Preparation and Structures of Group 12 and 14 Element Halide–Carbene Complexes

Abstract

The synthesis of a series of N-heterocyclic carbene (NHC) complexes involving zinc, cadmium, and the heavy Group 14 elements germanium, tin, and lead is reported. The direct reaction between the bulky carbene IPr (IPr = (HCNDipp)2C:, Dipp = 2,6-iPr2C6H3) and the Group 14 halide reagents GeCl4 and SnCl4 afforded the 1 : 1 complexes IPr·ECl4 (E = Ge and Sn) in high yield; similarly, ZnI2 interacted with IPr in THF to give the THF-bound complex IPr·ZnI2·THF. CdCl2 underwent divergent chemistry with IPr and the major product isolated was the imidazolium salt [IPrH][IPr·CdCl3], which could be converted into IPr·CdCl2·THF upon treatment with Tl[OTf]. In addition, the stable PbII amide adduct, IPr·PbBr(NHDipp), was prepared. Each of the new carbene–element halide adducts was treated with the hydride sources Li[BH4] and Li[HBEt3] in order to potentially access new element hydride adducts and/or clusters. In most instances scission of the element–carbene bonds transpired, except in the case of IPr·ZnI2·THF, which reacted with two equivalents of Li[BH4] to yield the thermally stable bis(borohydride) zinc complex IPr·Zn(BH4)2.

Zinc Dihydride and Mixed Halo Hydrides Supported by an N‐Heterocyclic Carbene

“…Adducts 1a – c are highly soluble in THF but moderately soluble in aromatic hydrocarbons. The 1 H NMR spectra of 1a – c in [D 6 ]benzene are similar and exhibit the typical pattern for the IMes ligand coordinated to zinc , . In the 13 C{ 1 H} NMR spectra, the zinc‐bound carbene signals appear at δ = 174.0 ( 1a ), and 177.1 ( 1b and 1c ) ppm.…”

“…It is important to note that 1a – c contain variable quantities of THF as 1a – c·(THF) 0–1 unless rigorously dried. IPr‐bonded [(IPr)ZnI 2 ] was similarly isolated and crystallized from THF as [(IPr)ZnI 2 (thf)], whereas solvent‐free [(IPr)ZnBr 2 ] 2 was synthesized from toluene and crystallized as a dimer from benzene (Scheme ) …”

NHCs in Main Group Chemistry

“…One year later, the group of Rivard described the IDipp adduct of GeCl 4 ( 755 ) obtained in a straightforward reaction, by mixing the two components in diethyl ether (Figure ). This compound can be reduced to the donor–acceptor-stabilized germylene 756 , which will be discussed later …”

“…Rivard et al reported on the (IDipp)­SnCl 4 adduct ( 839 ), which is isostructural to the germanium congener 755 (vide supra) . It contains a trigonal bipyramidal-coordinated tin atom with the C NHC –Sn bond length of 2.186 Å, which compares well to 837c .…”

Modern Main Group Chemistry: From Renaissance to Revolution

“…However, it is worthwhile to give an indication of the broad areas of the field that are covered by the authors. Aspects of low oxidation state main group chemistry and ligand design are covered by Driess, [9] Goicoechea, [10] Jones, [11] Rivard, [12] Stasch, [13] and Weigand. [14] The application of main group compounds to synthetic methods is addressed in papers by Coles, [15] Driess, [9] Dutton, [16] Mulvey, [17] Scheschkewitz, [18] and Westerhausen.…”