Tungsten coordination chemistry of 1,4-bisdiphenylphosphinobutadiyne - Synthesis of coordination macrocycles and factors controlling diyne cycloaddition

The 1:1 reaction of [W(CO)(4)(2-picoline)(2)] (1) with Ph2PC C-C CPPh2 ( 2) led to {[cis-W(CO)(4)](2)(mu-Ph2PC4PPh2)(2)} (3), in which two bis(diphenylphosphino)butadiyne ligands bridge two tetracarbonyltungsten centres. Reaction of 1 with excess 2 led to [cis-W(CO)(4)(Ph2PC4PPh2-kappa(1)-P)(2)] (4), in which two dangling bis-phosphines are coordinated to one metal centre, and reaction of 2 with two equivalents of 1 led to {[W(2-picoline)(CO)(4)](2)(mu-Ph2PC4PPh2)} (5), in which one ligand bridges two tungsten centres. Combination of 4 and 5 led to the trimeric complex {[cis-W(CO)(4)](3)(mu-Ph2PC4PPh2)(3)} (6), in which three tetracarbonyltungsten centres are bridged by three bisdiphenylphosphinobutadiyne ligands. The dimeric complex 3 showed no reactivity towards alkyne cycloaddition; however, the trimeric complex 6 undergoes cycloaddition at moderate temperatures to form {[W(CO)(4)](3)[mu-3-C-12(Ph2P)(6)]} (8), which contains a cyclododecatrienetriyene ring. Comparison of structural data for the template complexes 3 and 6, as well that of previously described platinum template complexes, suggests that alkyne cycloaddition reactions are favoured by proximity of the alkynyl carbons a to phosphorus in adjacent ligands.