Isothiocyanates insertion reactions

Zirconium and hafnium dialkylamides are highly reactive compounds. They undergo (i) protolytic substitution reactions with reagents such as alcohols, cyclopentadiene and bisftrimethylsilyOamine 63 64 (ii) insertion reactions with C02, CS2, COS, nitriles, phenyl isocyanate, methyl isothiocyanate, carbodiimides and dimethyl acetylenedicarboxylate 69-72 and (iii) addition reactions with metal carbonyls.73 These reactions are summarized with reference to Zr(NMe2)4 in Scheme 1. 

Further reactions of P-hydridocyclotriphosphazenes (See Section IV,E) have been described. They undergo insertion reactions with aldehydes, ketones, isothiocyanates and electrophilic olefins. Addition of sulfur or oxidation with KMn04 gives thioxo-or oxo-cyclotriphos-phazene derivatives which are methylated at the chalcogen to afford methylthio- and methoxy- cyclotriphosphazenes (36). Hydridocyclo-phosphazenes can also be oxidized to give symmetric and unsymmetric bis(cyclotriphosphazenyl) oxides (35). 

The insertion reaction of heterocumulenes can be used to syuthesize carbodiimides having two different substituents. For example, the carbamate 157 derived from an isocyanate and bis(tributyltin)oxide can be reacted with an isothiocyanate to give a carbodiimide 158 with substituents derived from the isocyanate and the isothiocyanate. ... 

Heterocumulenes undergo insertion reactions with numerous substrates. In general, carbodiimides react faster than isocyanates and isothiocyanates, in that order. Insertions of carbodiimides into metal-hydrogen, metal-halogen, metal-mitrogen, metal-oxygen and metal-sulfur bonds are reported. Also insertions of carbodiimides into carbon-hydrogen bonds are known. 

Insertion Reactions of an Isocyanate, Isothiocyanate, Carbodiimide, Ketene, Diketene, or Ketenimine... 

Insertion Reactions into Element Oxygen and Heavier Group VIB Bonds 11.5.3. Reactions of Isocyanates, Isothiocyanates, and Carbodiimides... 

Metal alkoxides undergo insertion reactions across the M—O bonds (6) when treated with unsaturated substrates such as isocyanates, isothiocyanates, aldehydes, ketones, ketenes as well as with carbon dioxide, carbon disulfide, and sulfur dioxide. 

Complexes 25 also cycloadd the C=S double bonds in heteroallenes CS2, COS, " and aryl isothiocyanates. The reaction of 25a with CS2 (Scheme 6) gave an 80% yield of the expected bicyclo[2.2.2] complex 30, the structure of which has been established by X-ray crystallography. When the reaction was performed in the presence of water or HBF4, the amido nitrogen bridge in the initial bicyclo[2.2.1] adduct was protonated, which inhibited the insertion of isocyanide, and 31 was isolated in 80% yield. 

Both the formation of XX as well as the reaction of mercuric fluoride with isothiocyanates are examples of the well-known insertion reaction of heterocumulenes... 

The cycloaddition reactions are subdivided into di-, tri- and oligomerization reactions, [2-1-1]-, [2-1-2]-, [3-1-2]- and [4- -2] cycloaddition reactions and other cycloaddition reactions. The insertion reactions into single bonds are also discussed. The cyclodimerization or cyclotrimerization reactions are special examples of the [2-1-2] and the [2-I-2-I-2] cycloaddition reactions, respectively. The cumulenes vary in their tendency to undergo these reactions. The highly reactive species, such as sulfines, sulfenes, thioketenes, carbon suboxide and some ketenes, are not stable in their monomeric form. Other cumulenes have an intermediate reactivity, i.e. they can be obtained in the monomeric state at room temperature and only heat or added catalysts cause di- or trimerization reactions. In this group, with decreasing order of reactivity, are allenes, phosphorus cumulenes, isocyanates, carbodiimides and isothiocyanates. 

Across single bonds (insertion reactions) The addition of isothiocyanates across the polar single bond in dimethylaminobis-(trifluoromethyl)borane affords the switter ionic four-membered ring cycloadducts 78 . ... 

In the reaction of the liganded zirconium formaldehyde dimer 80 with excess t-butyl isothiocyanate insertion into both of the Zr-C bonds is observed to give the double insertion product 81 in 83 % yield . 

In the reaction of oxalyl chloride 82 with isothiocyanates, insertion into the C=C1 bond occurs with formation of 3-alkyl- or 3-aryl-2,2-dichlorothiazoUdine-4,5-diones 83. ... 

The nature of these insertion reactions is not fully understood. In the case of the silyl thiols, they are believed to proceed via precoordination of the isothiocyanate to ruthenium, while with thiol itself, direct nucleophilic insertion is proposed. In support of this, [CpRu(dppe)(SSi—i-Pr3)] does not react with isothiocyanates, while [CpRu(dppe)(SH)] does, giving monodentate products, [CpRu(dppe)(ri -S2CNHR)] (R = Ph, 1-naphth), a reaction that is reversible in one case (R = 1-naphth) (Eq. 36) (217). 

As in the case of silanone 9, the reaction of the silylene bis[2-(dimethylamino-methyl) phenyl]silanediyl (8) with phenyl isothiocyanate was examined.29 In this reaction the expected silanethione 36 was obtained as a single product even in the presence of (Me2SiO)3, no insertion product of 36 into a Si-O bond of (Me2SiO)3 was observed (Scheme 10). 

Various isothiocyanates (RNCS R = Buc, Ph) and CS react with exclusively with the Mg-C bonds of dinuclear Al-Mg compounds to give dinuclear insertion products (Scheme 7). In the case of the reaction of Me2Al(/i-Et2N)2Mg(CH3) 2 with PhNCO, a tetranuclear insertion product is formed.290... 

However, the reaction of the binuclear rj2-thioaldehyde titanocene complexes 112 (see Scheme 26) with valeronitrile, benzonitrile, and methyl thiocyanate proceeded in a similar fashion (Scheme 39).69 Related metalla-cyclic compounds were also obtained from the reactions of 112 with benzo-phenone (Scheme 39), various imines, phenyl isothiocyanate, or dicyclohexyl carbodiimide via insertion of the C = 0 and C = N bond, respectively, into the Ti-C bond.69,70... 

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