Hafnium alkyl complexes of the anionic PNP pincer ligand and possible alkylidene formation

Christina M. Brammell, Emily J. Pelton, Chun Hsing Chen, Andrey A. Yakovenko, Wei Weng, Bruce M. Foxman, Oleg V. Ozerov

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Abstract

The diarylamido-based PNP pincer ligand can be used successfully for support of organometallic Hf complexes (PNP = [(4-Me-2-iPr 2P-C6H3)2N]). (PNP)HfCl3 (3) was prepared via reaction of (PNP)Li (2) with HfCl4(OEt 2). Reactions of (PNP)HfCl3 with alkyl Grignards led to triple alkylation to produce (PNP)HfMe3 (4) with a small methyl or only double alkylation to give (PNP)Hf(CH2SiMe3) 2Cl (5) with a larger alkyl. Structures of 3, 4, and 5 in the solid state were established by X-ray diffraction studies. Structures of the alkyl complexes 4 and 5 display remarkably irregular coordination environments about Hf, while in 3 it is approximately octahedral. Compound 4 was found to be thermally stable at 75 °C. On the other hand, thermolysis of 5 at similar conditions led to a mixture of products, the major one of which is believed to be a Hf alkylidene on the basis of in situ NMR spectroscopic observations (e.g., δ 248.2 ppm in the 13C{1H} NMR spectrum).

Original languageEnglish (US)
Pages (from-to)4132-4137
Number of pages6
JournalJournal of Organometallic Chemistry
Volume696
Issue number25
DOIs
StatePublished - Dec 15 2011

Bibliographical note

Funding Information:
We are grateful to the US National Science Foundation for support of this research through grants CHE-0809522 and CHE-0944634 to O.V.O., through support of E.J.P. as an REU participant in 2007 (grant CHE-0552767 for an REU site at Brandeis University), through support of C.M.H. as an REU participant in 2008 (grant CHE-0552767 for an REU site at Brandeis University) and 2009 (grant CHE-0755207 for an REU site at Texas A&M University), and through grant CHE-0521047 for the purchase of a new X-ray diffractometer at Brandeis University. We are also grateful for the support from the Welch Foundation (grant A-1717 to O.V.O), the Dreyfus Foundation (Camille Dreyfus Teacher-Scholar Award to O.V.O.), and the Sloan Foundation (Alfred P. Sloan Research Fellowship to O.V.O.). We thank Dr. Christos Douvris and Yanjun Zhu for help with some of the experiments in this paper.

Copyright:
Copyright 2011 Elsevier B.V., All rights reserved.

Keywords

  • Alkylidene
  • Hafnium
  • Metal alkyl
  • Pincer
  • X-ray crystallography

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