Carbonylation of the hafnocene dinitrogen complex [(η 5- C 5H 2-1,2,4-Me 3) 2Hf] 2(μ 2,η 2:η 2-N 2) with 4 atm of carbon monoxide yielded the tetrametallic hafnocene oxamidide complex [(η 5-C 5H 2-1,2,4-Me 3) 2Hf(NCO)] 4, a new structural motif arising from CO-induced N 2 cleavage. The more commonly observed dimeric hafnocene oxamidide [(η 5-C 5H 2-1,2,4-Me 3) 2Hf] 2(N 2C 2O 2) was observed by multinuclear NMR spectroscopy when the carbonylation was performed at lower (∼1 atm) CO pressure. Over the course of 1 h at 23 °C, the dimeric hafnocene oxamidide undergoes dimerization to the tetrametallic compound, establishing its intermediacy for synthesis of the latter. Additional functionalization of the hafnium-nitrogen bonds in the tetrametallic complex was accomplished by cycloaddition of tBuNCO or 1,2-addition of CySiH 3. The former example maintains a tetrametallic hafnocene where only two of the four Hf-N bonds have undergone [C=O] cycloaddition of the heterocumulene. In contrast, the primary silane yielded a dimeric hafnocene product where all of the hafnium-nitrogen linkages have undergone 1,2-addition. Thermolysis of [(η 5-C 5H 2-1,2,4-Me 3) 2Hf(NCO)] 4 at 110 °C provided a route to a new μ-oxo hafnocene complex with both terminal isocyanate and cyanide ligands. This process is general among hafnocene oxamidides and provides a route to rare hafnium cyanide complexes that undergo preferential [CN] rather than [NCO] group transfer.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry