Synthesis and some coordination chemistry of the PSnP pincer-type stannylene Sn(NCH₂P^tBu₂)₂C₆H₄, attempts to prepare the PSiP analogue, and the effect of the E atom on the molecular structures of E(NCH₂P^tBu₂)₂C₆H₄ (E = C, Si, Ge, Sn)

Abstract

The non-donor-stabilized PSnP pincer-type stannylene Sn(NCH2PtBu2)2C6H4 (1) has been prepared by treating SnCl2 with Li2(NCH2PtBu2)2C6H4. All attempts to synthesize the analogous PSiP silylene by reduction of the (previously unknown) silanes SiCl2(NCH2PtBu2)2C6H4 (2), SiHCl(NCH2PtBu2)2C6H4 (3) and SiH(HMDS)(NCH2PtBu2)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(NCH2PtBu2)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 PE 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(NCH2PtBu2)2C6H4}(η4-cod)] (5), [RuCl{κ2Sn,P-SnCl(NCH2PtBu2)2C6H4}(η6-cym)] (6) and [IrCl{κ2Sn,P-SnCl(NCH2PtBu2)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 PSn interaction involving the non-coordinated P atom of complexes 5-7, similar to that found in stannylene 1.

The Transition Metal Chemistry of PGeP and PSnP Pincer Heavier Tetrylenes

“…Germylene XXV and stannylene XXVI were prepared by stepwise treating diamine o ‐{N(H)CH 2 P t Bu 2 } 2 C 6 H 4 with LiBu (Bu = n ‐butyl) and GeCl 2 (diox) (diox = 1,4‐dioxane) or SnCl 2 , respectively (Figure ), following an analogous procedure previously used to synthesize bis(phosphane)boranes and ‐silanes , …”

“…Interestingly, the X‐ray diffraction (XRD) structures of XXV and XXVI demonstrated that both molecules have the P atoms in the plane defined by the EN 2 C 6 H 4 scaffold, at short distances from the corresponding E atom (3.320(2) Å and 3.320(2) Å for XXV ; 3.277(1) Å and 3.313(1) Å for XXVI ). DFT calculations, indicated a weak (but non‐negligible) overlap between the lone pair of each P atom and an antibonding σ*(E–N) orbital. The particular structures of these tetrylenes seem to be forced by the short length of their CH 2 P t Bu 2 side arms, which prevents a “normal” intramolecular donor–acceptor interaction between the lone pair of one P atom and the empty perpendicular p orbital of the E atom.…”

“…Stannylene XXVI was the first PSnP pincer‐type stannylene to be studied as a ligand in transition metal chemistry . The syntheses of the chloridostannyl complexes [RuCl{κ 2 P , Sn ‐SnCl(NCH 2 P t Bu 2 ) 2 C 6 H 4 }( p ‐cym)] ( p‐ cym = p‐ cymene; 25 ), [IrCl{κ 2 P , Sn ‐SnCl(NCH 2 P t Bu 2 ) 2 C 6 H 4 }(Cp*)] (Cp* = pentamethylcyclopentadienyl; 26 ) and [RhCl{κ 2 P , Sn ‐GeCl(NCH 2 P t Bu 2 ) 2 C 6 H 4 }(cod)] ( 27 ) from the corresponding chlorido‐bridged dimers (Figure ) have demonstrated the tendency of stannylene XXVI to get inserted into M–Cl bonds and the preference of the resulting PSnP chloridostannyl group to act as a κ 2 P , Sn ‐chelating ligand, maintaining an uncoordinated phosphane group.…”

“…It its noteworthy that they all have been described in the last three years. Our contributions (compounds XXV , XXVI , XXIX and XXX , 2017–2019) have been complemented with results produced by Goicoechea's (compounds XXVII and XXVIII , 2018) and Tobita's (compound XXXI , 2019) research groups.…”

“…In 2016, stimulated by the above‐commented very interesting features of both HTs and pincer ligands, by the absence of metal‐free pincer ligands having an HT as the central donor group of the pincer framework, and taking advantage of our experience working with HTs,[2f], [2g], , , , [9b], [22a], [22b], our research group embarked the pincer‐type HT ship by preparing the first germylene and stannylene flanked by two phosphane groups. Phosphanes were chosen as side donor groups because, in addition to having excellent properties as ligands (they can be bulky and strong electron donors), they facilitate the monitoring of their reactions (by 31 P NMR).…”