Neutral and cationic germanium(iv) fluoride complexes with phosphine coordination – synthesis, spectroscopy and structures

The neutral complexes trans-[GeF4(PiPr3)2] and [GeF4(κ2-L)] (L = CH3C(CH2PPh2)3 or P(CH2CH2PPh2)3) are obtained from [GeF4(MeCN)2] and the ligand in CH2Cl2. Treatment of [GeF4(PMe3)2] with n equivalents of TMSOTf (Me3SiO3SCF3) leads to formation of the series [GeF4-n(PMe3)2(OTf)n] (n = 1, 2, 3), each of which contains six-coordinate Ge(IV) with trans PMe3 ligands and X-ray structural data confirm that the OTf groups interact with Ge(IV) to varying degrees. Unexpectedly, [GeF3(PMe3)2(OTf)] undergoes reductive defluorination in solution, forming the Ge(II) complex, [Ge(PMe3)3][OTf]2 (and [FPMe3]+). The bulkier PiPr3 leads to formation of the ionic [GeF3(iPr3P)2][OTf], containing a [GeF3(iPr3P)2]+ cation. [GeF4{o-C6H4(PMe2)2}], containing the cis-chelating diphosphine, also reacts with n equivalents of TMSOTf to generate [GeF4-n{o-C6H4(PMe2)2}(OTf)n] (n = 1, 2, 3). As for the PMe3 system, the trifluoride, [GeF3{o-C6H4(PMe2)2}(OTf)], is unstable to reductive defluorination in solution, producing the pyramidal Ge(II) complex [Ge{(o-C6H4(PMe2)2}(OTf)][OTf], whose crystal structure has been determined. The [GeF3{Ph2P(CH2)2PPh2}(OTf)] and [GeF2{Ph2P(CH2)2PPh2}(OTf)2], obtained similarly from the parent tetrafluoride complex, are poorly soluble, however their structures were confirmed crystallographically. The complexes in this work have been characterised via variable temperature 1H, 19F{1H} and 31P{1H} NMR studies in solution, IR spectroscopy and microanalysis and through single crystal X-ray analysis of representative examples across each series. Trends in the NMR and structural parameters are also discussed.