Reactivity of Amido-Digermynes, LGeGeL (L = Bulky Amide), toward Olefins and Related Molecules: Facile Reduction, C–H Activation, and Reversible Cycloaddition of Unsaturated Substrates

Abstract

Reactions of two sterically hindered amidodigermynes, L*GeGeL* (1; L* = −N(Ar*)(SiMe 3 ); Ar* = C 6 H 2 Me{C(H)Ph 2 } 2 -4,2,6) and L † GeGeL † (2; L † = −N(Ar † )-(SiPr i3 ); Ar † = C 6 H 2 Pr i {C(H)Ph 2 } 2 -4,2,6), with a variety of olefins and related molecules are investigated. These lead to the facile reduction, C−H activation, dehydrogenation, and/or cycloaddition of the unsaturated substrate. Specifically, reaction of L † GeGeL † with ethylene proceeds via a formal [2 + 2 + 2] cycloaddition to give the digermabicyclo[2.2.0]hexane L † Ge(μ-C 2 H 4 ) 2 GeL † (3). In contrast, treating L † GeGeL † with norbornadiene proceeds via reductive insertion of one olefin moiety of the organic substrate into the Ge−Ge bond of 1, yielding the norbornenediyl-bridged bis(germylene) L † Ge(μ-C 7 H 8 )GeL † (4). Similarly, L*GeGeL* doubly reduces cyclooctatetraene (COT) to give the planar cyclooctateraenediyl inverse sandwich complex L*Ge(μ-η 2 ,η 2 -COT)GeL* ( 5). An indication that this reaction occurs via an initial formal [2 + 2] cycloaddition intermediate comes from the reaction of L † GeGeL † with 1,5-cyclooctadiene (COD). This affords the [2 + 2] cycloaddition product L † Ge(COD)GeL † (6), which exists in solution in equilibrium with 2 and free COD. A computational study indicates that 6 readily dissociates, as the reaction that gave it is close to thermoneutral. Reaction of 1,3-cyclohexadiene (1,3-CHD) with L † GeGeL † yields the 1,4-bis(germylene) substituted cyclohex-2-enediyl L † Ge(μ-C 6 H 8 )GeL † (7), which is an isolated intermediate in the transfer hydrogenation, or C−H activation, reaction between L † GeGeL † and 1,3-CHD. Heating 7 gives benzene and the known digermene L † (H)GeGe(H)L † . Reactions of 1 or 2 with propyne, bis(trimethylsilyl)butadiyne, and azobenzene all lead to reductive insertion of the unsaturated substrate into the Ge−Ge bond of the digermyne and formation of L † Ge{μ-HCC(Me)}GeL † (8), L*Ge{μ-(Me 3 Si)CC(CCSiMe 3 )}GeL* (9), and L*Ge{μ-(Ph)NN(Ph)}GeL* (10), respectively. The reaction of 4-dimethylaminopyridine (DMAP) with L*GeGeL* gives the adduct complex L*(DMAP)GeGe(DMAP)L* (11). Taken as a whole, this study highlights both similarities and significant differences between the reactivities of the amido-digermynes 1 and 2 and those of their previously described terphenyl-substituted counterparts.

Reaction Mechanism of the Symmetry‐Forbidden [2+2] Addition of Ethylene and Acetylene to Amido‐Substituted Digermynes and Distannynes Ph2NEENPh2, (E=Ge, Sn): A Theoretical Study

“…In av ery recent study,J ones and coworkers found that the amido-digermynes also reactw ithv arious unsaturated substrates, such as olefins, dienes,a lkynes, and PhNNPh. [16] Similarities and differences among the reactions of amido-and aryl-substituted digermynes with unsaturated species were also discussed. Scheme 1s hows the reaction products for the addition of 1,4-cyclooctadiene (COD) and propyne to L + GeGeL + .T he product of the former reaction agrees with af ormal [2+ +2] cycloaddition of aC =Cb ond to aG e-Ge multiple bond,w hich, according to the WoodwardHoffman rules, is as ymmetry-forbidden process.…”

Reduction vs. Addition: The Reaction of an Aluminyl Anion with 1,3,5,7‐Cyclooctatetraene

“…[17] In contrast, transition metal complexes often feature COTl igands with "semi-aromatic" character involving h n -hapticity (n = 2-5). [19] Ther eaction of COT with multiply bonded group 14 element systems Ar'MMAr' (M = Ge,S n; Ar' = 2,6-Ar 2 C 6 H 3 )y ielded the inverse-sandwich complexes (Ar'M) 2 (m 2 -h 2 :h n -COT)( M= Ge, n = 2; M= Sn, n = 3) featuring COT-ligands (with parameters associated with 10paromatic systems) that bridge two metal centers (Scheme 2, IV-M;M= Ge,Sn). [19] Ther eaction of COT with multiply bonded group 14 element systems Ar'MMAr' (M = Ge,S n; Ar' = 2,6-Ar 2 C 6 H 3 )y ielded the inverse-sandwich complexes (Ar'M) 2 (m 2 -h 2 :h n -COT)( M= Ge, n = 2; M= Sn, n = 3) featuring COT-ligands (with parameters associated with 10paromatic systems) that bridge two metal centers (Scheme 2, IV-M;M= Ge,Sn).…”

“…[18] Examples of p-block metals featuring COT-derived ligands are rare. [19] Ther eaction of COT with multiply bonded group 14 element systems Ar'MMAr' (M = Ge,S n; Ar' = 2,6-Ar 2 C 6 H 3 )y ielded the inverse-sandwich complexes (Ar'M) 2 (m 2 -h 2 :h n -COT)( M= Ge, n = 2; M= Sn, n = 3) featuring COT-ligands (with parameters associated with 10paromatic systems) that bridge two metal centers (Scheme 2, IV-M;M= Ge,Sn). [20] In contrast, reaction with the group 13 digallene Ar'GaGaAr' forms an on-planar 1,5-cyclooctadiene-bridged bimetallic species (V), [21] demonstrating diver- We have recently shown that the dianionic bis(amidodimethyl)disiloxane ligands (abbreviated NON R ,R= tBu, Ar, Ar°= 2,6-(CHPh 2 ) 2 -4-tBuC 6 H 2 )w ill stabilize low oxidationstate bismuth [22] and indium species.…”

Activation of Small Molecules by Compounds that Contain Triple Bonds Between Heavier Group‐14 Elements

“…R N1 -Ge Ge-R N1 12 also reacts with COT to form as andwich cycloocatatetraenediyl complex that is similar to 29,but thermally stable. [38]…”