Complexes with Sterically Bulky Allyl Ligands: Insights into Structure and Bonding

Abstract

The allyl anion [C3H5]– is often found in combination with other ligands in organometallic complexes. Compounds in which allyl groups are the only or principal type of ligand, however, are often coordinatively unsaturated and prone to decomposition. It is possible to increase the thermal and sometimes oxidative stability of such complexes by adding sterically bulky substituents (e.g., –SiMe3) to the allyl group. Main group, transition metal, and f‐element compounds constructed with bulky allyl ligands display a wide range ofmonomeric, oligomeric, and polymeric structures. Some of these complexes have no counterparts with unsubstitutedallyl groups, and others are active polymerization catalysts. Research in this area has served to expand the range of structural types and bonding that can be incorporated into metal allyl chemistry.

A tetrameric allyl complex of sodium, and computational modeling of the 23Na–allyl chemical shift

“…For example, the contrast between the polymeric {K(1,3-(SiMe 3 ) 2 C 3 H 3 )(thf)} 1 and the tetrameric {Na(1,3-(SiMe 3 ) 2 C 3 H 3 )(thf)} 4 might be cited as an illustration of the general tendency for structures to oligomerize as the metal radii increase [1,2]. Yet allyl complexes of the smaller lithium cation are also found in polymeric [21] and oligomeric [69] forms.…”

“…We accordingly added three additional water molecules to bridge the directly coordinated waters of the T h structure. It optimized to a geometry of C 3h symmetry in which the immediate coordination environment of the sodium is trigonal prismatic (2). Although it also is not a minimum at the PBE1PBE/6-311 + G(2d,p) level (one frequency at À44 cm À1 ), it maintains a coordination number of 6 for the first ''shell" and adds the beginning of a second coordination sphere around sodium.…”

“…Silylated allyls have provided the majority of examples of the effects of such sterically enhanced ligands, and their complexes have been the subject of recent reviews [1,2]. Fraenkel reported the synthesis of lithiated derivatives of [(SiMe 3 ) n C 3 H 5Àn ] À in the early 1990s [3][4][5][6], and donor functionalized allyl ligands that provide both steric bulk and internal solvation to metal complexes are known [7][8][9][10][11][12][13].…”

Halide metathesis in overdrive: mechanochemical synthesis of a heterometallic group 1 allyl complex

“…Here we describe the application of mechanochemistry in an organometallic context to examine alkali metal halide exchange unassisted by solvents. The organic group used is the bulky 1,3-bis(trimethylsilyl)allyl anion, [1,3-(SiMe 3 ) 2 C 3 H 3 ] − ([A'] − ) [13–14], for which alkali metal complexes are known, including those of Li [15], Na [16], K [17–18], and Cs [18]. These have been formed via traditional solvent-based routes, by deprotonation of the substituted propene precursor with a metal alkyl or hydride (Eq.…”

Bis(1,3‐trimethylsilylallyl)beryllium

“…Bulky allyl ligands [12] and those with pendant groups [13] have been used to suppress oligomerization and enhance solubility in a wide range of metal complexes. The chance to use such ligands in organoberyllium chemistry is appealing, especially as the reactivity of alkyl and aryl beryllium chlorides may depend on their state of aggregation in solution.…”