CH–NH Tautomerism in the Products of the Reactions of the Methanide [HC(PPh₂NSiMe₃)₂]⁻ with Pnictogen and Tellurium Iodides

Abstract

The reactions of K[HC(PPh2NSiMe3)2] (K[1]) and MI3 (M = As, Sb) or TeI4 gave as the major products the complexes [{MI n }{C(PPh2NSiMe3)(PPh2NHSiMe3)}] (MI n = trans-AsI2, trans- or cis-SbI2, TeI3), which feature the ligand [C(PPh2NSiMe3)(PPh2NHSiMe3)]− (2). This anion, the NH tautomer of [HC(PPh2NSiMe3)2]−, is formally generated by a 1,3-hydrogen shift to give complexes in which the ligand is N,C-chelated to the main-group-metalloid center. The M–C distances are slightly longer than the sum of the covalent radii for M and C in the case of the group 15 metalloids but significantly shorter for M = Te. The arsenic derivative [{t-AsI2}2] is monomeric in the solid state, with As–I distances that differ by ca. 0.55 Å, whereas the antimony analogues [{t-SbI2}2] and [{c-SbI2}2] are dimeric through bridging iodide ligands and the disparity in Sb–I distances of the SbI2 units is 0.10 and 0.33 Å, respectively. The tellurium derivative [{TeI3}2] is monomeric with a distorted-square-pyramidal geometry at the Te center and Te–I distances in the narrow range 2.9142(4)–3.0337(4) Å. In contrast to the lighter pnictogens, the bismuth complex [{t-BiI2}1] is comprised of the methanide 1 coordinated in a tridentate (N,C,N) mode to a BiI2 + cation. In the case of arsenic triiodide, the metathesis is accompanied by Si–N bond cleavage to give [{AsI2}{CH2(PPh2N)(PPh2NSiMe3)}] (3), which was characterized by 31P NMR spectroscopy, and conversion to the corresponding salt [{AsI}{CH2(PPh2N)(PPh2NSiMe3)}][SbF6] (3A) by treatment with AgSbF6. The As–N distances in the six-membered CP2N2As ring in 3A differ by 0.20 Å due to the different coordination numbers (2 and 3) of the two N atoms in the novel N,N′-chelated [CH2(PPh2N)(PPh2NSiMe3)]− anion. In contrast, reaction of [{t-SbI2}2] with AgSbF6 gives the expected salt as the dimer {[{SbI}2][SbF6]}2. The two hydrolysis products [CH2(PPh2NSiMe3)(PPh2NHSiMe3)][SbF6] (4A) and [CH2(PPh2NSiMe3) (PPh2NHSiMe3)]2[Te2I6] (4B) were also structurally characterized and shown to contain the same cation. DFT calculations indicate that the N–H tautomer 2 is stabilized by strong M–N and M–C bonding interactions which include a small degree of π character. Weaker bonds, as in the Bi complex, favor the C–H tautomer 1 as the ligand.

Heavy Group 15 Element Compounds of a Sterically Demanding Bis(iminophosphorane)methanide and -methanediide

“…Such a proton shift can be seen as a P analogue of the known imine−enamine tautomerism and has been described by most recent works published in the course of the preparation of this paper. 5 On consideration of the Lewis acidity of a coordinated element halide fragment to cause a proton shift, it is interesting that for smaller elements with potentially more Lewis acidic fragments such as [AlCl 2 ] + , [AlBr 2 ] + , and [GaCl 2 ] + , a N,Nchelating coordination mode forming a six-membered ring is adopted and no proton shift occurs. 4d,7 A somehow comparable shift has already been described for neutral bis-(iminophosphorane)methane ligands coordinating to transition m e t al s ( R h , I r , P t ) .…”

“…The coordination geometry around bismuth in 2 as well as around antimony in 3 represents a distorted seesaw analogous to the reported "cis"-type complexes found for the trimethylsilyl-substituted derivatives, in which the [EX 2 ] + fragment features a bent alignment. 5 On the basis of a sole X-ray structure Chivers and Vargas-Baca et al found a symmetrically N,C,N-chelating coordination type for an almost linear [BiI 2 ] + fragment and applied quantum mechanical calculations to provide an explanation for the absence of the intramolecular 1,3-proton shift in the case of bismuth. In their findings the generally energetically favored CH tautomer of the ligand is overcompensated by a stabilizing interaction energy between the ligand anion and the metal fragment (for which only a linear arrangement was considered).…”

“…2a,c,4 In the course of the preparation of this paper, complexes of the monoanionic N-trimethylsilyl system with [EI 2 ] + (E = As, Sb, Bi) have been reported. 5 Bi and Sb compounds of the related dianionic bissulfido system bis(diphenylsulfidophosphorane)methane, [ECl{C(Ph 2 PS) 2 }] (E = Sb, Bi), have also been forthcoming, as well as complexes of the structurally related mono-and dianionic N-dipp-substituted diketiminates (nacnac) with bismuth chloride. 3,6 We have investigated the coordination chemistry of bis-(diphenyl(arylimino)phosphorane)methane systems toward the heavy group 15 elements bismuth and antimony, applying the bulky N-bonded dipp residue H 2 C(Ph 2 PNdipp) 2 (1).…”

Synthesis of a Molecule with Four Different Adjacent Pnictogens

“…Additionally, to the best of our knowledge, there is no species with four different pnictogens in one heterocycle. There are four reports on compounds including all four of the pnictogens N, P, As, and Sb, but among these, only [ClAs{μ‐(N‐PMe 3 ) 2 }SbCl 4 ] investigated by Dehnicke et al., is a molecular species …”

“…There are four reports on compounds including all four of the pnictogensN ,P ,As,a nd Sb, but among these, only [ClAs{m-(N-PMe 3 ) 2 }SbCl 4 ]i nvestigated by Dehnicke et al,i s am olecular species. [20][21][22][23] Recently,w ep repared the four-membered heterocycles [ClE(m-PTer)] 2 containing the heavy pnictogensE = P, As, Sb, Bi. [24] It is known that the supermesityl (Mes*)s ubstituent stabilize the monomeric species better than the dimer in heterocycles such as [ClE(m-NTer)] 2 compared to the terphenyls ubstitu-Scheme1.Synthesis of all pnictogen four-membered heterocycles.Scheme2.Selectedknown all pnictogen anionic analogs of allyl species.[a]Supporting information and ORCID(s)f rom the author(s) for this articleare available on the WWW under http://dx.…”