Phosphinines versus mesoionic carbenes: a comparison of structurally related ligands in Au(i)-catalysis

Abstract

Gold(i) complexes based on a 2,4,6-triarylphosphinine and a mesoionic carbene derivative have been prepared and characterized crystallographically. Although structurally related, both heterocycles differ significantly in their donor/acceptor properties. These opposed electronic characteristics have been exploited in Au(i)-catalyzed cycloisomerization reactions. For the conversion of the standard substrate dimethyl 2-(3-methylbut-2-enyl)-2-(prop-2-ynyl)malonate the results obtained for both Au-catalysts were found to be very similar and comparable to the ones reported in the literature for other carbene- or phosphorus(iii)-based Au(i)-complexes. In contrast, a clear difference between the catalytic systems was found for the cycloisomerization of the more challenging substrate N-2-propyn-1-ylbenzamide. A combination of the phosphinine-based complex and [AgSbF] or [Cu(OTf)] leads to a catalytic species, which is more active than the mesoionic carbene-based coordination compound. We attribute these differences to the stronger π-accepting ability of phosphinines in comparison to mesoionic carbenes. The here presented results show for the first time that phosphinines can be used efficiently as π-accepting ligands in Au(i)-catalyzed cycloisomerization reactions.

Structural, Electrochemical, and Photochemical Properties of Mono‐ and Digold(I) Complexes Containing Mesoionic Carbenes

“…The mono‐ and bitriazolium salts [ L1 ]I and [ L2 ](BF 4 ) 2 , which are the precursors to the MIC ligands, were synthesized according to reported synthetic routes. The chlorido complex 1 , which has been reported elsewhere, was synthesized through the transmetallation route using [ L1 ]I, Ag 2 O, and [AuCl(SMe 2 )]. Complex 1 was resynthesized for the present work for the investigation of its electrochemical and photochemical properties .…”

“…The chlorido complex 1 , which has been reported elsewhere, was synthesized through the transmetallation route using [ L1 ]I, Ag 2 O, and [AuCl(SMe 2 )]. Complex 1 was resynthesized for the present work for the investigation of its electrochemical and photochemical properties . Reaction of complex 1 with AgBF 4 led to the formation of the cationic mononuclear gold(I) complex [ 2 ]BF 4 , which contains two monodentate MIC ligands (Scheme and Experimental Section).…”

“…These data show the downfield shift of the MIC‐ C signal on replacing a chlorido ligand with a second MIC ligand. Single‐crystal diffraction data for complex 1 were reported elsewhere and we will briefly discuss the bond lengths and bond angles here for comparison purposes . Complex [ 2 ]BF 4 was crystallized by condensation of hexane into a dichloromethane solution at ambient temperatures, and [ 3 ](BF 4 ) 2 by slow condensation of diethyl ether into an acetonitrile solution at 8 °C.…”

“…Complex 1 : (1) Ag 2 O, CH 2 Cl 2 , room temperature; (2) AuCl(SMe 2 ), CH 2 Cl 2 , room temperature; complex [ 2 ]BF 4 : (3) AgBF 4 , CH 2 Cl 2 , room temperature; (4) Ag 2 O, CH 3 CN, 50 °C; complex [ 3 ](BF 4 ) 2 : (5) AuCl(SMe 2 ), CH 3 CN, room temperature. Complex 1 was previously reported and was resynthesized here for the investigation of its electrochemical and photochemical properties …”

(CF3)3Au as a Highly Acidic Organogold(III) Fragment

“…However,t he complexes formed with the heavier-elementh omologues PC 5 H 5 (D e = 152 kJ mol À1 )a nd tBuNSi (D e = 139 kJ mol À1 )a re less stable. 222 pm forR = Ph), [61] ClAu(PC 5 H 2 R-2-Ph 2 -4,6) (av 220.8(1) pm;R = C 6 H 3 (OMe) 2 -3,4), [62] ClAu{PC 5 HR-2-Me-3-Ph 2 -4,6} (220.40(7) pm;R = C 6 H 3 Me 2 -2,3), [63] ClAu{PC 5 H 3 (SiMe 3 ) 2 -2,6} (221.1(2) pm), and [Au{PC 5 H 3 (SiMe 2 R) 2 -2,6} 2 ][GaCl 4 ]( av 228.2(4) pm for R = Me;a v2 26.3(2) pm for R = CCPh). In the optimized geometry of the phosphabenzene complex (CF 3 ) 3 Au(PC 5 H 5 )( Figure S8 in the Supporting Information), little modification is observed in the heteroaromatic ring with respect to the free ligand, [57] in keeping with other structurally characterized metal complexes.…”