Complexes [AuCl{C(NHR)(NHR 0 )}] and [AuCl{C(NHR)(NEt 2 )}] (R= t Bu, p-Tol, Xylyl, p-C 6 H 4 -COOH, p-C 6 H 4 COOEt, R 0 = Me, n Bu, i Pr, n heptyl, p-Tol) have been prepared by reaction of the corresponding isocyanogold complexes [AuCl(CNR)] with either primary amines or diethylamine. All the prepared carbenes are reactive and highly selective catalysts for skeletal rearrangement, methoxycyclization of 1,6-enynes, and other mechanistically related gold-catalyzed transformations. Overall, these easily accessible nitrogen acyclic carbene (NAC) gold complexes were not second to NHC complexes and were advantageous to obtain different products.

Complexes [AuCl{C(NHR)(NHPy-2)}] (Py-2 ) 2-pyridyl; R ) Me, tBu, nBu, iPr, nheptyl) have been prepared in amodular way from [AuCl(CNPy-2)]. The carbene moiety has a hydrogen-bond supported heterocyclic structure similar to the nitrogen heterocyclic carbenes in the solid state, and in CH2Cl2 or acetone solution, which is open in the presence of MeOH. The compounds are good catalysts for the skeletal rearrangement of enynes, and for the methoxycyclization of enynes. In contrast, the complexes [AuCl{C(NHR)(NHPy-4)}] are scarcely active due to the blocking effect of the coordination position required for the catalysis by the nitrogen of the NHPy-4 group.

Mononuclear and dinuclear chiral gold(I) carbene complexes with carbene ligands of the type HBHC (hydrogen bonded heterocyclic carbenes) and NAC (nitrogen acyclic carbenes) have been prepared by reaction of isocyanide gold(I) complexes and chiral amines or diamines. The reaction of [AuCl(CNPy-2)] (1) (Py = pyridyl) with the corresponding chiral primary amines afforded the chiral HBHC complexes (R)-[AuCl{C(NH(CHMePh))(NHPy-2)}] ((R)-2), and (S)-[AuCl{C(NH{CHMe(1-naphthyl)})(NHPy-2)}] ((S)-3), while the reaction of 2 equiv of 1 with diamines produced (S)-2,2'-bis[NH{C(AuCl)(NHPy-2)}](2)-binaphthyl ((S)-4), (1R,2R)-1,2-bis[NH{C(AuCl)(NHPy-2)}]-diphenylethane ((1R,2R)-5), and (1R,2R)-1,2-bis[NH{C(AuCl)(NHPy-2)}]-cyclohexane ((1R,2R)-6). On the other hand the addition of alkyl amines to (S)-2,2'-[NCAuCl](2)-binaphthyl ((S)-8) gave the chiral NAC complexes (S)-2,2'-bis[NH{C(AuCl)(NMe(2))}](2)-binaphthyl ((S)-9) and (S)-2,2'-bis[NH{C(AuCl)(N(i)Pr(2))}](2)-binaphthyl ((S)-10), while the addition to (S)-2,2'-[NCAuCl](2)-3,3'-Ph(2)-binaphthyl ((S)-12) yielded (S)-2,2'-bis[NH{C(AuCl)(NMe(2))}](2)-3,3'-Ph(2)-binaphthyl ((S)-13) and (S)-2,2'-bis[NH{C(AuCl)(NEt(2))}](2)-3,3'-Ph(2)-binaphthyl ((S)-14). All the complexes are active catalysts in the cyclopropanation of vinyl arenes and in the intramolecular hydroalkoxylation of allenes, providing good yields and modest or poor enantioselectivity. The results show that all these ligands are compatible with different functions and reaction conditions and are worth considering as alternative systems to NHCs or phosphines in gold catalyzed reactions.

The Pt II complexes [( x bpy)Pt(Ph)(THF)] + ( x bpy = 4,4′-X 2 -2,2′bipyridyl; x = OMe (1a), t Bu (1b), H (1c), Br (1d), CO 2 Et (1e) and NO 2 (1f)] catalyze the formation of n-propylbenzene and cumene from benzene and propene. The catalysts are selective for branched products, and the cumene/n-propylbenzene ratio decreases with increasing donor ability of the x bpy ligand. DFT(D) calculations predict more favorable activation barriers for 1,2-insertion into the Pt−Ph bond to give branched products. The calculations indicate that 1,2-insertion of propene should be faster than 2,1-insertion for all Pt(II) catalysts studied, but they also indicate that cumene/n-propylbenzene selectivity is under Curtin−Hammett control.

This study deals with two striking phenomena: the complete protection against decomposition of hypothetically monocoordinated AuI intermediates [AuL]Y (L = strongly coordinating ligand; Y– = poorly coordinating anion) by addition of small substoichiometric amounts (5 mol % relative to Au) of not strongly coordinating ligands (e.g., AsPh3) and the fact that, in contrast, strongly coordinating ligands cannot provide this substoichiometric protection. The two phenomena are explained considering that (i) the existence of real monocoordinated [AuL]Y is negligible in condensed phases and the kinetically efficient existing species are dicoordinated [AuL­(W)]­Y (W = any very weakly coordinating ligand existing in solution, including OH2, the solvent, or the Y– anion) and (ii) these [AuL­(W)]Y intermediates give rise to decomposition by a disproportionation mechanism, via polynuclear intermediates formed by associative oligomerization with release of some W ligands. It is also shown that very small concentrations of [AuL­(W)]Y are still catalytically efficient and can be stabilized by overstoichiometric adventitious water, so that full decomposition of the catalyst is hardly reached, although eventually the stabilized concentration can be kinetically inefficient for the catalysis. These results suggest that, in cases of gold catalysis requiring the use of a significant quantity of gold catalyst, the turnover numbers can be increased or the concentration of gold catalyst widely reduced, using substoichiometric protection properly tuned to the case.

The catalytic activity of the recently reported nitrogen acyclic carbene (NAC) complexes of gold(I) has been investigated and compared with the reported activity of other gold(I) and gold(III) complexes. The complexes studied, [AuCl{C(NEt 2 )(NHTol-p)}], [AuCl{C(NEt 2 )(NHXylyl)}], and [Au(NTf 2 ){C(NEt 2 )(NHXylyl)}], are very active in processes such as the rearrangement of homopropargylsulfoxides, the intramolecular hydroamination of N-allenyl carbamates, the intramolecular hydroalkoxylation of allenes, the hydroarylation of acetylenecarboxylic acid ester, and the benzylation of anisole. Although the NAC ligands have not been optimized for the reactions tested, the yields obtained are usually similar and sometimes better than those reported with other catalysts, showing that the presence of N-H bonds and the wider N-C-N angle in the NAC (as compared to the NHC) complexes are not detrimental for the catalysis. For the hydroarylation reaction (where two competing products can be formed), the NAC complexes allow favoring one over the other. For the benzylation of anisole the selectivity is complementary to that obtained using H[AuCl 4 ] as catalyst, and depending on the substrate, the NAC gold(III) complexes outperform the activity of H[AuCl 4 ]. On average, the reactivity found suggests that the basicity of NACs toward gold(I) is very similar to that of NHCs and higher than that of phosphines.

Neutral gold complexes with hydrogen-bond-supported heterocyclic carbene (HBHC) and nitrogen acyclic carbene (NAC) ligands have been synthesized by the reactions of isocyanogold derivatives [AuCl(CNR)] with amines. Cationic [Au(carbene)(AsPh 3 )][SbF 6 ] complexes have also been prepared. The catalytic activity of both types of complex (for the former, AgSbF 6 is used to extract the halide ligand) in the skeletal rearrangement and methoxycyclization of enynes has been studied. The cationic complexes with AsPh 3 are[a]