Tetramethylguanidine and Benzophenoneimine as Ligands in Gold Chemistry
1997; Wiley; Volume: 130; Issue: 10 Linguagem: Inglês
10.1002/cber.19971301010
ISSN0009-2940
AutoresWolfgang Schneider, Andreas Bauer, Annette Schier, Hubert Schmidbaur,
Tópico(s)Catalytic Cross-Coupling Reactions
ResumoAbstract (Tetramethylguanidine)gold(I) chloride ( 1 ) and bromide ( 2 ) are readily prepared in high yield from (Me 2 N) 2 CNH and [AuCl(Me 2 S)] or [AuBr(tht) (tht = tetrahydrothiophene), repectively. NMR spectra of chloroform solutions of the two products indicate equilibria of the type 2 LAuX = L 2 Au + AuX 2 − . The cationic complex [Au(NHC(NMe 2 ) 2 )(PPh 3 )] + is obtained as the triflate salt 3 from tetramethylguanidine and [Au(PPh 3 )] + O 3 SCF 3 − . In solution at low temperature (−60°C), this compound adopts a rigid structure whereby the NMe 2 groups are rendered non‐equivalent, but at ambient temperature there is coalescence of the NMe 2 signals in the 1 H‐ and 13 C‐NMR spectra. The related benzophenoneimine complex [Au{NHCPh 2 }(PPh 3 )] + BF 4 − ( 4 ), which was synthesized as a reference3 compound, exhibits similar behaviour. In solution at low temperature (‐60°C) the two phenyl rings of the ligand are diastereotopic. In contrast, the triisopropylphosphane derivative [Au[NHCPh 2 ](P i Pr 3 )] + BF 4 − ( 5 ) is rigid on the NMR time scale, even at 25°C. Thbe solid‐state structures of 2, 3, 4 , and 5 have been determined by single‐crystal X‐ray diffraction. Compound 2 crystallizes in the ionic form with discrete Au … Au bonded ion pairs [Au[NHC(NMe 2 ) 2 ] 2 ] + [AuBr 2 ] − [Au … Au 3.1413(8) Å]. The cations of 3, 4 , and 5 show the [Au(PPh 3 )] + units N ‐coordinated to the imino groups, with the nitrogen atoms in a trigonal‐planar configuration.
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