Synthesis of singly and doubly bridged ansa-Zirconocene hydrides. Formation of an unusual mixed valence trimeric hydride by reaction of H2 with {(Me2Si)25- C5H3)2} Zr(CH3)2 and generation of a dinitrogen complex by reaction of N2 with a zirconocene dihydride

Paul J. Chirik, Lawrence M. Henling, John E. Bercaw

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Abstract

A series of singly and doubly bridged ansa-zirconocene dihydride complexes has been prepared from hydrogenation of the corresponding dimethyl complexes. For the singly [SiMe2]-bridged species, the hydrogenation reaction is facile at 25°C, whereas for the doubly [SiMe2]-bridged complexes hydrogenation occurs over the course of days at 87°C. Hydrogenation of {meso-Me2Si(η5-C5H3-3- CMe3)2}ZrMe2 affords the isomeric dimeric dihydrides [{meso-Me2Si(η5-C5H3- 3-CMe3)2} ZrH]22-H)2, one of which has been characterized by X-ray diffraction. The racemo isomer of Me2Si(η5-C5H2-2- SiMe3-4-CMe3)2ZrMe2 (BpZrMe2) reacts with dihydrogen, affording the first example of a monomeric ansa-zirconocene dihydride, {rac-Me2Si(η5-C5H2-2- SiMe3-4-CMe3)2}ZrH2 (rac-BpZrH2). In the presence of dinitrogen, rac-BpZrH2 undergoes thermal reductive elimination of H2 and reaction with N2, yielding the dinitrogen complex BpZr(μ222-N2)ZrBp, for which the dinitrogen ligand is coordinated in a side-on fashion to both zirconiums with a N - N bond distance of 1.241(3) Å. The doubly [SiMe2]-bridged zirconium dimethyl complex {(Me2Si)25-C5 H3)2} ZrMe2 (RpZrMe2) undergoes hydrogenation under forcing conditions, affording the mixed valent (Zr(IV)/Zr(IV)/Zr(III)) hydride trimer [RpZr]33-H)22- H)3, which has been characterized by X-ray diffraction. More substituted doubly [SiMe2]-bridged zirconocene dihydrides such as [{(Me2Si)25-C5H-3,5- (CHMe2)2)(η5-C5H2-4- CHMeEt}ZrH]22-H)2 [sec-BuThpZrH]22-H)2) and [(Me2Si)25-C5H-2,4- (CHMe2)2)(η5-C5H2- CHMe2)ZrH]22-H)2 ([iPrThpZrH]22-H)2) have been prepared and shown to be robust dimers in solution.

Original languageEnglish (US)
Pages (from-to)534-544
Number of pages11
JournalOrganometallics
Volume20
Issue number3
DOIs
StatePublished - Feb 5 2001
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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