Formation of paramagnetic metallacyclobutadienes by reaction of diaminoacetylenes with molybdenum alkylidyne complexes.

The reactions of the molybdenum alkylidyne complex [MesC[triple bond, length as m-dash]Mo{OCMe(CF3 )2 }3 ] (1) with the diaminoacetylenes R2 NC[triple bond, length as m-dash]CNR2 (2, NR2 = 4-methylpiperidinyl; 3, NR2 = NEt2 ; Mes = 2,4,6-trimethylphenyl) afforded the metallacyclobutadiene (MCBD) complexes 4 and 5. In contrast to all other MCBD complexes, 4 and 5 are paramagnetic and best described as Mo(iv) species containing an anionic diaminodicarbene of the type [(R2 N)CC(Mes)C(NR2 )]- .