Methyl isocyanate 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. 

Alkyl isocyanates insert into tungsten and iron hydride complexes to give the insertion products resulting from insertion into the metal-hydrogen bond. For example, reaction of CpW(CO)3H with methyl isocyanate affords the carbamate complex . Likewise, CpFe(CO)2H reacts with t-butyl isocyanate to give the carbamate complex 329 . 

The reactivities of hydrido(phenoxo) complexes of trons-[MH(OPh)L2] (6 M = Ni 7 M = Pt) (L = phosphine) were examined (Eqs. 6.29, 6.30 Scheme 6-16), and a high nucleophiUdty for the metal-bound phenoxide was suggested [9, 10]. Reaction with methyl iodide produced anisole and trans-[MH(I)L2] for both Ni and Pt complexes. Phenyl isocyanate also provided the insertion products into the metal-phenoxo... 

The insertion of various isocyanates into chromium(lll) alkoxide M—O bonds has been reported.737 The complexes are prepared by refluxing the isocyanates with a suspension of the alkoxide in benzene. No structural data were given for the products. Unusual bimetallic alkoxides have recently been prepared738 by the reaction of Cr[Al(OPr )4]3 with alcohols and acetylacetone (166). A wide range of spectroscopic methods were used to study them. In general, the results were in accord with a monomeric formulation similar to (166) below Cr[Al(OMe)4]3 was grossly insoluble the small size of the methyl groups may permit extensive polymerization. 

Another common process involves reaction with C=C or C=N species having adjacent CH2 or CH, groups. Initial attack of the isocyanate is on the electron-rich center of the double bond with subsequent migration and insertion of the CONR group into the CH bond. Suitable reagents include N-alkylated acetamidines, 1-methyl dihydroisoquinoline, and 2-methyl-2-oxazoline [1120-64-5] (35). 

The structures of donor-acceptor complexes of iyn-benzoyl azide, its 2-methyl- and 2,6-dimethyl-substituted derivatives with BF3, AICI3, and SbCls, and the transition states of the rearrangement into isocyanates have been reported by computational methods. The reaction of donor-substituted alkenes with a-diazo-a-nitro ethyl acetate under Rh catalysis have been reported which show that the nitro group is inserted forming cyclic nitronates, whereas the ester moiety was not incorporated into the ring system (Scheme 198). ... 

The reactivity of these group 4 metal complexes has been studied to some extent. Starting from complex [(6)MCl2], the reaction with nucleophiles such as alkylhthium led to the classical reactivity at M-Cl (Scheme 32) [89]. The reactions with strong electrophiles such as isocyanates, carbon dioxide, or carbodiimide did not show the expected insertion into the M=C bond, but rather a [2+2] cycloaddition. The basicity and nucleophilicity of the C center was proved by reactions with aromatic amines, phenols, aliphatic alcohols, or methyl iodide leading to the 1,2 addition product. 

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