Crystal structure of {(but-3-en-1-yl)bis[(pyridin-2-yl)methyl]amine-κ3 N,N′,N′′}dichloridocopper(II) diethyl ether hemisolvate

The hemi-diethyl etherate of the square pyramidal copper complex, 1-butene-bis(pyridin-2-ylmethyl)amine copper(II) chloride is reported. The basal plane consists of the three nitrogen atoms from the ligand and one chlorine. The second chlorine occupies the apical position of the square pyramid.


Chemical context
Transition-metal-catalyzed Atom Transfer Radical Addition (ATRA) reactions of haloalkanes and -halocarbonyls toolefins have emerged as some of the most atom economical methods for simultaneously forming C-C and C-X bonds, leading to the production of more attractive molecules with well-defined compositions, architectures, and functionalities (Pintauer & Matyjaszewski, 2005). Copper(I) complexes with tridentate and tetradentate nitrogen-based ligands are currently some of the most active multidentate ligand structures developed for use in ATRA reactions (Matyjaszewski et al., 2001). In view of the importance of these types of complexes, we report the synthesis and structural characterization of the title compound {(but-3-en-1-yl)bis[(pyridin-2-yl)methyl]amine-3 N,N 0 ,N 00 } dichloridocopper(II) diethyl ether hemisolvate, (I).

Structural commentary
The title complex, (I) (Fig. 1), adopts a typical-for-this-class of compounds (vide infra), slightly distorted square-pyramidal geometry, as shown in the bond angles about the Cu II atom. A ISSN 2056-9890 -5 analysis of the distortions about the Cu II atom yields a value of 0.01, close to an ideal value of zero for a perfect square-pyramidal geometry [Addison et al., 1984; -5 = ( À )/60 where and are the angles formed by atoms trans across the metal atom that do not include the apical atom]. In the complex, the Cu II atom lies 0.2761 (5) Å out of the mean basal plane formed by the three coordinating N atoms and atom Cl1, reflecting the slight distortion from a true square plane. The Cu-N bond lengths are all similar [1.9980 (11)-2.0700 (10) Å ] and the apical Cu-Cl2 distance is considerably longer [2.5134 (4) Å ] than that of Cu-Cl1 [2.2508 (4) Å ] in the basal plane. The diethyl ether molecule of crystallization is located in the unit cell with the O atom on the crystallographic twofold rotation axis at [ 1 2 , y, 3 4 ].

Supramolecular features
Despite an open coordination site on the Cu II atom, the complex does not dimerize through a chloride bridge, that is often observed in similar complexes (vide infra). There are weak electrostatic C-HÁ Á ÁCl interactions between pyridine rings and the basal chlorine of adjacent molecules (Table 1 and Fig. 2). Close contacts about the butenyl chain are typical van der Waals contacts. The orientation of the butenyl chain is such that it is anti to the apical Cl ligand, effectively proximal to the vacant sixth coordination site of the Cu II atom. Instead, the diethyl ether molecule of crystallization is located in the pocket formed by the butenyl chain and the basal coordination plane of the Cu II atom. Perhaps surprisingly, the ether O atom is not oriented towards, or spatially close to, the Cu atom [CuÁ Á ÁO1 ii = 4.9130 (9) Å ; symmetry code (ii) Àx + 1 2 , Ày + 3 2 , Àz + 1] and merely serves to occupy a void space that would otherwise be formed by molecular packing.

Database survey
Although there are 80 copper chloride structures that incorporate the bis(pyridin-2-ylmethyl)amine ligand (Groom & Allen, 2014; CSD Version 5.36 plus one update), only 20 have a sole bis(pyridin-2-ylmethyl)amine ligand chelating to a CuCl 2 moiety within an overall five coordination. The remaining 60 structures either have a tethered pair or tethered tiplet of ligands, or have the bridging chlorines between two complexes and are thus the more common geometry adopted by copper coordinated by a bis(pyridin-2-ylmethyl)amine based ligand. The geometry of the ligand and pendant group observed herein, is also a common feature of these structures, vis-a-vis, the pendant chain is oriented anti to the apical chlorine.

Synthesis and crystallization
For the preparation of (but-3-en-1-yl)bis[(pyridin-2-yl)methyl]amine (see Scheme 1 below), the bis(pyridin-2-ylmethyl)amine (BPMA) precursor was synthesized and purified following literature procedures (Carvalho et al., 2006). BPMA (8.064 g, 40.5 mmol) was dissolved in acetonitrile (15 ml) followed by the addition of triethylamine (4.098 g, 40.5 mmol) and 4-bromobutene (5.468 g, 40.5 mmol). The reaction vessel was sealed and allowed to mix for 4 d to ensure complete deprotonation and coupling occurred. Generation of the triethylamine hydrogen bromide salt, Et 3 NH + ÁBr À , was observed as white crystals in the brown-colored solution. The mixture was filtered and the desired product extracted from the filtrate using a hexane/water mixture. The hexane layer was separated and solvent removed to yield the ligand as a yellow colored oil (yield 8.516 g, 83%). The ligand was stored in a septum-sealed round-bottomed flask under argon gas in a refrigerator. The molecular structure and atom-labeling scheme for (I). Displacement parameters are depicted at the 50% probability level. [Symmetry code: (i) Àx + 1, y, Àz + 3 2 .]
For the synthesis of the title compound, (I), 1-butene-BPMA (2.000 g, 7.900 mmol) was dissolved in acetonitrile (20 ml) in a 50 ml round-bottomed flask. CuCl 2 (1.062 g, 7.900 mmol) was added to the flask to give a green-colored solution. The reaction was allowed to mix for 6 h, then pentane (20 ml) was added slowly to the solution to generate a bright-green precipitate. The solvent was removed from the round-bottomed flask by connecting it to a rotary evaporator. The precipitate obtained was washed twice by transferring two 15 ml aliquots of pentane into the flask and stirring vigorously for 30 min. The solvent was removed and the precipitate dried under vacuum for 2 h to yield a green solid (yield 2.909 g, 95%). Slow diffusion of diethyl ether into an acetonitrile solution of the complex at room temperature produced crystals of (I) suitable for X-ray analysis.