Insertion of Isonitriles into the M–C Bonds of Group 4 Dialkyl Complexes

Abstract

The 2,3-dimethylbutadiene complexes of Group 4 metals with constrained geometry (cg) ligands have been prepared and found to adopt a supine orientation with σ,π bonding. Treatment of cgTi(2,3-dimethylbutadiene) (1-Ti) with BuNC leads to the formation of a titana-aziridine (3) with a coordinated cyclopentenimine that arises from the formal [4+1] addition of the diene to the isonitrile. In contrast, the reactions of cgZr(2,3-dimethylbutadiene) (1-Zr) or cgHf(2,3-dimethylbutadiene) (1-Hf) with 2 equiv ofBuNC or XyNC proceeded in a more sophisticated manner to yield unsymmetrical 2,5-diazametallacyclopentane derivatives (4, 6-Zr, and 6-Hf) or symmetrical 2,5-diazametallacyclopentene complexes (7-Zr and 7-Hf). The unsymmetrical products contain coordinated cyclopropanes; the strength of the interaction is measured by the reduction in the J of the C-C bond that is coordinated. A detailed mechanistic analysis has been possible with the related cgM(Me) (M = Ti and Hf) complexes. The first insertion is too fast to monitor, but allows complete conversion to an alkyl iminoacyl intermediate. The second isonitrile (RNC) may react with that intermediate by either of two different mechanisms, reductive elimination and coordination/insertion. In the first mechanism (Ti), rate-determining C-C coupling gives a titana-aziridine, followed by fast coordination of the isonitrile. In the second mechanism (Hf), coordination is the slow step; insertion to form a bis(iminoacyl) Hf complex is rapid.

Insertion of Isonitriles into the Zr–CH3 Bond of Cp*2Zr(CH3)2 and Electrophilic Cleavage of the Remaining Methyl Group

“…The short Zr–N distance of 2.368(2) Å indicates η 2 coordination, as does an ATR-FTIR signal at 1610 cm –1 . There have been few other isolable monoiminoacyl group 4 complexes with the outside geometry. − However, at 80 °C in C 7 D 8 , 2 converts entirely to the inside isomer, as indicated by 1 H NMR (Figure S4).…”

Rare-Earth Metallacycloheptatrienes: Synthesis, Structure, and Reactivity

“…The whole process of the formation of 3 from 2-Sc and 2,6-Me 2 C 6 H 3 NC is exergonic by 47.5 kcal/mol with an energy barrier of 21.3 kcal/mol, consistent with the rapid formation of 3 at ambient temperature. The successive 1,1-insertion and 1,2-insertion of isocyanides into metallacycles containing two metal–carbon bonds are known in rare-earth or transition metallacycles, generally promoted by the following coordination of an extra ligand or other transformations to fill the emptied coordination position. , For the formation of 3 , one of the C–C π-bonds in the benzene rings acts as an intramolecular ligand.…”