Synthesis and some coordination chemistry of the PSnP pincer-type stannylene Sn(NCH2PtBu2)2C6H4, attempts to prepare the PSiP analogue, and the effect of the E atom on the molecular structures of E(NCH2PtBu2)2C6H4 (E = C, Si, Ge, Sn)

Abstract

The non-donor-stabilized PSnP pincer-type stannylene Sn(NCH₂P^tBu₂)₂C₆H₄ (1) has been prepared by treating SnCl₂ with Li₂(NCH₂P^tBu₂)₂C₆H₄. All attempts to synthesize the analogous PSiP silylene by reduction of the (previously unknown) silanes SiCl₂(NCH₂P^tBu₂)₂C₆H₄ (2), SiHCl(NCH₂P^tBu₂)₂C₆H₄ (3) and SiH(HMDS)(NCH₂P^tBu₂)₂C₆H₄ (4; HMDS = N(SiMe₃)₂) have been unsuccessful. The almost planar (excluding the tert-butyl groups) molecular structure of stannylene 1 (determined by X-ray crystallography) has been rationalized with the help of DFT calculations, which have shown that, in the series of diphosphanetetrylenes E(NCH₂P^tBu₂)₂C₆H₄ (E = C, Si, Ge, Sn), the most stable conformation of the compounds with E = Ge and Sn has both P atoms very close to the EN₂C₆H₄ plane, near (interacting with) the E atom, whereas for the compounds with E = C and Si, both phosphane groups are located at one side of the EN₂C₆H₄ plane and far away from the E atom. The size of the E atom and the strength of stabilizing donor–acceptor P⋯E interactions (both increase on going down in group 14) are key factors in determining the molecular structures of these diphosphanetetrylenes. The syntheses of the chloridostannyl complexes [Rh{κ²Sn,P-SnCl(NCH₂P^tBu₂)₂C₆H₄}(η⁴-cod)] (5), [RuCl{κ²Sn,P-SnCl(NCH₂P^tBu₂)₂C₆H₄}(η⁶-cym)] (6) and [IrCl{κ²Sn,P-SnCl(NCH₂P^tBu₂)₂C₆H₄}(η⁵-C₅Me₅)] (7) have demonstrated the tendency of stannylene 1 to insert its Sn atom into M–Cl bonds of transition metal complexes and the preference of the resulting PSnP chloridostannyl group to act as a κ²Sn,P-chelating ligand, maintaining an uncoordinated phosphane fragment. X-ray diffraction data (of 6), ³¹P{¹H} NMR data (of 5–7) and DFT calculations (on 6) are consistent with the existence of a weak P⋯Sn interaction involving the non-coordinated P atom of complexes 5–7, similar to that found in stannylene 1.