Toward Permetalated Alkyne/Azide 3 + 2 or “Click” Cycloadducts
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The Cu(I)-catalyzed reaction of the platinum butadiynyl complex trans-(C6F5)(p-tol3P)2Pt(CC)2H and rhenium cyclopentadienylazide complex (η5-C5H4N3)Re(CO)3 yields the 1,2,3-triazole trans-(C6F5)(p-tol3P)2PtCCCCHN((η5-C5H4)Re(CO)3)NN (54%), which upon treatment with Re(CO)5OTf or Re(CO)5Br affords Re(CO)5+TfO– or cis-Re(CO)4Br adducts derived from attack at N(3) (84–98%). The crystal structures of solvates of these three complexes are compared, but attempts to metalate the CH groups were unsuccessful. However, the reaction of monometallic trans-(C6F5)(p-tol3P)2PtCCCCHN(CH2C6H5)NN and MeI gives an N(3)-methyl triazolium salt (81%), which upon addition of Ag2O and [RhCl(cod)]2 yields the N-heterocyclic carbene complex trans-(C6F5)(p-tol3P)2PtCCC...C(RhCl(cod))...N(CH2C6H5)...N...N(Me). Further experiments and analyses suggest that CH derivatization is possible only when the 1H NMR chemical shift is downfield of ca. δ 7.9 ppm. Electropositive metal fragments generally effect upfield shifts, meaning that insulating spacers, electronegative ligands, and/or new chemical methodologies will be required to construct tetrametallic arrays via click chemistry.
