1,3-Dipolar Cycloaddition of Nitrones to Gold(III)-Bound Isocyanides

Treatment
of gold­(III)-isocyanides [AuCl3(CNR1)] (R1 = Xyl 1, Cy 2, But 3) with an equimolar amount
of 5,5-dimethyl-1-pyrroline-N-oxide (4) in CH2Cl2 at −74 °C leads to
the generation of the heterocyclic aminocarbene species [AuCl3{C­(ONaCMe2CH2CH2CbH)NeR1}­(Na–Cb)­(Cb–Ne)] 8 (for R1 = But) or gold­(III) complexes cis-[AuCl2{Na(CMe2CH2CH2CbNeR1)­CdO}­(NaCb)­(Ne–Cd)] 9 and 10 (for R1 = Xyl and Cy) in
good isolated yields (75–87%). DFT calculations show that deprotonation
of the endocyclic CH group in the carbene ligand leads to spontaneous
N–O bond cleavage, and acidity of this group is a factor controlling
the different chemical behavior of 1–3 depending on the nature of substituent R1. The reaction
of equimolar amounts of the aldonitrone p-TolCHN+(Me)­O– (5) or the ketonitrones
Ph2CN+(R2)­O– (R2 = Ph 6, CH2Ph 7) with 1–3 in CD2Cl2 at −70 °C in air (or under N2) revealed
the formation of the carbene complexes [AuCl3{C­(ONMeCaH-p-Tol)NbR1}­(Ca–Nb)] (R1 = Cy 11, Xyl 12, But 13), [AuCl3{C­(ONPhCaPh2)NbR1}­(Ca–Nb)] (R1 = Cy 14, But 15), or [AuCl3{C­(ON­(CH2Ph)­CaPh2)NbR1}­(Ca–Nb)]
(R1 = Cy 16, Xyl 17), as studied
by 1H NMR. The reaction of 6 with 1 and of 7 with 3 did not furnish carbene
products. Compounds 8–10 were characterized
by ESI-MS, IR, 1D (1H, 13C­{H}) and 2D (1H,1H–COSY, 1H,13C-HSQC, 1H,13C-HMBC) NMR spectroscopic techniques, and,
only for 8, elemental analyses (C, H, N), while compounds 11–17 were characterized by 1D (1H, 13C­{H}) and 2D (1H,13C-HSQC)
NMR. Structures of compounds 8, 9, and 13 were additionally established by single-crystal X-ray diffraction.