ortho-Bis(cyanomercurio)tetrafluorobenzene as a Bidentate Lewis Acid Co-catalyst in the Cyanosilylation of Benzaldehyde

Reaction of o -C 6 F 4 (HgCl) 2 ( 1 ), m -C 6 F 4 (HgCl) 2 ( 2 ), C 6 F 5 HgCl ( 3 ), and C 6 F 4 H(HgCl) ( 4 ) with TMSCN in MeCN affords the corresponding organomercury cyanide derivatives o -C 6 F 4 (HgCN) 2 ( 5 ), m -C 6 F 4 (HgCN) 2 ( 6 ), C 6 F 5 HgCN ( 7 ), and C 6 F 4 H(HgCN) ( 8 ), respectively. These compounds have been characterized by elemental analysis, 1 H, 13 C, 19 F, and 199 Hg NMR, and IR spectroscopy. The infrared spectra of 5 − 8 display a cyanide stretching band in the range 2170−2183 cm - 1, while their 199 Hg NMR chemical shifts are all within the range −1170 to −1250 ppm. The crystal structures of [ 2· DMF], [ 5· MeCOH], [ 5· PhCOH], and 8 have been determined. In [ 2· DMF], the DMF molecule acts as a terminal ligand and coordinates one of the mercury centers through the formation of a Hg−O bond of 2.746(14) Å. A similar situation is encountered in [ 5· MeCOH] and [ 5· PhCOH], wherein the aldehyde ligand is terminally ligated to one of the mercury centers through a Hg−O bond of 2.855(19) and 3.009(12) Å, respectively. In these compounds, the neighboring molecules engage in long intermolecular Hg···N contacts. In [ 5· MeCOH], these interactions lead to the formation of a hexameric aggregate whose shape is reminiscent of a capsule. The ability of 5 − 8 to catalyze the cyanosilylation of benzaldehyde has been studied. While little or no product formation is observed when the pure cyanide derivatives 5 − 8 are employed as catalysts, their combination with TMSCl leads to the formation of active catalytic species. The combination of bidentate 5 and TMSCl provides the most active system. The results are rationalized on the basis of a working model in which TMSCl is activated by the halophilic bidentate fluorinated mercury derivative 5, which produces a catalytically active Lewis acidic silicon species.