Three‐coordinate divalent Group 14 element derivatives and related compounds

Abstract

INTRODUCTIONThis paper is an overview of a particular part of our systematic investigation of the divalent germanium and tin species focusing on the use in this chemistry of a β-diketiminato ligand with no encumbering aryl groups on the nitrogen. The bidentate three-atom bridging ligand L 2 (L 2 = PhNC(Me)CHC(Me)NPh), by its remarkable stabilizing properties, allows for easy isolation of subvalent germanium and tin compounds and, as such, permits a general insight on the chemistry of such species. The emphasis here will be on the divalent species L 2 (X)M (M = Ge, Sn), the germanechalcogenones L 2 (Cl)Ge Y, the transition- L (n−x) and the cationic ger- IntroductionThe divalent species of Group 14 elements are the heavier carbene analogues; for recent reviews, see Refs 6-10. They are generally transient species. As a general rule, when these species contain unfunctionalized organic ligands, they undergo rapid oligomerization and polymerization. In the last two decades, two principal methods of stabilization have been particularly investigated. Thus, various kinetically and/or thermodynamically stabilized divalent germanium and tin compounds have been isolated in a monomeric state. 1 -5,11 -81 The use of bulky groups bound to the Group 14 element to prevent aggregation permitted the first syntheses of stable monomer divalent species; the most noticeable are the dialkyl-germylene and -stannylene reported by Lappert and co-workers, 12 the first stable monomeric arylgermylene ((Mes * ) 2 Ge (Mes * = 2,4,6-t Bu 3 -phenyl)) described by Du Mont and co-workers, 14 and the well-known aryl-germylene and -stannylene Tbt(Tip)M 14 (M 14 = Ge, Sn; Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Tip = 2,4,6-i Pr 3 -phenyl) of Okazaki and co-workers. 25,29The ligand backbone may also play an important role in improving stability. Thus, the presence of ligands with donor side arms on the germanium or the tin element can (by transfer of electron density) reduce the deficit on 37 is, to our knowledge, the first example of an intramolecular base stabilized homoleptic dialkylgermylene. Various amino-, phosphino-, thioalkoxy-, alkoxy-and aryloxy-divalent species have also been isolated in monomeric form owing to this method of stabilization; one should mention in particular the studies of Jutzi and co-workers, 28,32,54,71 Veith and coworkers, 15,18,40,66 Parkin and co-workers, 67 Jurkschat and co-workers, 77,78 Dias and co-workers 31,35,42,69,80,81 and Roesky and co-workers. Main Group Metal Compounds -5Although a large number of homoleptic divalent germanium and tin species have been isolated using these concepts of stabilization, there are fewer examples of heteroleptic compounds having been reported, though the first functional heteroleptic germylenes R(Cl)Ge (R = Et, Ph) were obtained as viscous oils in the 1970 by our group.6 Few solidstate structures of such heteroleptic compounds have been described. Noteworthy examples are in the area of thermodynamic stabilization, the acetylacetonatogermylene R(I)Ge (R = OC (Me) 46...

Silylenes and germylenes: The activation of H–H bond in hydrogen molecule

“…Silylenes and germylenes [71][72][73][74][75][76][77][78][79][80][81][82][83][84], the heavier analogues of carbenes [85][86][87], are important species in numerous thermal and photochemical reactions . Similar to carbenes, most of silylenes and germylenes can function as Lewis acid or Lewis base, in which the vacant p orbital is responsible for electrophilic character (Lewis acid), while the non-bonding electron pair can act as the nucleophilic (Lewis base) attack region [77].…”

Reactions of some organogermanium(II) chlorides

“…Moreover, reaction of 14 with an equivalent amount of Using the ␤-diketiminato ligand, Barrau and coworkers investigated the possibility of isolating cationic germanium(II)-transition metal complexes [15,16] (Scheme 6). Though the novel cationic germanium(II) compound [{( i Pr) 2 ATI}]Ge[CpZrCl 2 (-Cl) 3 ZrCl 2 Cp] (29) was prepared by Dias and co-workers [18], no studies have dealt with cationic germanium(II)-transition metal complexes.…”

Can N-heterocyclic germylenes behave as Lewis acids - is there another side to Meller germylenes?

“…Whereas Meller germylenes are divalent and dicoordinate heterocycles with two normal covalently bonded nitrogen atoms, there are NHGe that are tricoordinate and derived from the closely related monoimino germylene system. Examples of this include amidinates [17], aminotroponiminates [18] and ß-diketiminates [19,20] (see Scheme 2). They form ring systems with an even number of ring members (amidinates 4; ß-diketiminates 6; aminotroponiminates 10) and thus have to form a N-Ge normal covalent and a N-Ge coordinative bond in order to maintain a fully conjugated double bond system in the ring.…”

“…The chlorine atom is usually loosely bonded and can be abstracted by reaction with a chloride scavenger like a silver salt yielding a cationic species [6]. This cationic germylene is considerably planarised, but usually coordinates to the "noncoordinating" anion [20].…”

“…Their "empty" germanium p-orbitals can no longer be filled sufficiently by p-interaction with the adjacent nitrogen atoms (they have already partial donor bond character in the neutral molecules). The result is a pyramidal germanium centre exhibiting a weak coordination to the otherwise uncoordinating anion [19,20]. They act as Lewis acids.…”