Mesityl group

The rhodium(III) triaryls have pseudo-octahedral structures therefore, in the air-stable trimesityl rhodium, the three mesityl groups are arranged in /ac-positions, with ort/io-methyls blocking the other coordination sites (Figure 2.107). 

To further illustrate the effect of steric hindrance, a bulky mesityl group was... 

These different catalysts were first tested in the desymmetrization of the achiral triene 63 (Scheme 40). The best enantioselectivities (up to 39%) were obtained with complexes 60b and 61c-d bearing carbene ligands derived from 1,2-diphenyl-1,2-diaminoethane (R = Ph). ligands derived from 1,2-diaminocyclohexane gave poor enantioselectivities (< 9% ee). Replacement of the mesityl group in complex 60b by o-methyl- or o-isopropylphenyl groups (complexes 61c-d) slightly increases the enantioselectivity (from 13... 

While related to its carbon analogs, the existence of the RsSi species as a free ion in condensed phases had been doubted for a long time. However, NMR characterization using bulky aryl substituents has provided evidence for the triply coordinated silicon cation. " However, definitive evidence was recently reported by the groups of Reed and Lambert with a silyl cation species bound to three mesityl groups and a carborane [HCBnMesBrg] counterion (Eig. 7.5). It was suggested that... 

The solid state structure of complex 7b is shown in Figure 25.1. Similar to parent chelating ether complex [9b], the solid-state structure of 7b shows a distorted square-pyramidal structure with the benzylidene moiety at the apical position. The N-aryl ring is located above the benzylidene moiety resulting in the relatively close contact of the benzylidene proton with the 7r-aromatic system of the mesityl group. 

In a number of rearrangements of siienes the Si=C bnd has been observed to react with a C—H bond of a methyl group that is usually attached at the ortho position of an adjacent mesityl group. Formally, these can be regarded as 2tt + 2cr reactions, although other descriptions may be possible. For example, a 1,5-H shift followed by an electrocyclic rearrangement of a Si=C with a C=C would effect the same results. Little is known about the mechanisms involved. Several examples of these types of reaction are described below, some being effected photochemically and some thermally. 

Brook et al. 5X1 observed such reactions during the formation of siienes by photolysis. Using radiation with A > 360 nm, they photolyzed acylsi-lanes such as 127, which bears a mesityl group attached to the carbonyl carbon. On prolonged photolysis of the initially formed silene 128, the C—H bond of the ortho methyl group of the mesityl group added to the silicon-carbon double bond to form the benzocyclobutane 129. Alternatively a 1,5-H shift would lead to the species 130, which would also yield the benzocyclobutane on electrocyclic rearrangement. 

The classic disilene 1 is unusual in that it exists in at least three crystalline modifications orange and yellow unsolvated forms and a yellow toluene solvate (Fig. 2). The orange polymorph has a helical conformation in which all of the mesityl substituents are twisted in the same direction thus molecules of 1 in this form are chiral.51 The toluene solvate has an unusual conformation in which two mesityl rings cis to each other are nearly coplanar with the Si=Si bond, while the other two cis mesityl groups are nearly orthogonal.41 The structure of the yellow unsolvated form is not yet known. Because of the flat potential surface for the Si=Si... 

A stable diarylstannanethione has been synthesized by the reaction of an extremely bulky stannylene with either styrene episulfide95 or less than one equivalent of elemental sulfur.9 If the 2,4,6-tris[bis(trimethylsilyl) methyl]phenyl group (Tb) is replaced by the smaller mesityl group, no monomeric products are observed thus the stability of the stannanethione is attributed to the demand of the substituents. 

Even after the boron s electrophilicity has been arrested intermolecularly, intramolecular reorganization of the boraethene may still proceed. A remarkable instance is the structure 60 (by XRD) resulting from the oxidation of 57 by SnCl2. Intermediates in this impressive transformation might well be carbene 58 and boraethene 59. The borons in 59 are still sufficiently electrophilic to cause the mesityl group to bridge (Scheme l).61... 

The loss of nitrogen and migration of the mesityl group very likely constitute a single concerted process although they have been written here as two separate steps. 

H and 13C NMR. These are rare examples of thermally stable monomeric germaimines. At room temperature die mesityl and die N-Me groups are not equivalent. At 55 °C the split signals coalesce. This is possibly due to interaction between Ge and NMe2. Stability is adduced to intramolecular Ge—O coordination, electron withdrawal by the C=0 group and bulkiness of die mesityl groups. ... 

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