SCHEDULED MAINTENANCE
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(μ-η1:η1-MeCN)DPFN](NTf2)2, was treated with phosphaalkynes (RC![[triple bond, length as m-dash]](https://www.rsc.org/images/entities/char_e002.gif)
P, isoelectronic analogues of nitriles) to yield dicopper complexes that exhibit phosphaalkynes in rare μ-η2:η2 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 tBu). Only one isomer is observed in both solution and the solid state for R = Me (sideways) and tBu (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(μ-η1:η1-MeCN)DPFN](NTf2)2 with 2-butyne affords [Cu2(μ-η2:η2-(MeCCMe))DPFN](NTf2)2: its similar ligand geometry demonstrates that the tilted μ-η2:η2 binding mode is not limited to phosphaalkynes but reflects a more general trend, which can be rationalized via an NBO analysis showing maximization of π-backbonding.
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