Crystal structure of tricarbonyl(N-diphenylphosphanyl-N,N′-diisopropyl-P-phenylphosphonous diamide-κ2 P,P′)cobalt(I) tetracarbonylcobaltate(−I) toluene 0.25-solvate

The title compound {Co(CO)3[Ph2PN(i-Pr)P(Ph)N(H)i-Pr]}[Co(CO)4] is an ionic species consisting of a Co(CO)3[Ph2PN(i-Pr)P(Ph)N(H)i-Pr] cation and a [Co(CO)4] anion.


Chemical context
Reaction of the PNPNH ligand N-(diphenylphosphanyl)--N,N 0 -diisopropyl-diaminophenylphosphine, Ph 2 PN(i-Pr)-P(Ph)N(H)i-Pr, with the cobalt precursor Co 2 (CO) 8 was performed to prepare a noble-metal-free catalyst for lightdriven water reduction to produce hydrogen. These compounds are attractive in terms of environmental acceptability as well as for economic reasons. Several very active intermolecular water-reduction systems using 3d metal complexes as catalytically active centres are known, examples include work on iron (e.g. Mejía et al., 2013), nickel (e.g. Zhang et al., 2011) and cobalt (e.g. Tong et al., 2014 complexes. It is likely that the NH group of the ligand and the Co atom cooperate in the proton-reduction process as has been reported for other water-reduction complexes (Han et al., 2012). We found that, apart from the previously described catalytically active dinuclear CO-bridged product Co 2 (CO) 6 (PNPNH) (Hansen et al., 2013), an ionic complex is also formed in this reaction. Both complexes can be separated by fractionated crystallization from toluene. It should be noted that in solution, the title compound is rapidly converted into the neutral dinuclear species Co 2 (CO) 6 (PNPNH) and therefore the IR and NMR spectra were measured only from freshly prepared samples. ISSN 1600-5368

Structural commentary
The title compound crystallizes in the monoclinic space group P2 1 /n with eight cations, eight anions as well as two molecules of toluene in the unit cell. The toluene solvent molecules are found to be disordered about inversion centres. The asymmetric unit is shown in Fig. 1. In the cation, the Co I atom is fivefold coordinated by three carbonyl ligands and the PNPNH ligand, which is bound via both P atoms (Fig. 2). Thus, the bidentate ligand forms a four-membered metallacycle at the Co I atom with the central N atom being tilted out of the plane formed by the Co and the two P atoms [the dihedral angles between the CoP 2 and NP 2 planes are 15.73 (10) and 14.44 (9) ]. The terminal secondary amine is not involved in complexation with the Co I atom and acts as a spectator group.

Supramolecular features
A weak hydrogen-bonding interaction is observed between the NH group of the cation and one of the O atoms of the tetracarbonylcobaltate(ÀI) anions (Table 1) et al., 1992), no 3c-4e hydrogen-bond-like N-HÁ Á ÁCo interaction has been found.

Database survey
For a similar, carbonyl-bridged dinuclear cobalt complex with this PNPNH ligand, see: Hansen et al. (2013). Examples for structural reports of other Co I -Co ÀI ion-pair complexes can be found in Fellmann et al.

Synthesis and crystallization
General: N-(diphenylphosphanyl)-N,N 0 -diisopropyl-diaminophenylphosphine was synthesized by a literature method (Peitz et al., 2010). Co 2 (CO) 8 was purchased from Strem and used without further purification. Toluene was dried over CaH 2 and distilled prior to use. Synthesis: A solution of Co 2 (CO) 8 (0.30 g, 0.88 mmol) in toluene (10 ml) was added to N-(diphenylphosphanyl)-N,N 0 -diisopropyl-diaminophenyl- The asymmetric unit of the title compound. Hydrogen atoms are omitted for clarity. Displacement ellipsoids correspond to the 30% probability level. Only one orientation of the disordered toluene molecule is shown.

Figure 2
Interionic N-HÁ Á ÁO hydrogen bond (dashed line) connecting an ion-pair in the title compound. Hydrogen atoms not involved in hydrogen bonding, the co-crystallized toluene molecule and the second ion-pair of the asymmetric unit are omitted for clarity. Displacement ellipsoids are drawn at the 30% probability level. Table 1 Hydrogen-bond geometry (Å , ). phosphine, Ph 2 PN(i-Pr)P(Ph)N(H)i-Pr (0.36 g, 0.88 mmol) in a glove box. After gas evolution subsided, the 50 ml Schlenk flask was closed and heated to 383 K for 35 min without stirring to preserve the two-phase system. After crystallization from toluene at room temperature for three days, two crystal fractions were separated from the solvent and washed with n-hexane (2 Â 5 ml). The fraction of cubic brown crystals showed space-group and lattice parameters identical to X-ray diffraction data published previously (Hansen et al., 2013). The second fraction contained yellow needles with the crystal structure presented here. Further isolation of this new complex was not possible as it inevitably forms the known dinuclear product when dissolved in organic solvents. Manual picking of the crystals was difficult as the material proved too delicate. Analytics

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Atoms H1 and H3 were located in a difference Fourier map and their coordinates were refined with the restraint N-H = 0.87 (1) Å . All other H atoms were placed in idealized positions with d(C-H) = 0.95-1.00 (CH) and 0.98 Å (CH 3 ) and refined using a riding model with U iso (H) fixed at 1.2 U eq (C) for CH and 1.5 U eq (C) for CH 3 . The ring of the half-occupied toluene molecule was constrained to resemble an ideal hexagon with C-C distances of 1.39 Å . SADI instructions were used to improve the geometry of one phenyl ring (C24-C25, C25-C26) and one i-propyl group (C13-C14, C13-C15).