Crystal and molecular structures of six-coordinate germanium difluorides and dibromides containing lactamomethyl C,O-chelating ligands

Reaction of N-trimethylsilyl derivatives of amides and lactams with chloro(chloromethyl)dimethylstannane: Crystal and molecular structure of 1-(chlorodimethylstannylmethyl)-2-piperidone

“…Apparently, the increased local-symmetry distortion in 3b causes a variation in the crystal packing: while Si-3b and Ge-3b have similar crystal structures (space group P2 1 2 1 2 1 , corresponding unit cell dimensions differ by only 0.04-0.21 Å ), that of 3b is totally different (Pbca). This contrasts with the isomorphism observed in bis-N-lactamomethyl derivatives of hexacoordinate Ge and Sn dihalogenides [4,14].…”

Synthesis of the Elusive Branched Fluoro-oligogermane (Ph3Ge)3GeF: A Structural, Spectroscopic, Electrochemical, and Computational Study

“…A survey of the Cambridge Structural Database indicates that crystallographically characterized compounds containing a germanium–fluorine bond are somewhat uncommon, with only ca . 35 hits. − The Ge–F bond in Ph 3 GeF is 1.749(2) Å, and the other Ge–F distances that have been reported for organometallic germanium fluoride compounds range from 1.629(3) Å in ( o -Mes 2 C 6 H 3 ) 2 ­Ge­(H)­F to 1.839(2) Å in (3-Bu t -6-(OMe)­C 6 H 3 ) 3 ­CGeF 3 , although the zwitterionic complex pentafluoro­(4-methyl-1,4-diazonia­cyclohex-1-yl)­methyl­germanate has a Ge–F bond measuring 1.867(2) Å . Of the compounds reported, only [Ag 2 {C 6 H 3 -2,6-(C 6 H 3 -2,6-Pr i 2 ) 2 }­GeGe­(F)­{C 6 H 3 -(C 6 H 3 -2,6-Pr i 2 ) 2 }]­[SbF 6 ] contains a direct germanium–germanium single bond, but this is bridged by two silver atoms .…”

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

“…The solid-state structures of germanium dichlorides 4 − 6 (as well as analogous complexes of germanium 1 − 3 , 7 , 8 and tin 9 − 12 ) generally have a cis- orientation of two Ge←O coordination bonds and the Ge atom adopts a distorted octahedral geometry with the two carbon atoms in trans -positions (159.8−167.1°). 26a, In two nearly linear Cl−Ge←O fragments (170.6−175.0°) the Ge←O distances (2.09−2.24 Å) are longer than that of the sum of covalent radii (1.925 Å) and essentially less than the sum of van der Waals radii (3.67 Å). , In contrast to dichlorogermanes 4 − 6 , containing only one cis -diastereomer in solution, the NMR spectra of analogous lactamomethyl and amidomethyl dibromides ( 7 and 8 ) reveal the simultaneous existence of two diastereomers with cis - and trans -orientation of the Br atoms (and the Ge←O bonds too), which may be caused by the sterically overcrowded cis -GeBr 2 group, where the Br−Ge−Br angles in 7 are 96.2° ( a ), 95.1° ( b ), and 96.4° ( c ) 27a. The presence of a geminal interaction for Br atoms in the germanium coordination sphere probably excludes the existence of the hexacoordinate dianion GeBr 6 2- compared with the known GeCl 6 2- …”

“…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, …”

“…For dibromide complexes 7 and 8 , an exchange between the cis / trans -diastereomers takes place at higher temperatures (Δ G ⧧ = 15−16 kcal·mol -1 ), while enantiomerization is observed in the cis -diastereomers at lower temperatures (Δ G ⧧ = 10−12 kcal·mol -1 ) 27b. On the basis of the dependence of the activation energy for cis -diastereomers on the Ge←O bond length, a regular nondissociative mechanism of enantiomerization involving the formation of a neutral bicapped intermediate was anticipated 27b. At the same time, the authors suggest that the alternative twist mechanism may not be excluded (Scheme ).…”