Crystal structures of fac-trichloridotris(trimethylphosphane-κP)rhodium(III) monohydrate and fac-trichloridotris(trimethylphosphane-κP)rhodium(III) methanol hemisolvate: rhodium structures that are isotypic with their iridium analogs

The structures of two solvates (water and methanol) of the facial isomer of (Me3P)3RhCl3 are reported and compared with previously published facial (Me3P)3IrCl3 solvates with which they are isostructural and isomorphous.


Chemical context
Phosphane complexes of noble metals, especially those of rhodium and iridium, have proven to be important in catalysis as well as in studying fundamental reactions at metal surfaces. Chlorido compounds of rhodium and iridium with phosphane ligands provide important starting materials for other metal complexes of that family through replacement of the chlorine. For example, we have shown that (Me 3 P) 3 IrCl 3 can be converted into (Me 3 P) 3 IrMe 3 through reaction with methylmagnesiumchloride. This trimethyliridium compound can, in turn, be used to study organometallic reactions at the iridium(III) atom (Merola et al., 2013). Thus, the fundamental study of crystal structures of phosphane-chlorido complexes of iridium and rhodium is important to help understand the structures, the bonding and the stereochemistry of this class of compounds. This paper adds to the body of knowledge of rhodium complexes that complement the already published structures of the analogous iridium compounds. It contributes to the information on crystal structures of L 3 MCl 3 compounds, comparing the rhodium structures to the iridium structures as well as confirming the nature of solvate formation in both the iridium and rhodium structures. ISSN 2056-9890

Structural commentary
The title complexes fac-trichloridotris(trimethylphosphane-P)rhodium(III) monohydrate, RhP 3 Cl 3 water, and fac-trichloridotris(trimethylphosphane-P)rhodium(III) methanol hemihydrate, RhP 3 Cl 3 MeOH, are isotypic with their iridium counterparts (CCDC 896072, 896073;Merola et al., 2013). Isotypism in rhodium and iridium complexes is not unusual, largely owing to the lanthanide contraction resulting in very similar radii for both second-and third-row transition elements (Cordero et al., 2008). Fig. 1 is a displacement ellipsoid rendering of compound RhP 3 Cl 3 water and Fig. 2 is a displacement ellipsoid rendering of compound RhP 3 Cl 3 MeOH. For compounds RhP 3 Cl 3 water and RhP 3 Cl 3 MeOH reported here, the comparison with their iridium analogs can be found in Tables 1 and 2 which list the corresponding unit-cell parameters for the rhodium and iridium water solvates (Table 1) and the rhodium and iridium methanol solvate ( Table 2). The iridium compounds show a   Displacement ellipsoid (50% probability level) rendering of the factrichloridotris(trimethylphosphane)rhodium-0.5(methanol) compound, RhP 3 Cl 3 MeOH. Table 1 Comparison of unit-cell dimensions (Å , ) for water solvate complexes RhP 3 Cl 3 water and IrP 3 Cl 3 water.     (17) very slight lengthening of the unit-cell dimensions compared to rhodium but they are clearly isotypic overall. Table 3 lists the important bond lengths for RhP 3 Cl 3 water and IrP 3 Cl 3water while Table 4 lists these for RhP 3 Cl 3 MeOH and IrP 3 Cl 3 MeOH. Bond-length comparisons show little significant difference between the rhodium and iridium analogs.

Supramolecular features
It is not surprising that fac-tris(trimethylphosphane)trichloroidium(III) and -rhodium(III) complexes form lattice solvates since the shape of the individual molecules leads to packing with voids in the lattice. Thus, every structure we have determined with the iridium compounds, as well as the ones reported here, contains a solvent. In the case of the water solvate, Fig. 3 shows the packing diagram for RhP 3 Cl 3 water looking down the c axis. One can see that the packing involves alternating layers of rhodium molecules and water molecules. The water molecules show close, hydrogen-bonding interactions (Table 5) between the water and the chlorines on one layer of the rhodium compound as well as close C-HÁ Á ÁO interactions between the phosphane methyl groups and the water oxygen. One should not make much of the hydrogen positions on the water since, although they were originally found in difference maps, the O-H bond lengths and the H-O-H angle were restrained with DFIX and DANG commands (Sheldrick, 2015). Fig. 4 shows the packing diagram for RhP 3 Cl 3 MeOH, looking down the c axis, illustrating the O-HÁ Á ÁCl hydrogen bonding (Table 6) and the location of the methanol molecules in a channel in the crystal.

Database survey
A search of the Cambridge Structural Database (Groom & Allen, 2014) surprisingly shows very few structurally characterized trichloridotrisphosphaneiridium or rhodium compounds. In the case of iridium, beside the structures we recently published (CCDC 896072-896076; Merola et al., 2013), there are only three other P 3 IrCl 3 compounds in the database -the mer and fac isomers with P = phenyldimethylphosphane (refcodes CTPIRA01, CTPIRC: Marsh, 1997;Robertson & Tucker, 1981) and one entry where P 3 is cis,cis-1,3,5-tris(diphenylphosphino)cyclohexane (refcode LEXFAV; Mayer et al., 1994). For rhodium, P 3 RhCl 3 structurally characterized compounds are also rare with one mixed-ligand complex (two tri-n-butylphosphane ligands and one trimethylphosphite ligand; refcode CBPMRH; Allen et al., 1970) Packing diagram of the fac-trichloridotris(trimethylphosphane)rhodiumwater compound, RhP 3 Cl 3 water, viewed down the c axis, showing the alternating layers of complex and water molecules. Hydrogen atoms except for water H atoms are omitted for clarity.

Synthesis and crystallization
The rhodium complexes described herein could not be characterized spectroscopically as pure materials, but were isolated as crystals from complex mixtures. In contrast to the iridium complex [IrCOD(PMe 3 ) 3 ]Cl (COD = cyclooctadiene) (Frazier & Merola, 1992) which is the starting material for much of our iridium work, attempts to synthesize the analogous rhodium compound met with no success. Reaction between various Rh I olefin complexes, including COD, especially in dichloromethane solvent, led to complex mixtures of Rh(PMe 3 ) n compounds in all cases. That these compounds are compounds of Rh is clearly seen in the Rh-P chemical coupling in the complicated 31 P NMR spectra. Attempts at extracting a pure compound from the complex mixture with various solvents including dichloromethane, water, methanol and acetone did not yield clean materials. Following extraction, the solutions were allowed to sit in the open air for several days and, in the case of water and methanol, a few crystals suitable for X-ray crystallography were formed and used for the data collection described in this communication.

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.

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

Refinement
Refinement on F 2 Least-squares matrix: full R[F 2 > 2σ(F 2 )] = 0.029 wR(F 2 ) = 0.071 S = 1.08 4858 reflections 328 parameters 0 restraints Primary atom site location: structure-invariant direct methods Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained w = 1/[σ 2 (F o 2 ) + (0.0286P) 2 + 4.1793P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 1.03 e Å −3 Δρ min = −0.41 e Å −3 Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.00519 (17) 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.