Tetrahedral versus Planar Four‐Coordinate Carbon: A Sulfonyl‐Substituted Methandiide

Abstract

Flattened! The mono‐ and dilithiation of a sulfonyl‐substituted phosphane sulfide is reported. The new dilithio methandiide features a distorted carbon environment between the typical tetrahedral and planar arrangement (see figure). This geometry results from geometrical restrictions of the donor functions and can be described by two unusual bonding modes of the lithium atoms with the sp2‐hybridized methanide carbon.

Synthesis and Characterization of a Sulfonyl- and Iminophosphoryl-Functionalized Methanide and Methandiide

“…These observations are consistent with those reported for other mono-and dimetallated systems [14][15][16][17][18][19][20]. For example, the bond length changes in 1-Li2 are similar to those found in the corresponding thiophosphoryl compound C (Table 1), despite of the different structures formed in the solid state [26]. (2) Another interesting feature of the crystal structure of 1-Li2 concerns the coordination environments of the methandiide carbon atoms which strongly deviate from an ideal tetrahedron.…”

“…Such a planar carbon environment was already predicted by Schleyer and coworkers on the basis of theoretical studies [42]. The unsymmetrical methandiide C was found to form a complex molecular structure, which however also showed a strong deviation from the ideal tetrahedral geometry of carbon [26]. group also gave way to the formation of transition-metal complexes with open coordination-sides [27][28][29].…”

“…As shown in Figure 7, C(1), S(1), P(1) and Li(1) are almost in one plane, while Li(2) is coordinating almost orthogonally to that plane with an Li-C-Li angle of 72.9(2)°. This has also been observed in the crystal structure of methandiide C. On the basis of theoretical methods [26] this coordination mode can be explained by the two methandiide lone pairs populating two different orbitals, one of sp 2 -and the other of p-symmetry. The Li-C bond lengths with an average value of 2.235(6) Å are in the expected range compared to known methandiides featuring sulfonyl or iminophosphoryl groups [3,17,26].…”

“…This has also been observed in the crystal structure of methandiide C. On the basis of theoretical methods [26] this coordination mode can be explained by the two methandiide lone pairs populating two different orbitals, one of sp 2 -and the other of p-symmetry. The Li-C bond lengths with an average value of 2.235(6) Å are in the expected range compared to known methandiides featuring sulfonyl or iminophosphoryl groups [3,17,26]. The Li-N contacts are (with an average bond length of 2.006 Å) a bit shorter than those found in other iminophosphoryl stabilized geminal dianions, while the Li-O bonds (with an average length of 1.973(6) Å) are well in line with reported data [3,17].…”

“…More recently, our group has focused on non-DPPM derived methandiides, to expand the carbene chemistry of these compounds also to ligands with other substituents. The dilithium compound C with a sulfonyl functionality turned out to be easily accessible and similarly stable than the bis(phosphonium)-substituted systems [26]. The weaker coordination ability of the sulfonyl group also gave way to the formation of transition-metal complexes with open coordination-sides [27][28][29].…”