To Rearrange or not to Rearrange: Reactivity of NHCs towards Chloro‐ and Hydrostannanes R₂SnCl₂ (R = Me, Ph) and Ph₃SnH

Abstract

The reaction of 1,3-diisopropylimidazolin-2-ylidene (iPr 2 Im) with diphenyldichlorostannane and dimethyldichlorostannane, respectively, leads to the formation of the adducts (iPr 2 Im)·SnPh 2 Cl 2 (1) and (iPr 2 Im)·SnMe 2 Cl 2 (2). These compounds are stable in solution to temperatures up to 80°C for several days and rearrangement to backbonetethered bis(imidazolium) salts or ring expansion reaction to six mem-* Prof. Dr. U. Radius 1282 bered heterocyclic rings was not observed. The reaction of iPr 2 Im with triphenylstannane Ph 3 SnH leads to reductive dehydrocoupling of the stannane to yield distannane Sn 2 Ph 6 and iPr 2 ImH 2 . Thus, the reactivity of these tin compounds is completely different compared to those of the lighter congener silicon, for which rearrangement (chlorides) and NHC ring expansion (hydrides) was reported earlier.

NHCs in Main Group Chemistry

“…In 2016, Schneider and co-workers used rather uncommon NHC I i Pr 2 to coordinate dialkyl­(dichloro)­stannanes, yielding the adducts 840 . Compound 840a is structurally very related to Kuhn’s 837c and displays nearly the same 119 Sn NMR shift (−317.7 ppm, CDCl 3 ).…”

“…In 2016, Schneider and co-workers used rather uncommon NHC I i Pr 2 to coordinate dialkyl(dichloro)stannanes, yielding the adducts 840. 754 Compound 840a is structurally very related to Kuhn's 837c and displays nearly the same 119 In analogy to their pentafluorogermanium NHC complex 754, the group of Roschenthaler prepared the tin congener 841 (Scheme 166). 707 Addition of the difluoro−NHC adduct 751 to a suspension of tin difluoride in acetonitrile leads to a clear solution of 841.…”

Molecular Main Group Metal Hydrides

“… On a related topic, the dehydrocoupling of SnH 4 to yield H 3 Sn-SnH 3 was modelled computationally with Cp 2 LaH as a catalyst, while the photoactivated iron­(II) complex [CpFe­(CO)­(PPh 3 )­Me] is able to promote the selective monodehydrocoupling of t Bu 2 SnH 2 into [ t Bu 2 (H)­Sn–Sn­(H) t Bu 2 ] with [CpFe­(CO)­(PPh 3 )­{Sn­(H) t Bu 2 }] ( 1056 ) as an isolable intermediate . The metal-free dehydrocoupling of Ph 3 SnH to give Ph 3 Sn-SnPh 3 is also possible with N -heterocyclic carbenes, yielding the dihydroaminal byproducts (NHC)­H 2 . The direct dehydrocoupling polymerization of diorgano­stannanes R 2 SnH 2 to form [SnR 2 ] n polymers has been widely documented, with a red-shift in UV-vis absorption maxima and enhanced light sensitivity noted in poly­(stannanes) in relation to poly­(silanes) [SiR 2 ] n and poly­(germanes) [GeR 2 ] n , due to a decrease in E–E bond strength and a narrowing of the σ/σ* orbital energy differences. ,,− In an interesting 2018 study, Foucher and coworkers used condensation copolymerization, with loss of Et 2 NH to form new libraries of polystananes (eq 86 ); , a related process has also been used to generate oligomeric diorganogermanes [GeR 2 ] x …”

“…1189 The metal-free dehydrocoupling of Ph 3 SnH to give Ph 3 Sn-SnPh 3 is also possible with N-heterocyclic carbenes, yielding the dihydroaminal byproducts (NHC)H 2 . 1190 1069) can be prepared in high yield by combining K[HB i Bu 3 ] with 1068 at −10 °C in toluene. 1203 The reactivity of ( Dipp Nacnac)SnH ( 1069) was then studied extensively, and documented examples of Sn−H insertion reactions with CO, CN, and CC bonds are presented as part of Scheme 155.…”

Unusual Rearrangement of an N-Donor-Functionalized N-Heterocyclic Carbene Ligand on Group 8 Metals

“…The N -heterocyclic carbenes (NHCs) are widely used ancillary ligands in coordination chemistry . Despite the generally assumed role as spectator ligands, NHCs have shown noninnocent behaviors, including the ring opening and expansion of the N -heterocycle, C–H activation at the backbone, C–H and C–C activation at N -substituents, loss of an N -substituent followed by the coordination of imidazole N -donor, ring expansion of an N -bound aryl group, reductive elimination, and insertion of an unsaturated group into M–C­(NHC) bonds. − Although some of the noninnocent behaviors of NHCs result in undesired ligand decompositions, the reversible transformations (such as C–H cleavage) of the N -substituents can be utilized in a productive manner toward small molecule activation and catalysis through metal–ligand cooperation. ,, In particular, pincer complexes featuring picolyl–NHC moieties can break and form C–H or C–C bonds reversibly at the pyridylic positions accompanied by the dearomatization-rearomatization of the pyridine ring . These picolyl–NHC-containing pincer complexes arguably stemmed from Milstein’s versatile pincer systems containing picolyl–phosphine moieties; NHCs have been used in lieu of phosphines for more electron-rich and robust late metal complexes because of their superb σ-donating ability and the soft nature of the carbon donor.…”