Tetrazolyl and tetrazolylidene complexes of gold: a synthetic and structural study

Abstract

Lithiation of 1-benzyl-1H-tetrazole followed by transmetallation with [AuCl(PPh₃)], [Au(C₆F₅)(tht)] or [AuCl(tht)] (tht = tetrahydrothiophene) and subsequent alkylation afforded cationic 1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene(triphenylphosphine)gold(I), 1, neutral 1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene(pentafluorophenyl)gold(I), 2, and a cationic biscarbene complex, bis(1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene)gold(I), 3. The first complex underwent a homoleptic rearrangement in solution to form 3. Reaction of [Au(N₃)PPh₃] with the three isocyanides (CH₃)₂C₆H₃NC, ^tBuNC and CyNC, respectively, yielded the corresponding neutral tetrazolyl(phosphine) complexes of gold, [1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(I), 4, [1-(tert-butyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(I), 6, and [1-(cyclohexyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(I), 7. Alkylation of 4 with methyl triflate on N⁴ allowed isolation of the crystalline carbene complex 1-(2,6-dimethylphenyl)-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene)(triphenylphosphine)gold(I), 5. Complex 7 was not isolable in pure form but converts by isocyanide substitution of triphenylphosphine into [1-cyclohexylisocyanide][1-(cyclohexyl)-1H-tetrazol-5-yl]gold(I), 8. From a product mixture of 7 and 8 the transformed molecules [(cyclohexylamino)(ethoxy)carbene](1-cyclohexyl-1H-tetrazol-5-yl)gold(I), 9, and [bis(cyclohexylamino)carbene](1-cyclohexyltetrazol-5-yl)gold(I), 10, co-crystallised spontaneously after a long time at −20 °C.