Bis(3-methylphenolato-κO)(nitrosyl-κN)[tris(3,5-dimethylpyrazol-1-yl-κN 2)hydridoborato]molybdenum(II)

The title complex, [Mo(C15H22BN6)(C7H7O)2(NO)], contains an {MoNO}4 core stabilized by κ3-hydrotris(3,5-dimethylpyrazol-1-yl)borate, [TpMe2]−, and two anionic m-cresolate ligands, leading to a distorted octahedral geometry for the Mo atom. The short Mo—O bond lengths [1.935 (2) and 1.971 (2) Å], as well as large Mo—O—Csp 2 angles [134.2 (2) and 143.54 (19)°], indicate dπMo—pπO interactions, which are clearly weaker when compared with {Mo(NO)(TpMe2)} alkoxides. The nitrosyl system is virtually linear [179.3 (3)°] with Mo—N and N—O bond lengths of 1.760 (2) and 1.205 (3) Å, respectively. Intra- and intermolecular C—H(Ph or CH3)⋯π(Ph) interactions between adjacent phenyl rings are found in the crystal structure (d H⋯Ph in the range 2.743–2.886 Å). One of the Ph rings shows disorder, i.e. swinging in the ring plane.


Comment
The stable 16e complexes containing {MoNO} 4 core stabilized by tripodal hydrotris(3,5-dimethylpyrazol-1-yl)borate and two anionic co-ligands undergo easily reversible 1e reduction at a potential, E 1/2 , which can be tuned in the huge range of 2200 mV by selecting suitable co-ligands (Włodarczyk et al., 2008c). The 17e species based on the {Mo(NO)(Tp Me2 )(O-) 2 } moiety very efficiently catalyse the dehalogenation of CHCl 3 ; their activity is strictly associated with the E 1/2 value (Włodarczyk et al., 2008b). The structural study of title complex is a part of a larger project concerning examination of molecules which may be potentially applied as electrocatalysts.
The title complex (Fig. 1) contains a pseudo-mirror plane of symmetry passing through Mo, NO, B and the N31/N32/C33/ C34/C35 pyrazolyl ring (approximate C s symmetry which is reflected in 1 H NMR spectrum). The longer Mo-O distances, i.e. weaker π-donation from O to Mo, in the bis-cresolato complex, than compared with those found for {Mo(NO)(Tp Me2 )}alkoxides, certainly result from additional electron delocalization to sp 2 -hybridized carbon (which is precluded in the case of the latter complexes, hence Mo-O alkoxide av. distance is 1.88Å, see: Romańczyk et al., 2007;Włodarczyk et al., 2008c) and is reflected in hypsochromically shifted ν NO band in the title complex (McCleverty et al., 1983). The lengthening of the Mo1-N31 bond is attributed to the trans-influence of the NO group. Intermolecular Ph···Ph interactions between adjacent nearly perpendicular rings (C46B···H54 i distance is 2.873Å) and also between rings and methyl groups (C44···H48B ii distance is 2.886Å), stabilize the crystal structure (Fig. 2), symmetry codes: (i) 1+x, y, z; (ii) 1-x, -y, -z. As mentioned above one of the Ph rings (linked with O41) is disordered, i.e. it swings in the ring plane.

Experimental
The complex was synthesized following the literature from the reaction of [Mo(NO)(Tp Me )I 2 ].C 6 H 5 CH 3 and m-cresol in the presence of Et 3 N in boiling dichloromethane and characterized by mass spectrometry, IR, 1 H NMR spectroscopy as well as cyclic voltammetry (Włodarczyk et al., 2008a). A dark brown crystals were grown by slow evaporation of solvent from a dichloromethane/n-hexane solution.

Refinement
The shape of the displacement elipsoids of atoms C43, C44, C45, C46, C47 and C48 suggests some kind of swinging disorder of the aromatic ring, however attempts to modelling of this disorder hasn't gave satisfactory results. All hydrogen atoms joined to carbon atoms of the discussed compound were positioned with an idealized geometry and refined using a riding model with C-H = 0.93Å and U iso (H) = 1.2U eq (C) for aromatic, C-H = 0.96Å and U iso (H) = 1.5U eq (C) for the methyl groups. Hydrogen atom joined to boron atom was found from the difference Fourier map and fully refined.

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