Separating the Racemic and Meso Diastereomers of a Binucleating Tetraphosphine Ligand System through the Use of Nickel Chloride

Abstract

The reaction of a 1:1 mixture of rac- and meso-et,ph-P4 (et,ph-P4 = (Et(2)PCH(2)CH(2))(Ph)PCH(2)P(Ph)CH(2)CH(2)PEt(2)) with 2 equiv of NiCl(2).6H(2)O in EtOH produces soluble rac-Ni(2)Cl(4)(et,ph-P4) and precipitates meso-Ni(2)Cl(4)(et,ph-P4), allowing facile isolation of each bimetallic complex. Subsequent reaction with more than 250 equiv of NaCN in H(2)O/MeOH releases the et,ph-P4 ligand and [Ni(CN)(4)](2-). The rac,trans- and meso,trans-Ni(CN)(2)(eta(2.5)-et,ph-P4) form as intermediates in the cyanolysis of rac- and meso-Ni(2)Cl(4)(et,ph-P4). These have been characterized by X-ray crystallography. The unusual partial isomerization of the meso- to rac-et,ph-P4 ligand via the monometallic trans-Ni(CN)(2)(eta(2.5)-et,ph-P4) intermediate complex is discussed.

Unusual structural motif in a zwitterionic Fe(ii) complex of a tetradentate phosphine

“…[5][6][7] In a square pyramidal nickel complex Ni(CN) 2 (P 4 ) (P 4 = meso-Et 2 PCH 2 CH 2 P(Ph)(CH 2 )P(Ph)CH 2 CH 2 PEt 2 ) there are two strong P-Ni bonds in the equatorial plane, and a weak interaction between nickel and a third phosphorus located in the apical position. 3 These bonding patterns are in accord with the preferred square planar/pyramidal geometry of divalent group 10 metals. The preferred octahedral geometry in iron complexes, combined with the steric bulk of meso-DPPEPM appear to be better accommodated by the bonding pattern in 1.…”

“…Partial isomerization of meso-P 4 (n = 1, R = Et) to the rac form while coordinated to Ni(II) has also been documented. 3 Recently we prepared several mononuclear iron and ruthenium complexes of a closely related rac-P 4 (n = 1, R = Ph), 4 abbreviated hereafter as rac-DPPEPM. In these complexes the ligand is bound in either κ 3 or κ 4 mode, the latter resulting in cis-α geometry at the metal.…”

14 Iron, cobalt and nickel

“…These can be separated off and the ligand stripped off by treatment with excess KCN, though the rac,trans-[Ni(CN) 2 (η 2.5 -Et,Ph-P4)] and meso,trans-[Ni(CN) 2 (η 2.5 -Et,Ph-P4)] can also be identified. 78 The structure of a new polymorph of [NiCl 2 (dppe)], formed by reduction of a Ph 2 PCH᎐ ᎐ CHPPh 2 ligand, has been reported. 79 The use of a bulky chelating phosphine has assisted in the synthesis of nickel complexes with low co-ordination numbers, notably the three-co-ordinate amide [Ni(dtbpe)(NH(2,6-Pr…”

A Monometallic Rh(III) Tetraphosphine Complex: Reductive Activation of CH2Cl2 and Selective Meso to Racemic Tetraphosphine Ligand Isomerization

“…18 We have recently cleaned up this separation chemistry significantly through the use of NiCl 2 ‚6H 2 O. 29 Because only the racemic form of the ligand is useful in our bimetallic hydroformylation catalytic studies, 9 the possibility that one could use this isomerization chemistry to selectively convert mixed-et,ph-P4 to pure rac-et,ph-P4 via 3 is exciting.…”