End-On and Side-On π-Acid Ligand Adducts of Gold(I): Carbonyl, Cyanide, Isocyanide, and Cyclooctyne Gold(I) Complexes Supported by N-Heterocyclic Carbenes and Phosphines

Abstract

N-heterocyclic carbene ligand SIDipp (SIDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) and trimesitylphosphine ligand have been used in the synthesis of gold(I) cyanide, t-butylisocyanide, and cyclooctyne complexes (SIDipp)Au(CN) (3), (Mes(3)P)Au(CN) (4), [(Mes(3)P)(2)Au][Au(CN)(2)] (5), [(SIDipp)Au(CN(t)Bu)][SbF(6)] ([6][SbF(6)]), [(SIDipp)Au(cyclooctyne)][SbF(6)] ([8][SbF(6)]), and [(Mes(3)P)Au(cyclooctyne)][SbF(6)] ([9][SbF(6)]). A detailed computational study has been carried out on these and the related gold(I) carbonyl adducts [(SIDipp)Au(CO)][SbF(6)] ([1][SbF(6)]), [(Mes(3)P)Au(CO)][SbF(6)] ([2][SbF(6)]), and [(Mes(3)P)Au(CN(t)Bu)](+) ([7](+)). X-ray crystal structures of 3, 5, [6][SbF(6)], [8][SbF(6)], and [9][SbF(6)] revealed that they feature linear gold sites. Experimental and computational data show that the changes in π-acid ligand on (SIDipp)Au(+) from CO, CN(-), CN(t)Bu, cyclooctyne as in [1](+), 3, [6](+), and [8](+) did not lead to large changes in the Au-C(carbene) bond distances. A similar phenomenon was also observed in Au-P distance in complexes [2](+), 4, [7](+), and [9](+) bearing trimesitylphosphine. Computational data show that the Au-L bonds of "naked" [Au-L](+) or SIDipp and Mes(3)P supported [Au-L](+) (L = CO, CN(-), CN(t)Bu to cyclooctyne) have higher electrostatic character than covalent character. The Au←L σ-donation and Au→L π-back-donation contribute to the orbital term with the former being the dominant component, but the latter is not negligible. In the Au-CO adducts [1](+)and [2](+), the cationic gold center causes the polarization of the C-O σ and π orbitals toward the carbon end making the coefficients at the two atoms more equal which is mainly responsible for the large blue shift in the CO stretching frequency. The SIDipp and Mes(3)P supported gold(I) complexes of cyanide and isocyanide also exhibit a significant blue shift in υ(CN) compared to that of the free ligands. Calculated results for Au(CO)Cl and Au(CF(3))CO suggest that the experimentally observed blue shift in ν(CO) of these compounds may at least partly be caused by intermolecular forces.

Gold‐Mediated Isomerization of ­Cyclooctyne to Ring Fused Olefinic Bicycles

“…The 6 ] in CD 2 Cl 2 at room temperature showed a carbon resonance of the gold bound alkyne moiety at δ 97.7 ppm, which is shifted downfield in comparison to the corresponding signal of the free cyclooctyne (δ = 94.9 ppm) and is comparable to the signal observed for related [(SIPr)Au(cyclooctyne)][SbF 6 ] (δ = 97.4 ppm). [25] The carbene carbon signal of 4[SbF 6 ] was displayed at δ = 182.5 ppm, which is upfield of the corresponding resonance for [(SIPr)Au(cyclooctyne)][SbF 6 ] (δ = 202.5 ppm). This is expected as they have dif-ferent (i.e., unsaturated and saturated) carbene supporting ligands, IPr and SIPr.…”

“…[66] and was dried using 4 Å molecular sieves (see below as well). (IPr)AuCl, [54] (IPr)AuCl 3 , [67] [(SIPr)Au(cyclooctyne)][SbF 6 ], [25] and AgNTf 2 , [68] bicyclo [3.3.0]oct-1(5)-ene, [56,57,69] and cis-bicyclo [3.3.0]oct-2-ene [58] were prepared according to reported procedures. AgSbF 6 was purchased from commercial sources and used as received.…”

“…N-heterocyclic carbene ligands are particularly useful in this regard. [17,19,53] The cyclooctyne-gold(I) adduct [(SIPr)Au(cyclooctyne)][SbF 6 ] {SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene} [25] reported by us represent one such example. …”

A hexanuclear gold carbonyl cluster

“…4,5 Well-established gold carbonyls for appropriate comparison are therefore valuable species, although they still remain scarce. 6 Aside from the following dinuclear derivatives: Cl 3 Au(μ-Cl)AuCO, 7 ( t Bu F O) 3 Al(μ-Cl)AuCO and [Cl(AuCO) 2 ][Al(O t Bu F ) 4 ], 8 the handful of currently isolated gold carbonyls are all mononuclear, either neutral XAuCO (X = Cl, 9 CF 3 , 10 OSO 2 F, 11 HB(pz*) 3 12 ) or cationic LAuCO + species (L = CO, 11,13 SIDipp, 14,15 IDipp, 15 PMes 3 , 14,16 DPCb 17 ). Additionally, some oligomers of unknown nuclearity have been suggested to form in frozen concentrated solutions of ClAuCO in CH 2 Cl 2 .…”

Au(I)-complexes ligated by hybrid P,S,N-ligands as the efficient catalysts for hydration of phenylacetylene

“…The Au(I)-complexes typically possessing the linear configuration at Au(I)-centered vectors are of great interest to be used to catalyze hydration of alkynes following Markovnikov's rule for the generation of the corresponding ketones [3][4][5][6][7][8][9][10], because of the replacement of the uses of highly toxic mercury salts and strong Brönsted or Lewis acids [10][11][12][13][14][15].…”