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Title:Zirconium and hafnium organometallic compounds: Molecular geometry for five-, and seven-coordinate species
Author(s):Nelsen, Melissa Jane
Doctoral Committee Chair(s):Girolami, Gregory S.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Abstract:Alkylation of ZrCl$\sb4$ with phenyllithium affords the new d$\sp0$ complex $\rm\lbrack Li(Et\sb2O)\rbrack\sb2\lbrack ZrPh\sb6\rbrack ;$ the $\rm\lbrack ZrPh\sb6\sp{2-}$) anion adopts a trigonal prismatic geometry. Despite the presence of orbitals on the phenyl ligands that are of the right symmetry to serve as $\pi$-donors, the trigonal prismatic geometry clearly shows that the phenyl groups are not acting as $\pi$-donors. The lithium cations form weak interactions with the ipso carbons of the phenyl rings.
In an attempt to prepare six-coordinate d$\sp0$ species that lack Li$\sp\cdots$C interactions, the synthesis of zirconium pentafluorophenyl complexes was investigated. The compounds (Li(12-crown-4)$\rm\sb2\rbrack\sb2\lbrack ZrCl\sb2(C\sb6F\sb5)\sb4$) and $\rm\lbrack Li(tmed)\sb2\rbrack\lbrack Li(tmed)\rbrack\sb2\lbrack ZrF\sb2(C\sb6F\sb5)\sb5$) were isolated; the first adopts an octahedral structure owing to the $\pi$-donor character of the chloride ligands, while the latter adopts a regular pentagonal bipyramidal structure. The latter compound also shows that C-F bond activation has occuned.
Alkylatidn of the phosphine complexes ZrCl$\sb4$(PP) and HfCl$\sb4$(PP) complexes with $\rm LiCH\sb2SiMe\sb3$ affords unusual lithium salts of five-coordinate zirconium auryls; one of these salts, $\rm\lbrack Li(dcype)\sb2\rbrack\lbrack Zr(CH\sb2SiMe\sb3)\sb5$) where dcype is 1,2-bis(dicyclohexylphosphino)ethane, was structurally characterized. The structure of the anion is best described as a distorted square pyramid; the structure is consistent with molecular orbital calculations which predict that square pyramidal structures should be adopted for such d$\sp0$ species. Equally interesting is the structure of the cation, which consists of a lithium atom surrounded by a distorted tetrahedral array of two diphosphine ligands. These results bear on important issues such as whether five-coordinate d$\sp0$ alkyls are susceptible to Jahn-Teller distortions, and whether trialkylphosphine ligands should be classified as hard or soft Lewis bases.
Treatment of $\rm (C\sb8H\sb8)ZrCl\sb2(thf)\sp{\cdot}2KCl$ with one equivalent of p-tolyllithium, followed by the addition of $\rm N,N,N\sp\prime ,N\sp\prime$-tetramethylethylenediamine (tmed), yields red crystals of the mono(p-tolyl) complex $\rm\lbrack Li(tmed)\rbrack\lbrack (C\sb8H\sb8)Zr(p$-$\rm C\sb6H\sb4Me)Cl\sb2$); this compound has been crystallographically characterized. Treatment of $\rm (C\sb8H\sb8)MCl\sb2{\cdot}2KCl$ (M = Zr, Hf) with three equivalents of methyl-, phenyl-, or p-tolyllithium in tetrahydrofuran or diethyl ether, followed by addition of $\rm N,N,N\sp\prime ,N\sp\prime$-tetramethyl-ethylenediamine, yields several new organozirconium and -hafnium compounds of stoichiometry $\rm\lbrack Li(tmed)\sb2\rbrack\lbrack (C\sb8H\sb8)MR\sb3$) where R = Me, Ph, or p-$\rm C\sb6H\sb4Me$. With larger alkyl groups, electrically neutral organozirconium and -hafnium complexes can be isolated: treatment of $\rm (C\sb8H\sb8)MCl\sb2(thf)\sp{\cdot}2KCl$ with 2 equiv. of LiCH(SiMe$\sb3)\sb2$ gives products of stoichiometry $\rm (C\sb8H\sb8)M\lbrack CH(SiMe\sb3)\sb2\rbrack\sb2$. The structure of this latter complex has been determined. Interestingly, this latter 14-electron molecule reacts reversibly with carbon monoxide but is unaffected by dihydrogen even at elevated pressures.
Issue Date:1996
Rights Information:Copyright 1996 Nelsen, Melissa Jane
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9712387
OCLC Identifier:(UMI)AAI9712387

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