Isomerism and dynamic behavior of bridging phosphaalkynes bound to a dicopper complex.

ABSTRACT: A dicopper complex featuring a symmetrically bridging nitrile ligand and supported by a binucleating naphthyridine-based ligand, [Cu2(?-? 1 :? 1 -MeCN)DPFN](NTf2)2, was treated with phosphaalkynes (RC[triple bond, length as m-dash]P, isoelectronic analogues of nitriles) to yield dicopper complexes that exhibit phosphaalkynes in rare ?-? 2:? 2 binding coordination modes. X-ray crystallography revealed that these unusual "tilted" structures exist in two isomeric forms (R "up" vs. R "sideways"), depending on the steric profile of the phosphaalkyne's alkyl group (R = Me, Ad, or t Bu). Only one isomer is observed in both solution and the solid state for R = Me (sideways) and t Bu (up). With intermediate steric bulk (R = Ad), the energy difference between the two geometries is small enough that both are observed in solution, and NMR spectroscopy and computations indicate that the solid-state structure corresponds to the minor isomer observed in solution. Meanwhile, treatment of [Cu2(?-? 1:? 1-MeCN)DPFN](NTf2)2 with 2-butyne affords [Cu2(?-? 2:? 2-(MeC[triple bond, length as m-dash]CMe))DPFN](NTf2)2: its similar ligand geometry demonstrates that the tilted ?-? 2:? 2 binding mode is not limited to phosphaalkynes but reflects a more general trend, which can be rationalized via an NBO analysis showing maximization of ?-backbonding.

SUBMITTER: Nicolay A 

PROVIDER: S-EPMC7069238 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature