Insertion of isocyanides into group 4 metal-carbon and metal-nitrogen bonds. Syntheses and DFT calculations

The reactions of [Ti(eta(5)-Ind)(NMe2)(2)Me], [Ti(eta(5)-Ind)(NMe2)Cl-2], and [Zr(eta(5)-Ind)(NMe2)(2)Cl] with 2,6-dimethylphenyl isocyanide (CN(2,6-Me2Ph)) and tert-butyl isocyanide (CN-t-Bu) have been investigated. For the first complex, insertion occurs exclusively into the Ti-C bond to give [Ti(eta(5)-Ind)(NMe2)(2){C(Me)=N-t-Bu}] (1), which, according to DFT results, is due to the weakness of the Ti-CH3 bond when compared to Ti-NR2. [Ti(eta(5)-Ind)(NMe2)Cl-2] was found to react with 1 equiv of CN(2,6-Me2Ph) to yield [Ti(eta(5)-Ind){C(NMe2)=N(2,6-Me2Ph)}Cl-2] (2). Two equivalents of 2,6-dimethylphenyl isocyanide reacts with [Zr(eta(5)-Ind)(NMe2)(2)Cl] to give the double insertion compound [Zr(eta(5)-Ind){C(NMe2)=N(2,6-Me2Ph)}(2)Cl] (3). The same reaction performed with CN-t-Bu proceeds slowly and enabled the characterization, by NMR, of [Zr(eta(5)-Ind)(NMe2){C(NMe2)=N-t-Bu}Cl] (4) and [Zr(eta(5)-Ind){C(NMe2)=N-t-Bu}(2)Cl] (5). The molecular structures of 2 and 3 have been determined by X-ray diffraction. DFT calculations of the insertion of CNH in the zirconium nitrogen bonds of [Zr(eta(5)-Ind)(NR2)(2)Cl] (R = H, Me) have been performed and show that the progressive stability of the insertion products accounts for the experimentally found double insertion product.