Synthesis and solvent dependent reactivity of chelating bis-N-heterocyclic carbene complexes of Fe (II) hydrides

Sergey Zlatogorsky, Michael J. Ingleson*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The synthesis and isolation of low coordinate methylenebis-(N-DIPP- imidazole-2-ylidene)iron (II)hydrides, (( DIPPC) 2CH 2)FeH 2-yI y ((DIPP = 2,6-di-isopropylphenyl, y = 1 or 0), was complicated by competitive reactions with solvent, rapid reductive elimination of H 2 and/or dissociation of the bis-N-heterocyclic carbene ligand. Addition of KH to (( DIPPC) 2CH 2)FeI 2 in THF/haloalkane mixtures enabled a short lived mono-hydride to be trapped by reaction with CH 2Cl 2 or cyclo-heptylbromide to form (( DIPPC) 2CH 2)FeI(X) (X = Cl or Br, respectively). Toluene coordination stabilises iron-mono hydride complexes as (( DIPPC) 2CH 2)Fe IIH{η 6- (toluene)} species, which can be isolated in low yield from combination of borohydride salts and (( DIPPC) 2CH 2)FeI 2 in toluene, including an imidazole C4 deprotonated carbene-borane, methylene(N-DIPP-imidazole-2-ylidene)(N-DIPP-4-triethyl-borane-imidazole-2- ylidene)](hydrido)(η 6-toluene)iron. In the absence of toluene, or at short reaction times compounds with empirical formula (( DIPPC) 2CH 2)Fe(H)(HB(R) 3)·LiI (R = Et or sec-Bu) that function as a masked Fe (II)-dihydride are isolated. Whilst (( DIPPC) 2CH 2)Fe(H)(HB(R) 3)·LiI was stable for days in Et 2O, more polar solvents (MeCN, THF) led to formation of the carbene borane adducts (( DIPPC) 2CH 2)(BR 3) 2. The addition of CO or cyclo-heptylbromide to (( DIPPC) 2CH 2)Fe(H)(HB(R) 3)·LiI formed (( DIPPC) 2CH 2)Fe(CO) 3 and (( DIPPC) 2CH 2)FeBr 2, respectively with BR 3 evolved from both reactions as a by-product.

Original languageEnglish
Pages (from-to)2685-2693
Number of pages9
JournalDalton Transactions
Volume41
Issue number9
DOIs
Publication statusPublished - 7 Mar 2012

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