Bis{2-[(diisopropylphosphanyl)amino]pyridine-κ2 N 1,P}copper(I) hexafluoridophosphate

The crystal structure of the title compound, [Cu(C11H19N2P)2]PF6, is composed of discrete [Cu(PN-iPr)2]+ cations [PN-iPr is 2-(diisopropylphosphanylamino)pyridine] and PF6 − anions. The Cu(I) atom is bis-chelated by two independent PN-iPr ligands. It has a distorted tetrahedral coordination by two P atoms [Cu—P = 2.2277 (4) and 2.2257 (4) Å] and two pyridine N atoms [Cu—N = 2.0763 (11) and 2.0845 (12) Å]. Bond angles about Cu vary from 85.11 (3) (P—Cu—N) to 130.37 (2)° (P—Cu—P). In the crystal, N—H⋯F hydrogen bonds link the Cu complexes and the PF6 − anions into continuous chains, which show a cross-bedded spatial arrangement. In addition, several weaker C—H⋯F interactions contribute to the coherence of the structure.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: ZS2038).  (PN-ligands) in which 2-pyridyl and phosphane moieties are linked by an amino group as spacer are of interest in organometallic chemistry because they contain both hard (nitrogen) and soft (phosphorus) donor atoms at P-N distances of about 3 Å, very suitable for the chelation of transition metals. Moreover, they are readily accessible in a modular fashion via the ease of phosphane-nitrogen bond-forming reactions (e.g. Benito-Garagorri et al., 2006). Some transition metal complexes of these ligands, mainly with diphenylphosphane moieties, are catalytically active and have been applied for carbonylation of olefins and other transformations (Aguirre et al., 2007;Benito-Garagorri, Wiedermann et al., 2007). In continuation of earlier work on Ni(II), Pd(II), and Mo(0/II)-complexes of such ligands Standfest-Hauser et al., 2009) we recently focused on Cu(I) complexes and report here the synthesis and crystal structure of the title compound [Cu(PN-iPr) 2 ]PF 6 . A view of the asymmetric unit is shown in Fig. 1. Copper is bis-chelated by two independent PN-iPr ligands and adopts a strongly distorted tetrahedral coordination by two P and two N atoms with well-balanced bond distances of Cu1-P1 = 2.2277 (4) Å, Cu1-P2 = 2.2257 (4) Å, Cu1-N1 = 2.0763 (11) Å, and Cu1-N3 = 2.0845 (12) Å. Bond angles about Cu vary from ca. 85° for the two bite angles P1-Cu1-N1 and P2-Cu1-N3 to 130.37 (2)° for P1-Cu1-P2. The twist angle between the planes P1-Cu1-P2 and N1-Cu-N3 is 60.50 (3)° and thus about 30° off from 90°, the value for an ideal undistorted coordination tetrahedron. The complex approaches a molecular non-crystallographic C 2 symmetry, which makes both PN-iPr ligands pseudo-equivalent; this includes also the isopropyl groups and their orientations (Fig. 1). A Cu(I)(PN) 2 complex closely related in ligand characteristics to that of the title compound was reported for bis(6-chloro-2-(diphenylphosphinoamino)benzothiazole)copper(I) hexafluoridophosphate (Hursthouse et al., 2003); it has Cu-P ≈ 2.26 Å, Cu-N ≈ 2.06 Å, and a twist angle P-Cu-P vs. N-Cu-N of 63.2°. Cu(I) complexes with separate non-chelating two P-and two N-ligands have generally more regular CuP 2 N 2 tetrahedra with twist angles P-Cu-P vs. N-Cu-N near 90°, e.g. bis(pyridine)-bis(triphenylphosphane)copper(I) tetrafluoridoborate (Healy, 2008).
A characteristic feature of PN-iPr ligands and their homologues is the acidity of the N-H bond (here N2-H2N and N4-H4N), which is a good hydrogen bond donor. In the title compound each NH group is hydrogen bonded to the F-atom of an adjacent PF 6 octahedron at N···F distances of ca. 3.1 Å (Table 1). These hydrogen bonds link the cation and anion complexes into infinite chains, which extend parallel to [110] at z ≈ 0.15 and parallel to [110] at z ≈ 0.65 resulting in a cross-bedded arangement (Fig. 2). Several weaker C-H···F interactions contribute to the coherence of the structure. The most significant two of them with H···F < 2.6 Å are included in Table 1, seven more have H···F distances in the range 2.60 to 2.70 Å.

Experimental
To a solution of [Cu(CH 3 CN) 4 ]PF 6 (100 mg, 0.27 mmol) in THF (10 ml for X-ray diffraction were obtained by evaporation crystallization from acetone.

Refinement
All H atoms were placed in calculated positions and thereafter treated as riding. A torsional parameter was refined for each methyl group. U iso (H) = 1.2U eq (C non-methyl ) and U iso (H) = 1.5U eq (C methyl ) were used. The title compound is racemic but crystallizes in a non-centrosymmetric polar lattice, space group Pn. The Flack test indicated that the investigated crystal is a merohedral (polar) twin. In the final refinement this was taken into account by the use of the instructions TWIN and BASF of program SHELXL97 (Sheldrick, 2008). According to this refinement the amounts of the two twin components are 0.590 (4) and 0.410 (4). Fig. 1. The asymmetric unit of (I) with displacement ellipsoids for the non-hydrogen atoms drawn at the 50% probability level. The red broken line shows one of the C-H···F interactions listed in Table 1.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq