Palladium-isonitrile catalyst

The combination of the Pd-catalyzed bis-silylation and subsequent Peterson-type elimination was applied to the synthesis of aUenylsilanes from propargylic ethers. Scheme 7 shows a preparation of optically active aUenylsilane and its use in the synthesis of syn-homopropargylic alcohol. Use of the palladium-isonitrile catalyst is crucial to promote the bis-silylation effectively. 

With the palladium-isonitrile catalyst, terminal alkynes with a variety of substituents and internal alkynes were subjected to the silaboration with 2-silyl-l,3,2-dioxaborolane in refluxing toluene (Table 4). The reaction proceeded not only with high yields but also... 

Another variation of the oxidation reaction with dioxygen can be efficiently accomplished by a catalytic condensation of amines and isonitriles using a palladium complex catalyst and iodine at 100 °C to give dialkylcarbodirmides in yields of 35-86% [1283]. Dicyclohexylcarbodirmide was obtained in 67% yield from cyclo-hexylisonitrile 1748 and cyclohexylamine 1749 (see Section 4.5.3.5, Table 4.48). 

To palladium acetate (1.8 mg, 7.8 //mol) placed in a Schlenk-type tube under a nitrogen atmosphere is added 1,1,3,3-tetramethylbutyl isocyanide (16.8 mg, 0.12 mmol) under stirring at rt. >eep red color is observed immediately, indicating the formation of active palladium(0)-isonitrile catalyst. To the mixture successively added at rt are toluene (0.1 mL), (dimethylphenylsilyl)(pinacolato)borane (102 mg, 0.39 mmol), and 3-(/er/-butyldimethylsilyloxy)-l-propyne (91 mg, 0.53 mmol). The resulting mixture is heated to reflux for 1-4 h, then cooled down to rt, and finally subjected to a short column chromatography on silica gel (diethyl ether) to remove the catalyst. Further purification by bulb-to-bulb distillation of the crude product gives the title compound in 83% 3deld. 

Dimethyl-4-methylene-l,3-dioxolan-2-one reacts with isonitriles in the presence of a palladium catalyst to afford iminofurans (Equation (121)).480 Successive insertion of isonitriles to the carbon-palladium bond of 7r-allylpalladium intermediate is postulated. 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

Two new classes of ligands, bicyclic phosphate 47 [45] and ferf-alkyl isonitriles [46] on palladium, enable bis-silylation with hexaalkyldisilanes, which have been regarded to be much less reactive than the activated disilanes (Eq. 20). Reactions of the terminal alkynes with hexamethyldisilane in the presence of these palladium catalysts afford (Z)-l,2-bis(trimethylsilyl)alkenes 48 in high yields. 

Under extremely high pressure, the isonitrile-palladium catalyst promotes intramolecular bis-silylation of bis(silyl)acetylenes 51 to give tetrakis(silyl) alkenes 52, which are otherwise difficult to synthesize the reaction under atmospheric pressure hardly proceeds even at 200°C (Eq. 22) [48,49]. 

Bis(disilanyl)dithiane 32 is a good precursor for intermolecular bis-silylation of alkynes. In the presence of the isonitrile-palladium catalyst 34, the facile intramolecular Si-Si bond metathesis produces reactive four-membered cyclic bis(organosilyl)palladium(II) intermediate 34, which then reacts with alkynes to afford five-membered cyclic products 55 in high yields (Eq. 24) [20,30]. 

Similar 1,4-bis-silylation of a,p-unsaturated ketones with 32 is catalyzed by the isonitrile-palladium catalyst 34 to afford seven-membered ring silyl enol ether 69 in high yields (Eq. 35). Reactions of 32 with acrylic esters and acrylonitrile, however, give five-membered products 70 [20,30]. 

Insertion of isonitriles into Si-Si bonds takes place in the presence of palladium catalysts to give bis(silyl)imines 85, which show characteristic UV absorbance around 400 nm arising from n-Ji transition (Eq.43) [79]. Aryl and alkyl isonitriles except for tertiary alkyl isonitrile give the corresponding N-substituted imines. 

Curran and Du reported that the cascade reaction of the isonitriles 520 with B-iodo-Af-propargylpyri-done 521 in the presence of a palladium-catalyst gave the 1 l//-indolizino[l,2-6]quinolin-9-ones 522 in high... 

Table 16.4, which is adapted from a comprehensive review by Miyaura from 2001, illustrates the scope and types of catalysts that have been used for the diboration, silylboration, and stannylboration of alkynes. These data illustrate that the simple platinum(O) complex of PPhj is a suitable catalyst for diboration. ° - ° These data also show that both B rin and BjCat add to terminal alkynes, but that the tetraaminodiboron reagent does not. Finally, these data illustrate that palladium complexes of isonitrile ligands catalyze the silylboration of alkynes and that simple Pd(PPhj) catalyzes the stannylboration of terminal alkynes. ... 

As in the case of bis-silylation of acetylenes, intramolecular bis-silylation of alkenes is more effectively performed compared to the intermolecular reactions. The isonitrile-palladium catalyst provides 5-exo cyclization products stereospeciflcally from (Z)- and ( )-alkenes tethered to disilanyl groups by ether linkage (Scheme... 

Intramolecular bis-silulation of alkenes has also been achieved more effectively than intermolecular reactions. The use of optically active isonitrile ligand on palladium catalyst provides us with a synthetic method for an enantioselective intramolecular bis-silylation of homoallylic alcohols. The method has successfully been applied to the synthesis of highly enantio-enriched allylsilanes. 

---