Chemistry Of Organo Zirconium And Hafnium Compounds

Author : Melissa Jane Nelsen
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (774 download)

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Download or read book Zirconium and Hafnium Organometallic Compounds: Molecular Geometry for Five-, and Seven-coordinate Species written by Melissa Jane Nelsen and published by . This book was released on 1996 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Alkylation of ZrCl$sb4$ with phenyllithium affords the new d$sp0$ complex $rmlbrack Li(Etsb2O)rbracksb2lbrack ZrPhsb6rbrack ;$ the $rmlbrack ZrPhsb6sp{2-}$) 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$spcdots$C interactions, the synthesis of zirconium pentafluorophenyl complexes was investigated. The compounds (Li(12-crown-4)$rmsb2rbracksb2lbrack ZrClsb2(Csb6Fsb5)sb4$) and $rmlbrack Li(tmed)sb2rbracklbrack Li(tmed)rbracksb2lbrack ZrFsb2(Csb6Fsb5)sb5$) 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 $rm LiCHsb2SiMesb3$ affords unusual lithium salts of five-coordinate zirconium auryls; one of these salts, $rmlbrack Li(dcype)sb2rbracklbrack Zr(CHsb2SiMesb3)sb5$) 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 $rm (Csb8Hsb8)ZrClsb2(thf)sp{cdot}2KCl$ with one equivalent of p-tolyllithium, followed by the addition of $rm N,N,Nspprime ,Nspprime$-tetramethylethylenediamine (tmed), yields red crystals of the mono(p-tolyl) complex $rmlbrack Li(tmed)rbracklbrack (Csb8Hsb8)Zr(p$-$rm Csb6Hsb4Me)Clsb2$); this compound has been crystallographically characterized. Treatment of $rm (Csb8Hsb8)MClsb2{cdot}2KCl$ (M = Zr, Hf) with three equivalents of methyl-, phenyl-, or p-tolyllithium in tetrahydrofuran or diethyl ether, followed by addition of $rm N,N,Nspprime ,Nspprime$-tetramethyl-ethylenediamine, yields several new organozirconium and -hafnium compounds of stoichiometry $rmlbrack Li(tmed)sb2rbracklbrack (Csb8Hsb8)MRsb3$) where R = Me, Ph, or p-$rm Csb6Hsb4Me$. With larger alkyl groups, electrically neutral organozirconium and -hafnium complexes can be isolated: treatment of $rm (Csb8Hsb8)MClsb2(thf)sp{cdot}2KCl$ with 2 equiv. of LiCH(SiMe$sb3)sb2$ gives products of stoichiometry $rm (Csb8Hsb8)Mlbrack CH(SiMesb3)sb2rbracksb2$. 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.