Fluoro-Germanium Cations with Neutral Co-Ligands - Synthesis, Properties and Comparison with Neutral GeF[sub.4] Adducts

The reaction of [GeF[sub.4] L[sub.2] ], L = dmso (Me[sub.2] SO), dmf (Me[sub.2] NCHO), py (pyridine), pyNO (pyridine-N-oxide), OPPh[sub.3] , OPMe[sub.3] , with Me[sub.3] SiO[sub.3] SCF[sub.3] (TMSOTf) and monodentate ligands, L, in a 1:1:1 molar ratio in anhydrous CH[sub.2] Cl[sub.2] formed the monocations [GeF[sub.3] L[sub.3] ][OTf]. These rare trifluoro-germanium (IV) cations were characterised by microanalysis, IR, [sup.1] H, [sup.19] F{[sup.1] H} and, where appropriate, [sup.31] P{[sup.1] H} NMR spectroscopy. The [sup.19] F{[sup.1] H} NMR data show that in CH[sub.3] NO[sub.2] solution the complexes exist as a mixture of mer and fac isomers, with the mer isomer invariably having the higher abundance. The X-ray structure of mer-[GeF[sub.3] (OPPh[sub.3] )[sub.3] ][OTf] is also reported. The attempts to remove a second fluoride using a further equivalent of TMSOTf and L were mostly unsuccessful, although a mixture of [GeF[sub.2] (OAsPh[sub.3] )[sub.4] ][OTf][sub.2] and [GeF[sub.3] (OAsPh[sub.3] )[sub.3] ][OTf] was obtained using excess TMSOTf and OAsPh[sub.3] . The reaction of [GeF[sub.4] (MeCN)[sub.2] ] with TMSOTf in CH[sub.2] Cl[sub.2] solution, followed by the addition of 2,2′:6′,2”-terpyridine (terpy) formed mer-[GeF[sub.3] (terpy)][OTf], whilst a similar reaction with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me[sub.3] -tacn) in MeCN solution produced fac-[GeF[sub.3] (Me[sub.3] -tacn)][OTf]. Dicationic complexes bearing the GeF[sub.2] [sup.2+] fragment were isolated using the tetra-aza macrocycles, 1,4,7,10-tetramethyl-1,4,7,10-tetra-azacyclododecane (Me[sub.4] -cyclen) and 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane (Me[sub.4] -cyclam), which reacted with [GeF[sub.4] (MeCN)[sub.2] ] and two equivalents of TMSOTf to cleanly form the dicationic difluoride salts, cis-[GeF[sub.2] (Me[sub.4] -cyclen)][OTf][sub.2] and trans-[GeF[sub.2] (Me[sub.4] -cyclam)][OTf][sub.2] . The [sup.19] F{[sup.1] H} NMR spectroscopy shows that in CH[sub.3] NO[sub.2] solution there are four stereoisomers present for trans-[GeF[sub.2] (Me[sub.4] -cyclam)][OTf][sub.2] , whereas the smaller ring-size of Me[sub.4] -cyclen accounts for the formation of only cis-[GeF[sub.2] (Me[sub.4] -cyclen)][OTf], and is confirmed crystallographically. New spectroscopic data are also reported for [GeF[sub.4] (L)[sub.2] ] (L = dmso, dmf and pyNO). Density functional theory calculations were used to probe the effect on the bonding as fluoride ligands were sequentially removed from the ge