[N,N-Bis(diphenylphosphino)isopropylamine]dibromidonickel(II)

The title compound, [NiBr2(C27H27NP2)], was synthesized by the reaction of NiBr2(dme) (dme is 1,2-dimethoxyethane) with N,N-bis(diphenylphosphino)isopropylamine in methanol/tetrahydrofuran. The nickel(II) center is coordinated by two P atoms of the chelating PNP ligand, Ph2PN(iPr)PPh2, and two bromide ions in a distorted square-planar geometry.


Related literature
This work was supported by the Leibniz-Institut fü r Katalyse e. V. an der Universitä t Rostock.
[N,N-Bis(diphenylphosphino)isopropylamine]dibromidonickel(II) M. Hapke, A. Wöhl, S. Peitz, B. H. Müller, A. Spannenberg and U. Rosenthal Comment Ligands containing the "PNP" moiety as the structural motif of the coordination unit have been used for different purposes in coordination chemistry. During the recent period, they were used with different metals including nickel for investigations into oligomerizations, polymerizations (Cooley et al., 2001) or copolymerizations (Majoumo-Mbe et al., 2005) with ethene or other alkenes (Sun et al., 2006). The Ni(PNP) core was also used for investigations into the reactivity behaviour of the nickel-coordinated HN(PPH 2 ) 2 ligand (Sushev et al., 2005). During these studies allylation of the N-H yielded a comparable nickel complex to the one that is described here. Dinuclear Ni(PNP)-complexes with arene-bridged PNP units have been prepared that have two independent and structurally identical Ni(PNP) moities (Majoumo-Mbe et al., 2005).
We became interested in nickel complexes during our studies on the selective oligomerization of ethene via transition metal-catalyzed tri-or tetramerization, yielding 1-hexene or 1-octene (Wöhl et al., 2009). Our initial experimental work was focusing on a chromium-based catalyst system (CrCl 3 (THF) 3 /Ph 2 PN(iPr)PPh 2 /MAO) and we recently became interested in the kinetic behaviour of this catalyst system, to gain a better understanding of the underlying catalytic mechanism in dependence from different metal/ligand ratios. However, for reasons of comparison we wanted to examine the corresponding nickel complex containing the same simple isopropyl-substituted PNP ligand. We deployed a simple preparation procedure, that is described here, to obtain the complex in high yields for our screening experiments.

Experimental
NiBr 2 (1,2-dimethoxyethane) (334 mg, 1.08 mmol) was dissolved in dry methanol and heated to 333 K. N,Nbis(diphenylphosphino)isopropylamine (462 mg, 1.08 mmol) was dissolved in dry THF and the solution was cannulated into the nickel complex solution under argon. The red solution obtained was stirred for an hour at 333 K and after cooling, the red solid obtained was collected on a glas frit and washed twice with methanol and three times with water and finally with ether. The red solid was dried in high vacuo to yield 645 mg of pure red complex. The identity of the product was proven by 1 H, 13 C and 31 P NMR (solvent: CD 2 Cl 2 ). Single crystals suitable for X-ray analysis were grown from a chloroform-diethyl ether solution (2:1).
supplementary materials sup-2 Refinement All H atoms were placed in idealized positions with d(C-H) = 0.98 (CH 3 ) and 0.95-1.00 Å (CH) and refined using a riding model with U iso (H) fixed at 1.5 U eq (C) for CH 3 and 1.2 U eq (C) for CH. Fig. 1. The molecular structure of the title compound showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.