Crystal structure of di-μ-iodido-bis{[1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]lithium}

In the title binuclear complex, [Li2(C27H36N2)2I2], the unique LiI cation is coordinated by two iodide anions and one ylidene C atom from a 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene ligand in a distorted trigonal–planar geometry. The two symmetry-related iodide anions bridge two LiI cations, forming an inversion dimer in which the Li2I2 plane is nearly perpendicular to the imidazol-2-ylidene ring, with a dihedral angle of 85.5 (3)°. No hydrogen bonding is observed in the crystal.


S2. Experimental
A flame-dried Schlenk tube under a nitrogen atmosphere was charged with 1,3-Bis(2,6-diisopropylphenyl)imidazolinium iodide (0.516 g, 1mmol) and THF (10mL) at -78°C. To this was added a THF solution of lithium hexamethyldisilazide (0.167 g, 1 mmol). The mixture was allowed to slowly warm to room temperature and was stirred for 3 h.

S3. Refinement
The H atoms bonded to C atoms were introduced at calculated positions and refined using a riding model, with U iso (H) = 1.2U eq (C) and C-H distances of 0.93-0.96 Å.

Figure 1
The molecular structure of the title compound with the atom-numbering scheme and 30% probability displacement ellipsoids.

Figure 2
The packing diagram viewed along the a axis.

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.