A dipyrromethane-based diphosphane–germylene as precursor to tetrahedral copper(i) and T-shaped silver(i) and gold(i) PGeP pincer complexes

Abstract

A dipyrromethane-based PGeP germylene has allowed the synthesis of unusual tetrahedral copper(i) and T-shaped silver(i) and gold(i) germyl complexes.

The Transition Metal Chemistry of PGeP and PSnP Pincer Heavier Tetrylenes

“…Germylene XXX was prepared by treating GeCl 2 (diox) with the dilithiated form of the diphosphane (HpyrmP i Pr 2 ) 2 CMe 2 (Figure ), which was in turn synthesized in two steps from 5,5‐dimethyldipyrromethane, (HpyrH) 2 CMe 2 , by a synthetic method previously used to prepare other phosphane‐functionalized pyrroles and dipyrromethanes . Its XRD structure showed that the Ge atom is in a pyramidal arrangement attached to both pyrrolyl rings and to one phosphane group, but the compound is fluxional in solution, as it easily exchanges the pendant and the attached phosphane groups.…”

“…Germylene XXX reacted readily with [Cu 4 (µ 3 ‐Cl) 4 (PPh 3 ) 4 ] (1:1/4 mol ratio) to give the PPh 3 ‐containing derivative [Cu{κ 3 P , Ge , P ‐GeCl(pyrmP i Pr 2 ) 2 CMe 2 }(PPh 3 )] ( 39 ; Figure ); however, under similar reaction conditions, the silver(I) and gold(I) precursors [Ag 4 (µ 3 ‐Cl) 4 (PPh 3 ) 4 ] (1:1/4 mol ratio) and [AuCl(PPh 3 )] (1:1 mol ratio) led to the PPh 3 ‐free complexes [M{κ 3 P , Ge , P ‐GeCl(pyrmP i Pr 2 ) 2 CMe 2 }] (M = Ag ( 40 ), Au ( 41 ); Figure ) . Complex 41 was more conveniently prepared using [AuCl(tht)] as gold precursor, but intractable mixtures were formed when CuCl and AgCl were used as metal precursors.…”

“…Interestingly, while the coordination environment of the copper complex 39 is approximately tetrahedral (the Cu atom is also attached to a PPh 3 ligand), that of the silver ( 40 ) and gold ( 41 ) complexes is T‐shaped (both are isostructural). DFT and QTAIM calculations indicated that the bonding between the Ge and M atoms of 39 – 41 is a weak Ge→M donor‐acceptor interaction, the bond strength decreasing in the series 39 > 40 > 41 …”

“…This minireview collects and discusses the synthesis and transition metal derivative chemistry of the currently known metal‐free heavier tetrylenes having a PEP pincer topology (E = Ge, Sn; to date, no metal‐free PSiP and PPbP tetrylenes have been reported). Although it is a research field that has started to be investigated very recently (all contributions have been published in the last three years), it is already clear that PEP (E = Ge, Sn) pincer tetrylenes can be successfully synthesized by treating GeCl 2 (diox), GeCl 2 (NHC) or SnCl 2 with two equivalents of lithiated phosphine fragments (these reagents have been used to prepare XXV – XXXI ), and that they are excellent precursors to PEP halogenidotetryl metal complexes (as, for example, compounds 4 – 8 , 21 – 27 , 30 – 33 and 35 – 41 ) because the tetrylene E atom has a great tendency to get inserted into M–X bonds, being therefore useful alternatives to bis(phosphanyl)halogenidogermanes and ‐stannanes, which have so far been the only precursors to metal complexes containing PEP halogenidotetryl ligands. The very few reported reactions of PEP (E = Ge, Sn) pincer tetrylenes with metal complexes lacking halogenide ligands have rendered interesting PEP pincer metal derivatives (compounds 34 and 42 ).…”

“…It its noteworthy that they all have been described in the last three years. Our contributions (compounds XXV , XXVI , XXIX and XXX , 2017–2019) have been complemented with results produced by Goicoechea's (compounds XXVII and XXVIII , 2018) and Tobita's (compound XXXI , 2019) research groups.…”