Chiral Self-Recognition between Stereogenic Tetrapalladium Units Affording Pd Chains Supported by Homochiral Tetraphosphines.

By using a chiral tetraphosphine, rac-bis[(diphenylphosphinomethyl)phenylphosphino]methane (rac-dpmppm), linear octapalladium chains were synthesized as discrete molecules of [Pd (μ-rac-dpmppm) L ](BF ) (L=CH CN, dmf, XylNC), [Pd (μ-rac-dpmppm) ](BF ) , and [Pd (μ-rac-dpmppm) (Cl) ](BF ) , which are stable in the solution states and characterized by spectroscopic and crystallographic methods to reveal the octapalladium chains supported by homochiral four tetraphosphines. Variable-temperature NMR studies for a 1:1 mixture of [Pd (μ-rac-dpmppm) (dmf) ](BF ) and [Pd (μ-meso-dpmppm) (dmf) ]-(BF ) in [D ]DMF revealed that the Pd chains were dissociated at higher temperature (T≈140 °C) into the Pd units of {Pd (μ-rac-dpmppm) } and {Pd (μ-meso-dpmppm) } , and they were thermodynamically self-aligned to restore the Pd chains at lower temperature (T<60 °C), through perfect chiral self-recognition between the stereogenic tetrapalladium units.