequent reaction of the alkane or arene complex to generate the amido alkyl or amido aryl complexes. - ... 

Inter- and intramolecular (cyclometallation) reactions of this type have been ob-.served, for instance, with titanium [408,505,683-685], hafnium [411], tantalum [426,686,687], tungsten [418,542], and ruthenium complexes [688], Not only carbene complexes but also imido complexes L M=NR of, e.g., zirconium [689,690], vanadium [691], tantalum [692], or tungsten [693] undergo C-H insertion with unactivated alkanes and arenes. Some illustrative examples are sketched in Figure 3.37. No applications in organic synthesis have yet been found for these mechanistically interesting processes. 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

Sixteen-electron bis(arene) complexes of formally zero-valent zirconium, hafnium, and titanium have been made by cocondensation of the metal atoms with bulky ligands such as 1,3,5-tri-t-butylbenzene71 ... 

Triangular zirconium mixed-valence complexes stabilized by arenes, [Zr3(/x-Cl)6( ] -C6Me6)3]"+ (n = 1, 2) (see Arene Complexes), have been isolated as salts with the [Al2Cl7] anion (equation 28). Arenes also stabilize divalent hafiiium in the complexes (/x-) -C6H5R)[Hfl2(PMe2Ph)2]2 (R = H, Me), which have a piano stool structure (see Piano Stool Structure) ... 

Incorporation of sterically demanding aryl substituents allows isolation of bis(arene)zirconium and hafnium complexes. The bond enthalpies of (7]6-(l,3,5-tBu)3C6H3)2M (M = Ti, 1 Zr, 2 Hf, 3) have been measured by iodinolytic bath calorimetry and values of 49(1), 64(3), and 67(4) kcal mol-1 have been determined for the respective metal-arene bond enthalpies (Scheme l).4 Computational studies establish that the major metal-arene bonding interaction is a 5-backbond formed from the overlap of metal dxz-yz and orbitals with the appropriate linear combination of arene p-orbitals. The observed increase in metal-arene bond strength is consistent with increased backbonding down the... 

Comparison of IR-spectra of CEP and CEP-PVP shows that bands at 1620, 950 and 930 cm characterizing non-saturation of CEP disappear after grafting of PVP and band at 1600 cm associated with pyridine ring appears. After treatment of CEP-PVP with dibutoxyzirconium dichloride bands at 1640 cm, 1600 cm, and 1500 cm with shoulder at 1529 cm appear. Similar picture can be also observed in the case of treatment of CEP-PVP with dibutoxytitanium dichloride. One could assume that in these cases, coordination with zirconium and titanium takes place not only with nitrogen atom but also with t-electron system of the pyridine ring, i.e. an arene complex is formed. 

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