Insertion of Isocyanides into Group 4 Metal−Carbon and Metal−Nitrogen Bonds. Syntheses and DFT Calculations

The reactions of [Ti(η⁵-Ind)(NMe<INF>2</INF>)<INF>2</INF>Me], [Ti(η⁵-Ind)(NMe<INF>2</INF>)Cl<INF>2</INF>], and [Zr(η⁵-Ind)(NMe<INF>2</INF>)<INF>2</INF>Cl] with 2,6-dimethylphenyl isocyanide (CN(2,6-Me<INF>2</INF>Ph)) 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(η⁵-Ind)(NMe<INF>2</INF>)<INF>2</INF>{C(Me)&dbd;N-t-Bu}] (<BO>1</BO>), which, according to DFT results, is due to the weakness of the Ti−CH<INF>3</INF> bond when compared to Ti−NR<INF>2</INF>. [Ti(η⁵-Ind)(NMe<INF>2</INF>)Cl<INF>2</INF>] was found to react with 1 equiv of CN(2,6-Me<INF>2</INF>Ph) to yield [Ti(η⁵-Ind){C(NMe<INF>2</INF>)&dbd;N(2,6-Me<INF>2</INF>Ph)}Cl<INF>2</INF>] (<BO>2</BO>). Two equivalents of 2,6-dimethylphenyl isocyanide reacts with [Zr(η⁵-Ind)(NMe<INF>2</INF>)<INF>2</INF>Cl] to give the double insertion compound [Zr(η⁵-Ind){C(NMe<INF>2</INF>)&dbd;N(2,6-Me<INF>2</INF>Ph)}<INF>2</INF>Cl] (<BO>3</BO>). The same reaction performed with CN-t-Bu proceeds slowly and enabled the characterization, by NMR, of [Zr(η⁵-Ind)(NMe<INF>2</INF>){C(NMe<INF>2</INF>)&dbd;N-t-Bu}Cl] (<BO>4</BO>) and [Zr(η⁵-Ind){C(NMe<INF>2</INF>)&dbd;N-t-Bu}<INF>2</INF>Cl] (<BO>5</BO>). The molecular structures of <BO>2</BO> and <BO>3</BO> have been determined by X-ray diffraction. DFT calculations of the insertion of CNH in the zirconium nitrogen bonds of [Zr(η⁵-Ind)(NR<INF>2</INF>)<INF>2</INF>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.