Organometallic hafnium compounds

Only a small number of zirconium(III) and hafnium(III) complexes are known. Nearly all of these are metal trihalide adducts with simple Lewis bases, and few are well characterized. Just one zirconium(III) complex has been characterized structurally by X-ray diffraction, the chlorine-bridged dimer [ ZrCl PBu,) ]- Although a number of reduced halides and organometallic compounds are known in which zirconium or hafnium exhibits an oxidation state less than III, coordination compounds of these metals in the II, I or 0 oxidation states are unknown, except for a few rather poorly characterized Zr° and Hf° compounds, viz. [M(bipy)3], [M(phen)3] and M Zr(CN)5 (M = Zr or Hf M = K or Rb). 

Coordination Chemistry Supported Organotransition Metal Compounds Titanium Organometallic Chemistry Vanadium Organometallic Chemistry Zirconium Hafnium Organometallic Chemistry. 

D. J. Cardin, M. F. Lappert and C. L. Raston, Chemistry of Organo-zirconium and -hafnium Compounds , Wiley, New York, 1986 R. S. P. Courts, P. C. Wailes and H. Weigold, Organometallic Chemistry of Titanium, Zirconium, Hafnium , Academic Press, New York, 1974 G. E. Coates, M. L. H. Green and K. Wade, in Organometallic Compounds , Chapman and Hall, London, 1968, vol. 2. 

The first organometallic compound of zirconium reported was bis(iT-cyclopentadienyl)zirconium dibromide (592). Since the initial report many new organozirconium compounds have been prepared, most of which contain at least one cyclopentadienyl ring. Only a few compounds of hafnium have been prepared, presumably because everyone assumes that hafnium behaves in a fashion identical to zirconium, a proposition which should be examined more closely. 

One promising approach to the adjustment of coordinative saturation is to alter the number of cyclopentadienyl rings. Since the great bulk of titanium, zirconium, and hafnium organometallic chemistry is that of ( 5115)2X1X2 systems, compounds such as the recently reported ( 5115)2-UCI2 (95) would seem to be ideal precursors. We (96) as well as others (97) have found this to be an incorrect formulation of the reaction product of U U and 2Tl 5H5. When the reaction is carried out in dimethoxy-ethane (DME) we find (96) by NMR that the product is actually a mixture of ( 5H5)3U land ( 5H5)U l3 DME (98). 

This chapter reviews the literature up to approximately January 1984. Previous comprehensive reviews of the chemistry of zirconium and hafnium are available, and annual surveys of the inorganic and coordination chemistry of these elements have been published since 1981 The present treatment emphasizes the chemistry of discrete, isolable complexes, although some attention has been given to the extremely complex aqueous solution chemistry of Zr and Hf. In general, zirconium forms slightly more stable complexes in solution than does hafnium stability constants may be found in standard compilations.In cases where the structural chemistry of discrete complexes is closely related to that of chain, layer or extended three-dimensional structures, the discussion of the discrete complexes has been set in the broader context the section on fluorometallate complexes is a case in point. Organometallic compounds of zirconium and hafnium have been excluded almost entirely. 

Barium oxide, barium salicylate and/or other organobarium salts 2) Organometallic salts of lanthanum, hafnium and tantalum and their oxides Replacements for lead and copper compounds currently employed for ballistic modification. Particularly attractive due to production of considerably less smoke during combustion of propellants [245]. 

There has been no recent comprehensive review of this area, although a book on the organometallic chemistry of titanium, zirconium, and hafnium deals, in part, with some of the hydride derivatives (1). In the present review, the first part of the discussion reflects the fact that much of the early work on organotitanium hydrides was, often unknowingly at the time, interwoven with attempts to prepare titanocene, Cp2Ti (Cp = tj3-C5H5). Subsequent sections deal with similar compounds containing an additional metal (e.g., aluminum), miscellaneous titanium hydride compounds, and a summary of the main properties of the above species. 

J. J. W. Eshuis, Y. Y. Tan, A. Meetsma, and J. H. Teuben, Organometallics, 11, 362 (1992). Kinetic and Mechanistic Aspects of Propene Oligomerization with Ionic Organozirconium and -Hafnium Compounds Crystal Structures of [CpJMMe(THT)]"[BPh4] (M = Zr, Hf). 

F. Hoffmann und G. Roewer reported on reactions of cyclohexasilylpotassium with transition metal compounds, and C. Marschner described a Cp-fiee hafnium silyl-substituted complex. A series of four papers from the group of W. Malisch deal with the description of silanol functionalities in organometallic iron and tungsten complexes and the synthesis of perchlorinated metallo siloxanes. 

In this chapter, we review the progress in coordination chemistry of zirconium and hafnium from the 1960s to 2002. Thus, this chapter was written as an extension of the previous issue of Comprehensive Coordination Chemistry (CCC, 1987). In defining the scope of this review, we have specifically limited the discussion to exclude compounds deemed to be principally organometallic in nature. 

Introduction.—A text describing the co-ordination compounds of zirconium and hafnium with organic ligands has been published,and the history of the discovery of hafnium and its separation from zirconium has been described. There have been reviews of the structures of zirconium and hafnium compounds, of hydrozircona-tion, and of the organometallic chemistry of zirconium and hafnium. ... 

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