Synthesis and Catalytic Use of Gold(I) Complexes Containing a Hemilabile Phosphanylferrocene Nitrile Donor
Abstract
Removal of the chloride ligand from [AuCl(1-P)] (2) containing a P-monodentate 1-(diphenylphosphanyl)-1-cyanoferrocene ligand (1), by using silver(I) salts affords cationic complexes of the type [Au(1)]X, which exist either as cyclic dimers [Au(1)](2)X-2 (3a, X=SbF6; 3c, X=NTf2) or linear coordination polymers [Au(1)](n)X-n (3a, X=SbF6; 3b, X=ClO4), depending on anion X and the isolation procedure. As demonstrated for 3a, the polymers can be readily cleaved by the addition of donors, such as Cl-, tetrahydrothiophene (tht) or 1, giving rise to the parent compound 2, [Au(tht)(1-P)][SbF6] (5a) or [Au(1-P)(2)][SbF6] (4a), respectively, of which the last two compounds can also be prepared by stepwise replacement of tht in [Au(1-P)(2)][SbF6].
The particular combination of a firmly coordinated (phosphane) and a dissociable (nitrile) donor moieties renders complexes 3/3 attractive for catalysis because they can serve as shelf-stable precursors of coordinatively unsaturated Au-I fragments, analogous to those that result from the widely used [Au(PR3)(RCN)]X catalysts. The catalytic properties of the Au-1 complexes were evaluated in model annulation reactions, such as the synthesis of 2,3-dimethylfuran from (Z)-3-methylpent-2-en-4-yn-1-ol and oxidative cyclisation of alkynes with nitriles to produce 2,5-disubstituted 1,3-oxazoles.
Of the compounds tested (2, 3a, 3b, 3a, 4a and 5a), the best results were consistently achieved with dimer 3c, which has good solubility in organic solvents and only one firmly bound donor at the gold atom. This compound was advantageously used in the key steps of annuloline and rosefuran syntheses.