Bis(μ2-diphenylphosphinamide-κ2 O:O)bis[bis(diphenylphosphinamide-κO)lithium] dichloride acetonitrile disolvate

The asymmetric unit of the title compound, [Li2(C12H12NOP)6]Cl2·2CH3CN, contains one-half of the centrosymmetric dication, one chloride anion and one acetonitrile solvent molecule. Each Li atom is coordinated by four O atoms [Li—O 1.891 (3) and 2.025 (3) Å] from the four diphenylphosphinamide ligands in a distorted tetrahedral geometry. In the crystal, weak N—H⋯Cl hydrogen bonds link the anions and dications into columns extending along [100].


Comment
The π-electron-rich phosphorus-nitrogen compounds had been known as a type of potential precursors for inorganic polymers with unusual properties, and led to considerable interest in their syntheses and coordination chemistry toward transition metals (Roesky & Lucke, 1989;Wong et al., 1997). The title lithium compound is a by-product in the preparation of this type compounds. Treatment of 1,2-dicyanobenzene with the equivalent LiN(SiMe 3 ) 2 and then the equivalent diphenylphosphinic chloride did not give the π-electron-rich phosphorus-nitrogen compound. The unexpectd title compound was obtained after csystallization in acetonitrile. The crystal structure was ascertained by elemental analysis.
The crystal structure of the compound showed that it has triclinic symmetry. Every lithium ion is coordinated via four oxygen of the ligands to give a tetrahedral geometry. The average bond length of Li-O is 1.945 Å. This value is comparable to the analogous lithium compound (Pisareva et al., 2004). The square-plane ring is formed by the two lithium ion and bridged O atoms in which the bond angle of O1-Li1-O1A is 91.28 (17)°. The average bond length of phosphors-nitrogen in the title compound is 1.623 Å. It is very similar to the bond length of phosphors-nitrogen in the crystal structure of diphenylphosphinamide determined in 1981 (Oliva et al., 1981).
The resultant yellow solution was warmed to room temperature and stirred for an additional 2 h. A solution of 1,2-Dicyanobenzene (0.64 g, 5 mmol) in THF (10 cm 3 ) was slowly added to the reaction mixture which was stirred at 0°C for two hours before warming up to room temperature. Then diphenylphosphinic chloride (0.95 cm 3 ,5 mmol) was added to the mixture at -78°C for an hour before warming up to room temperature and allowed to react overnight. Solvent was then removed in vacuum. The residue was extracted with dichloromethane and the solution was filtered. The solvent of the filtrate was removed in vacuum and was dissolveded in CH 3 CN at room temperature. Finally a coulourless product was obtained. Yield: 0.43 g, 0.83 mmol, 35%. Elemental analysis cacld (%) for C 72 H 72 N 6 O 6 P 6 Li 2 Cl 2 ·0.75CH 3 CN·0.25H 2 O: C 65.28, H 5.57, N 6.99; found: C 65.12, H 5.50, N 7.05.

Refinement
H atoms of phenyl were placed in their idealized positions and allowed to ride on the respective parent atoms with C-H 0.93 Å, and with U iso (H) = 1.2U eq . H atoms of acetonitrile were placed in their idealized positions and allowed to ride on the respective parent atoms with C-H 0.96 Å, and with U iso (H) = 1.5U eq . H atoms of amino were found from difference  A view of the molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level.
H atoms and the labels of C atoms were omitted for clarity [symmetry code: (A) 2 -x,-y,-z].

Bis(µ 2 -diphenylphosphinamide-κ 2 O:O)bis[bis(diphenylphosphinamide-κO)lithium]
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.25 e Å −3 Δρ min = −0.29 e Å −3 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.