Chiral Self‐Recognition between Stereogenic Tetrapalladium Units Affording Pd₈ Chains Supported by Homochiral Tetraphosphines

Abstract

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.

Alloyed Tetranuclear Metal Chains of Pd4−nPtn (n=0–3) Scaffolded by a New Linear Tetraphosphine Containing a PNP Bridge

“…The Pt 3 and Pt 2 Pd trinuclear chains with two dpmp ligands, [Pt 2 M(μ‐dpmp) 2 (RNC) 2 ] 2+ (M=Pt, Pd) were reduced to be coupled into the hydride bridged hexanuclear complexes, [Pt 2 M 2 Pt 2 (μ‐H)(μ‐dpmp) 2 (RNC) 2 ] 3+ , which were oxidized by 2 e − to afford the Pt 2 M 2 Pt 2 chains of [Pt 2 M 2 Pt 2 (μ‐dpmp) 2 (RNC) 2 ] 4+ . The tetraphosphines, meso and rac ‐dpmppm have recently proven to stabilize low‐valent octapalladium chains, [Pd 8 (μ‐ meso‐ or rac ‐dpmppm) 4 L 2 ] 4+ (L=none, acetonitrile, N , N ‐dimethylformamide, isocyanides) . Variable temperature NMR studies demonstrated that at higher temperature ( T >100 °C) the Pd 8 chain dissociated into two Pd 4 fragments of [Pd 4 (μ‐ meso‐ or rac ‐dpmppm) 2 L 2 ] 2+ and they were thermodynamically self‐aligned to restore the Pd 8 chain at lower temperature ( T <60 °C).…”

Dinuclear Copper Complexes Triply Bridged by a Tetraphosphane, rac‐Ph2PCH2P(Ph)CH2P(Ph)CH2PPh2

“…Multinuclear transition‐metal complexes have extensively been studied to explore new aspects of functional materials because a variety of synergistic effects in multimetallic centers are expected to play key roles in developing catalytic systems, electronic, optical, and magnetic devices, and biomimetic functional molecules . To create desired multinuclear centers, design of multidentate metal supporting ligands is very important issue, and in this regard, we have prepared a methylene‐bridged linear tetraphosphane, meso ‐ and rac ‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), and demonstrated that it effectively stabilized versatile tetra‐, tri‐, and dinuclear homo and heterometallic systems as well as mononuclear centers (Scheme ) . First of all, meso ‐ and rac ‐dpmppm preferably supported linearly ordered tetranuclear metal centers in κ 1 ,κ 1 ,κ 1 ,κ 1 coordination mode (Scheme a, Scheme f), exemplified by the linear octapalladium rigid‐rods, [Pd 8 ( meso ‐ or rac ‐dpmppm) 4 L 2 ] 4+ (L = none, MeCN, N , N ‐dimethylformamide (dmf), and isocyanides),, which dissociate at higher temperature T > 100 °C into two tetrapalladium units of {Pd 4 ( meso ‐ or rac ‐dpmppm) 2 } 2+ and interestingly they are self‐aligned at lower temperature T < 60 °C to restore the original rods through asymmetric recognition between the tetrapalladium units .…”

“…To create desired multinuclear centers, design of multidentate metal supporting ligands is very important issue, and in this regard, we have prepared a methylene‐bridged linear tetraphosphane, meso ‐ and rac ‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), and demonstrated that it effectively stabilized versatile tetra‐, tri‐, and dinuclear homo and heterometallic systems as well as mononuclear centers (Scheme ) . First of all, meso ‐ and rac ‐dpmppm preferably supported linearly ordered tetranuclear metal centers in κ 1 ,κ 1 ,κ 1 ,κ 1 coordination mode (Scheme a, Scheme f), exemplified by the linear octapalladium rigid‐rods, [Pd 8 ( meso ‐ or rac ‐dpmppm) 4 L 2 ] 4+ (L = none, MeCN, N , N ‐dimethylformamide (dmf), and isocyanides),, which dissociate at higher temperature T > 100 °C into two tetrapalladium units of {Pd 4 ( meso ‐ or rac ‐dpmppm) 2 } 2+ and interestingly they are self‐aligned at lower temperature T < 60 °C to restore the original rods through asymmetric recognition between the tetrapalladium units . Two meso ‐ or rac ‐dpmppm ligands also assembled four Au I ions in syn ‐ and anti ‐arrangements with respect to the Au I 4 strings to form bent, linear, and zigzag Au 4 chains, which are strongly luminous from triplet states of multinuclear Au I centers and were sensitively quenched by capturing Cl – ions into their bent pockets , .…”

“…In contrast to the versatile coordination behaviors of meso ‐dpmppm ligand, that of rac ‐dpmppm has been restricted only to a dinuclear κ 2 ,κ 2 bridging structure besides linear κ 1 ,κ 1 ,κ 1 ,κ 1 M 4 ‐bridge (Scheme f, Scheme g) , . Reaction of a 1:1 mixture of meso ‐ and rac ‐dpmppm with [PdCl 2 (cod)] in CH 2 Cl 2 afforded [Pd 2 Cl 4 ( rac ‐dpmppm)] quantitatively, where a rac ‐dpmppm ligand triply bridges two Pd II Cl 2 units through a pair of inner and outer phosphorus atoms in κ 2 ,κ 2 fashion, resulting in a bridged bicyclo[3,3,1] dimetallanonane structure with two fused six‐membered chelate rings (Scheme g), that can be called “ Z ‐form” bridging structure from its shape .…”

Linear Triplatinum Tetrahydride Complex Supported by Triphosphine Ligands, [Pt3(µ‐H)2(H)2(µ‐dpmp)2](BF4)2 {dpmp = bis(diphenylphosphinomethyl)phenylphosphine}

“…In the course of developing low‐valent “extended metal atom chains (EMACs)”, we have studied transition‐metal complexes supported by linear tri‐ and tetraphosphine ligands, bis(diphenylphosphinomethyl)phenylphosphine (dpmp) and meso ‐ and rac ‐bis[(diphenylphosphinomethyl)phenylphosphanyl]methane (dpmppm), which are intended to be utilized as linearly incremental metal building blocks . During our studies, linear trinuclear complexes, [Pt 2 M(µ‐dpmp) 2 (XylNC) 2 ](PF 6 ) 2 {M = Pt ( 1a ), Pd ( 1b ); Xyl = 2,6‐xylyl}, were synthesized (Scheme ) and have proven to be good building blocks for further extended metal strings .…”