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Probing the Limits of Ligand Steric Bulk: Backbone CH Activation in a Saturated N‐Heterocyclic Carbene
Author(s) -
Phillips Nicholas,
Tirfoin Remi,
Aldridge Simon
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201304243
Subject(s) - carbene , steric effects , chemistry , ligand (biochemistry) , ring (chemistry) , nucleophile , alkene , stereochemistry , medicinal chemistry , crystallography , catalysis , organic chemistry , biochemistry , receptor
The consequences of extremely high steric loading have been probed for late transition metal complexes featuring the expanded ring N‐heterocyclic carbene 6‐Dipp. The reluctance of this ligand to form 2:1 complexes with d‐block metals (rationalised on the basis of its percentage buried volume, % V bur , of 50.8 %) leads to CH and CN bond activation processes driven by attack at the backbone β‐CH 2 unit. In the presence of Ir I (or indeed H + ) the net result is the formation of an allyl formamidine fragment, while Au I brings about an additional ring (re‐)closure step via nucleophilic attack at the coordinated alkene. The net transformation of 6‐Dipp in the presence of [(6‐Dipp)Au] + represents to our knowledge the first example of backbone CH activation of a saturated N‐heterocyclic carbene, proceeding in this case via a mechanism which involves free carbene in addition to the Au I centre.