trans-Acetyldicarbonyl(η5-cyclopentadienyl)(methyldiphenylphosphane)molybdenum(II)

The title compound, [Mo(C5H5)(C2H3O)(C13H13P)(CO)2], was prepared by reaction of [Mo(CH3)(C5H5)(CO)3] with methyldiphenylphosphane. The MoII atom exhibits a four-legged piano-stool coordination geometry with the acetyl and phosphane ligands trans to each other. There are several intermolecular C—H⋯O hydrogen-bonding interactions involving carbonyl and acetyl O atoms as acceptors. A close nearly parallel π–π interaction between the cyclopentadienyl plane and the phenyl ring of the phosphane ligand is present, with an angle of 6.4 (1)° between the two least-squares planes. The centroid-to-centroid distance between these groups is 3.772 (3) Å, and the closest distance between two atoms of these groups is 3.449 (4) Å. Since each Mo complex is engaged in two of these interactions, the complexes form an infinite π-stack coincident with the a axis.

The title compound, [Mo(C 5 H 5 )(C 2 H 3 O)(C 13 H 13 P)(CO) 2 ], was prepared by reaction of [Mo(CH 3 )(C 5 H 5 )(CO) 3 ] with methyldiphenylphosphane. The Mo II atom exhibits a fourlegged piano-stool coordination geometry with the acetyl and phosphane ligands trans to each other. There are several intermolecular C-HÁ Á ÁO hydrogen-bonding interactions involving carbonyl and acetyl O atoms as acceptors. A close nearly parallelinteraction between the cyclopentadienyl plane and the phenyl ring of the phosphane ligand is present, with an angle of 6.4 (1) between the two least-squares planes. The centroid-to-centroid distance between these groups is 3.772 (3) Å , and the closest distance between two atoms of these groups is 3.449 (4) Å . Since each Mo complex is engaged in two of these interactions, the complexes form an infinitestack coincident with the a axis.

Related literature
The synthesis of the title compound has been reported previously and its reactivity studied, though no structural information was provided (Adams et al., 1997;Barnett et al., 1972). A related structure has been reported for the triphenylphosphane-substituted version of the title compound (Churchill & Fennessey, 1968). For synthetic details, see: Gladysz et al. (1979).
group of the acetyl group is oriented in a syn fashion relative to the orientation of the methyl group of the PMePh 2 ligand.
A unit cell packing diagram is shown in Fig. 3.
There are several particularly short intermolecular distances involving H atoms. One short contact (2.421 Å) is present between O2 of a carbonyl ligand and H16 of a phenyl group (symmetry code: x -1/2, -y + 1/2, -z). Another short contact (2.414 Å) involves O1 of the acetyl group and H10A of the methyl group of a PMePh 2 ligand (symmetry code: -x + 1/2, y + 1/2,z). A third short contact (2.453 Å) is present between O1 of the acetyl group and H3 of a Cp ring (symmetry code: - x, -y, -z).
A close nearly parallel π-π intermolecular interaction between the Cp plane and the phenyl ring of a PMePh 2 ligand is present. The angle between the least-squares planes of these close π systems is 6.4 (1)° (Cp ring plane composed of atoms C1-C5; phenyl ring plane composed of atoms C17-C22). While the Cp centroid-phenyl ring centroid distance is 3.772 (3) Å, the closest distance between these groups is 3.449 (4) Å between C20 and C5 (symmetry code: 1/2 + x, 1/2y, -z). Each Mo complex is engaged in two of these interactions, forming an infinite stack that is coincident with the aaxis. Fig. 4 shows the π overlap of neighboring molecules. Fig. 5 shows the infinite π-stacking interaction.
A related structure has been reported for the triphenylphosphane-substituted version of (I) (Churchill & Fennessey, 1968).

Experimental
CpMo(CO) 3 (CH 3 ). This compound was prepared by a modification of the method used by Gladysz et al. (1979) for the synthesis of a related iron compound. In an inert atmosphere glove box, [CpMo(CO) 3 ] 2 (181 mg, 0.370 mmol) was dissolved in THF (10 ml). LiEt 3 BH (0.87 ml, 1M in THF) was added dropwise by syringe with stirring, causing the evolution of H 2 and a color change from purple to yellow. The solution was stirred for 30 min, then CH 3 I (75 µl, 1.2 mmol) was slowly added to the solution by micropipette, and the resulting solution was stirred for 2 h, causing a greenyellow precipitate to form. The solvent was removed in vacuo and the residues were extracted into pentane (2 × 15 ml) and filtered through a 2 cm plug of Al 2 O 3 on a 30 ml fritted funnel, leaving a clear pale-yellow liquid. The Al 2 O 3 was supplementary materials sup-2 Acta Cryst. (2012). E68, m1158-m1159 washed with about 10 ml of pentane, and the solvent was removed in vacuo to afford a solid yellow product (87 mg, 45%). IR and NMR ( 1 H and 13 C) spectral analyses confirmed the formation of the desired product.
CpMo(CO) 2 (PMePh 2 )(COCH 3 ), (I). In an inert-atmosphere glove box, CpMo(CO) 3 (CH 3 ) (87.2 mg, 0.335 mmol) was dissolved in 10 ml acetonitrile. PMePh 2 (93 µl, 0.50 mmol) was added with stirring, and the resulting solution was stirred for 48 h. Solvent was removed in vacuo, leaving an orange oil, which was dissolved in diethyl ether and dried in vacuo to a yellow powder. The powder was triturated with pentane (5 ml) and isolated by filtration to afford the desired product in pure form as a yellow powder (79 mg, 51%), as confirmed by IR and NMR ( 1 H, 13 C, and 31 P) spectral analyses.
Crystalline material was obtained as yellow prisms by chilling a concentrated solution of (I) in diethyl ether.

Refinement
H atoms were treated in calculated positions and refined in the riding model approximation with distances of C-H = 0.95, 1.00 and 0.98 Å for the phenyl, cyclopentadienyl and methyl groups, respectively, and with U iso (H) = kU eq (C), k = 1.2 for phenyl and cyclopentadienyl groups and 1.5 for methyl groups. Methyl group H atoms were allowed to rotate in order to find the best rotameric conformation. The maximum and minimum electron densities in the final difference Fourier map are located 0.87 and 0.75 Å, respectively, from atom Mo1.

Figure 1
Numbered thermal ellipsoid plot (50% probability ellipsoids for non-H atoms) of the structure of (I).

sup-3
Acta Cryst. (2012). E68, m1158-m1159  Unit cell packing diagram of (I) (50% probability ellipsoids).  View of two complexes of (I) showing the π overlap (black atoms) of the phenyl ring of one molecule and the Cp ring of another molecule (symm. codes x, y, z for Cp, -1/2 + x, 1/2 -y, -z for Ph ring). H atoms omitted for clarity.  View of infinite intermolecular π-π stacking in (I) between Cp and Ph groups of neighboring complexes along the a-axis.

trans-Acetyldicarbonyl(η 5 -cyclopentadienyl)(methyldiphenylphosphane)molybdenum(II)
Crystal data Special details Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).

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