TETRAMETHYLGUANIDINE AND BENZOPHENONEIMINE AS LIGANDS IN GOLD CHEMISTRY

(Tetramethylguanidine)gold(I) chloride (1) and bromide (2) are readily prepared in high yield from (Me2N)(2)C=NH and [AuCl(Me2S)] or [AuBr(t ht)] (tht = tetrahydrothiophene), respectively. NMR spectra of chlorof orm solutions of the two products indicate equilibria of the type 2 LA uX reversible arrow L2Au+AuX2-. The cationic complex [Au{NH = C(NMe2)( 2)}(PPh3)](+) is obtained as the triflate salt 3 from tetramethylguani dine and [Au(PPh3)]+O3SCF3-. In solution at low temperature (-60 degre es C), this compound adopts a rigid structure whereby the NMe2 groups are rendered non-equivalent, but at ambient temperature there is coale scence of the NMe2 signals in the H-1- and C-13-NMR spectra. The relat ed benzo-phenoneimine complex [Au{NH=CPh2}(PPh3)]+BF4- (4), which was synthesized as a reference compound, exhibits similar behaviour. In so lution at low temperature (-60 degrees C) the two phenyl rings of the ligand are diastereotopic. In contrast, the triisopropylphosphane deri vative [Au{NH = CPh2}(PiPr(3))]+BF4- (5) is rigid on the NMR time scal e, even at 25 degrees C. The solid-state structures of 2, 3, 4, and 5 have been determined by single-crystal X-ray diffraction. Compound 2 c rystallizes in the ionic form with discrete Au ... Au bonded ion pairs [Au{NH=C(NMe2)(2)}(2)](+) [AuBr2](-)[Au ... Au 3.1413(8) Angstrom]. T he cations of 3, 4, and 5 show the [Au(PPh3)](+) units N-coordinated t o the imino groups, with the nitrogen atoms in a trigonal-planar confi guration.