Organic Azide and Auxiliary-Ligand-Free Complexes of Coinage Metals Supported by N-Heterocyclic Carbenes.

Organic azide complexes of copper(I) and silver(I), [(SIPr)CuN(1-Ad)NN][SbF6], [(SIPr)CuN(2-Ad)NN][SbF6], [(SIPr)CuN(Cy)NN][SbF6], and [(SIPr)AgN(1-Ad)NN][SbF6] have been synthesized by using Ag[SbF6] and the corresponding organic azides with (SIPr)CuBr and (SIPr)AgCl (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene). The copper and silver organic azide complexes were characterized by various spectroscopic techniques and X-ray crystallography. Group trends of isoleptic Cu(I), Ag(I), and Au(I) organic azide complexes are presented on the basis of experimental data and a detailed computational study. The νasym(N3) values of the metal-bound 1-AdNNN in [(SIPr)MN(1-Ad)NN]+ follow the order Ag < Cu < Au. DFT calculations show that gold(I) forms the strongest bond with 1-AdNNN in this series, while silver has the weakest interaction. Furthermore, auxiliary ligand free coinage metal N-heterocyclic carbene complexes, [(SIPr)M][SbF6], have been synthesized via metathesis reactions of (SIPr)MCl (M = Cu, Ag, Au) with Ag[SbF6]. X-ray crystal structures of dinuclear [(SIPr)Ag]2[SbF6]2 and [(SIPr)Au]2[SbF6]2 are also reported. They show close metallophilic contacts. [(SIPr)Au]2[SbF6]2 reacts with OEt2, SMe2, and CNtBu to afford [(SIPr)Au(OEt2)][SbF6], [(SIPr)Au(SMe2)][SbF6], and [(SIPr)Au(CNtBu)][SbF6] adducts, respectively.

Acetylene and terminal alkyne complexes of copper(i) supported by fluorinated pyrazolates: syntheses, structures, and transformations.

Trinuclear {µ-[3,5-(CF3)2Pz]Cu}3 reacts with acetylene to produce the 2 : 1 copper(i) acetylene complex, Cu4(µ-[3,5-(CF3)2Pz])4(µ-HC[triple bond, length as m-dash]CH)2. Related Cu4(µ-[4-Br-3,5-(CF3)2Pz])4(µ-HC[triple bond, length as m-dash]CH)2 and Cu4(µ-[4-Cl-3,5-(CF3)2Pz])4(µ-HC[triple bond, length as m-dash]CH)2 have also been isolated using the corresponding copper(i) pyrazolate and acetylene. The 1 : 1 adducts Cu2(µ-[3,5-(CF3)2Pz])2(HC[triple bond, length as m-dash]CH)2 and Cu2(µ-[4-Br-3,5-(CF3)2Pz])2(HC[triple bond, length as m-dash]CH)2 are significantly less stable to the acetylene loss and can be observed in solution at low temperatures under excess acetylene. The X-ray crystal structures of 2 : 1 and 1 : 1 complexes, Cu4(µ-[3,5-(CF3)2Pz])4(µ-HC[triple bond, length as m-dash]CH)2 and Cu2(µ-[4-Br-3,5-(CF3)2Pz])2(HC[triple bond, length as m-dash]CH)2 are reported. Raman data show a reduction in [small nu, Greek, macron]C[triple bond, length as m-dash]C stretching frequency by about ∼340 and ∼163 cm-1 in the 2 : 1 and 1 : 1 Cu(i)/acetylene complexes, respectively, from that of the free acetylene. Copper(i) pyrazolate complexes of the terminal alkynes, phenylacetylene, 1,8-nonadiyne, and 1,7-octadiyne are also reported. They form adducts involving one copper atom on each alkyne moiety. The {µ-[3,5-(CF3)2Pz]Cu}3 is also a very versatile and competent catalyst for alkyne transformations as evident from its ability to catalyze the alkyne C(sp)-H bond carboxylation chemistry with CO2, azide-alkyne cycloadditions leading to 1,2,3-triazoles including the use of acetylene itself as a substrate, and thiol addition to phenylacetylene affording vinyl sulfides.

Heterobimetallic Complexes Featuring Fe(CO)5 as a Ligand on Gold.

Iron(0) pentacarbonyl complexes of gold(I), [Mes3 PAu-Fe(CO)5 ][SbF6 ] (1) and [(IPr*)Au-Fe(CO)5 ][SbF6 ] (2) (Mes=2,4,6-trimethylphenyl; IPr*=1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) have been synthesized using Mes3 PAuCl and (IPr*)AuCl as the gold(I) precursor, AgSbF6 halide ion abstractor, and the Lewis base Fe(CO)5 . The Au-Fe bond lengths of these metal-only Lewis pair complexes are significantly shorter than the sum of the experimentally derived covalent radii of Au and Fe. The v̄(CO) bands of the molecules show a notable blueshift relative to those observed for free Fe(CO)5 , indicating a substantial reduction in Fe→CO backbonding upon its coordination to gold(I) with either Mes3 P or IPr* supporting ligands (L). The analysis of the electronic structure with quantum chemical method suggests that the Au-Fe bond consists mainly of [LAu]+ ←Fe(CO)5 σ-donation and weaker [LAu]+ →Fe(CO)5 π-backdonation. The donor strength of Fe(CO)5 is similar to that of CO.

Dinuclear zinc(ii) pyrazolates with different degrees of ring-fluorination and their use in zinc(ii) mediated olefin aziridination.

Zinc complexes [{(3,5-(CF3)2Pz)ZnEt}2(µ-THF)] (1), [{(3-(CF3),5-(t-Bu)Pz)ZnEt}2(µ-THF)] (2), and [{(3,5-(i-Pr)2Pz)ZnEt}2(µ-THF)] (3) adopt dinuclear structures with zinc sites bridged by a THF molecule and two pyrazolate ligands. The zinc complex 1 that features the weakest donating pyrazolate is the best catalyst among the three for the aziridination of styrene and cis-cyclooctene with PhI[double bond, length as m-dash]NTs.