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

Abstract

The synthesis of [H 2 C(PPh 2 =NSiMe 3 )(SO 2 Ph)] (1) and its mono-and dimetalation are reported. Due to the strong anion-stabilizing abilities of the iminophosphoryl and the sulfonyl group monometalation to 1-K and dimetalation to 1-Li 2 proceed smoothly with potassium hydride and methyllithium, respectively. Both compounds could be isolated in high yields and were characterized by NMR spectroscopy as well as XRD analysis. The methanide 1-K forms a coordination polymer in the solid state, while in case of the methandiide a tetrameric structure is observed. The latter features an unusual structural motif consisting of two (SO 2 Li) 2 eight-membered rings, which are connected with each other via the methandiide carbon atoms and additional lithium atoms. With increasing metalation a contraction of the P-C-S linkage is observed, which is well in line with the increased charge at the central carbon atom and involved electrostatic interactions.Keywords: methandiides; lithium; potassium; molecular structures BackgroundIn the past 20 years, methandiides with a doubly metalated carbon atom (R 2 CM 2 with M mostly being Li) have attracted intense research interest in organometallic chemistry. This is mainly due to their applicability as ligands for the preparation of carbene-type complexes by simple salt metathesis reactions [1][2][3]. Thereby, methandiides revealed to be highly efficient ligand systems stabilizing a variety of carbene complexes with main group metals [4][5][6][7], early and late transition metals [8][9][10][11][12] as well as lanthanides and actinides [13][14][15][16]. The first dilithium compound, which was employed in this chemistry, was the bis(iminophosphorano) system {Li 2 (bipm TMS )} 2 (A, bipm TMS =C(PPh 2 NSiMe 3 ) 2 ), which was simultaneously reported by the groups of Cavell and Stephan in 1999 (Figure 1) [17,18]. Unlike all other methandiides reported before [19][20][21], A was found to be conveniently accessible by double deprotonation and isolable in high yields, thus allowing its application in carbene complex synthesis [22]. The high stability and facile synthesis of A can be explained by the strong anion-stabilizing ability of the P(V) moieties as well as the additional nitrogen donor side-arms, which efficiently coordinate lithium to form stable complexes. Analogously, the corresponding thiophosphoryl system B reported by Le Floch also proved to be a stable and powerful ligand system [23][24][25]. 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].

Isolation and structure determination of a tetrameric sulfonyl dilithio methandiide in solution based on crystal structure analysis and 6Li/13C NMR spectroscopic data

“…The C–Li, C–S, and O–Li bond lengths ( Table 1 ) of the tetramer ( 2a ) 4 ·(THF) 6 are in the range of those found in the hexamer ( 2a ) 6 ·Li 2 O·(THF) 6 and functionalized dilithio sulfonyl methandiides [ 40 , 43 ].…”

“…Besides the crystal structures of ( 2a ) 4 ·(THF) 6 and ( 2a ) 6 ·Li 2 O·(THF) 6 those of the sulfonyl dilithio methandiides IIIa (FG 1 = SO 2 Ph, FG 2 = P(S)Ph 2 ) [ 36 ] and IIIb ((FG 1 = SO 2 Ph, FG 2 = P(NSiMe 3 )Ph 2 ) [ 43 ] have been determined. Methandiides IIIa and carbanion IIIb have in contrast to 2a a further lithium atom coordinating and stabilizing heteroatom-substituent.…”

“…An X-ray crystal structure analysis had shown a C i symmetric hexamer, ( 2a ) 6 ·Li 2 O·(THF) 6 , the dianionic C atoms of which are each coordinated by two Li atoms in a non-planar fashion (vide infra) [ 15 ]. Because of the general interest in dilithio methandiides that remains unabated to this day, crystal structure analysis has been carried out of a large number of derivatives [ 16 – 43 ]. They generally showed intricate aggregates with complex C–Li and C–Li–heteroatom chains, containing doubly lithiated C atoms.…”

“…They generally showed intricate aggregates with complex C–Li and C–Li–heteroatom chains, containing doubly lithiated C atoms. However, as much as there is now knowledge of the structure of dilithio methandiides in the crystal, as little is known about the structure and dynamics in solution [ 1 – 2 16 – 43 ]. The main obstacles at characterizing dilithio methandiides in terms of aggregate size, C–Li connectivity, Li coordination of the dianionic C atoms, and dynamics were poor solubility and problems to locate the 13 C signals of the dianionic C atoms or the detection of only broad ones.…”

Kudos and Renaissance of s-Block Metal Chemistry

“…In the recent past, increasing efforts have been undertaken to develop a sophisticated chemistry of these elements [19][20][21]. The chemistry of methanediides [22] and the relevance of secondary interactions [23], discussed in this Special Issue, may be viewed as representative examples. In contrast to lithium, the heavier homologous elements, sodium and potassium as well as calcium, are globally abundant, easily available, inexpensive and of low toxicity.…”