Synthesis and crystal and molecular structures of six-coordinate tin dibromides and diiodides containing lactamomethyl C,O-chelating ligands

Abstract

New (O--Sn)-bischelate bis(lactamomethyl)dibromo-and -diiodostannanes [L(n)I2SnX 2 (L is the bidentate lactamomethyt C,O-chelating ligand: n is the size of the lactam ring, 5--7; X = Br or 1) were prepared both by the direct method from metallic tin and the corresponding N-(halomethyl)lactams and by the reactions of dichlorides [k(n)]2SnCI 2 with lithium halides. According to the data of X-ray diffraction analysis, the tin atom in {L(n)I2SnBr2 (n = 5--7) and [L(nqzSnl2 (n = 5 or 6) adopts an octahedral configuration with the carbon atoms in trans positions and the coordinating oxygen and halogen atoms in cispositions with respect to each other. A comparison with the structures of analogous lactamomethyl halide derivatives of Give-and six-coordinate Si, Ge. and Sn demonstrates that the spatial structures of the hypetwalent fragments containing six-coordinate atoms are less sensitive to the replacement of the halide ligands and the central atom. The covalence of the M--Hal bond increases and the covalence of the M--O bond decreases in the series M = Si, Ge, and Sn.Key words: six-coordinate tin compounds, synthesis, multinuclear N MR spectroscopy. X-ray diffraction study.Recentl3/~ we l~ave perforrfled sy~femati~ StudiesO1 s-ix= coordinate silicon, germanium, and tin compounds containing the amidomethyl and related C,O-chelating ligands. !-4 These studies were an extension of investigations of analogous five-coordinate silicon 5,6 and germanium 7,8 derivatives. One of the major lines of investigation of the characteristic features of these compounds involves the elucidation of the properties of three-center hypervalent X--:M::Y-bonds, where-Mis an atom with-an increased coordination number (Si, Ge, or Sn) and X and Y are electronegative atoms or groups (N--C=O, Hal, OTf, etc.).Investigations of tin derivatives as compounds containing six-coordinate atoms allow one to reveal the effects of the involvement of the M atom simultaneously in two hypervalent bonds and to follow the dependence of the properties of these bonds in the series M = Si, Ge, and Sn.

Stereochemical Flexibility of Bis(amidomethyl)dichlorogermanes. A Novel Dissociative Mechanism of Ligand Exchange in Neutral Hexacoordinated Bischelate Complexes

“…It is therefore evident that the smaller influence of halogen changes on the Δ G # values and smaller influence of chelate ligand structure on the coordination bonds are the result of the stronger intramolecular Sn←O interaction in hexacoordinate tin complexes 9 − 11 compared to germanium complexes 4 − 7 . Besides, the differences between the two cis -(M←O) bond lengths in the molecules of germanium dichlorides 4 ( a − c ),26a Δ d (Ge←O) = 0.056 Å ( a ), 0.127 Å ( b ), and 0.024 Å ( c ), are greater compared to Δ d (Sn←O) = 0.040 Å ( a ), 0.009 Å ( b ), and 0.023 Å ( c ) for tin dichlorides 9 ( a − c ),28b which can be ascribed to the smaller influence of the crystal packing effects 76b, on much stronger coordinate Sn←O bonds.…”

“…In the tin complexes 9 ( a − c ) and 11 ( a − c ), the larger vicinal tin coupling constants for the cyclic methylene carbons, 3 J ( 119 Sn−C−N− 13 CH 2 ) = 82.2−99.3 Hz, than for the carbonyl groups, 3 J ( 119 Sn−C−N− 13 CO) = 21.4−29.7 Hz, and the absence of 3 J ( 119 Sn←OC− 13 C) coupling, were suggested to originate from a direct coupling pathway through the covalent Sn−C−N−C bonds, while the contribution through the coordination bond is very weak or even absent. 28b, Consequently, the observation of coupling constants between the tin and the carbonyl group is not in contrast to ligand-site exchange processes involving the dissociation of the coordinate bond in tin complexes 9 and 11 .…”

“…The symmetrically substituted cis- coordinated bischelate germanium difluorides 1 − 3 , dichlorides 4 − 6 , and dibromides 7 and 8 , as well as their tin analogues 9 − 12 , have no chiral center, but get an element of chirality by virtue of an enantiomeric arrangement of ligands about the metal. In a solution of these derivatives, a dynamic equilibrium including ligand-site exchange is observed, and fluxional processes were discussed with respect to the analysis of various types of possible mechanisms. 27b, However, it remains to be determined whether the mechanism of the enantiomerization is due to the Ge←O bond rupture or not. 27b, …”

Halogen exchange in complexes of hexacoordinate tin (LnCH2)2SnX2 and (LnCH2)2SnY2 containing lactamomethyl n-membered C,O-chelate ligands LnCH2 (n=5–7; X, Y = Cl, Br, I)

“…In contrast to germanium complexes, the reaction of organotin dichlorides cis-(L n CH 2 ) 2 SnCl 2 with lithium halides produces structurally similar cis-dihalides (L n CH 2 ) 2 SnX 2 (X = Br, I) [13,17]. An attempt to synthesise a monosubstituted product with trans-configuration of monodentate ligands by the reaction of [L 5 CH 2 ] 2 SnCl 2 with AgBF 4 was unsuccessful and led to a dinuclear cationic complex 1 as a result of partial hydrolysis [18].…”

“…The synthesis, structure, and spectra of initial homodihalides (L n CH 2 ) 2 SnX 2 (X = Cl, Br, I) have been reported in review [13] and research papers [17,20].…”