Monoanionic Tin Oligomers Featuring Sn–Sn Or Sn–Pb Bonds: Synthesis and Characterization of a Tris(Triheteroarylstannyl)Stannate and -Plumbate
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inorganics Communication Monoanionic Tin Oligomers Featuring Sn–Sn or Sn–Pb Bonds: Synthesis and Characterization of a Tris(Triheteroarylstannyl)Stannate and -Plumbate Kornelia Zeckert Institute of Inorganic Chemistry, University of Leipzig, Johannisallee 29, D-04103 Leipzig, Germany; [email protected]; Tel.: +49-341-9736-130 Academic Editor: Axel Klein Received: 20 May 2016; Accepted: 14 June 2016; Published: 20 June 2016 6OtBu 6OtBu Abstract: The reaction of the lithium tris(2-pyridyl)stannate [LiSn(2-py )3] (py = C5H3N-6-OtBu), 6OtBu 1, with the element(II) amides E{N(SiMe3)2}2 (E = Sn, Pb) afforded complexes [LiE{Sn(2-py )3}3] for E = Sn (2) and E = Pb (3), which reveal three Sn–E bonds each. Compounds 2 and 3 have been characterized by solution NMR spectroscopy and X-ray crystallographic studies. Large 1J(119Sn–119/117Sn) as well as 1J(207Pb–119/117Sn) coupling constants confirm their structural integrity in solution. However, contrary to 2, complex 3 slowly disintegrates in solution to give elemental lead 6OtBu and the hexaheteroarylditin [Sn(2-py )3]2 (4). Keywords: tin; lead; catenation; pyridyl ligands 1. Introduction The synthesis and characterization of catenated heavier group 14 element compounds have attracted attention in recent years [1–5]. However, contrary to silicon and germanium, there are limitations for tin and lead associated with the significant decrease in element–element bond energy. Hence, homonuclear as well as heteronuclear molecules with E–E bonds become less stable when E represents tin and or lead. Moreover, within this class of compounds, discrete branched oligomers with more than one E–E bond are rare compared with their linear analogs [6–10]. It has been shown that reactions of lead(II) halides with Grignard reagents involved disproportionation processes leading to plumbates of type [MgBr(THF)5][Pb(PbPh3)3][11] and [Mg(THF)3(µ-Cl)3Mg(THF)3][Pb(PbBp3)3] ´ (Bp = 4-Biphenyl) [12]. The formation of closely related anions [Sn(SnR3)3] (R = Me or Ph) was found as part of decomposition of corresponding stannyl anions in the presence of distannanes [13–16]. Further rare investigations included the reduction reaction of SnPh4 with elemental lithium in liquid ammonia to give [Li(NH3)4][Sn(SnPh3)3][17] or reactions of the organotin chlorides SnPh2Cl2 as well as SnMe3Cl with lanthanoid metals, yielding complexes [Yb(DME)3Cl]2[Sn(SnPh3)3]2 [18] and [Ln(THF)4{Sn(SnMe3)3}2] (Ln = Sm, Yb) [19]. Complete structural characterizations, however, are missing due to the very low solubility and sensitivity of all compounds reported. Recently, conventional salt metathesis reactions have been employed for synthesis of i neutral distannylstannylene species Sn(SnAr3)2 (Ar = C6H3-2,6-(O Pr)2)[20] and Sn(SnPh2Ar*)2 i (Ar* = C6H3-2,6-(Trip)2, Trip = C6H2-2,4,6- Pr3)[21], bearing a divalent tin atom bonded to two triarylstannyl groups. In both cases, the catenation was implemented by a stannyl lithium derivative LiSnAr3 or LiSnPh2Ar*, respectively. Our studies on related triheteroaryltin(II) compounds revealed a R R diverse reactivity. Thereby, it was found that compounds [Li(THF)Sn(2-py )3] (py = C5H3N-5-Me or C5H3N-3-Me), in which the lithium cation is well embedded within the tris(pyridyl)stannate core, can either act as a two-electron donor leading to a tin–element bond formation [22,23] or may be used for salt metathesis reactions with the lone pair of electrons at the tin(II) atom remaining available [24]. Inorganics 2016, 4, 19; doi:10.3390/inorganics4020019 www.mdpi.com/journal/inorganics Inorganics 2016, 4, 19 2 of 8 Inorganics 2016, 4, 19 2 of 8 used for salt metathesis reactions with the lone pair of electrons at the tin(II) atom remaining available [24]. ContinuingContinuing thesethese studies,studies, itit isis nownow shown that that the the reaction reaction between between the the lithium lithium tris(2-pyridyl)stannate [LiSn(2-py6O6OttBu)3] (py6O6OtButBu = C5H3N-6-OtBu), 1, with group 14 element(II) tris(2-pyridyl)stannate [LiSn(2-py )3] (py = C5H3N-6-OtBu), 1, with group 14 element(II) amides E{N(SiMe3)2}2 (E = Sn or Pb) lead to the straight formation of the lithium salts amides E{N(SiMe3)2}2 (E = Sn or Pb) lead to the straight formation of the lithium salts [LiSn{Sn(2-py6OtBu)3}3] (2) and [LiPb{Sn(2-py6OtBu)3}3] (3) each with the lithium cation intramolecularly [LiSn{Sn(2-py6OtBu) } ](2) and [LiPb{Sn(2-py6OtBu) } ](3) each with the lithium cation intramolecularly coordinated by the3 3novel tris(stannyl)metallate en3 abled3 through the unique donor functionality of coordinated by the novel tris(stannyl)metallate6OtBu − enabled through6OtBu the unique− donor functionality of the the complex anion [Sn{Sn(2-py6OtBu )3´}3] as well as [Pb{Sn(2-py6OtBu)3}3] itself.´ complex anion [Sn{Sn(2-py )3}3] as well as [Pb{Sn(2-py )3}3] itself. 2. Results 2. Results Compounds 2 and 3 have been prepared in reactions of the lithium stannate 1 upon addition of Compounds 2 and 3 have been prepared in reactions of the lithium stannate 1 upon addition of tin(II) or lead(II) amide E{N(SiMe3)2}2 (E = Sn, Pb) in a 3:1 stoichiometry (Scheme 1). The initial yellow tin(II)THF or solution lead(II) of amide 1 gradually E{N(SiMe changed3)2}2 (E to= a Sn,reddish-brownish Pb) in a 3:1 stoichiometry solution of (Scheme2 and a green1). The solution initial yellowof 3. THFThe solution complexes of 1 weregradually obtained changed as the only to a products reddish-brownish in good isolated solution yields of 2 asand colorless a green (2) solution as well as of 3. Theyellow complexes (3) crystalline were obtained material as upon the only work products up and inre-cry goodstallization isolated yieldsfrom toluene as colorless or benzene. (2) as wellIt is as yellowlikely ( 3that) crystalline neutral E{Sn(2-py material upon6OtBu)3} work2 was up initially and re-crystallization generated. However, from toluenethis molecule, or benzene. which It could is likely 6OtBu thatneither neutral be E{Sn(2-pyisolated nor detected,)3}2 was may initially have generated.then reacted However, further with this another molecule, equiv which of 1 couldto give neither the belithium isolated complexes nor detected, 2 or 3 may, respectively, have then by reacted virtuefurther of a donor– withacceptor another interaction equiv of 1 betweento give thetwo lithium low complexesvalent group2 or 314, respectively, element species. by virtue This of may a donor–acceptor be explained interactionwith the less between steric requirement two low valent of groupthe 14pyridyl element ligand species. as This well may as bethe explained pronounced with two-electron the less steric donor requirement ability of the1 comparable pyridyl ligand to other as well astris(2-pyridyl)stannates the pronounced two-electron [22–24]. donor ability of 1 comparable to other tris(2-pyridyl)stannates [22–24]. SchemeScheme 1. 1. IllustrationIllustration of ofthe thepossible possible reaction reaction pathway pathway to give compounds to give compounds 2 and 3; with2 pyandR = py3;6O withtBu R 6OtBu py= C=5H py3N-6-O=tBu. C5 H3N-6-OtBu. Indeed, the molecular structures of complexes 2 and 3 (Figure 1, Table 1) imply the donation of Indeed, the molecular structures of complexes 2 and 3 (Figure1, Table1) imply the donation of a lithium stannate fragment to the central element(II) atom of a E{Sn(2-py6OtBu)3}2 molecule due to the a lithium stannate fragment to the central element(II) atom of a E{Sn(2-py6OtBu) } molecule due to intramolecular N-coordination of the lithium cation by only one tris(2-pyridyl)stannyl3 2 unit in 2 and 3 theas intramolecular found for previouslyN-coordination reported tris(2-pyridyl)stannate of the lithium cation complexes by only one [22–25]. tris(2-pyridyl)stannyl Thus, compounds unit2 and in 2 and3 can3 as be found described for previously as zwitter-ionic reported complexes tris(2-pyridyl)stannate with a Li···Sn separation complexes of [3.339(14)22–25]. Thus, Å in 2 compounds as well as 2 and3.321(10)3 can be Å described in 3. as zwitter-ionic complexes with a Li¨ ¨ ¨ Sn separation of 3.339(14) Å in 2 as well as 3.321(10)In complex Å in 3. 2, the central Sn atom adopts a trigonal pyramidal geometry with Sn–Sn(1)–Sn anglesIn complex of 92.52(2),2, 93.22(2), the central and Sn96.13(2)°. atom adoptsThe Sn–Sn a trigonal bond lengths pyramidal range from geometry 2.8127(7) with to 2.8217(6) Sn–Sn(1)–Sn Å ˝ anglesand lie of well 92.52(2), within 93.22(2), the previously and 96.13(2)known rang. Thee (2.811–2.836 Sn–Sn bond Å) for lengths complexes range of the from [Sn(SnPh 2.8127(7)3)3]– to 2.8217(6)anion [16–19] Å and but lie are well considerably within the shorter previously than those known found range for (2.811–2.836the distannylstannylenes Å) for complexes Sn(SnAr of3) the2 – i [Sn(SnPh(Ar = 3C)36H] 3anion-2,6-(O [Pr)16–219) (2.86] but areÅ) considerably[20] as well shorteras Sn(SnPh than2 thoseAr*)2 found(Ar* = for C the6H3-2,6-(Trip) distannylstannylenes2, Trip = i i Sn(SnArC6H2-2,4,6-3)2 (ArPr3) = (2.96 C6H Å)3-2,6-(O [21]). ThePr)2 geometry) (2.86 Å) at [20 Sn(2),] as wellwhos ase interligand Sn(SnPh2Ar*) angles2 (Ar* vary = from C6H 393.8(2)°-2,6-(Trip) to 2, i Trip132.5(2)°, = C6H2 -2,4,6-is strikinglyPr3) (2.96 distorted Å) [21 from]).