Silylamide groups

In contrast to the borylation of alkane C-H bonds, the coupling of aryl halides with amines was based on a literature precedent from another group published about a decade before our initial studies. Kosugi, Kameyama and Migita published the coupling of aryl halides with tin amides." Mechanistic studies we conducted on this process led us to the perhaps obvious realization that the reaction" could be conducted with amines and a silylamide base instead of tin amides (equation 4)." Surveys of bases with similar p a values led Janis Louie to conduct reactions with alkoxide bases. Similar studies were conducted at nearly the same time by Steve Buchwald and coworkers."... 

To summarize die effects of the nature of groups R and Y on the structure of bis(silylamides) (I) it can be concluded that relative increase of the it character in the carbon-nitrogen bond is probably responsible for the relative stabilization of the... 

Si H M agostic interactions in silylamido complexes have been extensively studied to date. The earlier examples were prepared by halide displacement in the coordination sphere of a metal by a silylated amide, which puts severe limitations on the nature of the substituents at silicon (usually, robust methyl groups are used). More recently, a new route to p-agostic silylamides based on the direct coupling of silanes with imido ligands was discovered that allows one to trace the effect of substitution at silicon on the extent of the Si-H bond complexation (vide infra). 

Silica-grafted group 3 and lanthanide silylamides have been used as precursor to surface (3-diketonate complexes [(=SiO) Ln( Bu-COCHCO- C3F7)m(THF)i]... 

Supposedly, lanthanide chemistry is lagging behind main group and d-transition metal chemistry. The concluding statement which Bradley made with respect to transition metal dialkylamides and silylamides almost 20 years ago [19b] is a current topic in lanthanide amide chemistry To date homogenous transition-metal catalysis has been restricted to hydrocarbon systems involving the facile formation and rupture of M-H, M-C, C-H and C-C bonds. An extension to include M-N, C-N, M-O, and C-O bonds seems plausible and could lead to substantial advances in transition-metal catalysis. ... 

Synthetic strategies to alkoxide complexes have been covered in full by previous reviews [14]. The silylamide route proved to be an advantageous method of preparation, especially in the case of homoleptic derivatives [15]. The group (IIIA) elements - scandium, yttrium and lanthanum - are considered as lanthanides on the basis of their general chemical similarity to the true lanthanides. 

Silylamido groups are used throughout the periodic table to stabilize unusual types of bonding, coordination numbers and oxidation states. Lithium silylamides, generally prepared by reaction of the silylamine with alkyl- or aryllithium derivatives, play an important role in the synthesis of such molecules. 

In 1995, Hartwig and Buchwald published concurrently their two groups results on tin-free amination of aryl halides [79,80], Instead of isolating or generating a tin amide in situ, the amination reactions were conducted by reacting an aryl halide with the combination of an amine and either an alkoxide or silylamide base (Eq. (5)). These reactions were typically conducted between 80 and 100 °C in toluene solvent. The catalysts used initially were 1, 3, or a combination of [Pd2(dba)3] (Sa) (dba = trans, trans-dibenzylidene acetone) and P(o-C6H4Me)3. Catalysts used subsequently will be described below. As shown in Table 7.1, secondary amines were viable substrates, but primary amines gave substantial yields with... 

In 1995, Hartwig and Buchwald published concurrently their respective groups results on tin-free amination of aryl halides [98, 99]. Instead of isolating or generating a tin amide in situ, the amination reactions were conducted by allowing an aryl halide to react with a combination of an amine and either an alkoxide or silylamide base (Eq. (5)). 

Lanthanum dibenzyl complexes with triazanonane-silylamide, amidine and 1,3-diketiminate monoanionic ancillary ligands were also prepared by in situ peralkylation in the presence of the protonated ligand or by com-plexation (for 1,3-diketiminate) with lanthanum tribromide and subsequent alkylation. The coordination polymer [p-r 2 r 1-ArNC(Me)CHC(CH2)-NAr]2La[K(THF)4] n formed by H-abstraction from one of the diketimi-nate Me groups and a ligand redistribution.14... 

Carbamoyl silanes 100 could be prepared by reaction of lithium silylamides 97 with CO at room temperature and under pressure (30 atm) followed by reaction with methyl iodide (Scheme 25)101. The intermediate carbamoyllithium 98 suffers a rearrangement of the silyl group to afford a new lithium (silylcarbonyl)amide 99, which is finally methylated. 

It is well recognised that, in some circumstances, the prior coordination of a nucleophile to tetracoordinate silicon can produce a pentacoordinate silicon centre that is activated to nucleophilic attack [1,8]. We have previously published preliminary data on the use of chelated pentacoordinate silylamides as reactivity probes for nucleophilic activation [8]. The work presented here is an extension of those studies and incorporates a stereochemical and kinetic investigation in a single series of experiments. The compound chosen for the experiments was 18 which has several advantages for a kinetic and stereochemical study. The coordinated A -methylimidazole (NMI) group is readily displaced by another NMI molecule in a degenerate substitution reaction. 

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