Hydrido(prolinato-κ2 N,O)tris(trimethylphosphane-κP)iridium(III) hexafluoridophosphate

The title complex, [Ir(C5H8NO2)H(C3H9P)3]PF6, has two independent anion–cation pairs in the asymmetric unit. The geometry about each IrIII atom is pseudo-octahedral with a meridional arrangement of the P(CH3)3 ligands, N,O-bidentate coordination of prolinate and a hydride ligand trans to the prolinate N atom. The independent IrIII moieties are joined by N—H⋯O hydrogen bonds and the N—H⋯O bonding motif continues throughout the structure, creating an extended chain parallel to the c-axis direction. The methyl groups of one P(CH3)3 ligand are rotationally disordered over two sets of sites in a 0.62 (2):0.38 (2) ratio.

The title complex, [Ir(C 5 H 8 NO 2 )H(C 3 H 9 P) 3 ]PF 6 , has two independent anion-cation pairs in the asymmetric unit. The geometry about each Ir III atom is pseudo-octahedral with a meridional arrangement of the P(CH 3 ) 3 ligands, N,O-bidentate coordination of prolinate and a hydride ligand trans to the prolinate N atom. The independent Ir III moieties are joined by N-HÁ Á ÁO hydrogen bonds and the N-HÁ Á ÁO bonding motif continues throughout the structure, creating an extended chain parallel to the c-axis direction. The methyl groups of one P(CH 3 ) 3 ligand are rotationally disordered over two sets of sites in a 0.62 (2):0.38 (2) ratio.

Related literature
For the valine structure analogous to the proline structure described herein, see: Roy et al. (2006). For a Cp*Ir complex with proline and a t-butylethynl ligand, see: Carmona et al. (2000). For a Cp*Ir complex with proline and a chloride ligand, see: Carmona et al. (2012). For the preparation of [Ir(COD)(PMe 3 ) 3 ]Cl, see : Frazier & Merola (1992). For a selection of amino acid complexes in general, their structures and their extended lattice features, see: Urban et al. (1996); Shimazaki et al. (2009). For a description of the Cambridge Structural Database, see: Allen (2002).

Experimental
Crystal data [Ir(C 5 H 8
Financial support for this work was provided by ACS-PRF (grant #23961-C1) and by the National Science Foundation (CHE-902244). The Virginia Tech Subvention Fund is gratefully acknowledged for covering the open-access fee.

Synthesis and crystallization
A 100 mL flask equipped with a stir bar and septum was charged with 117.5 mg (1.02 mmol) of L-proline. The flask was then charged with 250 mg (0.443 mmol) of [Ir(COD)(PMe 3 ) 3 ]Cl under N 2 in a drybox. The flask was then connected to a double manifold (vacuum/nitrogen) Schlenk line and 20 mL of distilled water was added to the flask via syringe. The solution was stirred magnetically and heated to reflux. After 18 hours at reflux the reaction mixture was allowed to cool and solvent was removed in vacuo. The white solid residue was treated with distilled methylene chloride (3 x 10 mL) to extract the product from the excess amino acid. The solution was filtered from the solid using cannula techniques. The methylene chloride was removed in vacuo and the solids were dried under reduced pressure to yield 150 mg (0.263 mmol, 60.7% yield based on the amount of Ir(COD)(PMe 3 ) 3 ]Cl) of [Ir(L-pro)(H)(PMe 3 ) 3 ]Cl C,H analysis: Calculated for C 14 H 36 NO 2 P 3 IrCl:C, 29.4% H,6.3% Found: C, 29.17%; H, 6.2% An aqueous solution of the chloride salt was treated with an aqueous solution of K[PF 6 ] to precipitate [Ir(L-pro)(H)(PMe 3 ) 3 ][PF 6 ]. Crystals suitable for X-ray diffraction were grown from dichloromethane/diethylether.

Refinement
Hydrogen atoms were treated with a combination of restrained refinement (i.e. for the Ir-H hydrogens) and constrained riding models. Values of U iso (H) were set to either 1.2U eq or 1.5U eq of the parent atom. Crystal data, data collection and structure refinement details are summarized in Table 1.

Results and discussion
The chemistry of amino acid complexes of transition metals has a long history (Shimazaki et al., 2009). A search of the CSD data base (Allen, 2002) reveals over 1400 hits for compounds with bidentate N,O coordination of amino acids to transition metals. Restricting the search to the specific amino acid proline, yields over 140 hits. Finally, restricting the search to iridium compounds, there are 6 CSD structures with proline coordinated to iridium. We reported on the crystal structure of [hydrido-valinato-tris(trimethylphosphine)iridium][hexafluorophosphate] (CSD:20060907) (Roy et al., 2006) in the space group P4 3 , which has very strong intermolecular N-H···O hydrogen bonding that results in a 4 3 helical arrangement of the iridium complexes. In this report, the title proline complex has a "flatter" intermolecular motif with the N-H···O hydrogen bonding resulting in a one-dimenional chain motif with the chain parallel to the c-axis. Hydrogen  Table 1. A similar motif has been reported for (η 5 -Pentamethyl-cyclopentadienyl)-(t-butylethynyl)-(L-prolinato-N,O)-ιridium (CSD:20010919) (Carmona et al., 2000), but when the t-butylethynyl group is replaced by chloride (CSD: 19911024) (Carmona et al., 2012), the motif changes to alternating N-H···O and N-H···Cl bonding to generate the full lattice.

Figure 1
The asymmetric unit of the title compound, showing both sets of independent cations and anions. Hydrogen atoms are omitted for clarity. The displacement ellipsoids are shown at the 50% probability level and only the major component of the disordered methyl groups on P1 is shown.

Figure 2
Hydrogen bonding motif for the title compound. Hydrogen atoms (with the exception of the metal hydrides and N-H atoms) and phosphorus methyl groups are omitted for clarity.) The displacement ellipsoids are shown at the 50% probability level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.