Cyclopentadienylnickel Chelates with Secondary or Tertiary Phosphane Tethers Bearing Imidazol‐2‐ylidene Ligands

Abstract

Treatment of cyclopentadienylnickel chloro or bromo chelates bearing either a tertiary 2‐(di‐tert‐butyl)phosphanylethyl or a secondary 2‐(2,4,6‐trimethylphenyl)phosphanylethyl tether with imidazolylidene (Arduengo carbene) ligands results in cationic or electroneutral carbene complexes with either a decoordinated or a chelated tether. The outcome depends on the nature of the carbene, the counter anion, and the reactant stoichiometry. The results are the basis of ongoing investigations directed towards a deprotonation of the chelated cationic complexes with a secondary phosphorus atom.

New Reactions of Cyclopentadienylnickel Chelates with Secondary Phosphane Tethers

“…In the context of our research the first late transition metal cyclopentadienylalkylphosphane complexes 6-12 with a secondary phosphane tether have recently been prepared (Scheme 3). [17,35] Chelate 6, which was obtained in up to 50 % yield, is the result of an unexpected protiodesilylation of the respective tertiary (tert-butyldimethylsilyl)-tert-butylphosphanyl chelate in the course of a column chromatography on silica gel. [17] Chelates 7 and 8 were obtained in a one pot reaction sequence starting from (2,4,6-tri-tert-butylphenyl)phosphane, [36] which was subsequently treated with butyllithium, spiro [2.4]hepta-4,6diene, [37] and NiCl 2 (dme) 2 or NiBr 2 (thf) 2 , in an overall yield of 48 % or 69 %, respectively.…”

“…The P,H coupling constants ( 1 J P,H = 365.8-374.7 Hz) are in accord with a coordinated phosphane tether. [35] Isonitrile complexes 26, 28, and 31 were also crystallographically characterized. However, the analyses obtained suffered from poor crystal quality and were therefore not suited for deposition or a detailed discussion.…”