Crystal structure of μ-1κC:2(η2)-carbonyl-carbonyl-1κC-chlorido-2κCl-μ-chloridoborylene-1:2κ2 B:B-[1(η5)-pentamethylcyclopentadienyl](tricyclohexylphosphane-2κP)iron(II)platinum(II) benzene monosolvate

The title compound [η5-(C5(CH3)5)(CO)Fe{(μ-BCl)(μ-CO)}PtCl(P(C6H11)3)]·C6H6 shows a piano-stool coordination geometry at the FeII atom and a distorted square-planar coordination geometry at the Pt atom. Both metals are bridged by one carbonyl and one chloridoborylene unit. Additionally, one benzene solvent molecule aligns in a staggered position relative to the (pentamethyl)cyclopentadienyl ligand of the FeII centre.

In the molecular structure of the dinuclear title compound [ 5 -(C 5 (CH 3 ) 5 )-(CO)Fe{(-BCl)(-CO)}PtCl(P(C 6 H 11 ) 3 )]ÁC 6 H 6 , the two metal atoms, iron(II) and platinum(II), are bridged by one carbonyl (-CO) and one chloridoborylene ligand (-BCl). The Pt II atom is additionally bound to a chloride ligand situated trans to the bridging borylene, and a tricyclohexylphosphane ligand (PCy 3 ) trans to the carbonyl ligand, forming a distorted square-planar structural motif at the Pt II atom. The Fe II atom is bound to a pentamethylcyclopentadienyl ligand [ 5 -C 5 (CH 3 ) 5 ] and one carbonyl ligand (CO), forming a piano-stool structure. Additionally, one benzene solvent molecule is incorporated into the crystal structure, positioned staggered relative to the pentamethylcyclopentadienyl ligand at the Fe II atom, with a centroid-centroid separation of 3.630 (2) Å .

Structural commentary
The molecular structure of compound (I) is shown in Fig. 1. As already reported for these type of reactions, the chloride ligand at the Pt atom adopts the trans position relative to the borylene unit due to its trans influence (Braunschweig et al., 2010). The Fe-Pt distance of 2.6455 (5) Å is slightly longer than the sum of the covalent radii and is most likely influenced by the two bridging ligands between both metals. The bridging borylene ligand and the additional semi-bridging carbonyl ligand, together with the phosphane and chloride ligand, form a distorted square-planar structural motif at the Pt atom ( Fig. 1). The Pt-B bond length [1.910 (4) Å ] is shorter than the Fe-B bond length [2.009 (4) Å ], indicating a stronger bonding interaction. Compared to the similar parent compound [( 5 -C 5 H 5 )(CO) 2 FeBCl 2 ], (II), which has a Fe-B bond length of 1.942 (3) Å , there is an obvious lengthening of this bond in the target molecule. In the structure of (I), the Fe atom is additionally bound to a (pentamethyl)cyclopentadienyl ligand ( 5 -C 5 Me 5 ) and one carbonyl ligand (CO), forming an overall piano-stool structure. The 11 B NMR resonance in the spectrum of (I) is shifted downfield to 107.4 p.p.m. from the previous resonance at 95.3 p.p.m. in compound (II).
The 31 P NMR spectrum shows a peak at 56.55 p.p.m. with a coupling constant of 1 J P-Pt = 4864 Hz, which is typical for a bridging square-planar platinum complex (Arnold et al., 2012). Furthermore, the observed FT-IR signals are indicative of one semi-bridging carbonyl ligand at 1913 cm À1 and one terminal carbonyl ligand at 1978 cm À1 .

Supramolecular features
The orientation of the benzene solvent molecule in the crystal structure of (I) with its staggered conformation with respect to the (pentamethyl)cyclopentadienyl ligand and a centroidcentroid distance of 3.630 (2) Å ( Fig. 1) raises the possibility of intermolecular interactions, such asstacking. However, as no further interactions are detected in the crystal structure ( Fig. 2), it seems that the benzene molecule occupies a free void in the asymmetric unit and mainly supports the crystallization process.

Synthesis and crystallization
[( 5 -C 5 Me 5 )(CO) 2 Fe(BCl 2 )] (50.0 mg, 0.11 mmol) was dissolved in 2 ml of benzene and bis(tricyclohexylphosphane)platinum (86.9 mg, 0.11 mmol) was added to the solution. After 5 h of stirring, the solvent was removed, by-products were extracted with two portions of 2 ml of hexane, and the bright-yellow residue was redissolved in 2 ml of benzene. Upon slow evaporation, yellow crystals suitable for X-ray diffraction were obtained at room temperature (yield: 72.4 mg, The molecular structure of the title compound, showing the atomnumbering scheme and displacement ellipsoids for the non-H atoms at the 50% probability level. H atoms have been omitted for clarity.

Figure 2
Packing plot of the title compound.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms were placed at idealized positions and treated as riding atoms; C-H = 0.98 (CH 3 ) or 1.00 Å (aliphatic). U iso (H) values were fixed at 1.5 (for primary H atoms) and 1.2 times (tertiary H atoms) U eq of the parent C atoms. Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT-Plus (Bruker, 2009); data reduction: SAINT-Plus (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXLE (Hübschle et al., 2011); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.01 e Å −3 Δρ min = −0.78 e Å −3 Special details Experimental. The crystal was immersed in a film of perfluoropolyether oil, mounted on a glass fiber and transferred to stream of cold nitrogen. 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